relative timing of uplift along the zagros mountain front ...the zagros fold–thrust belt...

Solid Earth 10 663ndash682 2019httpsdoiorg105194se-10-663-2019copy Author(s) 2019 This work is distributed underthe Creative Commons Attribution 40 License

Relative timing of uplift along the Zagros Mountain Front Flexure(Kurdistan Region of Iraq) Constrained by geomorphic indices andlandscape evolution modelingMjahid Zebari12 Christoph Gruumltzner1 Payman Navabpour1 and Kamil Ustaszewski11Institute of Geological Sciences Friedrich Schiller University Jena 07749 Jena Germany2Geology Department Salahaddin University-Erbil Erbil 44002 Kurdistan Region of Iraq

Correspondence Mjahid Zebari (mjahidzebariuni-jenade)

Received 22 November 2018 ndash Discussion started 28 November 2018Revised 17 April 2019 ndash Accepted 20 April 2019 ndash Published 17 May 2019

Abstract The Mountain Front Flexure marks a dominant to-pographic step in the frontal part of the Zagros FoldndashThrustBelt It is characterized by numerous active anticlines atopof a basement fault So far little is known about the relativeactivity of the anticlines about their evolution or about howcrustal deformation migrates over time We assessed the rela-tive landscape maturity of three along-strike anticlines (fromSE to NW Harir Perat and Akre) located on the hangingwall of the Mountain Front Flexure in the Kurdistan Regionof Iraq to identify the most active structures and to gain in-sights into the evolution of the foldndashthrust belt Landscapematurity was evaluated using geomorphic indices such ashypsometric curves hypsometric integral surface roughnessand surface index Subsequently numerical landscape evo-lution models were run to estimate the relative time differ-ence between the onset of growth of the anticlines usingthe present-day topography of the Harir Anticline as a basemodel A stream power equation was used to introduce flu-vial erosion and a hillslope diffusion equation was appliedto account for colluvial sediment transport For different timesteps of model evolution we calculated the geomorphic in-dices generated from the base model While Akre Anticlineshows deeply incised valleys and advanced erosion Harirand Perat anticlines have relatively smoother surfaces and aresupposedly younger than the Akre Anticline The landscapematurity level decreases from NW to SE A comparison ofthe geomorphic indices of the model output to those of thepresent-day topography of Perat and Akre anticlines revealedthat it would take the Harir Anticline about 80ndash100 and 160ndash200 kyr to reach the maturity level of the Perat and Akre an-ticlines respectively assuming erosion under constant con-

ditions and constant rock uplift rates along the three anti-clines Since the factors controlling geomorphology (lithol-ogy structural setting and climate) are similar for all threeanticlines and under the assumption of constant growth anderosion conditions we infer that uplift of the Akre Anti-cline started 160ndash200 kyr before that of the Harir Anticlinewith the Perat Anticline showing an intermediate age A NW-ward propagation of the Harir Anticline itself implies that theuplift has been independent within different segments Ourmethod of estimating the relative age difference can be ap-plied to many other anticlines in the Mountain Front Flexureregion to construct a model of temporal evolution of this belt

1 Introduction

The Zagros FoldndashThrust Belt (hereafter referred to as Za-gros) is an active orogen that resulted from the collision be-tween the Arabian and Eurasian plates and contains the de-formed portions of the NE part of the former Arabian passivemargin (Fig 1 Berberian 1995 Mouthereau et al 2012)Many aspects of the structural configuration and the evolu-tion of the Zagros FoldndashThrust Belt are by now satisfactorilyconstrained but the detailed spatial and temporal distribu-tion of deformation across the belt is not yet well understoodThis concerns especially the NW part of the belt in the Kur-distan Region of Iraq (KRI) due to a lack of comprehensivestudies and for geopolitical reasons that make access to thefield challenging The style timing and relative activity offront thrusts deformation propagation and along-strike vari-

Published by Copernicus Publications on behalf of the European Geosciences Union

664 M Zebari et al Relative timing of uplift along the Zagros Mountain Front Flexure

ations have not been sufficiently studied It is not well knownwhich structures are currently the most active ones either

One of the morphologically most conspicuous structuralelements of the Zagros FoldndashThrust Belt is the MountainFront Flexure (MFF) which separates the High Folded Zoneand the Foothill Zone (known in Iran as the Zagros SimplyFolded Belt and Zagros Foredeep respectively Figs 1 and 2Berberian 1995 Jassim and Goff 2006 McQuarrie 2004Mouthereau et al 2012 Vergeacutes et al 2011) In most partsof the Zagros Mountains the MFF marks a pronounced topo-graphic step separating folds with high amplitudes narrowwavelengths and higher topography in the High Folded Zonefrom folds with relatively low amplitudes long wavelengthsand lower topography in the Foothill Zone (Fig 2) The MFFis characterized by numerous active anticlines atop of faultstrands emerging from a basement fault It was suggestedthat the onset of the MFF activity in the NW Zagros wasabout 5plusmn1 Ma based on low-temperature thermochronology(Koshnaw et al 2017) The timing of this activity is expectedto differ along-strike of the belt and hence the initiation ofuplift of the anticlines on the hanging wall of the MFF is thekey to understand this temporal and spatial evolution In theneighboring Iranian part the MFF was a relatively long-livedstructure active from 81 to 72 Ma to about the PliocenendashPleistocene boundary After that only the southwesternmostanticline remained active in front of the MFF This was in-ferred from progressive unconformities and magnetostratig-raphy (Hessami et al 2001 2006 Homke et al 2004)

In active orogens the main factor that contributes to build-ing up topography is ongoing convergence (eg Bishop2007 Burbank and Anderson 2012 Whittaker 2012) Re-cent advancements in the availability of high-resolution dig-ital elevation models (DEMs) and geographic informationsystem (GIS) software allows us to quantitatively analyzethe landscape (Bishop 2007 Tarolli 2014) Tectonic geo-morphology approaches and landscape maturity studies havebeen used extensively and proven to be efficient in studyingthe relative tectonic activity of different areas in contractionalsettings (Cheng et al 2012 Mahmood and Gloaguen 2012Ramsey et al 2008 Regard et al 2009) Nevertheless theNW part of the Zagros lacks modern studies on tectonicgeomorphology ndash with few exceptions Bretis et al (2011)detected sets of wind gaps (ie segments of river valleysabandoned due to lateral and vertical fold growth) in theHigh Folded Belt NE of the MFF suggesting that largerfolds grew by linkage of smaller shorter folds Zebari andBurberry (2015) performed detailed analyses of various geo-morphic indices for numerous anticlines in the High FoldedZone concluding that the combination of clearly asymmet-ric drainage patterns and the mountain front sinuosity in-dex (Bull 2007 Keller et al 1999) is a valuable tool foridentifying putatively active fault-related folds Obaid andAllen (2017) studied the landscape maturity of various an-ticlines within the Zagros Foothill Zone and constrained theorder of deformation of these anticlines by proposing an out-

of-sequence propagation of underlying faults into the fore-land They proposed that the Zagros Deformation Front wasamong the earliest faults that have been reactivated withinthe Foothill Zone

In an active orogen such as the Zagros a better under-standing of the temporal and spatial distribution of deforma-tion due to ongoing tectonics can be achieved with landscapemodeling In the last 2 decades numerical models have beenextensively used to study landscape evolution (Chen et al2014 Tucker and Hancock 2010) and several software pack-ages were specifically developed for this purpose (eg Han-cock and Willgoose 2002 Hobley et al 2017 Refice et al2012 Salles and Hardiman 2016 Tucker et al 2001) Mostof these models include algorithms for bedrock fluvial inci-sion and hillslope creep as input parameters Several studieshave constrained the landscape evolution with the involve-ment of the corresponding tectonics and structures elsewhere(Collignon et al 2016 Cowie et al 2006 Miller et al 2007Refice et al 2012)

In this study we assessed variations in the landscape ma-turity of three anticlines (from SE to NW the Harir Peratand Akre anticlines) located on the hanging wall of the MFFby quantitatively analyzing landscape indices (hypsometriccurve hypsometric integral surface roughness and surfaceindex) in order to distinguish more mature segments fromless mature ones and to reconstruct the relative variation inuplift time andor rate along these anticlines We then com-puted the difference in the onset of uplift between more ma-ture anticlines and less mature ones using a landscape evolu-tion model The present-day topography of the least matureanticline served as an input model for computing the timethat it takes this anticline to reach the same state as the mostmature one Also three structural cross sections were con-structed across the three anticlines to delineate their struc-tural style and to link it with their landscape maturity

2 Geological setting

The Zagros FoldndashThrust Belt is the result of the collision be-tween the Arabian and Eurasian plates (Fig 1 Berberian1995 Mouthereau et al 2012) Continental collision startedin the Early Miocene following the progressive subduc-tion of Neo-Tethyan oceanic lithosphere underneath Eura-sia (Agard et al 2011 Csontos et al 2012 Koshnaw etal 2017 Mouthereau et al 2012) The Zagros FoldndashThrustBelt extends for about 2000 km from the Strait of Hormuz insouthern Iran to the KRI and further into SE Turkey Sincethe onset of collision the deformation front has propagated250ndash350 km southwestward involving the northeastern mar-gin of the Mesopotamian Foreland Basin and the PersianGulf into a largely NWndashSE-trending foreland foldndashthrust belt(Mouthereau 2011 Mouthereau et al 2007) The shorten-ing across different sectors of the Zagros FoldndashThrust Beltis estimated to range between 10 and 32 (Blanc et al

Solid Earth 10 663ndash682 2019 wwwsolid-earthnet106632019

M Zebari et al Relative timing of uplift along the Zagros Mountain Front Flexure 665

Figure 1 Tectonic subdivision of the NW segment of the Zagros FoldndashThrust Belt (modified after Berberian 1995 Emre et al 2013Koshnaw et al 2017 Zebari and Burberry 2015) Names within the parentheses are known in the Iranian part of Zagros

2003 McQuarrie 2004 Molinaro et al 2005 Mouthereauet al 2007 Vergeacutes et al 2011) GPS-derived horizontal ve-locities between Arabia and Eurasia show present-day con-vergence rates between 19 and 23 mm yrminus1 (McClusky etal 2003) It is suggested that deformation partitioning oc-curs between the external and internal portions of the Iranianpart of the Zagros FoldndashThrust Belt While the internal Za-gros FoldndashThrust Belt currently accommodates 3ndash4 mm yrminus1

of right-lateral displacement along the Main Recent Fault(Fig 1 Reilinger et al 2006 Vernant et al 2004) the ex-ternal part accommodates 7ndash10 mm yrminus1 of shortening bythrusting and folding (Hessami et al 2006 Vernant et al2004) 2ndash4 mm yrminus1 of which is taken up by the MFF in theFars Arc (Oveisi et al 2009) However no such estimatesare available for the Iraqi segment of the Zagros It is hencenot known how much of the total ArabiandashEurasia plate con-vergence is being accommodated across the Iraqi part of theZagros FoldndashThrust Belt

The NW segment of the Zagros FoldndashThrust Belt in theKRI is subdivided into several NW-trending morphotectoniczones These zones from NE to SW are (i) Zagros SutureZone (ii) Imbricated Zone (iii) High Folded Zone and (iv)Foothill Zone (Figs 1 and 2 Jassim and Goff 2006) Thesezones are bounded by major faults in the area The faults in-

clude Main Zagros Fault separating the Zagros Suture Zonefrom the Imbricated Zone High Zagros Fault that separatesthe Imbricated Zone from the High Folded Zone and theMountain Front Flexure that separates the High Folded Zonefrom the Foothill Zone (Figs 1 and 2 Berberian 1995 Jas-sim and Goff 2006)

The deformed sedimentary succession is composed of 8ndash12 km thick Paleozoic to Cenozoic strata that rest on the Pre-cambrian crystalline basement (Aqrawi et al 2010 Jassimand Goff 2006) The thick sedimentary cover consists of var-ious competent and incompetent rock successions separatedby detachment horizons The infra-Cambrian Hormuz saltwhich acts as a basal detachment in much of the southernand central Zagros in Iran pinches out towards the north-west (Hinsch and Bretis 2015 Kent 2010) Other interme-diate detachment horizons influence the structural style ofthe central Zagros in Iran (eg Sepehr et al 2006 Sherkatiet al 2006) but their behavior is uncertain in NW Zagrosdue to limitations in outcrops and insufficient seismic pro-files southwest of the Main Zagros Fault Some proposeddetachment levels include Ordovician and Silurian shales(Aqrawi et al 2010) TriassicndashJurassic anhydrites (Aqrawi etal 2010 Hinsch and Bretis 2015 Zebari 2013 Zebari andBurberry 2015) and Lower Miocene anhydrite (Aqrawi et

wwwsolid-earthnet106632019 Solid Earth 10 663ndash682 2019


Figure 2 Geological map of the Zagros FoldndashThrust Belt in KRI showing the location of the three anticlines Harir Perat and Akre withrespect to the MFF that separates the High Folded Zone from the Foothill Zone (modified after Csontos et al 2012 Sissakian 1997 Zebariand Burberry 2015)

al 2010 Csontos et al 2012 Jassim and Goff 2006 Kent2010 Zebari and Burberry 2015)

The exposed geological units within the High Folded Zoneare limited to ca 5 km thick Upper TriassicndashQuaternarystratigraphic succession (Fig 2 Jassim and Goff 2006 Lawet al 2014) Most anticlines are made up of Cretaceous car-bonate rocks while Upper TriassicndashLower Cretaceous strataare only exposed in the core of some anticlines The Tertiaryclastic rocks are preserved within the adjacent synclinesWithin the studied structures the Upper JurassicndashLower Cre-taceous Chia Gara and Lower Cretaceous Sarmord forma-tions only crop out in Bekhme and Zinta gorges and con-sist of medium to thick bedded marly limestone dolomiticlimestone and shale (Figs 2 and 3) The Lower Cretaceoussuccession of Qamchuqa and Upper Cretaceous Bekhme andAqra formations consist of thick bedded and massive reef

limestone dolomitic limestone and dolomite These unitsare generally rigid and resistant to erosion Thus they buildthe raised cores of anticlines The Upper CretaceousndashTertiarysuccession consists primarily of clastic rocks which aremostly denuded and alternating upper Paleocene and up-per Eocene limestone of Khurmala and Pila Spi formationsrespectively They form a ridge surrounding the anticlines(Figs 2 and 3) Unconsolidated Quaternary sediments in thestudy area consist of slope deposits residual soil alluvial fandeposits and river terraces

There is no agreement concerning the overall structuralstyle of the NW Zagros in KRI Several authors (Al-Qayimet al 2012 Ameen 1991 Fouad 2014 Jassim and Goff2006 Numan 1997) suggested that the Iraqi part of the Za-gros FoldndashThrust Belt reveals a combination of both thin-and thick-skinned deformation Partly relying on reflection



Figure 3 Stratigraphic column of the exposed rock units in thearea Thicknesses are given as in well Bijeel-1 (Fig 2) which islocated 5 km to the south of Perat Anticline (modified after Law etal 2014) The column is scaled to the stratigraphic thicknesses

seismic data it was also suggested that contraction has beenlocalized on inherited passive-margin normal faults in thebasement which were inverted during the late stage of de-formation since ca 5 Ma (Abdulnaby et al 2014 Burberry2015 Koshnaw et al 2017) The structural relief across theMFF (Fig 2) is likely linked to blind thrusts in the basement(Al-Qayim et al 2012 Ameen 1991 1992 Fouad 2014Koshnaw et al 2017 Numan 1997) The same linkage be-tween structural relief and a regional basement blind thrust isalso documented in the Iranian Zagros (Blanc et al 2003Emami et al 2010 Leturmy et al 2010 Sherkati et al2006) Alternatively Hinsch and Bretis (2015) argued thatthe structural relief in the hanging wall of the MFF is related

to an underlying duplex structure that is linked to a steppeddetachment horizon rooting in a lower Paleozoic detachmentin the internal parts of the orogen The relief has been at-tributed to the accumulation of the Hormuz salt in the IranianZagros (McQuarrie 2004) Even though the MFF is believedto be a major blind thrust in the basement (Berberian 1995)it is usually mapped along the southwestern limb of the lasthigh anticline where the Pila Spi limestones or the Bekhmeand Aqra limestones crop out (Fouad 2014 Jassim and Goff2006 Numan 1997) Given that landforms in the vicinity ofthe MFF indicate ongoing tectonic deformation we suspectthat these blind faults might be active at present Unfortu-nately however instrumental seismicity in the entire regionis too diffusely distributed to be attributed to any particularfaults (Jassim and Goff 2006)

Structurally this segment of the Zagros FoldndashThrust Beltis dominated by NWndashSE trending fault-related folds thetrend of folds changes to nearly EndashW to the west of the GreatZab river (aka Greater Zab River Fig 2) The folds areusually S-verging and the related faults emerge to the sur-face within both the Imbricated Zone and High Folded Zonewhile they remain blind within the Foothill Zone (Fouad2014 Hinsch and Bretis 2015)

3 Data and methods

We calculated and analyzed landscape indices from DEMsfor the studied anticlines and built a landscape evolutionmodel that simulates progressive uplift and erosion of thelandscape We also constructed structural cross sectionsacross these anticlines based on literature data and our ownfield observations

31 Geomorphic indices

The present-day relief in the study area resulted from a com-petition between rock uplift triggered by horizontal contrac-tion and erosion destroying it Parameters controlling thesecompeting processes are the rate of tectonic accretion rockerodibility and climate (Bishop 2007 Burbank and Ander-son 2012)

In order to quantitatively analyze the landscape for theHarir Perat and Akre anticlines (Figs 2 and 4) we cal-culated hypsometric curves and determined three geomor-phic indices (i) hypsometric integral (ii) surface roughnessand (iii) surface index These are considered proxies for therelative maturity of a particular landscape The hypsometriccurve and integral refer to the distribution of surface area of alandscape with respect to the elevation (Strahler 1952) Thesurface roughness value is mainly sensitive to incision (An-dreani et al 2014 Andreani and Gloaguen 2016 Pike andWilson 1971) the surface index is a measure for the amountof erosion When referring to the results obtained by using



this set of geomorphic indices we colloquially refer to themas ldquolandscape maturityrdquo parameters

311 Hypsometric curve

The hypsometric curve for a basin is the frequency distri-bution of elevation of the watershed area below a givenheight (Strahler 1952) Convex-shaped hypsometric curvesrepresent relatively youthful stages of the basin S-shapedand concave curves refer to more mature and old stages(Strahler 1952) Hypsometric curves are usually calculatedfor a specific drainage basin In this study we calculated theweighted mean of the hypsometric curves for basins with ar-eas gt 025 km2 within each anticlinal ridge weighted by thebasin area within the anticline We restricted our analyses tothose basins where Upper Cretaceous carbonates are exposed(Fig 4) This allowed us to make realistic comparisons be-tween the three anticlines neglecting the differences in rockerodibility that arise when varying lithologies are includedWind gaps and water gaps as well as the plunging crests ofthe anticlines were also excluded from the calculation

312 Hypsometric integral

The hypsometric integral (HI) is the ratio of area under thehypsometric curve (Strahler 1952) It is used to highlight theerosional stage of a landscape with high values correspond-ing to less mature landscapes and low values indicating ad-vanced stages of erosion The hypsometric integral is com-puted for a certain area by the following equation (Pike andWilson 1971)

HI=hmeanminushmin

hmaxminushmin (1)

where hmean hmin and hmax are the mean minimum andmaximum elevations (m) of the examined area

313 Surface roughness

The surface roughness (SR) measures how much an areadeviates from being totally flat It differentiates flat planarsurfaces with values close to 1 from irregular surfaces withhigher values It increases with the increase in incision bystreams The surface roughness is calculated using the fol-lowing equation (Grohmann 2004 Hobson 1972)

SR=TSFS

(2)

where TS and FS are the areas (m2) of the actual topographicsurface and the corresponding projection of that surface ontoa planar surface respectively

314 Surface index

The surface index (SI Andreani et al 2014) combines ele-vations hypsometric integral and surface roughness to map

simultaneously preserved and eroded portions of an ele-vated landscape It is calculated using Eq (3) (Andreani andGloaguen 2016)

SI= (NHI middotNh)minusNSR (3)

where NHI Nh and NSR are the normalized hypsometric in-tegral elevations and surface roughness values respectivelyElevated and poorly incised landscapes with high hypsomet-ric integral and low surface roughness show positive surfaceindex values Highly dissected landscapes with a high surfaceroughness yield negative surface index values This meansthat the surface index is also sensitive to elevation

32 Digital elevation models

The geomorphic indices for this study were calculated fromthe 12 m resolution TanDEM-X DEM (Krieger et al 2007)obtained from the German Aerospace Center (DLR) and the30 m resolution SRTM1 (Shuttle Radar Topography Mis-sion Global 1 arc second Data) DEM (NASA JPL 2013)these two inputs were used since different DEM inputs giveslightly different geomorphic results (Andreani et al 2014Koukouvelas et al 2018 Obaid and Allen 2017) Geomor-phic indices were calculated using both the TanDEM-X andthe SRTM1 data However the TanDEM-X data revealed nu-merous artifacts and voids which made calculations unstableand results unreliable (also see the comparison in the Supple-ment) All results of the geomorphic indices and subsequentcalculations presented in the following sections were calcu-lated from a 100times 100 cell (3kmtimes 3 km) moving windowon the 30 m resolution SRTM1 data A larger moving win-dow makes the obtained measurements smoother and viceversa The size of the moving window must be chosen basedon the scale of the target here we targeted anticlines withwavelengths varying from 5 to 8 km A 3 km moving windowcovered almost an entire limb of an anticline We also testedthe method proposed by Peacuterez-Pentildea et al (2009) in order toaccount for the neighboring cells in the calculation of the ge-omorphic indices Rather than using a moving window thisapproach uses a spatial autocorrelation of neighboring cellsand maps clusters of high and low values of indices usingMoranrsquos I statistic (Moran 1950) and Gilowast statistics (Ord andGetis 1995) We have tested the same method here by cal-culating the HI for a 500mtimes 500 m grid of the SRTM dataWe applied a hot spot analysis using Gilowast statistics with a dis-tance of 15 km to define neighbor cells Then we resampledthe HI map calculated from a 100times 100 cell (3kmtimes 3 km)moving window to 500mtimes500 m grid from SRTM data Thecalculations were performed using the focal and zonal toolsets in ESRI ArcGIS 104 software In addition the SRTMDEMs with 30 m resolution were used to extract topographicprofiles drainage networks watersheds stream slopes andupstream drainage areas wherever required



Figure 4 Topography and slope maps of the studied anticlines obtained from 30 m resolution SRTM1 DEM data showing the location ofwater and wind gaps across these anticlines

33 Modeling landscape evolution

We built a landscape evolution model to quantify the timedifference in between the maturity level of the more matureand less mature anticlines by comparing the geomorphic in-dices of the evolved landscape with those of both anticlinesbased upon the open-source Landlab toolkit (Hobley et al2017 httplandlabgithubio last access 13 March 2019)

We used two components in our model one simulatingerosion due to fluvial action and another simulating sedi-ment transport along slopes due to hillslope diffusion pro-cesses Chen et al (2014) showed that consideration of onlythese two components is sufficient for many landscapes butcannot model fluvial sedimentation However from field ob-servations and from satellite imagery we know that no sig-nificant fluvial sedimentation takes place on the slopes ofthe analyzed anticlines On slopes of anticline flanks thedetachment-limited erosion due to the fluvial system tends tobe the dominant process (Howard 1994) To detect changesin the landscape due to fluvial erosion through time we ap-plied the commonly accepted idea that the rate of stream inci-sion is directly proportional to the hydraulic shear stress of astream (Braun and Willett 2013) Consequently we used thestream power incision law (Sklar and Dietrich 1998 Whip-ple and Tucker 1999)

partz

partt=KAmSn (4)

where partzpartt is the erosion rate (m yrminus1) K is an erodibilitycoefficient (yrminus1 m(1minus2 m)) that encompasses the influence of

climate lithology and sediment transport processes A is theupstream drainage area (m2) and is typically taken as a proxyfor discharge (Wobus et al 2006) S = partzpartx is the localchannel slope (m mminus1) z is the elevation (m) and m and n

are the area and slope exponents respectively The streampower incision law (Eq 4) is derived since the upstreamdrainage area A scales with channel discharge and channelwidth The magnitude of the sediment flux in the channel isassumed to equal unity in the standard detachment-limitedstream power model (Perron 2017 Whipple 2002) In themodel an incision threshold (C) was included below whichno incision occurs (Hobley et al 2017)

To account for the provision of sediment due to hillslopediffusion processes from slopes outside the river system weused the hillslope diffusion equation (Culling 1963 Tuckerand Bras 1998)

partz

partt=Kdnabla

2z (5)

where Kd is the diffusivity coefficient (m2 yrminus1) z is the el-evation (m) and nabla2 is the Laplace operator ie the diver-gence of the gradient

Finally the overall evolution of the landscape in differenttime steps was calculated as the uplift rate subtracted by thechanges due to both fluvial erosion and the hillslope diffusion(Temme et al 2017)

partz

partt= U minusKAmSn

minusKdnabla2z (6)

where U is the uplift rate (m yrminus1)



A DEM raster grid of the present-day less mature anticline(Harir) and the surrounding basins (Fig 5a) served as modelinput The advantage of using Harir Anticline was that theevolved drainage network overprinted the pre-existing oneThe boundary conditions were set as closed on all sides ex-cept in pre-existing outlets in the input grid The basins sur-rounding Harir Anticline were also included in the input gridto minimize the effect of the boundary conditions on theHarir Anticline itself In the input raster grid a flow routeof each cell was connected with neighboring cells both di-agonally and orthogonally This means that each cell had thepossibility to be linked with eight surrounding cells across itssides and corners (Hobley et al 2017 Tucker et al 2016)

Concerning the parameter used in the model the value ofmn n and K were found following the methodology de-scribed by Harel et al (2016) Mudd et al (2014) and Per-ron and Royden (2013) and by comparison with data fromHarel et al (2016) The value of mn was found by plottingthe elevation against X (elevationndashX plot) for streams in theinput grid (Fig 5a) where X is found following the equationdescribed by Perron and Royden (2013)

X =

xintxb

(A0

A(x)

)mn

dx (7)

where A0 is the reference drainage area (m2) of 166 160 m2

and x is the horizontal upstream distance (m) In this ap-proach we ascribed values for mn range from zero to oneand X was calculated for each time from Eq (7) The value ofmn with maximum regression (R2) value in the elevationndashXplot was taken as the best-fitting value which was 041 in ourcase for the present-day Harir Anticlinersquos drainages (Fig 5b)This value of mn is located within the theoretically pre-dicted values of mn which ranges from 03 to 07 based onthe stream power incision model (Kwang and Parker 2017Temme et al 2017 Whipple and Tucker 1999)

In the model n= 17 and K = 30times10minus6 yrminus1 mminus04 wereused these values were estimated as mean of K and n inHarel et al (2016) for those areas that are comparable withour study area in aspect of lithology climate and precipita-tion The value of m was 07 We used an incision thresholdof C = 10times 10minus5 m yrminus1 which is widely adopted for ero-sion of an upland landscape (Hobley et al 2017) A present-day annual mean precipitation of ca 07 m yrminus1 was usedthrough the time due to the lack of nearby paleoclimate datawith good quality The average of the modeled precipita-tion anomaly data for Lake Van in SE Turkey (200 km tothe NNW of the studied anticlines) is close to zero (Stock-hecke et al 2016 Supplement) The current elevation ofthe Bekhme and Aqra formations in the crest of Harir An-ticline is about 1500 m asl Above that 2070 m of UpperCretaceousndashMiocene units (Law et al 2014) and 300 m ofupper Miocene Lower Bakhtiari were exhumed before expo-sure of the Bekhme and Aqra formations If we consider that

the Lower Bakhtiari have been deposited close to sea levelbefore onset of the MFF ca 5 Ma there would be 3872 m ofrock uplift at a rate of sim 00007 m yrminus1 which was used inthe model This rate of vertical uplift is reasonable for thearea and it matches with the vertical uplift in Kurdistan thathas been presented by Tozer et al (2019) Since soil (re-golith) is rare and very thin when present on the slopes alow diffusivity coefficient of Kd = 0001 m2 yrminus1 was used(Fernandes and Dietrich 1997)

There are minor variations in lithology between the threeanticlines (they consist of a thick pile of dominantly Creta-ceous carbonate) and no variation in climate can be expectedon such a relatively local scale Therefore no significant vari-ances are expected in the used parameters Lastly the param-eters were calibrated by comparing the nature of the evolvedlandscape to other anticlines within the High Folded Zonethat are cored by Cretaceous carbonates and more maturethan the Harir Anticline to evaluate how realistic the evolvedlandscape is

4 Results

41 Landscape maturity

The three studied anticlines are composed of the raised Cre-taceous carbonates in their crests whereas the Tertiary clas-tic rocks have been denuded but conserved in the adjacentsynclines The three anticlines are dissected by rivers thatform water gaps across them Bekhme and Zinta gorges cutthe Perat and Akre anticlines respectively We also observedwind gaps such as those in the NW end of Harir Anticline(Zebari and Burberry 2015) Therefore neither the locationof these water and wind gaps nor the plunging tips of anti-clines have been considered in interpreting the geomorphicindices as proxies for relative landscape maturity

The anticlines reach up to ca 1500 m asl The minimumaltitude is ca 700 in the adjacent synclines and ca 400 m inthe Great Zab river (aka Greater Zab River) course Thehypsometric curves for the three anticlines are presented inFig 6 Harir Anticlinersquos curve is more convex and its shapeis close to the youthful stage of Strahlerrsquos diagram (Ohmori1993 Strahler 1952) with 78 of the area above the meanelevation while Akre Anticline is less convex and close toa mature stage with only 50 of the area above the meanelevation Perat Anticlinersquos values are located in between andcloser to the Harir Anticline curve with 64 of its area abovethe mean elevation

The three calculated geomorphic indices (HI SR and SI)seem to be substantially influenced by the local structure andwind and water gaps (Fig 7) Hypsometric integral valuesvary between 02 and 077 with lower values in the adja-cent synclines and higher values in the crest of the anticlinesThe HI values decrease toward the plunging ends of the an-ticlines and at gorges eg Perat Anticlinersquos HI values are



Figure 5 (a) DEM grid drainage network and basins for the present-day Harir Anticline that is used as an input for the model White linesare basin divides (b) mn plotted against regression values of elevationndashX plot for streams in the Harir Anticline The highest regression isachieved for mn= 041

Figure 6 Present-day hypsometric curves of the studied anticlinesThe curves are calculated as a total weighted mean for drainagebasins within each anticline We only use those parts where UpperCretaceous carbonate rocks crop out and we exclude wind gapswater gaps and the plunging tips of anticlines n is the number ofbasins used in the calculation of the hypsometric curve for eachanticline

minimum at the Great Zab river In general Harir Anticlineshows higher values than the other two anticlines Harir An-ticline has a broad crest and has been incised by narrow val-leys This makes the mean elevation within the moving win-dow in the calculation close to the maximum elevation andthus causes higher values of the hypsometric integral PeratAnticline shows high values of HI on its crest to the west ofBekhme Gorge Among the three anticlines Akre Anticlineshows the lowest values of HI in its central part which isdue to the presence of more incised and wider valleys Ele-vation drops rapidly from the hinge of the anticline toward

the limbs which causes the mean elevation within the win-dow to fall

The surface roughness values range between 1 and 133 inthe area The lowest values of the SR are also present in theadjacent synclines and in the plunging tips of the anticlinesThe highest values are associated with the location of watergaps These are areas where rivers are deeply incised at bothBekhme and Zinta gorges Harir Anticline has lowest surfaceroughness values Perat Anticline shows the highest value ofSR especially in its northern limb Akre Anticline has mod-erate SR values in its central segment and western side wherea wind gap is present

The results of the surface index range between minus004 to070 in the three anticlines studied Few locations show neg-ative values These are associated partly with adjacent syn-clines and with Bekhme Gorge Apart from these locationsthe area shows positive surface indices Harir Anticline ex-hibits higher values on its broad crest Perat Anticline showsmoderate values of SI on its crest to the west and east ofBekhme Gorge For Akre Anticline SI values are lower thanin both Harir and Perat anticlines with highest values on itscrest east of Zinta Gorge These high values of SI highlightthe flat areas with high elevation and high hypsometric in-tegral The surface index values also highlight the Pila Spiand Khurmala limestone ridges encircling the anticlines withvalues close to zero

In our calculation the results of geomorphic indiceschange with changing the size of the moving window andthe resolution of the input data (see the Supplement) Thiswas also detected by Andreani et al (2014) and Obaid andAllen (2017) Andreani et al (2014) found that the DEMresolution does not affect the hypsometric integral but it af-fects the surface roughness while the size of the movingwindow affects both hypsometric integral and surface rough-ness The results become smoother with an increasing size ofthe moving window Here we found that it is reasonable touse a 100times 100 cell (3kmtimes 3 km) moving window whichcovers approximately one limb of the anticline with 6ndash7 kmwidth It therefore highlights the desirable signal The clus-ter map for the HI Gilowast statistics was calculated following the



Figure 7 Surface index maps for the three anticlines calculated from 100times 100 cell (3kmtimes 3 km) and moving windows (a) hypsometricintegral (b) surface roughness and (c) surface index

approach by Peacuterez-Pentildea et al (2009) for the 500mtimes 500 mgrid We obtained results similar to the HI map calculatedfrom a 100times100 cell (3kmtimes3 km) moving window and re-sampled to 500mtimes 500 m grid in terms of highlighting thecluster of high and low HI values (Fig S19a and b in the Sup-plement) This comparison proves that our method is equallyapplicable and valid We therefore ran all analyses based onthe 100times 100 cell moving window as described above

According to the hypsometric curves and the geomorphicindices we found that there is a measurable difference inlandscape maturity between the three anticlines We clas-sified our anticlines as relatively mature (Akre Anticline)moderately mature (Perat Anticline) and less mature (HarirAnticline) The difference in the maturity level must be dueto a difference in one or more of the factors tectonics cli-mate or rock erodibility No variation in the climate is ex-



pected for the scale of the studied area therefore its impacton the landscape maturity can be neglected The three anti-clines show essentially the same lithology (Figs 2 and 3)ie similar lateral rock type and erodibility Thus the onlyfactors that may vary along the anticlines are uplift rate oronset time of the uplift This can be interpreted with one ofthe following scenarios either the anticlines started to up-lift in the order (1) Akre (2) Perat and (3) Harir from westto east or all of them started at the same time but with dif-ferent rates In the latter case the uplift rate would have beenhighest at Akre and lowest at Harir exposing Akre to erosionearlier than Harir

42 Landscape evolution model

The aged landscape from the model run (Figs 8 and 9) isthe result of fluvial erosion and hillslope diffusion on the onehand and uplift due to folding on the other hand In the land-scape modeling various simulations with different parame-ters and time spans were performed (Figs S24ndashS27) HarirAnticline was used as an input model and the landscape evo-lution model was run for a time span of 10 up to 100 kyrand then it was run for a time span of 20 kyr The evolvingdrainage system overprints the pre-existing one in the inputand gradually becomes more deeply incised from the anti-cline flanks carving toward its core (Fig 8) Harir Anticlineis a box-shaped anticline with a wide and flat crest area Withongoing incision towards the core of the anticline this plaincrest narrowed gradually and finally became a sharp ridgethat divided the drainage basins of the SW flank from thoseof the NE

We compared the hypsometric curves of the model out-puts to the present-day curves of the anticlines The hypso-metric curves were calculated first as total weighted meanfor basins within the anticline and later calculated for theentire anticlinal ridges (Fig 9) Statistically (with minimumRMS) the hypsometric curve of Harir Anticline was clos-est to the present-day Perat Anticline after 100 and 80 kyr oferosion when using total weighted mean and entire anticli-nal ridge respectively in the calculation of the hypsometriccurves The output curve after 160 and 200 kyr matched bestwith present-day Akre Anticline when using total weightedmean and entire anticlinal ridge respectively in the calcu-lation of the hypsometric curves We conclude that it willtake Harir Anticline roughly 80ndash100 kyr to reach the matu-rity level of Perat Anticline and about 160ndash200 kyr to reachthe level of Akre Anticline based on our model and compar-ison of the hypsometric curves if the uplift rates of the threeanticlines were the same The other possibility is that the an-ticlines started to grow at the same time but with different up-lift rates In this case it is not possible to find the differencein uplift rates via our landscape modeling Since the factorsthat control geomorphology (lithology structural setting andclimate) were similar for all three anticlines and under theassumption of constant growth and erosional conditions we

infer that uplift of Akre and Perat anticlines started respec-tively 160ndash200 and 80ndash100 kyr before Harir started to growif their uplift rates were the same

43 Geometry of the studied anticlines

The structural cross sections for the three anticlines (Fig 10)constructed from field data and literature (Syan 2014) showthat the anticlines are box-shaped with broad crests They areasymmetrical verging toward the SW with a nearly vertical oroverturned forelimb The three anticlines are thrust-relatedin accordance with published studies of the area (Csontos etal 2012) and have a thrust in their forelimb Perat Anti-cline additionally exhibits a back thrust in its NE limb Theshortening across the three anticlines was calculated usingline-length balancing We found 26 28 and 29 short-ening for Harir Perat and Akre anticlines respectively andconclude that there is no significant variation A differencein the fold amplitude between the three anticlines can be dis-cerned in the cross sections The amplitude of Perat Anticlineis higher than that of both Harir and Akre anticlines Anotherdifference concerns the thickness of the Upper Cretaceousndashmiddle Eocene clastic succession which dwindles towardthe Akre Anticline The whole Miocene succession how-ever is the thickest in the Akre Anticline Both the UpperCretaceousndashMiddle Eocene and Miocene successions con-sist of highly erodible clastic rocks and the thicker Miocenesuccession in the Akre Anticline counterbalances the thinnerUpper Cretaceousndashmiddle Eocene succession Therefore itis not expected that these variations in the structural geom-etry and stratigraphic thickness have a great impact on thevariation in the landscape maturity in the three anticlines andthe landscape model

5 Discussion

51 Landscape maturity and modeling

Any relative change in the base level induced by tectonics orclimate leads to a change of erosion rates A relict landscapesurvives when its uplift is not completely counterbalanced byerosion (Andreani and Gloaguen 2016 Burbank and Ander-son 2012 Peacuterez-Pentildea et al 2015) The relative relict land-scape and its distribution on these three anticlines atop theMFF reveal clues about underlying tectonics since there isno significant variation in climate and lithology

Within the three studied anticlines the geomorphic in-dices effectively highlighted their incision The surface in-dex which combines both hypsometric integral and surfaceroughness sets apart relict landscapes of positive and highvalues from transient landscapes of negative values that arepreferentially incised (Andreani et al 2014) There is a no-table relative deviation in areas where anticlines are crossedby rivers eg Bekhme and Zinta gorges which show highsurface roughness Also variations in surface index are found



Figure 8 The input landscape (a) which is the present-day Harir topography and the evolved landscape through time (b) 80 (c) 100(d) 160 (e) 180 (f) 200 (g) 220 and (h) 240 kyr

Figure 9 Hypsometric curves of the studied anticlines and those of the evolved Harir landscape from the model for different time spans(a) The curves were calculated using the total weighted mean for drainage basin within each anticline indicating that the evolved landscapesafter 100 and 160 kyr are the closest ones to the present-day Perat and Akre anticlines respectively n is the number of basins used inthe calculation of the hypsometric curve for each time (b) the curves were calculated for the entire anticline indicating that the evolvedlandscapes after 80 and 200 kyr are the closest ones to the present-day Perat and Akre anticlines respectively



Figure 10 Structural cross sections across the three studied anticlines (a) Harir section (modified after Syan 2014) (b) Perat sectionconstructed from field data and thrusts inferred from a seismic line by Csontos et al (2012) and (c) Akre section constructed from field data(see Figs 2 and 4 for the locations) In Akre and Perat anticlines the data were collected along gorges and the topographic profile across theanticline along an adjacent transect to the gorges are delineated by a dotted line The shortening percentage since Late Miocene is shown oneach cross section

in comparable areas in the three anticlines Focussing on thecrest of the anticlines we observe that the Harir Anticlineshows higher values than the two others The lowest valuesare found in Akre Anticline Harir has low incision at ele-vated surfaces while Akre has a more incised uneven land-scape because erosion has worked deeper into the core of theanticline This can also be inferred from the valley shapesWe observe tight V-shape valleys in the flanks of Harir andopen V-shape valleys in Akre (Fig 11a and b) We relate thisdifference to the tectonic uplift and to the effects of longererosion acting on Akre The observation can be interpretedwith one of the following two premises either the anticlinesstarted to uplift successively (first Akre then Perat and fi-nally Harir) or all of them started at the same time but withdifferent uplift and exhumation rates (Akre the fastest Harirthe slowest) In other words the Cretaceous carbonates inHarir Anticline were exposed to the erosion later than in AkreAnticline and consequently incised less

The current landscape of these anticlines exposes Creta-ceous carbonates of the Qamchuqa Bekhme and Aqra for-mations which became exposed to erosion only after unroof-ing of the entire PalaeogenendashNeogene succession The upperMiocenendashPliocene Bakhtiari Group which is the youngeststratigraphic unit in the area is affected by folding asobserved from growth strata (Csontos et al 2012) Thishas also been observed in the upper Bakhtiari (Pliocenendash

Pleistocene) close to the MFF (Koshnaw et al 2017) In be-tween Bekhme and Aqra and the Upper Bakhtiari formations237 km of the Upper CretaceousndashMiocene clastic rocks in-terbedded with thin units of limestone (Law et al 2014) havebeen exhumed due to successive rock uplift in the crest ofthe studied anticlines triggered by shortening and erosionThey are only preserved in the adjacent synclines The Creta-ceous carbonates themselves have been exposed in the crestsof Akre Perat and Harir anticlines for ca 09 km above thelevel of the other exhumed units Based on the thickness theamount of the exposed Cretaceous carbonate makes ca 28 of the total exhumed and exposed thickness in the crest ofthe anticlines Therefore with both scenarios (different uplifttime or different uplift rate) and with assumption of constant(linear) rock uplift rate through time the Cretaceous carbon-ate in Harir Anticline was exposed to erosion later than in theAkre Anticline (Fig 12a)

The steeper valley flanks in Harir Anticline compared tothose of Akre also support higher uplift rates of the Harir An-ticline Furthermore the relationship between stream slopeand upstream drainage area at any given point of the streamsin the Harir Anticline is positive (Fig 12b) This means thatthe streams have a convex shape and the streamsrsquo segmentswith steeper slopes are still located in the flanks of the an-ticline In the Akre Anticline this relationship is negative(Fig 12b) which means that the streams have a concave



Figure 11 Different shape of valleys in the Harir (a) and Akre anticlines (b) See Figs 2 and 4 for the locations

Figure 12 (a) Diagram showing the exposure time of the Upper Cretaceous carbonates in Akre and Harir Anticlines Two different scenariosare plotted for Harir having a slower uplift rate than Akre or onset of uplift later than Akre (b) Channel slopendashdrainage area plots for streamsin both Akre and Harir Anticlines

shape and the segments with steeper slopes have migratedtoward the core of the anticline This implies that tectonicactivity in the Harir Anticline is younger than in the AkreAnticline in other words the Harir Anticline was exposed toerosion later than the Akre Anticline Therefore the premiseof having Harir Anticline starting its uplift later than AkreAnticline is most likely This is our preferred scenario in themodel for the successive tectonic evolution of the study areapresented below

The geomorphic indices have been widely used to assessthe landscape maturity and subsequently active tectonics(Andreani and Gloaguen 2016 Mahmood and Gloaguen2012 Peacuterez-Pentildea et al 2009) The challenging aspect oflandscape maturity modeling is to obtain an absolute quan-tification of tectonics and the relevant time spans The sameholds true with using a landscape evolution model to estimatethe relative time difference between two landscapes becauseit is difficult to compare two landscapes in terms of maturityby absolute means The results of the landscape modelingapproach yielded a numerically derived estimate on the rela-

tive age difference between the studied anticlines but withoutabsolute growth ages

In the model various parameters and two well-knownlandscape evolution equations for the fluvial erosion and hill-slope diffusion were used but in general it is impossibleto mimic nature perfectly The relative time difference oflandscape evolution of these anticlines was estimated fromthe model assuming that the climate has not changed muchduring the evolution of the landscape since there was notmuch variation in the precipitation based on the modeleddata (Stockhecke et al 2016) and for the sake of simplic-ity admitting that climatic change has a significant impacton the landscape In addition neither rock fall nor karstifi-cation were included in the model for simplicity Field ob-servations suggest that karstification does not have a signifi-cant impact on the landscape Overall the evolved landscapefrom the model seems to be plausible in comparison with theother anticlines that surround Harir Anticline and the land-scape models are more mature with respect to the developedtopography and to the overall drainage patterns



Figure 13 Total weighted mean hypsometric curves for drainagebasin within the studied anticlines as compared to those of theShakrok and Safin anticlines The Harirrsquos curve is more convex thanthose of both Shakrok and Safin n is the number of basins used inthe calculation of the hypsometric curve for each anticline

52 Structural style and regional tectonics

An orogenic bend is depicted in the area where the trend ofstructures changes across the Great Zab river from NWndashSE atthe eastern side of the river to nearly EndashW at its western sideThe course of the Great Zab River is suggested to overlie aNE-trending transversal basement fault with right-lateral dis-placement (Ameen 1992 Burberry 2015 Jassim and Goff2006) evidenced by an offset of the High Folded Zone prop-agation forelandward At the eastern side of the river the de-formation has propagated for about 25 km further than on itswestern side (Figs 1 and 2) The origin of this fault reachesback to the late Proterozoic tectonic history of the ArabianPlate This fault has been reactivated later in subsequent tec-tonic events (Ameen 1992 Aqrawi et al 2010 Burberry2015 Jassim and Goff 2006) This can also be noticed inthe thickness of the sedimentary cover which is thinner tothe west of the Great Zab River (Ameen 1992 Zebari andBurberry 2015) This change in thickness is attributed to aseries of uplift events and erosional or non-depositional gapsduring the Mesozoic (Ameen 1992 Aqrawi et al 2010)Further propagation of the deformation (Mountain Front) inthe eastern side of the Great Zab River may be due to theexistence of a thicker sedimentary cover than on the westernside which in turn may have influenced the foreland-wardpropagation of deformation (Marshak and Wilkerson 1992)The deference in propagation of deformation may also be due

Figure 14 Simplified history of the formation of anticlines duringthe propagation of the deformation front over time in the study areaThe Harir anticline is likely the latest to have formed within theHigh Folded Zone in its SE end It occupies the position of a relaystructure during the linkage of two adjacent but overlapping seg-ments of the deformation front The anticlines were outlined basedon the exposure of Cretaceous carbonates

to the convergence being accommodated differently acrossthe curved foldndashthrust belt (Csontos et al 2012) In the east-ern side of the Great Zab River the convergence is accommo-dated across NWndashSE trending structures through belt-normalslip and right-lateral strikendashslip components while in thewestern side of the river the convergence is accommodatedonly by a belt-normal slip across EndashW trending structures(Csontos et al 2012 Reilinger et al 2006)

Zebari and Burberry (2015) found that anticlines to theeast of the Great Zab River (Harir Shakrok and Safinanticlines) demonstrate pronounced NW-ward propagation



based on their geomorphic criteria and the start point of theNW-ward propagation of the Harir Anticline is close to itsSE end This implies that progressing uplift in the hangingwall of the MFF was not gradually continuing from the AkreAnticline towards the Perat Anticline and further SE-wardto the Harir Anticline The uplift progress is probably ratherpartitioned into segments along the belt In addition otheranticlines to the south (Safin Anticline) and to the south-west (Shakrok Anticline) of Harir Anticline are more ma-ture than Harir Anticline itself based on their hypsometriccurves (Fig 13) and geomorphic indices (Figs S1ndashS18) im-plying that the forelandward propagation of the deformationwas also out of sequence in this part of the High FoldedZone This has also been noted in the Foothill Zone basedon thermochronological dating (Koshnaw et al 2017) andlandscape maturity (Obaid and Allen 2017) Thus the mostplausible scenario is that deformation in the Harir segmentstarted sometime after that in Akre segment (160ndash200 kyraccording to our landscape evolution modeling) Harir An-ticline uplift would also postdate Perat Anticline uplift (80ndash100 kyr) to the west and the onset of Safin and Shakrok an-ticlines to the south and southeast which are not included inthe model (Fig 14) As discussed by Csontos et al (2012)the fold relay corresponds to the change in strain partitioningand rotation of the horizontal stress direction from NEndashSWto NndashS in Late Pliocene (Navabpour et al 2008 Navabpourand Barrier 2012) During the latest stage of the NndashS con-vergence a right-lateral shear and superposed folding alongthe NWndashSE trending anticlines (Csontos et al 2012) can beobserved from the relay of the Shakrok Harir and Perat an-ticlines (Figs 2 and 14) Applying this concept requires acomprehensive paleostress analysis investigation especiallywithin these studied anticlines which is beyond the scope ofthis paper

6 Conclusions

The geomorphic indices used in this study allowed us toquantitatively differentiate between variably degraded land-forms in the frontal Zagros Mountains of NE Iraq This areais characterized by active folding due to ongoing conver-gence between the Eurasian and Arabian plates Three ac-tive thrust-related anticlines that are aligned along-strike ofthe MFF were studied in detail While the Akre Anticlineshows deeply incised valleys indicative of advanced erosionthe Harir and Perat anticlines have relatively smooth surfacesand show younger landscape than Akre We related this dif-ference to the underlying tectonics This can be interpretedwith one of the following concepts either anticlinal growthstarted at different times or all of them started to grow at thesame time but with different surface uplift and exhumationrates

A comparison of the geomorphic index values of themodel output with those of the present-day topography ofAkre and Perat anticlines revealed that it will take Harir Anti-cline about 160ndash200 kyr to reach the maturity level of todayrsquosAkre Anticline and about 80ndash100 kyr to reach the maturitylevel of the Perat Anticline assuming constant uplift ratesalong the three anticlines Due to similarity in the lithologystructural setting and climate along the three anticlines andby assuming constant growth and erosion conditions we in-fer that Akre Anticline started to grow 160ndash200 kyr beforeHarir Anticline The onset of growth of Perat Anticline liesin between that of Harir and Akre anticlines A NW-wardpropagation of Harir Anticline itself implies that the uplifthas been independent within different segments rather thanhaving been continuous from the NW to the SE Our methodof estimating relative age differences in variously degradedanticlines can be applied to many other anticlines along theMFF and could eventually develop into a model of the tem-poral evolution of this fold and thrust belt

Data availability For this study we used the freely availableSRTM1 data TanDEM-X digital elevation models were obtainedfrom the DLR

Supplement The supplement related to this article is availableonline at httpsdoiorg105194se-10-663-2019-supplement

Author contributions MZ and KU designed the study MZ did thefield work the geomorphological analyses and the landscape mod-eling MZ CG PN and KU interpreted the results and wrote thepaper

Competing interests The authors declare that they have no conflictof interest

Acknowledgements The German Academic Exchange Service(DAAD) is acknowledged for providing a scholarship (ResearchGrants ndash Doctoral Programmes in Germany 201617 57214224)to the first author to conduct his PhD research in Germany The au-thors express their gratitude to the German Research Foundation(DFG) project no 393274947 for providing financial research sup-port The German Aerospace Agency (DLR) and Thomas Buschein particular are thanked for providing TanDEM-X digital eleva-tion models We also thank Bernard Delcaillau and two anonymouspeers for their very thorough reviews that helped us to further clarifyand improve numerous aspects of our work

Review statement This paper was edited by Federico Rossetti andreviewed by Bernard Delcaillau and two anonymous referees



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Andreani L and Gloaguen R Geomorphic analysis of transientlandscapes in the Sierra Madre de Chiapas and Maya Moun-tains (northern Central America) Implications for the NorthAmerican-Caribbean-Cocos plate boundary Earth Surf Dynam4 71ndash102 httpsdoiorg105194esurf-4-71-2016 2016

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Bishop P Long-term landscape evolution linking tectonicsand surface processes Earth Surf Proc Land 32 329ndash365httpsdoiorg101002esp1493 2007

Blanc E J-P Allen M B Inger S and Hassani H Structuralstyles in the Zagros Simple Folded Zone Iran J Geol Soc Lon-don 160 401ndash412 httpsdoiorg1011440016-764902-1102003

Braun J and Willett S D A very efficient O(n) implicit and par-allel method to solve the stream power equation governing fluvialincision and landscape evolution Geomorphology 180181170ndash179 httpsdoiorg101016jgeomorph2012100082013

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Burberry C M The effect of basement fault reactivation on theTriassic-Recent Geology of Kurdistan North Iraq J Pet Geol38 37ndash58 httpsdoiorg101111jpg12597 2015

Chen A Darbon J Ocirc and Morel J M Land-scape evolution models A review of their fun-damental equations Geomorphology 219 68ndash86httpsdoiorg101016jgeomorph201404037 2014

Cheng K Y Hung J H Chang H C Tsai H andSung Q C Scale independence of basin hypsometry andsteady state topography Geomorphology 171172 1ndash11httpsdoiorg101016jgeomorph201204022 2012

Collignon M Yamato P Castelltort S and Kaus B J PModeling of wind gap formation and development of sed-imentary basins during fold growth application to the Za-gros Fold Belt Iran Earth Surf Proc Land 41 1521ndash1535httpsdoiorg101002esp3921 2016

Cowie P A Attal M Tucker G E Whittaker A C Nay-lor M Ganas A and Roberts G P Investigating the sur-face process response to fault interaction and linkage usinga numerical modelling approach Basin Res 18 231ndash266httpsdoiorg101111j1365-2117200600298x 2006

Csontos L Sasvaacuteri Aacute Pocsai T Koacutesa L Salae A T and AliA Structural evolution of the northwestern Zagros KurdistanRegion Iraq Implications on oil migration GeoArabia 17 81ndash116 2012

Culling W E H Soil Creep and the Development of HillsideSlopes J Geol 71 127ndash161 1963

Emre Ouml Duman T Y Oumlzalp S Elmacı H Olgun S andSaroglu F Active Fault Map of Turkey with an ExplanatoryText 1 1250000 Scale General Directorate of Mineral Re-search and Exploration Ankara 2013

Emami H Vergeacutes J Nalpas T Gillespie P Sharp I KarpuzR Blanc E P and Goodarzi M G H Structure of the Moun-tain Front Flexure along the Anaran anticline in the Pusht-e KuhArc (NW Zagros Iran) insights from sand box models GeolSoc London 330 155ndash178 httpsdoiorg101144SP33092010

Fernandes N F and Dietrich W E Hillslope evolu-tion by diffusive processes The timescale for equilib-rium adjustments Water Resour Res 33 1307ndash1318httpsdoiorg10102997WR00534 1997

Fouad S F A Western Zagros Fold ndash Thrust Belt Part II TheHigh Folded Zone Iraqi Bull Geol Min 6 53ndash71 2014

Grohmann C H Morphometric analysis in geographicinformation systems Applications of free softwareGRASS and R Comput Geosci 30 1055ndash1067httpsdoiorg101016jcageo200408002 2004

Hancock G R and Willgoose G R The use of a landscape simu-lator in the validation of the Siberia landscape evolution modelTransient landforms Earth Surf Proc Land 27 1321ndash1334httpsdoiorg101002esp414 2002

Harel M A Mudd S M and Attal M Global analy-sis of the stream power law parameters based on world-wide 10Be denudation rates Geomorphology 268 184ndash196httpsdoiorg101016jgeomorph201605035 2016

Hessami K Koyi H A Talbot C J Tabashi H and ShabanianE Progressive unconformities within an evolving foreland fold-thrust belt Zagros Mountains J Geol Soc London 158 969ndash981 httpsdoiorg1011440016-764901-007 2001



Hessami K Nilforoushan F and Talbot C J Activedeformation within the Zagros Mountains deduced fromGPS measurements J Geol Soc London 163 143ndash148httpsdoiorg1011440016-764905-031 2006

Hinsch R and Bretis B A semi-balanced section in the north-western Zagros region Constraining the structural architectureof the Mountain Front Flexure in the Kirkuk Embayment IraqGeoArabia 20 41ndash62 2015

Hobley D E J Adams J M Siddhartha Nudurupati S Hut-ton E W H Gasparini N M Istanbulluoglu E and TuckerG E Creative computing with Landlab An open-source toolkitfor building coupling and exploring two-dimensional numeri-cal models of Earth-surface dynamics Earth Surf Dynam 521ndash46 httpsdoiorg105194esurf-5-21-2017 2017

Hobson R D Surface roughness in topography quantitative ap-proach in Spatial analysis in geomorphology edited by Chor-ley R J Methuen London 225ndash245 1972

Homke S Vergeacutes J Garceacutes M Emami H and KarpuzR Magnetostratigraphy of Miocene-Pliocene Zagros fore-land deposits in the front of the Push-e Kush Arc (LurestanProvince Iran) Earth Planet Sc Lett 225 397ndash410httpsdoiorg101016jepsl200407002 2004

Howard A D A detachment limited model of drainagebasin evolution Water Resour Res 30 2261ndash2285httpsdoiorg10102994WR00757 1994

Jassim S Z and Goff J C Geology of Iraq Dolin Prague andMoravian Museum Brno Czech Rep 341 pp 2006

Keller E A Gurrola L and Tierney T E Geomorphic criteria todetermine direction of lateral propagation of reverse faulting andfolding Geology 27 515ndash518 1999

Kent W N Structures of the Kirkuk Embayment northern IraqForeland structures or Structures of the Kirkuk Embaymentnorthern Iraq Foreland structures or Zagros Fold Belt struc-tures GeoArabia 15 147ndash157 2010

Koshnaw R I Horton B K Stockli D F Barber D E Tamar-Agha M Y and Kendall J J Neogene shortening and exhuma-tion of the Zagros fold-thrust belt and foreland basin in the Kur-distan region of northern Iraq Tectonophysics 694 332ndash355httpsdoiorg101016jtecto201611016 2017

Koukouvelas I K Zygouri V Nikolakopoulos K and VerroiosS Treatise on the tectonic geomorphology of active faults Thesignificance of using a universal digital elevation model J StructGeol 116 241ndash252 httpsdoiorg101016jjsg2018060072018

Krieger G Moreira A Fiedler H Hajnsek I WernerM Younis M and Zink M TanDEM-X A satel-lite formation for high-resolution SAR interferometryIEEE Trans Geosci Remote Sens 45 3317ndash3341httpshttpsdoiorg101109TGRS2007900693 2007

Kwang J S and Parker G Landscape evolution models us-ing the stream power incision model show unrealistic behav-ior when mn equals 05 Earth Surf Dynam 5 807ndash820httpsdoiorg105194esurf-5-807-2017 2017

Law A Munn D Symms A Wilson D Hattingh S BobleckiR Al Marei K Chernik P Parry D and Ho J CompetentPersonrsquos Report on Certain Petroleum Interests of Gulf Key-stone Petroleum and its Subsidiaries in Kurdistan Iraq ERCEquipoise Ltd Croydon httpswwwgulfkeystonecommedia

79962gkp_cpr-report-2014pdf (last access 14 May 2019)2014

Leturmy P Molinaro M and de Lamotte D F Structure timingand morphological signature of hidden reverse basement faultsin the Fars Arc of the Zagros (Iran) Geol Soc London 330121ndash138 httpsdoiorg101144SP3307 2010

Mahmood S A and Gloaguen R Appraisal of active tec-tonics in Hindu Kush Insights from DEM derived geomor-phic indices and drainage analysis Geosci Front 3 407ndash428httpsdoiorg101016jgsf201112002 2012

Marshak S and Wilkerson M S Effect of overburden thicknesson thrust belt geometry and development Tectonics 11 560ndash566 httpsdoiorg10102992TC00175 1992

McClusky S Reilinger R Mahmoud S Ben Sari D and TealebA GPS constraints on Africa (Nubia) and Arabia plate motionsGeophys J Int 155 126ndash138 httpsdoiorg101046j1365-246X200302023x 2003

McQuarrie N Crustal scale geometry of the Zagrosfold-thrust belt Iran J Struct Geol 26 519ndash535httpsdoiorg101016jjsg200308009 2004

Miller S R Slingerland R L and Kirby E Char-acteristics of steady state fluvial topography abovefault-bend folds J Geophys Res-Earth 112 1ndash21httpsdoiorg1010292007JF000772 2007

Molinaro M Leturmy P Guezou J C Frizon de Lam-otte D and Eshraghi S A The structure and kinemat-ics of the southeastern Zagros fold-thrust belt Iran Fromthin-skinned to thick-skinned tectonics Tectonics 24 1ndash19httpsdoiorg1010292004TC001633 2005

Moran P P Notes on continuous stochastic phenomenaBiometrika 37 17ndash23 httpsdoiorg101093biomet371-217 1950

Mouthereau F Timing of uplift in the Zagros beltIranianplateau and accommodation of late Cenozoic Arabia-Eurasia convergence Geol Mag 148 726ndash738httpsdoiorg101017S0016756811000306 2011

Mouthereau F Tensi J Bellahsen N Lacombe O DeBoisgrollier T and Kargar S Tertiary sequence of de-formation in a thin-skinnedthick-skinned collision belt TheZagros Folded Belt (Fars Iran) Tectonics 26 TC5006httpsdoiorg1010292007TC002098 2007

Mouthereau F Lacombe O and Vergeacutes J Building the Zagroscollisional orogen Timing strain distribution and the dynamicsof ArabiaEurasia plate convergence Tectonophysics 532 27ndash60 httpsdoiorg101016jtecto201201022 2012

Mudd S M Attal M Milodowski D T Grieve S W Dand Valters D A A statistical framework to quantify spa-tial variation in channel gradients using the integral method ofchannel profile analysis J Geophys Res-Earth 119 138ndash152httpsdoiorg1010022013JF002981 2014

NASA JPL NASA Shuttle Radar Topography Mission Global1 arc second NASA EOSDIS Land Processes DAAChttpsdoiorg105067MEaSUREsSRTMSRTMGL10032013

Navabpour P and Barrier E Stress states in the Zagrosfold-and-thrust belt from passive margin to collisional tec-tonic setting in Crustal Stresses Fractures and FaultZones The Legacy of Jacques Angelier edited by Gud-



mundsson A and Bergerat F Tectonophysics 581 76ndash83httpsdoiorg101016jtecto201201011 2012

Navabpour P Angelier J and Barrier E Stress state reconstruc-tion of oblique collision and evolution of deformation partition-ing in W-Zagros (Iran Kermanshah) Geophys J Int 175 755ndash782 2008

Numan N M S A plate tectonic scenario for the phanerozoic suc-cession in Iraq J Geol Soc Iraq 30 85ndash110 1997

Obaid A K and Allen M B Landscape maturity foldgrowth sequence and structural style in the Kirkuk Embay-ment of the Zagros northern Iraq Tectonophysics 717 27ndash40httpsdoiorg101016jtecto201707006 2017

Ohmori H Changes in the hypsometric curve through moun-tain building resulting from concurrent tectonics and denuda-tion Geomorphology 8 263ndash277 httpsdoiorg1010160169-555X(93)90023-U 1993

Ord J K and Getis A Local Spatial Autocorrelation StatisticsDistributional Issues and Application Geogr Anal 27 286ndash306 httpsdoiorg101111j1538-46321995tb00912x 1995

Oveisi B Laveacute J Van Der Beek P Carcaillet J Benedetti Land Aubourg C Thick- and thin-skinned deformation rates inthe central Zagros simple folded zone (Iran) indicated by dis-placement of geomorphic surfaces Geophys J Int 176 627ndash654 httpsdoiorg101111j1365-246X200804002x 2009

Peacuterez-Pentildea J V Azantildeoacuten J M Booth-Rea G Azor A and Del-gado J Differentiating geology and tectonics using a spatial au-tocorrelation technique for the hypsometric integral J GeophysRes 114 F02018 httpsdoiorg1010292008JF001092 2009

Peacuterez-Pentildea J V Azantildeoacuten J M Azor A Booth-Rea G GalveJ P Roldaacuten F J Mancilla F Giaconia F Morales J andAl-Awabdeh M Quaternary landscape evolution driven by slab-pull mechanisms in the Granada Basin (Central Betics) Tectono-physics 663 5ndash18 httpsdoiorg101016jtecto2015070352015

Perron J T Climate and the Pace of Erosional Land-scape Evolution Annu Rev Earth Planet Sc 45 561ndash591httpsdoiorg101146annurev-earth-060614-105405 2017

Perron J T and Royden L An integral approach to bedrockriver profile analysis Earth Surf Proc Land 38 570ndash576httpsdoiorg101002esp3302 2013

Pike R J and Wilson S E Elevation-relief ratio hypsometricintegral and geomorphic area-altitude analysis Bull Geol SocAm 82 1079ndash1084 1971

Ramsey L A Walker R T and Jackson J Fold evolution anddrainage development in the Zagros mountains of Fars provinceSE Iran Basin Res 20 23ndash48 httpsdoiorg101111j1365-2117200700342x 2008

Refice A Giachetta E and Capolongo D SIGNUM A Mat-lab TIN-based landscape evolution model Comput Geosci 45293ndash303 httpsdoiorg101016jcageo201111013 2012

Regard V Lagnous R Espurt N Darrozes J Baby P Rod-daz M Calderon Y and Hermoza W Geomorphic evidencefor recent uplift of the Fitzcarrald Arch (Peru) A response tothe Nazca Ridge subduction Geomorphology 107 107ndash117httpsdoiorg101016jgeomorph200812003 2009

Reilinger R McClusky S Vernant P Lawrence S ErgintavS Cakmak R Ozener H Kadirov F Guliev I StepanyanR Nadariya M Hahubia G Mahmoud S Sakr K ArRa-jehi A Paradissis D Al-Aydrus A Prilepin M Guseva T

Evren E Dmitrotsa A Filikov S V Gomez F Al-GhazziR and Karam G GPS constraints on continental deformationin the Africa-Arabia-Eurasia continental collision zone and im-plications for the dynamics of plate interactions J GeophysRes-Sol Ea 111 1ndash26 httpsdoiorg1010292005JB0040512006

Salles T and Hardiman L Badlands An open-source flexibleand parallel framework to study landscape dynamics ComputGeosci 91 77ndash89 httpsdoiorg101016jcageo2016030112016

Sepehr M Cosgrove J and Moieni M The impact ofcover rock rheology on the style of folding in the Za-gros fold-thrust belt Tectonophysics 427 265ndash281httpsdoiorg101016jtecto200605021 2006

Sherkati S Letouzey J and De Lamotte D F Central Za-gros fold-thrust belt (Iran) New insights from seismic datafield observation and sandbox modeling Tectonics 25 1ndash27httpsdoiorg1010292004TC001766 2006

Sissakian V K Geological Map of Arbeel and Mahabad Quadran-gles Sheets NJ-38- 14 and NJ-38-15 Scale 1 250000 1997

Sklar L and Dietrich W E River Longitudinal Profilesand Bedrock Incision Models Stream Power and the In-fluence of Sediment Supply in Rivers Over Rock Flu-vial Processes in Bedrock Channels edited by Tinkler KJ and Wohl E E American Geophysical Union 237ndash260httpsdoiorg101029GM107p0237 1998

Stockhecke M Timmermann A Kipfer R Haug G KwiecienO Friedrich T Menviel L Litt T Pickarski N and Ansel-metti F S Millennial to orbital-scale variations of drought in-tensity in the eastern Mediterranean Quaternary Sci Rev 13377ndash95 httpsdoiorg101016jquascirev201512016 2016

Strahler A Hypsometric (Area-Altitude) Anal-ysis of Erosional Topography GSA Bull63 1117ndash1142 httpsdoiorg1011300016-7606(1952)63[1117HAAOET]20CO2 1952

Syan S H A Tectonic Criteria from Shortening Estimation indifferent geological time and space using Balancing Cross Sec-tions in the Harir and Khatibian Anticlines Zagros Fold-ThrustBelt Kurdistan of Iraq MSc Thesis Salahaddin University-Erbil 2014

Tarolli P High-resolution topography for understanding Earth sur-face processes Opportunities and challenges Geomorphology216 295ndash312 httpsdoiorg101016jgeomorph2014030082014

Temme A J A M Armitage J Attal M van Gorp WCoulthard T J and Schoorl J M Developing choosing andusing landscape evolution models to inform field-based land-scape reconstruction studies Earth Surf Proc Land 42 2167ndash2183 httpsdoiorg101002esp4162 2017

Tozer R Hertle M Petersen H I and Zinck-Joergensen KQuantifying vertical movements in fold and thrust belts subsi-dence uplift and erosion in Kurdistan Northern Iraq Geol SocLondon 490 httpsdoiorg101144SP490-2019-118 2019

Tucker G E and Bras R L Hillslope processes drainage densityand landscape morphology Water Resour Res 34 2751ndash2764httpsdoiorg10102998WR01474 1998

Tucker G E and Hancock G R Modelling land-scape evolution Earth Surf Proc Land 35 28ndash50httpsdoiorg101002esp1952 2010



Tucker G Lancaster S Gasparini N and Bras R The channelhillslope integrated landscape development model (CHILD) inLandscape erosion and evolution modeling edited by HarmonR S and Doe III W W Kluwer AcademicPlenum PublishersNew York USA 349ndash388 2001

Tucker G E Hobley D E J Hutton E Gasparini N M Is-tanbulluoglu E Adams J M and Siddartha Nudurupati SCellLab-CTS 2015 Continuous-time stochastic cellular automa-ton modeling using Landlab Geosci Model Dev 9 823ndash839httpshttpsdoiorg105194gmd-9-823-2016 2016

Vergeacutes J Saura E Casciello E Fernagravendez M VillasentildeorA Jimeacutenez-Munt I and Garciacutea-Castellanos D Crustal-scalecross-sections across the NW Zagros belt Implications forthe Arabian margin reconstruction Geol Mag 148 739ndash761httpsdoiorg101017S0016756811000331 2011

Vernant P Nilforoushan F Hatzfeld D Abbassi M R VignyC Masson F Nankali H Martinod J Ashtiani A Bayer RTavakoli F and Cheacutery J Present-day crustal deformation andplate kinematics in the Middle East constrained by GPS measure-ments in Iran and northern Oman Geophys J Int 157 381ndash398httpsdoiorg101111j1365246X200402222x 2004

Whipple K X Implications of sediment-flux-dependent river in-cision models for landscape evolution J Geophys Res 1072039 httpsdoiorg1010292000JB000044 2002

Whipple K X and Tucker G E Dynamics of the stream-power river incision model Implications for height limitsof mountain ranges landscape response timescales and re-search needs J Geophys Res-Sol Ea 104 17661ndash17674httpsdoiorg1010291999JB900120 1999

Whittaker A C How do landscapes record tectonics and climateLithosphere 4 160ndash164 httpsdoiorg101130RFL00312012

Wobus C Whipple K X Kirby E Snyder N Johnson J Spy-ropolou K Crosby B and Sheehan D Tectonics from topog-raphy procedurses promise and pitfalls Geol Soc Am SpecPap 398 55ndash74 httpsdoiorg10113020062398(04) 2006

Zebari M Geometry and Evolution of Fold Structures within theHigh Folded Zone Zagros Fold-Thrust Belt Kurdistan Region-Iraq University of Nebraska-Lincoln 91 pp 2013

Zebari M M and Burberry C M 4-D evolution of anticlines andimplications for hydrocarbon exploration within the Zagros Fold-Thrust Belt Kurdistan Region Iraq GeoArabia 20 161ndash1882015


Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve

Hypsometric integral

Surface roughness

Surface index

Digital elevation models

Modeling landscape evolution

Results

Landscape maturity

Landscape evolution model

Geometry of the studied anticlines

Discussion

Landscape maturity and modeling

Structural style and regional tectonics

Conclusions

Data availability

Supplement

Author contributions

Competing interests

Acknowledgements

Review statement

References


ations have not been sufficiently studied It is not well knownwhich structures are currently the most active ones either

One of the morphologically most conspicuous structuralelements of the Zagros FoldndashThrust Belt is the MountainFront Flexure (MFF) which separates the High Folded Zoneand the Foothill Zone (known in Iran as the Zagros SimplyFolded Belt and Zagros Foredeep respectively Figs 1 and 2Berberian 1995 Jassim and Goff 2006 McQuarrie 2004Mouthereau et al 2012 Vergeacutes et al 2011) In most partsof the Zagros Mountains the MFF marks a pronounced topo-graphic step separating folds with high amplitudes narrowwavelengths and higher topography in the High Folded Zonefrom folds with relatively low amplitudes long wavelengthsand lower topography in the Foothill Zone (Fig 2) The MFFis characterized by numerous active anticlines atop of faultstrands emerging from a basement fault It was suggestedthat the onset of the MFF activity in the NW Zagros wasabout 5plusmn1 Ma based on low-temperature thermochronology(Koshnaw et al 2017) The timing of this activity is expectedto differ along-strike of the belt and hence the initiation ofuplift of the anticlines on the hanging wall of the MFF is thekey to understand this temporal and spatial evolution In theneighboring Iranian part the MFF was a relatively long-livedstructure active from 81 to 72 Ma to about the PliocenendashPleistocene boundary After that only the southwesternmostanticline remained active in front of the MFF This was in-ferred from progressive unconformities and magnetostratig-raphy (Hessami et al 2001 2006 Homke et al 2004)

In active orogens the main factor that contributes to build-ing up topography is ongoing convergence (eg Bishop2007 Burbank and Anderson 2012 Whittaker 2012) Re-cent advancements in the availability of high-resolution dig-ital elevation models (DEMs) and geographic informationsystem (GIS) software allows us to quantitatively analyzethe landscape (Bishop 2007 Tarolli 2014) Tectonic geo-morphology approaches and landscape maturity studies havebeen used extensively and proven to be efficient in studyingthe relative tectonic activity of different areas in contractionalsettings (Cheng et al 2012 Mahmood and Gloaguen 2012Ramsey et al 2008 Regard et al 2009) Nevertheless theNW part of the Zagros lacks modern studies on tectonicgeomorphology ndash with few exceptions Bretis et al (2011)detected sets of wind gaps (ie segments of river valleysabandoned due to lateral and vertical fold growth) in theHigh Folded Belt NE of the MFF suggesting that largerfolds grew by linkage of smaller shorter folds Zebari andBurberry (2015) performed detailed analyses of various geo-morphic indices for numerous anticlines in the High FoldedZone concluding that the combination of clearly asymmet-ric drainage patterns and the mountain front sinuosity in-dex (Bull 2007 Keller et al 1999) is a valuable tool foridentifying putatively active fault-related folds Obaid andAllen (2017) studied the landscape maturity of various an-ticlines within the Zagros Foothill Zone and constrained theorder of deformation of these anticlines by proposing an out-

of-sequence propagation of underlying faults into the fore-land They proposed that the Zagros Deformation Front wasamong the earliest faults that have been reactivated withinthe Foothill Zone

In an active orogen such as the Zagros a better under-standing of the temporal and spatial distribution of deforma-tion due to ongoing tectonics can be achieved with landscapemodeling In the last 2 decades numerical models have beenextensively used to study landscape evolution (Chen et al2014 Tucker and Hancock 2010) and several software pack-ages were specifically developed for this purpose (eg Han-cock and Willgoose 2002 Hobley et al 2017 Refice et al2012 Salles and Hardiman 2016 Tucker et al 2001) Mostof these models include algorithms for bedrock fluvial inci-sion and hillslope creep as input parameters Several studieshave constrained the landscape evolution with the involve-ment of the corresponding tectonics and structures elsewhere(Collignon et al 2016 Cowie et al 2006 Miller et al 2007Refice et al 2012)

In this study we assessed variations in the landscape ma-turity of three anticlines (from SE to NW the Harir Peratand Akre anticlines) located on the hanging wall of the MFFby quantitatively analyzing landscape indices (hypsometriccurve hypsometric integral surface roughness and surfaceindex) in order to distinguish more mature segments fromless mature ones and to reconstruct the relative variation inuplift time andor rate along these anticlines We then com-puted the difference in the onset of uplift between more ma-ture anticlines and less mature ones using a landscape evolu-tion model The present-day topography of the least matureanticline served as an input model for computing the timethat it takes this anticline to reach the same state as the mostmature one Also three structural cross sections were con-structed across the three anticlines to delineate their struc-tural style and to link it with their landscape maturity

2 Geological setting

The Zagros FoldndashThrust Belt is the result of the collision be-tween the Arabian and Eurasian plates (Fig 1 Berberian1995 Mouthereau et al 2012) Continental collision startedin the Early Miocene following the progressive subduc-tion of Neo-Tethyan oceanic lithosphere underneath Eura-sia (Agard et al 2011 Csontos et al 2012 Koshnaw etal 2017 Mouthereau et al 2012) The Zagros FoldndashThrustBelt extends for about 2000 km from the Strait of Hormuz insouthern Iran to the KRI and further into SE Turkey Sincethe onset of collision the deformation front has propagated250ndash350 km southwestward involving the northeastern mar-gin of the Mesopotamian Foreland Basin and the PersianGulf into a largely NWndashSE-trending foreland foldndashthrust belt(Mouthereau 2011 Mouthereau et al 2007) The shorten-ing across different sectors of the Zagros FoldndashThrust Beltis estimated to range between 10 and 32 (Blanc et al






















3 Data and methods












HI=hmeanminushmin

hmaxminushmin (1)




SR=TSFS

(2)


314 Surface index













partz

partt=KAmSn (4)





partz

partt=Kdnabla

2z (5)



partz

partt= U minusKAmSn

minusKdnabla2z (6)






X =

xintxb

(A0

A(x)

)mn

dx (7)






4 Results




























5 Discussion


































6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References





















3 Data and methods












HI=hmeanminushmin

hmaxminushmin (1)




SR=TSFS

(2)


314 Surface index













partz

partt=KAmSn (4)





partz

partt=Kdnabla

2z (5)



partz

partt= U minusKAmSn

minusKdnabla2z (6)






X =

xintxb

(A0

A(x)

)mn

dx (7)






4 Results




























5 Discussion


































6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References







HI=hmeanminushmin

hmaxminushmin (1)




SR=TSFS

(2)


314 Surface index













partz

partt=KAmSn (4)





partz

partt=Kdnabla

2z (5)



partz

partt= U minusKAmSn

minusKdnabla2z (6)






X =

xintxb

(A0

A(x)

)mn

dx (7)






4 Results




























5 Discussion


































6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References






partz

partt=KAmSn (4)





partz

partt=Kdnabla

2z (5)



partz

partt= U minusKAmSn

minusKdnabla2z (6)






X =

xintxb

(A0

A(x)

)mn

dx (7)






4 Results




























5 Discussion


































6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References




X =

xintxb

(A0

A(x)

)mn

dx (7)






4 Results




























5 Discussion


































6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References























5 Discussion


































6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References






























6 Conclusions











References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References


References











































































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References












































































Abstract

Introduction

Geological setting

Data and methods

Geomorphic indices

Hypsometric curve


Surface roughness

Surface index



Results

Landscape maturity



Discussion



Conclusions

Data availability

Supplement


Competing interests

Acknowledgements

Review statement

References

relative timing of uplift along the zagros mountain front ...the zagros fold–thrust belt...

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