tectonic interactions between india and arabia since the jurassic reconstructed from marine geophysics ophiolite geology and seismic tomography gondwana breakup since the jurassic and the northward motion of india toward eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the indian and arabian margins here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in nw india and se arabia and seismic tomography of the mantle below the nw indian ocean the north somali and proto owen basins formed due to 160 133 ma n s extension between india and somalia subsequent convergence destroyed part of this crust simultaneous with the uplift of the masirah ophiolites most of the preserved crust in the owen basin may have formed between 84 and 74 ma whereas the mascarene and the amirante basins accommodated motion between india and madagascar east africa between 85 and circa 60 ma and 75 and circa 66 ma respectively between circa 84 and 45 ma oblique arabia india convergence culminated in ophiolite obduction onto se arabia and nw india and formed the carlsberg slab in the lower mantle below the nw indian ocean the nne ssw oriented slab may explain the anomalous bathymetry in the nw indian ocean and may be considered a paleolongitudinal constraint for absolute plate motion nw india asia collision occurred at circa 20 ma deforming the sulaiman ranges or at 30 ma if the hindu kush slab north of the afghan block reflects intra asian subduction our study highlights that the nw india ophiolites have no relationship with india asia motion or collision but result from relative india africa arabia motions instead key points we present a new tectonic model for the evolution of nw indian ocean subducted slab under the carlsberg ridge resulted from arabia india convergence

seismotectonic and seismicity of makran a bimodal subduction zone se iran abstract the present study combined spatial distribution and mechanism of seismicity seismicity parameters geomorphology in satellite imagery and tectonic features in makran inland to show that the makran low angle thrust fault is divided into two separate segments depth dispersal of earthquakes especially relocated events shows that the sinking plate is steeper in the west than in the east of makran significant facts were identified from the variation of moho depth between west and east slip rates of the inland faults and crustal shortenings in the north of makran the sistan suture zone plays a significant role in dividing the overriding plate into a non deforming helmand block and a less deforming lut block these blocks have different resistances against the northward subduction large and great events such as the 1989 chabahar mw 5 5 and 1945 gwadur mw 8 1 occurred in the south of subduction fronts of the western and eastern makran respectively they occurred in shallow depth and were the pieces of evidence of weak and strong coupling between the oceanic and continental crusts on a low angle and a very low angle reverse faults respectively spectral analysis and depth determination of the instrumental and pre instrumental earthquakes respectively helped to separate some plate boundary and intraplate events this separation geometry and non characteristic behavior of the subduction zone revealed from spatial and temporal distribution of the earthquakes probably dedicate a mature aleutian type for the subduction zone in the east missing great m 6 1 earthquakes less slip rate of the continental faults and steeper dipping of the sinking plate in the west probably indicate a kurile type for the iranian part of subduction makran is a bimodal subduction because geomorphological and seismic pieces of evidence indicate a nnw surficial and right lateral fracture zone in the continental crust and a nw deep and left lateral fracture zone in the oceanic crust respectively the fractures and geometry of subductions showed that the eastern makran has seismotectonically a wider area for potential coupling of a larger earthquake than the western makran

basement characterization and crustal structure beneath the arabia eurasia collision iran a combined gravity and magnetic study abstract we present a study on the depth to basement and magnetic crustal domains beneath the iranian plateau by modeling aeromagnetic and gravity data first field processing of the aeromagnetic data was undertaken to estimate the general characteristics of the magnetic basement afterwards inverse modeling of aeromagnetic data was carried out to estimate the depth to basement the obtained model of basement was refined using combined gravity and magnetic forward modeling hereby we were able to distinguish different magnetic domains in the uppermost crust 10 20 km depths influencing the medium to long wavelength trends of the magnetic anomalies magnetic basement mapping shows that prominent shallow magnetic features are furthermore located in the volcanic areas e g the urumieh dokhtar magmatic assemblage the presence of ophiolite outcrops in se iran implies that shallow oceanic crust with high magnetization is the main source of one of the biggest magnetic anomalies in entire iran area located north of the makran

gaw khuni basin an active stepover structure in the sanandaj sirjan zone iran the gaw khuni basin is located in the central part of the sanandaj sirjan zone on the northeastern margin of the zagros orogen this basin is one of the continuous zones of sanandaj sirjan zone basins that is filled by pliocene holocene sediments the gaw khuni basin is surrounded by an en echelon to parallel arrangement of active faults in dextral strike slip fault zones that indicate a right step dilational stepover structure the boundary faults of this basin are the eastern and western gaw khuni ramsheh and nain dehshir faults earthquake distribution determined along the faults dissection and displacement of holocene sediments and also the development of pull apart basins filled with holocene deposits along the faults confirm that these faults are active the gaw khuni stepover was formed during transtensional movements produced between two dextral strike slip faults nain dehshir and ramsheh also the gaw khuni pull apart basin and the eastern and western gaw khuni faults developed in a releasing step between the faults and grew in two directions during the time of their formation

eastern turkish high plateau as a small turkic type orogen implications for post collisional crust forming processes in turkic type orogens abstract post collisional magmatism may be generated by extensive crustal melting in tibet type collisional environments or by falling out of slabs from under giant subduction accretion complexes in turkic type collisional orogens giving rise to decompression melting of the asthenospheric mantle replacing the removed oceanic lithosphere in turkic type post collisional magmatism the magmatic products are dominantly alkalic to peralkalic and greatly resemble those of extensional regions giving rise to much confusion especially in interpreting old collisional orogenic belts such magmatic regions are also host to a variety of economically valuable ore deposits including gold one place in the world where today active turkic type post collisional magmatism is present is the eastern anatolian high plateau produced after the terminal arabia eurasia collision in the late miocene the plateau is mostly underlain by the late cretaceous to oligocene east anatolian accretionary complex which formed south of the rhodope pontide magmatic arc this subduction accretion complex has been further shortening since the collision but it has also since been domed and became almost entirely covered by at least 15 000 km3 of volcanic rocks the volcanic rocks are calc alkalic in the north transitional in the middle and alkalic in the south of the plateau where the crust is thinnest today less than 38 km the volcanics are derived almost entirely from an enriched mantle the ages of the volcanics also become younger from north to south from about 11 ma to possibly 17th century ad we interpret the origin of the magmatic rocks as the result of decompression melting of the asthenospheric mantle sucked towards the exposed base of the east anatolian accretionary complex as the oceanic lithosphere beneath it fell out the lower density of the hot asthospheric material was the cause of the doming we believe that similar processes dominated the post collisional tectonics of such vast turkic type orogens as the altaids of central asia the late devonian early carboniferous lachlan belt in southeastern australia and the pan african collage of northeast afro arabia it is likely that archaean collisions were dominated by turkic type post collisional events rather than tibetan ones that only became common in the proterozoic

rapid assembly and rejuvenation of a large silicic magmatic system insights from mineral diffusive profiles in the kidnappers and rocky hill deposits new zealand abstract the timescales over which magmas in large silicic systems are reactivated assembled and stored remains a fundamental question in volcanology to address this question we study timescales from fe mg interdiffusion in orthopyroxenes and ti diffusion in quartz from the caldera forming 1200 km3 kidnappers and 200 km3 rocky hill eruptions from the mangakino volcanic centre taupo volcanic zone new zealand the two eruptions came from the same source area have indistinguishable 40ar 39ar ages 1 0 ma and zircon u pb age spectra but their respective deposits are separated by a short period of erosion compositions of pumice glass and mineral species in the collective eruption deposits define multiple melt dominant bodies but indicate that these shared a common magmatic mush zone diffusion timescales from both eruptions are used to build on chemical and textural crystal signatures and interpret both the crystal growth histories and the timing of magma accumulation fe mg interdiffusion profiles in orthopyroxenes imply that the three melt dominant bodies established through extraction of melt and crystals from the common source were generated within 600 years and with peak accumulation rates within 100 years of each eruption in addition a less evolved melt interacted with the kidnappers magma beginning 30 years prior to and peaking within 3 years of the eruption this interaction did not directly trigger the eruption but may have primed the magmatic system orthopyroxene crystals with the same zoning patterns from the kidnappers and rocky hill pumices yield consistently different diffusion timescales suggesting a time break between the eruptions of 20 years from core rim zones to 10 years outer rim zones diffusion of ti in quartz reveals similarly short timescales and magmatic residence times of 200 km 3 eruption our data support concepts of large silicic systems being stored as long lived crystal mushes with eruptible melts generated over extraordinarily short timescales prior to eruption

hematite u th he thermochronometry constrains intraplate strike slip faulting on the kuh e faghan fault central iran abstract the kuh e faghan strike slip fault system kff located to the northern edge of the lut block in central iran developed through a neogene quaternary pulsed history of eastward fault propagation and fault related exhumation this system is a consequence of the residual stresses transmitted from the arabia eurasia convergent plate boundary here we integrate structural and textural analysis with new and previously published apatite fission track aft and apatite u th he apatite he results chlorite thermomentry and hematite u th he data from hematite coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late miocene pliocene burial and exhumation associated with the propagation of the kff twenty nine hematite u th he hematite he dates from three striated hematite coated slip surfaces from the kff fault core and damage zone yield individual dates from 12 2 ma petrographic analysis and chlorite thermometry of a polyphase fossil fluid system in the kff fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal t 239 10 c fluids and hematite formation hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics no evidence of hematite comminution and similar hematite he closure temperatures 60 85 c in each sample integration of these results with thermal history modeling of aft and apatite he data shows that kff activity in the late miocene is characterized by an early stage of fault nucleation fluid circulation hematite mineralization and eastward propagation not associated with vertical movement that lasted from 12 to 7 ma hematite he aft and apatite he data track a second phase of fault system activity involving fault related exhumation initiating at 7 ma and continuing until present time our new data constrain the onset of the recognized late miocene pliocene tectonic reorganization in north central iran

systematic changes in orientation of linear mylonitic fabrics an example of strain partitioning during transpressional deformation in north golpaygan sanandaj sirjan zone iran abstract kilometer scale shallowly dipping nw striking top to the ne reverse and dextral strike slip shear zones occur in metamorphic rocks of north golpaygan these metamorphic rocks are exposed at the ne margin of the central part of the sanandaj sirjan zone in the hinterland of the zagros orogen nw striking top to the ne normal shear zones were also found in a small part of the study area structural evidence of three deformation stages were found pre mylonitization metamorphic mineral growth happened during d1 the main mylonitization event was during the d2 deformational event following coaxial refolding synchronous to retrograde metamorphism of amphibolite to greenschist facies in the late cretaceous paleocene and before d3 folding and related mylonitization we documented the systematic changes in the orientations of d2 linear fabrics especially stretching lineations and superimposition relations of structures it is concluded that the dextral strike slip and dip slip shear zones were coeval kinematic domains of partitioned dextral transpression the shallowly dipping reverse and strike slip shear zones are compatible with partitioning in a very inclined transpressional model fabric relations reflect that the top to the ne normal shear zones were not produced during deformation partitioning of inclined dextral transpression the late cretaceous paleocene strain partitioning was followed by later n s shortening and ne extension in the north golpaygan area

reconstructing greater india paleogeographic kinematic and geodynamic perspectives abstract key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of greater india the indian plate lithosphere that subducted since tethyan himalayan continental collision with asia here we discuss this reconstruction from paleogeographic kinematic and geodynamic perspectives and isolate the evolution scenario that is consistent with all three we follow recent constraints advocating a 58 ma initial collision and update a previous kinematic restoration of intra asian shortening with a recently proposed model that reconciles long debated large and small estimates of indochina extrusion our new reconstruction is tested against paleomagnetic data and against seismic tomographic constraints on paleo subduction zone locations the resulting restoration shows 1000 1200 km of post collisional intra asian shortening leaving a 2600 3400 km wide greater india from a paleogeographic sediment provenance perspective eocene sediments in the lesser himalaya and on undeformed india may be derived from tibet suggesting that all greater indian lithosphere was continental but may alternatively be sourced from the contemporaneous western indian orogen unrelated to india asia collision a quantitative kinematic paleomagnetic perspective prefers major cretaceous extension and a greater india basin opening within greater india but data uncertainty may speculatively allow for minimal extension finally from a geodynamic perspective assuming a fully continental greater india would require that subduction rates close to 20 cm yr was driven by a down going lithosphere crust assemblage more buoyant than the mantle which seems physically improbable we conclude that the greater india basin scenario is the only sustainable one from all three perspectives we infer that old pre collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates whilst post collisional continental and young greater india basin lithosphere did not inciting the rapid india asia convergence deceleration 8 myr after collision subsequent absolute northward slab migration and overturning caused flat slab subduction tibetan shortening arc migration and arc volume decrease

petrology geochemistry and tectonics of the sabzevar ophiolite north central iran abstract the sabzevar ophiolite is a highly dismembered ophiolite complex located along the northern boundary of the central iranian microcontinent cim and is one of the internal iranian group of ophiolites and colored melanges the igneous rocks of this complex consist of peridotites harzburgite dunite and lherzolite serpentinite minor pyroxenite gabbros and a volcanic sequence that exhibits a wide range of composition from basalts and basaltic andesites to rhyodacite dacites rhyolites and basanites sedimentary rocks include a variety of upper triassic to lower cretaceous deep and shallow marine rocks these include pelagic fossiliferous carbonates that are mixed with the pillow basalt and basaltic andesite as interlayers or exotic blocks ranging in size from 10 to 100 m also present are extensive units of radiolarian chert which are interbedded within the basalts and basaltic andesites a combination of petrographic observations and analyses of incompatible trace elements and rare earth elements indicates the presence of at least four different types of extrusive rocks in the sabzevar ophiolite the geochemical data clearly identifies some of the extrusive rocks to have formed from three distinct types of basaltic melts i the group 1 basaltic rocks which formed from an initial melt with n morb like lree depleted chemical signatures and are petrogenetically related to the gabbros ii group 2 basaltic rocks which have e morb chemical signatures and iii group 3 basaltic rocks with lree enriched signatures and incompatible trace element patterns that suggest an island arc affinity the data also suggest that the gabbros and the group 1 basaltic rocks are petrogenetically related and produced by fractionation of plagioclase and to a lesser extent clinopyroxene and hornblende similar to other studied iranian ophiolites e g khoy band e zeyarat dar anar neyriz kermanshah and baft the results from the sabzevar ophiolite demonstrate the presence of relics of mid ocean ridge basalt morb like signatures in the extrusive units of neo tethyan ophiolites and suggests that the fossil oceanic lithosphere preserved in these ophiolites developed at an oceanic spreading center in addition the sabzevar ophiolite contains other volcanic rocks that have non morb like geochemical signatures e g within plate island arc the differences between these geochemical signatures could be a result of a differing upper mantle composition or different degrees of partial melting of the same upper mantle the presence of sizable nb anomalies in the extended rare earth element ree patterns for andesites and the group 3 basalts is characteristic of volcanic arc magmas or possibly are products of the ascending magma that was modified by crustal contamination the presences of the basanites and the silica undersaturated rocks could be attributed to extrusive activity following ophiolite emplacement plate reconstructions suggest that rocks of the sabzevar ophiolite were part of the tethyan oceanic crust that was formed during rifting of a narrow but deep seaway that separated the cim from the eurasian plate the ophiolite was emplaced during northeast dipping subduction i e closure of this segment of the tethyan seaway sabzevar ocean

adakite differentiation and emplacement in a subduction channel the late paleocene sabzevar magmatism ne iran this study describes the structural setting petrogenesis and geochronology of a suite of acidic magmatic rocks that are intruded in the metamorphic core of the tertiary ophiolitic suture zone of the sabzevar range ne central iran these intrusive bodies show tabular geometries with solid state fabrics documenting syntectonic emplacement during crustal shortening in the total alkalis silica tas diagram their compositions define a medium k calc alkaline suite spanning from basaltic andesite to the dacite and rhyolite fields they show characteristic low mgo 0 15 0 60 wt and ni 40 ar 39 ar white mica and amphibole geochronology constrains the sabzevar magmatism to the late paleocene at ca 58 ma genesis of the sabzevar magmatic suite is interpreted in terms of prograde wet amphibolite melting during oceanic subduction within a pressure temperature range between a plagioclase out and a hornblende out boundary magma differentiation and high pressure amphibole fractionation of pristine slab melts are proposed as the dominant factors that imparted the adakite signature in the sabzevar structural zone implications in terms of the regional tectonic scenario are discussed and framed within the advancing and retreating evolution of the neotethyan subduction during the mesozoic tertiary time span

large scale sediment underplating in the makran accretionary prism southwest pakistan field relations in the emergent part of the makran accretionary prism show that a mid miocene to early pliocene slope and shelf sedimentary sequence was deposited directly on abyssal plain turbidites without any detectable stratigraphic or structural discordance sedimentological evidence for rapid shoaling however indicates that the underlying sediment column was tectonically thickened by a factor of between two and three during this period this can be explained by large scale underthrusting and underplating of sediment a mode of accretion that is also favored by mass balance considerations the visible deformation in the coastal makran occurred when the region was 70 100 km north of the contemporary prism front

the granite pluton of zahedan se iran a petrological and magnetic fabric study of a syntectonic sill emplaced in a transtensional setting abstract the 32 ma nw se elongate 75 km long granite pluton of zahedan is one of the most conspicuous geological features of southeast iran it is composed of metaluminous to weakly peraluminous rocks corresponding to magnetite and ilmenite bearing i type granitoids ranging from diorites to granites all rocks including the late andesitic to dacitic dykes belong to the high k calk alkaline series field and structural relationships as well as evidence for mixing mingling can be used to unravel the magmatic history of the different rock types microstructural examinations and magnetic fabric measurements were performed on a collection of oriented specimens from the northern part of the pluton ubiquitous flat lying foliations argue in favour of a sill like body except for the diorite the biotite bearing granitic facies at the pluton s periphery was the first batch of magma which initiated the sill this sill probably behaved as a n s directed decollement zone marked by conspicuous magmatic cataclastic microstructures and n s treading lineations the intrusion of the hornblende bearing granodiorite with typical magmatic structures inflated the sill deformation occurred at the same time with e w to nw se stretching marked by lineations the main dioritic stock forming the floor of the sill is considered to be a remnant of the feeder zone an abundant dyke swarm marks the end of the syntectonic emplacement of the zahedan sill a three dimentional model of emplacement is proposed in the context of the latest episodes in the closure of the neo tethys during which the lut block ended its northward migration with respect to the afghan blocks

zagros blueschists episodic underplating and long lived cooling of a subduction zone pressure temperature time p t tp t t trajectories of high pressure rocks provide important constraints to understand the tectonic evolution of convergent margins new field observations and p t tp t t constraints for the evolution of the only known blueschist facies exposure along the zagros suture zone in southern iran are reported here these blueschists now exposed in tectonic windows under the sanandaj sirjan zone upper plate constitute accreted fragments of the tethyan domain during n directed cretaceous subduction three units were identified in the field from top to bottom the ashin unit mafic and felsic gneisses the seghin complex mafic tuffs and ultramafics and the siah kuh massif coherent volcanic edifice microstructural observations p tp t estimates and rb sr deformation ages indicate that the ashin unit possibly underwent burial down to 30 35 km and 550 c along a relatively warm p tp t gradient c 17 km and was ultimately deformed between 85 and 100 ma the seghin complex exhibits remarkably well preserved hp lt assemblages comprising lawsonite glaucophane aragonite omphacite and garnet p t tp t t reconstruction indicates that this slice was subducted down to c 50 km at temperatures of c 500 c along a very cold subduction gradient c 7 km deformation in the seghin complex stopped at around 65 ma close to peak metamorphic conditions field relationships and estimates of the p tp t trajectory followed by the siah kuh volcanic edifice indicate that this massif was lately subducted down to 15 km depth along the same very cold gradient this slice stack represents a well preserved field example i highlighting the existence of transient underplating processes juxtaposing pluri kilometric tectonic slices along the subduction channel and ii imaging the discontinuous down stepping of the active main subduction thrust with ongoing accretion the zagros blueschists also record an apparent cooling of the zagros subduction zone between 90 and 65 ma most likely as a thermal response of a geodynamic perturbation toward the end of the cretaceous

3 d velocity structure of the 2003 bam earthquake area se iran existence of a low poisson s ratio layer and its relation to heavy damage abstract to understand the generation mechanism of the bam earthquake mw 6 6 we studied three dimensional v p v s and poisson s ratio structures in the bam area by using the seismic tomography method we inverted accurate arrival times of 19490 p waves and 19015 s waves from 2396 aftershocks recorded by a temporal high sensitivity seismic network the 3 d velocity structure of the seismogenic region was well resolved to a depth of 14 km with significant velocity variations of up to 5 the general pattern of aftershock distribution was relocated by using the 3 d structure to delineate a source fault for a length of approximately 20 km along a line 4 5 km west of the known geological bam fault this source fault dips steeply westward and strikes a nearly north south line the main shallow cluster of aftershocks south of the city of bam is distributed just under the minor surface ruptures in the desert the 3 d velocity structure shows a thick layer of high v s and low minimum 0 20 at a depth range of 2 6 km the deeper layer with a thickness of about 2 km appears to have a low v s and high maximum 0 28 from 6 km depth beneath bam to a depth of 9 km south of the city the inferred increase of poisson s ratio from 2 to 10 km in depth may be associated with a change from rigid and sio 2 rich rock to more mafic rock including the probable existence of fluids the main seismic gap of aftershock distribution at the depth range of 2 to 7 km coincides well with the large slip zone in the shallow thick layer of high v s and low the large slip propagating mainly in the shallow rigid layer may be one of the main reasons why the bam area suffered heavy damage

mineralogy hydrothermal alteration fluid inclusion and o h stable isotopes of the siah jangal sar kahno epithermal gold deposit se iran abstract siah jangal sar kahno deposit is located in the northern part of taftan volcano in the sistan and balouchestan provinces southeast of iran and is an example of a vein type epithermal gold system with related stockwork and shear zone mineralization the veins are hosted by flysch facies rocks of the makran zone and subvolcanic dioritic porphyry the ne sw fault systems played an essential role in the genesis of alteration and mineralization in the area diorite porphyry ranges from alkali na2o k2o content of 4 1 6 66 wt and plot in the calc alkaline to high k calc alkaline fields the chondrite normalized ree patterns for least altered porphyry diorite rocks altered host rocks and silica carbonate vein show a lree hree ratios of 10 40 4 03 4 00 and 2 66 respectively positive eu anomalies in the silica carbonate veins indicate the ca bearing minerals such as plagioclase decomposition causing release of eu into hydrothermal fluid and subsequent precipitation in silica carbonate veins mineralization consist of quartz adularia calcite pyrite arsenopyrite marcasite fe poor sphalerite galena chalcopyrite and native gold later supergene mineral assemblages consists of fe oxide and hydroxides covellite cerussite and scorodite hydrothermal alteration is generally well developed enveloping the ore bearing hydrothermal breccia and subdivided into prograde inner quartz chlorite pyrite muscovite and outer argillic alteration zones with a regional barren widespread near surface supergene blanket advanced argillic alteration zone chemical discrimination by means of cationic r1 r2 diagram indicates that r1 increases whereas r2 decreases with increasing argillic alteration microthermometry of fluid inclusions in quartz crystals from silica carbonate vein show the homogenization temperatures thv l of 167 332 c with salinities in the range of 0 21 4 24 wt nacl eq the o and h isotopic compositions of quartz from hydrothermal vein and argillic alteration simply show a low sulfidation epithermal environment with meteoric waters as the main fluid due to a narrow range in salinity of the fluids very low sulfide diversity sulfide volume and presence of adularia suggest dominantly meteoric water in the deposit supporting classification as a low sulfidation epithermal system

nature of the plate contact and subduction zones diversity abstract in recent studies we showed that the nature of the plate contact in subduction zones is an important physical feature in both oceanic lithospheric subduction and continental collision we investigated two fundamental states of the plate contact one based on a fault and the other based on a subduction channel using geodynamic modeling we determined the speci c signatures of both states of the subduction contact we established that the nature of the plate contact influences the dynamic response of the overriding and subducting plate and is one of the controlling factors whether back arc extension develops or not in the present study we combine results of our previous numerical experiments with a re analysis of published observations overall our synthesis connects seismic moment release with back arc deformation and tectonic processes at the margin it leads us to identify four classes of subduction zones the rst two classes result directly from our numerical experiments in class 1 subduction zones are characterized by a plate contact that is largely fault like with an accretionary margin in class 2 the plate contacts are largely channel type and have an erosive margin class 3 where the plate contact is entirely channel like consists of accretionary margins with a high sediment supply subduction zones of class 4 mostly characterized by an erosive convergent margin northern chile peru honshu and kuril are more complicated they can be explained by incorporating regional observations

rare earth elements geochemistry in springs from taftan geothermal area se iran abstract concentrations of rare earth elements rees were determined in springs and andesitic dacitic rocks of taftan geothermal field hydrochemical results of major ions indicate that thermal springs are na so 4 cl and ca so 4 cl types concentrations of rees are in ranges of 10 4 to 1 2 and 49 to 62 times of chondrite for springwater and rock samples respectively the thermal sts and tts and the cold aps springs with low ph values exhibit a very high ree contents 0 64 to 3 15 mg l saturation index indicates that fe and al phases can control dissolved ree concentration in fts and pf cold springs the speciation of ree complexes indicates dominant presence of lnso 4 and free ion in the taftan thermal springs in aps cold spring with ph 4 fluoride complexes are dominate over the free ion and sulfate species while in pf and fts cold springs with ph 6 4 and 7 respectively carbonate complexes lnco 3 are predominant species chondrite normalized pattern for the low ph waters show very distinctive gull wing patterns characteristic feature of acid sulfate geothermal systems and are similar to those of the host rocks chemical characteristics of rare earth elements in spring and volcanic rock samples indicate that rees are originated from the andesitic dacitic host rocks whole rock normalized ree patterns and petrographic evidences show that rare earth elements leached mainly from marginal alteration of minerals and matrix decomposition in volcanic rocks in chondrite normalized ree patterns significant negative eu anomaly in the cold springs compare to the thermal and acidic springs indicates that alteration of plagioclase is more intense in the later corresponding to increasing in temperature and acidic state of reactant water

geochemical characteristics 40ar 39ar ages and original tectonic setting of the band e zeyarat dar anar ophiolite makran accretionary prism s e iran abstract the makran accretionary prism in southeastern iran contains extensive mesozoic zones of melange and large intact ophiolites representing remnants of the tethys oceanic crust that was subducted beneath eurasia to the north of the makran accretionary prism lies the jaz murian depression which is a subduction related back arc basin the band e zeyarat dar anar ophiolite is one of the ophiolite complexes it is located on the west side of the makran accretionary prism and jaz murian depression and is bounded by two major fault systems the principal rock units of this complex are a gabbro sequence which includes low and high level gabbros an extensive sheeted diabase dike sequence late intrusive rocks which consist largely of trondhjemites and diorites and volcanic rocks which are largely pillow basalts interbedded with pelagic sedimentary rocks including radiolarian chert chondrite and primitive mantle normalized incompatible trace element data and age corrected nd pb and sr isotopic data indicate that the band e zeyarat dar anar ophiolite was derived from a midocean ridge basalt like mantle source the isotopic data also reveal that the source for basalts was indian ocean type mantle based on the rare earth element ree data and small isotopic range all the rocks from the band e zeyarat dar anar ophiolite are cogenetic and were derived by fractionation from melts with a composition similar to average e morb fractionation was controlled by the removal of clinopyroxene hornblende and plagioclase three 40ar 39ar plateau ages of 140 7 2 2 142 9 3 5 and 141 7 1 0 ma and five previously published k ar ages ranging from 121 4 to 146 5 ma for the hornblende gabbros suggest that rocks from this ophiolite were formed during the late jurassic early cretaceous plate reconstructions suggest that the rocks of this complex appear to be approximately contemporaneous with the masirah ophiolite which has crystallization age of 150 ma like masirah the rocks from the band e zeyarat dar anar ophiolite complex represent southern tethyan ocean crust that was formed distinctly earlier than crust preserved in the 90 100 ma bitlis zagros ophiolites including the samail ophiolite

the transition between makran subduction and the zagros collision recent advances in its structure and active deformation south east iran is the site of a rare case of young transition between subduction and collision we synthesized recent results in geodesy tectonics seismology and magnetism to understand the structure and kinematics of the zagros makran transition surface observations tectonics magnetism and geodesy draw a transpressive discontinuity consisting of several faults striking obliquely to the convergent plate motion whereas deeper observations seismology support a smooth transition across the fault system no lithospheric transform fault has been created even though the transition already behaves like a major boundary in terms of tectonic style seismic structure lithology and magnetism the zendan minab palami fault system consists of several faults that accommodate a transpressive tectonic regime it is the surface expression of a southward propagation of the n trending right lateral strike slip fault system of jiroft sabzevaran within each system the numerous faults will coalesce into a single lithospheric wrench fault

biostratigraphic zonation and 40ar 39ar ages for the neotethyan khoy ophiolite of nw iran abstract the khoy ophiolite in northwestern iran represents a piece of oceanic lithosphere formed in the mesozoic neotethys this ophiolite consists from bottom to top of well defined basal metamorphic rocks peridotites gabbros and a variety of upper to lower cretaceous deep marine rocks these include pelagic fossiliferous carbonates and basalts as interlayers or exotic blocks four hornblende separates from gabbros and amphibolites give values from 108 to 111 ma the results from microfossil studies show the presence of late cretaceous e g marginotruncana globotruncana and middle to late eocene e g globorotalia orbulonoides planktonic foraminifera the data suggest that although the initial rifting and crystallization of the oceanic crust of the khoy ophiolite began in the late albian the volcanic activities continued through to the late eocene time another possibility for such variation of lithofacies and biofacies and disturbances in the fossil record may be the result of bioturbation and transportation and rapid changes of depositional conditions during eruption of the basaltic lava flows pelagic sediments alone have been listed and of the foraminiferas the first three are planktonic as would be expected only orbulonoides is a benthic form and aberrant the third possibility is that the khoy ophiolite may represent a classic supra subduction type ophiolite where volcanic members of the different parts of oceanic environment e g morb volcanic arc ocean island are now juxtaposed

the origin of changes in structural style across the bandar abbas syntaxis se zagros iran abstract the bandar abbas syntaxis marks the transition between the zagros collisional belt and the makran subduction related prism and constitutes a major structural feature within the alpine himalayan mountain belt within the foreland part of the zagros the zagros fold thrust belt zftb the transition is marked by a sudden change in structural trends and style and a rapid decrease in seismicity and salt diapirism from west to east of the syntaxis the depth to decollement and lithology affect the geometry and size of the folds on each side of the syntaxis while different mechanical coupling along the basal decollement affects the degree of internal rock deformation thus the short and broad folds of the western side of the syntaxis are decoupled along the 8 km deep hormuz evaporites visible at surface in numerous salt diapirs strong seismicity in this area suggests that the basement is involved in the deformation by contrast the long and narrow folds of the eastern side of the syntaxis appear to be controlled by frictional slip along a 6 km deep detachment the absence of seismicity suggests that the basement is not involved in the deformation in this area we propose that the basal decollement for these structures corresponds to the eroded top of the nne ssw trending oman mesozoic nappes resulting from late cretaceous obduction of tethys on the arabian margin these structures are visible onshore in the northern tip of the oman peninsula and seen in offshore seismic profiles continuing northward beneath the strait of hormuz finally map view observations show that the main zagros thrust and the zendan fault separating the zftb from the internal zones of the orogen are shallow low angle thrust faults rather than steeply dipping faults

magnesium isotopic systematics of the makran arc magmas iran implications for crust mantle mg isotopic balance abstract continental crust loses mg by lower crustal foundering and chemical weathering to become its intermediate silicic composition both processes should preferentially retain heavy mg isotopes in the crust yet the estimated mg isotopic ratio for the bulk continental crust is indistinguishable from that for unmodified mantle this can be elucidated by two notions that are not mutually exclusive i the basaltic parent to the crust has mg isotopes lighter than the mantle and has since become mantle like as a result of mg loss by igneous and weathering fractionation and ii heavy mg isotopes in the continental crust are constantly balanced by a hidden input of light mg isotopes arc magmas are arguably building blocks of the continental crust and their mg isotopic signature could be used to place limits on the above views here we conducted a mg isotopic study of the makran arc a rare continental arc in iran within the alpine himalayan orogenic belt the measured mg isotopic ratios for most mafic and intermediate samples are mantle like with 26mg values ranging from 0 32 to 0 20 after excluding dubious samples affected by alteration the silicic samples span a broad range of isotopic ratios with 26mg values ranging from 0 32 to 0 32 beyond that of unmodified mantle 26mg 0 25 0 04 the isotopic data form a trend from mantle like 26mg at relatively high mgo towards elevated 26mg at low mgo requiring the isotopic variability be related to differentiation in an open system involving assimilation of high 26mg crustal rocks our results are generally consistent with mg isotopic data compiled for global arcs where magmas have mg isotopic ratios ranging from mantle like to 0 7 per mil above the mantle range and compositions substantially below that range are rare thus heavy mg isotopes in the continents predicted by igneous and weathering fractionation might have been compensated by a hidden input of light mg isotopes which is presumably in the form of carbonates leading to a bulk crustal mg isotopic composition that is mantle like

early cretaceous migmatitic mafic granulites from the sabzevar range ne iran implications for the closure of the mesozoic peri tethyan oceans in central iran terra nova 22 26 34 2010 abstract the ophiolitic melange of the sabzevar range northern iran is a remnant of the mesozoic oceanic basins on the northern margin of the neotethys that were consumed during the arabia eurasia convergence history occurrence of km scale dismembered mafic hp granulitic slices is reported in this study granulites record an episode of amphibole dehydratation melting and felsic tonalite throndhjemite melt segregation at c 1 1 gpa and 800 c in situ u th pb geochronology of zircon and titanite grains hosted in melt segregations points to an early cretaceous albian age for the metamorphic climax results of this study i impose reconsideration of the current palaeotectonic models of the neothetyan convergent margin during the early cretaceous and ii argue that punctuated events of subduction of short lived back arc oceanic basins accompanied the long lasting history of the neotethyan subduction in the region

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

magmatic evolution and porphyry epithermal mineralization in the taftan volcanic complex southeastern iran abstract the taftan volcanic complex is located above the makran subduction zone in sistan and baluchestan province southeastern iran the earliest volcanic activity at taftan started in the late miocene 8 ma with eruption of andesitic to dacitic lava onto a cretaceous to eocene volcanic and sedimentary paleosurface 20 km to the northwest of the current volcanic edifice later plio pleistocene volcanism consisted of voluminous andesitic and dacitic lavas and pyroclastic flows 3 1 to 0 4 ma taftan and the neighbouring bazman volcano are the southeasternmost and youngest manifestations of arc related volcanism in iran which began with the eocene miocene urumieh dokhtar magmatic arc udma in northwest and central iran and extends into western pakistan chagai arc major porphyry cu mo au deposits are associated with miocene to pliocene intrusive rocks in the kerman section of the eocene neogene urumieh dokhtar magmatic arc in southeastern iran e g sar cheshmeh meiduk and at reko diq and saindak in the late cretaceous quaternary chagai arc in western pakistan in a gap of 300 km between these two belts several porphyry and epithermal prospects are exposed in the miocene pliocene sections of the taftan volcanic complex including the kharestan 6 10 0 80 ma and bidester porphyry epithermal cu au deposits 4 3 ma and the siah jangal epithermal au deposit late miocene in addition several argillic to advanced argillic and fumarolic alteration zones occur in plio pleistocene volcanic rocks around the current volcanic edifice these deposits have received limited exploration electron microprobe analyses of amphibole magnesio hastingsite phenocrysts and magnetite ilmenite mineral pairs from the taftan and bazman volcanic rocks indicate a change of crystallization temperature and magmatic oxidation state from 1000 c and fmq 1 in andesitic rocks to 900 c and fmq 2 in dacitic rocks magmatic water content was 4 wt as indicated by the ubiquitous presence of amphibole phenocrysts major and trace element compositions of the taftan and bazman volcanic rocks show calc alkaline to high k calc alkaline affinity with relative depletions of nb ta and ti and enrichments of large ion c elements lile th and u on normalized diagrams these trace element patterns including listric shaped normalized rare earth element profiles and relatively high sr y and la yb ratios are similar to those of fertile miocene igneous rocks from the kerman belt and chagai arc and suggest that the taftan suite in particular should be prospective for porphyry cu ore formation regionally there is no clear geochemical difference between the neogene kerman belt rocks which are thought to post date the onset of collision between the afro arabian and eurasian plates late oligocene to earliest miocene and the subduction related bazman taftan and chagai belt magmas the porphyry deposits formed in these distinct settings are also virtually indistinguishable this suggests that most of the processes affecting the geochemistry and metallogeny of the magmas in both settings take place in the lithosphere albeit that the ultimate source of the magmas is in the supra subduction zone asthenospheric mantle wedge in collisional environments subduction related material previously crystallized in the deep lithosphere is simply being remobilized

successive shifts of the india africa transform plate boundary during the late cretaceous paleogene interval implications for ophiolite emplacement along transforms abstract the arabian sea in the nw indian ocean is a place where two major transform boundaries are currently active the owen fracture zone between india and arabia and the owen transform between india and somalia these transform systems result from the fragmentation of the india africa transform boundary which initiated about 90 myrs ago when the india seychelles block separated from madagascar to move towards eurasia therefore the geological record of the arabian sea makes it possible to investigate the sensitivity of a transform system to several major geodynamic changes here we focus on the evolution of the india africa transform system during the 47 90 ma interval we identify the late cretaceous 90 65 ma transform plate boundary along chain ridge in the north somali basin from 65 to 42 47 ma the india africa transform is identified at the chain fracture zone which crossed both the owen basin and the north east oman margin finally the transform system jumped to its present day location in the vicinity of the owen ridge these shifts of the india africa boundary with time provide a consistent paleogeographic framework for the emplacement of the masirah ophiolitic belt which constitutes a case of ophiolite emplaced along a transform boundary the successive locations of the india africa boundary further highlight the origin of the owen basin lithosphere incoming into the makran subduction zone

the owen ridge uplift in the arabian sea implications for the sedimentary record of indian monsoon in late miocene abstract the pelagic cover of the owen ridge in the arabian sea recorded the evolution of the indian monsoon since the middle miocene the uplift of the owen ridge resulted from tectonic processes along the previously unidentified miocene india arabia plate boundary based on seismic reflection data tied with deep sea drilling to track the miocene india arabia plate boundary we propose a new timing for the uplift of the owen ridge and highlight its impact on the record of climate changes in pelagic sediments the new dataset reveals a fracture zone east of the owen ridge corresponding to the fossil plate boundary and documents that the main uplift of the owen ridge occurred close to 8 5 ma and is coeval with a major uplift of the east oman margin late miocene deformation at the india arabia plate boundary is also coeval with the onset of intra plate deformation in the central indian ocean suggesting a kinematic change of india and surrounding plates in the late miocene the uplift of the owen ridge above the lysocline at 8 5 ma accounts for a better preservation of globigerina bulloides in the pelagic cover previously misinterpreted as the result of a monsoon intensification event

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 magmatic record in the arghash region northeast iran and tectonic implications the area of arghash in northeast iran promi nent for its gold mineralization was newly mapped on a scale of 1 20 000 with particular attention to the occurring generations of igneous rocks in addition geochronological and geochemical investigations were carried out the oldest geological unit is a late precambrian hornblende bearing diorite pluton with low k composition and primi tive isotope signatures this diorite u pb zircon age 554 6 ma is most likely a remnant from a peri gondwana island arc or back arc basin about one third of the map area is interpreted as an upper cretaceous mag matic arc consisting of a volcanic and a plutonic part the plutonic part is represented by a suite of hornblende bearing medium k i type granitoids minor diorite mainly quartz monzodiorite and granodiorite dated at 92 8 1 3 ma u pb zircon age the volcanic part comprises medium k andesite dacite and tuffitic rocks and must be at least slightly older because it is locally affected by contact metamorphism through the hornblende grani toids the upper cretaceous arc magmatism in the arg hash massif is probably related to the northward subduction of the sabzevar oceanic basin which holds a back arc position behind the main neotethys subduction front small occurrences of pillow basalts and sediments sandstone conglomerate limestone tectonically interca lated in the older volcanic series may be relics of earlier cretaceous or even pre cretaceous rocks in the early cenozoic the cretaceous magmatic arc was intruded by bodies of felsic weakly peraluminous granite u pb zircon age 55 4 2 3 ma another strong pulse of magmatism followed slightly later in the eocene producing large masses of andesitic to dacitic volcanic rocks the geo chemistry of this prominent eocene volcanism is very distinct with a high k signature and trace element contents similar to shoshonitic series high p zr cr sr and ba high sr y ratios feature affinities to adakite magmas the eocene magmatism in the arghash massif is interpreted as related to thermal anomalies in crust and mantle that developed when the sabzevar subduction system collapsed the youngest magmatic activities in the arghash massif are lamprophyres and small intrusions of quartz monzo diorite porphyries which cut through all other rocks including an oligocene miocene conglomerate cover series

exhumation of the west central alborz mountains iran caspian subsidence and collision related tectonics crystallization and thermal histories of two plutons in the west central alborz also elburz elburs mountains northern iran are combined with crosscutting relations and kinematic data from nearby faults to determine the cenozoic tectonic evolution of this segment of the youthful euro arabian collision zone u pb 40 ar 39 ar and u th he data were obtained from zircon biotite k feldspar and apatite the akapol pluton intruded at 56 2 ma cooled to 150 c by ca 40 ma and stayed near that temperature until at least 25 ma the nearby alam kuh granite intruded at 6 8 0 1 ma and cooled rapidly to 70 c by ca 6 ma these results imply tectonic stability of the west central alborz from late eocene to late miocene time consistent with miocene sedimentation patterns in central iran elevation correlated u th he ages from the akapol suite indicate 0 7 km m y exhumation between 6 and 4 ma and imply 10 km of alborz uplift that was nearly synchronous with rapid south caspian subsidence suggesting a causal relation uplift south caspian subsidence and subsequent folding reversal of alborz strike slip from dextral to sinistral and eastward extrusion of central iran coarse zagros molasse deposition dead sea transform reorganization red sea oceanic spreading and north and east anatolian fault slip all apparently began ca 5 2 ma suggesting a widespread tectonic event that we infer was a response to buoyant arabian lithosphere choking the neo tethyan subduction zone

sandstone petrology and geochemistry of the oligocene early miocene panjgur formation makran accretionary wedge southwest pakistan implications for provenance weathering and tectonic setting abstract the oligocene early miocene panjgur formation is comprised of submarine fan and abyssal plain turbidites deposited within the makran subduction complex sandstones of the formation are litharenite to feldspathic litharenite petrographic data indicates a quartzose recycled provenance dominated by plutonic and metamorphic fragments major elements concentrations reveal a moderate level of mineralogical maturity and high values of chemical proxy of alteration cpa 88 29 coupled with a high th u ratio 9 37 which reveals intense weathering in the source area the zr nb y and th concentrations are comparable to upper continental crust ucc values and trends in th cr th co and cr zr ratios support contribution from a felsic source however enrichment in ni and cr reinforced by trends in ni co cr v v ni and y ni ratios reveals mixing of the felsic source with mafic ultramafic source terrains tectonic discrimination plots suggest continental arc to active continental margin setting this study supports the katawaz delta panjgur submarine fan model and upholds the initial southward transport of predominantly felsic detritus from the himalayan orogenic belt controlled by the chaman ornach nal transform fault system this study further adds that the bela muslimbagh ophiolites associated melanges and the west pakistan fold thrust belt from the east and the chagai raskoh volcanic arc from the west were also concurrently shedding mafic ultramafic detritus to the basin and that the depositional system in the makran region turned westward roughly parallel to the present active margin of the makran accretionary wedge

tectonic magmatic and metallogenic evolution of the tethyan orogen from subduction to collision abstract this paper reviews the tectonic magmatic and metallogenic history of the tethyan orogen from the carpathians to indochina focus is placed on the formation of porphyry cu mo au deposits as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region relatively little is known about the history of the paleotethys ocean which opened and closed between gondwana and eurasia in the paleozoic and few ore deposits are preserved from this period the neotethyan ocean opened in the permian early triassic as the cimmerian continental fragments the cores of turkey iran tibet and indochina rifted from the northern gondwana margin and drifted northwards these microcontinents docked with the eurasian margin at various points in the mesozoic and cenozoic and formed a complex archipelago involving several small back arc basins and remnants of the paleotethyan ocean the main neotethyan ocean and these smaller basins were largely eliminated by collision with india and africa arabia in the early eocene and early mid miocene respectively although neotethyan subduction continues beneath the hellenic arc and the makran the majority of porphyry type deposits are found in association with neotethyan subduction mainly in the mesozoic and paleogene and syn to post collisional events in the mid paleogene to neogene they are found throughout the orogen but some sections are particularly well endowed including the carpathians balkans rhodopes eastern turkey lesser caucasus nw iran se iran sw pakistan southern tibet and se tibet indochina other sections that appear barren may reflect deeper levels of erosion young sedimentary cover or lack of exploration although there may also be real reasons for low prospectivity in some areas such as minimal subduction e g the western mediterranean region or lithospheric underthrusting as proposed in western tibet over the last decade improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction related are in fact broadly collision related some forming in back arc settings in advance of collision some during collision and others during post collisional processes such as orogenic collapse and or delamination of subcontinental mantle lithosphere while the formation of subduction related porphyries is quite well understood collisional metallogeny is more complex and may involve a number of different processes or sources these include melting of orogenically thickened crust previously subduction modified lithosphere including metasomatized mantle underplated mafic rocks or lower crustal arc plutons and cumulates or upwelling asthenosphere e g in response to delamination slab breakoff back arc extension or orogenic collapse the most fertile sources for syn and post collisional porphyry deposits appear to be subduction modified lithosphere because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events and retain the oxidized and relatively metalliferous character of the original arc magmatism unusually metallically enriched lithospheric sources do not seem to be required but the amount of residual sulfide phases in these rocks may control metal ratios e g cu au in subsequent magmatic hydrothermal ore deposits relatively au rich deposits potentially form in these settings as observed in the carpathians e g rosia montan turkey kisladag copler and iran sari gunay dalli although the majority of syn and post collisional porphyries are cu mo rich and resemble normal subduction related deposits e g in the gangdese belt of southern tibet this similarity extends to the associated igneous rocks which being derived from subduction modified sources largely retain the geochemical and isotopic character of those original arc magmas while still retaining a broadly calc alkaline character these rocks may extend to mildly alkaline shoshonitic compositions and may display adakite like trace element signatures high sr y and la yb ratios reflecting melting of deep crustal garnet amphibolitic sources but they are otherwise hard to distinguish from normal subduction related magmas small post collisional mafic alkaline volcanic centers are common throughout the orogen but for the most part appear to be barren however similar rocks in other post subduction settings around the world are associated with important alkalic type porphyry and epithermal au cu deposits and the potential for discovery of such deposits in the tethyan orogen should not be overlooked

review of platinum group element distribution and mineralogy in chromitite ores from southern iran abstract the platinum group element pge potential of four chromite mining districts in southern and south eastern iran was investigated using geochemical and mineralogical methods a total of 20 mines and prospects were sampled in the neyriz ophiolite the abdasht and sikhuran complexes in the esfandagheh district and the faryab district chromitite and dunite were analysed for major trace element and pge geochemistry and the platinum group element mineralogy pgm in all mining districts chromites analysed from mantle tectonite probable transition zone and cumulate zone chromitites are refractory low in tio2 pge concentrations range from 5000 ppb with median values around 200 ppb in all complexes investigated the 187os 188os isotope ratios of chromitite indicate chondritic to slightly suprachondritic initial os mantle normalised pt ir ratios are generally low in the sikhuran complex pods of sulphide bearing chromitite 0 2 1 2 sulphides occur in a dunite zone interpreted as an ultramafic cumulate zone chromites in chromitite are characterised by high cr 75 81 and intermediate mg numbers 45 65 in associated dunite chromites cr 74 80 are more fe rich mg 29 50 chromitite and dunite carry up to 5 2 ppm total pge and are characterised by high normalised pt ir up to 5 pt pd large degrees of partial melting in a supra subduction zone geotectonic setting probably in a two stage melting process produced boninitic melts that crystallised refractory cr mg rich and ti poor chromite in some cases sulphide saturation was achieved during and after chromite formation saturation during chromite crystallisation is evidenced by ni cu rich sulphide droplets preserved in some chromitites sulphur saturation after chromite crystallisation governed the formation of ni rich sulphide liquids that exsolved monosulphide solid solution which later crystallised to form pge bearing pentlandite platinum and pd did not partition into pentlandite but crystallised as pt and pd rich pgm associated with the pentlandite

correlation of fluvial terraces and temporal steady state incision on the onshore makran accretionary wedge in southeastern iran insight from channel profiles and 10be exposure dating of strath terraces we describe and summarize the geomorphology of fluvial terraces along the four major rivers draining the central onshore makran accretionary wedge in iran and describe uplifted marine terraces on the coast of this region thirty five strath terraces at different sites were dated using in situ produced cosmogenic 10 be concentrations from surfaces and depth profiles these new measurements reveal abandonment ages between ca 15 and 380 ka the age distribution allows determining the chronology of terrace levels and establishing regional correlations between two major regional levels the geographically widespread correspondence suggests that these two levels result from a regional climatically driven force systematic dating also provides evidence for time and spatial variations in incision rate which enables distinguishing between a regionally uniform incision rate of 0 3 0 4 mm a and higher local incision and or uplift 0 8 mm a rates these spatial changes are consistent with where localized tectonic activity is recognized in the field we also dated using 14 c in shells four uplifted marine terraces on the coast of the study area comparing incision rates derived from strath terraces 0 3 mm a with published uplift estimates from marine terraces 0 2 mm a reveals that fluvial rivers responded to a regional long term incision and surface uplift pattern this rate reflects the tectonically steady state of the wedge on a regional scale locally high incision rates delineate active faults and folds indicating that perfect steady state is unlikely on short length scales

present day strain distribution across the minab zendan palami fault system from dense gps transects summary the strait of hormuz area is a transition zone between the continental collision of the zagros west and the subduction of an oceanic part of the arabian plate beneath the makran wedge east geology and recent gps measurements indicate that about 15 mm yr 1 of relative motion in n10 e direction is accommodated by two major fault systems 1 the nnwtrending minab zendan palami mzp fault system that connects the main zagros thrust mzt to the inner makran thrust system and the frontal subduction thrust and 2 the n trending sabzevaran kahnuj jiroft skj fault system that bounds the jazmurian depression to the west we use dense gps measurements along four transects across these fault systems in order to determine the strains spatial distribution the northern gps transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses about 10 and 7 3 mm yr 1 in n10 direction across the mzp and skj fault systems respectively for both fault systems the elastic deformation spreads over shear zones that are several tens of kilometres wide however transects located close to latitude 27 n reveal a much narrower shear zone 10 km for the mzp fault system moreover we confirm that most of the present day strain is transferred towards the frontal subduction thrust rather than towards the inner makran thrusts in order to complement this new gps velocity field with spatially dense measurements we processed a set of ers radar images by the radar interferometry insar technique we used both a stacking and a persistant scatterers approach to differentiate the ground deformation signal which spatial gradient is expected to be very low from the atmospheric signal results from these interferograms appear to be relatively in agreement with the gps determined strain distribution nevertheless they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram finally we use a purely kinematic block model inversion process to calculate slip rates and locking depths for each fault system from our gps measurements these models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m so we may wonder if the mzp fault system is not late in the interseismic phase of its earthquake cycle

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

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

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

composite ferromagnetic fabrics magnetite greigite measured by ams and partial aarm in weakly strained sandstones from western makran iran summary we present examples of composite magnetic fabrics ams and partial aarm in five sites from the western makran accretionnary prism these rocks are weakly strained sandstones of mio pliocene age rock magnetic investigations show a large occurrence of magnetite and also some greigite at two sites partial anhysteretic remanent magnetization coercivity spectra reveal that grain size is not homogeneous suggesting several grain fractions ams foliations are close to bedding except at one greigite bearing site where ams foliation is almost perpendicular to bedding soft aarm 0 50 mt foliations are slightly oblique both to bedding and ams foliation surprisingly hard aarm 50 100 mt foliations are perpendicular to bedding comparison of two limbs of one fold suggests that ams foliations are pre tilting while hardaarm foliations are post tilting corrected degree of anisotropy parameters display similar trends for all sites p 1 04 p 1 11 p hardaarm 1 19 we suggest that ams soft aarm and hard aarm reflect distinct magnetic grain populations however a possible relationship between hard aarm and a component of natural remanent magnetization is possible our study shows that two orthogonal fabrics exist in these weakly strained rocks coarse grains are parallel to bedding while fine grains are aligned perpendicular to bedding

magma origins and geodynamic implications for the makran chagai arc from geochronology and geochemistry of bazman volcano southeastern iran abstract bazman is an isolated voluminous 3497 m elevation 300 km2 composite volcano that is located within the western segment of the makran chagai arc this arc obliquely tracks the modern ew trending trench offshore the oman sea coast of iran and pakistan with several quaternary stratovolcanoes bazman and taftan in se iran and kuh i sultan in western pakistan superimposed on a preexisting neogene arc high spatial resolution and high sensitivity u pb geochronology using secondary ionization mass spectrometry sims yielded four clusters of zircon ages for bazman volcanic rocks which range from ca 8 6 ma to 41 ka lava and pyroclastic materials erupted between 8 6 and 5 9 ma forming a thick neogene volcanic succession ngv these deposits were intruded by hypabyssal andesite dacite domes at ca 4 1 ma the next younger group of the quaternary bazman center comprises several eruptive pulses at 1 37 ma 1 13 ma 0 943 ma 0 853 ma and 0 635 ma which constructed the main edifice around a central vent through alternating eruptions of lava and pyroclastic rocks qtv and qa2 subsequently ignimbrite flows also sourced from the main vent erupted at 0 59 and 0 47 ma and covered the earlier erupted deposits the youngest dated eruptive phase qa3 comprises the emplacement of dacitic to andesitic lava around the top of volcano based on uranium series 238u 230th disequilibrium in qa3 zircons model ages of ca 41 ka define a maximum eruption age of these lavas which tapped a long lived magma reservoir with zircon crystallization ages predating eruption by 10 s to 100 s of ka low medium k calc alkaline basaltic andesitic eruptions formed parasitic cones located on northeastern flanks of the edifice as the youngest unit qa4 of bazman both neogene and quaternary rocks from bazman volcano exhibit homogeneous trace element characteristics including enrichments in large ion lithophile elements lile and light rare earth elements lree relative to the high field strength elements hfse and heavy rare earth elements hree respectively high th yb and negative anomalies of ta nb and ti are consistent with an enriched mantle source in a continental subduction zone trace element modeling for the most primitive basalts erupted at bazman suggests an origin of parental magmas through 15 partial melting of an enriched spinell lherzolite mantle whereas the genesis of bazman acidic volcanic rocks with sio2 62 involves partial melting in the middle lower continental crust which became subsequently overprinted through assimilation fractional crystallization afc processes compositional continuity of quaternary bazman volcanic rocks with their neogene precursors implies a steady magma source above the subducted oman slab consequently subduction geometry in the makran chagai arc has experienced little modification over the past few million years

temporal spatial distribution and tectonic setting of porphyry copper deposits in iran constraints from zircon u pb and molybdenite re os geochronology abstract porphyry copper deposits pcds in iran are dominantly distributed in arasbaran nw iran the middle segment of the urumieh dokhtar magmatic arc udma and kerman central se iran with minor occurrences in eastern iran and the makran arc this paper provides a temporal spatial and geodynamic framework of the iranian porphyry cu mo au systems based on geochronologic data obtained from zircon u pb and molybdenite re os dating of host porphyritic rocks and molybdenites in 15 major pcds the dating results define a long metallogenic duration 39 6 ma and suggest a long history of tectonic evolution from the accretionary orogeny related to early cenozoic closure of the neo tethys ocean to subsequent collisional orogeny for the iranian porphyry copper systems the oldest porphyry mineralization occurred in the eastern part of iran after the closure of a branch of the neo tethyan sistan ocean between the lut and afghan blocks in the late eocene 39 37 ma this was followed by mineralization in the kerman porphyry copper belt over a time interval of about 20 m y where two metallogenic epochs have been recognized including late oligocene 29 27 ma and miocene 18 6 ma the bondar e hanza deposit formed in the late oligocene while and the remaining dated deposits belong to miocene epoch according to the deposits characteristics and their ages the miocene epoch can be divided into early middle and late stages the darreh zar bakh khoshk chah firouzeh and sar kuh deposits formed during the early middle miocene the largest porphyry deposits occur in the middle stage during the middle miocene 14 11 ma and include the sar cheshmeh meiduk dar alu and now chun deposits these deposits were formed during crustal thickening uplift and rapid exhumation of the belt the final stage of porphyry mineralization occurred during the late miocene 9 6 ma and formed the iju kerver kuh panj and abdar deposits there were two porphyry mineralization stages in the arasbaran porphyry copper belt in nw iran including an older late oligocene 29 27 ma and a younger early miocene 22 20 ma events the haft cheshmeh deposit belongs to the older stage and the world class sungun and masjed daghi deposits formed during the early miocene in the middle segment of the udma saveh yazd porphyry copper belt pcds formed during middle miocene time 17 15 ma the geochronological results reveal that the porphyry mineralization moved from the northwest to southeast of udma over the time our dating results combined with the possible late eocene oligocene timing for collision between the arabian and iranian plates support a model for iranian pcd formation by partial melting of previously subduction modified lithosphere in a post subduction and post collisional tectonic setting

on the numerical computation of temperature in an ice sheet quadrature solutions for temperature fields in the central regions of ice sheets where flow is by internal deformation are presented and compared with numerical computations and the european ice sheet modelling initiative eismint benchmark standards the solution appears to be more accurate than the eismint benchmark standards for thermomechanically uncoupled temperature distributions the ability of finite difference and pseudo spectral methods to reproduce this solution is considered errors in the eismint benchmark are larger than expected the possibility that they could arise from inaccurate evaluation of the vertical velocity is considered and found to be unlikely formulae for computing the vertical velocity in jenssen s coordinate are complicated and may lead to programming errors a simple form of the heat transport equation in the coordinate for flow by sliding and internal deformation is derived arid presented and it is shown how this form is particularly suitable for finite element computations it is also shown that only two quadratures are necessary to compute the vertical and horizontal heat transport and the ice flux