Gondwana Research 38 (2016) 1–27

Contents lists available at ScienceDirect

Gondwana Research

j ourna l homepage: www.e lsev ie r .com/ locate /gr

Discovery of Neoarchean suprasubduction zone ophiolite suite fromYishui Complex in the North China Craton

M. Santosh a,b,c,⁎, Xue-Ming Teng a, Xiao-Fang He a, Li Tang a, Qiong-Yan Yang a,b

a School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, Chinab Department of Earth Sciences, School of Physical Sciences, University of Adelaide, SA 5005, Australiac Division of Interdisciplinary Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan

⁎ Corresponding author at: School of Earth Sciences andGeosciences Beijing, 29 Xueyuan Road, Beijing 100083, Ch

E-mail address: msantosh.gr@gmail.com (M. Santosh)

http://dx.doi.org/10.1016/j.gr.2015.10.0171342-937X/© 2015 International Association for Gondwa

a b s t r a c t

a r t i c l e i n f o

Article history:Received 31 July 2015Received in revised form 13 October 2015Accepted 18 October 2015Available online 26 November 2015

Handling Editor: S.J. Liu

The Archean tectonic realm of theNorth China Craton (NCC) is considered in recentmodels as a collage of severalmicroblocks which were amalgamated along zones of ocean closure during late Neoarchean. Here we report thefinding of a dismembered ophiolite suite from the southernmargin of the Jiaoliaomicroblock in the interior of theunified Eastern Block of the NCC. The suite is composed of lherzolite, pyroxenite, noritic and hornblende gabbro,and hornblendite intruded by veins and sheets of leuco granite. Together with transposed layers and bands ofmetavolcanics and amphibolites, banded iron formation (BIF), and diabase dykes in the adjacent locations, theYishui complex corresponds well with a dismembered suprasubduction zone ophiolite suite. Clinopyroxene inthe pyroxenite and gabbroic rocks is Mg rich and range in composition from augite to diopside. Amongorthopyroxenes, those in lherzolite show the highest XMg of 0.84–0.85. Plagioclase in hornblende gabbroshows high anorthite content (An50–64). Calcic amphiboles in the gabbroic rocks range in composition fromferropargasite to ferro-edenite, edenite and pargasite. Spinel inclusions in lherzolite are Cr-rich magnesiospinel.Geochemically, the mafic rocks from Yishui complex show subalkaline basaltic source, whereas the granitoidsshow volcanic arc affinity. The hornblende gabbro and gabbro, lherzolite and hornblendite show compositionalsimilarity to E-MORB and N-MORB respectively. The lherzolite and hornblendite possess arc-related ultramaficcumulate nature, with overall features straddling the fields of IAT and IAT-MORB. The geochemical features areconsistent with evolution in a suprasubduction regime with no significant crustal contamination. The majorityof zircon grains in the Yishui suite exhibit magmatic texture and high Th/U ratios. Zircon grains fromhornblendite define 207Pb/206Pb upper intercept age of 2538 ± 30 Ma. Zircons from the granite show ages of2538 ± 16 Ma and 2503 ± 21 Ma, and those from the gabbros yield ages of 2503 ± 16 Ma and 2495 ± 10 Ma.The well defined major age peak at 2500 Ma is broadly coeval with Neoarchean ages reported from themicroblocks in theNorth China Craton. The zircon Lu–Hf data from the Yishui suite display εHf(t) values between−2.5 and 5.0, with corresponding model ages suggesting magma derivation from Neoarchean juvenile sourcestogether with limited reworked Paleo-Mesoarchean crustal components.Our study is the first report of Neoarchean suprasubduction-type ophiolites from a locality far from the margins ofthemajor crustal blocks and suture zones in the NCC and strengthens the concept that the craton is amosaic of sev-eral microblocks with intervening oceans that closed alongmultiple subduction zones. We envisage that the amal-gamation between the Xuhuai and the Jiaoliao microblocks resulted in the accretion of the Yishui suprasubductionzone ophiolitic assemblages onto the southernmargin of the Jiaoliaomicroblock. TheNeoarcheanmicroblock amal-gamation in the North China Craton provides new insights into continental growth in the early Earth and confirmsthat modern style plate tectonics might have been initiated early in the history of our planet.

© 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Keywords:OphiolitePetrologyGeochemistryZircon U–Pb geochronology and Lu–Hf isotopesNeoarchean plate tectonics

1. Introduction

Anatomy of ancient accretionary orogens on the globe suggests thatthere has been no fundamental change in the processes of sea floor

Resources, China University ofina..

na Research. Published by Elsevier B.

spreading, oceanic sedimentation, subduction, and accretion duringthe past 3.8 billion years (Kusky et al., 2013). Among the imprints of ac-cretionary orogenesis is the presence of material scraped off from thesubducting oceanic lithosphere, including various types of ophiolites,together with other sedimentary and magmatic units (Kusky et al.,2013). Evidence for subduction–accretion accompanying continentalgrowth in convergent margins has been reported from several Archeanterranes (e.g., Santosh et al., 2012; Yellappa et al., 2012; Santosh et al.,2015; Yang et al., 2016).

V. All rights reserved.

2 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Although ophiolites have been loosely defined as accreted remnantsof oceanic crust in convergentmargins, recent concepts also include thetemporally and spatially associated ultramafic to felsic rock suites gener-ated through melting and magmatic differentiation in oceanic environ-ments as part of ophiolite suites (Dilek and Furnes, 2011; Furnes et al.,2014). Thus, ophiolites form in both subduction-related and unrelatedsettings. The subduction-related category includes suprasubductionzone ophiolites formed in backarc to forearc, forearc, oceanic backarcand continental backarc, as well as volcanic arc types, whereas thesubduction-unrelated variety includes continental margin, mid-oceanridge and plume types (Dilek and Furnes, 2011). From a global compila-tion of Precambrian and Phanerozoic ophiolite complexes, Furnes et al.(2014) correlated the secular trends in oceanic crust formation todecreasing degrees of partial melting of the upper mantle fromancient to modern Earth, with more than 75% of ophiolites showingsubduction-related origin. Further analysis by Furnes et al. (2015) sug-gests that nearly 85% of the greenstone sequences on the globe can beclassified as subduction-related ophiolites, generated in backarc toforearc tectonic environments, extending plate-tectonic processes backto the Hadean–Archean transition.

The North China Craton (NCC) is one of the ancient cratonic nucleiamong the Archean terranes on the globe, with Precambrian rock re-cords ranging in age from Eoarchean to Paleo- and Mesoproterozoic(Santosh, 2010; Zhai and Santosh, 2011; Zhao and Zhai, 2013; Zhai,2014, Yang and Santosh, 2015). The more popular tectonic models ofthe NCC consider it to be composed of three distinct crustal blocks, theYinshan Block, the Ordos Block and the Eastern Block (e.g., Zhao et al.,2005; Santosh, 2010; Zhao and Zhai, 2013) (Fig. 1). The Yinshan andOrdos Blocks were amalgamated during Paleoproterozoic along theInner Mongolia Suture Zone (Santosh, 2010; also known as theKhondalite belt; Zhao et al., 2005) into the unified Western Block,

Fig. 1. Tectonic framework of the North China Craton (after Zhao et al., 2005; Santosh, 2010; Yazones. The locations of ophiolitic complexes reported in previous studies (after Kusky and Zhai, 2CD—Chengde; NH—Northern Heibei; XH—Xuanhua; HA—Huai'an; HS—Hengshan; WT—Wutai;

following which the Eastern and Western Blocks collided along theTrans-North China Orogen. Recent studies also propose a thirdPaleoproterozoic suture, the Jiao-Liao-Ji Belt (Zhao and Zhai, 2013)within the Eastern Block. All the Paleoproterozoic sutures displaylithotectonic elements that are diagnostic of subduction and collisiontectonics including: (1) arc-related juvenile crust; (2) linear structuralbelts defined by strike-slip ductile shear zones, large-scale thrustingand folding, and sheath folds and mineral lineations; (3) high-pressure (HP) mafic and pelitic granulites, retrograde eclogites andultrahigh temperature (UHT) rocks; (4) clockwise metamorphic P–Tpaths involving near-isothermal decompression; (5) possible ancientoceanic fragments and mélange; and (6) back-arc or foreland basins(Zhao and Zhai, 2013). However, the age of these collision belts is debat-ed, with some workers suggesting amalgamation at the end of theArchean (e.g. Zhai, 2014), whereas others confirming the timing aslate Paleoproterozoic (Santosh, 2010; Zhao and Zhai, 2013).

In deviation to the above models, recent studies consider that thecore of the NCC is composed of a number of microblocks carryingrocks of ca. 2.7 Ga age such as the Jiaoliao Block (JL), the QianhuaiBlock (QH), the Ordos Block (OR), the Jining Block (JN), the XuchangBlock (XCH), the Xuhuai Block (XH) and the Alashan Block (ALS)(Zhai and Santosh, 2011, and references therein). These ancient tectonicblocks are bound by granite–greenstone belts that might represent thesite of closure of intervening ocean basins (Zhai and Bian, 2001). Arc-magmatism in convergent margin setting associated with the subduc-tion–collision tectonics of these microblocks during Neoarchean hasalso been identified in recent studies (Yang et al., 2016).

Archean ophiolites have been reported from some localities in theNCC in previous studies (Fig. 1) which include the dismemberedophiolites in Dongwanzi, Zunhua,Wutaishan,Western Liaoning, North-ern Taihang and Southern Taihang (Kusky et al., 2001; Li et al., 2002;

ng et al., 2016) showing themajor crustal blocks and intervening Paleoproterozoic suture012), and that of present study are also shown. Abbreviations ofmetamorphic complexes:FP—Fuping; LL—Lüliang; ZH—Zanhuang; ZT—Zhongtiao; DF—Dengfeng; TH—Taihua.

3M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Zhai et al., 2002; Zhang et al., 2003, 2004; Polat et al., 2005; Zhao et al.,2007; Kusky and Li, 2010; Kusky and Zhai, 2012). However, there is con-siderable debate surrounding the characterization, age and origin ofthese occurrences. In this study, we report for the first time a dismem-bered ophiolite suite far from the boundaries of the major crustal blocksand suture zones in the NCC, at the southern periphery of the Jiaoliaomicroblock well within the Eastern Block (Fig. 1). The rock suitesthat we report from this locality are comparable to Neoarcheansuprasubduction zone ophiolites reported from other Archean terranesand provide a robust case of subduction-related ophiolite suite in theNCC. We present petrological, geochemical, and zircon U–Pb and Lu–Hfisotope data and evaluate the significance of these results in the contextof ocean closure and Neoarchean microblock amalgamation in the NCC.

Fig. 2. Geological map of the Yishui terrane (modified after Shen et a

2. Geological background

The Eastern Block of the NCC is characterized by Archean–Paleoproterozoic basement rocks with rare rock records ranging inage up to 3.8 Ga. The block also preserves records of Paleoproterozoicrift–subduction–collision along the Jiao-Liao-Ji Belt during 2.2–1.9 Ga(e.g. Luo et al., 2004; Li et al., 2005, 2006; Lu et al., 2006; Li and Zhao,2007). The Archean basement rocks in this composite block are exposedin the Miyun, Eastern Hebei, Western Liaoning, Southern Liaoning,Anshan-Benxi, Northern Liaoning, Southern Jilin, Eastern Shandongand Western Shandong complexes. The Western Shandong complex iscomposed of the Luxi Granite–Greenstone Terrane in the west and theYishui Terrane in the east.

l., 2000). The sample locations of present study are also shown.

4 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

In the microblock amalgamation model of the NCC (Zhai andSantosh, 2011), at least seven microblocks have been identified includ-ing the Jiaoliao Block (JL), the Qianhuai Block (QH), the Ordos Block(OR), the Jining Block (JN), the Xuchang Block (XCH), the XuhuaiBlock (XH) and the Alashan Block (ALS). These microblocks were

Fig. 3. (a–e) Representative field photographs from the Yishui ophiolite suite (locality YS-17). ((c) Hornblendite. (d) Leuco granite vein intruding hornblende gabbro. The harzburgite block occomplex. (f–i) Representative field photographs from the Yishui ophiolite suite (locality YS-17tionation. (g) Leuco granite sheets emplaced within hornblendite. (h) Hornblende gabbro (loc

suggested to have been welded by 2.6–2.7 Ga and ~2.5 Ga Neoarcheangreenstone belts which are considered to represent arc–continent colli-sional belts (Zhai and Santosh, 2011). Examples include the Zunhuagreenstone belt located between the JN and QH Blocks, the Wutaishangreenstone belt between the OR and QH Blocks, the Yanlingguan

a) Blocks of lherzolite enveloped by pyroxenite. (b) Pyroxenite showing cumulate texture.curs to the right. (e) Isotropic gabbroic rocks constituting themajor lithology in the Yishuiexcept for panel h). (f) Layers of noritic and hornblende gabbro showing magmatic frac-ality YS-16). (h) Gabbroic domains grading into anorthosite.

Fig. 3 (continued).

5M. Santosh et al. / Gondwana Research 38 (2016) 1–27

greenstone belt between the JL and QH Blocks, the Dongwufenzi green-stone belt between the JN and OR Blocks, and the Dengfeng greenstonebelt between the XCH and OR Blocks (Zhai and Santosh, 2011).

The Yishui Complex is exposed at the southern margin of the JLBlock, at the eastern part of the Yishui County in the Shandong Province(Fig. 2). Themajor rock types in this complex aremetamorphosed gran-itoid plutons, minor mafic and felsic volcanics and mafic intrusions. Thegranitoid plutons are mainly composed of trondhjemites, charnockites/enderbites, granodiorites and granites, which are exposed in theDashan, Yinglingshan, Linjiaguanzhuang, Niuxinguanzhuang, Caiyu,Xueshan and Mashan areas (Fig. 2). Recent zircon U–Pb LA-ICP-MSgeochronology shows that the Mashan, Caiyu and Xueshan plutonswere emplaced at 2528 ± 8 Ma, 2559 ± 16 Ma and 2535 ± 11 Ma,

respectively (Wu et al., 2013). Zhao et al. (2008) reported zirconSHRIMP U–Pb ages of 2530 ± 7 Ma and 2531 ± 8 Ma from twoYinglingshan granites. The Yishui Group is predominantly composedof TTG (tonalite–trondhjemite–granodiorite) gneisses, amphibolites,mafic granulites and minor pelitic gneisses, and the group has beenfurther subdivided into three subgroups as: the Linjiaguanzhuangsubgroup, the Shishanguanzhuang subgroup, and the Beixiazhuang sub-group (Shen et al., 2000). The Linjiaguanzhuang subgroup consistsmainlyof amphibolites, garnet–clinopyroxene granulites, garnet–orthopyroxenegranulites and minor felsic gneisses. The Shishanguanzhuang subgroupis dominated by granulites and felsic gneisses, with minor pyroxenites.The Beixiazhuang subgroup comprises amphibolites, biotite gneisses,and biotite–garnet–sillimanite–K-feldspar paragneisses.

6 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

The ophiolite suite that we report in this study is exposed around500 m south of the Linjiaguanzhuang village, in a small ridge section.The lithological units here (Fig. 3) are considered to be part of a dis-membered suite, the remnants of which could be traced to the southof the map area of the Yishui Complex shown in Fig. 2. The layers ofmafic–ultramafic sequences in this exposure are highly deformed,folded, sheared and fragmented, obliterating the original stratigraphy.The rocks are exposed along a ridge running for around 100 m andoccur as thick bands and blocks ranging from a few meters to severalmeters. The major rock unit is isotropic gabbro which occurs in associa-tion with subordinate pyroxenite, lherzolite and hornblendite intrudedby sheets of leucocratic granite (Fig. 3). The lherzolite occurs as meter-sized fragmented blocks within the pyroxenite–gabbro sequence andis highly altered with serpentinite–talc texture. This rock representsthe basal section, although it has been deformed and incorporatedwith-in the overlying units. The pyroxenite is dark greenish gray in color andoccurs towards the base of the gabbro unit, representing the cumulatelayer. The gabbroic units show considerable compositional variationand banding ranging from noritic gabbro through leucogabbro andhornblende gabbro to hornblendite, suggesting crystallization and dif-ferentiation in a magma chamber, as also indicated by the prominentmagmatic layering. In the most fractionated domains, thin plagioclase-rich anorthositic veins occur dominantly composed of medium grainedplagioclase withminor amphibole and pyroxene. The hornblendites aregreenish brown and coarse to medium grained with interlocking am-phibole laths. The felsic granitoids occur as sheets, lenses and veinsranging in thickness from few tens of cm up to 2 m, and show intrusivecontacts. Hornblende-bearing noritic layers showing strong foliation areexposed in adjacent localities also (YS-16; Fig. 2). Although the volcanic(amphibolite, metavolcanics) and sedimentary (Banded Iron Formation)units are not exposed in this ridge, transposed layers and bands of theserocks occur in the surrounding regions to the north of the ophiolite expo-sure within the Yishui Complex (Fig. 2). Minor bands of quartzites andlayers of felsic volcanic tuffs are also exposed representing the trenchsequence. Several diabase dykes also intrude the various lithologies inadjacent localities.

The sub-rounded to angular blocks of lherzolite and pyroxenite with-in the dismembered ophiolite sequence are wrapped and surrounded bygabbros and hornblendites with a well-developed tectonic fabric. Thenature of occurrence of the various units suggests disruption of the orig-inal magmatic sequence and intercalation within a tectonic mélangecomprising irregular and randomly scattered blocks of different rocktype. The nature of exposure of the different rocks with regional north-ward thrust of imbricated units mimics a duplex structure. It is possiblethat the dismembered units of this ophiolitic complex were transposedover long distance.

3. Analytical techniques

3.1. Petrography and mineral chemistry

Polished thin sections were prepared for petrographic study at geo-logical department of Peking University. Representative samples werechosen for detailed petrology, electron microprobe analyses (EMPA).Electron ProbeMicroanalyses were carried out using an electronmicro-probe analyzer (JEOL JXA8100) at Beijing Research Institute of UraniumGeology. The analyses were performed under conditions of 15 kVaccelerating voltage and 10 nÅ sample current, and the data wereregressed using an oxide-ZAF correction program supplied by JEOL.The samples analyzed include lherzolite, pyroxenite, hornblendite, gab-bro, and granite.

3.2. Bulk chemistry

The least altered and homogeneous portions of rock samples werecrushed and powdered to 200 mesh for geochemical analyses after

detailed petrographic observation. Major and trace (including rareearth elements) element analyses were conducted in the National Re-search Center for Geoanalysis, Beijing. The major elements were deter-mined by X-ray fluorescence (XRF), with an analytical uncertaintiesranging from 1 to 3%. Loss on ignition was obtained using about 1 g ofsample powder heated at 980 °C for 30 min. The trace elements weredetermined as solute by Agilent 7500ce inductively coupled plasmamass spectrometry (ICP-MS). About 50 mg of powder was dissolvedfor about 7 days at ca. 100 °C using HF–HNO3 (10:1) mixtures inscrew-top Teflon beakers, followed by evaporation to dryness. The ma-terial was dissolved in 7 N HNO3 and taken to incipient dryness again,and then was re-dissolved in 2% HNO3 to a sample/solution weightratio of 1:1000. The analytical errors vary from 5 to 10% depending onthe concentration of any given element. An internal standard wasused for monitoring drift during analysis; further details are given byGao et al. (2008).

3.3. Zircon U–Pb and Lu–Hf analyses

Zircon grains were separated using standard procedures for U–Pbdating and Hf analyses at the Yu'neng Geological and Mineral Separa-tion Survey Centre, Langfang City, Hebei Province, China. The CL imag-ing was carried out at the Beijing Geoanalysis Centre. Individual grainswere mounted along with the standard TEMORA 1, with 206Pb/238Uage of 417 Ma (Black et al., 2003), onto double-sided adhesive tapeand enclosed in epoxy resin disks. The disks were polished to a certaindepth and gold coated for cathodoluminescence (CL) imaging andU–Pb isotope analysis. Zircon morphology, inner structure and texturewere examined by using a JSM-6510 Scanning Electron Microscope(SEM) equipped with a backscatter probe and a Chroma CL probe. Thezircon grains were also examined under transmitted and reflectedlight images using a petrological microscope.

U–Pb dating and trace element analyses of zircon were con-ductedsynchronously by LA-ICP-MS at the State Key Laboratory of GeologicalProcesses and Mineral Resources, China University of Geosciences,Wuhan. Detailed operating conditions for the laser ablation system,the ICP-MS instrument, and the data reduction process are describedby Liu et al. (2008, 2010). Laser samplingwas performed using a GeoLas2005. An Agilent 7500a ICP-MS instrument was used to acquire ion-signal intensities. Each analysis incorporated a background acquisitionof approximately 20–30 s (gas blank) followed by 50 s data acquisitionfrom the sample. The Agilent Chemstation was utilized for the acquisi-tion of each individual analysis. Off-line selection and integration ofbackground and analyte signals, time-drift correction, and quantitativecalibration for trace element analyses and U–Pb dating were performedby ICPMSDataCal (Liu et al., 2008, 2010).

Zircon 91500 was used as external standard for U–Pb dating, andwas analyzed twice in between every 5 analyses. Time-dependent driftsof U–Th–Pb isotopic ratios were corrected using a linear interpolation(with time) for every five analyses according to the variations of91500 (i.e., 2 zircon 91500 + 5 samples + 2 zircon 91500) (Liu et al.,2010). Preferred U–Th–Pb isotopic ratios used for 91500 are fromWiedenbeck et al. (1995). Uncertainty of preferred values for the exter-nal standard 91500 was propagated to the ultimate results of the sam-ples. Concordia diagrams and weighted mean calculations were madeusing Isoplot/Ex ver3 (Ludwig, 2003). Trace element compositions ofzircons were calibrated against reference material of GSE-1G combinedwith internal standardization (Liu et al., 2010). The preferred values ofelement concentrations for the GSE-1G reference glass are from theGeoReM database (http://georem.mpch-mainz.gwdg.de/).

In-situ zirconHf isotopic analyseswere conducted on the same spotsor in adjacent domains with same or similar textures where for U–Pbdating was done by a Neptune MC-ICP-MS equipped with a 193 nmGeolas Q Plus ArF exciplex laser ablation at the Tianjin Institute ofGeology and Mineral Resources, with spot sizes of 50 μm. Zircon GJ-1was used as an external standard for in-situ zircon Hf isotopic analyses.

Table 1Summary of locations, rock types and mineralogy of samples analyzed in this study from the Yishui ophiolite suite.

Sample no. Locality Co-ordinates Rock type Assemblage

YS-16 N 31° 41′ 59.9″; E 118° 41′ 34.0″ Hornblende gabbro Pl Opx Hbl Ilm Mag Hem ZrnYS-17A1, A2, A3 N 31° 41′ 55.8″; E 118° 41′ 31.8″ Lherzolite Pl Hbl Opx Mag Ser ZrnYS-17B1, B2, B3 N 31° 41′ 55.8″; E 118° 41′ 31.8″ Hornblendite Hbl Mag Ap ZrnYS-17C1, C2 N 31° 41′ 55.8″; E 118° 41′ 31.8″ Hornblendite Hbl Opx Mag Zrn ApYS-17D1, D2, D3, D4 N 31° 41′ 55.8″; E 118° 41′ 31.8″ Gabbro Pl Hbl Cpx Mag Ap ZrnYS-17E1, E2, E3 N 31° 41′ 55.8″; E 118° 41′ 31.8″ Leuco-granite Pl Qtz Msc Kfs Ap Zrn IlmYS-17F N 31° 41′ 55.8″; E 118° 41′ 31.8″ Pyroxenite Hbl Opx Cpx Ap ZrnYS-17G N 31° 41′ 55.8″; E 118° 41′ 31.8″ Hornblende gabbro Hbl Pl Cpx Mag Zrn

Mineral abbreviations: Pl—plagioclase; Opx—orthopyroxene; Hbl—hornblende; Mag—magnetite; Hem—hematite; Zrn—zircon; Ser—sericite; Ap—apatite; Cpx—clinopyroxene;Qtz—quartz; Msc—muscovite; Kfs—K-feldspar.

7M. Santosh et al. / Gondwana Research 38 (2016) 1–27

4. Petrology

4.1. Sample description

Eighteen representative samples from the Yishui ophiolite suitewere examined in this study for petrology. The sample locations areshown in Fig. 2, and their salient details are listed in Table 1. The sam-ples analyzed include lherzolite, pyroxenite, hornblendite, gabbro, andgranite. A brief description of the petrographic features of the differentrock types is given below, and representative photomicrographs areshown in Fig. 4.

4.1.1. YS-16 hornblende noriteSample YS-16 is a hornblende-bearing noritic gabbro from the

Yishui Complex, and is coarse to medium grained, dark colored andwell foliated in hand specimen. The rock is dominantly composed of pla-gioclase (40–50%), hornblende (30–40%) and minor orthopyroxene(10–20%), with magnetite, ilmenite and hematite as accessory opaqueminerals (Fig. 4a). Clinopyroxene is absent in this sample. The rockshows compositional banding composed of hornblende-rich andplagioclase-rich domains.

The hornblende crystals are euhedral to subhedral, brown to green-ish, coarse grained and tabular in shape, ranging in size from 0.5 to1.5 mm and showing preferred orientation. The mineral shows strongpleochroism from dark brown to light green. The orthopyroxene grainsaremostly anhedral, and set in equigranular texturewith high relief andhematite occurring along cleavage traces. The plagioclase is subhedralto anhedral,mainly granular shaped, and relatively fine grainedwith di-ameter from 0.5 to 1 mm. The calcic plagioclase crystals show typicalpolysynthetic twinning, and carry abundant inclusions of hornblende.

4.1.2. YS-17A lherzoliteSamples YS-17A1, A2 and A3 are ultramafic rocks from the Yishui

Complex. The outcrop rock is grayish green colored, partly altered andfoliated.

Sample YS-17A1 displays protogranular texture, comprisinghornblende (30–40%), orthopyroxene (15–20%), serpentine (25–30%),and minor spinel, with magnetite as the accessory mineral (Fig. 4b).The rock has undergone alteration. Clinopyroxene is very minor inthis sample and felsic minerals like plagioclase are totally absent. Thehornblende displays pale green color, and is slightly pleochroic, withsubhedral and granular texture and grain size of about 0.5 to 0.7mmdi-ameter. The mineral contains fine grained spinel inclusions of spinel atthe core domains. The orthopyroxene is fine grained (b0.1 mm),anhedral, and mostly present as broken fragments forming island-liketexture. It is usually surrounded by fine grained serpentine. Magnetiteoccurs along the grain boundary of hornblende and also associatedwith serpentine, as an alteration product.

The other two samples YS-16A2 and YS-16A3 are more freshwith slight alteration. They contain more coarse grained (2–3 mm),subhedral orthopyroxene with minor alteration along the cleavagetraces.

4.1.3. YS-17B hornblenditeSamples YS-17B1, B2 and B3 represent hornblendite from the Yishui

Complex. The rock is dark colored, medium grained with protogranulartexture. The dominant mineral is hornblende, constituting more than95% volume. Orthopyroxene and clinopyroxene are absent in this sam-ple. Minor magnetite is the only accessory mineral, which occurs alongthe cleavages of hornblende displaying schiller texture (Fig. 4c). Underthin sections, the rock shows coarse tomedium grained subhedral gran-ular texture.

The hornblende grains are mostly subhedral and granular shapewith serrated grain boundary. Two types of hornblendes are presentin the rock, with the relatively coarse grained greenish to brown horn-blende with a size about 0.5 ∗ 0.5 mm showing cumulate texture andfine grained magnetite along cleavages. The second type is composedof relatively fine grained hornblende with pinkish color and abundantmagnetite along the grain boundary. This type shows strongorientation.Along the hornblende grain boundary, clay mineral can be observedwhich may indicate siallitization.

The other two samples (YS-17B2, B3) also display similar mineralassemblage and petrological features.

4.1.4. YS-17C gabbroic hornblenditeSamples YS-17C1, C2 and C3 are also hornblende-rich rocks from the

Yishui Complex showing typical cumulate texture, but with the addi-tional presence of orthopyroxene. The rock is dark colored, mediumgrained and massive.

Sample YS-17C1 is composed of hornblende (80–90%) andorthopyroxene (10–20%),withmagnetite, zircon and apatite as accesso-ry minerals. Under thin sections, it shows coarse to medium grainedsubhedral granular texture. The hornblende is green colored and coarsegrained whereas the orthopyroxene is fine grained and colorless(Fig. 4d). It is mostly subhedral and granular with size range of 0.5 to0.7 mm in diameter, and the interstices of the amphibole laths are filledwith fine grained (0.1 to 0.2mm) orthopyroxene. Apatite inclusions canbe seen in the orthopyroxene.

Two more samples (YS-17C2, C3) of this rock also display similarmineral assemblage and petrological features.

4.1.5. YS-17D gabbroSamples YS-17D1, D2, D3 and D4 were collected from near sample

YS-17C. Sample YS-17D1 is dark colored, medium to fine grained, withobvious foliation in hand specimen. Under thin section, the rock dis-plays typical gabbroic texture composed of plagioclase (40–50%),clinopyroxene (25–35%), and hornblende (15–20%), with magnetiteand zircon as accessories (Fig. 4e).

The plagioclase is tabular subhedral, colorless with mediumdegree of sericitization. Plagioclase shows polysynthetic twinningand wavy extinction suggesting deformation. Clinopyroxene grainstypically occur as relict crystals interlocked with the plagioclase. Theclinopyroxene is pale green colored and slightly oriented, and carriesabundant iron oxide grains along the cleavages displaying schiller

Fig. 4. Photomicrographs showing textures of representative samples fromYishui complex. (a) A typical granoblastic texture of hornblende+ orthopyroxene+plagioclase in hornblendegabbro (sample YS-16); (b) altered lherzolite with serpentinite + orthopyroxene + hornblende assemblage and spinel (sample YS-17A1); (c) massive hornblendite (sample YS-17B1);(d) massive hornblendite with minor orthopyroxene (sample YS-17C1); (e) hornblende gabbro with gabbroic texture and an assemblage of plagioclase + clinopyroxene + hornblende(sample YS-17D1),with accessory magnetite (f) medium grained granite with an assemblage of plagioclase + K-feldspar + quartz + minor muscovite (YS-17E2); (g) pyroxenite withorthopyroxene hornblende (sample YS-17F); (h) hornblende gabbro showing hornblende rich and plagioclase rich bands with minor clinopyroxene (sample YS-17G).

8 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

texture. The orthopyroxene is surrounded by dark green colored amphi-bole rim. Hornblende is mostly present hornblende rich bands, togetherwith plagioclase. The hornblende in these bands are dark green tobrown colored, subhedral granular andwell oriented, whichmight sug-gest retrograde origin through alteration of clinopyroxene.

There are three more additional samples YS-17D2, YS-17D3, andYS-17D4a all of which show similar assemblage, although sampleYS-17D2 has more hornblende rich bands with mineral assemblage of

Amp (30–40%) + Pl (30–35%) + Cpx (20–30%). Samples YS-17D3 andYS-17D4 shows more coarse grained clinopyroxene.

4.1.6. YS-17E leuco graniteLeuco granite samples YS-17E1, E2 and E3 are white colored and in-

trude adjacent to the ultramafic layers. They display coarse grainedmassive texture in hand specimen.

9M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Sample YS-17E1 is highly altered, and composed of sodic plagioclase(30–40%), microcline (20–30%), quartz (25–30%) and minor muscovite(about 5%), with ilmenite and zircon as accessories (Fig. 4f). The plagio-clase is coarse grained (2–4 mm), and highly sericitized. Some of theplagioclase laths display polysynthetic twinning and are mainly oligo-clase. The K-feldspar in sample YS-17E1 is coarse to medium grained(1–3 mm) microcline showing typical cross hatch twinning. Quartz isfine grained and occurs as granular. Muscovite occurs sporadically andranges in grain size from 0.1 to 0.3 mm.

4.1.7. YS-17F pyroxenitePyroxenite sample YS-17F is dark colored and medium grained,

with hornblende (40–50%), clinopyroxene (15–25%) and ortho-pyroxene (15–25%), and iron oxide (limonite) and apatite as accessories(Fig. 4g). The rock has undergone medium grade Fe-alteration. Thehornblende is medium grained (0.5 to 1 mm), subhedral granular, andshows light green to brown color with strong pleochroism. Theclinopyroxene is present as anhedral fragments in the fine grainedlayer with orthopyroxene, with grain size of about 0.1 to 0.3 mm. Theorthopyroxene occurs as tabular relics and are colorless under plane-polarized light. The iron alterationmainly occurs along grain boundariesand cleavage traces of the orthopyroxene.

4.1.8. YS-17G hornblende leucogabbroThis hornblende leucogabbro sample YS-17G showsmassive texture

in hand specimen. The rock is composed of amphibole (40–50%), plagio-clase (35–45%) and clinopyroxene (10–15%) (Fig. 4h). Compared to

Fig. 5. Compositional diagrams showing chemistry of representative minerals of samples fromclinopyroxene and orthopyroxene, after Poldervaart and Hess (1951); (b) Anorthite–albite(1983); (c) Si (pfu) versus XMg diagram showing compositions of calcic amphibole, after Haw

the hornblende norite sample YS-16, this rock has only clinopyroxene,and orthopyroxene is absent. This sample shows similarmineral assem-blage as the gabbro sample (YS-17D) but with more plagioclase.

The rock shows plagioclase rich layer and hornblende rich layer. Theplagioclase rich portion is composed of calcic plagioclase (labradorite)and clinopyroxene. The characteristics of hornblende and clinopyroxeneare similar to the gabbro sample (YS-17D) in this study.

4.2. Mineral chemistry

Representative compositions of minerals from Electron MicroprobeAnalyses are given in Supplementary Table 2, the data are plotted inFig. 5, and the results are briefly discussed below.

4.2.1. PyroxenesClinopyroxene occurs in the pyroxenite and gabbroic rocks of the

present study. In all cases, the clinopyroxenes are Mg rich (XMg =Mg / (Mg + Fe) = 0.58–0.88) and are classified as augite (Fig. 5a), al-though their XMg varies depending on samples. The gabbro sample(YS-17D1) shows relatively low XMg values with a limited variationfrom 0.59 to 0.62. The hornblende gabbro sample (YS-17G) displaysslightly higher XMg values of 0.67–0.70. Clinopyroxene in the pyroxenitesample (YS-17F) has the highest XMg values of 0.87 to 0.88. It is compo-sitionally close to diopside according to the classification diagram(Fig. 5a). The clinopyroxenes do not show any compositional zoning.

Orthopyroxene also shows obvious compositional range of XMg

from 0.42 to 0.85. The orthopyroxene in lherzolite (sample YS-17A1)

Yishui Complex. (a) Wollastonite–enstatite–ferrosilite diagram showing compositions of–orthoclase diagram showing compositions of plagioclase and K-feldspar, after Ribbethorne et al. (1997).

10 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

shows the highest XMg of 0.84–0.85, slightly higher than that inhornblendite (sample YS-17C1) and pyroxenite (sample YS-17F),whereas orthopyroxene in hornblende gabbro (sample YS-16) is lessmagnesian as XMg = 0.42–0.44.

4.2.2. FeldsparsPlagioclase in hornblende gabbro (YS-16), gabbro (YS-17D1), and

granite (YS-17E2) shows slight compositional variations depending onlithologies (An15–38, Supplementary Table 2, Fig. 5b). Plagioclase inanother hornblende gabbro sample (sample YS-17G) (An50–64) showshigher anorthite contents (Fig. 5b). K-feldspar is present only in thegranite among all the samples, and is compositionally nearly homoge-neous as Or94–95 (Fig. 5b).

4.2.3. AmphibolesThe amphiboles in the Yishui rocks are characterized by high Ca and

(Na + K) contents (1.72–2.49 pfu and 0.28–0.70 pfu, respectively), andshow notable compositional variation depending on occurrence (Sup-plementary Table 2, Fig. 5c). In general, the gabbroic samples fromYishui Complex including gabbro and two hornblende gabbros showobviously lower XMg values than those in the other samples. Calcicamphiboles in the hornblende gabbro sample (sample YS-16) are allFe-rich, Si-poor, and classified as ferropargasite, with VIAl N Fe3+.There is no compositional difference between amphibole rim and core.Amphiboles in gabbro and hornblende gabbro (samples YS-17D1and YS-17G) are slightly more Si-rich and plot in the boundary offerro-edenite to ferropargasite and edenite to pargasite respectively(Fig. 5c). Two stages of amphiboles are recognized in the gabbro sample(sample YS-17D1). 1) Brownish amphiboles with euhedral to subhedralshape and characterized by higher Ti content (N0.185 pfu), whichmightrepresent the primary magmatic amphibole. Compositional zoning isrecognized as high Si (6.52–6.64 pfu), low Ti (0.186–0.195 pfu) coreand low Si (6.38–6.47 pfu), and high Ti (0.207–0.275 pfu) rim. 2)Green-ish amphibole occurring as symplectite or corona aroundclinopyroxene, and is characterized by low Ti content (0.158 pfu) andhigh iron content, which is regarded as retrograde amphibole. Calcicamphiboles in hornblendite (sample YS-17B1) are typically edenite(Fig. 5c) with high Si content (N6.65 pfu). No compositional variationis noted between core and rim. Amphiboles from theother hornblendite(sample YS-17C1) which also contains orthopyroxene plot in theboundary of pargasite and edenite. Amphiboles in hornblende gabbro(sample YS-17G) also comprises two types of amphibole. 1) Yellowisheuhedral amphibole displaying higher silica (SiO2 = 48.55 wt.%) andlow aluminum content (Al2O3 = 6.66 wt.%). 2) Brownish calcic amphi-bole occurring near clinopyroxene and showing lower Si and higher Alcontent. Amphiboles from the pyroxenite sample are also recognizedas typical edenite with low Ti content (TiO2 b 0.6 wt.%). Calcic amphi-boles from lherzolite are homogeneous without any compositionalzoning and are also identified as edenite (Fig. 5c).

4.2.4. SpinelsSpinel inclusions in lherzolite sample are all Cr-rich magnesiospinel

(XMg=Mg / (Fe +Mg)= 0.48–0.60, mostly N0.5), with Cr2O3 contentin the range of 9.09–13.26. Their Mg2+ (0.516–0.596 pfu) content isslightly higher than Fe2+ content (0.397–0.558 pfu).

5. Geochemistry

The major, trace and rare earth element data from representativerocks types of the Yishui ophiolite suite are listed in Table 3 and plottedin Figs. 6–12. In total,fifteen sampleswere analyzed including onehorn-blende gabbro (norite), three lherzolites, three hornblendites, one gab-broic hornblendite, four gabbros and three leuco granites. Their salientcharacteristics are briefly discussed below.

5.1. Alteration

Though the least altered and homogeneous portion of rock sampleswere selected for whole rock geochemical analyses in this study, it is es-sential to assess the effects and extent of post-magmatic alteration ongeochemical compositions for any rocks within the ophiolite suite asthese rocks have undergonemetamorphism and alteration. Several pre-vious geochemical studies have argued that ‘immobile’ elements such asthe HFSE (high field strength elements) and REE (rare earth elements,except “Ce” and “Eu”) are least sensitive to hydrothermal alteration,and can therefore be used to evaluate the petrogenesis of the rocks(Polat and Kerrich, 2000; Piercey et al., 2002). Among these immobileelements, Zr is the least mobile element and is mobile only undervery specific conditions (e.g., acid–sulfate conditions; presence ofF) (Winchester and Floyd, 1977; Pearce and Peate, 1995). Zirconium istherefore a very useful index to evaluate the variation of the other ele-ments. As proposed by Polat and Hofmann (2003), when elements areplotted against Zr, those with linear trends that pass through the originwere likely immobile, whereas those that were scattered might repre-sent mobile elements.

In the present case, binary plots of Y, Nb, La and Th versus Zr forYishui rocks display linear trends and pass near the origin, though aminor scatter is observed in some of these contents (Fig. 6). Further-more, the Yishui samples generally show low LOI values (b3.11 wt.%),together with their coherent REE patterns (see below), we infer thatthe immobile elements in these rocks have not been significantly mod-ified by metamorphism and alteration and can be utilized to interpretthe petrogenesis of these rocks (Polat and Hofmann, 2003).

5.2. Major and trace elements

All the rocks from Yishui analyzed in this study (except for threegranitoid samples) show limited variation in SiO2 contents (46.63–50.56 wt.%), and moderate variation in Al2O3 (4.34–13.84 wt.%), CaO(3.9–11.9 wt.%) and Fe2O3

t (10.67–18.33 wt.%). The total alkalis(Na2O + K2O) are in the range of 0.34 to 3.91 wt.%. The hornblendenorite and gabbros have relatively low Mg number in the range of 35to 51, whereas the lherzolites and hornblendites/gabbroic hornblenditeexhibit relatively highMgnumber varying from 77 to 81. In the TAS plot(Fig. 7a), these rocks fall in the field of basalt and display sub-alkalinenature. In terms of Zr/TiO2–Nb/Y diagram (Fig. 7b), all of the rocksfall in the andesite/basalt and sub-alkaline basalt field. The abovefeatures emphasize their sub-alkaline affinity. The three leuco granitesamples display the highest SiO2 content (73.67–75.71 wt.%) amongthe samples from Yishui ophiolite suite, with moderate variationsin Al2O3 (13.54–14.88 wt.%), CaO (0.44–0.71 wt.%) and total alkalis(Na2O + K2O, 7.32–9.25 wt.%), and low Fe2O3

t content of0.48–0.94 wt.%. Both in the TAS plot and Zr/TiO2–Nb/Y diagram(Fig. 7a and b), the granite samples fall in the field of rhyolite.

The gabbros/hornblende norite samples showeither slight depletionor enrichment of LREE on the chondrite-normalized REE patternswith (La/Sm)N value varying from 0.85 to 1.84 (Fig. 8a, Table 3). Thelherzolite and hornblendites/gabbroic hornblendite exhibit relativenarrow variation in the enrichment of LREE when compared to thegabbros/hornblende norite (Fig. 8b and c) with (La/Sm)N ranging from1.15 to 1.47 and from 0.96 to 1.36 (Table 3). Overall, there is nomarkedenrichment of REE/fractionation in these rocks. However, an obviousenrichment of LREE is noted in the case of leuco granites (Fig. 8d).These rocks also granites exhibit enrichment of HREE but depletion ofMREE. In Fig. 9, MORB and OIB data from Sun and McDonough (1989),Aldanmaz et al. (2008) and Safonova et al. (2011) are also plottedfor comparison. The hornblende norite and gabbro, lherzolite andhornblendite/gabbroic hornblendite exhibit compositional similarityto E-MORB and N-MORB with patterns and similar to the MORB datafrom Neotethyan Ophiolite in western Turkey (Aldanmaz et al., 2008)as well as those from the accretionary complex of Gorny Altai,

Table 3Whole-rock geochemical data for rocks from Yishui ophiolite suite.

Sample no. YS-16 YS-17A1 YS-17A2 YS-17A3 YS-17B1 YS-17B2 YS-17B3 YS-17C1 YS-17D1 YS-17D2 YS-17D3 YS-17D4 YS-17E1 YS-17E2 YS-17E3

Rock type Hornblende norite Lherzolite Lherzolite Lherzolite Hornblendite Hornblendite Hornblendite Gabbroic hornblendite Gabbro Gabbro Gabbro Gabbro Leuco granite Leuco granite Leuco granite

Major elements (wt.%)SiO2 46.63 46.68 46.87 49.45 47.87 48.14 47.81 47.99 50.56 49.35 50.53 49.93 74.28 73.67 75.71TiO2 2.72 0.37 0.36 0.2 0.35 0.32 0.36 0.47 1.33 1.84 1.83 0.99 0.06 0.07 0.04Al2O3 13.64 7.47 7.32 4.34 7.4 6.95 7.22 7.91 13.84 13.34 13.81 13.59 14.88 14.46 13.54Fe2O3T 18.33 11.28 10.98 13.71 11.17 10.96 10.67 12.22 13.00 14.70 13.38 14.31 0.94 0.61 0.48MnO 0.23 0.14 0.14 0.18 0.16 0.17 0.18 0.17 0.17 0.23 0.21 0.2 0.01 0.01 0.01MgO 4.9 22.35 22.04 25.32 20.78 21.6 21.76 19.99 5.96 4.88 4.38 7.41 0.39 0.1 0.1CaO 8.52 6.96 7.07 3.9 8.93 8.83 8.23 8.01 9.99 10.97 11.36 9.6 0.44 0.71 0.65Na2O 3.05 0.78 0.8 0.29 0.82 0.75 0.98 1.36 3.47 3.2 3.28 2.74 5.47 3.89 4.42K2O 0.62 0.17 0.17 0.05 0.11 0.11 0.2 0.14 0.44 0.49 0.33 0.52 1.85 5.36 4.06P2O5 0.26 0.03 0.05 0.03 0.04 0.04 0.04 0.06 0.2 0.2 0.2 0.09 0.01 0.01 0.01LOI (%) 0.24 2.48 3.11 1.42 1.16 1.05 1.44 0.54 0.37 0.09 −0.01 0.02 0.97 0.4 0.3Total 99.14 98.71 98.91 98.89 98.79 98.92 98.89 98.86 99.33 99.29 99.30 99.40 99.30 99.29 99.32

Trace elements (ppm)Sc 31.5 24.7 24.7 17.9 23.9 22.7 22.4 28.0 23.6 32.3 34.2 47.8 2.2 0.6 2.3V 398.0 135.0 137.0 128.0 137.0 133.0 127.0 175.0 225.0 320.0 328.0 325.0 6.2 8.0 5.5Cr 65.9 2861.0 2123.0 4494.0 2956.0 2516.0 2130.0 2639.0 79.5 192.0 202.0 131.0 7.4 4.9 5.0Co 42.8 79.6 73.1 100.0 72.5 73.4 68.7 84.3 58.7 58.7 56.0 50.6 2.4 0.5 0.3Ni 43.4 908.0 800.0 675.0 867.0 868.0 831.0 942.0 188.0 103.0 98.0 83.3 10.8 2.3 2.3Cu 38.5 11.0 3.6 82.9 59.2 89.1 19.6 11.8 88.2 126.0 156.0 23.8 8.3 8.3 4.2Zn 163.0 88.6 63.7 79.7 82.2 67.4 71.7 126.0 118.0 128.0 127.0 102.0 15.3 13.5 6.2Ga 22.9 7.5 6.9 5.0 7.4 6.9 7.1 12.7 19.6 18.9 20.7 16.6 18.0 17.4 21.2Rb 3.8 2.1 2.5 0.6 0.7 0.5 3.1 1.6 5.6 5.6 4.0 3.3 35.8 61.0 41.7Sr 227.0 6.6 7.0 19.1 7.2 6.1 4.9 9.1 335.0 205.0 220.0 108.0 241.0 99.1 86.8Y 27.2 10.0 10.0 5.9 10.3 9.1 9.1 10.3 14.8 22.9 21.7 20.8 1.0 0.6 9.0Zr 97.6 26.5 24.6 10.5 24.5 21.6 24.8 28.1 89.5 146.0 160.0 44.6 85.7 48.9 31.6Nb 7.0 1.0 0.9 0.4 1.0 0.9 0.9 1.2 8.5 11.5 11.8 2.0 0.3 0.2 b0.05Ba 1456.0 22.2 15.9 169.0 13.9 11.1 9.0 49.6 87.9 139.0 313.0 49.6 1182.0 411.0 221.0Hf 3.2 0.9 0.8 0.3 0.8 0.7 0.8 0.9 2.7 4.2 4.5 1.6 2.9 2.2 2.0Ta 0.6 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.7 1.0 1.0 0.2 b0.05 b0.05 b0.05Pb 1.5 0.6 0.7 0.7 2.2 0.7 0.7 0.4 2.2 2.3 2.3 2.0 4.8 15.5 12.8Th 0.2 0.2 0.2 0.1 0.2 0.1 0.1 0.2 1.1 0.8 0.7 0.3 0.1 0.1 b0.05U 0.1 b0.05 b0.05 0.1 b0.05 b0.05 b0.05 b0.05 0.3 0.4 0.4 0.1 0.2 0.1 0.2La 8.9 2.0 2.0 1.7 2.7 2.3 1.4 2.2 11.5 16.2 14.5 3.1 6.7 4.2 5.6Ce 27.0 4.9 5.1 3.1 5.1 5.9 3.4 6.0 29.9 41.0 35.7 8.4 9.1 6.6 12.4Pr 4.0 0.8 0.8 0.5 1.0 0.9 0.6 0.8 3.9 5.4 4.9 1.4 0.9 0.5 1.2Nd 19.7 3.8 3.7 2.3 4.5 4.2 3.1 4.1 16.9 23.7 22.0 6.9 2.7 1.6 3.9Sm 6.8 1.1 1.1 0.8 1.3 1.2 1.0 1.2 4.0 5.4 5.4 2.3 1.4 0.6 0.6Eu 1.9 0.4 0.4 0.2 0.5 0.5 0.4 0.4 1.4 1.8 1.7 0.9 0.4 0.2 0.2Gd 6.9 1.7 1.7 0.9 1.8 1.6 1.5 1.8 4.5 6.2 5.9 3.6 0.3 0.1 0.4Tb 1.1 0.3 0.3 0.2 0.3 0.3 0.3 0.3 0.7 0.9 0.9 0.7 b0.05 b0.05 0.1Dy 5.6 1.8 1.8 1.0 1.8 1.7 1.6 1.8 3.3 4.9 4.6 3.9 0.2 0.1 0.9Ho 1.2 0.4 0.4 0.2 0.4 0.4 0.4 0.4 0.7 1.0 1.0 0.9 b0.05 b0.05 0.4Er 3.1 1.2 1.3 0.7 1.2 1.1 1.1 1.2 1.7 2.5 2.5 2.4 0.1 0.1 1.3Tm 0.4 0.2 0.2 0.1 0.2 0.2 0.2 0.2 0.2 0.4 0.4 0.4 b0.05 b0.05 0.2Yb 2.7 1.2 1.2 0.8 1.2 1.1 1.1 1.2 1.5 2.4 2.3 2.5 0.2 0.1 1.6Lu 0.4 0.2 0.2 0.1 0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.4 b0.05 b0.05 0.2ΣREE 89.6 19.8 20.2 12.5 22.2 21.5 16.1 21.9 80.5 112.1 102.0 37.6 21.9 14.0 29.1(La/Sm)N 0.8 1.1 1.2 1.5 1.4 1.3 1.0 1.1 1.8 1.9 1.7 0.9 3.1 5.0 5.8Nb/Y 0.3 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.6 0.5 0.5 0.1 0.3 0.3 –Th/Yb 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.7 0.3 0.3 0.1 0.7 0.7 –Nb/Yb 2.6 0.8 0.8 0.6 0.8 0.8 0.8 1.0 5.5 4.8 5.2 0.8 2.3 1.8 –Nb/Th 31.9 6.4 6.0 4.3 6.4 7.3 7.1 5.1 8.1 14.2 15.9 6.3 3.1 2.7 –La/Sm 1.3 1.8 1.8 2.3 2.1 2.0 1.5 1.8 2.8 3.0 2.7 1.4 4.8 7.7 9.0

11M.Santosh

etal./Gondw

anaResearch

38(2016)

1–27

Fig. 6. Covariation diagrams of Zr versus selected REE, HFSE and LILEs to demonstrate the effect of alteration. (a) Y vs. Zr, (b) Nb vs. Zr, (c) La vs. Zr, (d) Th vs. Zr.

12 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Southwestern Siberia (Safonova et al., 2011). The obvious concave pat-terns for leuco granite and minor concave patterns for lherzolite andhornblendite/gabbroic can be interpreted as sourcing from basaltswith geochemically enriched components (Aldanmaz et al., 2008).

TheN-MORB normalized spider variation diagrams for samples fromthe Yishui ophiolite suite are shown in Fig. 9. The E-MORB and OIB

Fig. 7. Binary plots of (a) SiO2 vs. Na2O + K2O and (b) Nb/Y vs. Zr/TiO2. Fields in (a) after WilsoIrvine and Baragar (1971).

compositions (denoted by broken lines in the figure) and the normali-zation values are from Sun and McDonough (1989). The hornblendenorite/gabbro units show LILE enrichment such as Ba, K, Ta and Pband negative Th, U, Nb, Zr and Hf anomalies. They display compositionalrange broadly parallel to E-MORB (Fig. 9a). The lherzolites exhibit pos-itive Ba and Pb anomalies but negative Nb, Sr, Zr and Hf anomalies,

n (1989) and fields in (b) after Peccerillo and Taylor (1976). The dotted line in (a) is from

Fig. 8. Chondrite-normalized REE distribution diagrams for (a) hornblende norite/gabbro, (b) lherzolite, (c) hornblendite/gabbroic hornblendite and (d) leuco granite from the Yishuiophiolite suite. Normalizing values are from Sun and McDonough (1989). The data for average normal mid-ocean ridge basalt (N-MORB), enriched mid-ocean ridge basalt (E-MORB),and oceanic island basalt (OIB) shown by thick broken lines, are also from Sun andMcDonough (1989).MORB and OIBfields for comparison are fromAldanmaz et al. (2008) and Safonovaet al. (2011).

13M. Santosh et al. / Gondwana Research 38 (2016) 1–27

accompanied by distribution pattern sub-parallel to that of the E-MORB(Fig. 9b). The hornblendites/gabbroic hornblendite also exhibit patternssimilar to that of the lherzolite, butwith relativelymore negative anom-alies of U and Sr and positive anomaly of Pb (Fig. 9c). Compared to thehornblende norite/gabbros, lherzolite and hornblendites/gabbroichornblendite, the leuco granites exhibit more prominent compositionalrange with positive anomalies in Ba, K, Pb, Sr and negative anomalies inTh, Nb, P and Ti (Fig. 9d).

The geochemical data from the hornblende norite/gabbros,lherzolite, hornblendites/gabbroic hornblendite and leuco granitesfrom the Yishui ophiolite suite were plotted on various major, traceand REE tectonic discrimination diagrams (Figs. 10 and 11). For maficrocks, like gabbros and hornblendites, the discriminations are typicallyused for distinguishing Mid Ocean Ridge Basalt (MORB), and IslandArc Tholeiite (IAT). The V vs. Cr plots of all mafic rocks includinglherzolite show a tholeiitic to calc-alkaline trend (Fig. 10a). In the AFMdiagram (Fig. 11a), these rocks fall along the tholeiitic fractionationtrend showing pronounced Fe (+ Ti) enrichment, with the lherzolitesand hornblendites/gabbroic hornblendite showing arc-related ultramaficcumulate nature. In the Ti vs. Zr diagram (Pearce, 1980), all these samplesplot in the basic field except one lherzolite sample, where the plots fall inthe overlapping region of IAT (island arc tholeiites) and the IAT-MORB(mid ocean ridge basalt) (Fig. 10b). A similar feature is also displayed intheir distribution in the V vs. Ti diagram (Fig. 10c). All the samples plotin the IAT field on the Cr vs. Y diagram, which discriminates MORBfrom IAT (Fig. 10d). Similarly, in the Hf/3–Th–Nb/16 ternary diagram(Fig. 11b), the lherzolites and hornblendites/gabbroic hornblendite fall

into the area of IAT, the hornblende gabbro/gabbros fall in the field ofIAT + E-MORB. In the case of the granitoids, both in the Rb vs. Nb + Yplot (Fig. 10e) and Ta vs. Yb plot (Fig. 10f), the plots fall in the volcanicarc granite field (VAG). In summary, themafic rocks exhibit tholeiitic na-ture, straddling from island arc to tholeiitic affinity, whereas the granitesexhibit volcanic arc nature.

Ratios of incompatible elements are particularly useful for evaluat-ing the nature of mantle source since they are almost insensitive to var-iations in the degree of partial melting and fractional crystallization(Pearce and Peate, 1995; Pearce, 2008). Usually, lower incompatible el-ement ratios correspond to depleted mantle sources (e.g., N-MORB),whereas higher ratios correspond to more incompatible elementenriched mantle (e.g., OIB or sub-arc mantle). The elevated Th/Yb at agiven Nb/Yb value in this diagram could help to differentiate the sub-duction zone settings or melts contaminated by pre-existing continen-tal crust. In the Th/Yb–Nb/Yb diagram (Fig. 12a), the rocks from Yishuiophiolite suite fall within or above the MORB-OIB array and have Th/Yb ratios greater than that of N-MORB, and even up to E-MORB, suggest-ing that the protolith magmas were sourced from a moderatelyenriched mantle, as also evidenced by patterns similar to E-MORB. Thehigher Th/Yb ratios may be attributed to the conservative behavior ofNb in the subducting slab, with additions of Th and LREE from slab tothe wedge or through crustal contamination (Pearce, 2008).

In order to evaluate the extent of crustal contamination, the Nb/Th–La/Sm binary diagram has been utilized since these elements are sensi-tive to contamination. Samples that are influenced by crustal contami-nation show a hyperbolic trend, where the samples with the lowest

Fig. 9.N-MORB normalized trace element variation diagrams for a) hornblende norite/gabbro, (b) lherzolite, (c) hornblendite/gabbroic hornblendite and (d) leuco granite from the Yishuiophiolite suite. Normalizing values are from Sun andMcDonough (1989). The data for average normalmid-ocean ridge basalt (N-MORB), enrichedmid-ocean ridge basalt (E-MORB), andoceanic island basalt (OIB) shown by thick broken lines, are also from Sun and McDonough (1989).

14 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Nb/Th and highest La/Sm are themost contaminated. Rocks crystallizedfrom lesser contaminated magmas would have the opposite character-istics. The behavior of Yishui samples in Fig. 12b suggests evolution ina subduction-related regime with no significant crustal contamination.

6. Zircon geochronology and Lu–Hf isotopes

6.1. Zircon morphology and U–Pb geochronology

Five representative samples, including one hornblendite, two gabbrosand two leuco granites were chosen for geochronology. Representativecathodoluminescence (CL) images of the zircon grains from the differentrocks analyzed in this study are given in Figs. 13 and 14. TheU–Pb analyt-ical data are given in Supplementary Table 4. The age data are plotted inconcordia diagrams in Figs. 15 and 16 together with their computedweighted mean 207Pb/206U ages.

6.1.1. Hornblendite [YS-17B1]Zircon grains separated from this sample mostly show prismatic

to stumpy morphology, with only few grains exhibiting ellipticalshape with rounded terminations. They are colorless to lightbrown, with a size range of 20–110 μm × 10–60 μm and aspectratio ranging from 3:1 to 1:1. Under CL images (Fig. 13a), the grainsdisplay banded or patchy internal texture, with few grains showingdark inherited core and newly formed rims. A total of 25 U–Pb anal-yses were conducted on 25 zircon grains. The Th contents range from

44.9 to 1778 ppm and U contents range from 124 to 1902 ppm, withTh/U ratios in the range of 0.32–1.04 (Supplementary Table 4).Except for spot #3, #5, #20, #23, and #29 which show high uncer-tainty (one sigma) and high discordance, the other 20 zircon grainsplot along a discordia line indicating variable Pb loss, and define anupper intercept age of 2538 ± 30 Ma (MSWD= 0.31). Their weight-ed 207Pb/206Pb mean age is calculated as 2531 ± 20 Ma (MSWD =0.17) (Fig. 15a), which is close to the upper intercept age. The2538 ± 30 Ma age is taken to represent to the timing of the forma-tion of this rock.

6.1.2. Gabbro [YS-17D1]The zircon grains from this sample are transparent to translucent,

colorless, and euhedral to subhedral prismatic and elliptical inmorphol-ogy.Most of the grains vary from20 to 100 μm in length and 15 to 80 μmin width, with aspect ratio ranging from 3.5:1 to 1.25:1. Most zircongrains display patchy or sector zoning, whereas some grains exhibit ho-mogeneous internal texture (Fig. 13b). A very narrow (b5 μm), low Ucontent rim (dark under transmitted light and bright in CL) is visiblein many zircon grains, which could indicate metamorphic overgrowth.A total of 30 spots on magmatic domains were analyzed from 30 zircongrains. Their Th contents show a range of 204–901 ppm and U contentsshow a range of 530–1631 ppm, with Th/U ratios of 0.26–0.71 (Supple-mentary Table 4). On the U–Pb concordia diagram (Fig. 15b), all of theresults fall along or near the concordia line with concordance higherthan 90% and yield weighted 207Pb/206Pb mean age of 2477 ± 11 Ma

Fig. 10. Binary tectonic discrimination diagrams. (a) V (ppm)–Cr (ppm) diagram (afterMiyashiro and Shido, 1975) for hornblende norite/gabbros, lherzolites and hornblendites/gabbroichornblendite. TH: tholeiitic, CA: calcalkaline. (b) Ti (ppm) vs. Zr (ppm) discrimination diagram for hornblende norite/gabbros, harzburgites and hornblendites/gabbroic hornblendite(after Pearce, 1980), IAT: island arc tholeiite, MORB: mid ocean ridge basalt, WPB: within plate basalt. (c) Ti (ppm) vs. V (ppm) discrimination diagram for hornblende gabbro/gabbros,lherzolites and hornblendites (after Shervais, 1982). (d) Cr (ppm) vs. Y (ppm) diagram for hornblende gabbro/gabbros, harzburgites and hornblendites (after Pearce and Norry, 1979).(e) Y + Nb (ppm) vs. Rb (ppm) tectonic environment discrimination diagram for leuco granites (after Pearce et al., 1984). ORG: ocean ridge granites; VAG: volcanic arc granites;WPG: within plate granites. (f) Yb (ppm) vs. Ta (ppm) tectonic environment discrimination diagram for granites (after Pearce et al., 1984).

15M. Santosh et al. / Gondwana Research 38 (2016) 1–27

(MSWD = 0.77) and upper intercept age of 2503 ± 16 Ma (MSWD =0.76). By considering the Th/U ratios and the magmatic textures, theupper intercept age can be interpreted as the age of the crystallizationof this rock.

6.1.3. Gabbro [YS-17D2]The zircon grains in this sample are transparent to translucent, color-

less, and euhedral to subhedral, and some of the grains show irregularprisms. The prismatic grains are 20–100 μm × 40–70 μm in size with

Fig. 11. Ternary tectonic discrimination diagrams. (a) Fe2O3–Na2O+ K2O–MgO plot for hornblende norite/gabbros, lherzolites and hornblendites/gabbroic hornblendite (after Irvine andBaragar, 1971; Parlak et al., 2000). (b)Hf/3–Th–Nb/16diagram(Wood, 1980) for hornblendenorite/gabbros, lherzolites andhornblendites/gabbroic hornblendite, A:N-MORB, B: E-MORB,C: Alkaline with in plate basalts, D: Island arc tholeiites.

16 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

aspect ratios of about 2.5:1 to 1:1.Most grains display patchy linear zon-ing or are structureless in CL images (Fig. 13c). A total of 30 analyseswere made on 30 grains. The results show Th and U contents varyingfrom113 to 816ppm, and 497–2021 ppm, respectively, and Th/U valuesof 0.23 to 0.56 (Supplementary Table 4). All the age data form a singlecluster along the concordia, with a weighted 207Pb/206Pb mean ageof 2483 ± 11 Ma (MSWD = 0.47) and an upper intercept age of2495 ± 10 Ma (MSWD = 0.42) (Fig. 15c). We interpret the 2495 ±10 Ma as the timing of formation of this rock based on the magmaticfeatures of the zircons (including high Th/U ratios, and patchy linearzoning).

6.1.4. Leuco granite [YS-17E1]The zircon grains from this sample display prismatic to stumpy in

morphology and show patchy or clear oscillatory zoning. Only a fewgrains exhibit inhomogeneous internal texture. The zircons are colorlessor light brownish, with a size range of 60–200 μm × 50–90 μm and as-pect ratios of 2.5:1 to 1:1 (Fig. 14a). A total of 30 analyses were carriedout on 30 zircon grains. Their Th and U contents and Th/U ratios are inthe range of 158–411 ppm, 292–3616 ppm, and 0.09–0.80, respectively(Supplementary Table 4). All of the age data show high concordance(N97%) and their 207Pb/206Pb ages vary from 2431 Ma to 2658 Ma.These ages can be divided into two groups: 8 of the 30 analyses on

Fig. 12. (a) Nb/Yb vs. Th/Yb diagram (Pearce and Peate, 1995; Pearce, 2008) for the rocks from thare from Sun andMcDonough (1989). (b) La/Sm vs. Nb/Th plot where Yishui samples do not foand McDonough, 1989).

oscillatory zoned domains form a coherent group within analyticalerror and yield a weighted mean 207Pb/206Pb age of 2590 ± 25 Ma(MSWD = 1.07), which is interpreted to be the formation age ofxenocrystic zircons from older sources. The remaining 22 analyses fallslightly below the concordia line which suggests that the zircon grainsmay have experienced variable Pb loss. They yield an upper interceptage of 2503 ± 21 Ma (MSWD = 0.87), whereas their weighted mean207Pb/206Pb age is 2480±14Ma (MSWD=0.88) (Fig. 16a). The analyt-ical domains for the 22 analyses are mainly on the patchy zoned do-mains, and therefore the age of 2503 ± 21 Ma can be interpreted asthe timing of formation of this rock.

6.1.5. Leuco granite [YS-17E2]Most of the zircon grains in the analyzed sample are transparent

to translucent and colorless, although some grains show dark browncolor, with size of 80–140 μm × 30–70 μm and aspect rations of 3.5:1to 1:1. They are mostly long prismatic in shape with a few grains occur-ring as ellipsoidal or sub-rounded grains. Most of the grains exhibitpatchy zoning or sector zoning, with some inherited dark colored do-mains occurring at the center of some zircon grains (Fig. 14b). Total28 U–Pb analyseswere performed on 28 grains. Their Th and U contentsand Th/U ratios are in the range of 19–3798 ppm, 898–9398 ppm, and0.01–0.40, respectively (Supplementary Table 4). Except for two spots

e Yishui ophiolite suite. N-MORB, E (enriched)—MORB and OIB (ocean island basalt) datallow hyperbolic trend between the crust (UCC) and mantle (N-MORB) endmembers (Sun

Fig. 13. Representative cathodoluminescence (CL) images of zircons from hornblendite (YS-17B1), and gabbros (YS-17D1, YS-17D2). The analytical spots for U–Pb (small yellow dottedcircles) and Lu–Hf (large red dotted circles) and age, initial εHf(t) values (in Ma) are also shown.

17M. Santosh et al. / Gondwana Research 38 (2016) 1–27

(spots #20, #21) from inherited domains displaying 207Pb/206Pb age as2653Ma and 2695Ma, the other 26 spots define an upper intercept ageof 2538±16Ma (MSWD=0.77) and aweightedmean 207Pb/206Pb ageof 2537±13Ma (MSWD=0.70) (Fig. 16b). Both the patchy and sectorzoning and Th/U values indicatemagmatic origin for these zircon grains.Thus, the upper intercept age can be interpreted as the timing of forma-tion of this rock in the suite.

6.2. Zircon Lu–Hf isotopes

Lu–Hf isotope analyses were performed in the same domains or inadjacent domains with same or similar textures where U–Pb age data

were obtained. The results are listed in Table 5 and illustrated inFig. 17. The data obtained are briefly discussed below.

6.2.1. Hornblendite [YS-17B1]Because of the small size for zircon grains from sample YS-17B1, only

two analyses were obtained from two zircon with 207Pb/206Pb ageof 2577 Ma and 2526 Ma, which show initial 176Hf/177Hf values of0.281160 and 0.281269 (Table 5, Fig. 17a) and positive εHf(t) valuesof 0.8 and 3.5 (Fig. 17b), when calculated based on their own207Pb/206Pb age. Their corresponding εHf single stage model ages(TDM) are 2845 Ma and 2698 Ma, whereas the two stage model ages

Fig. 14. Representative cathodoluminescence (CL) images of zircons from leuco granites (YS-17E1, YS-17E2). The analytical spots for U–Pb (small yellow dotted circles) and Lu–Hf(large red dotted circles) and age, initial εHf(t) values (in Ma) are also shown.

18 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

(TDMC ) are 3010Ma and 2807Ma. The data indicate that themagmawaslikely sourced from Neoarchean juvenile components.

6.2.2. Gabbro [YS-17D1]Ten representative zircons from this sample were chosen for Lu–Hf

analyses. They show initial 176Hf/177Hf values between 0.281147 and0.281310 (Table 5, Fig. 17a), and εHf(t) values between −2.5 and 3.3(Fig. 17b) with an average of 0.8, when calculated by their own207Pb/206Pb age. Their corresponding εHf single stage model ages(TDM) and two stage model ages (TDMC ) range from 2643 Ma to2862 Ma and 2762 Ma to 3118 Ma respectively. The data indicate that

the zircons in the rock were possibly derived from Neoarchean juvenilecomponents with limited Mesoarchean continental crustal sedimentsdeposited in the trench and recycled during subduction.

6.2.3. Gabbro [YS-17D2]In this sample, Lu–Hf isotopes analyses were performed on 8 zircon

grains and the results show initial 176Hf/177Hf values ranging from0.281162 to 0.281289 (Table 5; Fig. 17a). They yield εHf(t) values rang-ing from −1.8 to 3.6 with an average of 1.2 (Fig. 17b) when calculatedby their 207Pb/206Pb ages. The data indicate εHf single stage model ages(TDM) ranging from 2671 Ma to 2840 Ma, while crustal residence ages

Fig. 15. U–Pb concordia plots for selected rock samples with inserted weighted mean 207Pb/206U age diagram. (a) hornblendite (YS-17B1), (b) gabbro YS-17D1 and (c) gabbro YS-17D2.

19M. Santosh et al. / Gondwana Research 38 (2016) 1–27

(TDMC ) in the range of 2779 to 3080Ma, suggestingmagma sources fromNeoarchean juvenile components with limited Mesoarchean reworkedcrustal materials, such as recycled continental trench sediments.

Fig. 16. U–Pb concordia plots for selected rock samples with inserted weighted mean 2

6.2.4. Leuco granite [YS-17E1]In this sample, ten zircon grains were analyzed for Lu–Hf isotopes,

and the results show initial 176Hf/177Hf values of 0.281209 to 0.281271

07Pb/206U age diagram. (a) Leuco granite YS-17E1 and (b) leuco granite YS-17E2.

Table 5LA-MC-ICP-MS Lu–Hf isotope data on zircons from YS-17B1 (hornblendite), YS-17D1 (gabbro), YS-17D2 (gabbro), YS-17E1 (leuco granite), and YS-17E2 (leuco granite).

No. Age (Ma) 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 2σ 176Hf/177Hfi eHf(0) eHf(t) TDM (Ma) TDMC (Ma) fLu/Hf

YS-17B1-13 2577 0.019735 0.000095 0.000579 0.000005 0.281189 0.000017 0.281160 −56.0 0.8 2845 3010 −0.98YS-17B1-30 2526 0.006630 0.000028 0.000241 0.000001 0.281281 0.000021 0.281269 −52.7 3.5 2698 2807 −0.99YS-17D1-01 2478 0.009339 0.000042 0.000260 0.000000 0.281238 0.000020 0.281226 −54.2 0.9 2756 2932 −0.99YS-17D1-03 2465 0.012588 0.000105 0.000366 0.000002 0.281262 0.000021 0.281245 −53.4 1.2 2731 2898 −0.99YS-17D1-06 2455 0.014590 0.000098 0.000398 0.000001 0.281280 0.000023 0.281262 −52.8 1.6 2710 2868 −0.99YS-17D1-07 2453 0.003084 0.000009 0.000106 0.000000 0.281223 0.000022 0.281218 −54.8 0.0 2766 2965 −1.00YS-17D1-11 2454 0.007092 0.000069 0.000278 0.000005 0.281160 0.000031 0.281147 −57.0 −2.5 2862 3118 −0.99YS-17D1-12 2461 0.008913 0.000028 0.000265 0.000000 0.281255 0.000024 0.281242 −53.7 1.0 2735 2907 −0.99YS-17D1-14 2466 0.011267 0.000130 0.000311 0.000002 0.281237 0.000020 0.281222 −54.3 0.5 2762 2948 −0.99YS-17D1-15 2456 0.005722 0.000043 0.000225 0.000002 0.281321 0.000034 0.281310 −51.3 3.3 2643 2762 −0.99YS-17D1-16 2444 0.011304 0.000058 0.000399 0.000006 0.281269 0.000027 0.281250 −53.2 0.9 2725 2901 −0.99YS-17D1-20 2481 0.005441 0.000060 0.000196 0.000003 0.281230 0.000027 0.281221 −54.5 0.8 2763 2941 −0.99YS-17D2-01 2522 0.006773 0.000036 0.000225 0.000001 0.281202 0.000028 0.281191 −55.5 0.7 2802 2978 −0.99YS-17D2-02 2500 0.007867 0.000051 0.000270 0.000001 0.281302 0.000019 0.281289 −52.0 3.6 2671 2779 −0.99YS-17D2-10 2502 0.009634 0.000103 0.000337 0.000004 0.281281 0.000020 0.281265 −52.7 2.8 2705 2832 −0.99YS-17D2-11 2522 0.005497 0.000021 0.000196 0.000001 0.281248 0.000018 0.281239 −53.9 2.3 2738 2875 −0.99YS-17D2-13 2462 0.005721 0.000057 0.000207 0.000003 0.281181 0.000019 0.281171 −56.3 −1.4 2829 3061 −0.99YS-17D2-22 2473 0.006425 0.000028 0.000207 0.000001 0.281243 0.000021 0.281233 −54.1 1.0 2746 2919 −0.99YS-17D2-24 2465 0.005391 0.000030 0.000170 0.000001 0.281279 0.000026 0.281271 −52.8 2.2 2696 2842 −0.99YS-17D2-26 2461 0.006532 0.000036 0.000204 0.000001 0.281172 0.000028 0.281162 −56.6 −1.8 2840 3080 −0.99YS-17E1-01 2465 0.044074 0.000144 0.001051 0.000001 0.281302 0.000019 0.281253 −52.0 1.5 2726 2882 −0.97YS-17E1-03 2444 0.026522 0.000246 0.000689 0.000001 0.281295 0.000018 0.281263 −52.2 1.4 2710 2872 −0.98YS-17E1-06 2477 0.032698 0.000240 0.000850 0.000008 0.281299 0.000017 0.281258 −52.1 2.0 2716 2861 −0.97YS-17E1-09 2487 0.032189 0.000552 0.000843 0.000011 0.281309 0.000019 0.281269 −51.7 2.6 2702 2832 −0.97YS-17E1-19 2480 0.035513 0.000123 0.001104 0.000002 0.281324 0.000015 0.281271 −51.2 2.5 2700 2831 −0.97YS-17E1-24 2587 0.027432 0.000070 0.000903 0.000001 0.281312 0.000018 0.281267 −51.6 4.8 2703 2772 −0.97YS-17E1-26 2576 0.041044 0.000073 0.001150 0.000005 0.281289 0.000016 0.281233 −52.4 3.4 2751 2854 −0.97YS-17E1-27 2563 0.026149 0.000067 0.000745 0.000001 0.281245 0.000019 0.281209 −54.0 2.2 2782 2915 −0.98YS-17E1-28 2533 0.037500 0.000135 0.001012 0.000001 0.281303 0.000019 0.281254 −51.9 3.1 2722 2835 −0.97YS-17E1-29 2524 0.032556 0.000165 0.000956 0.000001 0.281270 0.000018 0.281224 −53.1 1.9 2762 2906 −0.97YS-17E2-01 2540 0.047510 0.000620 0.001376 0.000017 0.281352 0.000018 0.281285 −50.2 4.4 2680 2762 −0.96YS-17E2-07 2531 0.022884 0.000104 0.000732 0.000004 0.281344 0.000012 0.281308 −50.5 5.0 2647 2718 −0.98YS-17E2-12 2536 0.051843 0.000490 0.002109 0.000019 0.281364 0.000021 0.281262 −49.8 3.5 2716 2816 −0.94YS-17E2-14 2535 0.044029 0.001100 0.001773 0.000045 0.281302 0.000026 0.281216 −52.0 1.8 2779 2917 −0.95YS-17E2-19 2536 0.056833 0.000537 0.002077 0.000025 0.281322 0.000027 0.281222 −51.3 2.1 2772 2903 −0.94YS-17E2-26 2522 0.032376 0.000536 0.001287 0.000020 0.281336 0.000070 0.281274 −50.8 3.6 2697 2799 −0.96YS-17E2-28 2512 0.044881 0.000663 0.001603 0.000015 0.281384 0.000022 0.281307 −49.1 4.5 2652 2732 −0.95

20 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

(Table 5; Fig. 17a). They display positive εHf(t) values in the range of 1.4to 4.8 (Fig. 17b) with an average of 2.5 when calculated by their own207Pb/206Pb age. Their εHf single stagemodel ages (TDM) and crustal res-idence ages (TDMC ) vary from 2700 to 2782 Ma and 2772 to 2915Ma re-spectively. The data indicate that the magma sources are derived fromNeoarchean juvenile components.

6.2.5. Leuco granite [YS-17E2]Seven zircon grains from this rock show initial 176Hf/177Hf values be-

tween 0.281216 and 0.281308 (Table 5; Fig. 17a) and positiveεHf(t) values between 1.8 and 5.0 (Fig. 17b) with an average of 3.6,

Fig. 17. Zircon Lu–Hf isotope plots for rocks from Yishui ophiolite suite. (a) 176Hf/177Hfi vs. agerocks from various regions of the North China Craton as compiled by Geng et al. (2012).

when calculated by their own 207Pb/206Pb age. The data show εHf singlestagemodel ages (TDM) in the range of 2647 to 2779Ma and crustal res-idence ages (TDMC ) in the range of 2718 to 2917 Ma. The data suggestmagma was likely sourced from Neoarchean juvenile components.

7. Discussion

7.1. Lithological and geochemical features of the Yishui ophiolites

The lithological assemblages in the Yishui suite reported in thisstudy are broadly identical to those recorded from Precambrian

(Ma), (b) εHf(t) vs. age (Ma). The shaded regions are data for Archean to Paleoproterozoic

21M. Santosh et al. / Gondwana Research 38 (2016) 1–27

suprasubduction zone ophiolite complexes, such as the ManameduComplex (Santosh et al., 2012) and the Agali Hills (Santosh et al.,2013) in southern India. The association of lherzolite, pyroxenite,hornblendite and leucogranite is similar to the ultramafic–mafic andfelsic units in dismembered ophiolite suites in the above examples,and also compares with those reported from some Phanerozoic exam-ples. Gabbros constitute the major rock type in Yishui with composi-tional gradation from noritic gabbro and hornblende gabbro tohornblendite. The more felsic variants also carry minor gabbroic anor-thosite and anorthositic domains. The gabbroic suite is intruded byveins and lenses of leucocratic granitoids of volcanic arc affinity. Togeth-er with the amphibolites and BIF bands, as well as diabase dykes ex-posed in the nearby locations of the Yishui complex, our findingrepresents a highly dismembered and deformed suprasubductionzone ophiolite suite. The presence of lherzolite in the Yishui suite iscomparable to similar examples in other ophiolite sections, such asthe lherzolites in the basal section of the central Oman ophiolites(Khedr et al., 2014).

Although olivine-bearing ultramafic rocks of harzburgite composi-tion have been reported from some suprasubduction zone ophiolites(Tamura and Arai, 2006), the basal section in the Yishui ophiolite doesnot show the typical modal mineralogy of harzburgite which shouldhave 40–90% olivine, b5% Cpx and 5–55% Opx. According to the assem-blage shown in Fig. 4b and also from our petrographic observations, themodal abundance of serpentinite in these rocks (which represent al-tered olivine) is only 25–30%. Furthermore, the high modal abundanceof Hbl, which is probably derived from Cpx, suggests that the rock islherzolite. Petrographic observation of the hornblendites suggests thatboth magmatic and metamorphic hornblendes are present in the rock.Magmatic Hbl-bearing mafic–ultramafic rocks imply high H2O contentof parentmagma. Hornblende-bearing gabbros are common in subduc-tion zones. This is also consistent with the geochemical data ofhornblendite which show arc-related ultramafic cumulate affinity.Thus, the presence of magmatic Hbl also suggests suprasubductionzone setting.

Geochemically, the mafic rocks from Yishui complex show sub-alkaline basaltic source, whereas the granitoids show volcanic arc affin-ity. The hornblende gabbro and gabbro, lherzolite and hornblenditeshow compositional similarity to E-MORB and N-MORB and are compa-rable to the features of Neotethyan Ophiolites. The lherzolite fromYishui shows positive Ba and Pb anomalies and negative Nb, Sr, Zr andHf anomalies with element distribution pattern sub-parallel to that ofE-MORB. Further evaluation using discrimination plots shows that the

Fig. 18. (a) Age data histograms and probability curves for all the zircons analyzed in this study.in this study.

lherzolite and hornblendites possess arc-related ultramafic cumulatenature, with overall features straddling the fields of IAT (island arc tho-leiites) and the IAT-MORB (mid ocean ridge basalt). The granitoids typ-ically display volcanic arc features. As discussed above, the protolithmagmas of the Yishui ophiolite suite were sourced from a moderatelyenriched mantle, with additions of Th and LREE from slab to thewedge or through crustal contamination as evidenced by higher Th/Ybratios, which may be attributed to the conservative behavior of Nb inthe subducting slab (Pearce, 2008). Plots shown in Fig. 12b clearly sug-gest evolution in a subduction-related regimewith no significant crustalcontamination.

7.2. Summary of U–Pb and Lu–Hf data of the Yishui ophiolites

The majority of zircon grains in all rock types from the Yishui suiteexhibit magmatic texture and high Th/U ratios (Fig. 18). Zircon grainsfrom hornblendite define an upper intercept age of 2538 ± 30 Ma. Zir-cons from one leuco granite sample (YS-17E2) also define a similarupper intercept age of 2538 ± 16 Ma, whereas those in the otherleuco granite (YS-17E1) define a slightly younger upper intercept ageof 2503±21Ma, together with another old groupwith the upper inter-cept age of 2590 ± 25Ma. The two gabbros define upper intercept agessimilar to that of the youngest group of zircons in the granite, at 2503±16 Ma and 2495 ± 10 Ma respectively. Among these age groups, theoldest groupwith age of 2590±25Ma could represent inherited grains.The other age group falls between ~2540Ma and ~2500Ma. In Fig. 18b,we show compiled histograms and probability curves of all the age datafrom the different rock types presented in this study. The major peak at2500Ma iswell defined, broadly coevalwithNeoarchean amalgamationof the microblocks in North China Craton (Yang et al., 2016). Fig. 18ashows compiled Th/U versus 207Pb/206Pb age of magmatic zirconsfrom the various rock types analyzed in this study. Although a smallgroup of zircons (from sample YS-17E2) shows low Th/U values, the do-main ages come from magmatic grains. Zircon grains from the otherfour samples exhibit Th/U ratios higher than 01, even up to 1.04, togeth-er and with their magmatic texture, the ages indicate the magmaticpulses during Neoarchean.

Lu–Hf data on zircons from the rock suites from Yishui provide in-sights into the nature of magma source from where the zircon crystal-lized. In summary, zircons from the one hornblendite sample and twoleuco granite samples exhibit positive εHf(t) values between 0.8 and5.0, and corresponding single stage model ages (TDM) range from2845 Ma and 2647 Ma, indicating their magma source from mostly

(b) Th/U versus 207Pb/206Pb age of magmatic zircons from the various rock types analyzed

Table 6Complied zircon U–Pa age data from the Yishui terrane.

Sample No. Rock type Geological unit Location Method Age Interpretation References

10SD07 Enderbite Mashan pluton Dongyuan LA-ICP-MS Mean age: 2528 ± 8 Ma Crystallization Wu et al. (2013)YS9566 Granite Mashan pluton Mashan SHRIMP Mean age: 2538 ± 6 Ma Crystallization Shen et al. (2007)11SD01-2 Garnet charnockite Caiyu pluton Caiyu LA-ICP-MS Mean age: 2559 ± 16 Ma Crystallization Wu et al. (2013)YS95-58 Granodiorite Caiyu pluton Caiyu SHRIMP Mean age: 2545 ± 10 Ma Crystallization Shen et al. (2004)11SD02-16 Charnockite Xueshan pluton Xueshan LA-ICP-MS Mean age: 2535 ± 11 Ma Crystallization Wu et al. (2013)YS9573 Enderbite Xueshan pluton Xueshan SHRIMP Mean age: 2532 ± 9 Ma Crystallization Shen et al. (2007)YS99-16 Monzonitic granite Dashan pluton Dashan SHRIMP Mean age: 2562 ± 14 Ma Crystallization Shen et al. (2004)YS06-30 Granite Yinglingshan pluton Yinglingshan SHRIMP Mean age: 2530 ± 7 Ma Crystallization Zhao et al. (2008)YS06-48 Granite Yinglingshan pluton Yinglingshan SHRIMP Mean age: 2531 ± 8 Ma Crystallization Zhao et al. (2008)08YS-7 Monzodiorite Yanquan pluton Yanquan (35°46.463′N, 118°40.884′E) LA-ICP-MS Mean age: 2543 ± 8 Ma Emplacement Peng et al. (2012)08YS-43 Monzodiorite Yanquan pluton Yanquan (35°48.661′N, 118°42.138′E) LA-ICP-MS Mean age: 2544 ± 4 Ma Emplacement Peng et al. (2012)10SD07-2 Metapelite Yishui Group Beixiazhuang LA-ICP-MS Mean age: 2535 ± 8 Ma Crystallization Wu et al. (2013)10SD012 Felsic gneiss Yishui Group Caiyu LA-ICP-MS Mean age: 2543 ± 6 Ma Intrusion Wu et al. (2013)10SD09 Biotite plagioclase gneiss Yishui Group Mashan LA-ICP-MS Mean age: 2559 ± 9 Ma Crystallization Wu et al. (2013)

Mean age: 2508 ± 12 Ma Metamorphism Wu et al. (2013)10SD06-4 Garnet biotite-plagioclase gneiss Yishui Group Caiyu LA-ICP-MS Mean age: 2570 ± 27 Ma Crystallization Wu et al. (2013)

Mean age: 2499 ± 8 Ma Metamorphism Wu et al. (2013)11SD02-18 Pyroxene bearing felsic gneiss Yishui Group Xueshan LA-ICP-MS 2559–2661 Ma Crystallization Wu et al. (2013)YS06-19 Plagioclase amphibolite Yishui Group Hujiazhuang SHRIMP Mean age: 2522 ± 5 Ma Metamorphism Zhao et al. (2009a)YS06-31 Spinel and garnet bearing granulite Yishui Group SHRIMP 2532–2719 Ma Constraint for metamorphism Zhao et al. (2009a)YS06-40 Garnet bearing granulite Yishui Group Fengjiazhuang SHRIMP Mean age: 2514 ± 5 Ma Metamorphism Zhao et al. (2009a)YS06-41 Plagioclase amphibolite Yishui Group Luojiazhuang SHRIMP Mean age: 2497 ± 4 Ma Metamorphism Zhao et al. (2009a)YS06-45 Garnet bearing granulite Yishui Group Hujiazhuang SHRIMP Mean age: 2488 ± 10 Ma Metamorphism Zhao et al. (2009a)YS06-49 Garnet bearing granulite Yishui Group Liujiashan SHRIMP Mean age: 2509 ± 5 Ma Metamorphism Zhao et al. (2009a)YS06-B2 Plagiogneiss Yishui Group Niuxinguanzhuang SHRIMP Upper intercept age: 2659 ± 32 Ma Crystallization Zhao et al. (2009b)YS0901-1 Mafic granulite Yishui Group Qinglongyu SHRIMP Mean age: 2498 ± 8 Ma Metamorphism Zhao et al. (2013)YS0901-2 Ultramafic rock Yishui Group Qinglongyu SHRIMP 2560–2702 Ma Crystallization Zhao et al. (2013)YS0902-2 Mafic granulite Yishui Group Qinglongyu SHRIMP Upper intercept age: 2561 ± 7 Ma Crystallization Zhao et al. (2013)NXO-3 Gneissic granodiorite Beixiaoyao SW 750 m SHRIMP Upper intercept age: 2491 ± 5 Ma Crystallization Li et al. (2011)YS06-29 Plagioclase amphibolite Yinglingshan SHRIMP Mean age: 2531 ± 6 Ma Magma alteration Zhao et al. (2008)

22M.Santosh

etal./Gondw

anaResearch

38(2016)

1–27

Fig. 19. Histogram and probability curves of published age data compiled from previousstudies in the Yishui terrene.

23M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Neoarchean juvenile components. The two gabbro samples displayεHf(t) values in the range of −2.5 and 3.6, with single stage modelages (TDM) ranging from 2643 Ma to 2862 Ma and two stage modelages (TDMC) varying from 2762 Ma to 3118 Ma, suggesting that themagma was sourced mostly from Neoarchean juvenile componentswith possible reworking of minor Mesoarchean crustal components,possibly involving the recycling of continental trench sediments duringsubduction.

7.3. Summary of previous geochronological studies in the Yishui Complex

Age data fromprevious geochronological studies on themajor lithol-ogies of the Yishui Terrane are compiled in Table 6 and illustrated inFig. 19. In previous studies, the zircon U–Pb analyses were mainly per-formed on granitoids and TTG gneisses, amphibolites, mafic granulites,pelitic gneisses and minor ultramafic rocks belonging to the YishuiGroup. As shown in Table 6, zircons in the granitoids and metamorphicrocks record U–Pb ages of 2.49–2.57 Ga, with some inherited grainsshowing ages up to 2.6–3.1 Ga (Shen et al., 2004, 2007; Zhao et al.,2008, 2009a,b; Li et al., 2011; Wu et al., 2013; Zhao et al., 2013).

The granitoid rocks, including granites, charnockites/enderbites,granodiorites andmonzodiorites from various granitoid plutons displayweighted mean 207Pb/206Pb ages between 2528 ± 8 Ma and 2562 ±14 Ma, interpreted as the crystallization age of the granitoid magma(Shen et al., 2004, 2007; Zhao et al., 2008; Peng et al., 2012; Wu et al.,2013).

For the metamorphic rocks from the Yishui Group, Wu et al. (2013)reported zircon U–Pb ages of TTG gneisses, metapelite and felsic gneiss,and the results show two age populations of 2535–2570Ma and 2499–2508Ma. The dominant age group of 2535–2570Mawas interpreted asthe crystallization age of the protolith magma and the younger agegroup revealed ametamorphic event at ~2.50Ga. Zhao et al. (2009a) re-ported zircon U–Pb ages of 2488± 10 Ma to 2522 ± 5Ma from severalgarnet bearing granulites and amphibolites, and suggested that theYishui Group experienced amphibolite to granulite facies metamorphicevent during 2522–2488 Ma. Furthermore, magmatic age of 2561 ±7 Ma and metamorphic age of 2498 ± 8 Ma were also reported fromtwo mafic granulites by Zhao et al. (2013).

Wu et al. (2013) reported inherited zircons from the granitoids withtwo older age groups of 2.67–2.60 Ga and 2.98–2.84 Ga. Shen et al.(2004) reported Mesoarchean inherited zircon ages (3.09–2.93 Ga)from the Caiyu pluton. The major magmatic event in all these studieswas dated as 2.57–2.53 Ga.

The results from our study on themagmatic ages are broadly consis-tent with those from previous studies, and the Mesoarchean Hf modelages that we report from these zircons correlate with the older ages ofinherited zircons reported in early studies suggesting that the Yishuiterrane is underlain by older basement.

7.4. The ophiolite debate in the NCC

Kusky et al. (2001) first reported a Neoarchean ophiolite complex inthe Dongwanzi area of the NCC. They described the complex as threeNE–SW trending belts, among which the central belt is composed ofmafic–ultramafic cumulates, and the northwestern and southeasternbelts are dominated bymetamorphosed gabbros, sheeted dikes and pil-low lavas. Kusky et al. (2001) obtained a zircon U–Pb age of 2505 ±2 Ma from a gabbro, and suggested that the Dongwanzi ophiolitewas formed in Neoarchean. However, Zhai et al. (2002) challengedthis discovery and claimed that there are no convincing pillow lavasand sheeted dikes in the northwestern and southeastern belts,and that the ultramafic–mafic cumulates only occur as pyroxenites,hornblendites and hornblende-pyroxene gabbro. Zhao et al. (2007)also refuted the ophiolite occurrence reported by Kusky et al. (2001)and presented SHRIMP U–Pb zircon data on the rocks of the Dongwanziultramafic–mafic units (gabbro, leucogabbro or pyroxenite) which showages of ca. 300 Ma, demonstrating that the Dongwanzi ultramafic–maficbody was not part of an Archean ophiolite. Kusky and Zhai (2012) pro-posed two possible interpretations to explain this discrepancy; one isthat Zhao et al. (2007) only dated the younger intrusions and missedthe older rocks, the other interpretation is that the zircons that Kuskyet al. (2001) dated may have been old xenocrystic cores caught in youn-ger intrusions.

The second occurrence is the Zunhua ophiolitic mélange composedof highly strained gneiss, BIF, 2.60–2.50 Ga greenstone belts andmafic–ultramafic complexes (Kusky and Li, 2010). Themafic–ultramaficcomplexes, together with numerous tectonic blocks of pillow lava, BIF,dike complex, gabbro, dunite, serpentinized harzburgite, and podiformchromitite occurring within biotite–gneiss matrix were interpreted asa high-grade ophiolitic mélange (Li et al., 2002). The ~2.5 Ga podiformchromitites from the Zunhua ophilitic mélange were also consideredto lend further support to the Archean Dongwanzi ophiolite occurrence(Li et al., 2002;Huang et al., 2004; Kusky et al., 2004a,b), thus promptingthe suggestion of the Dongwanzi–Zunhua ophiolite belt (Kusky and Li,2010; Kusky and Zhai, 2012). However, Zhang et al. (2003, 2004) sug-gested that the chromitites in the Zunhua complex were of the typeformed in continental mafic/ultramafic intrusions, and are not Alpine-type podiform chromitites.

The other occurrences reported from the NCC are in Wutaishan,Western Liaoning, Northern Taihang and Southern Taihang, consideredas the along-strike extensions of the Dongwanzi–Zunhua ophiolite belt.The serpentinized ultramafic rocks from Western Liaoning, Qinglong,Zhangjiakou, Miyun and some localities in the Henan–Shanxi Provincewere interpreted to form part of a large-scale ca. 2.5 Ga ophiolite belt(Polat et al., 2005; Kusky and Li, 2010; Kusky and Zhai, 2012).

Our present study provides a typical case of Archean dismemberedsuprasubduction-zone type ophiolite sequence similar to theNeoarcheanexamples reported from other cratons such as the Agali hills ophiolites insouthern India (Santosh et al., 2013). The lithological assemblages, pet-rological features and geochemical characteristics of the Yishui suiteconvincingly correlate them with supra-subduction zone ophiolitesuites. Based on a detailed evaluation of Archean suprasubductionzone ophiolite complexes, Dilek and Polat (2008) suggested thatPhanerozoic-type seafloor spreading and subduction zone processesmight have operated from ca. 3.8 Ga onwards, indicating that rigid lith-ospheric slabs via subduction might have been established since theEoarchean. In Yishui, the involvement of Mesoarchean components issuggested by our zircon Lu–Hf data.

24 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

7.5. Tectonic significance

In a recent study from the western margin of the northern segmentof the Jiaoliao microblock in the NCC (Fig. 20a), Yang et al. (2016) re-ported a suite of metagabbro, amphibolite and gneisses that show

compositional variation from diorite through syeno-diorite to granitewith dominant calc-alkaline affinity andmagnesian feature comparablewith arc-related magmatic suites. The geochemical features of theserocks confirm subduction-related origin. Yang et al. (2016) presentedzircon U–Pb age data in the range of 2587 ± 10 Ma to 2543 ± 17 Ma

25M. Santosh et al. / Gondwana Research 38 (2016) 1–27

for the charnockite suite, followed by metamorphism during 2533 Mato 2490 Ma. Similar ages of magmatism and metamorphism were alsoobtained from themetagabbros and amphibolites. The dominantly pos-itive εHf(t) values of the zircons from this suite were suggested to indi-cate magma derivation from Neoarchean juvenile components, and thecrustal residence ages suggest a possible input of Mesoarchean toNeoarchean crustal components through continental detritus in an ac-tive trench which were recycled during subduction. Thus Yang et al.(2016) proposed a major late Neoarchean magmatic event within arc-related subduction tectonic setting along the western margin of theJiaoliao Block.

Our present study area is far from the boundaries of themajor crust-al blocks and suture zones in the NCC, and is located along the southernperiphery of the southern segment of the Jiaoliaomicroblock,well with-in the interior of the unified Eastern Block (Fig. 20a). The lithologic as-semblages and petrological and geochemical features of the Yishuisuite are typical of dismembered suprasubduction zone ophiolites.We envisage that the amalgamation between the Xuhuai microblockand the Jiaoliao microblock with northward subduction (presentco-ordinates) resulted in the accretion of the suprasubductionzone ophiolitic assemblages into the southern margin of the Jiaoliaomicroblock (Fig. 20b, c). The Yishui ophiolite complex reported in thisstudy, as well as the Yanlingguan greenstone belt that separates thetwo microblocks confirm that this zone was an active convergent mar-gin during the Neoarchean with subsequent ocean closure. The distinctlithological features attesting to independent evolution of the variousmicroblocks in the NCC (Zhai and Santosh, 2011) and their final amal-gamation during the Neoarchean corresponds well with the Achaeanworld characterized bymultiple subduction zones andmicrocontinents,followed by their amalgamation to form larger continental masses(Santosh et al., 2009; Yang et al., 2016), through plate tectonic processeswhich were broadly analogous to those operating in the modern Earth.

8. Conclusions

• The lherzolite, pyroxenite, gabbros and hornblendite from the Yishuicomplex form part of a dismembered suprasubduction zone ophiolitesuite.

• The petrological characters including mineral chemical compositionsof the Yishui suite are comparable with those from Neoarcheanophiolite suites elsewhere on the globe.

• Major, trace and rare earth element features of the Yishui rocks showevolution in a suprasubduction realm with insignificant crustalcontamination. The ultramafic andmafic units show geochemical fea-tures consistent with magma sources of E-MORB and N-MORB affini-ty. The lherzolite and hornblendite possess arc-related ultramaficcumulate signature and compositional variation from IAT and IAT-MORB.

• LA-ICP-MS U–Pb dating of zircon grains yields 207Pb/206Pb upper inter-cept age of 2538 ± 30 Ma for the hornblendite, 2503 ± 16 Ma and2495 ± 10 Ma for the gabbros and. 2538 ± 16 Ma and 2503 ± 21for the granite. The well defined 2500 Ma age peak corresponds withsimilar ages reported from other microblocks. The zircon Lu–Hf datashow εHf(t) values between−2.5 and 5.0, and suggest magma deriva-tion mainly from Neoarchean juvenile as well as limited reworkedPaleo-Mesoarchean crustal components, possibly through reworkingby subduction of continental detritus deposited in an active trench.

Fig. 20. (a) Archean tectonic framework of theNorth China Cratonwithmicroblockswelded bytiple subduction zoneswith closure of the intervening ocean basinsmight have occurred duringThe major microblocks are the Jiaoliao Block (JL), Qianhuai Block (QH), Ordos Block (OR), Jinintectonic scenario to explain the formation of the Yishui ophiolite complex. Due to the highmantthat of the present day. Also, the geothermal gradients during Archeanweremuch higher than textensional regime is represented by several diabase dykes in the regionwhich showNeoarchelished data). The mixed pelagic and continental volcano-sedimentary sequences, as well as remand bands indifferent localities includingmetavolcanics, amphibolites, felsic volcanic tuff, BIF anschematically represents the stratigraphy of the Yishui ophiolite suite from harzburgite at the

• The Yishui ophiolite suite is considered to represent remnants ofthe destructed oceanic lithosphere accreted onto the southern marginof the Jiaoliao microblock during it amalgamation with the Xuhuaimicroblock.

• The suprasubduction ophiolite suite in our study is the first report of anophiolite suite far from the boundaries of the major crustal blocks andshear zones in the NCC and supports the model of microblock amal-gamation along multiple subduction zones at the end of Archean.

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.gr.2015.10.017.

Acknowledgments

We thank Dr. Shoujie Liu, Associate Editor of Gondwana Researchand two anonymous referees for very encouraging and helpful com-ments which improved this manuscript. This study was supported bythe Talent Award to M. Santosh under the 1000 Plan of the ChineseGovernment, as well as the Foreign Expert fund support from ChinaUniversity of Geosciences Beijing.

References

Aldanmaz, E., Yaliniz, M.K., Guçtekin, A., Goncuoglu, M.C., 2008. Geochemical characteris-tics of mafic lavas from the Neo-Tethyan ophiolites in western Turkey: implicationsfor heterogeneous source contribution during variable stages of ocean crust genera-tion. Geological Magazine 145, 37–54.

Black, L.P., Kamo, S.L., Allen, C.M., Aleinikoff, J.N., Davis, D.W., Korsch, R.J., Foundoulis, C.,2003. TEMORA 1: a new zircon standard for Phanerozoic U–Pb geochronology.Chemical Geology 200, 155–170.

Dilek, Y., Polat, A., 2008. Suprasubduction zone ophiolites and Archean tectonics. Geology36, 431–432.

Dilek, Y., Furnes, H., 2011. Ophiolite genesis and global tectonics: geochemical and tecton-ic fingerprinting of ancient oceanic lithosphere. Geological Society of America Bulletin123, 387–411.

Furnes, H., deWit, M., Dilek, Y., 2014. Four billion years of ophiolites reveal secular trendsin oceanic crust formation. Geoscience Frontiers 5, 571–603.

Furnes, Dilek, Y., de Wit, M., 2015. Precambrian greenstone sequences represent differentophiolite types. Gondwana Research 27, 649–685.

Gao, S., Rudnick, R.L., Xu, W.L., Yuan, H.L., Liu, Y.S., Walker, R.J., Puchtel, I.S., Liu, X., Huang,H., Wang, X.R., Yang, J., 2008. Recycling deep cratonic lithosphere and generation ofintraplate magmatism in the North China Craton. Earth and Planetary Science Letters270, 41–53.

Geng, Y.S., Du, L.L., Ren, L.D., Liu, D.Y., 2012. Growth and reworking of the early Precam-brian continental crust in the North China Craton: constraints from zircon Hf iso-topes. Gondwana Research 21, 517–529.

Hawthorne, F.C., Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Maresch,W.V.,Schumacher, J.C., Stephenson, N.C., Whittaker, E.J., 1997. Nomenclature of amphi-boles: report of the subcommittee on amphiboles of the International MineralogicalAssociation, Commission on New Minerals and Mineral Names. Canadian Mineralo-gist 35, 219–246.

Huang, X.N., Li, J.H., Kusky, T.M., Chen, Z., 2004. Microstructures of the Zunhua 2.50 Gapodiform chromite, North China Craton and implications for the deformation andrheology of the Archean oceanic lithospheric mantle. In: Kusky, T.M. (Ed.), Precam-brian Ophiolites and Related Rocks. In: Condie, K.C. (Ed.)Developments in Precambri-an Geology vol. 13, pp. 321–337.

Irvine, T., Baragar,W., 1971. A guide to the chemical classification of the common volcanicrocks. Canadian Journal of Earth Sciences 8, 523–548.

Khedr, M.Z., Arai, S., Python, M., Tamura, A., 2014. Chemical variations of abyssal perido-tites in the central Oman ophiolite: evidence of oceanic mantle heterogeneity. Gond-wana Research 25, 1242–1262.

Kusky, T.M., Li, J.H., 2010. Origin and emplacement of Archean ophiolites of the CentralOrogenic Belt, North China Craton. Journal of Earth Science 21, 744–781.

Kusky, T.M., Zhai, M.G., 2012. The Neoarchean ophiolite in the North China Craton:Early Precambrian plate tectonics and scientific debate. Journal of Earth Science 23,277–284.

greenstone belts that represent zones of ocean closure (after Zhai and Santosh, 2011). Mul-the amalgamation of themicroblocks duringNeoarchean as proposed in Yang et al. (2016).g Block (JN), Xuchang Block (XCH), Xuhuai Block (XH) and Alashan Block (ALS). (b) Platele potential temperatures during Archean, the oceanic crust was nearly three times thick ashose of the present earth, leading tomelting of the subducted slab at shallow domains. Thean emplacement ages similar to the lithological units in the ophiolite complex (our unpub-nants of the oceanic crust, are exposed to the north of the study area as transposed layersd quartzite. The inset is an enlargement of the area shown inside box in themainfigure andbase to BIF at the top.

26 M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Kusky, T.M., Li, J.H., Tucker, R.D., 2001. The Archean Dongwanzi ophiolite complex,North China Craton: 2.505-billion-year-old oceanic crust and mantle. Science 292,1142–1145.

Kusky, T.M., Li, J.H., Glass, A., Huang, X.N., 2004a. Origin and emplacement of Archeanophiolites of the Central Orogenic Belt, North China Craton. In: Kusky, T.M. (Ed.),Precambrian Ophiolites and Related Rocks. In: Condie, K.C. (Ed.)Developments inPrecambrian Geology vol. 13, pp. 223–274.

Kusky, T.M., Li, J.H., Raharimahefa, T., Carlson, R.W., 2004b. Re–Os isotope chemistry andgeochronology of chromite from mantle podiform chromites from the Zunhuaophiolitic mélange belt, N. China: correlation with the Dongwanzi ophiolite. In:Kusky, T.M. (Ed.), Precambrian Ophiolites and Related RocksDevelopments in Pre-cambrian Geology vol. 13. Elsevier, Amsterdam, pp. 275–282.

Kusky, T.M., Windley, B.F., Safonova, I., Wakita, K., Wakabayashi, J., Polat, A., Santosh, M.,2013. Recognition of ocean plate stratigraphy in accretionary orogens through Earthhistory: a record of 3.8 billion years of sea floor spreading, subduction, and accretion.Gondwana Research 24, 501–547.

Li, S.Z., Zhao, G.C., 2007. SHRIMP U–Pb zircon geochronology of the Liaoji granitoids: con-straints on the evolution of the Paleoproterozoic Jiao-Liao-Ji belt in the Eastern Blockof the North China Craton. Precambrian Research 158, 1–16.

Li, J.H., Kusky, T.M., Huang, X.N., 2002. Archean podiform chromitites and mantletectonites in ophiolitic mélange, North China Craton: a record of early oceanic mantleprocesses. GSA Today 12, 4–11.

Li, S.Z., Zhao, G.C., Sun, M., Han, Z.Z., Hao, D.F., Luo, Y., Xia, X.P., 2005. Deformation historyof the Paleoproterozoic Liaohe assemblage in the Eastern Block of the North ChinaCraton. Journal of Asian Earth Sciences 24, 659–674.

Li, S.Z., Zhao, G.C., Min, S., Luo, Y., Han, Z.Z., Zhao, G.T., Hao, D.F., 2006. Are the South andNorth Liaohe Groups different exotic terranes? — Nd isotope constraints on the Jiao-Liao-Ji orogen. Gondwana Research 9, 198–208.

Li, H.K., Yang, Y.B., Geng, K., 2011. Zircon SHRIMP U–Pb age and its geological significanceof the Xueshan intrusion in the Yishui County, Shandong Province. Geological Surveyand Research 34, 253–257 (in Chinese with English abstract).

Liu, Y.S., Hu, Z.C., Gao, S., Günther, D., Xu, J., Gao, C.G., Chen, H.H., 2008. In situ analysis ofmajor and trace elements of anhydrous minerals by LA-ICP-MS without applying aninternal standard. Chemical Geology 257, 34–43.

Liu, Y.S., Gao, S., Hu, Z.C., Gao, C.G., Zong, K., Wang, D., 2010. Continental and oceanic crustrecycling-induced melt-peridotite interactions in the Trans-North China Orogen:U–Pb dating, Hf isotopes and trace elements in zircons of mantle xenoliths. Journalof Petrology 51, 537–571.

Lu, X.P., Wu, F.Y., Guo, J.H., Wilde, S.A., Yang, J.H., Liu, X.M., Zhang, X.O., 2006. Zircon U–Pbgeochronological constraints on the Palaeoproterozoic crustal evolution of the East-ern block in the North China Craton. Precambrian Research 146, 138–164.

Ludwig, K.R., 2003. User's manual for Isoplot 3.00, a geochronological toolkit for MicrosoftExcel. Geochronological Center, Special Publication No. 4, Berkeley pp. 25–32.

Luo, Y., Sun, M., Zhao, G.C., Li, S.Z., Xu, P., Ye, K., Xia, X.P., 2004. LA-ICP-MS U–Pb zirconages of the Liaohe Group in the Eastern Block of the North China Craton: constraintson the evolution of the Jiao-Liao-Ji Belt. Precambrian Research 134, 349–371.

Miyashiro, A., Shido, F., 1975. Tholeiitic and calc-alkalic series in relation to the behavioursof Ti–V–Cr–Ni. American Journal of Science 275, 265–277.

Parlak, O., Hock, V., Delaloye, M., 2000. Suprasubduction zone origin of the Pozanti–Karsanti ophiolite (southern Turkey) deduced from whole rock and mineral chemis-try of the Gabbroic cumulates. In: Bozkurt, E., Winchester, J.A., Piper, J.D.A. (Eds.),Tectonics and Magmatism of in Turkey and the Surrounding Area. Geological Societyof London, Special Publications 69, pp. 33–47.

Pearce, J.A., 1980. Geochemical evidence for genesis and eruptive setting of lavas fromTethyan ophiolites. In: Panayiotou, A. (Ed.), Ophiolites. Geological Survey Depart-ment, Cyprus, pp. 261–272.

Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications toophiolite classification and the search for Archean oceanic crust. Lithos 100, 14–48.

Pearce, J.A., Norry, J.R., 1979. Petrogenetic implications of T, Zr, Y and Nb variations in vol-canic rocks. Contributions to Mineralogy and Petrology 69, 33–47.

Pearce, J.A., Peate, D.W., 1995. Tectonic implications of the composition of volcanic arcmagmas. Annual Review of Earth and Planetary Sciences 23, 251–285.

Pearce, J.A., Lippard, L.S., Roberts, S., 1984. Characteristics and tectonic significanceof supra-subduction zone ophiolites. Geological Society Special Publication 16,77–94.

Peccerillo, A., Taylor, S.R., 1976. Rare earth elements in East Carpathian volcanic rocks.Earth and Planetary Science Letters 32, 121–126.

Peng, T.P., Fan, W.M., Peng, B.X., 2012. Geochronology and geochemistry of late Archeanadakitic plutons from the Taishan granite–greenstone Terrain: implications for tectonicevolution of the eastern North China Craton. Precambrian Research 208–211, 53–71.

Piercey, S.J., Mortensen, J.K., Murphy, D.C., Paradis, S., Creaser, R.A., 2002. Geochemistryand tectonic significance of alkalic mafic magmatism in the Yukon–Tanana terrane,Finlayson Lake region, Yukon. Canadian Journal of Earth Sciences 39, 1729–1744.

Polat, A., Hofmann, A.W., 2003. Alteration and geochemical patterns in the 3.7–3.8 GaIsuagreenstone belt, West Greenland. Precambrian Research 126, 197–218.

Polat, A., Kerrich, R., 2000. Archean greenstone belt magmatism and the continentalgrowth-mantle evolution connection: constraints from Th–U–Nb-LREE systematicsof the 2.7 Ga Wawa subprovince, Superior Province, Canada. Earth and PlanetaryScience Letters 175, 41–54.

Polat, A., Kusky, T.M., Li, J.H., Fryer, B., Kerrich, R., Patrick, K., 2005. Geochemistryof Neoarchean (ca. 2.55–2.50 Ga) volcanic and ophiolitic rocks in the Wutaishangreenstone belt, central orogenic belt, North China craton: implications forgeodynamic setting and continental growth. Geological Society of America Bulletin117, 1387–1399.

Poldervaart, A., Hess, H.H., 1951. Pyroxenes in the crystallization of basaltic magma. TheJournal of Geology 59, 472–489.

Ribbe, P.H., 1983. The chemistry, structure and nomenclature of feldspars. Feldspar min-eralogy. Reviews in Mineralogy 2. Mineralogical Society of America, pp. 1–19.

Safonova, I.Y., Buslov, M.M., Simonov, V.A., Izokh, A.E., Komiya, T., Kurganskaya, E.V.,Ohno, T., 2011. Geochemistry, petrogenesis and geodynamic origin of basalts fromthe Katun' accretionary complex of Gorny Altai (southwestern Siberia). Russian Geol-ogy and Geophysics 52, 421–442.

Santosh, M., 2010. Assembling North China Craton within the Columbia supercontinent:the role of double-sided subduction. Precambrian Research 178, 149–167.

Santosh, M., Maruyama, S., Yamamoto, S., 2009. The making and breaking of superconti-nents: some speculations based on superplumes, super downwelling and the role oftectosphere. Gondwana Research 15, 324–341.

Santosh, M., Xiao, W.J., Tsunogae, T., Chetty, T.R.K., Yellappa, T., 2012. The Neoproterozoicsubduction complex in southern India: SIMS zircon U–Pb ages and implications forGondwana assembly. Precambrian Research 192–195, 190–208.

Santosh, M., Shaji, E., Tsunogae, T., Ram Mohan, M., Satyanarayanan, M., Horie, K., 2013.Suprasubduction zone ophiolite from Agali hill: petrology, zircon SHRIMP U–Pbgeochronology, geochemistry and implications for Neoarchean plate tectonics insouthern India. Precambrian Research 231, 301–324.

Santosh, M., Yang, Q.Y., Teng, X., Tang, L., 2015. Paleoproterozoic crustal growth in theNorth China Craton: evidence from the Lüliang Complex. Precambrian Research263, 197–231.

Shen, Q.H., Shen, K., Geng, Y.S., Xu, H.F., 2000. The Composition and Evolution ofthe Yishui Complex, Shandong Province. Geological Publishing House, Beijing(in Chinese).

Shen, Q.H., Song, B., Xu, H.F., Geng, Y.S., Shen, K., 2004. Emplacement and metamorphismages of the Caiyu and Dashan igneous bodies, Yishui County, Shandong Province: zir-con SHRIMP chronology. Geological Review 50, 275–284 (in Chinese with Englishabstract).

Shen, Q.H., Zhao, Z.R., Song, B., Song, H.X., 2007. Geology, petrology and SHRIMP zirconU\Pb dating of the Mashan and Xueshan granitoids in Yishui county, Shandong Prov-ince. Geological Review 53, 180–186 (in Chinese with English abstract).

Shervais, J.W., 1982. Ti–V plots and the petrogenesis of ophiolitic lavas. Earth and Plane-tary Science Letters 59, 101–118.

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and process. In: Saunders, A.D., Nony, M.J.(Eds.), Magmatism in the Ocean Basin. Geological Society London Special Publicationvol. 42, pp. 313–354.

Tamura, A., Arai, S., 2006. Harzburgite–dunite–orthopyroxenite suite as a record of supra-subduction zone setting for the Oman ophiolite mantle. Lithos 90, 43–56.

Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., Quadt, A.V., Roddick,J.C., Spiegel, W., 1995. Three natural zircon standards for U–Th–Pb, Lu–Hf, trace ele-ment and REE analyses. Geostandards Newsletter 19, 1–23.

Wilson, B.M., 1989. Igneous Petrogenesis: A Global Tectonic Approach. Springer.Winchester, J.A., Floyd, P.A., 1977. Geochemical differentiation of different magma series

and their differentiation products using immobile elements. Chemical Geology325–343.

Wood, D.A., 1980. The application of a Th–Hf–Ta diagram to problems of tectono-magmatic classification and to establishing the nature of crustal contaminations ofbasaltic lavas of British tertiary volcanic province. Earth and Planetary Science Letters56, 11–30.

Wu, M.L., Zhao, G.C., Sun, M., Li, S.Z., He, Y.H., Bao, Z.A., 2013. Zircon U\Pb geochronol-ogy and Hf isotopes of major lithologies from the Yishui Terrane: implicationsfor the crustal evolution of the Eastern Block, North China Craton. Lithos 170–171,164–178.

Yang, Q.Y., Santosh, M., 2015. Paleoproterozoic arc magmatism in the North China Craton:no Siderian global plate tectonic shutdown. Gondwana Research 28, 82–105.

Yang, Q.Y., Santosh, M., Collins, A.S., Teng, X.M., 2016. Microblock amalgamation in theNorth China Craton: evidence from Neoarchaean magmatic suite in the westernmargin of the Jiaoliao Block. Gondwana Research 31, 96–123.

Yellappa, T., Santosh, M., Chetty, T.R.K., Kwon, S., Park, C., Nagesh, P., Mohanty, D.P.,Venkatasivappa, V., 2012. A Neoarchean dismembered ophiolite complex fromsouthern India: geochemical and geochronological constraints on its suprasubductionorigin. Gondwana Research 21, 246–265.

Zhai, M.G., 2014. Multi-stage crustal growth and cratonization of the North China Craton.Geoscience Frontiers 5, 457–469.

Zhai, M.G., Bian, A.G., 2001. Amalgamation of the supercontinental of the North Chinacraton and its break up during late-middle Proterozoic. Science in China D 43,219–232.

Zhai, M.G., Santosh, M., 2011. The early Precambrian odyssey of the North China Craton: asynoptic overview. Gondwana Research 20, 6–25.

Zhai, M.G., Zhao, G.C., Zhang, Q., 2002. Is the Dongwanzi complex an Archean ophiolite?Science 295, 923a.

Zhang, Q., Ni, Z.Y., Zhai, M.G., 2003. Comments on the Archean ophiolites in Eastern Hebei.Earth Science Frontiers 10, 429–437 (in Chinese with English abstract).

Zhang, Q., Wang, Y., Zhou, G.Q., Qian, Q., Robinson, P.T., 2004. Ophiolites in China: theirdistribution, ages and tectonic settings. In: Dilek, Y., Robinson, P.T. (Eds.), Ophiolitesin Earth History. Geol. Soc. Spec. Publ. (London) vol. 218, pp. 541–566.

Zhao, G.C., Zhai, M.G., 2013. Litho tectonic elements of Precambrian basement in theNorth China Craton: review and tectonic implications. Gondwana Research 23,1207–1240.

Zhao, G.C., Sun, M., Wilde, S.A., Li, S.Z., 2005. Late Archean to Paleoproterozoic evolu-tion of the North China Craton: key issues revisited. Precambrian Research 136,177–202.

Zhao, G.C., Wilde, S.A., Li, S.Z., Sun, M., Grant, M.L., Li, X.P., 2007. U–Pb zircon age con-straints on the Dongwanzi ultramafic–mafic body, North China, confirm it is not anArchean ophiolite. Earth and Planetary Science Letters 255, 85–93.

27M. Santosh et al. / Gondwana Research 38 (2016) 1–27

Zhao, Z.R., Song, H.X., Shen, Q.H., Song, B., 2008. Geological and geochemical characteris-tics and SHRIMP U\Pb zircon dating of the Yinglingshan granite and its xenolithsin Yishui County, Shandong, China. Geological Bulletin of China 27, 1551–1558(in Chinese with English abstract).

Zhao, Z.R., Song, H.X., Shen, Q.H., Song, B., 2009a. The petro-geochemical characters andSHRIMP U\Pb zircon ages of meta-mafic rocks from the Yishui Complex, in YishuiCounty, Shandong Province. Geological Review 55, 286–299 (in Chinese with Englishabstract).

Zhao, Z.R., Song, H.X., Shen, Q.H., Song, B., 2009b. Geochemistry and age of a metapeliterock in the Yishui complex, Shandong Province. Acta Petrologica Sinica 25, 1863–1871(in Chinese with English abstract).

Zhao, Z.R., Song, H.X., Shen, Q.H., Song, B., 2013. Zircon SHRIMP U–Pb dating of ultramaficrock and mafic granulite from Qinglongyu in Yishui County, Shandong Province. ActaPetrologica Sinica 29, 551–563 (in Chinese with English abstract).