millennial to interannual climate variability in the mediterranean during the last glacial maximum climate change during the late pleistocene is dominated by periodicities on millennial time scales as documented by ice cores and sedimentary marine and terrestrial records of global distribution interannual to decadal variations have also been demonstrated in dust concentrations in greenland ice cores but there is lack of comparable detail in sedimentary records an 8 5 m long multiproxy record from lake albano central italy spanning the time interval between 15 0 and 28 0 cal kyr bp reveals a high temporal resolution window into climate change during the last glacial maximum lgm distinct warm cold cycles of millennial to centennial duration indicate a major response of the lake to climate induced environmental changes flickering interannual to interdecadal variations within these cycles are interpreted to reflect oscillations of the north atlantic nao implying shifts in temperature wind strength source of moisture and atmospheric circulation pattern

quantifying climatic change through the last glacial interglacial transition based on lake isotope palaeohydrology from central turkey questions remain as to the nature of climatic change through the last glacial interglacial transition in the eastern mediterranean region particularly the relative contribution of evaporation and precipitation to regional water balance here changes in oxygen isotope values through this time period from eski acigol a crater lake in central turkey are investigated using hydrological and isotope mass balance models these allow changes in evaporation and precipitation to be quantified and their relative importance evaluated we show that it is the volumetric flux rate of water passing through the lake system and not the precipitation to evaporation ratio per se which controlled the stable isotope record in eski acigol early holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day we test these calculated values against other records in the same region firstly with other lake records in anatolia the konya basin and lake van and secondly with isotope inferred palaeo precipitation data from soreq cave in israel this reveals a contrast between pre and post lgm precipitation values in turkey wetter and drier respectively and also suggests that during the last glacial interglacial transition there was a more marked precipitation gradient than at present between northern interior and southern coastal parts of the eastern mediterranean region

provenance of the greater himalayan sequence evidence from mafic granulites and amphibolites in nw bhutan abstract mafic granulites and amphibolites in the masang kang area of nw bhutan himalaya have been investigated for their geochemical and isotopic characteristics in order to determine their protolith history bulk rock major and trace element geochemistry indicate that the rocks were originally tholeiitic and alkali basalts with minor ultramafics u pb zircon sims data suggest an age of 1742 39 ma for mafic magmatism the age corrected e nd 1742 values of the rocks are highly variable ranging from high positive 8 4 to negative 3 3 the positive value suggests a primitive magma source similar to that of rift related tholeiites we suggest that the rocks of the masang kang suite were produced during a major late paleoproterozoic thermal event that caused the mobilization and enrichment of the sub continental lithospheric mantle beneath the north indian margin the geochemical signature of these rift related metabasic rocks may have been produced during an earlier episode of oceanic underplating or subduction from which the fluid required to mobilize and enrich the overlying sub lithospheric mantle may have been derived though their occurrence is rare paleoproterozoic igneous rocks within the greater himalayan sequence ghs in addition to sources identified throughout the lhs may have contributed to the detrital zircon population that form the 1 7 1 9 ga peak in the age spectra of the lesser himalayan sequence lhs in addition the coeval paleoproterozoic magmatism in both lhs and ghs suggests that the two lithotectonic units may have belonged to the same continental plate at that time period

slip along the sultanhani fault in central anatolia from deformed pleistocene shorelines of palaeo lake konya and implications for seismic hazards in low strain regions

back folds in the core of the himalayan orogen an alternative interpretation the hanging wall of the south tibetan detachment system in the central nepal himalaya is characterized by regional scale northeast verging folds classically interpreted as gravity induced structures developed during down to the north extensional shearing along the detachment system new structural observations and balanced cross sections of the tethyan sedimentary sequence in the kali gandaki area and new u pb geochronology support an alternative interpretation the northeast verging folds developed before ductile extensional shearing along the detachment system thereby recording some of the earliest contraction of this part of the orogen we propose a new model in which the northeast verging folds of the kali gandaki area represent the northern part of a late eocene to oligocene contractional fan structure

the identification and significance of pure sediment derived granites the characterization of the geochemical reservoirs of the earth s continental crust including the determination of representative upper and lower crustal compositions underpins our understanding of crustal evolution the classic i and s type granite classification has often been invoked to distinguish between melts derived from igneous protoliths and those derived from the melting of a sedimentary source recent geochemical studies suggest that most granites even those cited as typical examples of s type show evidence for a mixture of mantle and upper crustal sources thereby implying that granite formation is evidence for overall crustal growth we have examined the source of leucogranite bodies in one of the world s youngest collisional orogens using novel zircon techniques that can resolve the presence of even minor mantle contributions 232 zircons from 12 granites from the bhutan himalaya were analysed by in situ techniques for o hf and u pb isotopic signatures in combination with data from the granite host rocks our data show that the himalayan leucogranites were derived solely from metamorphosed crustal sediments and do not record any mantle contribution this finding is consistent with the time lag between crustal thickening and widespread crustal melting and the heat producing capacities of the pelitic source rocks we conclude that himalayan leucogranites provide a more suitable type locality for s type granites than the lachlan area in south east australia where the term was first defined the himalayan leucogranites therefore provide evidence that syn orogenic melting during collisional events does not necessarily result in crustal growth importantly crustal growth models should not always assume that crustal growth is achieved during collisional orogenesis

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

late neogene and active orogenic uplift in the central pontides associated with the north anatolian fault implications for the northern margin of the central anatolian plateau turkey 1 surface uplift at the northern margin of the central anatolian plateau cap is integrally tied to the evolution of the central pontides cp between the north anatolian fault naf and the black sea our regional morphometric and plate kinematic analyses reveal topographic anomalies steep channel gradients and local high relief areas as indicators of ongoing differential surface uplift which is higher in the western cp compared to the eastern cp and fault normal components of geodetic slip vectors and the character of tectonic activity of the naf suggest that stress is accumulated in its broad restraining bend seismic reflection and structural field data show evidence for a deep structural detachment horizon responsible for the formation of an actively northward growing orogenic wedge with a positive flower structure geometry across the cp and the naf taken together the tectonic plate kinematic and geomorphic observations imply that the naf is the main driving mechanism for wedge tectonics and uplift in the cp in addition the naf zone defines the boundary between the extensional cap and the contractional cp the syntectonic deposits within inverted intermontane basins and deeply incised gorges suggest that the formation of relief changes in sedimentary dynamics and 1 km fluvial incision resulted from accelerated uplift starting in the early pliocene the central pontides thus provide an example of an accretionary wedge with surface breaking faults that play a critical role in mountain building processes sedimentary basin development and ensuing lateral growth of a continental plateau since the end of the miocene

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

sedimentary structures preserved in greater himalayan gneiss phenomenon or fantasy abstractunder favorable conditions sedimentary structures may be preserved in high grade metamorphic rocks to yield valuable clues about the depositional and paleogeographic setting of the protolith two examples from gneisses of the greater himalayan sequence of bhutan demonstrate this potential laminated channeled dolostone within gneiss of upper amphibolite facies indicates tidal flat deposition and thus proximity of a paleoshoreline the type takhtsang gneiss within granulite facies consists of alternating millimeter bands rich in quartz and biotite interpreted as silt and clay interlaminations respectively in the protolith typical of tidal deposits or varves the gneissic banding drapes around isolated lenses of contrasting and varied compositions interpreted as dropstones this combination suggests deposition in a varved glacial lake published comparisons of takhtsang lithologies indicate a minimum dimension of 315 km for the postulated lake these examples demonstrate the potential of r

correlation of lithotectonic units across the eastern himalaya bhutan clastic sediments deposited in foreland basins and offshore fans allow the evolution of an orogen to be reconstructed provided their source regions are properly characterized isotopic data from the lithotectonic units of the eastern himalaya bhutan indicate clear isotopic differences directly comparable with the equivalent units from the central himalaya zircons from metaquartzites of the high himalayan series that range in age from 980 to 1820 ma and an orthogneiss intruded at 825 9 ma bracket deposition to between 816 and 980 ma model ages derived from nd isotopes of associated metapelites range from 1700 to 2200 ma in contrast zircons from a metaquartzite from the lesser himalayan series range from 1850 to 2550 ma a paleoproterozoic deposition age ca 1750 ma is inferred from the age of a metarhyolite associated with the sediments model nd ages of metapelites from the lesser himalayan series range from 2500 to 2600 ma the bhutanese himalayan units can be correlated more than 1000 km westward along strike from catchments of the brahmaputra to the headwaters of the sutlej on the basis of their structural position provenance and isotopes because current discharge from the brahmaputra carries the dominant sedimentary flux into the bengal fan results from this work validate the interpretation of isotopic variations observed in offshore deposits in terms of the unroofing history of the component lithologies of the himalaya

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

evolution of the melt source during protracted crustal anatexis an example from the bhutan himalaya the chemical compositions of magmatic zircon growth zones provide powerful insight into evolving magma compositions due to their ability to record both time and the local chemical environment in situ u pb and hf isotope analyses of zircon rims from oligocene miocene leucogranites of the bhutan himalaya reveal for the first time an evolution in melt composition between 32 and 12 ma the data indicate a uniform melt source from 32 ma to 17 ma and the progressive addition of an older source component to the melt from at least ca 17 ma age corrected ehf ratios decrease from between 10 and 15 down to values as low as 23 by 12 ma complementary whole rock nd isotope data corroborate the hf data with a progressive decrease in end t from ca 18 to 12 ma published zircon and whole rock nd data from different lithotectonic units in the himalaya suggest a chemical distinction between the younger greater himalayan series ghs and the older lesser himalayan series lhs the time dependent isotopic evolution shown in the leucogranites demonstrates a progressive increase in melt contribution from older lithologies suggestive of increasing lhs involvement in himalayan melting over time the time resolved data are consistent with lhs material being progressively accreted to the base of the ghs from ca 17 ma facilitated by deformation along the main central thrust from 17 ma decompression which had triggered anatexis in the ghs since the paleogene enabled melting in older sources from the accreted lhs now forming the lowermost hanging wall of the thrust

metamorphic response to collision in the central himalayan orogen abstract closure of the neotethys ocean and high angle continent continent collision between india and asia after about 55 ma resulted in low angle subduction of the indian plate below the tibetan plateau and by 30 ma established an arcuate 2300 km long shallow north dipping metamorphic fold thrust belt in the foreland this himalayan metamorphic front quickly established an upper plate lower plate paired metamorphic architecture centred on the median high himal thrust that largely controlled subsequent evolution the upper plate is a thick slab of high t moderate p high grade migmatized metamorphic rocks whereas the lower plate is an inverted series of moderate t high p schists in two crustal wedges the broad main central thrust zone and at lowest structural levels the footwall below the basal main central thrust spatial and temporal patterns of metamorphic response in the evolving himalayan metamorphic front has been characterized in a large scale integrated structural metamorphic study based on 8 profiles across eastern nepal metamorphic response at all structural levels is established using a large dataset n 160 of internally consistent quantitative pt determinations petrology of metapelite samples semi quantitative p t paths metamorphic mapping and metamorphic field gradients these results are integrated with previously published metamorphic studies structural profiles and metamorphic chronology from these datasets the architecture and evolution of the himalayan metamorphic front is constrained by rock kinematics metamorphic field gradients showing discontinuities and diachronous metamorphism with contrasting p t evolutions at different structural levels each of the three panels constituting the himalayan metamorphic front upper plate main central thrust zone and footwall experienced distinctly different tectono metamorphic histories crustal processes operating during metamorphism and exhumation differ between the upper and lower plates the upper plate experienced long lived metamorphism starting from at least 28 38 ma and tracking low p t clockwise p t paths that culminated at 19 27 ma in peak high grade condition with 27 31 c km thermal regimes protracted high grade conditions produced significant partial melt which facilitated gravity driven southward extrusion involving internal ductile flow processes southward extrusion of the upper plate was accommodated by coeval reverse movement on the high himal thrust and top down to the north normal reactivation of the south tibet detachment system between 22 10 ma transport of this thick slab to the south resulted in further prograde burial of the lower plate below culminating in peak metamorphism at the highest pressures attained in the lower plate rocks the lower plate consists of at least two deeply buried 7 5 9 4 kb crustal wedges both of which experienced steep p t hairpin clockwise p t paths with isothermal decompression the main central thrust zone experienced 20 26 c km metamorphism at 12 22 ma and was exhumed along the basal main central thrust after 11 ma whereas loading by the main central thrust zone gave rise to further prograde burial of the footwall which experienced 16 21 c km metamorphism at 4 10 ma and was exhumed along the main boundary thrust at 3 9 ma in contrast to the upper plate both crustal wedges were exhumed by a process of out wedging which involved upthrusting along basal and internal thrusts with coeval extensional slip in the hanging walls this three stage foreland propagating lateral exhumation history resulted in telescoping of the himalayan metamorphic front in concert with peak metamorphic events at different structural levels during main phase orogenesis and is not the result of superimposed retrograde reactivation of the belt

u pb zircon geochronology of major lithologic units in the eastern himalaya implications for the origin and assembly of himalayan rocks models for the origin and deformation of himalayan rocks are dependent upon geometric and age relationships between major units we present field mapping and u pb dating of igneous and detrital zircons that establish the lithostratigraphic architecture of the eastern himalaya revealing that 1 the south tibet detachment along the bhutan china border is a top to the north ductile shear zone 2 late triassic and early cretaceous sedimentary samples from the northern indian margin show a similar age range of detrital zircons from ca 3500 ma to ca 200 ma but the late triassic rocks are distinguished by a significant age cluster between ca 280 and ca 220 ma and a well defined age peak at ca 570 ma 3 an augen gneiss in the south tibet detachment shear zone in southeast tibet has a cambrian ordovician crystallization age 4 main central thrust hanging wall paragneiss and footwall quartzites from the far western arunachal himalaya share similar provenance and late proterozoic maximum depositional ages and 5 main central thrust footwall metagraywacke from the central western arunachal himalaya has a paleoproterozoic maximum depositional age indicated by a single prominent age peak of ca 1780 ma recent work in the eastern himalaya demonstrates that in the early middle miocene the himalayan crystalline core here was emplaced southward between two subhorizontal shear zones that merge to the south a proposed subsequent middle miocene brittle low angle normal fault accomplishing exhumation of these rocks along the range crest can be precluded because new and existing mapping demonstrates only a ductile shear zone here the ca 280 220 ma detrital zircons of the late triassic strata are derived from an arc developed along the northern margin of the lhasa terrane detritus from this arc was deposited on the northern margin of india during india lhasa rifting along strike heterogeneity in main central thrust footwall chronostratigraphy is indicated by detrital zircon age spectrum differences from central western to far western arunachal nonetheless the late proterozoic rocks in the main central thrust hanging wall and footwall in far western arunachal can be correlated to each other and to previously analyzed rocks in the south tibet detachment hanging wall to the west and in the indian craton to the south these findings are synthesized in a reconstruction showing late triassic india lhasa rifting and cenozoic eastern himalayan construction via in situ thrusting of basement and cover sequences along the north indian margin

on water detection in the martian subsurface using sounding radar several radar experiments are planned to map the martian subsurface down to several kilometers searching for subsurface liquid water reservoirs using different concepts and techniques all based on the penetration property of radio frequency waves in arid soils the penetration depth of low frequency radar is mainly related to the electromagnetic properties of the investigated medium thus a good knowledge of the martian subsurface dielectric profile along the first few kilometers is necessary for future water identification and data interpretation in this work we have investigated the electrical and magnetic properties of the martian surface and subsurface using terrestrial laboratory analogues in the frequency range 1 500 mhz covering the frequency domain of the mars advanced radar for subsurface and ionosphere sounding marsis experiment on board the mars express mission esa 2003 the netlander ground penetrating radar gpr cnes 2007 and future sounding radar that may be updated to the mars exploration program in the follow the water strategy in our approach we constructed experimentally the most common dielectric profile representative of the martian subsurface by measuring the electric permittivity and magnetic permeability of well defined mixtures of basaltic volcanic and sedimentary materials that have been reported for mars we also considered iron oxides hematite and maghemite and evaporites that may be present such as gypsum and their mixtures with representative amounts of the martian geological context under the most common petrophysical and geophysical conditions along the subsurface profile this led to synthetic representative samples of the martian subsurface materials under adequate conditions of porosity and temperature that should exist in the first 2 5 km of the upper crust dielectric measurements show that the first layers of the martian subsurface a few hundred meters which are mainly composed of volcanic iron rich materials could dramatically decrease the radar penetration depth initially foreseen thus limiting deep subsurface exploration we also investigated the constraints on subsurface water detectability in a radar lossy medium and its dielectric identification among surrounding geological materials

strain and rotation rate from gps in tibet anatolia and the altiplano 1 deformation measured by regional gps networks in continental plateaus reflects the geologic and tectonic variability of the plateaus for two collisional plateaus tibet and anatolia and one noncollisional the altiplano we analyze the regional strain and rotation rate by inverting gps velocities to calculate the full two dimensional velocity gradient tensor to test the method we use gridded velocities determined from an elastic block model for the eastern mediterranean middle east region and show that to a first order the deformation calculated directly from the gps vectors provides an accurate description of regional deformation patterns principal shortening and extension rate axes vertical axis rotation and two dimensional 2 d volume strain dilatation are very consistent with long term geological features over large areas indicating that the gps velocity fields reflect processes responsible for the recent geologic evolution of the plateaus differences between geological and gps descriptions of deformation can be attributed either to gps networks that are too sparse to capture local interseismic deformation or to permanent deformation that accrues during strong earthquakes the altiplano has higher internal shortening magnitudes than the other two plateaus and negative 2 d dilatation everywhere vertical axis rotation changes sign across the topographic symmetry axis and is due to distributed deformation throughout the plateau in contrast the collisional plateaus have large regions of quasi rigid body rotation bounded by strike slip faults with the opposite rotation sense from the rotating blocks tibet and anatolia are the mirror images of each other both have regions of positive dilatation on the outboard sides of the rotating blocks positive dilatation in the aegean correlates with a region of crustal thinning whereas that in eastern tibet and yunnan province in china is associated with an area of vertical uplift rollback of the hellenic trench clearly facilitates the rotation of anatolia rollback of the sumatra burma trench probably also enables rotation about the eastern syntaxis of tibet

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

short and long term deformation patterns in the aegean anatolian systems insights from space geodetic data gps geodetic measurements gps in the eastern mediterranean suggest higher rates of motion of about 10 mm yr in the aegean western anatolian zone with respect to those in the central eastern anatolia in this work we explore the plausibility of the hypothesis that the observed kinematics may be significantly influenced by post seismic relaxation processes induced by the seismic activation of the north anatolian fault since 1939 the major implications of this hypothesis are tentatively quantified by a simplified model constituted by an elastic lithosphere 100 km thick coupled with a viscous asthenosphere 250 km thick with a viscosity of 10 19 pas the predicted perturbation of the displacement and stress fields is consistent with geodetic velocities and could also account for the major features of seismic activity in the period considered

metamorphic reactions related to decompression and synkinematic intrusion of leucogranite high himalayan crystallines bhutan the high himalayan crystallines hhc of bhutan were penetratively deformed intruded by leucogranite and metamorphosed during the collision of the indian and asian plates metamorphic reaction textures in the hhc show that it experienced decompression while maintaining a laterally heterogeneous and locally inverted internal temperature range of c 600 750c this thermal structure was produced by thrusting hot migmatitic rocks over lower grade rocks within the hhc and by the advection of heat from the intrusion of leucogranite dykes and sills during decompression a variable velocity field within the hhc during exhumation and extrusion between india and tibet caused the inversion of top to the south sense of shear present throughout most of the hhc to top down to the north shear near its top

the geology and tectonics of central bhutan lithotectonic mapping metamorphic observations and u pb zircon ages underpin a substantial revision of central bhutan geology notably a more extensive and continuous outcrop of the tethyan sedimentary series tss than previously mapped metamorphic grade in the tss increases downward towards a basal north vergent tectonic contact with the underlying greater himalayan series ghs interpreted as a southward continuation of the south tibetan detachment std miocene c 17 20 ma leucogranite sheets are associated with the std in this region but appear to diminish southwards two leucogranite dykes that cross cut tss structures yield ages of 17 8 0 2 and 17 9 0 5 ma a 500 4 ma u pb zircon metamorphosed ash bed in the pele la group within the psammite dominated lower tss yields the first direct isotopic age for the tss in the eastern himalaya confirming existing age constraints from detrital zircon and fossil studies a continuation of the paro metasedimentary unit underlying the ghs was mapped near wangdue phodrang our observations notably the exposure of a wholly ductile std so far south and the significance of large nappe like structures in the tss prompt a major revision to the geological map of the bhutan himalaya and require a reassessment of tectonic interpretations of the bhutan himalaya supplementary materials zircon u pb geochronological data sample locations and descriptions features of analysed zircons sample processing method and detailed analytical conditions are available at http www geolsoc org uk sup18876

environmental and climatic changes during the last 20 000 years at lake tuz central turkey abstract our study demonstrates the importance of detailed lithostratigraphic and biostratigraphic analyses of deposits of lake side terraces and alluvial fans in attempts to identify fluctuations of climate characteristics such as precipitation and evaporation rates and of local conditions for water balance changes in the central part of turkey during the last 20 000 years lake tuz basin central part of the anatolian plateau turkey had two high lake level stages dated as about 20 000 17 000 years ago and about 13 000 years ago at the high lake stages water level rose more than 15 m higher than the present lake level and the lake area spread widely to near the southern edge of the basin as inferred by lithologic and chronological investigation of drilling cores in the holocene lake level fell and the southeast part of the basin became extensive lake terraces alluvial fans have formed along the edge of the upland area on the terraces in the holocene stratigraphy and dating of the fan deposits show the fluctuations in the depositional rates of the fans major formative stages of the fans are dated about 7000 5500 and 2500 2000 years bp and several times of minor stages probably 4300 and 3000 years bp occurred between the two major stages our archaeological research shows that there are strong relationships between the distributions of archaeological sites of this area and the above geo environmental histories

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

evaluation of wasatch fault segmentation and slip rates using lake bonneville shorelines 1 analysis of lake bonneville shorelines using lidar digital elevation data challenges accepted models of wasatch fault deformation since the late pleistocene while footwall deformation of the weber segment of the wasatch fault is consistent with back rotation of the footwall block and greatest displacement rate toward the center of the segment shorelines along the footwall of the salt lake city segment decrease in elevation toward the interior and are highest at the segment boundaries an opposite pattern of footwall deformation than predicted for boundaries arresting or strongly inhibiting displacement during earthquakes the spatial pattern of footwall rebound implies that some of the proposed persistent fault segment boundaries do not stop earthquake ruptures that originate on adjacent fault segments nor constrain ruptures initiated within the salt lake city segment net vertical fault displacement at the boundary between the salt lake and provo segments is 16 20 m over the past 16 3 18 5 ka corresponding to a vertical displacement rate of 0 8 1 2 mm yr a net fault slip rate of 2 0 2 8 mm yr and horizontal extension rate of 1 8 2 6 mm yr on the 25 west southwest dipping fault that forms the southern salt lake city segment boundary shoreline analysis suggests isostatic rebound caused by a drop in lake level was concentrated during a relatively short 2000 year time period following the bonneville flood at 16 ka lidar derived topography in conjunction with robust geomorphic datums improves our ability to map deformation associated with lithospheric flexure and faulting while demonstrating the limitation of lacustrine shorelines in this type of analysis

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

cambrian ordovician orogenesis in himalayan equatorial gondwana an early paleozoic tectonic event the kurgiakh orogeny has long been known from the western tethyan himalaya and it is conspicuously recorded by an angular unconformity between cambrian marine shelf deposits and coarse ordovician conglomerate as well as widespread granitic plutons although the lateral extent of this event is poorly known two regions in the central and eastern himalaya the kumaon of india and klippen of bhutan contain conglomerate units that may be correlative with this event in the kumaon the ralam formation which contains a basal polymictic conglomerate unit with detrital zircon grains as young as ca 512 ma is overlain by sandstone containing the arthropod walking trace diplichnites gouldi an ichnospecies known from ordovician and younger strata the late early cambrian trilobite redlichia sp recovered from the underlying martoli group indicates that the conglomerate is post early cambrian and based on stratigraphic analysis also likely records the kurgiakh orogeny in central bhutan the lower paleozoic succession contains conglomerate units with monomictic quartz sandstone clasts and less mature sandstone matrix these units have also been assigned to a variety of ages but rocks that apparently underlie these strata contain the furongian late cambrian zonal trilobite kaolishania granulosa here we show that detrital zircon ages of a conglomerate clast no grains younger than ca 781 ma are distinctly older than those of the matrix which contains a large peak at 490 500 ma thus these conglomerate units are also potential lateral correlatives of the ordovician conglomerate deposits of the western himalaya our paleontological and geochronologic data suggest that the kumaon and bhutan conglomerate units and possible equivalents in tibet correlate with those of the western himalaya this increases their known along strike extent by over 1000 km bringing the total extent to 1200 km thus the kurgiakh orogeny spanned much of the himalayan orogen along the northern gondwanan margin and reflected a widespread tectonic reorganization of the peri gondwanan realm to andean type margins recent work indicates that it also likely extended into the lhasa block and both the north and south china blocks this event was associated with widespread ca 500 ma arc related plutonism recorded in the himalaya and with abundant detrital zircon grains of that age in younger himalaya strata based on current fossil data the duration of the hiatus associated with the cambrian ordovician boundary which separates pre and postdeformational strata ranges from 22 to 36 m y available geochronological data do not provide greater constraint if the event was close in age to the depositional age of the ordovician molasse then the main phase of tectonic uplift erosion and deposition may have been much later than the presumed cambrian ordovician boundary interval age of ca 485 ma

geologic correlation of the himalayan orogen and indian craton part 2 structural geology geochronology and tectonic evolution of the eastern himalaya despite being the largest active collisional orogen on earth the growth mechanism of the himalaya remains uncertain current debate has focused on the role of dynamic interaction between tectonics and climate and mass exchanges between the himalayan and tibetan crust during cenozoic india asia collision a major uncertainty in the debate comes from the lack of geologic information on the eastern segment of the himalayas from 91 e to 97 e which makes up about one quarter of the mountain belt to address this issue we conducted detailed field mapping u pb zircon age dating and 40ar 39ar thermochronology along two geologic traverses at longitudes of 92 e and 94 e across the eastern himalaya our dating indicates the region experienced magmatic events at 1745 1760 ma 825 878 ma 480 520 ma and 28 20 ma the first three events also occurred in the northeastern indian craton while the last is unique to the himalaya correlation of magmatic events and age equivalent lithologic units suggests that the eastern segment of the himalaya was constructed in situ by basement involved thrusting which is inconsistent with the hypothesis of high grade himalaya rocks derived from tibet via channel flow the main central thrust in the eastern himalaya forms the roof of a major thrust duplex its northern part was initiated at ca 13 ma while the southern part was initiated at ca 10 ma as indicated by 40ar 39ar thermochronometry crustal thickening of the main central thrust hanging wall was expressed by discrete ductile thrusting between 12 ma and 7 ma overlapping in time with motion on the main central thrust below restoration of two possible geologic cross sections from one of our geologic traverses where one assumes the existence of pre cenozoic deformation below the himalaya and the other assumes flat lying strata prior to the india asia collision leads to estimated shortening of 775 km 76 strain and 515 km 70 strain respectively we favor the presence of significant basement topography below the eastern himalaya based on projections of early paleozoic structures from the shillong plateau i e the central shillong thrust located 50 km south of our study area since northeastern india and possibly the eastern himalaya both experienced early paleozoic contraction the estimated shortening from this study may have resulted from a combined effect of early paleozoic and cenozoic deformation

southern tibet detachment system at khula kangri eastern himalaya a large area shallow detachment stretching into bhutan abstract a new map and cross sections of the khula kangri and kankar punzum monlakarchung high himalayan ranges in the tibet bhutan frontier area are presented from integration of unpublished mapping from the summit section of khula kangri and new remote sensing together with previous mapping the ranges define an orographic bifurcation of the high himalaya that results in a north south repetition of the main geological section and coincides with the morphological repetition the southern tibet detachment system that juxtaposes the tethyan sedimentary rocks against the gneisses and granites of the high himalayan crystalline can be continuously traced around both ranges and is not imbricated postdetachment kilometer scale flexure and faulting account for the features of the observed bifurcation the true map extent of the khula kangri and monlakarchung passalum granite batholiths is now apparent we propose that the two plutons are part of the same originally continuous body

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

pre miocene deformation of the himalayan superstructure hidden valley central nepal abstract throughout the himalaya the tethyan sedimentary sequence forms the detached carapace or superstructure to exhumed mid crustal rocks in central nepal low metamorphic grade cambrian to jurassic rocks of this carapace preserve five phases of deformation structurally dominated by second phase d 2 north verging back folds that oppose the vergence of the orogen the folds are overprinted and cross cut by the c 22 ma south tibetan detachment system and the manaslu leucogranite new structural mapping in hidden valley provides further constraints on the character of d 2 megascopically large asymmetric north verging folds define d 2 microscopically it is characterized by an axial planar cleavage balanced cross sections and bed length restoration of f 2 folds indicate a minimum of 32 38 shortening and 180 thickening during d 2 these data indicate that north verging folds played a significant role in pre miocene crustal thickening of the himalayan superstructure the formation of these folds is compatible with wedge extrusion or channel flow of the underlying mid crustal rocks whereby their geometry reflects early coupling between the upper and middle crust

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

probing the depths of the india asia collision u th pb monazite chronology of granulites from nw bhutan 1 rocks metamorphosed to high temperatures and or high pressures are rare across the himalayan orogen where peak metamorphic conditions recorded in the exposed metamorphic core the greater himalayan sequence ghs are generally at middle to upper amphibolite facies however mafic garnet clinopyroxene assemblages exposed at the highest structural levels in bhutan eastern himalaya preserve patchy textural evidence for early eclogite facies conditions overprinted by granulite facies conditions monazite hosted within the leucosome of neighboring granulite facies orthopyroxene bearing felsic gneiss yields la mc icp ms u th pb ages of 13 9 0 3 ma monazite associated with sillimanite grade metamorphism in granulite hosting migmatitic gneisses yields u th pb rim ages between 15 4 0 8 ma and 13 4 0 5 ma monazite associated with sillimanite grade metamorphism in gneiss at structurally lower levels yields u pb rim ages of 21 17 ma these data are consistent with miocene exhumation of ghs material from a variety of crustal depths at different times along the himalayan orogen we propose that these granulitized eclogites represent lower crustal material exhumed by tectonic forcing over an incoming indian crustal ramp and that they formed in a different tectonic regime to the ultrahigh pressure eclogites in the western himalaya their formation and exhumation in the miocene therefore do not require diachroneity in the timing of the initial india asia collision

when did the roof collapse late miocene north south extension in the high himalaya revealed by th pb monazite dating of the khula kangri granite th pb ion microprobe measurements made on 12 monazite grains from the khula kangri granite tibet bhutan frontier are interpreted to indicate that crystallization occurred at 12 5 0 4 ma the leucogranite is cut by the gonto la detachment part of the southern tibet detachment system that has allowed upper level north directed extension of the himalayan orogen significant orogen normal extension in southern tibet appears to have continued 8 10 m y later than previously recognized this is the first reported crystallization age for a leucogranite east of the yadong cross structure an apparent 70 km offset of the high himalaya and southern tibet detachment west of the yadong cross structure reliable ages for high himalaya events major main central thrust slip granite generation and emplacement attainment of critical topography and major detachment extension group between ca 24 and 19 ma we interpret the west to east change across the yadong cross structure to be due to either 1 an abrupt 10 m y younging of principal high himalayan events or 2 a deeper thus younger exposed part of the footwall of the southern tibet detachment near khula kangri the southern tibet detachment is cut by the highly oblique yadong gulu rift a manifestation of tibet plateau east west extension integrated estimates of magnitude and rate of detachment displacement suggest that the observed postcrystallization north directed extension lasted for 1 3 m y after which time the yadong gulu rift formed this interpretation is consistent with initiation of east west extension of tibet at ca 8 ma

exhumation of the main central thrust from lower crustal depths eastern bhutan himalaya geothermometry and mineral assemblages show an increase of temperature structurally upwards across the main central thrust mct however peak metamorphic pressures are similar across the boundary and correspond to depths of 35 45 km garnet bearing samples from the uppermost lesser himalayan sequence lhs yield metamorphic conditions of 650 675 c and 9 13 kbar staurolite kyanite schists about 30 m above the mct yield p t conditions near 650 c 8 10 kbar kyanite bearing migmatites from the greater himalayan sequence ghs yield pressures of 10 14 kbar at 750 800 c top to the south shearing is synchronous with and postdates peak metamorphic mineral growth metamorphic monazite from a deformed and metamorphosed proterozoic gneiss within the upper lhs yield u pb ages of 20 18 ma staurolite kyanite schists within the ghs a few metres above the mct yield monazite ages of c 22 1 ma we interpret these ages to reflect that prograde meta morphism and deformation within the main central thrust zone mctz was underway by c 23 ma u pb crystallization ages of monazite and xenotime in a deformed kyanite bearing leucogranite and kyanite garnet migmatites about 2 km above the mct suggest crystallization of partial melts at 18 16 ma higher in the hanging wall south verging shear bands filled with leucogranite and pegmatite yield u pb crystallization ages for monazite and xenotime of 14 15 ma and a 1 2 km thick leuco granite sill is 13 4 0 2 ma thus metamorphism plutonism and deformation within the ghs con tinued until at least 13 ma p t conditions at this time are estimated to be 500 600 c and near 5 kbar from these data we infer that the exhumation of the mct zone from 35 to 45 km to around 18 km occurred from 18 to 16 to c 13 ma yielding an average exhumation rate of 3 9 mm year 1 this process of exhumation may reflect the ductile extrusion by channel flow of the mctz from between the overlying tibetan plateau and the underthrusting indian plate coupled with rapid erosion

highly fractionated himalayan leucogranites and associated rare metal mineralization abstract the formation of the himalaya was associated with the exhumation of high grade metamorphosed rocks of the higher himalayan sequence hhs complex which underwent amphibolite granulite to eclogite facies metamorphism and anatexis occurring along the himalayan mountain crest in the south and the lhagoi kangri mountain in the north the himalayan leucogranites contain varying proportions of biotite

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

a short duration pulse of ductile normal shear on the outer south tibetan detachment in bhutan alternating channel flow and critical taper mechanics of the eastern himalaya in easternmost bhutan the south tibetan detachment std is a ductile shear zone that juxtaposes the radi or sakteng klippe of the tethyan sedimentary series from underlying high grade greater himalayan rocks in situ la icpms u th pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the std within the shear zone at the base of the klippe constrains north vergent normal shear to between 25 and 20 ma coeval thrusting on the main central thrust during this time supports a phase of channel flow viscous wedge model activity lasting only ca 3 ma geochronologic data from the eastern himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the late oligocene through to the late miocene switching from channel flow viscous wedge behavior to critical taper frictional wedge behavior each phase lasting approximately only 2 to 5 ma the tectonic evolution of the eastern himalaya is comparable to central and western himalayan tectonics during the early miocene but during the middle miocene metamorphism and magmatism in the eastern himalaya migrated towards the orogenic hinterland a process not widely documented elsewhere in the himalaya thus highlighting the need for an orogenic model in three spatial dimensions

preliminary stratigraphic and structural architecture of bhutan implications for the along strike architecture of the himalayan system article i nfo preliminary mapping and stratigraphic correlation of lesser himalayan rock in eastern bhutan using field characteristics u pb detrital zircon dating and nd geochemistry define the first order stratigraphic architecture of the indian passive margin sequence in the eastern himalaya we use this new image of the lateral and vertical relationships of the original stratigraphy to determine the structural framework of the eastern himalayan fold thrust belt in bhutan we propose that lesser himalayan rock in bhutan can be divided into lower lesser himalayan rocks with a paleoproterozoic detrital zircon signal and upper lesser himalayan rocks with detrital zircon signals of 1000 500 ma the 500 ma detrital grains are from rocks in the frontal portions of the fold thrust belt north of the main boundary thrust as well as directly in the footwall of the main central thrust in the hinterland our preliminary stratigraphic study coupled with mapping allows us to construct a composite balanced cross section through the kuru chu valley in eastern bhutan which provides the first image of the geometry and amount of shortening through bhutan the main frontal thrust tilts a 6 km of thick section of neogene foreland basin deposits these deposits are separated from folded and faulted upper lesser himalayan rocks by the main boundary thrust north of the main boundary thrust we propose two duplex systems the southernmost duplex contains 9 repeated sections of upper lesser himalayan units including the permian gondwana sequence and the cambrian or younger baxa group the northernmost duplex is located in the footwall of the main central thrust and is comprised of two repeated sections of the proterozoic shumar and daling formations the southern boundary of this northern duplex is the shumar thrust which acts as a roof thrust for the southern duplex system and may correlate to the ramgarh thrust in nepal and india we propose that the development of the duplex systems passively folded overlying tethyan and greater himalayan rocks minimum shortening for this part of the himalayan fold thrust belt is 359 km all of which has occurred from 22 ma to present defining a long term shortening rate of 16 mm yr

flattening the bhutan himalaya a detailed thermobarometric transect of 35 samples across the greater and tethyan himalayan sequences in central bhutan demonstrates a tectonostratigraphically intact section with uniform apparent thermal and baric field gradients of 2072 1c km and 0 5770 08 kbar km pressure temperature paths determined from chemically zoned garnets in 6 samples demonstrate that these p t conditions correspond with maximum pressures the super lithostatic baric gradient cannot be explained by pre to syn metamorphic tectonic processes or by extension within an inclined slab instead the data imply 50 post peakmetamorphic flattening of the himalayan metamorphic core accommodated by distributed top to thenorth shear consistent with microstructural analysis orogenic flattening best explains the development of the south tibetan detachment system as a strain incompatibility feature rather than a structure bounding the top of a tectonically inserted wedge and helps reconcile debate attributing first order himalayan structural features to either wedge failure critical taper or pipe flow channel flow

tectonics of a part of the shumar allochthon in eastern bhutan abstract the lesser himalaya of eastern bhutan is made up of a pile of thin thrust sheets stacked on one another and the shumar allochthon lies at the top of this pile the shumar allochthon is a composite tectonic unit divisible into two structurally discordant sub units the upper sub unit system b is made up of a layered sequence of quartzite phyllite and marble that repeats several times through the sequence several subsidiary thrusts in the lower sub unit system a form a imbricate system arranged as a hinterland dipping duplex this imbricate system is spatially related to a transverse footwall ramp where the shumar thrust has cut up the underlying buxa stratigraphic sequence at the crest of this ramp the shumar thrust and the roof thrust of the duplex join forming a splay a detailed map of a part of the shumar allochthon reveals that alternate blocks parcels or horses of metasediments and sheared granitic gneisses constitute the stack of imbricates in this duplex analysis of the imbricate system indicates accretion of footwall elements in the course of forward propagation of the shumar allochthon and thus provides an idea about the nature of the basement on which the allochthon moved these accreted footwall elements suggest that the thrust sheets of the lesser himalaya of eastern bhutan moved and now rest on a basement of precambrian gneisses the top part of this gneissic basement was mobilized and involved in the thrusting process as is shown by the horses of the basement repeated at several levels within the shumar allochthon isolated patches of younger sediments on the precambrian gneisses were also involved in the thrusting

great earthquakes in low strain rate continental interiors an example from se kazakhstan the lepsy fault of the northern tien shan se kazakhstan extends e w 120 km from the high mountains of the dzhungarian ala tau a subrange of the northern tien shan into the low lying kazakh platform it is an example of an active structure that connects a more rapidly deforming mountain region with an apparently stable continental region and follows a known palaeozoic structure field based and satellite observations reveal an 10 m vertical offset exceptionally preserved along the entire length of the fault geomorphic analysis and age control from radiocarbon and optically stimulated luminescence dating methods indicate that the scarp formed in the holocene and was generated by at least two substantial earthquakes the most recent event dated to sometime after 400 years b p is likely to have ruptured the entire 120 km fault length in a m w 7 5 8 2 earthquake the lepsy fault kinematics were characterized using digital elevation models and high resolution satellite imagery which indicate that the predominant sense of motion is reverse right lateral with a fault strike dip and slip vector azimuth of 110 50 s and 317 343 respectively which is consistent with predominant n s shortening related to the india eurasia collision in light of these observations and because the activity of the lepsy fault would have been hard to ascertain if it had not ruptured in the recent past we note that the absence of known active faults within low relief and low strain rate continental interiors does not always imply an absence of seismic hazard

pressure temperature structural distance relationships within greater himalayan rocks in eastern bhutan implications for emplacement models in the himalayan orogen greater himalayan gh rocks were buried to mid to lower crustal levels and are now exposed across the strike of the orogen within the eastern himalaya in the kingdom of bhutan the gh is divided into structurally lower lower gh and upper upper gh levels by the kakhtang thrust kt pressure temperature estimates from lower and upper gh rocks collected on two transects across the kt yield similar p t structural distance trends across each transect in the eastern transect temperatures are similar from 730 to 650 c over a structural thickness of 11 km but peak pressures decrease from 10 to 6 kbar with increasing structural level in comparison peak temperatures in the central bhutan transect are similar from 730 to 600 c but pressures decrease from 10 to 6 5 kbar with increasing structural level over a structural thickness of 6 km the structurally highest sample reveals slightly higher pressures of 8 0 kbar in comparison to pressures of 6 5 kbar for samples collected from within the kt zone 4 km below within each transect there are increases in pressure temperature within the overall upright p t gradient that may demarcate intra gh shear zone s these p t results combined with evidence that the timing of initial melt crystallization becomes older with increasing structural level suggest that the intra gh shear zones emplaced deeper gh rocks via progressive ductile underplating these shear zones including the kt likely aided in the initial emplacement and construction of the gh as a composite tectonic unit during the late oligocene to early miocene from c 27 to 16 ma

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

temperature and age constraints on the metamorphism of the tethyan himalaya in central nepal a multidisciplinary approach abstract metasediments of devonian to triassic age of the tethyan himalaya th from several areas in central and western nepal between western dolpo and marsyandi valley were sampled for thermo metamorphic studies illite and chlorite crystallinity vitrinite reflectance calcite dolomite and chlorite chloritoid geothermometers k ar dating on illite rich fractions and zircon fission track thermochronology this paper reports for the first time the occurrence of chloritoid in the th out of the range of granite contact aureoles it also presents the first zircon fission track dating performed on th metasediments the peak temperatures of metamorphism have been around 250 300 c 320 350 c 330 370 c and 400 450 c in the western dolpo hidden valley manang and marpha areas respectively in the manang and hidden valley areas illite k ar data are interpreted as ages of recrystallized k white micas newly formed during metamorphism at around 25 30 ma in the marpha area illite k ar and zircon fission track ages 12 15 ma are consistent representing cooling ages after metamorphic overprinting of higher grade than in the other areas the joint investigation of the organic maturation and zircon ft chronology yields insight on the thermal calibration of zircon reset the rmax of 5 7 to 8 0 indicates a temperature range of ca 315 325 c which is in the partial annealing zone of the zircon ft thermochronometer our results might be explained by the presence of a thick thrust sheet once existing above the study area

synthetic aperture radar interferometry observations of the m 6 0 orta earthquake of 6 june 2000 nw turkey reactivation of a listric fault we study the coseismic surface displacement field due to the orta earthquake of 6 june 2000 a moderate sized mw 6 0 oblique slip event that took place on a previously unknown fault located about 70 km north of the capital ankara turkey and about 35 km south of the north anatolian fault we use european space agency ers synthetic aperture radar sar data to generate high resolution maps of the surface displacements by a two pass differential sar interferometry method the surface displacement field reaching up to 15 cm line of sight subsidence is captured in several coseismic interferograms from descending orbits and is inverted to determine the source parameters of the earthquake using elastic dislocations on rectangular fault surfaces with a nonlinear minimization procedure based on simulating annealing algorithm modeling of the coseismic interferograms indicates that the earthquake was associated with a shallow 6 km left lateral oblique normal displacement that occurred on a north south striking eastward dipping listric fault trending at a high angle to the plate boundary right lateral strike slip north anatolian fault careful analyses of multiple interferograms together with the field observations allow us to infer the rupture geometry in fine detail modeling shows that coseismic slip occurs nearly only on the lower portion of the listric fault at a centroid depth of about 5 km but partially reaches to the surface along the surface trace of the dodurga fault in agreement with the field observations we show that in the absence of field observations additional measurements or multiple interferograms that capture the surface deformation from different look angles sar interferometry alone may not be sufficient to constrain earthquake rupture geometry if there is no clear surface faulting the results suggest that the dodurga fault developed most probably as a result of a restraining bend along the north anatolian fault and its left lateral kinematics is consistent with the stress regime that favors the right lateral north anatolian fault

quantitative kinematic flow analysis from the main central thrust zone nw himalaya india implications for a decelerating strain path and the extrusion of orogenic wedges quantitative kinematic indicators from the main central thrust zone mctz in the nw himalaya have been used to characterize the type of flow during deformation different generations of tension gashes have been rotated by variable angles with respect to the mylonitic foliation forming associated fringe folds these record the late stage brittle ductile flow and reveal that a strong pure shear component of deformation occurred throughout the mctz to characterize earlier deformation increments fabrics from highly deformed quartz ribbons were analyzed well developed shape and lattice preferred orientation patterns show a systematic change of the glide systems and suggest inverted palaeotemperatures within the mctz investigations of the c axes patterns reveal a strong asymmetry at the top of the mctz whereas the samples from the base of the mctz show almost perfectly symmetrical type i crossed girdles deformation within the mctz probably started close to simple shear flow at higher temperatures which progressively became a more general shear during cooling and ended in a pure shear dominated flow during the final stages of brittle ductile deformation i e a decelerating strain path using the higher himalaya crystalline as an example a kinematic model for the extrusion of crustal wedges above major thrust zones is suggested

late quaternary alluvial fans of emli valley in the ecemis fault zone south central turkey insights from cosmogenic nuclides abstract alluvial fans within the paraglacial ecemis river drainages on the aladaglar mountains in south central turkey were studied using geomorphological sedimentological and chlorine 36 terrestrial cosmogenic nuclide tcn surface exposure dating methods to examine the timing of alluvial fan abandonment incision and to understand the role of climatic and tectonic processes in the region these alluvial fan complexes are among the best preserved succession of alluvial fans in turkey and they were offset by the major strike slip ecemis fault of the central anatolian fault zone the alluvial fans are mostly composed of well lithified limestone cobbles 5 to 25 cm in size and comprise crudely stratified thick beds with a total thickness reaching up to about 80 m tcn surface exposure dating indicates that the oldest alluvial fan surface yalak fan was likely formed and subsequently abandoned latest by 136 0 23 4 ka ago largely on the transition of the penultimate glaciation marine isotope stage 6 mis 6 to the last interglacial mis 5 i e termination ii the second set of alluvial fan emli fan was possibly developed during the last interglacial mis 5 and incised twice by between roughly 97 0 13 8 and 81 2 13 2 ka ago a younger alluvial fan deposit placed on relatively older erosional terraces of the emli fan suggests that it may have been produced during the last glacial cycle mis 2 these events are similar to findings from other fluvial and lacustrine deposits throughout central anatolia the incision times of the ecemis alluvial fan surfaces largely coincide with major climatic shifts from the cooler glacial periods to warmer interglacial interstadial conditions this indicates that alluvial fans were produced by outwash sediments of paleoglaciers during cooler conditions and later when glaciers started to retreat due to a major warming event the excess water released from the glaciers incised the pre existing fan surfaces an alluvial fan in the study area was also cut by the ecemis fault highlighting the influence of tectonics on fan development it was offset vertically 35 3 m since at least 97 0 13 8 ka which suggests a 0 36 0 06 mm a 1 vertical slip rate of the fault

using isotopic and chronologic data to fingerprint strata challenges and benefits of variable sources to tectonic interpretations the paro formation bhutan himalaya 1 we combine detrital zircons dz and epsilon neodymium nd signatures with field mapping in the paro formation in western bhutan dz age spectra are strongly variable and display signatures that have been used to uniquely identify both greater himalayan gh and lesser himalayan lh strata dz age peaks from six quartzite samples require sources for 0 5 0 8 1 2 1 4 1 7 1 8 and 2 5 ga zircons in the paro formation the youngest 0 5 ga zircons argue for a cambrian maximum deposition age two samples have a youngest 1 8 ga peak typically attributed to paleoproterozoic lh rocks a 450 ma crystallization age from two granite samples constrains the minimum deposition age as ordovician new nd signatures from six detrital samples from the paro formation show significant variation with lithology schists have nd 0 values between 12 0 and 16 9 while quartzite values vary between 18 8 and 24 5 these data imply that the paro formation was derived from both young and old sources with dz and nd values obtained from the same quartzite samples requiring old detritus while the nd values obtained from interbedded schist require younger detritus using published isotopic and chronologic definitions of himalayan strata schist rich layers wouldbeconsideredgh whiletheinterbeddedquartzite

placing limits on channel flow insights from the bhutan himalaya article i nfo article history along the majority of the himalayan orogenic belt high grade metamorphic rocks of the greater himalaya gh are separated from lower grade metasedimentary rocks by two shear zones the basal top to the south main central thrust mct and the upper top to the north south tibetan detachment std seemingly pervasive ductile deformation within gh rocks and a lack of exposed hanging wall or footwall cut offs for the mct and std have permitted models that predict 100 s of km of coeval displacement on both structures extruding the gh section via gravitational loading from tibet and focused erosion along the himalayan topographic front we present new mapping stratigraphic columns mineral assemblages u pb zircon ages and a suite of structural data from gh and tethyan himalayan th rocks in eastern and central bhutan our observations highlight significant 250 300 c along strike changes in the deformation temperature conditions recorded by gh rocks in eastern bhutan th rocks are separated from gh rocks displaying ubiquitous partial melt textures by a top to the north sense shear zone correlated with the std however in central bhutan limited partial melt textures are only present near the base of the gh section a biotite muscovite garnet mineral assemblage persists from 0 2 to 3 km above the mct through th rocks and distinct lithologies interfinger at the gh th contact which suggests that th strata are in depositional contact above gh strata the same strata exposed on both sides of the std limits slip along this structure to 20 km thin section scale top to the south shear is focused in a 2 3 km thick zone above the mct while the overlying 11 km thick section displays top to the north shear suggesting asymmetric channel behavior strained quartz grains allow us to quantify 23 34 km of top to the north shear our data suggest that the gh th section in central bhutan acted as a cool viscous low displacement channel and when compared to sections in eastern bhutan highlights dramatic changes in temperature conditions viscosity and possibly displacement along strike however we suggest that the erosion rates needed to remove low viscosity material limit channel flow even in regions containing significant partial melt and that the magnitude of channel flow is small compared to the total mass balance of the system

the dune systems of the konya plain turkey their relation to environmental changes in central anatolia during the late pleistocene and holocene abstract several sand flats located on the northern shores of the late pleistocene palaeolake of the konya plain inner anatolia turkey are related to changes in lake levels in this paper the two main dune systems are mapped according to their geomorphological sedimentological and dynamic characteristics and their significance is discussed with regard to the environmental changes since the late pleistocene both at time of the former lake and during the drier periods of the holocene cross sections show the relationship of the dunes to the topography of the basement analyses of the sand fraction show distinct characteristics in size distribution quartz and shell contents wind erosion effects on the quartz grains and petrographic composition interpretation of the results coupled with information provided by the geomorphology of the dune systems studied in the field and from aerial photographs and satellite images highlights the importance and variations in time of local factors such as prevailing winds sand sources changes in lake levels and vegetation a chronology of the main sand fields is proposed based on the evidence of three main droughts during the upper pleistocene the older one much eroded maximum height 3 m covers a limestone surface at 50 m above the bottom of the dried lake an optical scanning luminescence osl date shows a last period of accumulation at 14 328 3220 years the younger one maximum height 12 m has moved over the emerged late pleistocene lacustrine marls an osl date gives an age of 5674 988 years for the last accumulation period evidence of very recent activation of this younger dune system is apparent as a result of overgrazing and excessive land reclamation a third period of dominant wind action and dune construction is responsible for the installation of a younger and thin dune field over the mid holocene lacustrine deposits of the karapinar lake the success of the stabilization programme of the dunes over the last 30 years shows that the last period of dune movement is not related to climate change but to overpressure on the land due to the needs and activities of an increasing population

high pressure metasediments in central turkey constraints on the neotethyan closure history 1 the distribution of oceanic domains and continental blocks in central anatolia remains a challenge in understanding the alpine geodynamic evolution of the tethys realm the consumption of a neotethys oceanic branch at the mesozoic cenozoic boundary welded the central anatolian crystalline complex in central turkey and the anatolide tauride block in western turkey with the northerly eurasian margin whether those two regions constituted a single or two distinct continental masses is still matter of debate high pressure metamorphism has been locally evidenced in the afyon zone which was however defined as a greenschist facies metamorphic zone of the anatolide tauride block since the afyon zone composes a metamorphic equivalent of a continental margin exposed far south of the izmir ankara suture zone this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central turkey our investigations reveal that the high pressure minerals fe mg carpholite and glaucophane are present in the entire afyon zone which we reconsider as a blueschist facies zone we additionally present a tectonic reconstruction stripping off the postcollisional tectonics it reveals that today s bending of the high pressure belt is consistent with an eocene collision of the anatolide tauride block around the southern edge of the central anatolian crystalline complex we argue that the central anatolian crystalline complex and the anatolide tauride block were two distinct continental masses separated by a neotethyan oceanic stripe the closure of which engendered subduction related metamorphism in the latter and arc volcanism and high grade metamorphism in the former by late cretaceous to early cenozoic

earthquake induced flooding and paleoseismicity of the el asnam algeria fault related fold late quaternary activity of the el asnam thrust fault responsible for the october 10 1980 ms 7 3 earthquake and 36 km coseismic faulting is explored through diverse paleoseismological field methods we trenched through the main and secondary 1980 coseismic scarps made an analysis of earthquake induced flood deposits conducted a geomorphic study of leveling profiles and offset geological units across thrust and normal scarps and considered the geomorphology of the active fold twenty five radiocarbon ages from colluvial and alluvial deposits along with conventional fossils and artefacts dating of geological units show the timing of successive net vertical displacements on the thrust related fold and bending moment faults previous work showed that eight pre 1980 earthquakes occurred in clusters during the late holocene cumulative net vertical slip that amounts to 3 times the 1980 displacement is observed on multiple thrust fault scarps and offsets of geological units on bending moment faults maximum cumulative vertical displacements which are visible in different zones along the fault segments can reach 10 to 25 times the 1980 coseismic displacements the late quaternary uplift rate on the el asnam fault is 0 6 mm yr and taking into account slip variation along the fault this rate may range between 0 25 1 6 mm yr from which we obtain a shortening rate of 0 17 1 2 mm yr because the tell atlas mountains exhibit comparable seismogenic fault related folds with parallel and sequential structures of active faults a total average shortening rate of 2 05 mm yr during the late quaternary represents part of the convergence accommodated along the africa eurasia plate boundary

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

investigation of sinkholes spatial distribution using the weights of evidence method and gis in the vicinity of karapinar konya turkey abstract there are many sinkholes 182 in the vicinity of karapinar approximately 20 large sinkholes 10 m in diameter were formed within the obruk plateau between 1970 and 2012 the formation of sinkholes is the most important geological hazard in the study area because they can damage engineering structures settlements agricultural areas and eventually be a source of casualties to date no study has been conducted on the distribution of sinkholes in this region in this study the spatial distribution of the sinkholes and the factors controlling sinkhole development were studied through the use of geographical information systems using a sinkhole inventory and a spatial database containing information on the topography geology hydrogeology and land use initially 182 sinkholes were identified in the area by examining the digital elevation model produced for this study the sinkholes were verified in the field thirty two factor maps were produced to investigate their relationship with sinkholes using the weights of evidence method the sinkholes are mainly related to dissolution of the neogene age lacustrine insuyu formation consisting of limestone and clayey limestone sinkhole frequency increases in the vicinity of drainages 2000 3000 m and faults

himalayan metamorphic sequence as an orogenic channel insight from bhutan the bhutan himalayas differ from the rest of the himalayas in two major ways i low grade sedimentary rocks lie above the greater himalayan sequence as klippen i e erosional remains of the south tibetan detachment and ii an out of sequence thrust the kakhtang thrust lies structurally above the klippen and it doubles the exposed thickness of the greater himalayan sequence our field observations and geochronological data constrain the main kinematic events in the bhutan himalayas crystallisation ages of leucogranite dykes deformed by the main central thrust and the south tibetan detachment indicate that these two structures operated together between 16 and 22 ma the out of sequence kakhtang thrust was active at 10 14 ma and was concurrent with reactivation of the south tibetan detachment restoration of the bhutan himalayas prior to the out of sequence thrusting shows that the greater himalayan sequence was the core of a long low viscosity crustal channel extending under the tibetan plateau we propose that the gravity driven southward extrusion of the channel material from underneath the tibetan plateau caused the inverted metamorphic sequence in the lesser himalayan sequence and in the greater himalayan sequence this process also led to occurrences of present day surface rocks that were derived from variable distances down dip but from similar crustal depths such an exhumation pattern can explain the similar peak pressures for the greater himalayan sequence along the length of the himalayas

structural and geochronological evidence for the leading edge of the greater himalayan crystalline complex in the central nepal himalaya abstract the himalaya is commonly described as a three layer two fault stack namely a high grade crystalline core featuring an inverted metamorphic field gradient the greater himalayan crystalline complex ghc is separated from units above and below by shear zones the lesser himalayan sequence lhs underlies the ghc below the main central thrust and the tethyan himalayan sequence ths overlies it along the south tibet detachment however the southern main central thrust hanging wall consists of a lower unit dominated by a right way up metamorphic sequence of biotite garnet schists bhimphedi group and an upper unit with only anchizone metamorphism pulchauki group the bhimphedi group is commonly equated to the ghc while the pulchauki group is well correlated to the ths however no shear zone separates these units we present new structural and geochronological data along the boundary between the ghc and the bhimphedi group in the kathmandu region these data reveal an 200 m thick early middle miocene top north northeast shear zone that we term the galchi shear zone we correlate this shear zone to the south tibet detachment on the basis of lithological metamorphic structural and chronological criteria the galchi shear zone merges with the main central thrust to the south bounding the leading edge of the ghc this result combined with recent work in the western himalaya suggests that the locally preserved leading edge of the ghc is sub parallel to the arc of the orogen and the southern main central thrust hanging wall is dominated by ths rocks this orogenic architecture rules out wedge extrusion and channel flow focused denudation kinematic models for the himalayan orogen but is accommodated by tectonic wedging kinematic models including channel tunneling models with modified timing

documenting basin scale geometry and provenance through detrital geochemical data lessons from the neoproterozoic to ordovician lesser greater and tethyan himalayan strata of bhutan abstract detrital zircon dz ages augmented with end 0 and 13 c isotopic values from 18 new and 22 published samples collected from lesser himalayan lh greater himalayan gh and tethyan himalayan th rocks in bhutan support deposition of 7 km of sedimentary rock in late cambrian ordovician time and provide a stratigraphic framework for the pre collisional indian margin youngest gh dz grains become younger upsection from 900 ma to 477 ma youngest dz grains in th samples are 490 460 ma both the lh jaishidanda formation fm and the lh baxa group overlie paleoproterozoic lh rocks the jaishidanda fm exhibits distinct populations of youngest dz peaks 475 550 ma and 800 1000 ma the baxa group manas pangsari and phuntsholing formations contains youngest dz peaks at both 500 525 ma and 0 9 1 0 ga however most samples from the baxa group in western bhutan contain no grains younger than 1 8 ga samples from the lh paro fm which sits directly under the mct in western bhutan have youngest dz peaks at 0 5 0 8 1 0 1 7 1 8 ga end values generally match dz spectra with samples that contain old youngest grain populations corresponding to more negative end signatures the paro fm is an exception where end 0 values from quartzite samples are quite negative 19 to 24 whereas the end 0 values from interbedded schist contain younger detritus 12 to 17 13 c values from the jaishidanda paro and manas formations have 13 c values 1 8 to 6 suggestive of deposition over late neoproterozoic to ordovician time 13 c values from the pangsari fm vary from 2 8 to 1 8 compatible with deposition in the early to middle neoproterozoic the young latest cambrian ordovician grains preserved in th gh and lh rocks suggest that the late cambrian ordovician orogeny documented in gh rocks throughout the orogen served as a significant sediment source in bhutan

tectonic implications of fluvial incision and pediment deformation at the northern margin of the central anatolian plateau based on multiple cosmogenic nuclides 1 we document quaternary fluvial incision driven by fault controlled surface deformation in the inverted intermontane gok rmak basin in the central pontide mountains along the northern margin of the central anatolian plateau in situ produced 10be 21ne and 36cl concentrations from gravel covered fluvial terraces and pediment surfaces along the trunk stream of the basin the gok rmak river yield model exposure ages ranging from 7 1 ka to 346 45 ka and average fluvial incision rates over the past 350 ka of 0 28 0 01 mm a 1 similarities between river incision rates and coastal uplift rates at the black sea coast suggest that regional uplift is responsible for the river incision model exposure ages of deformed pediment surfaces along tributaries of the trunk stream range from 60 5 ka to 110 10 ka demonstrating that the thrust faults responsible for pediment deformation were active after those times and were likely active earlier as well as explaining the topographic relief of the region together our data demonstrate cumulative incision that is linked to active internal shortening and uplift of 0 3 mm a 1 in the central pontide orogenic wedge which may ultimately contribute to the lateral growth of the northern anatolian plateau

genesis of the bangbu gold deposit in the southern tibet evidenced from in situ sulfur isotopes and trace element compositions of pyrite abstract the bangbu orogenic gold deposit in the north himalaya of the southern tibet contains more than 40 t au at an average grade of 7 0 g t in this deposits gold bearing quartz veins were controlled by nearly e trending qusong cuogu zhemulang shear zone and occurred within the secondary faults which crosscut late triassic greenschist facies rocks to further understand the sulfur source and ore forming process we have conducted a compressive study of in situ sims sulfur isotopes and la icp ms trace element compositions of two stages of pyrite at bangbu early stage pyrite py1 is coarse grained mostly 0 2 2 mm and euhedral and has gold concentrations of less than 0 3 54 ppm mean of 20 ppm and 34s values of 1 6 5 1 mean of 3 2 late stage pyrite py2 is generally fine grained mostly

coeval extension and compression in late mesozoic recent thin skinned extensional tectonics in central anatolia turkey abstract the central anatolian crust is composed of high grade metamorphic rocks covered by tertiary shallow marine to continental sedimentary rocks with a middle miocene recent volcanic activity in cappadocia after the late cretaceous closure of the tethyan ocean and following plate collision core complexes formed in nigde and kirsehir regions of central anatolia recent geophysical studies indicate the presence of low seismic velocity zones beneath central anatolia interpreted as regionally thinned and or hot mantle lithosphere or asthenospheric upwelling we present new structural data covering a 300 km wsw nne trending transect between konya and yozgat cities to suggest that central anatolian cenozoic tectonic regime is extensional and the narrow fold thrust zones once taken as evidence of crustal convergence resulted from gravitational movements curie point depths map of central anatolia shows a large scale diameter 140 km upwarping c 15 km of the regional crust we interpret as due to asthenospheric upwelling these considerations suggest that 1 the central anatolian crust deforms by extension transcurrent faults like the central anatolian fault zone accommodate the crustal stretching by transfer faulting 2 post late cretaceous crustal extension favored the placement of hot and low density asthenospheric material in cappadocia by processes that may be explained by rayleigh taylor instability phenomenon 3 in central anatolia large post eocene horizontal crustal displacements we estimate a minimum of 50 km are not achieved by crustal contraction as previously proposed but thin skin extensional tectonics and 4 tethyan suture lines need to be reviewed since their traces may be modified by later extensional displacements

relationships between displacement and distortion in orogens linking the himalayan foreland and hinterland in central nepal greater himalayan sequence rocks exposed in the manaslu himal chuli himalaya can be separated into distinct upper and lower parts deformation recorded in both parts occurred at temperatures ranging between 450 c and 640 c and is characterized by almost equal coaxial and noncoaxial components across the upper greater himalayan sequence peak metamorphic temperatures are essentially isothermal whereas corresponding metamorphic pressure estimates across the same section decrease downward with an apparent gradient of 620 bars km in the lower greater himalayan sequence however both metamorphic pressure and temperature decrease with structural depth the abnormal pressure gradient in the upper greater himalayan sequence is attributed to 50 vertical thinning during southward displacement while the inverted gradient in the lower portion is interpreted to be the result of coeval exhumation and downward expansion of the main central thrust shear zone and the progressive incorporation of more rock into the greater himalayan sequence deformation in the upper portion of the greater himalayan sequence was characterized by extending flow i e extension in the direction of flow whereas deformation in its lower portion was characterized by compressing flow i e compression in the direction of flow extending flow is a distinctive feature of displacement and distortion in deep orogenic hinterlands while compressing flow is emblematic of displacement and distortion in orogenic foreland regions the transition between the upper and lower parts of the greater himalayan sequence therefore represents a fundamental transition between hinterland style deformation involving processes such as lateral midcrustal flow and foreland style deformation involving critical taper thrust fold wedge development

20 years of geological mapping of the metamorphic core across central and eastern himalayas abstract the largest crystalline unit representing the mid crust in the himalayan belt is the greater himalayan sequence ghs which stretches all over the 2400 km of length of the belt the ghs recognized since the first geological explorations of the himalayas has been considered for a long time as a coherent tectonic unit exhumed by the contemporaneous shearing along the main central thrust and the south tibetan detachment system in the time span 25 17 ma a multidisciplinary approach integrating geological mapping structural analysis petrology and geochronology allowed to better constrain on its internal architecture characterized by several levels of tectonic metamorphic discontinuities on the regional scale with a top to the s sw sense of shear and active since 40 ma the ghs is consequently divided in three main tectonic units exhumed progressively from the upper part to the lower one by ductile shear zones later involving the lesser himalayan sequence above the main central thrust a cryptic tectono metamorphic discontinuity higher himalayan discontinuity hhd has been recognized and mapped in central eastern himalaya the mapping of the hhd has been allowed by the use of a multidisciplinary approach involving structural analysis geochronology and petrology a new map of western nepal is presented in this framework the popular models of exhumation of the ghs mainly based on the contemporaneous activity of the two bounding shear zones main central thrust and the south tibetan detachment and considering the ghs as a coherent tectonic unit should be reconsidered an in sequence shearing tectonic model from the deeper to the upper structural levels further affected by out of sequence thrusts is more appropriate to explain the deformation metamorphism and exhumation of the mid crust in the himalayan belt geological mapping of the himalayan belt is very far away to be exhaustively completed anyway during the last 20 and particularly during the last few years it has been notably improved due to a new multidisciplinary approach

early palaeozoic orogenesis along the indian margin of gondwana tectonic response to gondwana assembly abstract shrimp u pb dating of zircons from a peralkaline s type lesser himalayan granite from the kathmandu region nepal indicate an age of emplacement of 475 ma the granites along with metasedimentary xenoliths show a similar signature of inherited detrital zircon ages ranging from archaean to early palaeozoic with prominent late mesoproterozoic grenvillian and neoproterozoic pan african age peaks and have a maximum age of 500 ma based on the youngest detrital grains deformation structures in xenoliths are truncated by the granite and along with the granites are assigned to a cambro ordovician orogenic event herein termed the bhimphedian orogeny that can be traced across the himalaya from pakistan to the eastern himalaya and possibly extends west into afghanistan we interpret the orogeny as being related to andean type orogenic activity on the northern margin of the indian continent following gondwana assembly the magmatic arc was associated with andesitic and basaltic volcanism and was active from c 530 to 490 ma the arc activity overlaps with and is succeeded by regional deformation crustal melting and s type granite emplacement that extended to 470 ma orogenic activity was driven by coupling across the plate margin either during on going subduction or through accretion of microcontinental ribbons possibly represented by the lhasa and qiangtang blocks it represents the termination of an orogenic cycle termed the north indian orogen that commenced with neoproterozoic rifting and passive margin development and terminated with the bhimphedian orogeny this was succeeded by a return to passive margin setting along the northern indian margin of gondwana which continued until the cenozoic himalayan orogeny

turkish karst aquifers one third of turkey s surface is underlain by carbonate rocks that have been subdivided into four karst regions the carbonate rock units are about 200 km wide along the taurus mountains that attain elevations of 2500 m karst features of western turkey bordering the aegean and mediterranean seas demonstrate the tectonic lithological and climatic controls on the occurrence movement and chemical characteristics of groundwater in turkey all karstic feature such as lapies caves sinkholes uvalas poljes ground river valleys developed in all karstic areas karstification is related not only to the thickness and to purity of limestone climate and height but also to tectonic movements water resources of karst terrains of turkey are relatively rich and as such are very important for the economic development of the country high mountain chains very often associated with the karst terrains are responsible for some important and beneficial characteristics of these water resources four karst regions are 1 taurus karst region 2 southeast anatolia karst region 3 central anatolia karst region and 4 northwest anatolia and thrace karst regions

effective elastic thickness variations along the andean margin and their relationship to subduction geometry 1 we present a new map of the spatial variations in effective elastic thickness te along the andes estimated using bouguer coherence the te variations reflect interactions between subducting slab and preexisting terrane structure in the forearc conductive cooling of the continent by the subducting slab exerts primary control on rigidity resulting in te that is highest 40 km where the oceanic lithosphere is oldest and coldest 20 s in the central andes te is relatively low 20 km along the volcanic chain and the altiplano and puna plateaus we interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes a shallow and hot asthenosphere and a very weak lower crust throughout this region east of the plateaus high te delineates underthrusting of the brazilian shield finally north and south of the plateaus flat subduction areas are characterized by high te high shear wave velocity thick thermal lithosphere and low heat flow indicating that continental lithosphere there is thicker colder and stronger on the basis of these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere in particular we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge which control the suction moment responsible for the subduction angle at depths 70 100 km for example when oceanic lithosphere subducts beneath thin continental lithosphere the low viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles however when oceanic lithosphere subducts close or beneath thick and strong continental lithosphere the asthenospheric wedge narrows and corner flow drags high viscosity mantle from the base of the thick 150 km cold continent into the wedge suction forces increase with both narrowing of the wedge and its increasing viscosity we estimate the asthenospheric viscosity underneath thick cold continents to be 1020 pa s sufficient to induce flat subduction later after prolonged hydration and weakening of the continent s base asthenospheric flow into the wedge may resume allowing the slab to sink again into the mantle at normal angles

late pleistocene piedmont glaciations in the eastern mediterranean insights from cosmogenic 36cl dating of hummocky moraines in southern turkey abstract we report the presence of late pleistocene piedmont glaciers represented by the largest hummocky moraine field observed in the eastern mediterranean the piedmont glaciers originated from the geyikdag ice cap 40 km 2 situated between 2350 and 2650 m above sea level a s l central tauride mountains of turkey and deeply carved the north facing hillslopes before reaching the namaras valley 2000 2050 m a s l the hummocky moraines resulted from in situ deposition of stagnant glacier ice where debris cover was heterogeneously distributed on the glacier surface thirty four boulders from hummocky disintegration lateral and terminal moraines from the namaras valley and the tributary susam valley 2100 2200 m a s l were dated by cosmogenic 36 cl surface exposure dating the moraine ages indicate three phases of deglaciation during the late pleistocene the oldest deglaciation occurred in the namaras valley at 18 0 1 1 ka ka thousand years ago towards the end of the last glacial maximum lgm and is recorded entirely by hummocky moraines we speculate that hummocky moraine forming processes with cycles of relief inversion gave rise to boulder apparent ages up to a few thousand years younger in our study area therefore 18 0 1 1 ka should be regarded as a minimum age with a probable true age much closer to the local lgm values 20 ka as observed in the surrounding mountains paleo piedmont glaciers also deposited several lateral moraines that are 50 m higher than the hummocky moraines although the lateral moraines probably represent the build up and the hummocky moraines the final phase of the same local lgm pulse both lateral moraines started to retreat from the late glacial 14 0 2 7 ka and gradually disappeared by mid holocene 5 2 1 0 ka encompassing the younger dryas yd stadial in the susam valley the late glacial is represented by a terminal moraine 13 4 1 5 ka the glacier retreat was very fast as indicated by an almost instantaneous disappearance of 5 km long susam valley glacier represented by disintegration and hummocky moraines 14 0 1 3 ka alternatively in case the oldest boulder age is taken into account the susam valley glacier can be also attributed to the late lgm 17 ka to late glacial 14 ka transition near the exit of the susam valley a right lateral moraine was deposited 11 6 1 3 ka ago confirming the presence of the yd in geyikdag comparable glacial chronologies were obtained from other turkish and mediterranean mountains

a structural transect in the lower dolpo insights on the tectonic evolution of western nepal abstract we present the results of a structural transect in lower dolpo cross cutting the upper part of the lesser himalaya lh the higher himalayan crystallines hhc and the lower part of the tibetan sedimentary sequence tss the mct zone affects the upper part of the lh as well as the lower part of the hhc and shows a later brittle reactivation mean vorticity in the mct points to non coaxial deformation these data together with available kinematic data along the belt on the south tibetan detachment system stds and in the core of the hhc point to increasing simple shear toward the tectonic boundaries a top to the sw high temperature shear zone toijem shear zone is recognized in the middle part of the hhc at the boundary between units 1 and 2 it developed during the earlier stages of exhumation of the hhc enhancing the decompression of the hanging wall and the emplacement of leucogranite dykes and sills its development could be explained by a change in the velocity profile during the extrusion of the hhc triggered by first order changes in rock types of the tectonic unit the stds is marked by a wide zone of high strain and by a metamorphic jump from amphibolite facies in the carbonate rocks of the upper part of the hhc to greenschist facies marbles in the lower part of the tss the development of a pervasive foliation towards the bottom of the tss indicates increasing strain related to top down to the ne tectonic transport a low p metamorphic event marked by the growth of post d1 biotite porphyroblasts at the base of the tss is related to the conductive heating from the underlying hhc

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

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

yadong cross structure and south tibetan detachment in the east central himalaya 89 90 e the yadong cross structure ycs occurring at 89 30 east longitude in the himalaya is the largest across strike discontinuity in the geologic structure and topography of the high himalaya between the himalayan syntaxes it is manifest by a plan view left offset of the topographic crest of the range and a coincident apparent left strike offset of the south tibetan detachment system stds of about 70 km new field mapping indicates that the stds intersects the west side of the ycs at zherger la and further suggests that the ycs is the surface expression of a large north northeast striking west facing lateral ramp in the himalayan thrust system the greater himalayan allochthon is apparently draped across this lateral ramp resulting in a north northeast striking monoclinal flexure of the allochthon manifest in the chomolhari range superimposed steep west northwest directed normal shear appears to have obliterated earlier northerly directed stds shear fabric along along the ycs segment of the tethyan belt greater himalayan belt contact recent seismicity suggests that the greater himalayan allochthon is still moving southward along the lateral ramp u pb monazite dates on leucogranites in the footwall of the stds on opposite sides of the ycs are suggestive of a south to north decrease in the crystallization age of these granites the age pattern is consistent with southward extrusion of the greater himalayan allochthon and suggests the possibility of determining an average slip rate for the stds by dating granites in the immediate footwall of the stds that are substantially separated in north south section an average slip rate of about 7 mm yr between 23 and 12 ma is suggested by the data presented here

crustal strength in central tibet determined from holocene shoreline deflection around siling co abstract controversial end member models for the growth and evolution of the tibetan plateau demand quantitative constraints of the lithospheric rheology direct determinations of bulk crustal rheology however remain relatively sparse here we use the flexural rebound of lacustrine shorelines developed during the lingtong highstand around siling co in central tibet to place bounds on the effective elastic thickness t e and viscosity of tibetan crust shoreline features associated with the lingtong highstand complex 60 m above present lake level are deflected from horizontal by 2 4 m over wavelengths of 200 km optically stimulated luminescence dating of aggradational shoreline deposits indicates that these lake levels were reached at 6 4 ka assuming that surface loads were entirely supported by an elastic layer overlying an inviscid fluid the range and spatial distribution of variations in shoreline elevation are consistent with deflections predicted by a uniform elastic plate with thickness t e of 20 30 km if viscoelastic relaxation in response to lake withdrawal is complete our data suggest an average viscosity 10 19 pa s these results imply that the apparent viscosity of the lower crust inferred over millennial timescales is comparable with that estimated from post seismic relaxation over decadal timescale

leucogranite geochronological constraints on the termination of the south tibetan detachment in eastern himalaya abstract the south tibetan detachment system stds developed between the very low grade tethyan himalayan sequence ths and the high grade metamorphic greater himalayan sequence ghs over an along strike distance exceeding 2000 km within the himalayan orogen motion along the stds has been associated with the exhumation of the ghs and the uplift of the himalayan mountains geological field mapping and u th pb geochronological analyses were performed to trace and date the stds in the yadong region of southern tibet where it is a top to the north shear zone juxtaposing the yadong klippe of the ths with the high grade ghs this shear zone is intruded by multiple generations of leucogranites emplaced mainly at ca 23 ma ca 20 18 ma and ca 17 16 ma the undeformed textures of the leucogranites and their cross cutting relationships with the shear zone indicate that ductile motion along the stds terminated by ca 20 ma this is largely consistent with the deformation history of the stds in central and western himalaya the termination of shearing along the stds during the early miocene occurred well before the rapid cooling of the ghs during the middle miocene suggesting that exhumation and decompression of the ghs was still ongoing after the cessation of motion along the stds