oblique convergence during the cimmerian collision evidence from the triassic aghdarband basin ne iran abstract the lower middle triassic aghdarband basin ne iran consists of a strongly deformed arc related marine succession deposited along the southern margin of eurasia in a highly mobile tectonic context this basin is a key area for the study of the cimmerian events as the triassic units show severe deformations which occurred short time after the collision of iran with eurasia and were sealed by the middle jurassic succession in this work we document the structural setting and evolution of this area based on detailed mesoscopic structural analyses of faults and folds paleostress reconstruction and revision of the triassic stratigraphy the triassic sequences are deeply involved in a n verging thrust stack interacting with an important left lateral transpressional fault zone characterized by strike slip faults vertical folds and high angle reverse faults generating intricate positive flowers systematic folds asymmetry indicates that they developed in a left lateral transpressional zone coeval to thrust imbrication to the south due to a marked strain partitioning the extent of the transpressional zone shows that important left lateral movements developed parallel to the belt during the cimmerian collision in response to oblique convergence between iran and eurasia inversion of triassic syn sedimentary faults possibly inherited from palaeozoic structures of the kopeh dagh basement and favouring strain partitioning is suggested by unconformities significant differences in the sedimentary successions repeated olistoliths scarp related coarse breccias and rapid tectonic drowning occurring especially along the northern tectonic boundary of the basin paleostress analyses point to a complex stress pattern showing a 45 rotation of the stress field along the left lateral fault system related to a complete deformation partitioning in two domains respectively characterized by pure reverse dip slip and strike slip motions the main direction of compression possibly oriented ne sw in present days coordinates favoured the development of large shear zones disrupting the eastern portion of the cimmerian orogen

the anarak jandaq and posht e badam metamorphic complexes in central iran new geological data relationships and tectonic implications abstract the anarak jandaq and posht e badam metamorphic complexes occupy the nw part of the central east iranian microcontinent and are juxtaposed with the great kavir block and sanandaj sirjan zone our recent findings redefine the origin of these complexes so far attributed to the precambrian early paleozoic orogenic episodes and now directly related to the tectonic evolution of the paleo tethys ocean this tectonic evolution was initiated by late ordovician early devonian rifting events and terminated in the triassic by the eocimmerian collision event due to the docking of the cimmerian blocks with the asiatic turan block the variscan accretionary complex is a new name we proposed for the most widely distributed metamorphic rocks connected to the anarak and jandaq complexes this accretionary complex exposed from sw of jandaq to the anarak and kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal sea ophiolitic remnants including gabbro basalts with a supra subduction geochemical signature new 40ar 39ar ages are obtained as 333 320 ma for the metamorphism of this sequence under greenschist to amphibolite facies moreover the limy intercalations in the volcano sedimentary part of this complex in godar e siah yielded upper devonian tournaisian conodonts the northeastern part of this complex in the jandaq area was intruded by 215 15 ma arc to collisional granite and pegmatites dated by id tims and its metamorphic rocks are characterized by some 40ar 39ar radiometric ages of 163 156 ma the variscan accretionary complex was northwardly accreted to the airekan granitic terrane dated at 549 15 ma later from the late carboniferous to triassic huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the anarak and kabudan this new period of accretion is supported by the 280 230 ma 40ar 39ar ages for the anarak mild high pressure metamorphic rocks and a 262 ma u pb age for the trondhjemite rhyolite association of that area the triassic bayazeh flysch filled the foreland basin during the final closure of the paleo tethys ocean and was partly deposited and or thrusted onto the cimmerian yazd block the paleo tethys magmatic arc products have been well preserved in the late devonian carboniferous godar e siah intra arc deposits and the triassic nakhlak fore arc succession on the passive margin of the cimmerian block in the yazd region the nearly continuous upper paleozoic platform type deposition was totally interrupted during the middle to late triassic local erosion down to lower paleozoic levels may be related to flexural bulge erosion the platform was finally unconformably covered by liassic continental molassic deposits of the shemshak one of the extensional periods related to neo tethyan back arc rifting in late cretaceous time finally separated parts of the eocimmerian collisional domain from the eurasian turan domain the opening and closing of this new ocean characterized by the nain and sabzevar ophiolitic melanges finally transported the anarak jandaq composite terrane to central iran accompanied by large scale rotation of the central east iranian microcontinent ceim due to many similarities between the posht e badam metamorphic complex and the anarak jandaq composite terrane the former could be part of the latter if it was transported further south during tertiary time

the eo cimmerian late triassic orogeny in north iran the eo cimmerian orogen results from the late triassic collision of iran a microplate of gondwanan affinity with the southern margin of eurasia the orogen is discontinuously exposed along the northern side of the alborz mountains of north iran below the siliciclastic deposits of the shemshak group late triassic jurassic a preserved section of the external part of the belt crops out in the neka valley eastern alborz south of gorgan here the mesozoic successions shemshak group upper cretaceous limestones overlay a pre jurassic eo cimmerian thrust stack with a sharp unconformity the stack includes the gorgan schists an upper ordovician lower silurian low grade metamorphic complex overthrusted southward above a strongly deformed late palaeozoic middle triassic succession belonging to north iran in the talesh mountains western alborz the shanderman complex previously interpreted as an ophiolitic remnant isolated along the eo cimmerian suture is considered an allochthonous nappe of deeply subducted continental crust the new evidence for this is the occurrence of previously unknown eclogites dating to the carboniferous and probably related to the variscan history of transcaucasia south of the shanderman complex upper palaeozoic slates and carbonates occurring below the lower jurassic shemshak group also record the occurrence of an eo cimmerian metamorphic event based on our new data the eo cimmerian structures exposed in the alborz appear to be remnants of a collisional orogen consisting mainly of deformed continental crust where no ophiolites are preserved

paleomagnetism of peninsular malaysia abstract paleomagnetic results from upper jurassic to paleocene rocks in peninsular malaysia show counter clockwise ccw rotations while clockwise rotations cw are predominantly found in older rocks continental redbeds of the upper jurassic to lower cretaceous tembeling group have a post folding remagnetization giving a vgp at n54 e29 corresponding to approximately 40 of ccw rotation relative to eurasia and 60 ccw relative to the indochina block khorat plateau samples from cretaceous to paleocene mafic volcanics of the kuantan dike swarm and the segamat basalts give vgps at n59 e47 and n34 e36 respectively these malayasian data are indistinguishable from the late eocene and oligocene vgps reported for borneo and the celebes sea and are similar to the eocene vgps reported for southwest sulawesi and southwest palawan the occurrence of ccw deflected data over this large region suggests that much of malaysia borneo sulawesi and the celebes sea rotated approximately 30 to 40 ccw relative to the geocentric axial dipole gad between the late eocene and the late miocene although not necessarily synchronously nor as a single rigid plate these regional ccw rotations are not consistent with simple extrusion based tectonic models cw declinations have been measured in late triassic granites permian to triassic volcanics and remagnetized paleozoic carbonates the age of this magnetization is poorly understood and may be as old as late triassic or as young as middle or late cretaceous the plate or block rotations giving rise to these directions are correspondingly weakly constrained

the mid cimmerian tectonic event bajocian in the alborz mountains northern iran evidence of the break up unconformity of the south caspian basin

late cretaceous and early miocene andean type plutonic activity in northern makran and central iran two calc alkaline plutonic complexes bazman and natanz intruded through the south eastern active and south western ancient continental margins of central iran have been dated by the rb sr whole rock isochron method at 74 2 and 24 4 5 ma respectively detailed trace element studies together with low 87 sr 86 sr initial ratios 87 sr 86 sr ratios and the gabbros at least were intruded some 10 ma earlier

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

syn rift thermal structure and post rift evolution of the oslo rift southeast norway new constraints from fission track thermochronology abstract the permo carboniferous 240 305 ma oslo graben in southeast norway is a classical magmatic continental rift we present fission track ft data on apatites zircons and sphenes from the rift and surrounding areas in order to clarify its syn and post rift thermal evolution zircons and sphenes within the rift record ft ages of between 270 and 180 ma i e syn post rifting in contrast the precambrian basement surrounding the graben yields zircon ft sphene ft ages of 500 650 ma indicating that heating associated with rifting was focused inside the rift as a result of advective heat flow syn rift to early post rift temperatures reached 240 c at the present erosion level in the graben syn rift advective heating 260 270 ma was probably a result of large scale batholith intrusion post rift 180 220 ma heating seems to have occurred by hydrothermal circulation of high temperature 100 300 c fluids the ft data organic geochemical indicators and fluid inclusions suggest that hydrothermal circulation followed a highly complex pattern controlled by the tectonic and volcanic structure of the rift apatite ft ages and confined track length distributions reveal the post rift exhumation history of the area apatite ft ages are continuous within and outside the graben and decrease from triassic 200 240 ma in the southeast to jurassic 160 ma in the northwest indicating that post rift exhumation took place on a much larger scale than permian rifting modelling of apatite ft ages and track lengths suggests cooling denudation events in the triassic jurassic and neogene accounting for a total post permian erosion of 3 4 km triassic jurassic denudation coincides with the migration of rifting from the oslo skagerrak area to the north sea danish basin as revealed by offshore seismic data and caused destruction of the hydrothermal regime neogene uplift and erosion of the area is also supported by seismic evidence the inferred timing and amount of regional post rift erosion suggests that post rift subsidence and sedimentation within the oslo graben was minimal

late cretaceous intraplate thrusting in central europe effect of africa iberia europe convergence not alpine collision a well established event of intraplate basin inversion and basement thrusting affected central europe in late cretaceous time it is widely accepted to have resulted from the collision of the alpine orogen with europe s margin at that time an early alpine orogen located on the leading edge of the adria microplate still lay far southeast of its present day position and had entered a phase of extension after a first orogenic event characterized by w to nw directed thrusting this configuration is not likely to have induced ssw nne directed thrusting and folding in the future european foreland that was still separated from the alpine wedge by a strip of oceanic lithosphere by contrast the onset of intraplate contraction coincides with an important change in relative motion between the european and african plates at ca 90 ma africa s sse directed sinistral transform motion relative to europe changed to ne directed convergence this agrees well with the timing and kinematics of intraplate thrusting in central europe structures of similar age and kinematics occurring in southern france spain and north africa suggest that the late cretaceous pulse of contraction was caused by pinching west central europe s thin lithosphere between baltica and africa only since the onset of n directed thrusting in the alps in paleocene or eocene time are the kinematics of the alps and their european foreland compatible indicating that mechanical coupling between africa europe and the adria microplate had been achieved

post cimmerian jurassic cenozoic paleogeography and vertical axis tectonic rotations of central iran and the alborz mountains according to previous paleomagnetic analyses the northward latitudinal drift of iran related to the closure of the paleo tethys ocean resulted in the late triassic collision of iran with the eurasian plate and cimmerian orogeny the post cimmerian paleogeographic and tectonic evolution of iran is instead less well known here we present new paleomagnetic data from the upper jurassic bidou formation of central iran which we used in conjunction with published paleomagnetic data to reconstruct the history of paleomagnetic rotations and latitudinal drift of iran during the mesozoic and cenozoic paleomagnetic inclination values indicate that during the late jurassic the central east iranian microcontinent ceim consisting of the yazd tabas and lut continental blocks was located at low latitudes close to the eurasian margin in agreement with the position expected from apparent polar wander paths apwp incorporating the so called jurassic massive polar shift a major event of plate motion occurring in the late jurassic from 160 ma to 145 140 ma at these times the ceim was oriented wsw ene with the lut block bordered to the south by the neo tethys ocean and to the southeast by the neo sistan oceanic seaway subsequently the ceim underwent significant counter clockwise ccw rotation during the early cretaceous this rotation may have resulted from the northward propagation of the sistan rifting spreading axis during late jurassic early cretaceous or to the subsequent late early cretaceous eastward subduction and closure of the sistan oceanic seaway underneath the continental margin of the afghan block no rotations of or within the ceim occurred during the late cretaceous oligocene whereas a second phase of ccw rotation occurred after the middle late miocene both the late jurassic early cretaceous and post miocene ccw rotations are confined to the ceim and do not seem to extend to other tectonic regions of iran finally an oroclinal bending mechanism is proposed for the origin of the curved alborz mountains which acquired most of its curvature in the last 8 myr

neogene block rotation in central iran evidence from paleomagnetic data paleomagnetic results from oligocene miocene sedimentary units in central iran are used to reconstruct the history of neogene tectonic deformation of this region paleomagnetic data show that in central iran crustal blocks bounded by sets of strike slip faults are rotated to accommodate nne ssw shortening related to arabia eurasia convergence counterclockwise rotations of 20 35 have been measured in the tabas and anarak areas south of the great kavir fault characterized by the presence of n s to nnw sse right lateral strike slip faults conversely in the great kavir and torud areas where ene wsw left lateral strike slip faults have been recognized paleomagnetic results are less conclusive because the small amount of measured clockwise rotation shows a statistically uncertainty which also includes the possibility of no rotation some of these faults have been active during the quaternary up to present day suggesting the possibility that block rotation is still occurring in central iran

structure and evolution of the bukhara khiva region during the mesozoic the northern margin of the amu darya basin southern uzbekistan the bukhara khiva region forms the northern margin of the mesozoic amu darya basin we reconstructed several cross sections across this margin from subsurface data the objectives included examining the structure of the bukhara and chardzhou steps and determining the tectonic sedimentary evolution of the basin during the jurassic subsequent to the cimmerian collision in the middle triassic an extensional event controlled the deposition of the early middle jurassic siliciclastic succession in the bukhara khiva region the main late palaeozoic inherited structures were reactivated as normal faults during this period continental coarse grained siliciclastic sediments are mainly confined to the basal lower jurassic section probably pliensbachian toarcian in age whereas marine siliciclastic sediments occur in the early late bajocian in the early middle jurassic the bukhara and chardzhou steps were predominantly sourced by areas of relief the remains of late palaeozoic orogens located to the north the rate of extension significantly declined during the middle callovian kimmeridgian period deposition of the overlying lower cretaceous continental red coloured clastic sediments was related to the interaction of basin subsidence a fall in eustatic sea level and sediment supply subsequent marine transgression in the late barremian partially related to broad thermal subsidence in the amu darya basin resulted in the deposition of an extensive late cretaceous clay marl succession

magnetic fabrics and microstructures of the jurassic shah kuh granite pluton lut block eastern iran and geodynamic inference abstract the jurassic shah kuh granite pluton was emplaced in the northeastern part of the lut block eastern iran while this block was a part of the active margin under which the tethys ocean that separated arabia from central iran was subducting since this time the lut block has rotated and migrated northward up to its present position this structural study of the shah kuh aims at strengthening the evidence of its original geodynamical location thanks to a systematic collection of oriented samples in the field well defined fabric and microstructural patterns were deduced from magnetic fabric measurements and optical microscopy observations the overall magnetic fabric of the pluton yields vertical north south striking foliations and shallow lineations plunging to the north the corresponding microstructures attest to their formation in the magmatic stage i e during emplacement subsequent deformation characterized by sub mylonitic microstructures has modified the original fabric into a northwest and locally a west northwest trend inside a two kilometre wide corridor this corridor reflects the trace of a sinistral shear zone that offsets the previous north south magmatic pattern of the pluton the latter magmatic pattern is proposed to result from the shear component of strain that was parallel to the ancient active margin during pluton emplacement as a result of strain partitioning a situation frequently documented at convergent margins sinistral shear along an e w directed south facing active margin assuming a northeastward slip vector for the tethys ocean during the jurassic and accepting a 150 counterclockwise rotation of the lut block after emplacement of the shah kuh pluton best explains both the magmatic and the solid state lineation patterns

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

the drift history of iran from the ordovician to the triassic new late ordovician and triassic palaeomagnetic data from iran are presented these data in conjunction with data from the literature provide insights on the drift history of iran as part of cimmeria during the ordovician triassic a robust agreement of palaeomagnetic poles of iran and west gondwana is observed for the late ordovician earliest carboniferous indicat ing that iran was part of gondwana during that time data for the late permian early early tri assic indicate that iran resided on subequatorial palaeolatitudes clearly disengaged from the parental gondwanan margin in the southern hemisphere since the late early triassic iran has been located in the northern hemisphere close to the eurasian margin this northward drift brought iran to cover much of the palaeotethys in approximately 35 ma at an average plate speed ofc 7 8 cm year 21 and was in part coeval to the transformation of pangaea from an irvin gian b to a wegenerian a type configuration

an overview of the cretaceous stratigraphy and facies development of the yazd block western central iran abstract the cretaceous successions of the yazd block the western of three structural blocks of the central east iranian microcontinent ceim have been studied using an integrated approach of litho bio and sequence stratigraphy associated with litho bio and microfacies analyses the cretaceous system of that area is in excess of 5 km thick and a generalized relative sea level curve can be inferred from the facies and thickness development this curve can be subdivided into two transgressive regressive megacycles trms separated by a major tectonic unconformity in the upper turonian trm 1 comprises the early cretaceous to middle turonian trm 2 the coniacian to maastrichtian trm 1 starts with up to 1500 m thick conglomerates and sandstones covering palaeozoic triassic basement rocks metasediments or upper jurassic lowermost cretaceous granites the basal tectonic unconformity related to the late cimmerian event jurassic cretaceous boundary interval shows a pronounced palaeo relief that is levelled by the basal siliciclastic formations sparse biostratigraphic data from calcareous intercalations in the upper part of these strata indicate a hauterivian to barremian age the aptian facies development is marked by the onlap of thick bedded micritic carbonates with abundant orbitolinid foraminifera and rudists representing a large scale shallow marine carbonate platform system that fringed the yazd block in the north and west these platforms are up to 1000 m thick and drowned during the middle to late aptian followed by up to 1500 m thick basinal marly sediments of late aptian to mid late albian ages representing the maximum relative sea level during trm 1 during the latest albian middle turonian a gradual shallowing is indicated by progradation of shallow water skeletal limestones separated by marl tongues representing a carbonate ramp system strata of trm 2 overlie older units along a regional angular unconformity and indicate tectonic stability and lowered subsidence rates as shown by widespread uniform coniacian maastrichtian facies and thickness development above a thick basal conglomerate the coniacian campanian facies is characterized by shallow water limestones of a large scale epeiric platform relative sea level peaked in the late campanian followed by maastrichtian infilling the cretaceous succession is truncated along a tectonic unconformity at the base of the palaeocene the major tectonic unconformities recognized at the base of the succession late cimmerian event in the late turonian and in the cretaceous palaeogene boundary interval are evidence of significant tectonic activity of the yazd block their formation is probably related to plate tectonic processes in response to the opening and closure of ocean basins surrounding the ceim

the shir kuh pluton central iran magnetic fabric evidences for the coalescence of magma batches during emplacement abstract the 136 ma nw se elongate shir kuh pluton is one of the most poorly understood geological feature of central iran it is composed of peraluminous rocks corresponding to ilmenite bearing s type granites compositionally ranging from granodiorites to leucogranites these rocks show a continuum in their chemistry attributed to progressive differentiation this allows using the anisotropy of magnetic susceptibility technique to tempt establishing the relative chronology between emplacements of magma batches in the pluton the rather low susceptibility magnitudes km

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

the cimmerian orogeny in northern iran tectono stratigraphic evidence from the foreland from the permian onwards the gondwana derived iran plate drifted northward to collide with eurasia in the late triassic thereby closing the palaeotethys this eo cimmerian orogeny formed the cimmeride fold and thrust belt the upper triassic middle jurassic shemshak group of northern iran is commonly regarded as the cimmerian foreland molasse however our tectono stratigraphic analysis of the shemshak group resulted in a revised and precisely dated model for the triassic jurassic geodynamic evolution of the iran plate initial cimmerian collision started in the carnian with subsequent late triassic synorogenic peripheral foreland deposition flysch lower shemshak group subduction shifted south in the norian onset of neotethys subduction below iran and slab break off around the triassic jurassic boundary caused rapid uplift of the cimmerides followed by liassic post orogenic molasse middle shemshak group during the toarcian aalenian upper shemshak group neotethys back arc rifting formed a deep marine basin which developed into the oceanic south caspian basin during the late bajocian late jurassic