late miocene stepwise aridification in the asian interior and the interplay between tectonics and climate abstract the mid latitudinal central asian continent is characterized by large sand deserts and gobi stony desert in this context it is of interest to study the timing and forcing mechanisms of aridification in the region here we present multiple geochemical climatic proxies from late cenozoic strata in the tarim basin of northwestern china a region sensitive to climatic change the results yield long term climatic records covering a time interval of 13 3 to 2 5 ma we find that a general trend towards a dry climate was superimposed by two stepwise aridification events the first lesser aridity phase occurred at 7 5 3 ma and the second extreme aridity episode was initiated at 5 3 ma based on the correlation between climatic change and regional tectonic events we propose a mechanism to explain the climatic variations the general long term drying trend since the mid miocene was a response to global climatic cooling while the stepwise aridification since the latest miocene was controlled mainly by regional tectonic uplift

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

carboniferous permian tectonic evolution and sedimentation of the turpan hami basin nw china implications for the closure of the paleo asian ocean abstract the tectonic evolution and sedimentary characteristics of the carboniferous permian rocks of the turpan hami basin have been analysed initially a joint inversion of gravity magnetic seismic data and the established model of electrical profiles was synthesized to create a new geological interpretation discussion on the tectonic characteristics of piedmont zone in the northern part of the basin then followed according to the analysis of balanced cross sections the tectonic evolutionary history of carboniferous permian sedimentary rocks of the turpan hami basin can be divided into three stages an extensional stage in the carboniferous a tectonic transition stage in the early permian and a compression and inversion stage after the middle permian it is found that the tectonic evolution controlled the sedimentary facies under these three stages and the sedimentation evolution has undergone marine facies marine lacustrine transitional facies and lacustrine facies meanwhile based on the recent seismic gravity magnetic and electrical data and combined with the field surveying of outcrops the residual distribution of carboniferous permian strata is characterized by the widely distributed residual upper carboniferous except for the southern liaodun uplift and locally in the eastern area and the denudation of middle permian strata mainly distributed in the turpan depression and the turpan hami depression after comprehensive analysis of the sedimentary facies and erosion of permian strata it is concluded that the tectonic evolution and sedimentation of the turfan hami basin can be used as a constraint on permian subduction related accretionary orogenesis of northern xinjiang nw china and the closure time of the paleo asian ocean

a re evaluation of the stratigraphy and evolution of the kohistan arc sequence pakistan himalaya implications for magmatic and tectonic arc building processes new field mapping and structural data combined with published geochemical data from the kohistan arc in the nw himalaya enable a re evaluation of the arc stratigraphy key lithological units and their relationships are more clearly defined permitting the construction of a revised magmatic tectonic history for the arc the oldest units are transitional oceanic type basalts which form the basement to the subduction related sequence arc type gabbroic sheets and plutons intrude the oceanic basalts together these form the kamila amphibolite belt metasediments and basaltic lavas were deposited within an extensional basin onto the kamila amphibolite belt basement this sequence exposed across the arc forms a distinct stratigraphic unit which is formally defined here as the jaglot group sediment charged turbidity currents transported material into the basin whilst submarine eruptions contributed the basaltic component this period of extension culminated in the eruption of high mg boninites of the chalt volcanic group which overlie the rocks of the jaglot group the earliest granitoids of the kohistan batholith predate suturing and intrude the jaglot and chalt sequences at c 100 ma kohistan sutured to asia suturing being accompanied by thickening of the arc with the development of major intra arc shear zones and a penetrative regionally developed steep cleavage at c 85 ma intra arc rifting permitted the emplacement into the arc of the voluminous gabbronorites of the chilas complex which clearly intrudes the kamila amphibolite belt to the south and the jaglot group to the north the chilas complex has been regarded as part of the pre suturing juvenile arc sequence field evidence summarized here show this to be not so heat advection associated with emplacement of the complex caused amphibolite facies regional metamorphism melting of the lower arc and plutonism some of the resultant granitoid plutons were unroofed and eroded during a compressional phase at between 80 and 55 ma before emplacement of further plutons and extrusion of basaltic through to rhyolitic volcanic rocks at between 55 and 40 ma at least three phases of extension and rifting each separated by short lived phases of compression charac terized arc evolution much of the magmatism is controlled by extensional tectonics within the overriding plate of the kind commonly associated with a retreating subduction zone

the thermo tectonic history of the song kul plateau kyrgyz tien shan constraints by apatite and titanite thermochronometry and zircon u pb dating abstract the song kul basin sits on a plateau at the northern and middle kyrgyz tien shan junction it is a lacustrine basin occupied by lake song kul and predominantly developed on igneous basement this basement was targeted for a multi method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present day morphology zircon u pb dating by la icp ms revealed four different magmatic episodes a late cambrian 500 ma island arc system a late ordovician 450 ma subduction related intrusion an early permian 290 ma collisional stage and a middle to late permian 260 ma post collisional magmatic pulse middle to late triassic 200 230 ma titanite fission track ages and late triassic early jurassic 180 210 ma apatite fission track ages and thermal history modeling indicate the song kul basement was already emplaced in the shallow crust at that time an exhumed fossil apatite fission track partial annealing zone is recognized in the bordering song kul mountain ranges the area experienced only minor post early mesozoic denudation the igneous basement was slowly brought to apatite u th he retention temperatures in the late cretaceous palaeogene miocene to present reactivation of the tien shan does not manifestly affect this part of the orogen

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

mesozoic reactivation of the beishan southern central asian orogenic belt insights from low temperature thermochronology abstract the beishan orogenic collage boc is located in the southeast of the central asian orogenic belt caob and formed during final consumption of the palaeoasian ocean in the late palaeozoic this study applies low temperature thermochronology to constrain the meso cenozoic history of the boc apatite fission track and u th sm he data obtained for granitoid samples along a north south transect through the boc indicate three distinct phases of exhumation during 1 the late triassic early jurassic 225 180 ma 2 early cretaceous 130 95 ma and 3 late cretaceous early palaeogene 75 60 ma samples from the northern boc reveal a more profound early cretaceous signal and a weaker late triassic early jurassic signal than those in the southern boc a possible explanation for this discrepancy is the presence of crustal scale fault zones in the northern boc that are interpreted to have undergone repeated reactivation throughout the mesozoic exposing deeper exhumed sections of the boc these faults may thus have acted as a major control on exhumation in the region this pattern is consistent with results from elsewhere in the caob such as in the tianshan and the altai where regional widespread exhumation occurred since the early cretaceous while major fault zones record localised exhumation during the late cretaceous and cenozoic late cretaceous early palaeogene cooling ages were found only in the south of the boc suggesting that exhumation at that time was more localised and did not reach the northern margins of the study area the meso cenozoic cooling events described here are thought to be related to the progressive closure of the palaeo tethys ocean to the south associated collision and accretion of micro continental blocks and island arcs at the southern eurasian margin are interpreted to have induced more widespread reactivation and exhumation in central asia than previously anticipated extending to the northern margin of the tarim craton this observation hence refines the existing tectonic history models for central asia

middle late jurassic tectonostratigraphic evolution of central asia implications for the collision of the karakoram lhasa block with asia mesozoic basins in different regions of central asia provide important records for investigating relationships between intraplate deformation in central asia and tectonic processes at asian boundaries the present study gives a review of the stratigraphic and structural evolution of basins in different regions of central asia during the middle late jurassic it is shown that basins and mountain belts in northwest china experienced compressional deformation and were wholly or partially uplifted during the late middle late jurassic compared to extensively distributed middle jurassic coal bearing strata in northwest china upper jurassic strata characterized by red mudstones and conglomerates have a much smaller distribution in the mean time the tibet pamir plateau also underwent a folding and uplift event and upper jurassic sedimentary rocks are generally missing in the pamir and western tibet the intense compressional deformation and uplift event of the late middle late jurassic from the tibet pamir plateau to northwest china requires a new tectonic model as proposed here we suggest that the karakoram and lhasa blocks were a single giant block which was accreted to asia in the late middle jurassic earliest cretaceous and cross cut by the karakoram fault in the cenozoic during the callovian the western part of the karakoram lhasa block initially collided with the southern asian margin collision and continued convergence during the late middle late jurassic caused sinistral strike slip faulting along the central badakhshan fault and south tian shan suture accommodating crustal shortening in areas to the southeast of the faults the pamir western tibet tarim block qilian qaidam block and bei shan meanwhile the northeastward transpressional motion of the tarim block produced strong compressional stresses to areas north of the tarim block the kyrgyz tian shan central tian shan junggar basin and turfan basin with the northward movement of the karakoram lhasa block the eastern part of the karakoram lhasa block began to collide with the southern asian margin during the latest jurassic earliest cretaceous resulting in strong crustal deformation and thickening in east asia and central asia

tectonic history of the kyrgyz south tien shan atbashi inylchek suture zone the role of inherited structures during deformation propagation 1 multimethod chronology was applied on intrusives bordering the kyrgyz south tien shan suture stss to decipher the timing of 1 formation and amalgamation of the suturing units and 2 intracontinental deformation that built the bordering mountain ranges zircon u pb data indicate similarities between the tien shan and tarim precambrian crust caledonian 440 410 ma and hercynian 310 280 ma zircon u pb ages were found at the edge of the stss related to subduction and closure of the turkestan ocean and the formation of the suture itself permian triassic 280 210 ma titanite fission track and zircon u th he data record the first signs of exhumation when the stss evolved into a shear zone and the adjacent tarim basin started to subside low temperature thermochronological apatite fission track zircon and apatite u th he analyses reveal three distinct cooling phases becoming younger toward the stss center 1 jurassic cretaceous cooling ages provide evidence that a mesozoic south tien shan orogen formed as a response to the cimmerian orogeny 2 early paleogene 60 45 ma data indicate a renewed pulse of stss reactivation during the early cenozoic 3 neogene ages constrain the onset of the modern tien shan mountain building to the late oligocene 30 25 ma which intensified during the miocene 10 8 ma and pliocene 3 2 ma the cenozoic signals may reflect renewed responses to collisions at the southern eurasian border i e the kohistan dras and india eurasia collisions this progressive rejuvenation of the stss demonstrates that deformation has not migrated steadily into the forelands but was focused on pre existing basement structures

mongolian summits an uplifted flat old but still preserved erosion surface in gobi altay and altay mongolia several flat surfaces worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m suggests disruption of a single large scale surface new thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during jurassic time the gobi altay and altay flattopped massifs are tectonically and geomorphologically unique their preservation for 150 m y implies that no further tectonic movements occurred before the onset of the last deformation episode 5 3 m y ago it also suggests that very low erosion rates were maintained by a dry climate over millions of years

meso cenozoic building of the northern central asian orogenic belt thermotectonic history of the tuva region abstract the tuvinian and west sayan mountain ranges form part of the central asian orogenic belt caob more specifically they align along the altai sayan hangay zone its precambrian paleozoic basement has been subjected to mesozoic and cenozoic tectonic reactivation two north south transects across the mountain belts and intervening basins of tuva were sampled for apatite fission track aft thermochronology in order to elucidate the thermal history of the tuvinian basement in relation to the mesozoic and cenozoic reactivation of the caob most aft ages are late cretaceous and range between 55 and 115 ma mean lengths of confined fission tracks are relatively long with most values between 13 and 14 m thermal history modeling shows a rapid late jurassic cretaceous cooling for the sampled tuvinian crystalline rocks related to exhumation of the paleozoic basement this exhumation is possibly related to the building and subsequent orogenic collapse of the mongol okhotsk orogen that formed between the siberian and north china mongolian sino korean or amurian continental blocks during the late mesozoic far field effects of this orogeny and its collapse might have affected the baikal altai and sayan units of the central asian orogenic belt including the tuvinian basement also at the mesozoic southern eurasian margin growth of the asian continent continued and several collision accretion events asserted distal tectonic influence into the caob after a paleogene period of stability thermal history models for some samples hint at a renewed period of basement cooling during the neogene in support of this neogene event a single sample from the main west sayan fault zone contains an apatite population with 2 ma reset aft ages this is interpreted in the framework of ongoing building of the modern central asian orogens and associated fault movements and exhumation of the basement presumably related with the ongoing india eurasia convergence

fission track dating of faulting events accommodating plastic deformation of biotites we performed fission track ft analyses to constrain the timing of fault slip events associated with plastic deformation of biotite grains formed at high temperature higher than 200 300 c apatite ft ages of 49 6 16 7 ma were obtained from late cretaceous granites near the fault with younger ages near a basaltic dike that intruded at 19 ma by comparing the distribution of apatite ft ages using forward thermal and ft annealing calculations we interpreted the younger ages as being explained by basaltic intrusion we concluded that the plastic deformation of the biotite grains could have occurred associated with the following events 1 primal cooling of the granitic body at 68 50 ma and or 2 basaltic intrusion at 19 ma a combination of detailed observation of microscale deformation structures and dense ft measurements successfully constrained timing of fault events distributed in bedrock without covering layers

episodic exhumation and related tectonic controlling during mesozoic in the eastern tian shan xinjiang northwestern china abstract the eastern tian shan ets which is located in the southern margin of the central asian orogenic belt experienced multiple cooling episodes during the mesozoic however the topography and cooling pattern of the region have been extensively affected by complex structural deformations here we combined a detailed structural analysis with new and existing low temperature thermochronological data from the eastern ets moqingwula range to constrain the process of deformation and exhumation during the mesozoic our results indicate that two phases deformation occurred in the late jurassic and the late cretaceous to the paleocene that transformed the landscape of the moqingwula range the first phase tilted the northern moqingwula range coinciding with folding and thrusting the second phase of deformation disrupted planation surfaces which dominantly formed in the early cretaceous and were preserved on the summit of the ranges our new data reveals three prominent cooling episodes during the 222 ma 138 113 ma and 68 57 ma as well as another subdued cooling phase during 113 92 ma in addition through integration of the regional cooling history and topographic evolution we discuss the geodynamics of the deformations and exhumations associated with tectonism within the central asian orogenic belt

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

structural framework of a major intracontinental orogenic termination zone the easternmost tien shan china the barkol tagh and karlik tagh ranges of the easternmost tien shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range barkol and karlik tagh and lesser ranges to the north are bounded by active thrust faults that locally deform quaternary sediments major thrusts in karlik tagh connect along strike to the east with the left lateral gobi tien shan fault system in sw mongolia from a mongolian perspective karlik tagh represents a large restraining bend for this regional strike slip fault system and the entire system of thrusts and strike slip faults in the karlik tagh region defines a horsetail splay fault geometry regionally there appears to be a kinematic transition from thrust dominated deformation in the central tien shan to left lateral transpressional deformation in the easternmost tien shan this transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the nne directed maximum horizontal stress in the region and the pre existing basement structural grain which is northwesterly in the central tien shan orthogonal to sh max but more east west in the eastern tien shan acute angular relationship with sh max ar ar ages indicate that major range bounding thrusts in barkol and karlik tagh are latest permian triassic ductile thrust zones that underwent brittle reactivation in the late cenozoic it is estimated that the modern mountain ranges of the extreme easternmost tien shan could have been constructed by only 10 15 km of late cenozoic horizontal shortening

focused pliocene quaternary exhumation of the eastern pamir domes western china abstract the kongur shan and muztagata domes are the most prominent topographic features in the eastern pamir indenter corner in spite of several previous bedrock thermochronology studies the extent processes and mechanisms of dome exhumation remain unclear we present 1158 detrital zircon fission track dzft ages from modern glacier and river sediments along the domes to better constrain the spatial distribution of exhumation our thermochronologic dataset from the chakragil massif shows a sharp increase in the proportion of dzft ages 10 ma from basins that drain the peak region to those further to the north which suggests that the kalagile fault forms the northern boundary of the rapidly exhuming dome structure a cluster of middle miocene dzft ages in these samples documents pre doming cooling possibly associated with motion on the main pamir thrust and or oytag fault large fractions of dzft grain ages

spatio temporal evolution of aseismic slip along the haiyuan fault china implications for fault frictional properties article history we use 20 years of synthetic aperture radar acquisitions by the ers and envisat satellites to investigate the spatial and temporal variations of strain rates along the 35 km long creeping section of the haiyuan fault at the north eastern boundary of the tibetan plateau we then use the derived displacements to infer the fault s frictional properties and discuss the relationship between creep and the seismic behavior of the fault located in between a millennial seismic gap and the 1920 m8 surface rupture trace this section has an average creep rate of 5 1m m yr about the interseismic loading rate the comparison of average surface velocity profiles derived from sar interferometry across the creeping section reveals a creep rate increase and or a creep migration to shallower depth between the 1990s and the 2000s we apply a smoothed time series analysis scheme on envisat insar data to investigate the creep rate variations during the 2004 2009 time period our analysis reveals that the creep rate accelerated in 2007 although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude both decadal and short term transient behaviors are coeval with the largest earthquakes m 4 5 along the fault segment in recent years from the precise mapping of the surface fault trace we use the fault strike variations and the mohr circle construction to compute the along strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate we find that the creep rate scales logarithmically with the friction coefficient in agreement with the rate and state friction law in a rate strengthening regime the estimated value of log v 2 10 3 indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segment s creep rate and that the recorded micro seismicity is most likely creep driven finally given the size and frictional properties of the creeping section we estimate based on previous models of dynamic rupture simulations a 0 20 probability for a rupture to break through this section together with the geometrical configuration of the haiyuan fault these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation

exhumation history of the western kyrgyz tien shan implications for intramontane basin formation the dextral talas fergana fault separates the western from the central tien shan recent work has shed light on the cenozoic evolution of the eastern and central tien shan much less attention has been paid to the western tien shan in this contribution we present new thermochronological ages for the fergana and alai ranges that combined with the available data set constrain the cenozoic exhumation history of the western tien shan following a tectonically quiet early cenozoic period we suggest an onset of exhumation at 25 ma this early onset was followed by a period of slower exhumation and in some areas minor reheating a final strong late miocene rapid cooling event is well represented in the western tien shan as in other sectors of the range the early onset of uplift of the western tien shan dissected the previously continuous westernmost parathethyan sea progressively isolating basins e g fergana tarim and alai basins in the central asian hinterland moreover the coeval timing of late miocene uplift along the length of entire tien shan implies that neither the pamir nor tarim can be the sole driver for exhumation of the entire range

counter clockwise rotation of the eastern part of the mongolia block early cretaceous palaeomagnetic results from bikin far eastern russia summary we present palaeomagnetic results from lower cretaceous rocks in bikin area of the alchan basin 46 5 n 134 7 e sikhote alin orogenic belt far eastern russia a high temperature magnetization component with maximum unblocking temperatures at about 590 c was isolated from six sites of dacite welded tuffs in the albian alchanskaya formation the fold tests for these six sites are positive suggesting that primary magnetization is preserved in the studied rocks the tilt corrected mean direction of d 309 3 i 68 7 95 10 1 with a corresponding palaeopole position at 57 0 n 76 8 e a95 15 1 indicates a counter clockwise ccw rotation for the studied area ccw rotation is also indicated from west directed declinations d 249 1 i 64 1 95 11 2 obtained from secondary magnetization of the berriasian kultukha formation combining with the previously reported studies the west directed cretaceous palaeomagnetic directions cover widely the eastern part of the mongolia block comparison with 100 ma palaeomagnetic pole for eurasia shows that the eastern part of the mongolia block experienced a ccw rotation of over 36 with respect to the eurasian continent later than late cretaceous this rotation is ascribed to post late cretaceous extension that affected the continental basins the middle amur sanjiang razdolnian amur zeya and songliao basins of the northeast chinese plain along the eastern margin of the mongolia block contemporaneous with this ccw rotation similar extension resulted in clockwise rotation of the eastern part of the north china block

tectonic evolution from subduction to arc continent collision of the junggar ocean constraints from u pb dating and hf isotopes of detrital zircons from the north tianshan belt nw china the junggar ocean once situated north present coordinate of the yili and central tianshan blocks during early paleozoic to late carboniferous time was a major southern branch of the paleo asian ocean the opening expansion and final closure of which led to the development of the central asian orogenic belt between eastern europe siberia and tarim north china however the detailed evolution of the junggar ocean has not been well constrained this paper reports u pb and lu hf isotopic data of detrital zircons from sandstones in the north tianshan belt which can provide new insights into understanding the paleozoic development of the junggar ocean most detrital zircons exhibit oscillatory zoning and high th u ratios typical of igneous origin the predominant paleozoic zircons yield major age populations at ca 294 313 327 338 375 440 455 and 474 502 ma and are interpreted to have been derived from the long lived volcanic and island arc systems formed by the southward subduction of the junggar ocean and subsequent collisional and postcollisional magmatism the minor precambrian zircons yield ages scattering at ca 550 680 765 890 970 990 1160 1250 1500 1690 1750 1840 1970 2440 2500 and 2615 2700 ma which are nearly but not fully congruent with those from the adjacent beishan and kuluketage precambrian terranes therefore our results indicate that the central tianshan block was once part of the tarim block during precambrian time most of the 541 440 ma zircons possess low negative ehf t values while the 440 300 ma zircons exhibit dominantly positive ehf t values which can be linked to the junggar oceanic slab rollback since ca 440 ma this event subsequently gave rise to the opening of the south tianshan back arc basin ocean between the central tianshan and tarim blocks exhumation of high pressure granulites and formation of a series of island arcs in the junggar ocean combined with previous studies we suggest that the junggar ocean was probably closed at ca 300 ma in association with arc continent collision followed by postcollisional magmatism it deserves mentioning that the ca 0 5 and 1 4 1 5 ga detrital zircons and contemporaneous magmatic rocks only occur in the central tianshan block not in the tarim block therefore more detailed investigations are needed to better elucidate the origin and precambrian evolution of the central tianshan block

oceanic style subduction controls late cenozoic deformation of the northern pamir orogen abstract the northern part of the pamir orogen is the preeminent example of an active intracontinental subduction zone in the early stages of continent continent collision such zones are the least understood type of plate boundaries because modern examples are few and of limited access and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes in the pamir it has been assumed that most of the plate convergence was accommodated by overthrusting along the plate bounding main pamir thrust mpt which forms the principal northern mountain and deformation front of the pamir however the synopsis of our new and previously published thermochronologic data from this region shows that the hanging wall of the mpt experienced relatively minor amounts of late cenozoic exhumation the pamir orogen as a whole is an integral part of the overriding plate in a subduction system while the remnant basin to the north constitutes the downgoing plate with the bulk of the convergence accommodated by underthrusting herein we demonstrate that the observed deformation of the upper and lower plates within the pamir alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback subduction erosion subduction accretion and marginal slab tear faults we suggest that the curvature of the north pamir is genetically linked to the short width and rollback of the south dipping alai slab northward motion indentation of the pamir is accommodated by crustal processes related to this rollback the onset of south dipping subduction is tentatively linked to intense pamir contraction following break off of the north dipping indian slab beneath the karakoram

tectonic history of the irtysh shear zone ne kazakhstan new constraints from zircon u pb dating apatite fission track dating and palaeostress analysis abstract the irtysh shear zone isz is an important structure in the framework of the central asian orogenic belt caob it represents the site of final collision of kazakhstan with siberia during hercynian times and records up to 1000 km of lateral displacement during subsequent reorganization in the caob edifice we present new zircon u pb apatite fission track and fault kinematic data along the isz and consequently derived its tectonic history with emphasis on its formation and reactivation episodes carboniferous 340 320 ma zircon u pb ages were obtained for the syn and post collisional kalba narym intrusives dating their emplacement in the framework of the siberia kazakhstan collision during this period the isz experienced an early brittle left lateral mainly transtensional stress regime late carboniferous early permian post collisional intrusives were emplaced and the stress regime changed to a late brittle regime characterized by more compressional conditions indicating rheological strengthening as a response to cessation of ductile shearing and cooling of the isz crust apatite fission track data and thermal history modeling reveal late cretaceous 100 70 ma cooling of the isz basement rocks as a response to denudation of a bordering late mesozoic altai orogen after this denudation event the tectonic activity ceased during the late mesozoic early cenozoic a final step of cooling from 25 ma exhibited by some of the thermal history models may reflect reactivation of the isz and initiation of cenozoic altai mountain building the late plio pleistocene phase of mountain building coincides with a new change in the palaeostress field characterized by minor transpressional right lateral shear conditions

late palaeozoic and meso cenozoic tectonic evolution of the southern kyrgyz tien shan constraints from multi method thermochronology in the trans alai turkestan alai segment and the southeastern ferghana basin abstract in this paper we present new geochronological and thermochronological data from the turkestan alai segment of the southern kyrgyz tien shan the ferghana basin transition and the trans alai pamir foreland in the southern and central parts of the alai range towards the alai valley mainly post collisional granitoids were targeted for zircon u pb dating by laser ablation inductively coupled plasma mass spectrometry la icp ms apatite fission track aft and apatite u th sm he ahe thermochronology these granitoids and their thermally metamorphosed contact aureole yielded middle permian zircon crystallization ages of 284 4 to 264 5 ma aft ages both using the traditional external detector approach as well as using la icp ms for these samples are constrained to the miocene and range between 22 3 1 1 and 8 4 0 3 ma while the ahe ages are somewhat younger between 12 5 0 8 and 5 0 0 3 ma this low temperature thermochronological data suggests an early miocene onset of denudation in this area in the tien shan orogen continuing through the miocene and pliocene this denudation is interpreted as a response to reactivation of the mountain belt in the framework of india eurasia convergence and specific to this region of the pamir tien shan interaction on the northern slopes of the alai range at the edge of the ferghana basin a late palaeozoic conglomerate yielded a reset early cretaceous aft age of 118 7 ma pointing to an older denudation event with respect to those identified in the southern and central parts of the alai range a mesozoic sediment sample from the same region only contains a late triassic age component of 223 ma mesozoic and cenozoic age components on the other hand are all detected in the cenozoic sediments of the trans alai range at the transition between the southern alai valley and the pamirs revealing several meso cenozoic denudation events in the adjoining basement source rocks the age components in these detrital apatites are 207 ma 75 ma 18 ma and 3 ma

differential exhumation and crustal tilting in the easternmost tianshan xinjiang china revealed by low temperature thermochronology the easternmost tianshan forms the eastern extremity of the modern central asian orogenic belt and represents a key locality to investigate strain propagation from the meso cenozoic plate margins to the eurasian interior the tianshan as a whole has been reactivated multiple times throughout the meso cenozoic but the extent of these reactivation events is yet to be fully understood this study applies apatite fission track and apatite u th sm he thermochronology to the mountain ranges of the easternmost tianshan our new results suggest that the area experienced two phases of rapid cooling in the mesozoic during the early middle triassic and the late cretaceous these cooling phases are linked to tectonic events at the distant plate margins such as the permian mid triassic closure of the paleoasian ocean and the late jurassic early cretaceous mongol okhotsk orogeny fault controlled differential exhumation and block tilting are recorded in the distribution of apatite fission track ages across the region finally we show through a combination of multiple thermochronometers and the integration of structural analysis that the easternmost tianshan has experienced insufficient exhumation to constrain the timing of reactivation in response to the cenozoic collision of india with eurasia and instead records older mesozoic tectonic events

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

a centennial scale variability of tropical north atlantic surface hydrography during the late holocene abstract sea surface temperature sst and sea surface salinity sss fluctuations in the northeastern caribbean have been reconstructed through the last 2000 yr using an artificial neural network and 18 o analyses of planktonic foraminifera a warmer period prevailed in the ne caribbean from ad 700 950 which may reflect the occurrence of stronger and or more frequent el nino events a 2 c cooling of winter ssts from ad 1400 to 1550 coincides with the occurrence of reduced solar output the sporer event episodes of lower ssss with marked minima at the onsets of the dark ages in europe ad 500 600 and little ice age ad 1400 are cyclically recurrent at intervals of 200 400 yr and coincide with drier periods in mexico this may indicate that the tropical atlantic evaporation precipitation budget and ssss are affected by a centennial scale modulation involving the freshwater export import from into the atlantic ocean coeval changes recorded in the deep north atlantic circulation indicate that low latitude sss anomalies may be advected polewards by the north atlantic current system thus affecting deep ocean convection and strength of the thermohaline circulation

long term exhumation history of the inner mongolian plateau constrained by apatite fission track analysis the inner mongolian plateau along the southeastern flank of the wider mongolian plateau is a vast undulating surface ranging in elevation between 900 and 1500 m above sea level the peculiar topography of this area is assumed to be closely related to its complex tectono thermal evolution since late paleozoic the lithospheric structure of the plateau includes three continental blocks the mandula and the bart obo blocks form the southern margin of the central asian orogenic belt in that area and to the south the plateau includes the northern margin of the north china craton apatite fission track aft ages and track length distributions from 13 basement outcrops situated in the main tectonic blocks forming the inner mongolian plateau were determined in order to reconstruct its denudation history the thermal histories inferred from these data imply multi phased differential exhumation burying processes from the late paleozoic to the early cretaceous this complex thermal history is largely related to the early middle triassic closure of the paleo asian ocean the jurassic closure of the mongol okhotsk ocean and the early cretaceous orogenic collapse of the mongol okhotsk belt finally since late cretaceous no further major tectonic movement occurred and the inner mongolian plateau has been largely peneplained

differential uplift of the chinese tianshan since the cretaceous constraints from sedimentary petrography and apatite fission track dating the chinese tianshan is one of the important international natural laboratories for studying continental geodynamics but its uplift time kinematics and mechanism of formation are key unresolved questions in order to constrain the timing kinematics and mechanism of uplift of the chinese tianshan we applied sedimentary petrography and apatite fission track dating to cretaceous tertiary series from the northern tarim basin and the tianshan mountains we collected and analyzed 79 sandstone samples and 75 detrital heavy mineral samples from the kezilenuer kuqa profile northern tarim basin with a well defined magnetostratigraphy our data indicate that detrital mineral maturity abruptly decreased at the disconformity between the upper and lower cretaceous and decreased again after 15 12 ma the sediments in the northern tarim basin changed their provenance at 124 ma 26 24 ma and 15 12 ma respectively in addition we collected and analyzed 36 primary apatite samples from the south central and north tianshan our results show that the chinese tianshan underwent three phases of differential uplift the first phase of uplift started at the southern central tianshan during the early cretaceous and propagated southward the second phase of uplift started at the northern central tianshan during the late cretaceous and propagated also southward the third phase of uplift started at the northern central tianshan during the eocene and propagated both northward and southward these differential uplifts have caused development of disconformity and drops in mineral maturity of detrital sediments in the northern tarim basin such a differential and heterogeneous uplift process might have been trigged by collisions of different microcontinents i e lhasa kohistan dras and india at the southern margin of asia these collisions reactivated the south tianshan fault and then the north tianshan suture and uplifted the chinese tianshan step by step

emplacement of the ophiolitic melanges in the west karamay area implications for the late paleozoic tectonic evolution of west junggar northwestern china abstract the darbut and karamay ophiolitic melanges in the west karamay area at the southeastern margin of west junggar southern altaids represent the relict fragments of the paleozoic junggar ocean basin the melanges contain structurally complex tectonic blocks of ultramafic rocks gabbro basalt and chert that are dispersed within an extensively sheared serpentinite matrix this study presents new field observations structural analyses geochronological and geophysical data for the melanges and the overlying carboniferous strata three stages of deformation d1 d3 have been identified d1 is only locally preserved in the melanges and is characterized by thrust imbricated faults recording the subduction and accretion of the paleo oceanic crust in the early carboniferous d2 mainly consists of map scale upright folds f1 in the carboniferous strata and ne sw striking sub vertical right lateral shear zones in the melanges d3 is characterized mainly by ne sw striking transcurrent left lateral strike slip faults and s shaped drag folds f2 the extensive tectonic reworking during d2 and d3 deformations eradicated most of the d1 structures our structural observations combined with geophysical data suggest that the basement of the west karamay area consists of trapped oceanic crust or dismembered ophiolitic fragments and that the darbut and karamay ophiolitic melanges were extruded through right lateral shear zones our results and the published data further suggest that the emplacement of the melanges and the formation of f1 folds represent regional scale amalgamation processes between different tectonic blocks and or plates in the late carboniferous these processes resulted in the closure of the west junggar remnant ocean basin and other sub oceanic basins in the paleo asian ocean leading to the formation of the kazakhstan orocline furthermore the d3 deformation was associated with anticlockwise rotation of the west junggar region in a post collisional setting in the permian

jurassic tectonostratigraphic evolution of the junggar basin nw china a record of mesozoic intraplate deformation in central asia mesozoic basins in northwest china provide important records for investigating relationships between intraplate deformation in central asia and tectonic processes at asian boundaries the present study using well seismic outcrop and thermochronology data in the junggar basin and neighboring areas describes the main features of jurassic strata in the basin analyzes the jurassic evolution of the basin and neighboring mountain belts and discusses possible mechanisms of jurassic intraplate deformation in central asia during the early middle jurassic episodic uplift of surrounding mountain belts kept the junggar basin a contractional closed basin and alluvial fan fluvial delta and lacustrine depositional environments successively developed from surrounding ranges to the central basin during the late jurassic the western and central parts of the basin were folded and uplifted and deposition migrated mainly to the eastern basin during the latest jurassic earliest cretaceous pre cretaceous strata in the eastern and northeastern junggar basin were folded and uplifted and coarse grained sediments were transported from surrounding uplifts to the central basin we suggest that jurassic episodic deformation events in the junggar basin and other areas of central asia are related to the qiangtang collision during the late triassic early jurassic the closure of the western mongol okhotsk ocean at the early middle jurassic boundary a collision of a microcontinent in the pamir with the southern asian margin during the late middle jurassic early late jurassic the collision of the kolyma omolon block with siberia at the end of the jurassic and the subsequent closure of the eastern mongol okhotsk ocean during the latest jurassic earliest cretaceous

thermo tectonic history of the issyk kul basement kyrgyz northern tien shan central asia abstract lake issyk kul occupies a large late mesozoic cenozoic intramontane basin between the mountain ranges of the northern kyrgyz tien shan these ranges are often composed of granitoid basement that forms part of a complex mosaic assemblage of microcontinents and volcanic arcs several granites from the terskey kungey trans ili and zhetyzhol ranges were dated with the zircon u pb method shrimp la icp ms and yield concordant late ordovician silurian 456 420 ma emplacement ages these constrain the caledonian accretion history of the northern kyrgyz tien shan in the amalgamated palaeo kazakhstan continent the ancestral tien shan orogen assembled in the early permian when final closure of the turkestan ocean ensued collision of palaeo kazakhstan and tarim a late palaeozoic structural basement fabric formed and middle late permian post collisional magmatism added to crustal growth of the tien shan permo triassic cooling 300 220 ma of the ancestral tien shan was unraveled using 40 ar 39 ar k feldspar and titanite fission track ft thermochronology on the issyk kul granitoids apatite thermochronology ft and u th sm he applied to the broader issyk kul region elucidates the meso cenozoic thermo tectonic evolution and constrains several tectonic reactivation episodes in the jurassic cretaceous and cenozoic exhumation of the studied units occurred during a protracted period of intracontinental orogenesis linked to far field effects of late jurassic cretaceous accretion of peri gondwanan blocks from the tethyan realm to eurasian following a subsequent period of stability and peneplanation incipient building of the modern tien shan orogen in northern kyrgyzstan started in the oligocene according to our data intense basement cooling in distinct reactivated and fault controlled sections of the trans ili and terskey ranges finally pinpoint important miocene pliocene 22 5 ma exhumation of the issyk kul basement late cenozoic formation of the tien shan is associated with ongoing indentation of india into eurasia and is a quintessential driving force for the reactivation of the entire central asian orogenic belt

a short lived but significant mongol okhotsk collisional orogeny in latest jurassic earliest cretaceous abstract the central asian orogenic belt caob is one of the largest orogenic collages on earth which records a long history of accretionary orogenesis from the late proterozoic to the mesozoic although paleomagnetic studies have unanimously suggested that the major mongol okhotsk ocean in the eastern caob closed mainly during the late jurassic early cretaceous few conclusive and self consistent geological studies in central asia and east asia have confirmed the occurrence of this significant collisional orogeny based mainly on basin evolution in the caob tarim block north china block and qaidam qialian block during the late jurassic early cretaceous the present study proposes that a short lived but significant mongol okhotsk collisional event occurred in the latest jurassic earliest cretaceous the rapid closure of the mongol okhotsk ocean was possibly related to the clockwise rotation of siberia which was driven by the continental collision between the siberia craton and the kolyma omolon microcontinent in northeast russia in the late jurassic owing to the clockwise rotation of siberia and the subsequent closure of the mongol okhotsk ocean a number of areas to both the east and the west of the mongol okhotsk suture underwent uplift and erosion including lake baikal transbaikalia sayan ranges altai shan junggar basin turfan basin tarim basin tian shan mohe basin great xing an ranges hailar tamsag basin erlian basin songliao basin east gobi basin yingen basin bei shan yin shan yan shan belt ordos basin chaoshui yabulai basin and northern qaidam basin forming a giant fold and thrust belt in northern china and mongolia the collision probably caused a prominent gap between late jurassic and early cretaceous magmatic episodes in the eastern caob and north china block after lasting for about 10 million years the main portion of the mongol okhotsk ocean closed forming a northeast trending suture during the early cretaceous a remnant ocean still remained in the easternmost part of the mongol okhotsk ocean and the regional compressional setting in east asia related to the closure of the mongol okhotsk ocean changed to escape tectonics driven by the collision of the lhasa block at the southern margin of asia strike slip faulting triggered gravitational collapse of upper crust and delamination of lower crust and mantle lithosphere that was thickened during the mongol okhotsk collision resulting in the development of a continental scale extensional setting in east asia associated with rift basins metamorphic core complexes and igneous rocks

uplift age and rates of the gurvan bogd system gobi altay by apatite fission track analysis abstract the dating of the uplift onset of the mongolian mountain ranges the northernmost relief associated with the india eurasia convergence is a fundamental issue to better understand the mechanisms of propagation of the cenozoic transpressive deformation in central asia using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the gurvan bogd system in the gobi altay since the middle mesozoic to the late cenozoic the region was firstly affected by a lower middle jurassic tectonic phase characterized by a vertical crustal movement larger than 2 km then followed a protracted period without major crustal vertical movements until the last uplift phase the peneplanation of the jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 ma this same surface corresponds to the present summit plateaux of the massifs standing about 2000 m above the surrounding region which corresponds to the vertical movement produced by the ongoing uplift modelling of fission track data from the massifs of ih bogd and baga bogd shows that this uplift phase probably started at 5 3 ma the gobi altay mountain range appears therefore as one of the youngest mountain ranges in central asia which is consistent with the idea of a northward propagation of the transpressional deformation from the himalayan front to the siberian craton the cenozoic uplift rate of the massifs is estimated to be between 0 25 and 1 mm yr which is slightly higher than the upper pleistocene vertical slip rates of the bordering faults this suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries

mesozoic tertiary exhumation history of the altai mountains northern xinjiang china new constraints from apatite fission track data abstract this study uses apatite fission track ft analysis to constrain the exhumation history of bedrock samples collected from the altai mountains in northern xinjiang china samples were collected as transects across the main structures related to palaeozoic crustal accretion events ft results and modeling identify three stages in sample cooling history spanning the mesozoic and tertiary stage one records rapid cooling to the low temperature part of the fission track partial annealing zone circa 70 10 c stage two records a period of relative stability with little if any cooling taking place between 75 and 25 20 ma suggesting the altai region had been reduced to an area of low relief support for this can be found in the adjacent junngar basin that received little if any sediment during this interval final stage cooling took place in the miocene at an accelerated rate bringing the sampled rocks to the earth s surface this last stage linked to the far field effects of the himalayan collision most likely generated the surface uplift and relief that define the present day altai mountains

tibetan basement rocks near amdo reveal missing mesozoic tectonism along the bangong suture central tibet the u pb and 4 0 ar 3 9 ar studies of a unique exposure of crystalline basement along the jurassic early cretaceous bangong suture of central tibet reveal previously unrecognized records of mesozoic metamorphism magmatism and exhumation the basement includes cambrian and older orthogneisses that underwent amphibolite facies metamorphism coeval with extensive granitoid emplacement at 185 170 ma the basement cooled to 300 c by 165 ma and was exhumed to upper crustal levels in the hanging wall of a south directed thrust system during early cretaceous time we attribute jurassic metamorphism and magmatism to the development of a continental arc during bangong ocean subduction and early cretaceous exhumation to northward continental underthrusting of the lhasa terrane beneath the qiangtang terrane we speculate that a jurassic arc extended regionally along the length of the bangong suture but in all other places in tibet has been buried either depositionally or structurally beneath supracrustal assemblages

late cretaceous palaeogene topography of the chinese tian shan new insights from geomorphology and sedimentology abstract the cenozoic growth of the intra continental tian shan range initiated during the late eocene oligocene and led to a tectonic reactivation of the complex palaeozoic and mesozoic lithospheric structure due to the very low erosion rates linked to the semi arid climate that characterised the tian shan region during most of the cenozoic the topography of the range is not at equilibrium with deformation fragments of pre orogenic low relief surfaces are preserved among the late cenozoic alpine type topography using field observations and satellite image mapping of those fragments as well as sedimentology and biostratigraphic analysis we show that the pre oligocene topography of the tian shan region was indeed complex combining hundreds of metres to one and a half kilometre high reliefs with a multi phased mesozoic planation surface incised by late mesozoic paleo valleys the occurrence of several metres thick late cretaceous palaeogene calcareous paleosols in the basins surrounding the range further implies a semi arid climate very low subsidence rates and no uplift at that time late cretaceous and early miocene fossil records in the northern tian shan suggest a possible connection even if episodic between the drainage system of the south junggar foreland basin and the proto paratethys sea to the west a renewed late eocene early oligocene sedimentation probably marks the onset of the tian shan uplift we argue that in addition to the growth of the pamir and western kunlun ranges this incipient uplift was one of the driving mechanisms for the final retreat of the proto paratethys sea from the tarim basin this regression apparently did not change the climate in the studied area because semi arid conditions seem to prevail at least since the late cretaceous finally the tian shan uplift remained very limited up to the miocene as revealed by the occurrence of burdigalian lake deposits preserved in the paleo valleys inside the present day range in contrast post early miocene deformation of the northern tian shan has produced 4000 to 5000 m of differential vertical movement between the uplifted range and the subsiding proximal foreland basin

controls on cenozoic exhumation of the tethyan himalaya from fission track thermochronology and detrital zircon u pb geochronology in the gyirong basin area southern tibet the gyirong basin southern tibet contains the record of miocene pliocene exhumation drainage development and sedimentation along the northern flank of the himalaya the tectonic controls on basin formation and their potential link to the south tibetan detachment system stds are not well understood we use detrital zircon zft and apatite aft fission track analysis together with detrital zircon u pb dating to decipher the provenance of gyirong basin sediments and the exhumation history of the source areas results are presented for nine detrital samples of gyirong basin sediments aft zft and u pb two modern river sediment samples zft and aft and six bedrock samples zft from transect across the gyirong fault bounding the basin to the east the combination of detrital zircon u pb and fission track data demonstrates that the gyirong basin sediments were sourced locally from the tethyan sedimentary sequence this provenance pattern indicates that deposition was controlled by the gyirong fault active since 10 ma whose vertical throw was probably 5000 m rather than being controlled by normal faults associated with the stds the detrital thermochronology data contain two prominent age groups at 37 41 and 15 18 ma suggesting rapid exhumation at these times a 15 18 ma phase of rapid exhumation has been recorded widely in both southern tibet and the himalaya a possible interpretation for such a major regional exhumation event might be detachment of the subducting indian plate slab during the middle miocene inducing dynamic uplift of the indian plate overriding its own slab

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

accommodating large scale intracontinental extension and compression in a single stress field a key example from the baikal rift system the baikal rift system in southern siberia is one of the main intracontinental extensional features on earth the rift system represents the northwestern boundary of the amuria plate and in that respect can be considered as an evolving plate boundary the baikal rift system has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution however the age of the initiation of deformation and the mechanism driving this deformation are still largely debated while major extension has occurred since the late miocene pliocene the onset of extension seems older than the india asia collision implying that several driving mechanisms may have acted together or in relay through time in this work we review the available data and models for deformation in an area encompassing the baikal rift system the sayan ranges to the west and the transbaikal to the east using a synthesis of this data and our own field and mapping observations we show that the baikal rift system along with transpressional deformation in the sayan ranges and transtension in the transbaikal area can be explained through major left lateral strike slip systems the deformation is strongly controlled by inherited crustal and lithospheric structures and is distributed over a wide area within the western amuria plate that consequently cannot be considered as a rigid block such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

structural control on meso cenozoic tectonic reactivation and denudation in the siberian altai insights from multi method thermochronometry abstract the siberian altai forms part of the central asian orogenic belt and currently is an active intracontinental mountain belt this siberian altai orogen was shaped during multiple phases of intense mountain building and associated denudation throughout the mesozoic and cenozoic we performed a multi method thermochronometric study on the altai basement in siberia in order to distinguish these denudation episodes and to place them in an absolute time frame our data shows that inherited suture zones such as the charysh terekta ulagan sayan suture played a dominant role during this episodic deformation in the altai titanite fission track results reveal late triassic early jurassic cooling which is best expressed in intrusions close to the suture zone apatite fission track aft results reveal a second phase of steady basement cooling during the late jurassic and cretaceous in the suture aft and additional apatite u th sm he ahe data reveal a consistent late cretaceous early palaeogene phase of fast cooling we interpret the mesozoic cooling signals as far field effects of the mongol okhotsk orogeny the intense late cretaceous palaeogene basement cooling signal in the suture zone can be explained as a result of fault reactivation during the collapse of this orogen and the subsequent re organization of crustal blocks during most of the palaeogene and early neogene basement cooling stagnated indicating tectonic quiescence neogene ahe ages for the kurai range directly adjacent to the suture may reflect renewed rapid cooling as a result of denudation of the present day altai mountains we interpret this most recent cooling as an indirect consequence of stress propagation from the india eurasia collision into the caob interior which thus reached as far as southern siberia this study further demonstrates the importance of thermochrological studies on intrusions along major fault zones in order to date and distinguish fault reactivation episodes