morphological thermoelectrical geochemical and isotopic anatomy of auriferous pyrite from the bagrote valley placer deposits north pakistan implications for ore genesis and gold exploration abstract the bagrote valley in north pakistan belonging to the kohistan island arc is well known for regional placer gold mining however no economically feasible in situ hydrothermal gold deposits have been discovered in this region due to rugged terrain and remote nature of its location in the western himalaya the streams draining the main karakoram thrust mkt shyoke suture zone carry placer gold in sediments as well as old river terraces although the primary source remains unknown in this paper we employ a multiparametric approach including x ray diffraction xrd analysis thermoelectricity major and trace element geochemistry and isotopic characteristics of pyrite associated with placer gold with a view to identify the nature of the unknown deposits and ore forming fluids on the catchment of the bagrote valley pyrite in the bagrote valley placers is euhedral to subhedral indicating the proximal gold sources the high rate of occurrence of n type thermoelectric coefficients 89 with low p type 11 and crystallization temperature 290 c 380 c combined with chemical features indicate that the pyrite was derived from porphyry or epithermal type of magmatic hydrothermal gold deposits from the hinterlands of the bagrote valley the x ray elemental maps show that fe as mo and ni are homogenously distributed from core to rim suggesting stable crystallization condition without any alteration by later fluids the calculated chemical formula of pyrite of our samples is au0 0006fe s2 004 plots of au as and au fe shows that gold occurs in pyrite as micro to nano inclusion as au 0 the 34 s v cdt values of pyrite range from 0 6 to 0 9 with an average of 0 02 indicating the derivation of sulfur from a homogeneous magmatic source the pb isotope data indicates that the pb was sourced from orogenic type source with minor contribution of lower crust the narrow variations in 206 pb 204 pb and 208 pb 204 pb values suggest a single lead source the low medium and high mo ni ratios reflect a mixed provenance for the auriferous pyrite the average value of 71 8 of pyrite computed from thermoelectric parameters xnp suggests that the dominant part of the primary source that contributes to the placers might have already been eroded however the proximal source and with high content of gold in the pyrite grains up to 1160 ppm suggest the possibility of significant economic mineralisation below the present erosion level of the deposits in the hinterlands of bagrote valley

lateral variation of the mantle transition zone beneath the tibetan plateau insight into thermal processes during indian asian collision abstract the indian plate began to subduct under the eurasian plate in the late mesozoic since the eocene continuous continental collision has resulted in the uplift of the tibetan plateau with extensive volcanic activities geophysical and geochemical studies have suggested that the indian plate subducted and that volcanism originated in the deep upper mantle however the depth range of the subduction and volcanism and the relationship between them are still unclear here to image the mantle transition zone mtz structures we deployed new seismic stations and collected as much seismic data as possible from the tibetan plateau we then calculated the receiver functions and analyzed them using the common conversion point stacking method we found that the mtz is thickened by 20 km under the lhasa block where high velocity anomalies are obvious in the mtz apparent thinning of the mtz by 20 km was revealed under the qiangtang and songpan ganze blocks confirming a component of depleted mid oceanic ridge basalt in the magmatic rocks our results suggest that the indian plate has at least subducted to the mtz which has further induced mantle upwelling and volcanism in the tibetan plateau

the uplift history of the haiyuan liupan shan region northeast of the present tibetan plateau integrated constraint from stratigraphy and thermochronology abstractthe haiyuan liupan shan delimits the northeastern margin of the tibetan plateau we present the integrated results of new stratigraphic investigations apatite fission track analyses and related thermal history modeling tied to the structural fabric of this region these constraints provide insight into the timing of northward propagation of the plateau with 1 local relief creation and enhanced erosion in the latest jurassic to earliest cretaceous representing the local element of a complex regional far field deformation response to the lhasa qiangtang collision with the south asian margin 2 evidence for likely late cretaceous exhumation but this is uncertain given the regional sedimentary gap that exists across this interval 3 eocene relief generation as a first likely response to far field effects of the india asia collision and related to wider regional events recognized in this part of northwestern china and 4 the latest deformation episode propagating strongly into the haiyuan

historical pattern and behavior of earthquake ruptures along the eastern boundary of the sichuan yunnan faulted block southwestern china abstract the eastern boundary of the sichuan yunnan faulted block in southwestern china which contains four major fault zones named xianshuihe anninghe zemuhe and xiaojiang behaves as a huge left lateral strike slip active fault system where the most frequent seismicity in continental china occurs to uncover the history of earthquake ruptures of this fault system we developed an empirical relation between rupture extent and seismic intensity distribution based on data of those earthquakes whose rupture extents and intensity distributions are well known through analyzing various types of data including distributions of damage or intensity of historical earthquakes as well as surface ruptures and aftershock zones of modern earthquakes we determined systematically the locations and spatial extents of ruptures for 36 main earthquakes and built up a spatial temporal pattern of the rupture history of the fault system for the last several hundred years the spatial temporal rupture pattern contains information of multi cycle and broad scale ruptures from which we find that for most fault segments scales of segment ruptures are time or cycle variable and only in two or three cases do scales of segment ruptures in successive cycles seem to be characteristic in infrequent cases several adjacent and connecting fault units may rupture simultaneously resulting in cascading ruptures triggering of ruptures is common along the fault system but differs in various periods even on a single fault zone triggered ruptures may not occur on fault segments adjacent to a preceding rupture of major earthquake but on other segments at some distance away from the preceding rupture implying that the rupture history determines whether a segment can be triggered or not recurrence intervals of major segment ruptures are longer on the anninghe and zemuhe fault zones and on the southernmost segment of the xiaojiang fault zone than that on the xianshuihe fault zone and the northern and middle segments of the xiaojiang fault zone probably due to the partitioning of slip along major and secondary faults and their complicated fault geometry four seismic gaps along the fault system are recognized where major earthquakes have been absent for a long time

geological investigations at a high altitude remote coal mine on the northwest pakistan and afghanistan frontier karakoram himalaya abstract the northwest pakistan and afghanistan frontier is located one of the most remote inaccessible and inhospitable part of the himalayan orogenic belt in this region two of the world s largest and most distinct mountain belts intersect the karakoram himalaya mainly in pakistan and the hindu kush mainly in afghanistan located at high altitude in a remote part of northwest pakistan close to the border with afghanistan tribal villagers began excavating a series of adits into the steep mountain slopes beneath glaciers to extract valuable coal and carbonaceous shale resources these were discovered in 1996 by the villagers whilst hunting and may represent some of the highest mine workings in the world small scale mining operations subsequently developed using rudimentary mining methods and the mine became known as the reshit or pamir coal mine the coal deposits are sedimentary highly disturbed and tectonised having been subjected to multiple phases of orogenic crustal deformation the coal occurs as discrete lenses several tens of metres in their lateral dimension between steeply dipping overturned and thrusted limestone beds of jurassic age the coal provided a vital alternative source of fuel for the villagers since the local traditional fuel supply was wood which had become severely depleted and imports of kerosene from neighbouring china and afghanistan were too expensive the mining operations experienced severe problems these included several collapses of mine entrances the failure of the adits to intersect the coal bearing zones the potential threat of geological hazards mining induced hazards and harsh high altitude operating conditions particularly during the winter months international aid was provided to assist the villagers and a geological investigation was commissioned to investigate the problems at the mine the geology of karakoram himalaya is relatively poorly understood until recently the region was restricted to foreign visitors and large areas of this mountain belt are virtually unmapped existing geological and topographic maps are difficult to obtain or are unavailable due to the close proximity of political frontiers national borders and security reasons the mineral resource potential of this region is virtually unknown few western geologists have visited this area due to its inaccessibility and political constraints being situated close the frontiers with china afghanistan and the disputed pakistan and india territory of kashmir the pakistan and afghanistan border is once again now closed to foreign visitors the objectives of this paper are to document the occurrence of coal and carbonaceous shale at high altitude in the karakoram himalaya and to provide details on the geology geological hazards reserves and labour intensive mining operations these observations and information may provide the basis for future mineral exploration mining geology mining engineering feasibility studies and engineering geological investigation in the karakoram himalaya

stable drainage pattern and variable exhumation in the western himalaya since the middle miocene abstractsedimentary records in peripheral basins of mountain belts record changes in erosion dynamics and drainage network reorganization but it is often difficult to discriminate between these different controls geochemical provenance data on paleo indus deposits from the western himalayan foreland provide constraints on the possible variation of the position of the drainage divide between the indus and ganges river systems here we present geochemical trace element and hf nd isotopic and thermochronological detrital zircon fission track dzft analyses of modern indus and miocene siwalik sediments from northern pakistan and compare these with published data on the indus fan available bedrock isotopic data are used to define three end member sediment sources himalaya karakorum and the kohistan ladakh arc and to calculate the contribution of each of these sources to the foreland basin and indus fan our results indicate that since the miocene the contribution of the himalayan rivers reaching th

reconnaissance geology in upper chitral baroghil and karambar districts northern karakorum pakistan during the summer of 1992 a geological expedition crossed the northern karakorum range in northern pakistan from the chitral to karambar valleys from the villages of mastuj to imit some of the areas visited were geologically unknown a number of structural units were crossed belonging to the karakorum block or to other crustal blocks north of it they are a the axial batholith in which three plutonic bodies have been identified and b the northern sedimentary belt nsb in which three major tectonostratigraphic units form thrust stacks dipping to the north their internal stratigraphy and structural style are partly different the most complete contains a crystalline basement transgressed by a marine succession during the early ordovician the youngest strata are represented by the reshun conglomerate of inferred cretaceous age the northernmost unit of the nsb is tightly folded whereas the central one forms a monocline vertical faults mainly strike slip dissect the thrusted slabs metamorphic deformation is absent or reaches only the anchizone in the studied sector of the karakorum nsb to the north of the karakorum proper there are several other tectonic units separated by vertical faults they are from south to north a the tas kupruk zone with metavolcanics of basaltic to latibasaltic composition b the atark unit mostly consisting of massive carbonate rocks of mesozoic age and c the wakhan slates which consist of a thick widespread succession of dark slates metasiltites and sandstones the fine grained elastic rocks are supposed to be palaeozoic to early triassic in age the wakhan slates are intruded by plutons belonging to the east hindu kush batholith from which a single k ar age on muscovite gave a jurassic age

past and future earthquakes on the san andreas fault the san andreas fault in calfornia is one of the best studied earthquake generating faults in the world in their perspective weldon et al discuss recent efforts to construct rupture scenarios that is possible histories of the date location and length of fault rupture of past earthquakes on the fault existing knowledge of the locations and dates of past earthquakes can be explained by different scenarios but the authors argue that the evidence favors the hypothesis that the fault breaks in relatively infrequent large earthquakes they caution that the current 148 year hiatus since the last big earthquake is likely to end within the next 50 years with a large rupture or sequence of ruptures spanning a substantial part of the fault

the timing of india asia collision onset facts theories controversies abstract the timing of initial collision between india and asia has remained controversial for half a century this paper attempts to review this crucial and hotly debated argument describing first the different methods used to constrain the age of collision and discussing next the rationale results inferences and problems associated with each we conclude that stratigraphy represents the best direct way to unravel collision chronology other methods focusing on the magmatic metamorphic or paleomagnetic record provide additional fundamental constraints but cannot provide a robust direct estimate of collision onset initial collision in the central eastern himalaya is dated directly at the middle paleocene 59 1 ma by the abrupt change in sediment provenance recorded in trench settings the quasi synchronous unconformities documented along both tethyan passive margin of india and active margin of asia from tibet to zanskar ladakh confirm that orogeny was underway at the close of the paleocene 56 ma well before the disappearance of marine seaways in the himalaya during the early middle eocene 50 45 ma sedimentary evolution and provenance changes in marine to fluvio deltaic successions are recorded synchronously within error from the western to the central eastern himalaya failing to provide conclusive evidence for diachronous collision these coherent observations are hard to reconcile with three widely cited hypotheses invoking either paleogene arc continent collision or late cretaceous ophiolite obduction or the protracted existence of a greater india basin which are all not favored after discussing the geological evidence critically point by point a scenario no more complex than the one involving solely the passive continental margin of india and the active continental margin of asia is needed to explain the geological evolution of the nascent himalaya the collision between the tethys himalaya and the transhimalayan arc trench system does represent the collision between india and asia because the yarlung zangbo ophiolite is the forearc basement of the asian active margin its obduction onto india could not have preceded the initial closure of neo tethys ophiolite obduction began when collision began in the middle paleocene

paleocene initial indentation and early growth of the pamir as recorded in the western tarim basin abstract it is presently unclear as to when and how the pamir were uplifted to their current elevation because a cenozoic sedimentary record is lacking on the pamir plateau and the pamir domes only record metamorphism associated with crustal shortening since 37 ma studies of the tectonic and geomorphological evolution of the pamir in the early stages of the india asia continental collision are also lacking the western tarim basin at the northeastern margin of the pamir provides an ideal opportunity to investigate their formation and evolution four cretaceous paleogene stratigraphic sections were examined in this study from these we infer that the west kunlun mountains were topographic highs during the mesozoic that divided the adjacent central pamir tianshuihai terrane from the tarim basin this paleo topographic configuration lasted until a marine transgression occurred in the aksai chin and central pamir areas in the latest cretaceous provenance analysis indicates that sediments in the western tarim basin were derived solely from the west kunlun mountains until the paleocene the appearance of pamir derived detrital zircons in paleocene and eocene strata of the tarim basin suggests that the pamir was experiencing uplift and reached an elevation similar to or even higher than the west kunlun mountains at that time the sandstone composition documents a provenance change from a stable continental block to an active thrust belt of the proto west kunlun mountains indicating that the western tarim basin evolved from an intraplate to a foreland basin setting during the paleocene alluvial fan conglomerates were deposited along the northeastern margin of the pamir and a thick gypsum unit began to be deposited in the tarim basin all these lines of evidence indicate that the north verging thrusting foreland basin subsidence uplift and northward indentation of the pamir began in the paleocene 62 58 ma

neocimmerian events in central and western afghanistan abstract the neocimmerian orogenic belt of afghanistan is about 350 wide and lies between a northern eocimmerican orogenic belt which resulted from the closure of the paleotethys to the north and the alpine himalayan orogenic belt which resulted from the closing of the neotethys to the south this neocimmerian orogenic belt resulted from the closure of the waras penjaw oceanic realm at some time between the neocomian and the cenomano turonian the waras penjaw oceanic realm opened during or shortly after the triassic breaking off from continental asia where the ascent of the northern eocimmerian orogenic belt had recently ended it was located behind an active tectonic and magmatic arc which resulted from the neotethyan subduction during this opening the adjacent continental blocks were subjected to extension at that time the entire region was of the same type as the present japanese archipelago sea of japan eastern continental asia system located behind the western pacific subduction zone when the waras penjaw oceanic realm began to close its southern margin was activated the subsequent collision affected a vast region particularly the remnants of the northern eocimmerian orogenic belt this collision continued to act on the region during the neotethyan subduction shortly after these neocimmerian events the region was of the same type as the present southern andean region located between the south american continent and the eastern pacific subduction zone

thermal tectonic history of the baogutu porphyry cu deposit west junggar as constrained from zircon u pb biotite ar ar and zircon apatite u th he dating abstract understanding postmineralization tectonic movements in porphyry deposits is critical to interpreting the complete thermal tectonic history this study reports new zircon u pb ages hydrothermal biotite 39ar 40ar age and zircon and apatite u th he ages from the baogutu porphyry copper deposit which in conjunction with pre existing geochronology and thermochronology and inverse modeling simulations constrain the thermal tectonic history of the deposit zircon la icp ms u pb concordia ages indicate a late carboniferous age of 320 1 2 2 ma for the diorite complex and 309 8 2 2 ma for the mineralized granodiorite porphyry hydrothermal biotite selected from a quartz biotite chalcopyrite vein yields a plateau age of 311 0 1 8 ma which agrees with the age of the granodiorite porphyry and a previously reported molybdenite re os age and suggests that hydrothermal fluid circulated about 310 m y ago diorite and granodiorite porphyry yield weighted mean zircon u th he ages of 200 6 5 7 ma and 241 1 8 1 ma respectively with ages ranging from 221 0 ma to 174 3 ma and 225 9 to 261 6 ma weighted mean diorite and granodiorite porphyry apatite u th he ages of 87 4 2 3 ma and 120 0 4 2 ma were obtained with ages ranging from 68 9 ma to 100 8 ma and from 91 0 ma to 152 0 ma respectively the wide range of zircon u th he ages may be due to the combined effects of u and th zonation and radiation damage and radiation damage effect may also account for the wide range of apatite u th he ages the combined effects of depth and cooling due to meteoric water circulation contribute to an older u th he age for the granodiorite porphyry relative to the diorite a five episode cooling rate history for the diorite can be deduced by inverse model simulation fast cooling moderate fast cooling relatively slow cooling fast cooling again very slow cooling the thermal and tectonic history of the wall rock indicates that it suffered significant far field effects from the qiangtang eurasia and lhasa qiangtang collision however no visible thermal effect from the india asia collision is observed

tectonic evolution of the northeastern pamir constraints from the northern portion of the cenozoic kongur shan extensional system western china the late cenozoic kongur shan extensional system lies along the northeastern margin of the pamir at the western end of the himalayan tibetan orogen accommodating east west extension in the pamir at the northern end of the extensional system the kongur shan normal fault juxtaposes medium to high grade metamorphic rocks in both its hanging wall and footwall which record several mesozoic to cenozoic tectonic events schists within the hanging wall preserve a buchan metamorphic sequence dated as late triassic to early jurassic 230 200 ma from monazite inclusions in garnet metamorphic ages overlap with u pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the paleo tethys ocean the northern portion of the footwall of the extensional system exposes an upper amphibolite facies unit 650 c 8 kbar which structurally overlies a lowgrade metagraywacke unit the high grade unit records late early cretaceous crustal thickening at ca 125 110 ma followed by emplacement over the low grade metagraywacke along a north northeast directed thrust prior to ca 100 ma together these results indicate signifi cant middle cretaceous crustal thickening and shortening in the northern pamir prior to the indo asian collision a third late miocene ca 9 ma amphibolite facies metamorphic event 650 700 c 8 kbar is recorded in footwall gneisses of the kongur shan massif north of the kongur shan massif rapid cooling in the footwall beginning at 7 8 ma is interpreted to date the initiation of exhumation along the kongur shan normal fault a minimum of 34 km of east west extension is inferred along the kongur shan massif based on the magnitude of exhumation since the late miocene 29 km and the present dip of the kongur shan normal fault 40 field observations and interpretation of satellite images along the southernmost segment of the kongur shan extensional system indicate that the magnitude of late cenozoic east west extension decreases signifi cantly toward the south this observation is inconsistent with models in which east west extension in the pamir is driven by northward propagation of the right slip karakoram fault suggesting instead that extension is driven by vertical extrusion due to topographic collapse radial thrusting along the main pamir thrust or oroclinal bending of the entire pamir region

arcuate pamir in the paleogene insights from a review of stratigraphy and sedimentology of the basin fills in the foreland of ne chinese pamir western tarim basin abstract the tectonic evolution of the pamir bears essential information for understanding intracontinental tectonic processes within the context of india asia convergence however it is unclear whether the arcuate shape of the pamir is entirely the result of the india asia collision or may have been in part an inherited pre cenozoic feature in this study we address the evolution of the ne chinese pamir during the paleogene by reviewing the stratigraphy of twelve sections in the western tarim basin and the establishment of sedimentary facies the results indicate three episodes of deposition of alluvial coarse sediments in the foreland regions of ne chinese pamir during the 1 early paleocene 2 late paleocene to early eocene and 3 middle eocene to oligocene respectively these are correspondingly attributed to 1 retroarc deformation in an andean type margin of the southern asia during subduction of the neo tethys ocean 2 the immediate response in the pamir to the india asia collision and 3 continued india asia convergence the alluvial conglomerates with grain size up to 5 10 cm imply a transport distance

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

afghanistan structure greater india concept and eastern tethys evolution abstract the large and complex area between central asia and the arabia india block includes from north to south the tien shan and hindu kush kun lun hercynian belts the turkman farah rud and tanghla shan neokimmerian belt the zagros makran baluch himalayan alpine belt and relics of corresponding oceanic spaces the angarian or gondwanian affinities of the different blocks separated by these successive peri indian belts are discussed an interpretation is proposed for the paleogeographic and structural evolution of this area from early paleozoic to present this interpretation is based on geologic and paleomagnetic data and on global tectonic considerations the hindu kush kun lun pre hercynian ocean probably separated laurasia from gondwanaland it was an early paleozoic tethys tethys 1 the tien shan ocean may have been a marginal basin for the hindu kush kun lun ocean the turkman farah rud tanghla shan pre neokimmerian ocean resulted from the break up of the gondwanaland margin its opening seems to have been related to the pre hercynian ocean closure resulting in the formation of a new tethys tethys 2 its subsequent closure may also have been related to the opening of the zagros baluch indus tsang po pre alpine ocean tethys 3 according to this interpretation eurasia appears to have increased from early paleozoic to cenozoic by successive accretion of cratonic blocks which came from the south through the tethys this evolution can be compared to the similar mediterranean evolution this interpretation is in agreement with the greater india concept however the northern border of greater india differs according to the stage of the gondwanaland evolution which is considered actually greatest india extended north to the caledonian belt and consequently has recorded the whole history of the eastern tethys

insights into the evolution of the hindu kush kohistan karakoram from modern river sand detrital geo and thermochronological studies the hindu kush kohistan karakoram region is critical to understanding the long term accretion history of the south asian margin pre and post india asia collision and the impact of these collisions on the development of high topography however knowledge about this region remains incomplete due to sparse studies here we present a study comprising detrital zircon u pb geochronology detrital muscovite 40ar 39ar thermochronology and numerical modeling on 40ar 39ar dates the study identifies zircon u pb age peaks at 200 ma 110 130 ma 60 80 ma and 28 40 ma supporting the polyphase collisions and crustal growth in the south asian margin modeling study reveals fast cooling erosion at 115 129 ma 69 71 ma 27 35 ma and 8 ma which are synchronous with collision related crustal growth indicating the significant impact of accretion both prior to and post india asia collision this study along with studies in eastern karakoram reveals along strike variations in erosion and exhumation with young since late miocene intense erosion focusing on the east central karakoram we suggest that this east west spatial variation in exhumation may have been associated with more intense crustal shortening and thus the greater crustal thickness topographic relief and altitude observed in the eastern compared to western karakoram

hercynian and eocimmerian events in afghanistan and adjoining regions abstract the area centered around afghanistan is a collage of continental blocks derived from gondwanaland this collage comprises among others 1 1 a hercynian orogenic belt widely represented in afghanistan and also by some sparse outcrops in the northern iran it is a subduction type orogen constructed at the margin between the paleotethys and the turan turkestan tarim block 2 2 a northern eocimmerian orogenic belt widely represented in afghanistan and the north of iran it is a collision type orogen constructed in the same place as the hercynian orogenic belt and resulted from the closure of the paleotethys and the collision of the central iran and central afghanistan blocks with the turan turkestan tarim block 3 3 a southern eocimmerian orogenic belt of which outcrops are now confined to southern iran but which may project beneath the neogene and quaternary formations of southern afghanistan it is a subduction type orogen constructed at the margin between the neotethys and the central iran central afghanistan block which itself was at that time subjected to regional extension this belt is now incorporated in the alpine himalayan orogen the geology of these belts suggests that the opening of the neotethys became effective only from the permian or triassic and was in a red sea type phase during the upper devonian its initial rifting possibly occurred during the lower paleozoic much like the paleotethys in which initial rifting also occurred in lower paleozoic time and whose opening became effective from the ordovician thus each of the oceanic realms in this region appears to have possibly resulted from the same extension of gondwanaland during the lower paleozoic after which they followed more or less different paths of evolution moreover the proposed geodynamic interpretation implies that during the permian and triassic there was in this region a certain coexistence of the vanishing paleotethys with the relatively young neotethys which was beginning to subduct

geologic offsets across the northern karakorum fault implications for its role and terrane correlations in the western himalayan tibetan orogen abstract while the 1000 km long karakorum right slip fault is one of the most prominent structures in the himalayan tibetan orogen considerable disagreement exists as to the total magnitude of offset across the fault and the role it has played in accommodating convergence between india and asia using satellite images i have correlated a well defined carbonate unit the late triassic early jurassic aghil formation across the northern portion of the karakorum fault from the southwest pamir to the tianshuihai terrane of western tibet the northern and southern exposure limits of the aghil formation have 149 167 km of separation which i interpret to represent the magnitude of displacement on the northern karakorum fault these values overlap with estimates correlating the bangong nujiang and shyok sutures across the central karakorum fault and maximum offsets of the miocene baltoro granite and rule out correlations of the bangong nujiang suture and the rushan pshart suture the displacement yields a geologic slip rate of 10 8 1 3 mm yr using an initiation age of 14 7 1 ma or 6 89 0 8 mm yr with an initiation age of 23 1 ma this result supports previous work showing limited offset across the karakorum fault and indicates that the fault that has not accommodated either large magnitudes i e 100 s of km of eastward lateral extrusion of tibet or hundreds of kilometers of offset between terranes of the western and central portions of the orogenic belt

a geological transect from kun lun to karakorum sinkiang china the western termination of the tibetan plateau preliminary note a geological geophysical expedition ev k2 cnr 1988 visited the area from west kun lun to karakorum k2 gasherbrum seven tectonic units including sedimentary magmatic and metamorphic rocks were distinguished in this area the northernmost are suggested to belong to the kun lun and qiangtang microplates the sedimentary sequence of shaksgam is proved to extend from the permian to the jurassic with carboniferous and cretaceous ages more doubtful this sequence shows intermediate affinities between the karakorum and the qiangtang the two southernmost units belong to the karakorum microplate the karakorum fault zone comprises a complex pattern of faults and thrusts with brittle deformation and uplifting of granitoid bodies

mesozoic tectonics of the gondwanan terranes of the pamir plateau abstract the central and southern pamir terranes represent gondwanan crustal fragments within the pamir plateau and are bounded by the tanymas rushan pshart and wakhan tbz suture zones from north to south stratigraphic and geochronologic data suggest that collision of the central and southern pamir terranes with the southern margin of asia was broadly coeval during the latest triassic earliest jurassic cimmerian orogeny 200 ma the cimmerian orogeny in the pamir region does not appear to have resulted in significant crustal thickening of the central and southern pamir as both terranes are overlain by lower to middle jurassic carbonate platform deposits post suturing latest triassic earliest jurassic sandstones with a strong arc signature in the southern pamir suggest derivation from the karakul mazar terrane to the north implying the northern pamir were a region of elevated topography relative to the gondwanan terranes immediately after closure of the palaeotethys and rushan ocean basins a key question in the post cimmerian tectonic evolution of the pamir is the extent and magnitude of mesozoic deformation of the central and southern pamir three lines of evidence suggest that much of the post jurassic crustal shortening documented in the central and southern pamir is related to mesozoic tectonic activity rather than the cenozoic india asia collision as generally interpreted 1 the southern pamir does not record post jurassic marine deposition indicating the terrane elevated above sea level by the early cretaceous most likely due to crustal shortening and thickening 2 coarse terrigenous deposits distributed throughout the central and southern pamir interpreted to be syn tectonic with regional folding and thrust faulting are poorly dated with many studies interpreting them to be jurassic to cretaceous rather than paleogene 3 strong cretaceous crustal thickening and shortening documented to the south in the karakoram terrane and to the north in the northern pamir suggest that the central and southern pamir were similarly affected these relationships suggest that most of the upper crustal shortening documented in the central and southern pamir is related to retroarc deformation north of the jurassic cretaceous andean margin that developed within the karakoram and southern pamir terranes during subduction of the neotethys ocean thus the pamir plateau may have been a westward continuation of the pre cenozoic lhasa plano of the tibetan plateau

the north karakorum side of the central asia geopuzzle an italian geological team visited a remote and in part never studied area in the northern hunza region pakistan which represents the link between the karakorum and pamir ranges the north karakorum sequence commences in the permian with terrigenous sediments followed by shallow to deep marine carbonates deposited on a newly formed passive margin deep water sedimentation continued till the end of the middle triassic when carbonate platform conditions resumed an episode of deltaic red sandstones with orogenic provenance is interbedded in the liassic and it is transgressed by a middle to upper jurassic shallow water marine unit eventually all of the sequence was faulted and folded with weak metamorphic imprint before fluviatile red polygenic conglomerates sealed the succession in a spectacular unconformity the north karakorum provides an example of a microplate that rifted away from gondwana in the permian reached deep marine conditions in the early triassic and marginally recorded compressive movements in the liassic a subsequent orogenic episode points to a reorganization of the southern asian margin possibly around middle cretaceous time finally the north karakorum was affected by strong fold thrust deformation and low to very low grade metamorphism in the cainozoic related to the india asia collision

geology of the cenozoic indus basin sedimentary rocks paleoenvironmental interpretation of sedimentation from the western himalaya during the early phases of india eurasia collision this study reassesses the stratigraphy sedimentology and provenance of the indus basin sedimentary rocks deposited within the indus tsangpo suture zone itsz during the early phases of india eurasia collision using field observations biostratigraphy and petrographic and isotopic analyses we create a paleodepositional reconstruction within the paleotectonic setting of the early phases of india eurasia collision we then re examine existing constraints to the timing of india eurasia collision previously interpreted from the earliest occurrence of mixed indian and eurasian derived detritus in the succession from mid cretaceous to early paleocene times the jurutze and sumda formations were deposited within an arc bounded marine basin between the dras and kohistan ladakh island arcs the 51 ma aged deltaic chogdo formation then filled the basin until deposition of the 50 8 49 4 ma aged nummulitic limestone during a marine incursion before continental facies developed in an evolving intermountain basin with the deposition of the paleogene indus group within these systems sediment was sourced from the eurasian margin to the north and was transported southward into the suture zone in this section we see no unequivocal evidence of indian plate input to the sedimentary succession and thus no evidence of mixed indian eurasian derived detritus indicative of india asia collision until the upper stratigraphic horizons of the indus group when facies are representative of an axial northwesterly flowing river system we suggest that the paleo indus river was initiated within the itsz during late oligocene early miocene times sedimentation of the indus group continued until the late miocene

k ar and ar ar geochronology of the himalayan collision in nw pakistan constraints on the timing of suturing deformation metamorphism and uplift mica and hornblende k ar and ar ar data are presented from each of the three crustal components of the himalayan collision zone in north pakistan the asian plate the kohistan island arc and the indian plate together with u pb and rb sr data published elsewhere these new data 1 date the age of suturing along the northern suture which separates kohistan from asia at 102 85 ma 2 establish that the basic magmatism in kohistan which postdates collision along the northern suture predates 60 ma and that the later granite magmatism spanned a range of 60 25 ma 3 show that uplift amounts within kohistan are greater toward the nanga parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 ma to a current figure of about 5 5 mm a year 4 show that much of southern kohistan had cooled to below 500 c by 80 ma and that the major deformation which imbricated kohistan probably predated 80 ma and certainly predated 60 ma and was related to the kohistan asia collision rather than the kohistan india one 5 imply that uplift along the hunza shear in the asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 ma and was associated with breakback thrusting in the hanging wall of the main mantle thrust 6 suggest that the indian plate has a lengthy pre himalayan history with an early metamorphism at about 1900 ma major magmatism at 500 550 ma and early jurassic lithospheric extension or inversion and 7 show that the indian plate rocks were metamorphosed shortly after the collision within kohistan which occurred at circa 50 ma and subsequently cooled back through 500 c at circa 38 ma and 300 c at 30 35 ma with ages of cooling through 200 and 100 c as determined by fission track data locally controlled by nanga parbat related uplift tectonics

sedimentary and tectonic evolution of the southern qiangtang basin implications for the lhasa qiangtang collision timing the mesozoic stratigraphic record of the southern qiangtang basin in central tibet records the evolution and closure of the bangong nujiang ocean to the south the jurassic succession includes toarcian aalenian shallow marine limestones quse formation aalenian bajocian feldspatho litho quartzose to feldspatho quartzo lithic sandstones shallow marine sewa formation and deep sea gaaco formation and bathonian outer platform to shoal limestones buqu formation this succession is truncated by an angular unconformity overlain by upper bathonian to lower callovian fan delta conglomerates and litho quartzose to quartzo lithic sandstones biluoco formation and callovian shoal to outer platform limestones suowa formation sandstone petrography coupled with detrital zircon u pb and hf isotope analysis indicate that the sewa and gaaco formations contain intermediate to felsic volcanic detritus and youngest detrital zircons 183 170 ma with ehf t ranging widely from 13 to 25 pointing to continental arc provenance from igneous rocks with mixed mantle and continental crust contributions an arc trench system thus developed towards the end of the early jurassic with the southern qiangtang basin representing the forearc basin above the angular unconformity the biluoco formation documents a change to dominant sedimentary detritus including old detrital zircons mainly 500 ma ages in the lower part of the unit with age spectra similar to those from paleozoic strata in the central qiangtang area a major tectonic event with intense folding and thrusting thus took place in late bathonian time 166 1 ma when the qiangtang block collided with another microcontinental block possibly the lhasa block

granites of western karakorum and northern kohistan pakistan a composite mid cretaceous to upper cenozoic magmatism abstract the petrography the chemical mineralogical typology and the ages of six plutonic units four from the karakorum axial batholith darkot pass ghamu bar batura and hunza units and two of northern kohistan gindai and nomal plutons are defined and compared based on field data and analyses of up to 78 samples major elements ree rb s sbnd sr and k ar isotopes the karakorum axial batholith is a composite body three major intrusive stages occurred 1 around mid cretaceous times ca 110 95 ma with the emplacement of subalkaline i e monzonitic darkot pass and calc alkaline hunza ghamu bar units 2 during palaeogene maybe up to 43 ma batura subalkaline unit a strong tectonommetamorphic event recorded in the gneissification of the cretaceous intrusives occurred between these two stages it may be of palaeocene age p t estimates of the highest metamorphic grade rocks of the hunza unit have yielded values of 580 640 c and 5 0 5 kbar and 3 during upper miocene ca 9 ma baltoro subalkaline unit debon et al 1986c in addition a conspicuous network of aplo pegmatitic dykes emplaced into the hunza area possibly from the eocene up to the upper cenozoic with a maximum during the middle miocene ca 15 ma most of these major magmatic stages are met again among the acidic intrusives and dykes of northern kohistan the first one as blastomylonitic tholeiitic plutons nomal ca 102 ma petterson and windley 1985 the second one as subalkaline plutons gindai ca 59 ma and a third one as leucocratic dykes of oligocene age ca 30 ma petterson and windley 1985 these data may be related to the geodynamic evolution of the nw part of the india eurasia suture zone thus allowing better constraints on the major steps of this evolution the partly synchronous closures by n dipping subduction of the two tethys branches which are assumed to have encircled the kohistan arc in upper mesozoic times may have generated both the karakorum and the kohistan intrusives of cretaceous and palaeogene ages the northern branch very likely closed before the southern one at the time of the second intrusive stage palaeogene a kohistan and karakorum had already collided were welded and had suffered the same major tectonometamorphic event b subduction of the southern tethys floor beneath the welded kohistan karakorum was still active c however collision between india and kohistan karakorum may have already begun particularly at the level of the nanga parbat promontory finally it is emphasized that the intrusive processes continued in the karakorum long after the collision e g baltoro granite

evolution of the middle strand of north anatolian fault and shallow seismic investigation of the southeastern marmara sea gemlik bay abstract the gemlik bay is developed as a pull apart basin during the late pliocene early pleistocene mainly controlled by west trending dextral strike slip faults along the middle strand of the north anatolian fault zone with the nw trending thrace eskisehir fault playing secondary role the north anatolian fault reached the eastern marmara sea 3 5 ma ago where its middle strand intersected the thrace eskisehir fault gps slip vectors measured on the armutlu and mudanya blocks show a displacement of 7 8 km during the last 3 5 ma the middle strand of the north anatolian fault zone has lower tectonic activity than the northern strand because uplift of the southeast marmara sea region has been continuous since the late pliocene the presence of fluviatile lacustrine and deltaic environments in the gemlik pull apart basin over the same period supports a lower lever of tectonic activity the transgressive marmara formation was deposited on top of these fluvio lacustrine deposits following the mediterranean inundation at 600 ka via the strait of canakkale the gemlik basin was affected both by two major sea level falls at 160 132 and 24 11 ka and minor short lived sea level variations as a result of becoming a lacustrine setting five times since 600 ka during these lowstands stacked delta successions were deposited around the lake and on the transgressed shelves of the marmara sea

age of crystallization and cooling of the k2 gneiss in the baltoro karakoram the mountains of k2 8611 m and broad peak 8047 m in the baltoro karakoram northern pakistan are composed of plagioclase homblende and biotite hornblende k feldspar orthogneisses and amphibolite facies paragneisses intruded by garnet biotite muscovite tourmaline leucogranitic veins a u pb zircon age of 115 120 ma was obtained on an orthogneiss from the south face of k2 40 ar 39 ar analysis on hornblende yields a plateau age of 90 6 1 8 ma consistent with a mid cretaceous phase of magmatism concomitant with early subduction related components of the karakoram batholith muztagh tower unit hunza plutonic unit we interpret the k2 gneiss as representing a culmination of mid crustal rocks along a discontinuous but wide zone north of the karakoram batholith

incipient india eurasia collision and plutonism the lower cenozoic batura granites hunza karakorum north pakistan plutonism of the karakorum north of the india eurasia suture zone comprises two major intrusive stages the oldest mid cretaceous predates the collision the youngest miocene is post suturing in between lower cenozoic plutonism roughly syn suturing and represented by the batura complex is made up of a few small and usually undeformed plutons the complex has a subalkaline i e intermediate between alkaline and calc alkaline and ferriferous association dominated by light coloured metaluminous and slightly peraluminous granites and adamellites with biotite amphibole titanite whole rock rb sr isochron ages of 63 ma this study and 43 ma debon et al 1987b have been obtained for two plutons with rather low initial 87 sr 86 sr ratios 0 7050 0 7056 a comparison with granitoids of similar age from kohistan suggests that the complex relates to the subduction of the tethys ocean and originates from a mantle source with but small crustal contribution through a two stage melting process the apparently limited extent of lower cenozoic plutonism in the karakorum contrasts with its wider development in the transhimalaya and kohistan this contrast could be partly accounted for by changes in tectonic and magmatic suduction related processes after the initial contact between india and eurasia was established in the nw himalaya

field relationships and geochemistry of pre collisional india asia granitoid magmatism in the central karakoram northern pakistan in the central karakoram range northern pakistan seven major granitic units which were emplaced prior to the eocene ca 50 ma india asia collision have been mapped and analysed geochemically the mid cretaceous hunza plutonic complex dominates the karakoram batholith in the west and is composed of quartz diorite granodiorite plutons which have been deformed in the south by later collision related thrusting the sost and khunjerab plutons intrude the palaeozoic early mesozoic sediments north of the batholith in the east pre collision magmatic units occur both north of k2 gneiss broad peak quartz diorite muztagh tower unit and south of hushe gneiss the batholith which is dominated by a miocene monzogranite leucogranite pluton baltoro unit the plutonic units to the north of the batholith are mid to late cretaceous with an age range of ca 115 80 ma whereas the hushe gneiss to the south is dominantly jurassic spanning the age range 200 145 ma all the pre collision magmatic units display similar chemical and isotopic characteristics major trace and ree variations in the hunza plutonic complex are controlled by high level fractionation of clinopyroxene hornblende plagioclase biotite ilmenite and allanite high lile hfse and lree hree ratios together with negative nb p and ti anomalies suggest an ultimate source in the mantle wedge above the subducting slab 87sr 86sr initial ratios 0 7055 0 7157 in the hunza plutonic complex can best be explained by contamination of a mantle derived magma by a crustal component with highly radiogenic sr all the units except the hushe gneiss are probably related to subduction during closure of a back arc basin between the karakoram to the north and the kohistan dras arc to the south during the mid to late cretaceous and correlate with widespread plutonism from the same period in kohistan ladakh and southern tibet along the southern margin of asia the hushe gneiss is probably related to an earlier northward directed subduction phase during the jurassic