mid ocean ridge and island arc affinities in ophiolites from iran palaeographic implications complementary reference abstract fifty six samples of ophiolitic rocks from various late cretaceous eocene suture zones in iran have been analyzed for major and trace elements in order to assess their petrogenetic affinity and to determine their original tectonic setting in both southern baluchestan i e between the makran range and the lut block the fanuj maskutan sequence and northeastern baluchestan i e in the east iranian ranges the tchehel kureh sequence the ophiolitic complexes are well developed the rocks display affinities with mid ocean ridge tholeiites the basaltic rocks are comparable to respectively transitional fanuj maskutan and normal tchehel kureh morb in contrast the sequence along the zagros the sahneh sequence appears to have formed in an island arc setting in iranshar i e in southeastern baluchestan ophiolites are dismembered into a melange which includes cumulate intrusives similar to those from fanuj maskutan and lavas with island arc tholeiitic affinity a similar island arc origin may be inferred for the sabzevar ophiolitic sequence north of the lut block studied by other authors the chemical data thus help to elucidate the development of the jigsaw puzzle of microplates of gondwanian origin that during the mesozoic were intermediate in position between afro arabia india and eurasia and that now constitute the middle east ophiolite obduction in iran occurred during arc basin continent or ocean continent collisions in the late cretaceous early paleogene largely predating the final suturing between arabia and india with eurasia to which the intermediate microplates were already attached which did not take place before the neogene

geochemistry zircon u pb and hf isotope for granitoids nw sanandaj sirjan zone iran implications for mesozoic cenozoic episodic magmatism during neo tethyan lithospheric subduction abstract the sanandaj sirjan zone ssz of iran comprises sedimentary and metamorphic basement rocks which are generally regarded as having been derived from the southern active margin of the eurasian plate within the ssz a number of mesozoic to cenozoic granitoid intrusions of various size elongated in a nw se direction are exposed with the benefit of precise age dating geochemical and isotopic data over the past decade the magmatic history of these intrusions has become clearer this study presents further geochronological and geochemical data for previously dated and undated granitoids together with considerable zircon lu hf isotopic data which were limited in the past combined with previous work these new data including the finding of ca 170 ma adakite lead to improved constraints on the meso cenozoic tectonic evolution of neo tethyan lithospheric subduction the dominant early middle jurassic magmatism is proposed to have occurred with a major contribution of crustal components during the initiation of neo tethyan subduction subsequent late jurassic magmatism suggests the involvement of lower crust partial melting in an extensional tectonic setting cretaceous magmatism almost ceased after formation of a flat slab caused by a trench retreat rate exceeding that of slab roll back late paleocene eocene magma sources in the ssz are dominated by mantle derived input through an asthenospheric window with subordinate crustal contamination during the subduction of the neo tethyan ridge spreading center this interpretation differs from paleocene eocene magmatic flare up proposed for the northern iranian interior which may have been driven by an episode of slab retreat or slab roll back following cretaceous flat slab subduction

a continental drift flipbook abstract forty six miniature plate tectonic reconstructions are presented that can be assembled into a flipbook that illustrates the movement of the continents since the late precambrian 750 m yr ago six principal lines of evidence have been used to reconstruct the past positions of the continents 1 linear magnetic anomalies produced by sea floor spreading 2 paleomagnetism 3 hotspot tracks and large igneous provinces 4 the tectonic fabric of the ocean floor mapped by satellite altimetry 5 lithologic indicators of climate e g coals salt deposits tillites and 6 the geologic record of plate tectonic history i discuss the probable uncertainties associated with the plate tectonic reconstructions and give an estimate of the uncertainty in the positions of the continents back through time

geochemistry and zircon geochronology of the permian a type hasanrobat granite sanandaj sirjan belt a new record of the gondwana break up in iran the sanandaj sirjan metamorphic plutonic belt ssb in west central iran is a polyphase metamorphic terrain composed of dominantly greenschist grade metasedimentary and metavolcanic rocks and felsic to mafic plutons of neoproterozoic phanerozoic ages the hasanrobat granite in central ssb occurs as a single pluton 20 km 2 surface area with relatively consistent mineralogy and chemistry quartz alkali feldspars microcline and perthite sodic plagioclases and biotite are the main constituents commonly associated with minor amphibole accessory phases include zircon allanite apatite and magnetite the country rocks are upper carboniferous lower permian sandstones and dolomitic limestones scattered patches of skarn type assemblages dominated by tremolite and talc occur in the dolomitic limestones and sandstones are recrystallized to a coarse grained quartzite at contact with the granite the granite is metaluminous to slightly peraluminous and is distinguished by high feo t mgo ratios typical of ferroan a type granites the a type affinity is also reflected by high na 2o k 2o high ga al ratios high contents of large ion lithophile elements lile high field strength elements hfse and rare earth elements ree as well as low contents of sr and distinct negative eu anomalies the biotites are aluminous fe rich and plot near the siderophyllite corner in the quadrilateral biotite diagram they are further distinguished by high fluorine contents 0 61 to 1 33 wt amphibole is ferrohastingsite in composition ion microprobe analyses of zircon grains separated from a representative granite sample yielded concordant u pb ages with weighted mean 206 pb 238 u age of 288 3 3 6 ma the granite and the country rocks are cut by a set of mafic dykes with asthenosphere like geochemical signatures such association suggests anorogenic intraplate magmatism in lower permian in the region this provides further evidence for and significantly constrains timing of a major extension in upper paleozoic in iran previously inferred from the rock record the extension led to the gondwana break up and the opening of neotethys ocean between sanandaj sirjan and zagros in permian

petrology of the jurassic shah kuh granite eastern iran with reference to tin mineralization abstract the shah kuh granitic pluton of eastern central iran was emplaced 165 ma ago in an active continental margin setting it is made of two main units a granodioritic unit sio2 63 71 wt to the north west and a syenogranitic unit sio2 73 77 wt to the south east the former unit displays seriate medium grained textures and contains locally abundant mafic enclaves the latter unit is medium to coarse grained and porphyritic with 0 5 3 cm long k feldspar megacrysts fine grained granitic bodies are present in both units the rocks are metaluminous to slightly peraluminous i type and peraluminous s type and belong to the ilmenite series granites fractional crystallization appears to have been a very effective differentiation process in both units and the fractionated mineral assemblages are determined by mass balance calculations isotopic data sri 0 7065 and endt 2 5 are consistent with a young upper crustal protolith tin mineralization in sheeted quartz tourmaline cassiterite veins is spatially associated with the granodioritic unit the veins formed by hydraulic fracturing when the granodioritic to monzogranitic magma became water saturated and exsolved a fluid phase during crystallization the reduced nature of this magma is responsible for the incompatible behaviour of sn likely to favour sn concentration in the residual melt and then in the exsolved fluid another fluid phase was exsolved by the syenogranitic magma and was responsible for local greisenized granites characterized by high y and hree contents and non fractionated ree distribution patterns field and mineralogical data show that the b sn vein forming fluid was different from the f li greisen forming fluid

high resolution 3d numerical modeling of thrust wedges influence of decollement strength on transfer zones 1 the mechanics and dynamics of thin skinned compressible thrust wedges with prescribed offsets in the backstop i e transfer zones are investigated using a three dimensional finite difference numerical model with a visco brittle plastic rheology the main questions addressed are as follows i what is the influence of the initial length of the backstop offset and ii what is the effect of the frictional strength of the main decollement on the structural evolution of the brittle wedges along such transfer zones results show that the shorter the backstop offset the earlier these two thrust planes connect forming a curved frontal thrust along the entire width of the model younger in sequence thrusts are formed parallel to this curved shape long backstop offsets produce strongly curved thrust faults around the indenting corner simulations with a weak basal friction evolve toward almost linear frontal thrusts orthogonal to the bulk shortening direction increased basal drag in models with a strong decollement favors propagation of the backstop offset into a transfer zone up to the frontal thrust these simulations revealed that surface tapers of the wedge in front of the backstop promontory are larger than what the critical wedge theory predicts whereas the tapers on the other side of the transfer zone are smaller than analytical values this difference is amplified with increasing length of the backstop offset and or strength of the decollement modeled surface elevation schemes reproduce well the topographic patterns of natural orogenic systems such as the topographic low along the minab zendan transform transfer fault between the zagros and makran

reply to comment on jurassic igneous rocks of the central sanandaj sirjan zone iran mark a propagating continental rift not a magmatic arc azizi and stern terra nova 31 5 415 423 2019

geochemistry and zircon u pb geochronology of aligoodarz granitoid complex sanandaj sirjan zone iran the aligoodarz granitoid complex agc is located in the sanandaj sirjan zone ssz western iran and consists of quartz diorites granodiorites and subordinate granites whole rock major and trace element data mostly define linear trends on harker diagrams suggesting a cogenetic origin of the different rock types 87 sr 86 sr i and endt ratios are in the ranges 0 7074 0 7110 and 3 56 to 5 50 respectively the trace elements and sr nd isotopic composition suggest that the granitoids from the agc are similar to crustal derived i type granitoids of continental arcs the whole rock suite was produced by assimilation and fractional crystallization starting from a melt with intermediate composition likely possessing a mantle component in situ zircon u pb data on the granites with la icp ms yield a crystallization age of 165 ma inherited grains spanning in age from 180 ma up to 2027 ma were also found and confirm that assimilation of country rock has occurred chemical and chronological data on the agc were compared with those available for other granitoid complexes of the central ssz e g dehno boroujerd and alvand the comparison reveals that in spite of the different origins that have been proposed all these granitoid complexes are likely genetically related they share many chemical features and are derived from crustal melts with minor differences alvand granites have the most peculiar compositions most likely related to the presence of abundant pelitic component all these intrusions are coeval and reveal the presence of an extensive magmatic activity in the central sector of the ssz during middle jurassic

confirmation of arabia plate slow motion by new gps data in yemen 1 during the last 10 years a network of about 30 gps sites was measured in djibouti east africa additional points were also measured in yemen oman ethiopia iran and on la reunion island merged with data from the available international gps service permanent stations scattered on the different plates in the area eurasia anatolia africa arabia somalia this unique data set provides new insight on the current deformation in the africa somalia arabia triple junction area and on the arabian plate motion here we show that coherent motions of points in yemen bahrain oman and iran allow us to estimate a geodetically constrained angular velocity for the arabian plate 52 59 n 15 74 w 0 461 myr in itrf2000 this result differs significantly from earlier determinations and is based upon our vectors in yemen they provide new additional data and better geometry for angular velocity determination combined with the african and somalian motions this new angular velocity results in predicted spreading rates in the red sea and the gulf of aden which are 15 20 lower than those measured from oceanic magnetic anomalies and thus averaged over the last 3 myr with respect to eurasia the geodetic motion of arabia is also about 30 slower than predicted by nuvel 1a on the basis of the kinematic results presented here and on other evidence for a similar slower geodetic rate of the indian plate we suggest that the whole collision zone between africa arabia india on one hand and eurasia on the other hand has slowed down in the last 3 myr

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

locating earliest records of orogenesis in western himalaya evidence from paleogene sediments in the iranian makran region and pakistan katawaz basin a combination of sediment petrography detrital zircon u pb and fission track dating is used to show that provenance of the paleogene sedimentary rocks exposed in the makran region of southern iran and the katawaz basin of pakistan is consistent with a source from the nascent western himalaya and associated magmatic arc results from this important archive show that paleogene erosion was focused mainly on the arc and northern indian margin and in contrast to the east central himalaya we have not detected widespread rapid exhumation indicative of strong forcing by climate driven erosion at that time

reconstruction of holocene sea surface salinity in the skagerrak kattegat a climatic and environmental record of scandinavia holocene sea surface salinity in the skagerrak kattegat is reconstructed using weighted averaging regression and calibration wa of diatom data from core skagen 3 diatom data from surface sediments together with 10 yr mean values of salinity and water temperature were used as a modern training set canonical correspondence analysis cca was used to identify statistically significant directions of variation within the training set the results of forward selection of the environmental variables and associated monte carlo permutation tests of the statistical significance of each variable the canonical coefficients and the intraset correlations of the environmental variables with the cca axes suggest that summer and winter sea surface salinities sss wss are potentially reconstructable from fossil diatom assemblages the changes in sea surface salinity during the holocene can be correlated with changes in climate of the circum baltic area the current patterns of the skagerrak kattegat and the development of the baltic sea generally low sss and large differences between wss and sss dsw s during 9000 6000 yr bp might have resulted from a climate with higher precipitation than today in the circum baltic area and its catchment or a climate with maximum precipitation in late spring or early summer the mechanism behind these patterns may be the combination of the northward shift of the jet stream and a stronger surface westerly penetration into the continent caused by a reduced latitudinal insolation gradient and enhanced land sea contrast in the early to middle holocene it was however complicated by local events such as changes in the strength of various currents in the skagerrak kattegat successions of baltic brackish and freshwater phases and hydrodynamic conditions in the circum baltic area 1998 john wiley sons ltd

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

petrology and geochemistry of the granitoid complex of boroujerd sanandaj sirjan zone western iran abstract the middle jurassic boroujerd granitoid complex of the sanandaj sirjan zone with a u pb zircon age of 169 172 ma was emplaced in an active continental margin setting this complex consists of three main units an elongate nw se extending granodioritic unit sio2 58 71 wt which is widespread throughout the area a quartz dioritic unit sio2 52 63 wt exposed as small stocks within the granodioritic body and a monzogranitic unit sio2 70 75 wt widely scattered as separate small outcrops through the southern part of the area a series of nw trending aplites and pegmatites are present in the granodioritic unit and its aureole geochemically this complex is metaluminous to slightly peraluminous typical of i type granites it belongs to high k calc alkaline series and displays the geochemical characteristics typical of volcanic arc granites related to an active continental margin e g significant nb ti p and sr depletion isotopic data sri 0 7062 0 7074 and endt 3 02 to 3 62 are consistent with a crustal protolith in addition fractional crystallization may have played an important role in the formation of the whole spectrum of the granitoid types that occur in the boroujerd area

new palaeomagnetic data from central iran and a triassic palaeoreconstruction new pole positions for triassic and cretaceous times have been obtained from volcanic and sedimentary sequences in central iran these new results confirm the general trend of the apparent polar wander path apwp of the central east iran microplate ceim from the triassic through the tertiary as published by soffel and forster 1983 1984 two new palaeopoles for the triassic of the ceim have been obtained limestones and tuffs from the nakhlak region yield a mean direction of 094 0 25 0 n 12 k 4 1 95 24 7 after bedding correction corresponding to a palaeopole position of 310 8 e 3 9 s and volcanic rocks from the sirjan regions yield a mean direction of 114 5 35 1 n 44 k 45 9 95 3 2 after bedding correction and a palaeopole position of 295 8 e 10 3 n combining these with the two previously published results yields a new palaeopole position of 317 5 e 12 7 n for the triassic of the ceim thus confirming that large counterclockwise rotations of the ceim have occurred since the triassic time new results have also been obtained from cretaceous limestones from the saghand region of the ceim the mean direction of 340 7 26 3 n 33 k 44 3 95 3 8 and the corresponding palaeopole position of 283 1 e 64 4 n is in agreement with previously determined cretaceous palaeopole positions of the ceim furthermore results have also been obtained from triassic dolomite limestone sandstone and siltstone from the natanz region which is located to the west of the ceim a total of 161 specimens from 44 cores taken at five sites gave a mean direction of the five sites at 033 3 25 1 n 5 k 69 0 95 9 3 and a palaeopole position of 167 2 e 53 7 n they pass the positive fold test of mcelhinny 1964 on the level of 99 confidence this pole position is in fairly good agreement with the mean triassic pole position of the turan plate 149 e 49 n it indicates that the area of natanz has not undergone the large counterclockwise rotation relative to the turan plate since the triassic which has been shown for the ceim a triassic palaeogeographic reconstruction of iran arabia gondwana and the turan plate eurasia is also presented

reactive bulk assimilation a model for crust mantle mixing in silicic magmas bulk assimilation of small millimeters to 1 km fragments of crust driven and ultimately masked by reactions during xenolith melting and magma crystallization is an important mechanism for crust mantle mixing xenoliths containing mica or amphibole undergo dehydration melting when incorporated into a host magma yielding mainly plagioclase pyroxene fe ti oxides and hydrous melt the xenolith is physically compromised by partial melting and begins to disintegrate xenolithic melt and crystals are mixed into the host magma xenocrystic zircon is liberated at this stage the cryptic character of assimilation is greatly enhanced in any hydrous magma by hydration crystallization reactions the reverse of dehydration melting all pyroxenes and oxides phenocrysts xenocrysts or crystals having a hybrid signature will be subject to these reactions producing feldspars amphiboles and micas that incorporate material from several sources a particularly effective mixing mechanism implicit in the model is a reduced energy penalty for bulk assimilation much of the assimilant remains in solid form compared to melt assimilation models a large role for bulk assimilation supports stoping as a credible mechanism for the ascent of magmas while the assimilation of low density crust and concomitant fractionation provide the isostatic impetus for ascent the wholesale incorporation and processing of crustal rocks in the magma chamber helps create the room for ascent

geochemistry and u pb zircon geochronology of the alvand plutonic complex in sanandaj sirjan zone iran new evidence for jurassic magmatism abstract this paper presents geochemical sr nd isotopic and u pb zircon geochronological data on the alvand plutonic complex in sanandaj sirjan zone ssz western iran the gabbroic rocks show a trend of a calc alkaline magma suite and are characterized by low initial 87 sr 86 sr ratios 0 7023 0 7037 and positive e nd t values 2 9 3 3 which suggest derivation from a moderately depleted mantle source geochemical features of the granites illustrate a high k calc alkaline magma series whereas the leucocratic granitoids form part of a low k series granites have intermediate 87 sr 86 sr ratios 0 707 0 719 and negative e nd t values 1 0 to 3 4 while leucocratic granitoids have higher initial 87 sr 86 sr ratio 0 713 0 714 and more negative e nd t values 3 5 to 4 5 potential basement source lithologies for the granites are proterozoic granites and orthogneisses and those for the leucocratic granites are plagioclase rich sources such as meta arkoses or tonalites the u pb dating results demonstrate that all granitoids were exclusively emplaced during the jurassic instead of being cretaceous or younger in age as suggested previously the pluton was assembled incrementally over c 10 ma gabbros formed at 166 5 1 8 ma granites between 163 9 0 9 ma and 161 7 0 6 ma and leucocratic granitoids between 154 4 1 3 and 153 3 2 7 ma granites and leucocratic granitoids show some a type affinity it is concluded that the alvand plutonic complex was generated in a continental arc related extensional regime during subduction of neo tethyan oceanic crust beneath the ssz the u pb zircon age data recently corroborated by similar results in the central and southern ssz indicate that jurassic granitoids are more areally extensive in this belt than previously thought

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

active deformation in zagros makran transition zone inferred from gps measurements summary the bandar abbas strait of hormuz zone is considered as a transition between the zagros collision and the makran oceanic subduction we used gps network measurements collected in 2000 and 2002 to better understand the distribution of the deformation between the collision zone and the makran subduction analysing the gps velocities we show that transfer of the deformation is mainly accommodated along the nnw sse trending reverse right lateral zendan minab palami zmp fault system the rate is estimated to 10 3m m yr 1 near the faults assuming that the zmp fault system transfers the motion between the makran lut block and the arabian plate we estimate to 15 mm yr 1 and 6m m yr 1 respectively the dextral strike slip and shortening components of the long term transpressive displacement our geodetic measurements suggest also a 10 15 km locking depth for the zmp fault system the radial velocity pattern and the orientation of compressive strain axes around the straight of hormuz is probably the consequence of the subducting musandam promontory the n s jiroft sabzevaran js fault system prolongates southwards the dextral shear motion of the nayband gowk ng fault system at an apparent rate of 3 1 2 5 mm yr 1 the change from strong to weak coupling for underthrusting the arabian plate beneath the zagros strong and the makran weak may explain the dextral motion along the zmp js ng and neh zahedan fault systems which transfer the convergence from a broad zone in the western iran zagros tabriz fault system alborz caucasus and caspian sea surroundings to makran subduction

observations on the origins and ascent mechanisms of granitic magmas this review presents a summary of most current beliefs about the origins of granitic magmas together with calculations of some important properties of granitic melts and magmas turning attention to magma ascent mechanisms diapirism and dyking represent two competing end member models the differences in processes and products between the two are fundamental and the implications of the differences are profound for the evolution of the continental crust the weight of evidence favours dyke ascent for the majority of granitic magmas and modelling shows that dyke ascent is both rapid and thermally effcient furthermore the structural and petrological features expected in crust through which granitic diapirs have passed have not been discovered in nature granites in the upper crust commonly have forms and structures indicating that diapirism could not have been the emplacement mechanism in contrast granitic dykes are common suggesting that it is reasonable to consider the ascent of granitic magmas through fracture systems many granitic batholiths are tabular and some have been fed by large dykes the rate limit in granitic plutonism is not magma ascent but either the rate of melting and segregation near the magma source or the rate of deformation at the emplacement site

the gabbro shoshonitic monzonite granodiorite association of khankandi pluton alborz mountains nw iran abstract the khankandi pluton forms part of a group of gabbro granodiorite intrusions in the alborz mountains of nw iran a petrographical and geochemical study of this plutonic association reveals the existence of several magmatic cycles with different origins and slight differences in age the oldest cycle c1 is represented by granodiorites a second cycle c2 is formed by a gabbro monzonite association with a clear shoshonitic affinity that dominates most of the intrusive volume gabbros and monzonites form a co magmatic association zircons from the monzonites were analyzed by la icp ms for u pb dating an average age of 28 9 ma ranging from 23 7 to 33 6 ma was obtained gabbros monzonites and granodiorites share a nearly common isotopic ratio for sr and nd both initial sr and nd ratios are clustered within a narrow range from 0 7045 to 0 7047 for the 87sr 86sr ratio and end from 1 46 to 1 89 comparison with experimental studies together with mantle like isotopic ratios and comparisons of ree patterns points to an origin by variable melting rates from a common metasomatised mantle source for gabbros and monzonites melting of a subducted melange is suggested for the granodiorite magmas predating the gabbro monzonite intrusion the two sources a metasomatised mantle and ascending silicic plumes are direct consequence of subduction

jurassic rifting at the eurasian tethys margin geochemical and geochronological constraints from granitoids of north makran southeastern iran this study focuses on an east west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern dur kan complex a continental slice outcropping to the north of the exposed makran accretionary wedge in southeastern iran field observations petrographic descriptions trace element and isotope analyses combined with u pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks results document three magmatic episodes with different melt sources for 1 granites 2 a diorite trondhjemite plagiogranite sequence and 3 diabases and lavas granites dated at 170 175 ma represent crystallized melt with a strong continental isotopic contribution the diorite trondhjemite plagiogranite sequence is 165 153 ma old and derives from a mantle magma source with minor continental contribution east west trending diabase dikes and bodies intruded the granitoids which were eroded and then covered by valanginian 140 133 ma alkaline lavas and sediments alkaline dikes and lavas have a mantle isotopic composition temporal correlation with plutonites of the sanandaj sirjan zone to the northwest defines a narrow nw se striking and nearly 2000 km long belt of jurassic intrusions the increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling decompression melting accordingly the formation of the studied igneous rocks is related to the extension of the iranian continental margin which ultimately led to the formation of the tethys related north makran ophiolites

the geotectonic history of the makran and adjacent areas of southern iran abstract the makran mountain range in southern iran has been entirely covered by regional mapping on a scale of 1 250 000 but in contrast to the mapping of oman on the other side of the gulf the recent mapping is little known the cenozoic accretionary prism in the south fronts onto a mesozoic melange zone representing earlier subduction and to the north of this is an eastwards tapering microcontinental sliver which is followed by a zone of largely intact mesozoic ophiolite complexes to the north of this lies the jaz murian depression a desert expanse with no bedrock outcrop the sanandaj sirjan bajgan dur kan microcontinental sliver which extends from turkey through the zagros to the makran is one of a number of microcontinents which detached from gondwana no later than the early triassic nw iran yazd tabas lut birk helmand farah during the mesozoic these were enclosed by tracts of ocean now represented by ophiolites and the sectors closed at different times ranging from early cretaceous to end palaeogene an analogy is drawn with the present day mediterranean the sistan ocean in the east was infilled with an immense thickness of abyssal turbidites during the eocene before it closed the field evidence indicates that there was a second cenozoic accretionary prism here but sedimentation ceased after the eocene on its collision with the back of the main makran prism this eastern sistan trough now completely occluded is compared with the still open tract separating the makran from oman at the present time and its northern extension which has been similarly occluded by collision beneath the zagros some residual very shallow inland seas persisted inland from the makran through the neogene the occurrence of blueschists in the inner ophiolite belt of the makran is discussed abyssal turbidite sedimentation continued in the main southern zone of the makran into the early miocene to be succeeded by thick shallow water sequences including reefal limestones intense tectonic dislocation at the end of the miocene was accompanied by a shift of the subduction front to its present position out in the indian ocean and uplift leading to the deposition of spectacular pliocene pleistocene fanglomerates

the temporal evolution of the active margin along the southeast anatolian orogenic belt se turkey evidence from u pb ar ar and fission track chronology abstract the southeast anatolian orogenic belt saob resulted from the north dipping subduction of the southern neotethyan oceanic lithosphere in late mesozoic and early cenozoic however the timing and the rate of the continental collision are still under debate here we present new u pb ar ar and fission track ages from the i type calc alkaline granitoids esence dogansehir and baskil cutting the goksun ispendere and komurhan ophiolites and also the malatya keban metamorphics representing the tauride active continental margin along the saob in this study high to low temperature thermochronological methods applied to the granitoids are used to understand the temporal and geodynamic evolution of the tauride active continental margin and continental collision between tauride and arabian platforms in the frame of the neotethyan convergence during cretaceous and miocene the u pb zircon ages range from 83 to 88 ma for the baskil and from 81 to 83 ma for the esence granitoids the 39 ar 40 ar ages indicate that these late cretaceous granitoids cooled below 300 c in 6 10 ma the formation ages and the timing of the gradual cooling of the late cretaceous granitoids are similar to metamorphism age and the timing of the exhumation of the hp lt bitlis metamorphics during this stage the combined field geochemistry and geo thermochronological data suggest that the first continental collision event occurred between bitlis puturge micro continents to the south and tauride platform to the north in an oblique subduction zone between 84 and 74 ma the granitoids continued uplifting during early middle eocene together with the exhumation of hp uht berit metaophiolite in an extensional regime related to the opening of the maden back arc basin this period also let the intrusion of the dogansehir arc magmatism intruding the puturge and malatya keban metamorphics berit metaophiolite and maden complex the eocene dogansehir granitoid has similar u pb and 39 ar 40 ar ages suggesting a fast cooling the apatite fission track aft ages for all granitoid bodies suggest that they were mainly cooled or uplifted in two episodes where the first one is in the eocene in an extensional setting the aft data marked the final continental collision between the taurides and the arabian platform first in oligocene and the break off of the subducted slab and the delamination process caused fast uplift of the eastern anatolia during middle to late miocene

a type granite and the red sea opening abstract miocene oligocene a type granite intrudes the eastern side of the red sea margin within the zone of extension from jiddah saudi arabia south to yemen the intrusions developed in the early stages of continental extension as arabia began to move slowly away from africa around 30 20 ma within the narrow zone of extension silicic magmas formed dikes sills small plutons and extrusive equivalents in the jabal tirf area of saudi arabia these rocks occur in an elongate zone consisting of late precambrian basement to the east which is gradually invaded by mafic dikes the number of dikes increases westward until an igneous complex is produced parallel to the present red sea axis the jabal tirf igneous complex consists of diabase and rhyolite granophyre sills 20 24 ma although these are intrusine intrusive rocks their textures indicate shallow depths of intrusion the alkali granites of yemen consist primarily of perthitic feldspar and quartz with some minor alkali amphiboles and acmite these granites represent water poor hypersolvus magmas generated from parent alkali basalt magmas the granophyric two feldspar granites associated with the mafic dike swarms and layered gabbros formed by fractional crystallization from tholeiitic basalt parent developed in the early stages of extension initial 87sr 86sr ratios of these rocks and their bulk chemistry indicate that production of peralkaline and metaluminous granitic magmas involved both fractionation and partial melting as they ascended through the late precambrian crust of the arabian plate

the neotethyan sanandaj sirjan zone of iran as an archetype for passive margin arc transitions the sanandaj sirjan zone of iran is a northwest trending orogenic belt immediately north of the zagros suture which represents the former position of the neotethys ocean the zone contains the most extensive best preserved record of key events in the formation and evolution of the neotethys from its birth in late paleozoic time through its demise during the mid tertiary collision of arabia with eurasia the record includes rifting of continental fragments off of the northern margin of gondwanaland formation of facing passive continental margins initiation of subduction along the northern margin and progressive development of a continental magmatic arc the latter two of these events are critical phases of the wilson cycle that elsewhere in the world are poorly preserved in the geologic record because of superimposed events our new synthesis reaffirms the similarity between this zone and various terranes to the north in central iran late paleozoic rifting preserved as a type granites and accelerated subsidence was followed by a phase of pronounced subsidence and shallow marine sedimentation in permian through triassic time marking the formation and evolution of passive margins on both sides of the suture subduction and arc magmatism began in latest triassic early jurassic time culminating at 170 ma the extinction of arc magmatism in this zone and its shift northeastward to form the subparallel urumieh dokhtar arc occurred diachronously along strike in late cretaceous or paleogene time post cretaceous uplift transformed the zone from a primarily marine borderland into a marine archipelago that persisted until mid tertiary time

what controls chemical variation in granitic magmas abstract consideration of the models that have been applied to explain the chemical variations within granitic rock suites shows that most are inadequate to account for the main variations this stems from a variety of model deficiencies ranging from physical or energetic inadequacies to incompatibility with the chemical data or internal inconsistency between models based on for example isotope or trace element data and major element data we contend that any model that fails any of these tests of internal consistency cannot be considered further thus although we can point to examples in which many of the traditionally accepted mechanisms have played secondary roles in producing variation there presently remains but one viable choice for the primary mechanism by which most granitic magmas acquire compositions beyond the range defined by the compositions of crustal melts that primary mechanism is peritectic assemblage entrainment pae we infer that once a partial melt has formed in a crustal protolith it may segregate from its complementary solid residue carrying small crystals of the peritectic phase assemblage formed in the melting reaction and that the ratios of individual peritectic minerals in the entrained assemblage remains fixed in the ratio decreed by the stoichiometry of the melting reaction for those elements with low solubilities in granitic melts pae in varying degrees accompanied by co entrainment of accessory minerals is responsible for most of the primary elemental variation in granitic magmas in contrast the concentrations of elements with high solubilities in silicic melts reflect the protolith compositions in a simple and direct way the source is the primary control on granite magma chemistry it dictates what is available to dissolve in the melt and what will be formed as the entrainable peritectic assemblage the apparent complexity in granitic rock suites is largely a consequence of these processes in the source all other mechanisms contribute only as a secondary overlay

the eocene bimodal piranshahr massif of the sanandaj sirjan zone nw iran a marker of the end of the collision in the zagros orogen abstract the bimodal piranshahr massif is composed of coeval but geochemically unrelated mafic 40 7 0 2 ma zircon u pb sensitive high resolution ion microprobe shrimp age and a type felsic rocks 41 0 5 ma rb sr and 41 3 0 8 ma zircon u pb shrimp age the mafic rocks consist of two geochemical types of gabbros that derived from different magmas the more abundant gabbros are moderately alkaline have ratios of large ion lithophile elements to ree and high field strength elements to ree similar to those of intraplate mantle magmas 87 sr 86 sr 41 ma 0 7036 and e nd 41 ma 7 2 the less abundant gabbros have calc alkaline affinities 87 sr 86 sr 41 ma 0 7043 and e nd 41 ma 4 78 felsic rocks are metaluminous a2 type annite fayalite hedenbergite hypersolvus leucocratic coarse grained agpaitic syenites pulaskites and granites with 87 sr 86 sr 41 ma 0 7048 and e nd 41 ma 3 6 4 5 syenites pulaskites and granites are genetically related pulaskites probably represent alkali enriched water rich residual melts from which an f rich vapour phase was later separated granites were probably generated during open system processes in which f rich hydrous alkaline fluids released from the syenites acted upon pre existing felsic rocks the c 41 ma age of the post collisional piranshahr massif indicates that the related collision probably occurred at 50 60 ma i e late palaeocene or early eocene thus resolving a much debated question

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

a new tectonic scenario for the sanandaj sirjan zone iran abstract recent geochemical studies of volcanic rocks forming part of the ophiolites within the zagros and naien baft orogen indicate that most of them were developed as supra subduction ophiolites in intra oceanic island arc environments intra oceanic island arcs and ophiolites now forming the naien baft zone were emplaced southwestward onto the northeastern margin of the south sanandaj sirjan zone while those now in the high zagros were emplaced southwestward onto the northern margin of arabia thereafter subduction continued on opposite sides of the remnant oceans the floor of neo tethys ocean was subducted at a low angle beneath the entire sanandaj sirjan zone and the floor of the naien baft ocean was subducted beneath the central iranian micro continent the naien baft ocean extended into north west iran only temporarily this failed ocean arm between the urumieh dokhtar magmatic assemblage and the main zagros thrust was filled by thick upper triassic upper jurassic sediments the naien baft ocean finally closed in the paleocene and neo tethys closed in the early to middle eocene after arabia was sutured to iran the urumieh dokhtar magmatic assemblage recorded slab break off in the middle eocene

petrology geochemistry and tectonic setting of the khoy ophiolite northwest iran implications for tethyan tectonics abstract the khoy ophiolite in northwestern iran represents a remnant of oceanic lithosphere formed in the mesozoic neo tethys this northwest southeast trending ophiolite complex consists from bottom to top east to west of a well defined basal metamorphic zone peridotites dunite harzburgite and serpentinized peridotite gabbros sheeted dikes pillow and massive lava flows and pelagic sedimentary rocks including radiolarian chert the rocks of the metamorphic zone have an inverse thermal gradient from amphibolite facies to greenschist facies the high grade metamorphic rocks are immediately adjacent to the peridotite and the gabbros and the low grade rocks are in contact with the precambrian kahar formation based on mantle normalized incompatible trace element diagrams there are two distinct types of basalt flows present at the khoy ophiolite 1 massive basalts that have patterns virtually identical to e morb and 2 pillow basalts that have more primitive chemical composition whose trace element patterns plot between e morb and n morb the chondrite normalized ree patterns for the pillow basalts are lree depleted lan smn ave 0 70 similar to patterns for the mean diabase composition for the oman ophiolite and lree depleted basalts of the band e zeyarat ophiolite of southern iran the ree patterns for the massive basalts are similar in general ree abundances to the pillow basalt patterns but they are slightly lree enriched lan smn ave 1 09 and their patterns cross those of the pillow basalts the ree patterns for the gabbros and diorites indicates that the crustal suite rocks were most likely derived by a process of fractional crystallization from a common basaltic melt this basaltic melt was most likely generated by approx 20 25 partial melting of a simple lherzolite source and had ree concentrations of roughly 10 chondrite a comparison between the results from the khoy ophiolite and the data from other iranian ophiolites reveals geochemical evidence to suggest a tectonic link between the khoy ophiolite and the rest of the iranian ophiolites our results suggest that khoy ophiolite is equivalent to the inner group of iranian ophiolites e g nain shahr babak sabzevar tchehel kureh and band e zeyarat and was formed as a result of closure of the northwestern branch of a narrow mesozoic seaway which once surrounded the central iranian microcontinent

the petrogenesis and tectonic setting of lavas from the baft ophiolitic melange southwest of kerman iran a late cretaceous ophiolite complex in the baft area southwest of kerman iran is characteristic of the central iranian ophiolitic melange belt which wraps around the lut block despite the extensive tectonic disruption of the baft complex most ophiolitic lithologies are present and many original igneous contacts are preserved a lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the baft spreading axis geochemical data confirm the presence of two distinct compositional groups in the mafic lavas 1 tholeiitic basalt and 2 transitional tholeiitic basalt the tholeiitic lavas are similar to typical mid ocean ridge basalt compositions whereas the transitional tholeiites are similar to intraplate basalts the available data suggest that the baft ophiolite complex formed in a small ocean basin possibly at or near a ridge transform intersection emplacement may have occurred as a result of conversion of the transform fault to a subduc

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

detrital zircon and provenance analysis of late cretaceous miocene onshore iranian makran strata implications for the tectonic setting a multidisciplinary provenance study including sandstone framework heavy mineral analysis in situ u pb dating of detrital zircon and hf isotopic ratio analysis of dated zircons was undertaken on late cretaceous miocene deep marine turbiditic and deltaic sandstones of makran accretionary wedge se iran to determine their sedimentary provenance and tectonic setting sandstone framework modes reveal both magmatic arc rocks as a source of late cretaceous oligocene detritus and recycling of miocene sandstones heavy mineral assemblages cr spinel and blue amphibole indicate ophiolite and high pressure low temperature metamorphic rocks blueschists as a supplementary provenance in total 2931 laser ablation inductively coupled plasma mass spectrometry icp ms u pb detrital zircon ages on 21 sandstone samples yielded three major age peaks at ca 167 ma 88 7 ma and 48 9 ma also 241 in situ hf isotope analyses of dated zircons provide evidence for dominantly igneous source rocks two main detrital zircon ages are identified 1 abundant middle jurassic grains with hf isotopic compositions of continental crust suggesting a rifting related magmatic provenance and 2 late cretaceous eocene grains with hf isotopic compositions of continental crust and nondepleted mantle suggesting a continental magmatic arc provenance this change in provenance is attributed to the late cretaceous convergence between arabia and eurasia

formation and ascent of granitic magmas new results obtained by the investigation of liquidus and solidus phase relationships in the haplogranite system qz ab or are used to discuss the evolution of magmas during their ascent in the crust it is assumed that the magmas are formed at 720 c 820 c 920 c and at a depth corresponding to a pressure of 8 kbar the starting composition of the magma is taken as 50 melt plus 50 quartz and feldspars in case of a closed system no heat exchange and no transfer of elements the melt fraction of magmas the water activity and the viscosity increase with decreasing pressure the temperature slightly decreases at 700 c the viscosity is approximatively 2 orders of magnitude lower than at 900 c this is related to the higher amount of water in the h2o undersaturated melt at low t it is also shown that dehydration melting is only realistic at high t 900 c at lower temperatures water has to be added from outside to obtain an intrusive magma with approximatively 50 melt

rate of crustal shortening and non coulomb behaviour of an active accretionary wedge the folded fluvial terraces in makran se iran abstract we surveyed fluvial terraces to decipher the quaternary increment of crustal shortening and shortening rate in the on shore makran accretionary wedge we focused on three major catchment basins and associated fold systems terrace profiles reconstructed from differential gps measurements combined with dem revealed two regional dominant wavelengths about 5 km in the northern part of the study area and about 15 km to the south these two wavelengths suggest the existence of two active decollement layers at two rooting depths the average shortening rate due to folding is estimated at 0 8 1 2 mm a over the last 130 ka this accounts for 10 15 of the shortening rate 8 mm a given by kinematic gps measurements between chabahar and bazman and 3 of the convergence between arabia and eurasia across the makran subduction zone despite active deformation and a relatively high shortening rate the geophysical record shows nearly absent seismic activity in makran we propose that strain accumulated in folds over intermediate decollement levels within a thick incompletely lithified sedimentary cover explains the essentially aseismic recent tectonics in this region the importance of folds points to imperfect coulomb behaviour of the wedge

petrology geochemistry and geochronology of trondhjemites from the qori complex neyriz iran metamorphism magmatism and thrusting were the result of subduction of neotethys beneath the continental margin arc of the sanandaj sirjan shear zone sssz during the mesozoic the qori metamorphic complex is a part of the southern sssz leuco granitic trondhjemitic rocks crop out in the qori metamorphic complex and are rare rock types in the sssz these rocks have intruded into the marbles and garnet amphibolites the highest grade metamorphic rocks of the qori metamorphic complex and in some outcrops a transitional boundary between the amphibolites and the granitoids can be distinguished the granitoids are granular in texture and consist of plagioclase albite oligoclase quartz k feldspar muscovite and subordinate garnet spinel rutile and apatite which primarily occur as inclusions in the main phases the peraluminous trondhjemitic rocks are enriched in na2o and sio2 and depleted in feo mgo and cao similarities with some trondhjemitic liquids produced through partial melting of amphibolites or hydrous basalts i e low al2o3 content less than 15 wt low ba sr tio2 and eu content all with negative anomalies moderately enriched lrees and y and flat hree patterns suggest that the evolution of the parental magma was controlled by residual plagioclases during partial melting of a garnet amphibolite source concentrations of ferromagnesian elements mg fe and mn are low suggesting that the granitic rocks were not produced by high degrees of partial melting furthermore they display low amounts of ferromagnesian components from the protolith garnet amphibolite this is supported by consideration of compatible elements especially cr ni and ti and the less robust hree which respectively show very high and high bulk partition coefficients for relatively small degrees 20 of partial melting of the source the partial melting of the garnet amphibolites occurred at pressures and temperatures between 7 5 and 9 5 kbar at a depth of 25 to 32 km and 680 and 720 degrees c respectively based on the grt hbl and hbl pl thermometers and a grt hbl pl qtz barometer precise u th zircon shrimp ages of the trondhjemite show magmatic ages of 147 4 0 76 ma volgian late jurassic and suggest that neotethys began to subduct beneath the continental margin arc of the sssz as a result of this process an arc related metamorphism occurred leading to the development of the garnet amphibolites in the qori metamorphic complex c 2009 elsevier b v all rights reserved

structure and petrology of tauride ophiolites and mafic dike intrusions turkey implications for the neotethyan ocean cretaceous neotethyan ophiolites occur in four east west trending subparallel zones within the tauride tectonic belt in southern turkey the ophiolites of the inner intermediate and outer zones tectonically overlie the mesozoic platform carbonates of the tauride belt and are commonly underlain by a cenomanian ophiolitic melange these ophiolites consist mainly of tectonized mantle rocks mafic ultramafic cumulates and gabbros and commonly lack sheeted dike complexes and extrusive rocks of a complete ophiolite sequence metamorphic soles that are several hundred meters thick occur as thrust faulted slices beneath these ophiolites and show well developed metamorphic field gradients ophiolitic units and the metamorphic soles are intruded by mafic dike swarms that are truncated at the contact with the underlying melange unit dike rocks are made of subalkalic basalt to andesite typical of evolved island arc tholeiites they display large compositional variations with sio 2 content between 50 and 60 wt and mgo between 8 and 4 wt and contain higher ti augite phenocrysts and significantly less calcic plagioclase than their host cumulates the majority of the analyzed dike rocks show a slight depletion in light rare earth elements ree with low la smn ratios and are depleted in both high field strength hfs and heavy rees while enriched in large ion lithophile elements lile relative to normal mid ocean ridge basalt morb these characteristics suggest a mantle source that underwent previous melt extractions and subsequent metasomatism by lile and light ree enriched fluids geochemical modeling of trace elements shows that melting occurred at relatively low pressures under hydrous conditions and that it may have required the existence of an asthenospheric window in which the dike magmas developed through tapping and mixing of melts generated within a rising melting column starting slightly within the garnet stability field or in a transitional zone between the garnet and spinel stability fields at about 60 km depth this asthenospheric window was probably created during subduction of a neotethyan ridge system magmas ascending from the melt column within this window generated dikes that crosscut the metamorphic soles and were injected into the overlying mantle wedge and oceanic lithosphere the new 40 ar 39 ar hornblende dates of 92 90 ma and 90 91 ma from the metamorphic soles and dike swarms respectively show that evolution of these two geologic units was closely related in time and space and that they formed at the same intraoceanic subduction zone within the inner tauride seaway these data suggest that the tauride ophiolites within the three zones to the north originated from the same root zone situated north of the tauride carbonate platform and that they constitute remnants of a single ophiolitic nappe sheet derived from the inner tauride seaway within the neotethyan ocean

early jurassic rifting of the arabian passive continental margin of the neo tethys field evidence from the lurestan region of the zagros fold and thrust belt iran

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

geology of the onshore makran accretionary wedge synthesis and tectonic interpretation abstract this contribution is a synthesis of studies carried out since 2004 in the makran accretionary wedge exposed in se iran these studies were intended to improve our understanding of the behaviour of accretionary wedges and of the significance of the makran wedge in the frame of tethys tectonics reassessing the stratigraphy and structure of the iranian makran has allowed distinguishing four main litho tectonic units the lithological content of these four units is briefly described to discuss the sedimentary environments which record the general filling of an oceanic basin with clastic sediments derived from the north the petrology of ophiolites exposed in the backstop region to the north of the accretionary wedge itself demonstrates the existence of an oceanic basin formed in the jurassic late cretaceous to the north of continental slivers which had separated from central iran there is petrological evidence for a subduction related magmatic arc during the late cretaceous which sourced much of the clastic material in the cretaceous lower miocene turbidites present throughout the wedge the literature survey shows that the late cretaceous to present evolution of the pakistan part of the makran fold and trust belt is in its major attributes similar to that of the iranian makran these observations and results are discussed in a tectonic model that integrates knowledge on the oman mountains on the other side of the current oman subduction

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

the eastern iranian orocline abstract the eastern iranian range is seen as a large scale india eurasia collisional event and the subsequent amalgamation of the afghan and lut micro continents including the neo tethyan accretionary complexes and associated island arcs revised examination of the nature of tectono stratigraphic units distributed in both sides of the n s elongated eastern iranian orogen reveals two remarkable facts first from a general perspective it is structurally a giant parallel antiform in profile view second lithologically the most time equivalent comparable tectonic units from both northern and southern domains comprising the eastern iranian orogen are connectable follow the strike of hinge and limbs zones of the antiform and a m shaped disharmonic pattern in its core these characters are thought to be formed in response to two principal deformational phases resulting from two perpendicular stress directions the first was n s associated with the north dipping subduction of the tethyan oceanic lithosphere beneath the roughly ribbon shaped cimmerian supercontinent including the afghan and lut blocks before late eocene afterward the second was e w shortening originated by the westward escape of the afghan block as a consequence of the indian plate indentation into eurasia this orogen parallel stress was correspondingly accommodated by tens of degrees counter clockwise rotation of the lut block around a vertical axis the result of such shortening was oroclinal buckling and concomitant retreating of the subduction zone and closure of the sistan ocean a remaining wedge shaped part of the neotethys ocean formed by the ribbon curvature the development of the eastern iranian orogen already included the sistan suture zone an enormous mass of folded eocene flysch deposits with a general n s axial surface and some cretaceous ophiolitic remnants the plate scale buckling which was formed by this late stage orogenic event is hereby considered as an orocline call eastern iranian orocline lithosphere buckling around a vertical axis caused a large scale crustal folding coeval with the bending of its mantle part increasing the lithospheric thickness of the orocline compared to adjacent regions the syn orocline deformation associated delamination and resulting magmatic events took place in eastern iran during a short period of about 10 to 20 ma in the late paleogene the orocline hinge zone is occupied by the khorasan outer arc and the birjand core while its limbs are composed of the baluch inner arc and the southwestern and southeastern terminations of the lut and afghan blocks the eastern iranian orocline seems to be the middle segment of a triple bending belt with n s two opposite facing bend including afghan lut and sanandaj sirjan blocks this large curvature is possibly an example of secondary oroclines which was formed by collision related escape tectonics although the limited available kinematic data show a kind of progressive orocline

hydraulically drained flows in rotating basins part ii steady flow abstract the slow horizontal circulation in a deep hydraulically drained basin is discussed within the context of reduced gravity dynamics the basin may have large topographic variations and is fed from above or from the sides by mass sources dissipation is provided by bottom friction to the order of the appromixations made weak forcing and dissipation the nonlinear hydraulic control is found to influence only the mean level of the interface separating upper and lower layers and not the horizontal circulation for the case of forcing from above the interior basin flow is anticyclonic about closed geostrophic contours and feeds into diffusive boundary layers leading to the draining strait and sill with sidewall forcing the interior is motionless and flow is channeled directly to the strait in boundary layers the latter may circle the basin cyclonically or anticyclonically depending on the source distribution and a circulation integral is shown to predict the sense of the overall swirl velocity

the late jurassic panjeh submarine volcano in the northern sanandaj sirjan zone northwest iran mantle plume or active margin abstract the tectonic setting in which jurassic igneous rocks of the sanandaj sirjan zone sasz of iran formed is controversial sasz igneous rocks are mainly intrusive granodiorite to gabbroic bodies which intrude early to middle jurassic metamorphic basement jurassic volcanic rocks are rare here we report the age and petrology of volcanic rocks from the panjeh basaltic andesitic rocks complex in the northern sasz southwest of ghorveh city the panjeh magmatic complex consists of pillowed and massive basalts andesites and microdioritic dykes and is associated with intrusive gabbros the overall sequence and relations with surrounding sediments indicate that this is an unusually well preserved submarine volcanic complex igneous rocks belong to a metaluminous sub alkaline medium k to high k calc alkaline mafic suite characterized by moderate al2o3 13 7 17 6 wt and variable fe2o3 6 0 12 6 wt and mgo 0 9 11 1 wt contents zircon u pb ages 145 149 ma define a late jurassic tithonian age for magma crystallization and emplacement whole rock compositions are enriched in th u and light rare earth elements lrees and are slightly depleted in nb ta and ti the initial ratios of 87sr 86sr 0 7039 0 7076 and end t values 1 8 to 4 3 lie along the mantle array in the field of ocean island basalts and subcontinental metasomatized mantle immobile trace element ti v zr y nb yb th and co behavior suggests that the mantle source was enriched by fluids released from a subducting slab i e deep crustal recycling with some contribution from continental crust for andesitic rocks based the chemical composition of panjeh mafic and intermediate rocks in combination with data for other gabbroic to dioritic bodies in the ghorveh area we offer two interpretations for these and other jurassic igneous rocks of the sasz as reflecting melts from a subduction modified oib type source above a neo tethys subduction zone or b plume or rift tectonics involving upwelling metasomatized mantle mostly reflecting the 550 ma cadomian crust forming event