an archean quartz arenite–andesite association in …directory.umm.ac.id/data...

Precambrian Research 101 (2000) 313–340

An Archean quartz arenite–andesite association in theeastern Baltic Shield, Russia: implications for assemblage

types and shield history

P.C. Thurston a,*, V.N. Kozhevnikov b

a Precambrian Geoscience Section, Ontario Geological Sur6ey, 933 Ramsey Lake Rd., Sudbury, Ont., Canada P3E 6B5b Institute of Geology, Karelian Research Centre, Pushkinskaya, 11, Petroza6odsk, 185610, Russia

Abstract

Shallow water sedimentary units are generally considered scarce in Archean greenstone belts. We describe anunusual quartz arenite-subaerial andesite association within the Archean Hisovaara greenstone belt, a fragment of theParandovo-Tikshozero belt within the Karelian craton of the Baltic Shield. The Hisovaara greenstone belt consists ofseveral lithotectonic assemblages: (1) a komatiite-tholeiite assemblage\2803 Ma (based on ages of cross-cuttingdikes); (2) an andesite-quartz arenite assemblage cut by similar dikes; (3) an assemblage of coarse volcaniclastic rocks,and (4) an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks. Theandesite-quartz arenite assemblage (100 to ca. 750 m thick) has basal amygdaloidal fragmental andesites overlain bymassive andesites, then amygdaloidal and plagioclase phyric andesites. Unconformably overlying the andesite is a unitof quartz-rich sandstones (6–40 m thick) dominated by quartz arenite extending several km along strike. At the northend, the quartz arenite succession consists of basal andesite overlain by quartz arenite exhibiting hummockycross-stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlyingtholeiite/komatiite unit. At the south end, the succession is basal andesite, regolith, cross-bedded quartz arenite,weathered andesites, a second quartz arenite, argillite and then subaerial rhyolite. REE and HFSE geochemistry hasbeen obtained on the rocks of the andesite-quartz arenite assemblage. The quartz arenites contain low abundancesand chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grainsize, with pebbly units having higher abundance and more fractionated patterns. Combined major and trace elementgeochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistryof the quartz arenites. The andesites display moderately fractionated spidergrams with negative anomalies at Ti, Taand Nb typical of arc volcanism. The andesite-quartz arenite assemblage represents accumulation of shallow waterquartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerialat the southern end of the assemblage. However, at the north end, our evidence is interpreted as indicating subaerialandesitic volcanism, subsidence to a shallow marine basin which then deepens and rifts. Therefore the Hisovaaraandesite-quartz arenite assemblage provides a linkage in Archean greenstones between assemblages representingcontinental volcanism and a platform-to-rift setting. The presence of an erosional interval in\2.8 Ga greenstonessuggests possible pre-2.7 Ga orogeny in the Baltic shield. The pre-2.7 Ga quartzrich sedimentation is similar in age

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* Corresponding author.

0301-9268/00/$ - see front matter Crown copyright © 2000 Published by Elsevier Science B.V. All rights reserved.

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P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340314

to platformal assemblages in the pre-2.7 Ga North Caribou terrane of the Superior Province, Canada. Crowncopyright © 2000 Published by Elsevier Science B.V. All rights reserved.

Keywords: Archean; Sediments; Volcanism; Quartz arenite; Andesite; Baltic; Superior

1. Introduction

Quartz-rich metasedimentary rocks and spa-tially associated sedimentary carbonates, typicalof stable platforms, are generally scarce inArchean greenstone belts (Ojakangas, 1985). Re-cent work in the Superior Province has revealedArchean greenstone assemblages containingquartz-rich sedimentary units in at least threegeodynamic settings: stable shallow water plat-forms (Wood et al., 1986; De Kemp, 1987;Thurston and Chivers, 1990), submarine fans withevidence for cannibalization of platformal rocks(Cortis, 1991), and quartz-rich conglomerates andarenites in pull-apart basins (Born, 1995).Kozhevnikov (1992) identified a spatial associa-tion of andesites and quartz arenites withinArchean greenstones of the Parandovo-Tik-shozero greenstone belt near the Karelian Belo-morian collision zone boundary (Glebovitsky,1973; Volodichev, 1990; Glebovitsky, 1993;Lobach-Zhuchenko et al., 1995; Glebovitsky etal., 1996) which caused us to investigate twoquartz-rich sedimentary assemblages in this regionto assess their similarity with possible SuperiorProvince analogues. The andesite-quartz areniteassociation has not been seen in the SuperiorProvince quartz-rich sedimentary units (Thurston,1990).

In the classification of assemblages for Archeangreenstone belts, quartz-rich sedimentary units(including quartz arenites) are typical of platformassemblages (Thurston and Chivers, 1990;Thurston, 1994). The high mineralogical and tex-tural maturity of these rocks, the presence oftrough and hummocky bedding in them, associa-tion with stromatolitic carbonates, and, finally,their occurrence over thousands of km2 in theSachigo and central Wabigoon subprovinces,provide a basis for regarding many as members ofplatform successions formed under shallow-waterconditions along a passive continental margin(Thurston and Chivers, 1990).

The literature on Archean greenstone beltsshows that similar quartz arenites have been re-ported from platform assemblages in the manycratons (Thurston and Chivers, 1990). They areknown in the Dharwar craton, India (Srinivasanand Ojakangas, 1986), in the Bulawayo green-stone belt on the Zimbabwian Shield (Bickle etal., 1975), in the Moodies Group in the Barbertonbelt of the Kaapvaal craton (Eriksson, 1980),within the Tanzanian craton in the Dodomansystem (Kimambo, 1984), in the West Africancraton (Rollinson, 1978) and in the Yilgarn (Gee,1982) and Murchison (Watkins and Hickman,1988) blocks, Australia.

In the Baltic Shield, quartz arenite-bearing as-semblages have been described in some greenstonebelts (Fig. 1). In the Koitelainen area, CentralLapland, the sequence which consists of quartzarenites, mica schists, phyllites, volcanic conglom-erates and mafic to ultramafic volcanics has anage of less than 2.7 Ga and rests on ca. 3.1 Gagranitoids (Kroner et al., 1981). It represents aLapponian sequence of presumably LowerProterozoic age (Gaal and Gorvatschev, 1987). InNorth Karelia, Russia, a possible age analogue ofthe above strata is represented by Sumian rocksthat lie with a regolithic lower contact on Archeangranitoids. In these successions, cross-beddedquartz arenites form a basal horizon overlain byandesite-basaltic lava (Korosov, 1991). In theKostomuksha greenstone belt (Fig. 1), cross-bed-ded staurolite-sillimanite quartz arenites are asso-ciated with pillow basalt (Kozhevnikov, 1982). Inthe Tipasjarvi belt (Fig. 1), kyanite-staurolitequartz arenites associated with BIF and blackshales are present in the upper part of the felsicvolcanic unit in the lower Koivomaki Formation(Taipale, 1983). Discussing the origin of thesequartz arenites (weathering, fumarolic activity be-tween volcanic eruptions and metasomatic alter-ations), Taipale (1983) concluded that the quartzarenites could be produced during alteration of

P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 315

felsic volcanics in the course of ore formation. Inthe Kuhmo belt (Fig. 1), quartz arenites with2.8–3.0 Ga detrital zircons (Hypponen, 1983)were described from the Hietapera-Kivivaara area(Piirainnen, 1988), where they form part of a felsicvolcanic-sedimentary unit in the JuurikkaniemiFormation which consists of metarhyolites,metadacites, volcanic breccia, lapilli tuffs, tuffitesand tuffaceous turbidites. The age of this unit isestimated at 2798915 Ma (Hypponen, 1983).Northwards, in the Moisiovaara area (Fig. 1),immature sericitic quartz arenites associated withpolymictic conglomerates lie between tholeiitesand komatiites. An old tonalite–trondhjemite–granodiorite complex and felsic rocks from theKuhmo belt are regarded as sources of 2996960and 28039238 Ma detrital zircons (Hypponen,1983) as well as clasts in congomerates (Lu-ukkonen, 1988). In the Hisovaara greenstone belt(Fig. 2), quartz arenites are described in associa-tion with underlying andesites as well as overlyingfelsic volcanics and sedimentary rocks(Kozhevnikov, 1992; Kozhevnikov et al., 1992).

According to Thurston (1990), so far no andesiteshave been found in platform assemblages. Whendistinguishing the types of assemblages most re-cently proposed for Archean greenstone belts, theandesite-quartz arenite association revealed in theHisovaara greenstone belt is considered a fairlyrare type of assemblage with a ‘continental’ styleof volcanism whose depositional environment is‘open to speculation’ (Thurston, 1994). However,knowledge of such an assemblage type may beuseful in discussing models for the tectonic evolu-tion of greenstone belts and in comparative analy-sis and correlation of Archean cratons.

2. Geological setting

2.1. Regional setting

The Hisovaara greenstone structure is a frag-ment of the Archean Parandovo-Tikshozerogreenstone belt which extends for 300 km alongthe Belomoride-Karelide boundary, i.e. along the

Fig. 1. Map showing Archean greenstone belts in the Fenno-Karelian craton (after Rybakov and Kulikov, 1985). Revised after:(Lobach-Zhuchenko, 1988; Kozhevnikov, 1992; Glebovitsky, 1993). Numbered localities represent occurrences of Archean quartz-rich metasediments.


Fig. 2. Geological map of the Archean Hisovaara greenstone belt.


boundary between the Karelian granite-green-stone province and the Belomorian collision zone(Glebovitsky, 1973; Volodichev, 1990; Glebovit-sky, 1993; Slabunov, 1993; Lobach-Zhuchenko etal., 1995; Glebovitsky et al., 1996) (Fig. 1).

2.2. Structural geology and metamorphism

The Hisovaara greenstone structure is a syn-form thrown into composite folds, composedlargely of supracrustal rocks and surrounded bycrosscutting granitoids (Fig. 2). It displays evi-dence for multiple folding events (Systra and Sko-rnyakova, 1986; Shchiptsov et al., 1988)subsequently generalized into three deformationstages (Kozhevnikov, 1992). The rocks have suf-fered polymetamorphism of Archean and Sve-cofennian (1.8–2.0 Ga) ages, the latter takingplace in a high pressure regime with the followingparameters: T=580–640°C, P=6.5–7.5 kbar(Glebovitsky and Bushmin, 1983). Archean hy-drothermal processes associated with felsic mag-matism (Kozhevnikov, 1992, 1995) are apparenttogether with Svecofennian metasomatic rocksrepresented by retrograde metamorphism (T=300–350°C) (Bushmin, 1978; Glebovitsky andBushmin, 1983). The complicated tectonic andmetamorphic history of the Hisovaara greenstonebelt is largely due to its proximity to the 2.70–2.68 Ga Belomorian collision zone (Lobach-Zhuchenko et al., 1995) and later Proterozoicevents (1.95–1.75 Ga) (Bibikova, 1995).

2.3. Lithologic assemblages

Several major assemblages of supracrustalrocks are distinguished in the Hisovaara green-stone belt (Kozhevnikov, 1992). The northern andsouthern flanks of the synform differ substantiallyin character, largely as a function of lateral faciesvariation, and the types of crosscutting intrusiverocks etc. (Table 1). Because the andesite-quartzarenite association is revealed only on the north-ern flank of the structure, only units on the northflank are described below in detail. The unit ter-minology of Kozhevnikov (1992) is retained insubsequent sections of this paper for ease of ac-cess to the Russian literature.

2.3.1. Lower mafic assemblageThe lower essentially volcanic assemblage is

comprised from the base upwards of cumulateperidotitic komatiites, tholeiitic massive and rarerpillow basalts, basaltic to pyroxenitic komatiitesand ferrobasalts. This sequence is characterizedby thick (up to 10 m) massive and fairly uniformflows with scarce thin-bedded tuff horizons, theabsence of interflow sediments, and amygdaloidaltextures all indicative of a mafic plateau type ofvolcanic setting (Thurston, 1994). The U-Pb zir-con age of felsic dykes cutting this assemblage wasestimated by O.A. Levchenkov to be 2803935Ma (Kozhevnikov, 1992).

2.3.2. Second 6olcanic-sedimentary assemblageThe second assemblage consists of volcanics,

volcano-sedimentary, and chemical sedimentaryrocks of intermediate to felsic composition. Itslowermost unit is comprised of calcalkaline andes-ites. They are overlain by quartz arenites, and atpoint B (Fig. 2) there is an alternation of andesiteand quartz arenite. Resting on the quartz arenitesis a thick sequence of felsic rocks including lavas,ash-flows, tuffaceous turbidites and chemical sedi-ments with a clastic component that show compli-cated lateral relationships. Intense metasomaticand deformational processes strongly distort andsometimes obliterate the primary textures andcompositions of these strata making interpreta-tion difficult. Where these processes are least in-tense, there are some indications of graded ashflows and pyroclastic breccias as well as flowswith massive and flow top breccia textures. Thevolcano-sedimentary rocks have some features in-dicative of graded rhyolitic turbidites with alu-mina-enriched upper parts. Transitionalclastic-chemical sedimentary rocks represented bycarbonaceous schists (sulfidic argillites), alumino-silicates and cherty rocks occur as thin horizonsand lenses among felsic volcanosedimentaryrocks. The uppermost 100 m of this sequenceconsists of thin, graded carbonaceous and carbon-ate-bearing silty sandstones.

2.3.3. Third rudaceous assemblageCoarse clastic rocks dominate a third assem-

blage forming two wide zones in the centre of the

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Table 1Some characteristics of associations at the northern and southern flanks of the Hisovaara greenstone belt that illustrate its asymmetric geological structure

Assemblages Southern flankNorthern flank

Intensely foliated tholeiitic basalts and minor tuffs. Thickness50.15 km.Komatiitic, tholeiitic and ferrotholeiitic lavas and scarceLower Mafic assemblagetuffs. Thickness 0.5–1.7 km.Andesitic lavas and pyroclastic flows with indications ofSecond Predominantly bedded andesite tuffs. Thickness 0–300 m. Quartz-rich

volcanic–sedimentary sediments not found. Felsic volcanics not characteristic. Coarse-beddedsubaerial–subaqueous volcanism. Thickness 100–700 m.assemblage tuffs with oxide- and silicate-facies BIF horizons. Carbonaceous schistsQuartz-rich arenite horizons with hummocky and trough

cross-bedding. Thickness+n–40 m. Rhyolitic lava and not found. Individual beds and units laterally persistent in thickness,graded bedded ashflows, graded rhyolitic turbidites. bedding parallel in plan view, no indications of cross-bedding and theCarbon-bearing sulfidic argillites, conglomerates, absence of sharp lateral transitions are characteristic.alumino-silicate and siliceous rocks closely associatedwith felsic volcanics. Thickness+0–100 m. Gradedthin-laminated carbon- and carbonate-bearing siltstones.Variable thickness of individual beds and units as wellas complex lateral transitions are characteristic of theassociation. Indications of cross-bedding are common inthe quartz arenites.

Third Rudaceous Polymictic conglomerates with dominantly felsic volcanic pebbles of theThick oligomictic conglomerate (?) or volcaniclastic rockbelt.assemblage units with tuffmatrix (?) in the east closely associated

with felsic lava breccia.Massive and pillowed tholeiitic basalts with thinUpper Mafic assemblage Massive and pillowed tholeiitic basalts.komatiite horizons (?) at the base.Locally microclinized tonalites rimming the structure inIntrusive rocks Plagiomicrocline and garnet-muscovitic microcline granites rimming the

structure in the south. Scarce rhyolite dykes. Andesite-basalt–dacite sillsthe north. Rhyodacite-rhyolite dykes and stocks.not found. Gabbro, gabbro-pyroxenite, granodiorite and komatiite sillsAndesite-basalt–andesite-dacite sills. Gabbro,and dykes.gabbro-diorite and komatiite sills and dykes.


Fig. 3. Fragmental andesite with 15–30 cm fragments ofmassive andesite with fragments of uniform mineralogic com-position but varying in colour from grey to green. North shoreof Lake Verkhnee; hammer 35 cm long.

tion pattern with the sills and dikes concentratedon the northeast side of the belt (Fig. 2, Table 1).

As the goal of the present paper is to character-ize and interpret a quartz arenite–andesite associ-ation, uncommon for Archean greenstone belts,these units are described in more detail below.

3. Quartz arenite-bearing assemblage

This assemblage is comprised of three members:calc-alkaline andesites (unit A), quartz arenitehorizons (unit Q) and a unit dominated by felsicvolcanic, volcano-sedimentary, reworked volcanicand chemical sedimentary rocks (unit F). Theboundary between the andesites (unit A) and theunderlying Lower Mafic assemblage is most prob-ably a thrust, indicated by intense carbonatizationand silicification near the contact as well asmarked (up to 1300%) stretching of the andesite(amygdale elongation along the a-lineation paral-lel to dip) (Kozhevnikov et al., 1992). The upperboundary of the assemblage is the unconformityat the base of the coarse clastic assemblage andthe upper mafic assemblage.

3.1. Andesite unit (unit A)

3.1.1. Field descriptionMassive amygdaloidal, glomeroporphyritic and

coarse pyroclastic andesites are distinguished. Theandesite unit varies markedly in thickness (100–700 m) laterally (Fig. 2). In the thickest part ofthe andesite unit, the following succession of rocktypes is observed from the base upward: (1) ca.200 m-thick amygdaloidal, partly coarse, frag-mental andesites (Fig. 3); (2) massive andesiteslocally showing some vague indications of internalheterogeneity (thickness about 450 m); (3) amyg-daloidal types, seldom with indications of primi-tive pillow textures; thickness on the scale of a fewmetres to tens of metres; and (4) thick andesiteflows with concentrations of plagioclase phe-nocrysts (occasionally glomerophenocrysts) to-ward the top. The thin glomeroporphyriticandesite horizon is overlain by the quartz areniteunit that can be mapped laterally for several km.However, there are substantial structural differ-

belt as well as thin lenticular units among therocks of the previous assemblage. Some indica-tions of discordance between these rocks and theunderlying and overlying assemblages are appar-ent in the map patterns (Fig. 2). The dacite-rhyo-lite to rhyolite clasts within these rocks arecompositionally uniform and are more felsic thanthe dacitic matrix. This unit may represent eitheroligomictic conglomerates or matrix-supportedvolcaniclastic rocks. The latter interpretation isfavoured by their close association with felsic flowtop breccia observed at some localities.

2.3.4. Upper mafic assemblageThe fourth essentially volcanogenic assemblage

is represented by a thick pile of pillowed tholeiiticbasalts with some thin pyroxenitic komatiite flowsand sills in the lower part. This unit rests uncon-formably on the second and third assemblagesand is cut by individual undated rhyodacite andgranodiorite dykes.

2.3.5. Intrusi6e rocksNear the margins of the belt, supracrustal rocks

are cut by tonalites in the north and by granites inthe south. The interior of the belt is cut byandesite-dacite sills, rhyodacite-rhyolite (quartzand quartz-plagioclase porphyry) dykes andstocks as well as mafic and ultramafic sills anddykes. The rocks that cut the volcano-sedimentaryassemblages show an asymmetric areal distribu-


ences between detailed sections A and B (Fig. 2).The basic difference lies in the fact that on thesouthern shore of Lake Verkhneye (section B) twostratigraphic subunits of andesites (A1 and A2)are distinguished (Fig. 4). Here, as in section A,glomeroporphyritic andesites are overlain by across-bedded quartz arenite unit. Resting on thequartz arenites are two texturally similar andesitehorizons, each 6–7 m thick. The horizons consistof flow material succeeded upwards by subunitswhich display vertical grading from pyroclasticbreccia to tuff and lapilli tuff. The third horizon,a massive flow is overlain by a ca. 7.0 m-thickquartz arenite bed (Fig. 5). Except for this local-ity, no sedimentary rocks have been found in theandesite unit. All the contacts between andesitesand quartz arenites are well-defined and occasion-ally tectonized.

In section B, A.B. Samsonov exposed a contactbetween glomeroporphyritic andesites and a lower

quartz arenite horizon (Fig. 6). In the ca. 50cm-thick zone near the contact, weathering in theandesite is indicated by rock disintegration andfine regolith-filled cracks. The andesite immedi-ately beneath the quartz arenite contact displayscoarse garnet and quartz stringers not found else-where in the unit. These features suggest modifica-tion of original chemical composition near thecontact. At two points, the reddish colour ofandesite, observed near the contact within a ca.1.0 m-wide band, is due to groundwater circula-tion in the more porous contact zone.

3.1.2. PetrographyAll varieties of andesites have consistent min-

eral compositions. Their distinct crystallization,schistosity, mineral or aggregate lineation andnematogranoblastic structure indicate the meta-morphic nature of the mineral assemblages. Theassemblage green hornblende+plagioclase (An=

Fig. 4. Outcrop map of the andesite-quartz arenite association in the section B area.


Fig. 5. Stratigraphic columns for andesite-quartz arenite asso-ciation in sections A and B. Sample numbers appear to the leftof the columns.

23%)+quartz+brown biotite+chlorite+epi-dote is most common. Magnetite and apatite occuras accessories. Hornblende is clearly oriented alongthe earlier lineation which is parallel to the dip. Thehomoaxial replacement of hornblende by colour-less twinned cummingtonite, observed along ca. 10m-thick subconcordant zones within the andesiteunit, suggests a local rise in temperature in thesezones. The formation of carbonate (ankerite) nearthe lower contact with ferrobasalts is related to thecirculation of carbon dioxide solutions in the tec-tonically active contact zone. In a ca. 1.0 m-thickzone near the upper contact with the quartz areniteunit, the garnet poikiloblasts with numerous unde-formed rounded quartz inclusions are flattened inthe schistosity plane. Also in this zone, largehornblende poikiloblasts are oriented across earlierlineation along the late subhorizontal lineationwhich is parallel to the Ac-axes of late shear zones.Fine (up to 2.0 mm) granoblastic quartz veinletsand chlorite rosettes, concordant with schistosity,are observed here. In amygdaloidal andesites,amygdales are filled with milky quartz as well asquartz-plagioclase or quartz–chlorite–carbonateaggregates. Plagioclase plates, up to 1.0 cm inlength, that occasionally form stellate aggregatesare characteristic of glomeroporphyritic andesites.

3.1.3. GeochemistryThe Hisovaara andesites belong to the tholeiitic

magma clan using the scheme of Jensen (1976).With respect to major element geochemistry, theHisovaara andesites are tholeiitic andesites similarto those of the Blake River Group in the Abitibigreenstone belt (Xie, 1996). Based on the fieldappearance of the unit in general and the low LOIvalues, we expected to see little evidence for alter-ation. Two pairs of andesite samples (94-PCT-002& 004 and 94-PCT-022 & 023) were taken,with one of each pair from within a few cm of thequartz arenite and the other member of the pairfrom 1–2 m beneath the contact. When majorelement data for the andesites are compared,we observe with increasing proximity to the con-tact: addition of Fe+3, K, and P, loss of Mg andNa and variable behaviour of Si, Fe+2, Al, Na andCa. Spidergrams of trace element geochemistry(Fig. 7) display a fractionated pattern with nega-

Fig. 6. The basal contact of the quartz arenite with theunderlying andesite at location B. The lighter coloured quartzarenite lies above the lighter (about 7.5 cm long) and theweathered andesite beneath the lighter.


tive anomalies for TiO2, Ta and Nb typical ofisland arc volcanism. The negative Hf anomaliesin some samples are due to incomplete sampledissolution verified by comparing Zr values ob-tained by XRF with those obtained by ICP-MSand corroborated by complete dissolution of simi-lar samples using the closed beaker technique(Jenner, 1996).

REE data for these sample pairs are plotted inFig. 8a and b. The LREE are quite variable for asuite of samples obtained within a stratigraphicsection of a mesoscopically similar rock type afew metres in thickness. In basaltic rocks within acoherent unit, LREE variation is conventionallyascribed to fractionation of clinopyroxene9pla-gioclase. No conventional igneous fractionationprocess will yield sample-to-sample variation inCe anomalies or crossing REE patterns.

Comparison of the samples immediately under-lying the quartz arenite vs. those somewhat re-moved from the contact reveals: marked LREEdepletion, a negative Ce anomaly, some depletionof the HREE and loss of Rb and Cs (Figs. 7 and8a, b). A sample of the regolith (Fig. 8c) showsnegative Ce and Eu anomalies and extreme deple-

tion of the HREE. Precambrian weathering ofbasaltic rocks (Kimberley and Grandstaff, 1986)results in Na depletion, variable behaviour of theheavier alkalies (K,Rb, Cs) and the alkaline earths(Ca, Mg). Fe shows an upward decrease into thepaleosol but this pattern can be disturbed bydownward percolation of Fe-bearing ground-water. These authors also report depletion of theLREE in weathering of the Kinojevis basalts inthe Abitibi subprovince. In general the behaviourof REE in weathering of mafic rocks seems some-what variable (Braun et al., 1990; Marsh, 1991;Price et al., 1991). Leaching experiments indicatethat incipient alteration tends to release REE withbehaviour controlled by groundwater parameters(flux, Eh, pH) and the secondary minerals pro-duced during alteration (Price et al., 1991). Theproximity of samples 94-PCT-004 and 94-PCT-022 to the quartz arenite contact and the presenceof mineralogical changes near the contact and thesimilarity to the above studies of Precambrian andyounger basaltic weathering suggest that thechemical changes we observe may be related toweathering of andesite. If the alteration were dueto recent weathering, this cannot explain the min-

Fig. 7. Spidergram (extended trace element diagram) using the normalizing factors of Wood et al. (1986) for the Hisovaara andesites.


eralogical differences in samples proximal to thequartz arenites, reddening of the fresh surfacenear the quartz arenite or the more intense alter-ation being in samples taken closest to the quartzarenites. Therefore weathering took place prior toquartz arenite deposition.

3.2. Quartz-arenite (unit Q)

3.2.1. Field descriptionQuartz arenites associated with andesites were

traced over several kilometres on the northernflank of the Hisovaara structure and were studiedin detail at some localities (Fig. 2). Quartz areniteunit Q is subdivided into subunits Q1 and Q2.Lower subunit Q1, in contact with the andesiteunit, was revealed at all the points shown on themap (Fig. 2). Upper subunit Q2 was found onlyon the northern shore of Lake Verkhneye insection B. Considerable variations in diverse tex-tures and primary structures, apparent both later-ally and vertically, are characteristic of unit Q.For example, subunit Q1 varies in thickness from6–8 m (points C and D, Fig. 2) to 10–12 (pointsB, E, 913) and even 40 m in section A. Otherdifferences are apparent in comparing sections Aand B. In section A, white fine- to medium-grained thin-laminated quartz arenites rest with asharp direct contact on glomeroporphyritic andes-ites (Fig. 9). Hummocky cross-bedding with char-acteristic low angles between cross-bedded unitsand erosion surfaces is observed in some out-crops, depressions being filled with micaceous(argillic) material (Fig. 10). Quartz clasts are pre-dominantly sand sized, except sample 94-PCT-012that includes small (B1.0 cm) quartz pebbles.The fairly high degree of rounding of fine quartzpebble material reflects the textural maturity ofthe rocks. The prevalent white colour of the rockswith a very small admixture of stained mineralsindicates the high mineralogical maturity of thesequartz arenites. One-centimetre-thick feldspar-richlaminae are preserved locally. Primary stratifica-tion is retained, despite a pressure-solution cleav-age which cross-cuts bedding at a medium angle.The rocks are recrystallized strongly enough toform metamorphic quartz veins, with the degreeof recrystallization increasing toward the uppercontact of subunit Q1.

Fig. 8. (A) Chondrite normalized REE profile for andesites94-PCT-002 and 94-PCT-004 taken from beneath the quartzarenite at location A. (B) Chondrite normalized REE profilefor andesites 94-PCT-022 and 94-PCT-023 taken from beneaththe quartz arenite at location B. (C) Regolith.


Fig. 9. Unconformity between massive andesite (bottom ofphoto) and overlying quartz arenite. Lighter colour of andesiteadjacent to the quartz arenite can be seen. Lens cap, 52 mm indiameter.

tion A. Here, a 10–20 cm-thick fine pebble quartzconglomerate horizon lies at its base and has asharp contact with weathered glomeroporphyriticandesite. White, moderately rounded, flattenedquartz pebbles, up to 3.0 cm in size along the longaxis, are closely packed and supported by sand-sized mica and quartz matrix. These rocks gradu-ally pass upwards to fine pebble arenites. Poorlyrounded, often angular pebbles measuring 1.0–1.5cm are represented solely by white quartz. Thegrey quartz arenite matrix consists of unequallyrounded commonly angular quartz grains, 1.0–2.0 mm in size, with the addition of biotite, whichsuggests the low textural and mineralogical matu-rity of the rock. In this unit, which has an ex-posed thickness of ca. 7.0 m, trough bedding,most distinct in its lower half, is obvious. Theupper contact between subunit Q1 and the andes-ites of subunit A2 is not visible because it iscovered by Quaternary deposits.

In section B, both subunits are represented,with subunit Q1 markedly differing in some char-acteristics from its stratigraphic analogue in sec-

Fig. 10. Map of quartz arenite exposures with hummocky cross-bedding (subunit Q1) in section A.


The second quartz-rich rock horizon (subunitQ2) is up to 7.0 m thick. It rests with a sharpcontact on the weathered andesites of subunit A2.Subunit Q2 differs in some macroscopic featuresfrom subunit Q1. It is characterized by:1. The yellowish, locally rusty colour of the rocks

caused by the presence of finely dispersed al-tered iron sulphides.

2. Thin, locally deformed parallel lamination.3. A dominant sand size and smaller dimensions

of quartz grains and scarce thin (10–15 cm)horizons containing fine (B1.0 cm) quartzpebbles (sample 94-PCT-015).

4. The presence of ca. 30 cm-thick horizons withvery fine-grained (B0.05 mm) quartz (sample94-PCT-021).

5. The occurrence of thin (10–15 cm) muscovite-enriched horizons (sample 94-PCT-019) re-sponsible for the graded nature of individualbeds of this subunit.

Resting directly on subunit Q2 are 2.0–3.0 m ofcarbonaceous rocks overlain by felsic rocks thatrepresent rhyolitic ash flows.

3.2.1.1. Petrography. Highly siliceous rocks aredivided based upon microscopy into several typesthat differ in the nature of clastic material, thedegree of quartz recrystallization, and the rela-tionships between quartz and other silicates etc.

Quartz arenites, the most abundant rock typeof the unit, are bedded rocks in which quartz-richbeds alternate with beds that contain quartz andother silicates. Ninety to ninety-five per cent ofthe rock consists of quartz grains varying from0.2 to 2–3 mm in diameter. Intense recrystalliza-tion gives rise to the less common sutured polygo-nal boundaries of grains in quartz monocrystalsand deformation that continues until lenticularaggregates are formed. It is, therefore, impossibleto estimate the degree of roundness of fine clasticquartz. Two types of plagioclase are observed inthe quartz arenites: (a) fine, poorly rounded clas-tic grains are commonly filled with grey dust-likeopaque material along cleavage cracks, which ispresumably due to weathering; (b) newly-formedplagioclase grains occur together with garnet andamphibole in the form of fine chains that fillinterstices between quartz grains. Trace minerals

occur as newly-formed grains or chains of mica,amphibole, garnet, kyanite, staurolite and chloriteaggregates. Zircon, sphene and opaque ore miner-als occur as detrital accessories.

Pebbly quartz arenites are second in abundancein the section. Unlike the quartz arenites de-scribed above, they contain polycrystalline quartzinterpreted as vein quartz strongly elongatedalong the Ac axis which is parallel to the minerallineation and dip of the rocks. In cross section,normal to lineation, various shapes of quartzpebbles (subrounded to angular, but generallypoorly rounded) that vary in size from 0.2×1–1×2 cm (over 5 cm along lineation) in thesecross-sections are easily observed in sawed slabs.Individual quartz pebbles constitute thin centime-tre-scale laminae in quartz arenites that providethe matrix for coarser quartz. Trace minerals andaccessories are similar to those described above,but their quantities vary markedly. For example,pebbly quartz arenites from section B containmore biotite, and at station 913 zircon is presentin large amounts (about 30 grains in one thinsection).

In subunit Q2, two more rock types were seenin section B. In sample 94-PCT-021, fineequigranular quartz (grain sizeB0.05 mm) inwhich individual coarser (1–2 mm) deformed de-trital grains are observed. The quartz arenites passupwards into thin-laminated muscovitic quartzarenites. This subunit includes chemical sedimentsand tuffaceous material.

Several populations of zircon are found in thequartz-rich sedimentary rocks of the quartzarenite-andesite association at Hisovaara. Thetransparent long-prismatic grains are probablymetamorphic based upon similarity to metamor-phic zircons (cf. D.W. Davis, pers comm 1996)Rounded, transparent and dark metamict grainsare prominent among detrital zircons. Of greatinterest are scarce poorly rounded, broken zirconprisms that may indicate a fairly proximal sourceof zircon. It is also important that both macro-scopic and petrographic observations point to theabsence of lithic fragments in the quartz areniteunit. Vein quartz pebbles and clastic zircons arethe most distinct indications of detritus whosetextural maturity was presumably variable. A neg-


Table 2Mean chemical compositions of quartz-arenites from Hisovaara and other Archean regionsa

1 2 3 4 5 6 7 8

94.5 92.13SiO2 95.9794.4 87.02 88.65 92.11 93.450.05 0.06 0.02 0.10.04 0.26TiO2 0.07 0.04

2.21Al2O3 2.44 4.34 2.24 4.47 7.71 4.58 4.071.4 1.07Fe2O3 0.791.58 1.95 0.7 1.09 0.550.02 0.01 0.01 0.080.02 0MnO 0.01 0.02

0.42MgO 0.35 0.31 0.2 2.47 0.44 0.88 0.270.26 0.26 0.07 2.98CaO 0.10.43 0.09 0.140.46 0.98 0.04 0.070.76 0.36Na2O 0.24 0.17

0.15K2O 0.42 0.83 0.65 0.83 1.76 1.01 1.240.05 0.02 B0.01P2O5 0.020.02 0.01 0.01 0.03

38.8 21.2 42.8 19.542.7 11.5SiO2/Al203 20.1 230.2K2O/Na2O 0.9 0.8 16.2 11.9 4.9 4.21 7.3

5.3 4.2 56 63.9 21.4 19.1 23.9Al2O3/Na2O 2.963 62 71 n.d.52 74CIA 73 69

4 9N 110 22 3 8 49

a Recalculated to 100% on a volatile-free basis. (1–4) Quartz arenites from Hisovaara: quartz arenites, subunits Q1 (1) and Q2 (2);pebbly quartz arenites, subunits Q1 (3) and Q2 (4). (5–6) Quartz arenites, Keewaywin formation (5) and Keeyask Lake Formation(6), Sandy Lake greenstone belt Superior Province, Canada (Cortis, 1991). (7) Quartz arenites, Pongola supergroup, S. Africa(Wronkiewicz, Condie, 1989). (8) Quartz arenites, Yavanahalli belt, S. India (Argast and Donnelly, 1982).

ligible amount of plagioclase and the absence oflithic fragments suggest that in a quartz-feldspar-lithic fragment sandstone provenance, the compo-sitions of the quartz-rich metasediments of thequartz arenite-andesite assemblage at Hisovaaralie on the ‘quartz-feldspar line’ near the quartzapex (i.e. in field 1), suggestive of a cratonicprovenance (Dickinson, 1985).

3.2.1.2. Geochemistry. The major and rare earthelement geochemistry of quartz arenites and asso-ciated rocks from the Hisovaara greenstone belt isshown in Tables 2–4. Both field and microscopiccharacteristics are used to define three groups:quartz arenites Q1 and Q2 and pebbly quartzarenites Q1. Pebbly quartz arenite (sample 94-PCT-015) and mica quartz arenite (sample94PCT-019) from subunit Q2 were analysed sepa-rately. In the above groups, some major compo-nents such as SiO2, Al2O3, FeO, Fe2O3, CaO,Na2O and K2O vary over a wide range. Variationsin TiO2 and MgO content are less appreciable. Wecompare the average compositions of the Hiso-vaara quartz arenites with similar rocks fromother Archean regions (Table 2) but they havesome distinctive characteristics. For example,

Hisovaara quartz arenites contain more SiO2,CaO and Na2O and less Al2O3 and K2O. TheirSiO2/Al2O3 ratio is higher and K2O/Na2O ratio islower. The high CaO content of the quartzarenites in the Keewaywin Formation is obviouslydue to superimposed carbonatization (Cortis,1991). The CIA value (CIA= [Al2O3/(Al2O3+CaO+Na2O+K2O)]×100; Nesbitt and Young,1982) estimated for this group is not given be-cause in the calculations CaO represents Ca in asilicate form (McLennan et al., 1990). Many sam-ples collected in subunit Q1 show ultralow (B0.2)K2O/Na2O ratios (Fig. 11). The above character-istics of the rocks described, emphasized by thestrong predominance of Na2O over K2O, indicatethat the matrix of Hisovaara arenites, in whichundecomposed plagioclase grains play a majorrole and the pelite component is less significantand chemically immature. The only exception ismica quartz arenite (sample 94-PCT-019) which isabnormally poor in SiO2 and abnormally rich inAl2O3 and K2O.

The chemical indices of alteration (CIA; Nes-bitt and Young, 1982), calculated for the aboverock groups are much lower than those for quartzarenites from other Archean regions. This indi-


Fig. 11. SiO2/Al2O3-K2O/Na2O plot for quartz arenites.

cates the lower chemical maturity of quartzarenites at Hisovaara. The lowest mean CIA valueof 52 was determined for the quartz arenites ofsubunit Q1. A fairly unusual combination of lowchemical maturity and very high SiO2 content,observed in the rocks discussed, is largely respon-sible for their trace element geochemistry.

Analysis of REE content and REE distributionpatterns has revealed some distinctive features ofsedimentary rocks at Hisovaara. First of all, itshould be noted that their SREE values are muchlower than those of Pongola quartzose sandstones(Fig. 12). Extremely small quantities of rare earths(SREE=4.46–15.20 ppm) were determined forthe quartz arenites of subunit Q1. The pebblyarenites of both subunits and the quartz arenitesof subunit Q2 contain REE in much greater quan-tities. The REE content of mica quartz arenite insample 94-PCT-019 is abnormally high (SREE=96.76 ppm). This supports the conclusion thatREE dominantly form part of micas, i.e. theargillic matrix of quartz arenites (Wronkiewiczand Condie, 1989). All rock samples show a nega-tive Eu anomaly Eu* (Eu*=Eun/(Smn,Gdn)1/2)value of 0.67 (Taylor, 1979). About 80% ofArchean sedimentary rocks have Eu*]0.85(McLennan et al., 1984, 1990).

There are marked differences in REE distribu-tion pattern between the groups studied. Thisprimarily applies to the quartz arenites of sub-units Q1 and Q2. In subunit Q1, two types ofsamples are distinguished. Type 1 (samples 94-PCT-005 and 011) is characterized by slightlyfractionated REE distribution (LaN/YbN=2.78–4.32), flat HREE distribution (GdN/YbN=0.9–

Fig. 12. Chondrite-normalized generalized REE diagrams forquartz-rich sedimentary rocks at Hisovaara and Pongola(Wronkiewicz and Condie, 1989). Hisovaara rocks aremarkedly depleted in REE. Both groups are similar to typicalpost-Archean REE distribution pattern with a negative Euanomaly.


Fig. 13. Chondrite normalized REE profiles for Hisovaara quartz arenites. (A) Unit Q1 type 1; (B) unit Q1, type 2; (C) unit Q2fractionated REE patterns; and (D) pebbly quartz arenites.

1.02), a higher Eu/Eu* value (0.75) and a mini-mum SREE value (4.46–6.41 ppm) (Fig. 13A).Type 2 (samples 94-PCT-007, 008 and 010) ischaracterized by a higher LaN/YbN ratio (8.82–12.15), more fractionated SREE distribution(GdN/YbN=1.74–2.0), lower Eu/Eu* values(0.59–0.74) and higher SREE values (10.23–15.20 ppm) (Fig. 13B). Subunit Q2 shows evenmore diverse REE characteristics. For example,sample 94-PCT-016 is fairly similar in REE frac-tionation pattern (LaN/YbN=3.91, GdN/YbN=0.92) to samples of type 1 from subunit Q1.However, its higher REE value is observed to-gether with a far more intense negative Euanomaly (Eu/Eu*=0.59) (Fig. 9A). Samples 018and 020 occupy an intermediate position in termsof REE characteristics between types 1 and 2 insubunit Q1 (LaN/YbN=8.29–8.51, GdN/YbN=1.20–1.49, Eu/Eu*=0.70–0.73) (Fig. 13B). Sam-

ples 94-PCT-019 and 021 show maximum REE(LaN/YbN=24.57 and 25.43) and SREE (GdN/YbN=3.08 and 2.76) fractionation, but they dif-fer markedly in Eu/Eu* ratio (0.82 and 0.59,respectively) (Fig. 13C). In both subunits, pebblyquartz arenites generally have more persistentREE and SREE fractionation patterns, but theirEu/Eu* values vary substantially (0.53–0.80) (Fig.13D). Sample 94-PCCT-017 from altered felsictuff differs greatly in REE distribution from therocks described. It has a slightly fractionated(LaN/YbN=2.46) REE distribution, markedSREE enrichment (GdN/YbN=0.76) and a pro-nounced positive Eu anomaly (Eu/Eu*=2.00)(Fig. 13C).

In the GdN/YbN–Eu/Eu* diagram (McLennanand Taylor, 1991), Hisovaara quartz-rich sand-stones plot outside the Archean sedimentary rockfield because they have a stronger negative Eu


anomaly. Partial overlap with the Archean sedi-mentary rock field is observed in the low GdN/YbN range (Fig. 14A).

Th and U content varies between and withinthe rock groups differentiated (Fig. 14). In sub-unit Q1, quartz arenites contain less U (average Ucontent is 1.02 ppm) and especially Th (averageTh content is 3.62 ppm) than pebbly arenites(U=1.57 ppm, Th=8.95 ppm). One exception is

sample 94-PCT-013 with an abnormally smallamount of U (0.49 ppm) and, correspondingly, anabnormally high (15.1) Th/U ratio. The quartzarenites of subunit Q2 are markedly richer in bothelements (U=1.58 ppm and Th=7.28 ppm) thanthe quartz arenites of subunit Q1. Th/U valuesvary from 2.7 to 15.1, extremely high values beingdue to either extremely low U content (sample013) or abnormally high Th content (sample 94-PCT-021). Generally speaking, in Th versus Th/Ucoordinates (McLennan and Taylor, 1991) theHisovaara quartzose sandstones plot completelywithin the Archean sedimentary rock field. Thand U distribution seems to be largely controlledby the distribution of heavy minerals, primarilyzircon, indicated by the fact that anomalousquantities of some trace elements (Zr=933 ppm;Th=338 ppm; Y=57 ppm and Pb=72 ppm)that can only be explained by the accumulation ofrelatively abundant zircon as found in sample 913(Kozhevnikov, 1992).

3.2.1.3. Interpretation. The above geological, pet-rographic and geochemical data on the quartzarenite unit can be discussed from two aspects.One aspect is related to the source of both quartzand the other detrital components which consti-tute the unit. The other aspect is the reconstruc-tion of the depositional environment anddepositional mechanism of these rocks that arethe oldest sedimentary rocks in the Hisovaaragreenstone belt.

With respect to the provenance of the quartzarenites, identification of class types is the mostinformative data set. Hisovaara rocks contain nolithic fragments that directly indicate possiblesources. Therefore, data on the geochemistry ofimmobile elements such as REE, major elementchemistry, abundance of quartz pebbles and sometextural characteristics of the rocks discussed arecritical.

Vein quartz, normally present in addition toother types of rock fragments, has been reportedfrom practically all Archean quartz-rich sediments(Eriksson, 1980; Srinivasan and Ojakangas, 1986;Bhattacharyya et al., 1988; Wronkiewicz andCondie, 1989; Cortis, 1991, etc.). Several rocktypes can be proposed as hypothetical sources.

Fig. 14. GdN/YbN-Eu/Eu* (A) and Th-Th/U (B) plot forquartz-rich rocks. Same symbols as in Fig. 8. Negative Euanomalies are markedly higher in Hisovaara rocks than inArchean and a large part of Proterozoic rocks. In the Th-Th/U coordinates, they are, in fact, completely delineated byArchean rocks. In Proterozoic rocks, Th/U ratio is generallylower. Archean and Proterozoic rock fields are given afterMcLennan and Taylor, 1991; Fig. 7c, d and Fig. 8c, d.


Geochemical, mineralogical and other data placea limit on some sources that are probable inprinciple. It should be noted that when using REEgeochemistry to constrain source(s) of the clasticmaterial in the quartz arenites, we assume that:1. Quartz-rich clastic rocks adequately reflect

source area geochemistry. This follows fromflat REE distribution patterns in quartz sandsnormalized in terms of the REE content ofassociated muds in both present-day passivemargin environments (Biscay, Ganges) and ac-tive continental margin settings such as back-arc basins (Japan) and continental arcs (Java)(McLennan et al., 1990).

2. The low SREE content of Hisovaara rocks ispresumably due to the diluting effect ofquartz. This phenomenon was used to explainsmall quantities of SREE in Archean quartzarenites (McLennan et al., 1984; Wronkiewiczand Condie, 1989) and the commonly ob-served low REE content of modern sands incomparison to that of associated muds, inwhich La/Yb, La/Sm and Gd/Yb ratios beingeither unchanged or slightly disturbed(McLennan et al., 1990).

3. The role of vein quartz in the REE distribu-tion pattern, i.e. LaN/YbN, LaN/SmN, GdN/YbN and Eu/Eu* values, is presentlyimpossible to assess properly because there areno data on these parameters for the veinquartz of Hisovaara rocks. The relevant evi-dence, in the literature, is scanty (Siddaiah etal., 1994). Therefore, such an assessment is oflimited value.

4. Low CIA, low K2O/Na2O and Al2O3/Na2Oand high SiO2/Al2O3 values observed in theHisovaara quartz arenites indicate that theinitial geochemical parameters of the felsicsource area(s) are retained better here than insimilar rocks from other regions.

The chemical-exhalative mechanism for devel-opment of a high SiO2 concentration in a hypo-thetical source of clastic quartz cannot really beapplied to Hisovaara rocks because of their dis-tinct negative Eu anomaly which is sharply posi-tive in chemically precipitated rocks (Bavintonand Taylor, 1980; Siddaiah et al., 1994). An ad-mixture of chemically precipitated material is pos-

sible, in principle, in sample 94-PCT-017 whichhas slightly fractionated REE distribution and astrong positive Eu anomaly.

Weathering of quartz-rich amygdaloidal andes-ites could provide a source of quartz. It couldaccumulate in some settings, e.g. a nearshorebeach zone. However, the possible mechanism forsuch complete andesite decomposition, needed toexplain the complete absence of lithic fragments,remains obscure. Furthermore, weakly positiveEu anomalies in andesites do not favour thisoption.

Quartz-rich metasomatic rocks could be asource of quartz, as observed, for example, insome Proterozoic rocks in Karelia (Kozhevnikovand Golubev, 1995). Fragments of metasomaticrocks, fuchsite schists, tourmaline quartz arenitesand other rocks are found in some Archean belts(Luukkonen, 1988; Cortis, 1991; Kozhevnikov,1992). Metasomatic quartz rocks usually containno plagioclase, and the rocks consist of a quartz-mica association, Ca and Na being completelyremoved. The presence of plagioclase in the detri-tal material of quartz arenites at Hisovaara andtheir low CIA value does not seem to favour ametasomatic source. The REE distribution pat-tern of most of the samples analysed indicatesthat the major constituent of the source was rep-resented by felsic rocks, which is reflected inLREE enrichment, fractionated HREE distribu-tion and a negative Eu anomaly. Their sodicnature, which is retained even during partialweathering, suggests that they could be tonalite-type granitoids or felsic volcanics of a sodic series.Judging by the presence of at least two types ofdetrital zircon in the samples analysed, the felsicsource is assumed to be complex. Some problemsthat arise when the ‘quartz budget’ in quartz-richsediments is estimated using a granitoid destruc-tion mechanism (Pettijohn et al., 1972) can beovercome by assuming that hypabbysal subvol-canic bodies, typically containing abundant veinquartz, were destroyed.

To assess the possible source(s) of the material,which comprises subunit Q, calculations weremade using the REE content of the rocks. Theamount of REE in the tonalites, rhyolites andkomatiites of the lower mafic assemblage was


employed as end members. Komatiites were in-cluded in calculations for several reasons. Firstly,it has been found earlier that the Cr content ofsubunit Q1 varies over a very broad range from 42to 581 ppm (Kozhevnikov and Travina, 1993).Secondly, thin (maximum 15 cm) Cr-enrichedmetasandstone horizons that contain finely dis-persed metamorphic fuchsite were observed inquartz arenites at several levels above quartzarenite subunit Q, which testifies to the presenceand weathering of an ultramafic source(Kozhevnikov, 1992). Thirdly, flat HREE distribu-tion and slight LREE enrichment at low LaN/YbN

and a strong negative Eu anomaly require the useof an additional component for interpretation. Thiscomponent must have characteristics most similarto those of the komatiites in the lower maficassociation.

Table 5 shows the chondrite-normalized REEcontent of the rocks that hypothetically form theend members of possible sources (tonalites, komati-ites and rhyolites), for a series of quartz-richsamples from subunits Q1 and Q2 and in estimatedmixtures diluted with quartz containing negligibleREEs. Estimated normalized REE values are sim-ilar to those observed in the Hisovaara quartzarenites. Their distribution curves are similar, too(Fig. 15). This suggests that such REE distribution,e.g. those observed in samples from unit Q1, couldbe indicated by the deposition of the products ofdestruction of a bimodal source with various ratiosof felsic to ultramafic components. Tonalite de-struction products were deposited dominantlywithin individual thin horizons (sample 94-PCT-007). In the course of subunit Q2 formation, therole of a felsic source increased steadily, the degreeof quartz dilution being possibly lower.

Intense weathering of tonalites and ultramaficrocks must have followed the uplift and deeperosion of the roots of the greenstone belts domi-nated by the rocks of the mafic assemblage, includ-ing komatiites and hypabbyssal tonalitic plutonssaturated with vein quartz. In this case, conditionsfavourable for the concentration of the most resis-tant rock destruction products, e.g. quartz, heavyminerals and partly plagioclase, must have beenformed locally. A river channel in a deeply erodedmountain system or in any other small, seasonally

drained basin is a possible environment. It seemsto be the type of setting in which clastic (e.g. pebbly)quartz material could be abraded for a short timeand the multiple intense scour of deposits, accom-panied by the formation of quartz sands and coarsegravel, could occur. The proximity of source(s) ofclastic material and its very rapid transport withoutlong abrasion is indicated by:1. The textural immaturity of pebble-sized clasts.2. The occurrence of unrounded, euhedral zircon

fragments.Some characteristics of the quartz arenite accumu-lation field can be reconstructed by summarizingthe above evidence. Judging by the bedding pat-terns in quartz-rich and associated rocks, they weredeposited in a marine setting. In section A quartzarenites, hummocky cross bedding could be formedin a shelf zone affected by contour currents andstorm waves at a depth up to 90 m, i.e. above thestorm wave base (Duke, 1985). Other possibleenvironments for the occurrence of hummockycross stratification are known [flash-flood braideddelta (Hjellbakk, 1993), eolian systems Langford(1989), and antidunes in a fluvial channel (Rust andGibling (1990))]. The angularity of quartz pebblesis presumably due to limited transport distances.Furthermore, the transition to overlying sulfidicargillites, could represent basin deepening e.g.Hoffman, 1987) or development of lagoonal condi-tions. This transition could be rapid enough for theburial of texturally immature quartz-rich rocks.The trough cross-bedding, observed in the quartz-rich sandstones of section B, could form in smallchannels near the shoreline (Mueller and Dimroth,1985). Association of these rocks with subaerialandesites and rhyolites favours such a setting.

The two andesite units (Fig. 5) differ in texture,but are identical geochemically, thus indicatingsimilar magma-generating conditions. This pointsto a short time interval between the two episodesof andesite volcanism, the succession of processesbeing: andesite volcanism — a non-depositionalinterval — the formation of a thin weatheredcrust-rapid transport and deposition of quartz richsedimentary rocks. Addition of tuffaceous materialto subunit Q2 indicates that sedimentation associ-ated with the completion of andesite volcanismcontinued as well as rhyolite volcanism.

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Table 3Whole-rock chemical analyses (wt%) from Hisovaaraa

6 7 8 9 10 11 12 13 14 15 16 17 181 2 3 4 5

94-PCT- 94-PCT-92-8 92-12 92-14 94-PCT-92-10 94-PCT-92-16 094- 92-35 94-PCT- 92-37 92-38 94-PCT- 94-PCT-92-36 94-PCT-003012012008 003011 010 PCT-05007

93.80 94.40 96.08 96.48SiO2 96.9891.92 87.52 88.42 91.80 91.94 92.06 92.64 93.48 94.3092.00 93.00 93.24 03.500.08 0.02 0.02 0.02 B0.01 0.01 0.01 0.10 0.08 0.04 0.06 0.07 0.06 0.03 0.04TiO2 0.060.06 0.02

2.35 2.35 1.70 1.84 1.18 6.72 6.15 4.20 4.453.28 4.462.62 3.15 2.62 2.752.31Al203 2.36 2.030.161.29 1.16 1.28 0.04 0.16 0.10 1.14t 0.26 0.63t 0.63t 0.10 153t 0.44 0.44149 1.13 0.72Fe2O3

0.571.00 0.58 0.29 1.22 0.57 0.72 – 0.93 – – 0.72 – 0.86 0.501.00 0.43 1.15FeO0.00 0.99 0.01 0.01 0.01 0.02 0.01 B0.01 0.020.01 0.01MnO 0.02 0.01 0.010.020.000.020.100.35 0.20 0.20 0.15 0.45 0.30 0.60 0.20MgO B0.050.75 0.30 0.30 0.60 0.200.80 0.65 0.40 0.250.63 0.42 0.07 0.07 0.07 0.42 0.07 0.52 0.420.07 0.070.98 0.50 0.07 0.07CaO 0.300.491.12

1691.25 0.85 0.35 0.63 0.56 0.12 0.36 0.03 0.52 1.50 0.87 0.55 0.87 0.060.85 0.30 1.00Na2O0.05 0.31 0.06 0.10 0.21 2.23 0.19 1.15 0.33K2O 0.910.04 0.43 0.38 0.900.04 0.62 0.07 0.030.08 0.10 0.05 0.02 0.07 0.20 0.10 0.10 0.150.05 0.040.08 0.07 0.15 0.95H2O 0.040.080.10

0.140.25 0.16 0.23 0.17 0.19 0.11 0.76 011 0.58 0.18 0.28 0.56 0.21 0.350.27 0.28 0.20L.O.1P2O5 n.d.n.d.* n.d. B0.01 B0.01 B0.01 0.05 B0.01 0.03 0.03 B0.01 0.03 B0.01 0.01n.d. n.d. 0.24 B0.01

100.03 99.95 100.19 100.16 100.03 99.80 99.95 99.77 99.7199.77 99.8999.62 99.84 99.76 99.6899.76Total 100.08 99.785337 47 58 58 61 68 64 54 58 55 64 58 57 6936 56 50CIA

SiO2/ 28.5138.95 39.91 40.17 56.52 52.43 82.19 13.02 14.38 21.86 20.66 20.64 2941 35.68 34.2945.32 35.50 40.36Al2O3

0.02 0.06 0.89 0.10 0.18 1.75 6.19 0.06 2.212.07 0.220.07 105 0.78 0.44 15.00.050.03K2O/Na2O

1.94 2.76 6.71 2.70 3.28 9.82 18.67Al2O/ 2.031.89 8.08 3.00 5.13 8.73 3.01 45.832.39 8.73 2.31Na2O

24 25 26 27 28 29 30 3121 3220 33 34 35 36 3722 231994-PCT- 94-PCT-94-PCT-94-PCT- 94-PCT- 94-PCT-94-PCT-913 94-PCT- 94-PCT- 576-4578-2 577-2 92.39 94-PCT- 94-PCT- 831-194-PCT-94-PCT-

016 021 019 24 017018 004 002020 01402202302195.44 77.76 78.30 66.00 57.88 57.98 56.72 57.10 56.40 57.00 56.02 60.42 37.75SiO2 67.0094.36 21.10 93.48 95.20 96.20

0.02 0.12 0.35 0.72 0.77 0.60 0.84 1.32 1.300.02 1.04TiO2 1.42 0.64 0.31 0.350.040.080.070.052.23 13.02 12.38 17.74 13.39 13.25 15.73 14.48 14.88 14.20 14.41 14.27Al2O3 6.242.09 16.403.11 2.84 2.07 1.700.16 0.52 0.88 2.04 1.65 3.56 11.60t 2.99 2.820.44 2.920.84 3.44 2.02 1.90 1.100.12Fe2O3 1.55 0.68

0.500.50 0.57 1.15 1.01 1.94 7.64 6.36 – 8.38 8.98 8.62 9.05 7.54 4.57 2.151.01 0.50 1.15FeO0.01 0.01 0.02 0.04 0.12 0.17 0.14 0.13 0.11MnO 0.150.01 0.12 0.11 0.27 0.050.02 0.03 0.01 0.010.20 0.61 0.40 1.00 4.33 4.44 2.11 3.02 3.980.25 4.030.10 2.62 3.33 26.40 1.43MgO 0.400.360.40

0.070.07 0.07 0.42 0.70 2.10 6.03 6.20 6.16 5.68 6.10 4.28 6.00 4.51 5.74 3.270.42 0.42 0.14CaO0.05 0.15 0.04 0.32 1.51 2.42 5.17 5.98 5.47 4.33 3.45 5.15 4.01 5.17 0.08 5.88Na2O 1.220.07 0.41

0.65 4.00 2.75 2.91 0.08 0.26 0.27 0.52 0.330.42 0.400.76 0.51 0.23 0.02 1.22K2O 0.590.380.290.050.07 0.11 0.03 0.10 0.23 0.09 0.66 0.15 0.15 0.33 0.19 0.22 0.06 0.29 0.140.07 0.03 0.02H2O0.280.59 0.20 1.79 1.39 2.23 2.56 0.71 0.35 1.18 1.47 1.49 1.45 1.37 11.51 0.830.40 0.50 0.10L.O.1

B0.01 0.01 0.06 0.16 0.17 0.22 0.24 0.24 0.22B0.01 0.18P2O5 0.26 0.17 n.d. 0.15B0.01n.d.0.200.0199.70 99.77 99.85 99.52 99.94 99.74 99.78 99.52 100.37 99.65 99.53 99.87 100.08 99.96Total 100.23 99.98 99.87 99.89 100.0971 707350 6861CIA 66

46.0045.15 56.59 42.80 5.97 6.32 3.7229.61 32.92SiO2/Al2O3

2.80 16.25K2O/ 12.510.86 1.82 1.200.24 0.93 11.80Na2O

11.33 55.75 40.69 8.20 7.336.93 41.4Al2O3/ 29.86 2.55Na2O

a n.d. Not detected. t-Fe recalculated to Fe2O3. See Figs. 2–5 for locality locations. (1–10) Quartz arenites from the subunit Q1. (11–19) Pebbly quartz arenite from the subunit Q1. (20–23) Quartz arenites from the subunitQ2. (24) Pebbly quartz arenite from the subunit Q2. (25) Mica quartz arenite from the subunit Q2. (26) Altered rhyolite. (27) Altered luff-sandstone. (28–29) Amygdaloidal (28) and homogeneous (29) andesite fom the lowerpart of the andesite sequence (subunit Al). (30–32) Glomeroporphyritic andesites from the upper part of the subunit Al. Unaltered (30, 31) and altered (32) near contact with quartz-rich subunit Q1. (33–35) Andesites fromsubunit A2; homogeneous unaltered (33) and altered (34) near contact with quartz-rich subunit Q2, coarse pyroclastic (35) from dark fragment. (36) Peridotitic komatlite 2. (37) Tonalite.

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Table 4Trace element geochemistry (ppm) of Hisovaara rocks

6 7 8 9 10 111 2 3 4 5

94-PCT-011 94-PCT-005 94-PCT-012 94-PCT-013 94-PCT-003 94-PCT-001 94-PCT-021 94-PCT-02094-PCT-010 94-PCT-008 94-PCT-007

7.53 5.19 4.31 8.17 7.16 6.141.96La 0.702.233.061.122.59 1.67 15.48 10.46 9.50 13.95 13.52 11.216.59 5.04Ce 4.35

0.52 0.22 1.84 1.19 1.06 1.93 1.72 1280.78Pr 0.570.336.67 4.16 3.73 6.74 6.08 4.720.901.95 1.96Nd 1.25 2.94

0.220.27 1.17 0.67 0.68 1.12 0.93 0.850.58 0.35 0.40Sm0.21 0.11 0.16 0.16 0.15 0.19Eu 0.06 0.12 0.06 0.08 0.050.91 0.52 0.55 0.89 0.65 0.740.190.22Gd 0.330.280.42

0.020.03 0.13 0.06 0.07 0.11 0.08 0.110.05 0.03 0.04Tb0.61 0.26 0.34 0.56 0.33Dy 0.580.18 0.24 0.17 0.22 0.130.12 0.05 0.06 0.11 0.06 0.110.030.04Ho 0.03 0.05 0.030.33 0.14 0.18 0.32 0.17 0.37Er 0.11 0.14 0.10 0.13 0.100.04 0.02 0.02 0.04 0.02 0.060.02Tm 0.020.010.020.02

0.170.17 0.34 0.18 0.25 0.39 0.19 0.500.17 013 0.15Yb0.06 0.04 0.04 0.06 0.03 0.080.040.03Lu 0.030.020.03

0.466.41 35.44 23.05 20.95 34.55 31.09 26.9415.20 10.87 10.23SREE2.784.32 14.95 19.47 11.64 14.11 25.43 8.2912.15 11.58 8.82LaN/YbN

4.05 4.88 4.00 4.60 4.85 4.552.003.32 3.094.01LaN/SmN 2.611.781.02 0.90 2.16 2.34 1.78 1.84 2.76 1.202.00 1.74GdN/

YbN

0.62 0.57 0.80 0.49 0.59 0.73Eu/Eu* 0.75 0.74 0.59 0.67 0.759.33 7.39 8.46 10.62 14.59 6.353.324.38Th 2.8421.385.18

1.121.24 1.78 0.49 1.78 2.22 1.95 1.641.29 0.72 0.71U3.03.5 5.2 15.1 4.8 4.8 7.5 3.94.0 3.3 4.0Th/U

17 18 19 20 21 2215 2316 2414131294-PCT-017 568-2 577-2 94-PCT-004 94-PCT-002 94-PCT-023 94-PCT-02294-PCT-018 94-PCT-01494-PCT-016 94-PCT-015 94-PCT-019 94-PCT-024

6.89 24.64 4.09 4.24 9.73 14.6328.83 14.45La 3.5621.115.793.303.28690 58.82 145 46 50.80 12.42 9.81 23.35 49.79 39.43 9.50716 12.66Ce 43.54

1.93 6.14 1.71 1.78 3.00 4.596.70 4.400.82 1.58Pr 5.041.460.8423.632.96 706 25.70 857 8.71 12.70 19.68 18.49 8.073.14 5.26 18.02Nd

0.57 3.45 1.38 4.88 1.71 3.24 3.19 4.35 4.35 3.090.70 0.89Sm 2.990.93 1.26 0.43 1.22 1.18 1.370.83 1.460.13 1.030.69Eu 0.12 0.13

2.540.48 1.47 4.57 2.11 3.95 3.85 4.45 4.72 3.410.65 0.63 2.21Gd0.30 n.d. n.d. 0.64 0.62 0.62Tb 0.720.06 0.530.11 0.08 0.30 0.312.05 3.78 1.89 3.67 3.65 3.351.38 3.910.35 2.99Dy 1.300.360.70

0.230.07 0.47 n.d. n.d. 0.70 0.70 0.64 0.75 0.590.15 0.06 0.22HoEr 1.500.20 1.99 1.03 1.89 1.91 1.76 2.04 1.630.46 0.18 0.58 0.68

0.22 n.d. n.d. 0.26 0.25 0.240.08 0.280.03 0.23Tm 0.080.020.080.650.26 1.57 2.14 0.90 1.66 1.67 1.51 1.80 1.540.57 0.20 0.58Yb

0.24 0.28 0.17 0.24 0.24 0.21Lu 0.240.04 0.220.09 0.03 0.10 0.1041.47 124.19* 35.03* 42.01 66.04 107.19128.23 97.0416.19 37.97SREE 96.7627.7518.08

29.948.51 2.96 7.75 3.09 1.72 3.93 6.54 5.42 1.563.91 19.55 24.57LaN/YbN

3.14 3.18 1.50 0.82 1.92 2.12 2.09 0.72LaN/SmN 3.62 2.97 4.10- 4.44 5.263.16 0.76 1.72 1.91 1.92 1.86 2.383.08 2.120.92 1.792.55GdN/ 1.49

YbN

0.70 0.86 2.00 0.82 0.69 1.04 1.03 0.95 0.99 0.970.59 0.53Eu/Eu* 0.824.41 7.46 4.91 2.97 3.02 3.53 3.17Th 5.222.21 5.97 6.30 9.82 6.210.88 1.01 0.92 0.37 0.53 0.591.18 0.812.69 0.75U 0.81 1.90 1.52

Th/U 5.02.7 7.4 5.3 8.03 5.7 6.0 3.9 7.03.1 4.1 3.7 5.3

* SREE without Tb, Dy, Ho and Tm; breccia (Fig. 13).

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Table 5Chondrite-normalized REE contents in komatiite, tonalite, rhyolite and in quartz-rich rocks from Hisovaara and calculated compositions of mixtures that result with various dilutions byquartza

6 71 8 9 10 11 12 13 14 15 16 17 18 192 3 4 5

La 12.512.17 12.55 8.01 7.97 17.62 17.64 30.78 31.14 23.67 24.66 29.27 28.82 86.30 89.9249.43 117.9 4.58 4.6010.33 10.04 6.82 6.58 14.89 14.11 24.27 24.92 19.853.86 19.52Ce 21.19 22.65 68.25 70.634.0692.2140.802.48

Pr 8/092.18 7.86 5.39 5.56 11.00 11.06 19.09 19.77 15.15 15.12 17.84 17.29 52.28 53.8834.47 69.50 3.42 3.286.20 5.87 4.14 4.24 7.87 8.26 14.08 14.59 11.102.61 11.022.64 12.83 12.49 38.03 38.93Nd 2.98 26.32 49.873.77 3.13 2.60 2.56 4.42 4.41 7.60 7.62 5.78Sm 5.403.77 6/04 5.84 19.42 18.1915.91 22.40 1.75 1.762.07 1.92 1.38 1.58 2.76 2.70 3.62 4.78 2.241.03 3.41Eu 2.59 3.71 11.90 11.561.0314.319.831.722.06 1.90 1.62 1.48 2.69 2.68 4.45 4.33 3.08 3.04 3.18 3.26 10.82 10.16Gd 3.87 9.20 12.43 1.08 1.170.94 1.11 0.87 1.02 1.34 1.56 2.40 2.49 1.420.84 1.583.07 1.30 1.40 5.12 4.35Dy 0.715.436.34

0.662.71 0.84 0.87 0.78 0.76 0.84 1.22 1.99 1.87 1.08 1.18 1.02 1.17 3.49 3.644.70 4.10 0.66Er0.823.57 1.03 0.99 0.91 0.90 1.51 1.39 2.06 2.08 1.21 1.26 1.15 1.17 3.51 3.685.63 3.94 1/03Yb

1.18 1.13 1.18 1.02 1.57 1.59 2.36 2.26 1.180.92 1.33Lu 1.18 1.22 3.94 3.801.183.946.304.7212.15 11.11La/Yb 8.820.61 8.85 11.64 12.69 14.95 14.99 19.56 19.57 25.43 24.63 24.57 24.438.82 29.92 4.32 5.613.32 4.01 3.09 3.11 4.00 4.00 4.05 4.08 4.102.61 4.572.61 4.85 4.93 4.44 4.94La/Sm 0.58 3.11 5.262.00 1.68 1.78 1.64 1.78 1.93 2.16 2.08 2.55 2.41 2.76 2.79 3.08Gd/Yb 2.761.08 1.64 3.15 0.02 1.430.74 0.79 0.67 0.81 0.80 0.78 0.62 0.83 0.53 0.84 0.59 0.85 0.820.72 0.85Eu/Eu* 0.45 0.81 0.86 0.75

a (1) Komatiite (s.576-4); (2) tonalite (s.831-1); (3) rhyolite (94-PCT-.024); (4) quartz arenite (94-PCT-.011); (5) mixture of komatiite: tonalite=1; 1, diluted 5.6 times by quartz; (6) quartzarenite (94-PCT-010); (7) mixture of komatiite: tonalite: rhyolite :1:1:1 diluted 4.4 times by quartz; (8) quartz arenite (94-PCT-007); (9) contents in tonalite diluted 6.2 times by quartz; (10)pebbly quartz arenite (94-PCT-003); (11) mixture of komatiite:tonalite:rhyolite :1:1:1 diluted 3.1 times by quartz; (12) pebbly quartz arenite (94-PCT-012); (13) mixture of tonalite:rhyolitec 3.2 diluted 2.4 times by quartz; (14) pebbly quartz arenite (94-PCT-015); (15) mixture of tonalite:rhyolite=2:3. diluted 3.7 times by quartz; (16) quartz arenite (94-PCT-021); (17) mixtureof tonalite:rhyolite=1.4 diluted 3.6 times by quartz, 18-mica quartz arenite (94-PCT-019); (19) mixture of tonalite:rhyolite=1:4, diluted 1.1 times by quartz.


Fig. 15. Chondrite-normalized REE diagrams for tonalite, komatiite, rhyolite, some quartz-rich rock samples and rated mixtures atvarious degrees of quartz dilution. The normalized values given in Table 3 were used. Sample numbers in this figure are those usedin Table 3.

Fairly aggressive acid rains, related to fumarolicactivity between volcanic paroxysms, could wellbe responsible for the development of weatheringon andesites.

In summary, the Hisovaara quartz arenites areassociated with intermediate to felsic volcanics

providing an example of a combination of somefeatures characteristic of platformal settings withthose typical of environments that display anactive continental margin- or island-arc type ofcalcareous-alkaline volcanism. It is a rare case inArchean greenstone belts.


3.3. Felsic fragmental rocks (unit F)

3.3.1. Field descriptionThis unit is composed of felsic pyroclastic rocks

and subordinate reworked equivalents(Kozhevnikov, 1992). In this section we providethe field evidence for interpretation of the deposi-tional environment of the unit. In the vicinity oflocation B, the sequence consists of metre scaleunits of tuff breccia and lapilli tuff with occa-sional tuff intercalations. Primary textures andstructures indicate the presence of both pumiceand lithic fragments. Each unit is defined bydistinct size ranges of clasts, texture of pumice, adistinct phenocryst content and a regular succes-sion of size and density grading. Within individualunits as defined above, reverse grading of pumice,normal grading of lithic fragments, sporadic ex-amples of basal ground surge beds and thinlylaminated fine ash tuff beds occur whichindicate the units represent ignimbrite deposition(Sparks et al., 1973). Evidence for welding con-sists of the presence of branching fumarolic struc-tures (cf. Thurston, 1980) and the presence offlattened silicified pumice fragments concentratedtoward the middle of the stratigraphic unit. Thesilicified pumice ignores depositional unitboundaries and is thus interpreted as evidence ofvapour phase recrystallization (Ross and Smith,1961) indicative of subaerial eruption and deposi-tion.

At location A, in a few exposures, the quartzarenite is overlain by a few metres of a fragmentalaluminous metaconglomerate with granitoid andpossible metavolcanic clasts. This is overlain byabout a 100 m thickness of thin graded beds ofsulfidic argillite and carbonate bearing siltysandstones.

3.3.2. PetrographyThe rhyolites at location B consist of varying

proportions of quartz, plagioclase and minorpotassium feldspar with accessory biotite andsericite. Primary textures are completely obliter-ated by metamorphic recrystallization but grossgrain size variation seen mesoscopically is presentin thin section. Silicified pumice fragments containirregular polycrystalline plates of quartz whereas

the matrix contains finer rained quartz, feldspar,biotite and sericite.

3.3.3. GeochemistryThe sole analysis of the rhyolitic unit done for

the present study shows the unit to be a high silicarhyolite with potassium dominant over sodium(Table 3). In trace element terms, the unit displaysa fractionated REE pattern similar to the FIrhyolites of Lesher et al. (1986).

4. Summary and conclusions

The Hisovaara quartz arenites represent amixed provenance involving contributions fromTTG suite granitoids and a mafic to ultramaficcomponent with extensive weathering to explainthe lack of feldspar in the sandstones. Mature,quartzose, shallow-water sandstones are not com-mon in Archean greenstones (Thurston andChivers, 1990; Lowe, 1994). The quartz-rich sand-stones at Hisovaara are unusual in showingclearly the base of the sequence and evidence forweathering of the andesitic basement seen in field,petrographic and geochemical evidence. MostArchean quartz-rich sandstones are associatedwith platforms (De Kemp, 1987; Thurston andChivers, 1990) with one example of a cannibalizedplatform within a submarine fan environment(Cortis, 1991). As an Archean quartz rich sand-stone sequence, the Hisovaara quartz arenites areclosely associated with subaerial arc andesites andsubaerial rhyolites at the south end of the beltsimilar to the ‘continental’ style assemblage typeof Thurston (1994). However, at the north end ofthe belt, the quartz arenites are succeeded upwardby conglomeratic rocks, argillites, and an overly-ing tholeiite unit with komatiites. This end of theunit is then comparable to some of the SuperiorProvince platformal quartz arenites in thatquartz-rich sedimentation is followed by volcan-ism (cf. De Kemp, 1987). Thus the Hisovaaraquartz-rich sandstones demonstrate a relationshipin an Archean setting between subaerial volcan-ism in an arc setting and development of andeepening basin and subsequent volcanism relatedto rifting.


Post Archean quartz-rich sandstones are con-ventionally considered to represent multiplepasses through the sedimentary cycle (Pettijohn etal., 1972, p. 298) with the interplay of climate,relief, and provenance influencing the composi-tion of the sands (Basu, 1985). Recent work in theOrinoco basin has demonstrated the productionof single cycle quartz arenites in a regime ofintense chemical weathering (Johnsson et al.,1988). The process involves either long soil resi-dence times related to very low erosion and trans-port rates or storage of orogenically derivedsediments on alluvial plains enroute to the finaldepositional site. In spite of the variety of mecha-nisms for production of quartz rich sandstones,we here use their presence in the Hisovaara green-stone belt to indirectly indicate the presence ofgranitoid rocks in the source area. A granitoidsource area serves as a speculative indicator of atleast unroofing of plutons if not a possible cra-tonizing or orogenic event. If the latter is the case,the age constraints available in this greenstonebelt suggest the possibility of a pre-2.7 Ga oro-genic event in the Baltic shield. Much additionalwork is required to validate such a concept, butthe tantalizing indication seen in this project willperhaps point the way to further work on thisspeculation.

5. Geochemical methods

Sample preparation and major element analysisby X-ray fluoresence were carried out at the Kare-lian Research Centre. The XRF analyses weredetermined on fused glass discs after the methodof Norrish and Hutton (1969). Trace elementswere determined in the Geoscience laboratories ofthe OGS at Sudbury. Rb, Sr, Ba, Cr, Ni, Zr andY were determined by XRF on pressed powderpellets. All other trace elements were determinedby ICP-MS following a mixed acid digestion inopen beakers (OGS, 1990). Results were checkedfor dissolution problems by comparison of XRFdetermined Zr vs. ICP-MS values. Precision onreference materials has been at the level ofB10% using these methods (cf. Tomlinson et al.,1998).

Acknowledgements

This project is an outgrowth of the US–Rus-sia–Canada co-operative program during whichthe senior author visited Hisovaara with OGSsupport. At that time the andesite-quartz areniteassemblage was noted in the field as unusual.Subsequent field work was funded by the Geolog-ical Institute of the Karelian Research centre,Karelian Branch of the Russian Academy of Sci-ence in 1994 and 1996. We thank Dr Sergei I.Rybakov, Director of the Geological Institute forhis support of the project. This paper is publishedwith the permission of the Senior Manager Pre-cambrian Geoscience Section Ontario GeologicalSurvey (Ontario Geological Survey, 1990). Thisproject would not have been possible withouttranslation on the outcrop by Grigori N. Sokolovof the Institute and subsequent translation ofe-mails, letters and drafts of the paper. Dr K.I.Heiskanen of the Institute is gratefully acknowl-edged for his thoughtful review of an early ver-sion of the manuscript. R.W. Ojakangas and J.Dostal as journal reviewers helped clarify manypoints and sharpen the presentation. Major ele-ment analyses were done in the chemical labora-tory of the Institute of Geology of the KarelianResearch Centre (Saraphanova, R. Ph., Mokeeva,L.N., Punka G.P., and Pitka, N.V.) Field assis-tance was provided by E. Travina in 1994. Draft-ing has been done by O. Kozhenikova and S.Josey.

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