lithospheric structure beneath the zagros collision zone resolved by non linear teleseismic tomography the upper mantle structure across the zagros collision zone in southwest iran is investigated using a non linear weighted damped least squares teleseismic tomography approach the resolution of the structures transitions in the upper mantle is enhanced significantly by correcting the teleseismic relative arrival time residuals for an a priori crustal velocity model and then performing the inversion with fixed crustal blocks to investigate whether or not the lithospheric blocks and major transitions in the resulting model are required by the data or are artefacts of the inversion the data were inverted using two different inverse methods singular value decomposition and a quadratic programming method new high quality seismic velocity models show apparent correlation between surface geological features and seismic velocity structures at lithospheric depth across the zagros collision zone the image shows a sharp lithospheric boundary at the main zagros thrust between 100 km and 250 km depth with p wave velocity about 3 per cent faster within the arabian shield to the south a step like increase in lithospheric thickness across the zagros collision zone is assumed to separate two different mantle structures namely the arabian to the south and the eurasian to the north domains the most striking feature resolved is a north dipping slab like positive velocity anomaly

upper mantle s velocity structure and moho depth variations across zagros belt arabian eurasian plate boundary the collision of the arabian and eurasian plates in the early miocene after the subduction of neo tethys ocean beneath eurasia formed the zagros belt a seismically active continental continental plate boundary in southwest iran the zagros suture zone is an important seismotectonic boundary indicating an abrupt cutoff between the intense seismicity of the zagros and the almost aseismic central iran plateau compared with other more evolved plate boundaries little is known about the deep lithospheric structure of the zagros belt such as the fate of subducted neo tethys plate and ambiguity in the presence of intermediate and deep earthquakes under the zagros suture zone in this study we use the partitioned waveform inversion pwi method to image the upper mantle s velocity structure and moho depth variations across zagros collisional zone the resulting moho depth along the profile shows the average moho depth value of order of 40 45 km for most parts of the profile with abrupt crustal thickening in the middle of the profile up to about 65 km as expected the derived models show that the relatively old and cold arabian plate has higher velocity at depth than the younger lithosphere farther north in central iran a sharp and steep subcrustal boundary is found roughly coincident with the surficial expression of the main zagros thrust mzt separating two different mantle domains a high velocity anomaly possibly representing a fragment of subducted lithosphere has been imaged beneath central iran at a depth between 350 and 600 km which is quite similar to the case of indo asian collision in qinghai tibetan plateau these observations as well as the sudden changes of shallow velocities along the cross section with a sharp boundary under the zagros suture zone support the idea that subducted oceanic lithosphere has broken off under the region of maximum moho depth a relatively low velocity region beneath the arabian plate is also imaged in our high resolution tomography model which is interpreted as an indication of lithospheric delamination within the arabian lithosphere

the southern caspian a compressional depression floored by a trapped modified oceanic crust the south caspian intracontinental depression floored by oceanic basement is a relatively stable block with minor deformation surrounded by active fold thrust belts of arcuate form talesh alborz and kopeh dagh mountains which have undergone intense late cainozoic crustal shortening the basin is interpreted as a neogene quaternary compressional depression bounded by multi role mountain bordering reverse faults and apparently floored by a late paleozoic triassic or late mesozoic early tertiary modified oceanic crust trapped along an old geosuture it may be a relic of an old paleozoic triassic ocean or else a marginal sea developed behind a mesozoic paleogene ocean and analysis of geological and geophysical data enables a scheme to be suggested the general arcuate shape of the alborz and the talesh bordering mountain belts follows the pattern of the supposed rigid and thickened ocean crust of south caspian depression a tectono sedimentary study of the south caspian region coupled w

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

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

shear wave splitting lithospheric anisotropy and mantle deformation beneath the arabia eurasia collision zone in iran article i nfo records of core refracted phases from permanent and temporary seismological stations are analysed to provide a map of seismic anisotropy covering most tectonic provinces of iran anisotropy is coherent at the scale of a single province but it differs from one province to another no significant shear wave splitting is observed in the mountain ranges of zagros alborz and kopeh dagh anisotropy with average time lags of 1 1 0 3 s between fast and slow shear waves with axes of the faster polarization oriented mostly nw se is observed in central iran but the faster orientation is ne sw in ne iran the orientations of fast axes do not coincide with the directions of absolute plate motion in the no net rotation frame or in the hot spot frame suggesting that the observed anisotropy cannot be explained by a simple model of asthenospheric flow the heterogeneous orientation of fast axes with differences in length scales of a few hundreds km suggests that the anisotropy originates in the lithospheric mantle in the area where strike slip shear dominates the fast axes lie approximately parallel to the orientations of maximum shear estimated from gps measurements either with right lateral shear associated with the ns trending right lateral faults in central iran or left lateral shear associated with ew trending left lateral faults in northeast iran in the mountain belts the null measurements may be related to horizontal shortening and thickening by pure shear as proposed from synthetic models of olivine fabric which both imply a large amount of vertical strain not seen by sks splitting our data therefore do not agree with previous explanations of shear wave splitting in the neighbouring regions of eastern anatolia and saudi arabia in terms of simple asthenospheric flow they rather support the view that iran deforms over a broad area with vertically coherent deformation at a lithospheric scale that includes both shear between blocks in central iran and shortening at the mountain belts

the deep structure of the iranian plateau high resolution structures of the lithosphere asthenosphere system beneath a seismic profile in iran are obtained by the simultaneous inversion of data from receiver functions and fundamental mode rayleigh wave group velocity and validated by modeling bouguer gravity anomaly data the seismic data are gathered over a profile extending across zagros sanandaj sirjan zone ssz urumieh dokhtar magmatic arc udma central iran alborz binalud mountain ranges and kopeh dagh mountain ranges the results confirm the presence of crustal roots at the north and south of iranian plateau where it meets the arabian plate and eurasia the high velocity lithosphere of the arabian plate gently plunges nne ward beneath central iran supporting the subduction of the continental lithosphere responsible for the seismicity of the area the crust and lithosphere are thinner beneath central iran where two low velocity structures are very likely related to magma sources of the udma and in east of iran around lut block where the volcanism shows calcalkaline subduction related geochemistry the crustal lithospheric root to the north of the iranian plateau may represent the relict of a previous cimmeric subduction zone therefore the iranian lithosphere asthenosphere system could be the result of the coalescence of two separate subduction zones

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

joint inversion for three dimensional s velocity mantle structure along the tethyan margin abstract for purposes of studying the lateral heterogeneity as well as for ultimately predicting seismograms for this region we construct a new 3 d s velocity model by jointly inverting a variety of different seismic data we jointly invert regional waveforms surface wave group velocity measurements teleseismic s arrival times and crustal thickness estimates from receiver functions refraction lines and gravity surveys these data types have complementary resolving power for crust and mantle structures vertical and lateral variations shallow and deep mantle features local and global structure therefore a joint inversion of these data sets might help unravel the complexity of this tectonically diverse area these measurements are made from a combination of mantle investigation of the deep suture between europe and africa midsea program for array seismic studies of the continental lithosphere passcal geoscope geofon global seismographic network gsn international deployment of accelerometeres ida mednet national networks and local deployments throughout the study region which extends from the western mediterranean region to the hindu kush and encompasses northeastern africa the arabian peninsula the middle east and part of the atlantic ocean for reference we have fitted the waveforms of regional s and rayleigh waves from over 3800 seismograms using partitioned waveform inversion we include over 3000 crustal thickness estimates from receiver functions gravity measurements and refraction profiles we include rayleigh wave group velocities for hundred thousands of paths transecting the region we have over 3000 teleseismic s arrival times measured through cross correlation and over 170000 from picks originally reported to the international seismological centre isc

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

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

multiple melt injection along a spreading segment at askja iceland lower crustal earthquakes 12 25 km depth have been detected since august 2005 in the askja volcanic system along the north iceland rift in the normally ductile part of the crust the earthquakes occur in three clusters which have stable dimensions and locations through time and are interpreted as positions of repeated melt supply from the mantle to the lower crust seismic velocity vp vs ratios are consistent with the presence of partial melt in the lower crust at askja the spatial separation of the clusters shows that there are multiple positions of melt injection within this one magmatic segment and all three positions are currently active this pattern of melt supply is more like that observed on fast spreading ridges than slow spreading ridges and is probably a consequence of the increased melt production beneath iceland compared to the rest of the mid atlantic ridge however the relative number of earthquakes in each cluster shows that two thirds of the melt is supplied to the central volcano askja i e segment center during the last major rifting episode shallow lateral melt migration occurred from the magma chamber beneath the volcano therefore on long time scales melt supply is probably greater at the segment center with melt redistribution in the upper crust even though there are multiple points of lower crustal injection along the segment

tomographic pn velocity and anisotropy structure beneath the anatolian plateau eastern turkey and the surrounding regions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017391 shtml http atlas geo cornell edu turkey publications al lazki et al 2003 htm

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

numerical models of crustal scale convection and partial melting beneath the altiplano puna plateau we employ 2 d thermo mechanical modelling to study possible mechanisms for generating large scale crustal magmas in the altiplano puna region of the central andes the peak of ignimbrite activity in the late miocene and pliocene is associated in space and time with tectonic shortening and plateau uplift a seismic low velocity zone and other geophysical observations indicate that partial melting in the mid crust is still present under the ignimbrite province today we show that neither radiogenic heat production in a thickening crust nor shear heating due to tectonic shortening nor heat brought by intrusions of arc magmas into the mid crust can heat the mid crust to the degree and within the time frame suggested by the geologic petrologic and geophysical observations a viable mechanism to achieve high temperatures within the time constraints is convective heat and mass transfer by partially molten lower crust which itself was heated by enhanced mantle heat flow possibly associated with delamination of the mantle lithosphere during tectonic shortening and intensified magmatic arc activity the thermo mechanical models explain the mid crustal low velocity zone and the high and strongly variable surface heat flow observed in the altiplano convection by bulk flow of the crust appears when the middle and lower crust are mechanically weak quartz dominated rheology the basal heat flow from the mantle is high s 60 mw m 2 and tectonic shortening is active we argue that these conditions are satisfied in the central andes orogen 6 2002 elsevier science b v all rights reserved

flat versus steep subduction contrasting modes for the formation and exhumation of high to ultrahigh pressure rocks in continental collision zones abstract flat and steep subduction are end member modes of oceanic subduction zones with flat subduction occurring at about 10 of the modern convergent margins and mainly around the pacific continental margin subduction normally follows oceanic subduction with the remarkable event of formation and exhumation of high to ultrahigh pressure hp uhp metamorphic rocks in the continental subduction collision zones we used 2d thermo mechanical numerical models to study the contrasting subduction collision styles as well as the formation and exhumation of hp uhp rocks in both flat and steep subduction modes in the reference flat subduction model the two plates are highly coupled and only hp metamorphic rocks are formed and exhumed in contrast the two plates are less coupled and uhp rocks are formed and exhumed in the reference steep subduction model in addition faster convergence of the reference flat subduction model produces extrusion of uhp rocks slower convergence of the reference flat subduction model results in two sided subduction collision the higher lower convergence velocities of the reference steep subduction model can both produce exhumation of uhp rocks a comparison of our numerical results with the himalayan collisional belt suggests two possible scenarios 1 a spatially differential subduction collision model which indicates that steep subduction dominates in the western himalaya while flat subduction dominates in the extensional central himalaya and 2 a temporally differential subduction collision model which favors earlier continental plate flat subduction with high convergence velocity in the western himalaya and later flat subduction with relatively low convergence velocity in the central himalaya

variation of moho depth in the central part of the alborz mountains northern iran summary the alborz mountains of northern iran form a belt of active crustal deformation along the southern side of the caspian sea within the broad arabian eurasia continental collision zone although the range has an average elevation of about 3000 m with the volcanic peak damavand reaching an elevations of 5671 m early gravity studies found that the crust beneath the range is no thicker than that beneath the surrounding region suggesting the range is not supported by a crustal root we determine a model for the crust of the central alborz mountains using teleseismic receiver functions from data recorded on a network of broad band seismographs temporarily deployed across the central part of the range the receiver functions from these recordings have been inverted simultaneously with fundamental mode rayleigh wave group velocity measurements in the 10 100 s period range our analysis shows a thickening of the crust from 48 km beneath the northern part of the central iranian plateau to 55 58 km below the central part of the alborz mountains then a thinning of the crust to 46 km north of the alborz mountains beneath the coastal region of the south caspian sea our seismological results show that the central alborz mountains have a moderate crustal root but of insufficient thickness to compensate the elevation of the range the analysis of free air gravity shows that the elevation of the alborz mountains is largely supported by the elastic strength of the iranian plate the south caspian plate or both

3 d imaging using higher order fast marching traveltimes recently fast marching methods fmm beyond first order have been developed for producing rapid solutions to the eikonal equation in this paper we present imaging results for 3 d prestack kirchhoff migration using traveltimes computed using the first order and second order fmm on several 3 d prestack synthetic and real data sets the second order traveltimes produce a much better image of the structure moreover insufficiently sampled first order traveltimes can introduce consistent errors in the common reflection point gathers that affect velocity analysis first order traveltimes tend to be smaller than analytic traveltimes which in turn affects the migration velocity analysis falsely indicating that the interval velocity was too low

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

upper mantle seismic wave velocity effects of realistic partial melt geometries we investigate seismic wave velocity reduction resulting from the presence of partial melt in the upper mantle the amount of shear and bulk modulus reduction produced by the presence of a connected network of realistically shaped and naturally organized melt inclusions is found using finite element calculations the geometries of the inclusions are taken directly from laboratory experiments of mantle melting with finite element meshes constructed to conform to these shapes the shear and bulk moduli of the composite material are found for both the unrelaxed isolated inclusions and relaxed pressure equalized inclusions cases by assigning appropriate material properties to the fluid modulus reduction from deformation simulations of a solid containing realistically shaped and ellipse shaped melt inclusions quantify the effect of melt pocket cuspateness and melt pocket organization on seismic velocity reduction the three dimensional response is estimated from two dimensional distributions of the melt phase by determining the mode ii and mode iii components of elastic modulus reduction separately and summing their effects in general cuspate and naturally organized melt inclusions cause greater velocity reduction it is shown that v and vs reduction per percent partial melt are at least 3 6 and 7 9 respectively even higher values for velocity reduction are possible above 1 melt fraction if melt exists only in tubules below 1 melt fraction the lower more conservative values of velocity reduction are 070 greater for vp and 84 greater for vs than the analytically determined values for ellipsoidal inclusions somewhat greater effects are possible if nonrandom organization of melt occurs on scales greater than our model

presence of a layered lithosphere beneath the zagros collision zone abstract the continental collision between the arabian and eurasian plates following the subduction of the neo tethys ocean beneath eurasia resulted in a complex deformation across the zagros mountains we used more than 700 s receiver functions obtained from 61 permanent stations to provide a detailed image of the lithospheric interaction between the eurasian and arabian plates our results suggest the existence of two different lithospheric blocks a 200 km thick lithosphere was observed beneath the zagros collision zone and most likely represents the arabian lithosphere which has been strongly deformed thickened and depleted based on our results shortening due to the collisional process is differently accommodated by the crust and mantle lithosphere of the zagros collision zone we localized the thick arabian lithosphere beneath the zagros sanandaj sirjan zone ssz and urumieh dokhtar magmatic assemblage udma whereas the crustal thickening 70 km seems to be concentrated just beneath the ssz furthermore we found a thin lithosphere of about 80 90 km that we interpret here as the iranian lithosphere beneath central iran and alborz additionally our results suggest the presence of remnants of the fossil neo tethys subduction at depths ranging between 80 and 150 km within the arabian lithosphere this dipping structure can be seen beneath the zagros ssz and udma and seems to disappear towards the northeast beneath central iran and alborz these findings may support the idea of a breakoff of the oceanic neo tethyan slab beneath central iran which results in an asthenospheric upwelling and thinning of the iranian lithosphere beneath central iran and alborz the boundary between the arabian and iranian plates seems to be located northeast of the udma in the northwest of zagros and southwest of the udma in the central zagros region

petrochemistry of the siah kuh granitoid stock southwest of kerman iran implications for initiation of neotethys subduction abstract the upper triassic siah kuh granitoid stock is part of a series of triassic cretaceous intrusions in the phanerozoic sanandaj sirjan zone in the zagros orogenic belt south central iran the siah kuh stock intrudes lower paleozoic amphibolites of the abshur metamorphic complex and upper devonian lower carboniferous greenschists of the sargaz metamorphic complex the siah kuh granitoid stock consists mainly of coarse to medium grained leucogranodiorite leucomonzogranite and alkali granite with subordinate syenite it also contains a number of mafic enclaves of different sizes and is intruded by alkali granite and granophyre dikes along with monzonitic and a few dioritic dikes the siah kuh granitoid rocks are characterized by enrichment in large ion lithophile elements lile such as rb ba k ce and depletion in high field strength elements hfse such as y nb and zr the chondrite normalized ree patterns are characterized by moderate lree enrichment la yb n 1 31 4 82 and unfractionated hree gd yb n 0 50 to 1 33 granodiorites with the least fractionated hree and a general absence of eu anomalies suggest the involvement of plagioclase and absence of garnet during the melting processes alkali granites with the highest la yb n values and pronounced negative eu anomalies are more differentiated products nd isotope analyses of the siah kuh granitoids yield an errorchron age of 199 30 ma mswd 1 30 consistent with the field relationships and give nd model ages tdm from 0 81 to 1 64 ga and end t values from 1 81 to 2 45 at 200 ma these geochemical data suggest that the siah kuh granitoid stock has characterisitics of metaluminous to slightly peraluminous calc alkaline i type granite formed in a volcanic arc setting the onset of subduction of the neotethys oceanic crust beneath the central iranian microcontinent in triassic time could have accounted for the continental arc volcanism dehydration of subducted oceanic crust and partial melting of mantle wedge caused partial melting of subcontinental lithosphere which resulted in the formation of metasomatised and enriched mafic arc magmas at variable water fugacity and led to the formation of the siah kuh granitoid rocks

the present day deformation of the central zagros from gps measurements 1 in 1997 and in 2000 we measured the distances between 14 geodetic benchmarks across the central zagros mountain belt the results show that about 10 mm yr of shortening in the central zagros is distributed across the mountain belt this shortening corresponds to roughly 50 of the total convergence between arabia and eurasia and is consistent in direction the persian gulf does not deform significantly the main zagros reverse fault is not an active kinematic boundary the internal deformation of the folded belt is rather homogeneous at the scale of our survey which does not allow us to detect any individual active blind fault however the strain pattern suggests that n s dextral strike slip faults may accommodate part of the deformation

subduction history of the tethyan region derived from seismic tomography and tectonic reconstructions 1 in the mantle underneath the tethyan suture zone large volumes of positive velocity anomalies have been imaged by seismic tomography and interpreted as the present day signature of subducted tethyan lithosphere we investigate the mesozoic cenozoic subduction history of the region by integrating independent information from mantle tomography and tectonic reconstructions three different subduction scenarios for the tethyan oceanic lithosphere representative for the available tectonic reconstructions are used to predict the present thermally anomalous volumes associated with the lithospheric surface subducted since the late mesozoic next these predicted thermal volumes and their expected positions are compared to the relevant anomalous volumes derived from seismic tomographic images in this analysis we include among others the possible effects of ridge subduction and slab detachment after the cenozoic continental collisions absolute plate motion and slab thickening in the mantle our preferred subduction model comprises the opening of large back arc oceanic basins within the eurasian margin the model points to slab thickening by a factor of 3 in the mantle in which case the estimated volumes allow for active oceanic spreading 1 2 5 cm yr in the tethyan lithosphere during convergence our results further indicate the occurrence of early oligocene slab detachment underneath the northern zagros suture zone followed by both westward and eastward propagation of the slab tear and diachronous eocene to miocene slab detachment below the eastern to western himalayas free sinking rates of the detached material of 2 cm yr in the lower mantle provide the best fit between the tomographic mantle structure and our tethyan subduction model

lithospheric structure of tasmania from a novel form of teleseismic tomography in 2001 and 2002 a temporary array of 72 seismic recorders was deployed across northern tasmania se australia with the aim of imaging the underlying crust and upper mantle using three dimensional 3 d teleseismic tomography using a recently developed adaptive stacking technique 6520 relative p wave arrival time residuals have been picked from 101 distant earthquake records spanning a 5 month period a novel iterative nonlinear tomographic procedure based on a subspace inversion scheme and the fast marching method a grid based eikonal solver is used to map the residual patterns as p wave velocity anomalies the new scheme proves to be both fast and robust making it well suited to large data sets and the reconstruction of complex anomalies the resultant tomographic images of tasmania exhibit significant lateral perturbations in p wave velocity structure 5 from a 1 d reference model a marked transition from higher velocities in the east to lower velocities in the west strongly supports the idea that eastern tasmania is underlain by dense rocks with an oceanic crustal affinity contrasting with the continentally derived siliciclastic core of western tasmania significantly the tamar fracture system does not overlie the narrow transition from relatively fast to slow velocities which suggests that it may be a near surface feature rather than a manifestation of deeper crustal scale suturing as previously thought farther west an easterly dipping zone of relatively high velocity material beneath the rocky cape group and arthur lineament may be related to remnant subduction of oceanic lithosphere associated with the mid cambrian delamerian orogeny

thermomechanical modelling of slab detachment abstract slab detachment or breakoff is appreciated as an important geological process as shown by recent tomographic imaging using a 2 d upper mantle model 660 km deep and 2000 km wide we have investigated with a 2 d finite difference and marker in cell numerical technique the multi resolutional character of the thermomechanical phenomena related to this complex geological process our experiments show that this process can be initiated in form of slab necking by a prolonged 8 30 my period of slab weakening due to thermal diffusion 60 c my due to strong positive thermal feedback from shear heating detached slab fragments sink rapidly with a tendency for coherent rotation the influence of temperature and pressure dependent thermal conductivity on the process of thermal weakening of the slab is quite significant this supports the idea that the breakoff process is triggered by thermal diffusion on a time scale linearly dependent on heat conductivity rapid topographic changes and increasing volcanic activities due to the melting of subducted oceanic crust are possible scenarios of this vigorously driven geodynamic process

pn tomographic imaging of mantle lid velocity and anisotropy at the junction of the arabian eurasian and african plates an edited version of this paper was published by blackwell publishing in geophysical journal international copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02355 x http atlas geo cornell edu middleeastnorthafrica publications al lazki2004 htm

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

thermal histories from the central alborz mountains northern iran implications for the spatial and temporal distribution of deformation in northern iran we integrate new and existing thermochronological geochronological and geologic data from the western and central alborz mountains of iran to better constrain the late cenozoic tectonic evolution of northern iran in the context of the arabia eurasia collision new data are presented for two granitic plutons north of the alborz range crest additional new apatite u th he data are also presented for volcanic intrusive and detrital apatite grains from two transects south of the range crest our most definitive results include zircon and apatite u th he and limited k feldspar 40 ar 39 ar thermal history data from the cretaceous ca 98 ma nusha pluton that reveal that the alborz basement underwent generally slow denudation 0 1 km m y as late as 12 ma with more accelerated exhumation 0 45 km m y that likely began shortly after 12 ma the lahijan pluton a late neoproterozoic cambrian basement exposure near the caspian shore records apatite u th he closure at 17 13 ma additional u th he results from detrital apatites sampled along two separate horizontal transects all consistently yielded latest miocene to pliocene apparent ages that imply that even supracrustal cover rocks within the alborz have undergone significant regionally extensive exhumation overall our data are consistent with 5 km of regionally extensive denudation since ca 12 ma the onset of rapid exhumation in the alborz at ca 12 ma appears to be consistent with other timing estimates that place the onset of the arabia eurasia collision between 14 and 10 ma

the 2004 may 28 baladeh earthquake mw 6 2 in the alborz iran overthrusting the south caspian basin margin partitioning of oblique convergence and the seismic hazard of tehran we use teleseismic waveform analysis and locally recorded aftershock data to investigate the source processes of the 2004 baladeh earthquake which is the only substantial earthquake to have occurred in the central alborz mountains of iran in the modern instrumental era the earthquake involved slip at 10 30 km depth with a south dipping aftershock zone also restricted to the range 10 30 km which is unusually deep for iran these observations are consistent with co seismic slip on a south dipping thrust that projects to the surface at the sharp topographic front on the north side of the alborz this line is often called the khazar fault and is assumed to be a south dipping thrust which bounds the north side of the alborz range and the south side of the south caspian basin though its actual structure and significance are not well understood the lack of shallower aftershocks may be due to the thick pile of saturated overpressured sediments in the south caspian basin that are being overthrust by the alborz a well determined earthquake slip vector in a direction different from the overall shortening direction across the range determined by gps confirms a spatial separation partitioning of left lateral strike slip and thrust faulting in the alborz these strike slip and thrust fault systems do not intersect within the seismogenic layer on the north side though they may do so on the south the earthquake affected the capital tehran and reveals a seismic threat posed by earthquakes north of the alborz located on south dipping thrusts as well as by earthquakes on the south side of the range closer to the city

accounting for lateral variations of the upper mantle gradient in pn tomography studies 1 the effect of an upper mantle velocity gradient on regional arrival times has been approximated by a cubic distance term which can be extended to two dimensions for use in tomographic studies to demonstrate this we add a laterally varying upper mantle gradient to the standard pn time term tomography technique and apply to a data set from asia compiled using ground truth event location criteria we observe strong lateral variations in the gradient ranging from 0 001 to 0 003 s 1 with high gradients associated with the tethys convergence zone the gradient patterns may reflect lateral variations in the thermal gradient of the mantle lid variance reduction is 63 with respect to pn tomography without gradients adding gradients allows the use of longer path lengths improving velocity image definition in high gradient regions with sparse station distribution such as tibet

sn attenuation in the anatolian and iranian plateau and surrounding regions an edited version of this paper was published in geophysical research letters by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018020 shtml http atlas geo cornell edu turkey publications gok et al 2003 htm

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

microearthquake seismicity at the intersection between the kazerun fault and the main recent fault zagros iran summary seismicity and fault plane solutions of earthquakes at the intersection between the main recent fault a right lateral strike slip fault that bounds the zagros to the ne and the kazerun fault system another right lateral zone that crosses the zagros show slip to be partitioned into nearly pure strike slip at shallow depths and nearly pure thrust slip below 12 km such slip partitioning is commonly observed where oblique convergence occurs but in general faults of different styles lie adjacent to one another not at different depths with one below the other we provide evidence for this partitioning in a microearthquake study in which we deployed a temporary network of 29 seismographs for 7 weeks we located no activity north of the main zagros reverse fault mzrf which separates the zagros fold belt from central iran most earthquakes occurred between the northern termination of the kazerun fault and the mzrf but not near to known major faults activity is limited to the upper crust between 2 and 16 km most of the focal mechanisms show strike slip faulting dextral if the ns striking plane is the active plane but a few for the deepest events show reverse faulting distributed between the kazerun fault and the mzrf with p axis trending consistently ns this partitioning of the deformation with depth suggests that the brittle upper crust deforms by slip on pre existing faults that strike obliquely but that the lower crust accommodates the shortening by reverse faulting we infer that the deformation in the upper part of the crust reflects a stiffer medium in which pre existing faults localize the deformation the largest event recorded during this experiment located at the same place as the destructive 1977 naghan earthquake mw 5 9 348 victims shows reverse faulting likely related to the dopolan high zagros fault the crustal thickness deduced from receiver function analysis does not show a marked difference across the kazerun fault which suggests a pure strike slip motion on the fault

comparisons of the kinematics and deep structures of the zagros and himalaya and of the iranian and tibetan plateaus and geodynamic implications 1 we compare the geologic histories the deep structures and the present day kinematics of deformation of the himalaya and the adjacent tibetan plateau with those of the zagros and iranian plateau to test geodynamic processes of continental collision shortly after india and arabia collided with eurasia horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from india s and arabia s underlying crystalline basement subsequently slip on thrust faults stacked slices of india s basement to build the himalaya on india s northern margin such faulting has not yet developed in the zagros where collision is more recent and arabia penetrates into eurasia more slowly than india does so that postcollision convergence with eurasia is less the greater elevation thicker crust and more marked heterogeneity of the upper mantle beneath the tibetan than beneath the iranian plateau also reflect a more advanced stage of development moreover while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus normal faulting suggesting horizontal extension and crustal thinning occurs within tibet but not in iran hence the balance of forces that built the high tibetan plateau must have changed apparently some time since 15 ma removal of tibetan mantle lithosphere could have altered that balance if mantle lithosphere beneath the iranian plateau has been removed however the change in force balance has been too small to initiate normal faulting low seismic wave speeds in the uppermost mantle just beneath the moho of both plateaus suggest to us that lithosphere beneath both is thin consistent with late cenozoic removal of it but alternative explanations might account for these low speeds despite its apparently thin and hence presumably weak mantle lithosphere much of central iran undergoes little deformation it illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small whereas differences between the two regions clearly depend on the amount that arabia and india have penetrated into eurasia which scales with both the dates of collision and rates of convergence we see no differences in the operative processes that depend on the present day rates of convergence

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

the structure of the upper mantle beneath the delamerian and lachlan orogens from simultaneous inversion of multiple teleseismic datasets abstract distant earthquake data recorded by seven sub arrays of the ongoing wombat rolling seismic array deployment in southeast australia are combined for the first time to constrain 3 d variations in upper mantle p wavespeed via teleseismic tomography the seven arrays comprise a total of 276 short period recorders spaced at intervals of approximately 50 km thus allowing unprecedented resolution of the upper mantle over a large region in the mantle lithosphere immediately below the crust 50 km depth dominant variations in velocity tend to strike east west and share little resemblance to palaeozoic boundaries in the shallow crust inferred from surface geology and potential field data a broad region of elevated wavespeed beneath northern victoria may represent the signature of underplated igneous rocks associated with detachment faulting during the break up of australia and antarctica a distinct low velocity anomaly in southern victoria appears to correlate well with the quaternary newer volcanic provinces towards the base of the mantle lithosphere the dominant structural trend becomes north south and five distinct velocity zones become apparent of particular note is a transition from higher wavespeed in the west to lower wavespeed in the east beneath the stawell zone implying that the proterozoic lithosphere of the delamerian orogen protrudes eastward beneath the western subprovince of the lachlan orogen this transition zone extends northwards from southern victoria into central new south wales the northward limit of the arrays and is one of the dominant features of the model further east there is a transition from lower to higher wavespeeds in the vicinity of the boundary between the western and central subprovinces of the lachlan orogen which has several plausible explanations including the existence of a proterozoic continental fragment beneath the wagga omeo zone the presence of elevated wavespeeds beneath the melbourne zone in victoria although not well constrained due to limited data coverage provides some support to the selwyn block model which proposes a northward extension beneath bass strait of the proterozoic core of tasmania

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

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

upper mantle structure beneath the alpine orogen from high resolution teleseismic tomography 1 to understand the evolution of the alpine orogen knowledge of the actual structure of the lithosphere asthenosphere system is important we perform high resolution teleseismic tomography with manually picked p wave arrival times from seismograms recorded in the greater alpine region the resulting data set consists of 4199 relative p wave arrivals and 499 absolute p wave arrivals from 76 teleseismic events corrected for the contribution of the alpine crust to the travel times the three dimensional 3 d crustal model established from controlled source seismology data for that purpose represents the large scale alpine crustal structure absolute p wave arrival times are used to compute an initial reference model for the inversion tests with synthetic data document that the combination of nonlinear inversion high quality teleseismic data and usage of an a priori 3 d crustal model allows a reliable resolution of cells at 50 km 50 km 30 km hence structures as small as two cells can be resolved in the upper mantle our tomographic images illuminate the structure of the uppermost mantle to depth of 400 km along strike of the alps the inversion reveals a high velocity structure that dips toward the se beneath the adriatic microplate in the western and central alps in the eastern alps we observe a northeastward dipping feature subducting beneath the european plate we interpret this feature in the western and central alps as subducted mainly continental european lower lithosphere for the east we propose that parts of the vardar oceanic basin were subducted toward the ne forcing continental adriatic lower lithosphere to subduct northeastward beneath the european plate

sand movement patterns in the western desert of egypt an environmental concern wind action is the most dominant agent for erosion and deposition in the vast western desert of egypt analysis of wind data from seven meteorological stations distributed along the western desert reveals that this desert is characterized by high energy wind environments along the northern and southern edges and low energy wind environments throughout the rest of the desert accordingly sand drift potential follows the pattern of wind energy maximum sand drift potential was observed at the southern edge 571 vector units which equals 40 m3 m width year sand drift direction was observed towards the southeast except at the southern part of the desert where the trend of sand movement was towards southwest the major dune type recognized on satellite images was the simple linear type linear dunes are generally associated with bimodal wind regime rates of sand drift potential and sand dune migration were greatest at east of owinate region at the extreme southern part of the desert measurements of crescentic sand dune advance from two satellite images reveal a maximum advance rate of about 9 m year at the southern part of the desert dune movement creates potential hazard to the infrastructures in this open desert

the zagros core deformation of the continental lithospheric mantle 1 the zagros of iran form one of the youngest collisional orogenic belts on earth at shallow depths shortening across the zagros is accommodated by folding in the sediments high angle thrust faulting in the basement and thickening of the lower crust but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known we map the lateral variations in upper mantle shear wave speed beneath this region using a large multimode surface wave data set the upper mantle is slow for most of the middle east but a high shear wave speed lid extending to 225 km depth exists beneath the zagros we use at vs z relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere the upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling the lithosphere is less than 120 km thick over the region except for a thick lithospheric root beneath the zagros implying that shortening in the mantle is accommodated by lithospheric thickening the composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities 60 kg m 3 less than the morb source elsewhere in the middle east the volcanic source regions have compositions and densities similar to that of morb the shortening across the zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion

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

high resolution teleseismic tomography of upper mantle structure using an a priori three dimensional crustal model summary the effect of an a priori known 3 d crustal model in teleseismic tomography of upper mantle structure is investigated we developed a 3 d crustal p wave velocity model for the greater alpine region encompassing the central and western alps and the northern apennines to estimate the crustal contribution to teleseismic traveltimes the model is constructed by comparative use of published information from active and passive seismic surveys the model components are chosen to represent the present large scale alpine crustal structure and for their significant effect on the propagation of seismic wavefields they are first order structures such as the crust mantle boundary sedimentary basins and the high velocity ivrea body teleseismic traveltime residuals are calculated for a realistic distribution of azimuths and distances by coupling a finite difference technique to the iasp91 traveltime tables residuals are produced for a synthetic upper mantle model featuring two slab structures and the 3 d crustal model on top of it the crustal model produces traveltime residuals in the range between 0 7 and 1 5 s that vary strongly as a function of backazimuth and epicentral distance we find that the non linear inversion of the synthetic residuals without correcting for the 3 d crustal structure erroneously maps the crustal anomalies into the upper mantle correction of the residuals for crustal structure before inversion properly recovers the synthetic slab structures placed in the upper mantle we conclude that with the increasing amount of high quality seismic traveltime data correction for near surface structure is essential for increasing resolution in tomographic images of upper mantle structure

from subduction to collision control of deep processes on the evolution of convergent plate boundary 1 using laboratory experiments we investigate the dynamics of the collisional process that follows the closure of an oceanic basin the evolution of these experiments systematically shows four successive episodes of deformation which correspond to 1 the initiation of oceanic subduction 2 a mature period of oceanic subduction 3 an episode of continental subduction during which the trench absorbs all the convergence and the superficial tectonic regime does not change significantly within the continental plates and 4 continental collision that starts when the trench locks and convergence is absorbed by a system of thrust faults and folds we observe that the amount of continental material that subducts before the onset of collision depends on the slab pull exerted by the subducted oceanic lithosphere the slab pull force in turn depends on the amount of subducted oceanic material on the thickness of the convective mantle and also on the rheology of the slab our experiments indeed suggest that parts of the oceanic slab may separate from the superficial slab to sink rapidly in the mantle decreasing the slab pull level and triggering the rapid onset of collision we observe two possible modes of slab deformation slab break off and development of viscous instabilities we define two dimensionless rheological numbers to characterize the possible occurrence of these modes of deformation in all cases oceanic closure is followed by episode of continental subduction during which the continental lithosphere may reach depths varying between 50 and 450 km prior to the onset of continental collision

3d joint inversion modeling of the lithospheric density structure based on gravity geoid and topography data application to the alborz mountains iran and south caspian basin region abstract we present a 3d algorithm to obtain the density structure of the lithosphere from joint inversion of free air gravity geoid and topography data based on a bayesian approach with gaussian probability density functions the algorithm delivers the crustal and lithospheric thicknesses and the average crustal density stabilization of the inversion process may be obtained through parameter damping and smoothing as well as use of a priori information like crustal thicknesses from seismic profiles the algorithm is applied to synthetic models in order to demonstrate its usefulness a real data application is presented for the area of northern iran with the alborz mountains as main target and the south caspian basin the resulting model shows an important crustal root up to 55 km under the alborz mountains and a thin crust ca 30 km under the southernmost south caspian basin thickening northward to the apsheron balkan sill to 45 km central and nw iran is underlain by a thin lithosphere ca 90 100 km the lithosphere thickens under the south caspian basin until the apsheron balkan sill where it reaches more than 240 km under the stable turan platform we find a lithospheric thickness of 160 180 km

teleseismic p wave tomography and the upper mantle structure of the central tien shan orogenic belt abstract in this study an updated version of the teleseismic tomographic method is applied to 7176 high quality first p wave arrivals from four combined seismic networks to determine the detailed deep structure under the central tien shan our high resolution tomographic model not only displays the general features contained in the previous models but also reveals some new features a much narrower tilted columnar high velocity anomaly with a diameter of about 60 km below 150 200 km depth under the tien shan extends down to the mantle transition zone suggesting the breaking and dropping off of the collided portions of the southward underthrusting kazakh shield and the northward underthrusting tarim basin prominent low velocity low v anomalies above 150 200 km depth beneath the tien shan may be related to two branches of ascending hot anomalies one rises upward from the lower mantle beneath the tarim basin while the other rises up from the top of the mantle transition zone beneath the western kazakh shield these results suggest that the underthrusting of the tarim basin and kazakh shield and the upwelling of hot anomalies indeed play an important role in the mountain building of the central tien shan these dynamic processes might be related to the collision of the indian plate with eurasian plate

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

early permian pangea b to late permian pangea a the pre drift wegenerian model of pangea is almost universally accepted but debate exists on its pre jurassic configuration since tedirving introd ucedpangea b by placing gond wana farther to the east by v3000 km with respect to laurasia on the basis of paleomagnetic data new paleomagnetic data from radiometrically dated early permian volcanic rocks from parts of adria that are tectonically coherent with africa gondwana integrated with published coeval data from gondwana and laurasia again only from igneous rocks fully support a pangea b configuration in the early permian the use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for pangea b the ultimate option to reject pangea b is to abandon the geocentric axial dipole hypothesis by introducing a significant non dipole zonal octupole component in the late paleozoic time averaged geomagnetic field we demonstrate however by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from gondwana as well as laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for pangea b in the early permian we therefore regard the paleomagnetic evidence for an early permian pangea b as robust the transformation from pangea b to pangea a took place during the permian because late permian paleomagnetic data allow a pangea a configuration we therefore review geological evidence from the literature in support of an intra pangea dextral megashear system the transformation occurred after the cooling of the variscan mega suture andlasted v20 myr in this interval the neotethys ocean opened between india arabia and the cimmerian microcontinents in the east while widespread lithospheric wrenching and magmatism took place in the west around the adriatic promontory the general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right lateral shear couple between gondwana and laurasia during the permian transcurrent plate boundaries associated with the pangea transformation reactivated variscan shear zones andwere subsequently exploitedby the opening of western neotethyan seaways in the jurassic