petrogenesis of post collisional a type granitoids from the urumieh dokhtar magmatic assemblage southwestern kerman iran constraints on the arabian eurasian continental collision abstract three plutons deh siahan bande bagh and baghe khoshk sharghi collectively referred to as the dbb hereafter in southwestern kerman in the southeastern part of the urumieh dokhtar magmatic assemblage udma of the zagros orogenic belt differ from the typical calc alkaline metaluminous i type intrusions of the region the dbb intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite the dbb granitoids are metaluminous to slightly peraluminous alkaline to shoshonitic in composition and have high total alkali contents with k2o na2o high feot mgo values and low cao and mgo contents they are enriched in some liles such as rb and th and hfses such as zr y and rees except eu and depleted in sr and ba relative to primordial mantle and have low concentrations of transitional metals these features along with various geochemical discriminant diagrams suggest that the dbb granitoids are post collisional a type granitoids which had not been recognized previously in the udma the chondrite normalized ree patterns of the dbb granitoids show slightly enriched light rees la sm n 2 26 4 13 negative eu anomalies eu eu n 0 19 0 74 and flat heavy ree patterns gd yb n 0 80 1 87 the negative eu anomaly indicates an important role for plagioclase and or k feldspar during fractional crystallization whole rock rb sr isotope analysis yields an isochron age of 33 1 ma with an initial 87sr 86sr value of 0 7049 0 0001 whole rock sm nd isotope analysis gives endt values from 2 56 to 3 62 at 33 ma the positive endt and low isr values of the dbb granitoids together with their tdm of 0 6 0 7 ga suggest their formation from partial melting of a lithospheric mantle source modified by fluids or melts from earlier subduction processes melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability field as a consequence of lithospheric mantle delamination or break off of a subducted slab and melting of the lithospheric mantle by upwelling of hot asthenosphere on the basis of rb sr age dating and the post collisional geochemical signatures of the dbb granitoids along with extensive pre collisional volcanic eruptions in middle eocene we suggest late eocene for the time of collision between the arabian and central iranian plates this also implies that the calc alkaline i type intrusions in the southwestern kerman and in other parts of the udma may have formed in a post collisional context

gondwanan eoarchean neoproterozoic ancient crustal material in iran and turkey zircon u pb hf isotopic evidence the sanandaj sirjan zone is a basement culmination northeast of the neo tethys suture in iran in this zone near azna granite has a magmatic zircon u pb age of 568 11 ma with 900 800 ca 2400 and ca 3600 ma inherited cores the ca 3600 ma inherited zircon is the oldest crustal component yet detected in iran near chadegan orthogneiss has a magmatic zircon u pb age of 637 15 ma and carries ca 1000 and 2000 ma inherited zircons inherited 900 1000 ma zircons have juvenile initial ehf values of ca 8 to 9 whereas the younger 630 and 568 ma magmatic zircons show lower initial ehf values however the 3600 ma core has initial ehf 0 0 a neoproterozoic rim on the inherited 3600 ma core has the most extreme initial ehf value of 18 the hf isotopic data indicates generation of the magmatic protoliths from a mixture of juvenile neoproterozoic and archean sources previous studies showed that in turkey the central anatolian crystalline complex is underlain by neo eoarchean rocks the menderes mas

subduction of pacific antarctic intermediate water in an eddy resolving model the subduction process of pacific antarctic intermediate water paaiw in the pacific is investigated using output from an eddy resolving ocean model focus is on contribution of eddies to the subduction process to separate the subduction rate into contributions by eddies and mean flows the temporal residual mean trm velocity is used in the mean subduction rate lateral induction caused by the strong eastward flow of the antarctic circumpolar current acc is dominant the largest rate is located in the drake passage the estimated eddy induced subduction rate is comparable with the mean subduction rate and it tends to cancel the vertical mean component in many regions in the west of the drake passage however the eddy induced subduction is larger than the vertical mean component and this eddy induced subduction was not detected in previous studies using the thickness diffusion parameterization and an eddy permitting model results of idealized sensitivity studies to model resolution suggest that the subduction rate would be larger using a model with higher vertical resolution therefore the vertical resolution should be paid more attention in model studies investigating eddy induced subduction and not just the horizontal resolution

buildup of a dynamically supported orogenic plateau numerical modeling of the zagros central iran case study the iranian plateau is a vast inland region with a smooth average elevation of c 1 5 km formed at the rear of the zagros orogen as a result of the arabia eurasia collision i e over the last 30 35 myr this collision zone is of particular interest due to its disputed resemblance to the faster himalayan collision which gave birth to the tibetan plateau around 50 myr ago recent studies have suggested that a recent 10 5 ma slab break off event below central iran caused the formation of the iranian plateau here we test several hypotheses through large scale 3082 3 590 km numerical models of continental subduction mod els that incorporate a free upper surface erosion rheological stratification brittle elastic ductile rheologies and metamorphic phase changes density and physical properties and account for the specific crustal and thermal structure of the arabian and iranian continental lithospheres we test the impact of the transition from oceanic to continental subduction and the topographic consequences of the progressive slowdown of the convergence rate during continental subduction our results demonstrate the role of mantle flow beneath the overriding plate initiated as an indirect consequence of slab break off this flow creates a dynamic topography support during continental subduction and results in delamination of the overriding plate lithospheric mantle followed by isostatic readjustment hence of further uplift and maintenance of a plateau like topography without significant crustal thickening the slowdown of the convergence rate dur ing the development of the continental subduction collision phase largely contributes to this process by controlling the timing and depth of slab break off

the carbonate rock hosted epithermal gold deposit of agdarreh takab geothermal field nw iran hydrothermal alteration and mineralisation the disseminated gold deposit of agdarreh 24 5 t at 3 7 g t au is hosted in hydrothermally leached miocene reefal limestone in the takab geothermal field which is part of the cenozoic urumieh dokhtar volcanic arc of nw iran alteration and mineralisation are largely bedding controlled blanket like and include 1 pre ore decalcification 2 first stage silicification associated with pyrite early pyrite with 3 4 wt as late pyrite with 1 3 wt as and sphalerite 3 second stage silicification with precipitation of galena pb sb as sulphides sulphosalts tellurides and native bismuth 4 late stage cinnabar and barite in vugs 5 oxide ore stage and carbonate alteration complex mn fe rich oxyhydroxides arsenates sulphates aps minerals and rutile in residual leached rock and infill of karstic cavities gold occurs invisibly in the jasperoids and is enriched in the mn fe oxyhydroxide surface cap of the jasperoids gold mineralisation is associated with the hydrothermal metal suite of as sb hg te se tl ba zn ag cd bi and pb and is characterised by very low cu contents arsenian pyrite probably carried most of the primary invisible gold native gold occurs in association with the late stage cinnabar and the oxide ore

crustal lineament control on magmatism and mineralization in northwestern argentina geological geophysical and remote sensing evidence abstract the relationship between long lived deep crustal lineaments and the locations of magmatic centers and associated mineral deposits has been investigated in the puna region of northwestern argentina through the analysis of regional aeromagnetic surveys landsat images and geological information the good exposure and excellent preservation of basement and supracrustal geology in this region makes it particularly suitable for such a study at a regional scale several contrasting magnetic domains are recognized which correlate with crustal geology two basement domains are separated by a nne trending boundary which is believed to correlate with a paleozoic suture zone between the pampia to the southeast and arequipa antofalla terranes to the northwest locally overlying these basement terranes is the cenozoic magmatic domain which is best developed in the n s trending volcanic arc at the western edge of the puna the cordillera occidental in addition four southeast trending volcanic zones extend for several hundred kilometers across the puna many important mineral deposits and areas of hydrothermal alteration are associated with these volcanic breakouts and we have selected three such areas for more detailed study bajo de la alumbrera argentina s largest porphyry copper deposit cerro galan the largest ignimbrite caldera in argentina with associated hydrothermal alteration zones and el queva a historic polymetallic district located within a major volcanic range a comparison of lineament maps generated from aeromagnetic and landsat tm images reveals broad correlation between these different remote sensing techniques which respectively highlight subsurface magnetic and surface geological features in addition the locations of magmatic and hydrothermal centers can be related to the interpreted structural framework and are seen to occur near the intersections of major lineament zones it is suggested that in three dimensions such intersection zones form trans lithospheric columns of low strength and high permeability during transpressional or transtensional tectonic strain and may thereby serve as conduits for magma ascent to the shallow crust pooling of large volumes of deeply derived magma in shallow crustal magma chambers may then result in voluminous devolatilization and the formation of hydrothermal mineral deposits it is important to note that in this model structural intersections serve as facilitators for magma ascent and volatile exsolution but do not in themselves cause this process other factors such as magma supply rate and tectonic stress are essential primary ingredients and local magmatic and volcanic processes affect the ultimate potential for ore formation nevertheless we suggest that lineament analysis provides a valuable framework for guiding the early stages of mineral exploration other regional and local geological considerations must then be applied to identify priority targets within this framework

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

transition from oceanic to continental lithosphere subduction in southern tibet evidence from the late cretaceous early oligocene 91 30 ma intrusive rocks in the chanang zedong area southern gangdese little is known about the detailed processes associated with the transition from oceanic to continental lithosphere subduction in the gangdese belt of southern tibet gbst here we report zircon u pb age major and trace element and sr nd hf isotopic data for late cretaceous early oligocene similar to 91 30 ma intermediate acid intrusive rocks in the chanang zedong area immediately north of the yarlung tsangpo suture zone these rocks represent five magmatic episodes at similar to 91 similar to 77 similar to 62 similar to 48 and similar to 30 ma respectively the 91 48 ma rocks have slightly lower initial sr 87 sr 86 0 7037 to 0 7047 and higher epsilon nd t 1 8 to 4 3 and epsilon hf t 3 5 to 14 7 values in comparison with those 0 7057 to 0 7062 3 3 to 2 5 and 2 2 to 6 6 of the similar to 30 ma intrusive rocks the similar to 91 similar to 62 and similar to 30 ma rocks are geochemically similar to slab derived adakites the similar to 91 ma somka adakitic granodiorites were likely derived by partial melting of the subducting neo tethyan oceanic crust with minor oceanic sediments and the similar to 91 ma somka dioritic rocks with a geochemical affinity of adakitic magnesian andesites likely resulted from interactions between adakitic magmas and overlying mantle wedge peridotite the similar to 77 ma luomu diorites were probably generated by partial melting of juvenile basaltic lower crust the similar to 62 ma naika and zedong adaldtic diorites and granodiorites were likely generated mainly by partial melting of thickened juvenile mafic lower crust but the source region of the zedong adakitic rocks also contained enriched components corresponding to indian continental crust the similar to 48 ma lamda granites were possibly generated by melting of a juvenile basaltic crust the younger similar to 30 ma chongmuda adakitic quartz monzonites and minor granodiorites were most probably derived by partial melting of early oligocene north ward subducted indian lower crust beneath the southern lhasa block taking into account the regional tectonic and magmatic data we suggest that the gangdese belt of southern tibet gbst underwent a tectonodynamic transition from oceanic subduction to continental subduction between 100 and 30 ma it evolved through four stages 100 65 ma roll back of subducted neo tethyan oceanic lithosphere 65 60 ma initial collision between indian and asian continents 60 40 ma breakoff of subducted neo tethyan oceanic lithosphere and similar to 30 ma northward subduction of the indian continent c 2014 elsevier b v all rights reserved

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

geology timing and genesis of the high sulfidation au cu deposit of touzlar nw iran abstract the touzlar au cu deposit in northwestern iran is hosted by pyroclastics and lavas of andesitic to trachytic composition and by the coeval microdiorite stocks the ew to nw trending host volcano plutonic complex is part of the cenozoic urumieh dokhtar magmatic arc udma of the zagros orogenic belt a stratovolcano formed within the shallow marine environment of the oligo miocene red beds of northwestern iran that overlay a metamorphic core complex in an extensional regime the zircon u pb ages of the host volcanic and subvolcanic rocks are 18 1 1 0 to 19 3 0 3 ma the deposit with an estimated reserve of 1 5 mt of ore 2 2 g t gold and 0 3 cu consists of a number of sub parallel massive silicified zones and breccia quartz veins within a hydrothermal alteration zone that follows the e w trending extensional structures the hydrothermal alteration assemblages consist of extensive propylitic and argillic alteration advanced argillic alteration silicification and sulfidation in the core zone and of phyllic alteration the multi stage mineralization consists of disseminations veins veinlets and open space fillings advanced argillic alteration and silicification associated with different degrees of cu rich sulfidation occurred in phases a and b phase c is characterized by hydrothermal brecciation and precipitation of sulfides in open spaces that was followed by the precipitation of barite in phase d gold is found as free grains associated with quartz phase b and as overgrowth on pyrite grains in phase c supergene fe oxyhydroxides formed with minor amounts of azurite and malachite as well as gypsum and is associated with enrichment in mineable gold grades of up to 5 ppm homogenization temperatures of the lv fluid inclusion from the mineralized quartz veins range from 211 to 310 c and salinities from 0 3 to 8 wt nacl equiv these fluid inclusions coexist with low density co 2 bearing fluid inclusions suggesting low pressures dilation associated with the precipitation of gold at these lower temperatures isotope compositions of quartz and barite are similar and vary within a short range of 18 o h2o 5 58 to 8 95 and 6 8 to 8 77 respectively suggesting that the ore fluids formed from mixing of magmatic fluids with meteoric waters calculated 34 s h2s composition 2 68 to 15 59 of the sulfides indicate an igneous source for the sulfur that highly exchanged with a sedimentary source the touzlar deposit shows characteristic alteration assemblages and ore minerals of high sulfidation deposits it has been formed in relation with the lower miocene high level magmatic hydrothermal activity within an extensional regime at the last stages of the udma activity of northwestern iran

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

u pb zircon ages field geology and geochemistry of the kermanshah ophiolite iran from continental rifting at 79ma to oceanic core complex at ca 36ma in the southern neo tethys abstract the geodynamic evolution of the zagros mountains of iran remains obscure in particular the time of formation of the zagros ophiolites and the closure of the neo tethys ocean are highly controversial here we present new precise zircon u pb ages that show that the younger part sahneh kamyaran of the kermanshah ophiolite formed at 35 7 0 5 ma and the older part harsin at 79 3 0 9 ma field relations and geochemical evidence show that the younger sahneh kamyaran part is probably a fossil oceanic core complex and the older sahneh part is probably a continental oceanic transition complex both the sahneh kamyaran and sahneh parts were later emplaced into an accretionary complex we conclude and infer that the final closure time of the southern neo tethys ocean was after the late eocene our data and tectonic model have crucial implications for the geodynamic evolution of the zagros region

present day kinematics and fault slip rates in eastern iran derived from 11 years of gps data we analyze new gps data spanning 11 years at 92 stations in eastern iran we use these data to analyze the present day kinematics and the slip rates on most seismogenic faults in eastern iran the east lut west lut kuhbanan anar dehshir and doruneh faults are confirmed as the major faults and are found to currently slip laterally at 5 6 0 6 4 4 0 4 3 6 1 3 2 0 0 7 1 4 0 9 and 1 3 0 8 mm yr respectively slip is right lateral on the ns striking east lut west lut kuhbanan anar and dehshir faults and left lateral on the ew doruneh fault the ns faults slice the eastern iranian crust into five blocks that are moving northward at 6 13 mm yr with respect to the stable afghan crust at the eastern edge of the collision zone the collective behavior of the ns faults might thus allow the arabian promontory to impinge northward into the eurasian crust the ns faults achieve additional ns shortening by rotating counterclockwise in the horizontal plane at current rates up to 0 8 ma modeling the gps and available geological data with a block rotation model suggests that the rotations have been going on at a similar rate 1 0 4 ma over the last 12 ma we identify large strains at the tips of the rotating east lut west lut and kuhbanan faults which we suspect to be responsible for the important historical and instrumental seismicity in those zones

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

synchronous deformation on orogenic plateau margins insights from the arabia eurasia collision abstract the temporal and spatial distribution of deformation during the early phases of plateau formation is poorly known the iranian plateau is developing in response to arabia eurasia convergence and is a potential analog to the early phases of tibetan plateau deformation previous studies document the onset of the iranian plateau growth based on the kinematic history of the zagros to the south and the alborz mountains to the north here we present new detrital apatite fission track aft data from 13 modern rivers of the talesh mountains northwestern iranian plateau these mountains lie immediately south west of the rigid south caspian block a total of 1233 single grain cooling ages were measured and range between 185 and 4 ma deconvolution of grain age data documents three main phases of exhumation including the oligocene 30 23 ma early to middle miocene 18 12 ma and early pliocene 5 ma comparison between cooling ages from the talesh mountains and elsewhere across the iranian plateau indicates widespread plateau formation in the oligocene earlier than previously suggested for the northwestern plateau margin these results highlight deformation on both the northern and southern margins of the plateau over almost the entire history of iranian plateau formation a similar pattern of synchronous deformation on the north northeastern and southern margins of the tibetan plateau has recently been documented and highlights the significance of rigid basement blocks focusing far field deformation for both plateaus

retrodeforming the arabia eurasia collision zone age of collision versus magnitude of continental subduction the arabia eurasia collision has been linked to global cooling the slowing of africa mediterranean extension the rifting of the red sea an increase in exhumation and sedimentation on the eurasian plate and the slowing and deformation of the arabian plate collision age estimates range from the late cretaceous to pliocene with most estimates between 35 and 20 ma we assess the consequences of these collision ages on the magnitude and location of continental consumption by compiling all documented shortening within the region and integrating this with plate kinematic reconstructions shortening estimates across the orogen allow for 350 km of neogene upper crustal contraction necessitating collision by 20 ma a 35 ma collision requires additional subduction of 400 600 km of arabian continental crust using the oman ophiolite as an analogue ophiolitic fragments preserved along the zagros suture zone permit 180 km of subduction of the arabian continental margin plus overlying ophiolites wholesale subduction of this more dense continental margin plus ophiolites would reconstruct 400 500 km of postcollisional arabia eurasia convergence consistent with a ca 27 ma initial collision age this younger arabia eurasia collision suggests a noncollisional mechanism for the slowing of africa and associated extension

zircon u pb age constraints from iran on the magmatic evolution related to neotethyan subduction and zagros orogeny abstract this study reports zircon la icpms u pb ages of 50 igneous rock samples from the urumieh dokhtar magmatic arc udma and sanandaj sirjan structural zone ssz in iran these results together with literatures and our unpublished age data better delineate the magmatic evolution related to the neotethyan subduction and subsequent zagros orogeny that resulted from the arabia eurasia collision subduction related magmatism was active during jurassic time as evidenced by the presence of widespread i type granitoids from the middle to late jurassic 176 144 ma in the ssz after a protracted magmatic quiescence in the early cretaceous igneous activity renewed inland in the udma from which we identify late cretaceous granitoids 81 72 ma in jiroft and bazman areas the southeastern segment of the udma the udma volcanism was most active and widespread during the eocene and oligocene 55 25 ma much longer lasting than previously thought as just an eocene pulse such a prolonged igneous flare up event in the udma can be correlated to armenia where coeval calc alkaline rocks are common the udma magmatism ceased progressively from northwest to southeast with magmatic activities ending the early miocene ca 22 ma in meghri the middle miocene ca 16 ma in kashan and the late miocene ca 10 6 ma in anar respectively the southeastward magmatic cessation is consistent with the notion of oblique and diachronous collision between arabia and eurasia post collisional volcanism started ca 11 ma in saray east off the urumieh lake which along with later eruptions in sahand 6 5 4 2 ma and sabalan 0 4 ma volcanoes forms a compositionally unique component of the vast volcanic field covering much of the lesser caucasus nw iran and eastern anatolia regions

long lived eocene miocene stationary magmatism in nw iran along a transform plate boundary abstract the eocene miocene mianeh hashtroud igneous district in nw iran is part of the turkish caucasus iranian collision zone a key region to decipher the assembly and differentiation of gondwana derived terranes along the alpine himalayan convergence zone major inherited tectonic structures control in space and time the mesozoic cenozoic transition from oceanic subduction to continental collision in the region the geology of the study area is dominated by a polyphase long lived magmatic activity spanning from 45 to 6 ma the igneous products are subalkaline to alkaline with intermediate to acid compositions and a high k calcalkaline to shoshonitic affinity evidence of crustal contamination is attested by inherited zircons in the oldest eocene oligocene samples with ages spanning from neo archean to paleocene the sr nd isotopic compositions of the eocene oligocene samples plot close to the bulk silicate earth estimate whereas the miocene samples document stronger crustal contamination the lack of correlation between nd sr isotopes and sio2 supports a scenario of magma differentiation of different magma batches rather than crustal contamination major oxide and sr nd isotopic variation lead us to suggest that magmatism is the consequence of re melting of earlier underplated mesozoic tertiary magmatic products controlled by amphibole dominated fractionation processes regional scale correlations show long lived cenozoic magmatism in nw iran and caucasus region where the main porphyry and epithermal deposits occur we propose that the cenozoic collisional magmatism and the associated mineralisation at the junction between nw iran and caucasus was controlled by the activity of a major lithosphere scale inherited boundary transverse to the convergence zone in such a geodynamic setting the along strike segmentation of the lithosphere slab generated asthenospheric melts their upwelling into the metasomatised supra subduction mantle wedge and the potential activation of different mantle and crustal sources with consequent mineral endowment in the region

new constraints on upper mantle s velocity structure and crustal thickness of the iranian plateau using partitioned waveform inversion summary the continental collision between the african and eurasian plates resulted in a tectonically young and complex deformation in the iranian plateau the present day iranian plateau is characterized by diverse tectonic domains including the continental collisions e g zagros and alborz and the oceanic plate subduction e g makran partitioned waveform inversion method is used here to image the s velocity structure of the upper mantle and moho depth variations in the iranian plateau of nearly 3000 waveforms originally selected for the analysis we have fitted 974 waveforms from 101 events and 39 stations which result in 11 688 linear constraints on the upper mantle s velocity structure and moho depth for the region our new seismic images show seismically faster upper mantle beneath the zagros and the arabian plate compared to the central iran and alborz this high velocity anomaly has descended beneath the central iran along the main zagros thrust across the zagros collision zone the tomographic images show a slab stagnation in the transition zone at about 410 km depth in the form of a horizontal high velocity zone which does not penetrate the deeper parts of the mantle the lowest s velocities are concentrated beneath the central iran and alborz according to our velocity models a strong high velocity anomaly is resolved beneath the trapped south caspian basin with clear indication of westward underthrusting beneath the talesh and western alborz in makran southeast iran there is a clear evidence of subduction of oceanic crust of the arabian plate beneath the makran belt which is correlated with seismicity pattern across the makran zone also the inverted moho map using a priori information of crustal thickness constraints shows the large crustal thickness beneath the zagros suture zone in some places to a maximum depth of 65 km which indicates the influence of crustal thickening and shortening beneath arabian eurasian plate boundary a significantly crustal thinning is observable across the south caspian basin compared to its margins

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

geochemistry of quaternary lavas from ne sulawesi transfer of subduction components into the mantle wedge major and trace element and sr nd isotope compositions were determined for quaternary volcanic rocks from ne sulawesi the sangihe are indonesia in order to examine the origin of across arc variation in lava and magma source chemistry the arc is formed in an intraoceanic tectonic setting and is not associated with a backarc basin thereby minimizing possible contributions from non arc geochemical reservoirs the geochemistry of these arc lavas is likely to provide essential information about the chemical characteristics of subduction components all incompatible elements except pb increase away from the volcancic front major element data for mg rich lavas together with available experimental data suggest that primary magmas are produced at higher pressured by smaller degrees of partial melting beneath the backarc side volcanoes rb k and ba pb are higher and 87sr 86sr and 143nd 144nd are lower in backarc side lavas these variations may be attributed to generation of hydrous fluids in the downdragged hydrous peridotite layer at the base of the mantle wedge through the following reactions decompositions of pargasitic amphibole to form phlogopite and breakdown of phlogopite to crystallize k richterite beneath the volcanic front and the backarc side volcanoes respectively

tectonic control on sedimentary facies pattern and sediment accumulation rates in the miocene foreland basin of the southern alborz mountains northern iran 1 the southern alborz mountains of northern iran are an integral part of the arabia eurasia collision zone a magnetostratigraphic and rock magnetic investigation of the eyvanekey stratigraphic section in the southern alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the alborz foreland basin the section constitutes three coarsening upward units units 1 2 and 3 comprising the upper red and hezardarreh formations our data reveal that the upper red formation was deposited between 17 5 and 7 5 ma while the depositional age of the top of the hezardarreh formation can be extrapolated to 6 2 ma slow sediment accumulation rates correlate with sedimentary facies comprising prograding coarsening upward units this is likely the result of intraforeland uplift units 1 and 2 and basin inversion probably associated with a growth syncline located in the proximal foreland unit 3 in contrast fine grained strata at the bottom of each cycle are associated with faster sediment accumulation rates testifying to enhanced flexural basin subsidence in the course of thrust loading progradation of coarse grained facies also occurred during relatively fast sediment accumulation top of unit 2 suggesting that the influx of coarse grained sediment outpaced the storage capacity of the proximal foreland thus despite an overall southward propagation of deformation into the southern alborz foreland the locus of active deformation must have migrated back and forth on a time scale of circa 0 7 to 2 ma

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

oligocene uplift of the western greater caucasus an effect of initial arabia eurasia collision the greater caucasus is europe s largest mountain belt significant uncertainties remain over the evolution of the range largely due to a lack of primary field data this work demonstrates that depositional systems within the oligocene early miocene maykop series on either side of the western greater caucasus wgc display a similar provenance and divergent palaeocurrents away from the range constraining a minimum age for the subaerial uplift of the range as early early oligocene an eocene oligocene hiatus basal oligocene olistostromes and a marked increase in nannofossil reworking also point to initial deformation in the earliest oligocene the initial uplift of the wgc occurred during the final assembly of the tethysides to its south uplift commenced after the late eocene final suturing of northern neotethys and during the initial collision of arabia with the southern accreted margin of eurasia this suggests that compressional deformation was rapidly transferred across the collision zone from the indenting arabian plate to its northern margin

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

insights from the talysh of azerbaijan into the paleogene evolution of the south caspian region the age and mode of formation of the south caspian basin are disputed an 10 km thick predominantly middle eocene clastic and volcanic succession is exposed in the talysh mountains of azerbaijan at its western margin here high k alkali basalts pass laterally to the east and southeast into volcanogenic sandstone dominated turbidity current and debris flow deposits these southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western south caspian basin new ar ar ages cluster around 39 ma with an upper 1400 m thick volcanic interval being deposited in 2 2 0 2 m y we interpret that this rapid deposition and magmatism records a major back arc extensional transtensional event in the talysh north of the north dipping neotethyan subduction zone this event is recognized across much of southwest asia and may indicate a period of significant basin formation within the adjacent south caspian basin a transition into upper eocene lower oligocene strata dominated by fine grained turbidity current and hemipelagic sediments with slope instability features is interpreted to mark the end of rifting and volcanism in the talysh and the start of the arabia eurasia collision overlying oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the talysh region

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

reply to comment by wang et al on paleoproterozoic meta carbonates from the central segment of the trans north china orogen zircon u pb geochronology geochemistry and carbon and oxygen isotopes by tang et al 2016 precambrian research 284 14 29