mesozoic cenozoic tectonic relationships between the kuqa subbasin and tian shan northwest china constraints from depositional records abstract stratigraphic profiles in the kuqa subbasin located along the southern flank of the tian shan northwest china display similar mesozoic cenozoic evolutionary sequences of compositional maturity exist in conglomerate clasts sandstone framework grains and detrital heavy minerals the similarity of these time series profiles resulted from orogenesis and intracontinental deformation of the provenance area the ancestral tian shan mineralogical maturities of conglomerates and sandstones increase from triassic to middle jurassic and decrease from upper jurassic lower cretaceous to tertiary this trend parallels a similar decrease in maturity in detrital heavy minerals zircon rutile and tourmaline dominate in middle upper triassic to middle jurassic sandstone whereas unstable hornblende and pyroxene dominate the heavy mineral suites in the tertiary especially in miocene and pliocene strata these compositional trends are coeval with gradual southward migration of alluvial depositional fronts and depositional depocenters from cretaceous to miocene since the pliocene large scale southward migration of alluvial depositional systems occurred while depositional depocenters migrated northward based on the mesozoic cenozoic depositional records the tectonic evolution of the tian shan kuqa subbasin may be divided into five phases 1 in early triassic following compression and uplift since permian gravelly braided river alluvial plain depositional systems developing in the kuqa subbasin characterized by sands of mixed orogenic provenance type derived from the ancestral tian shan 2 from middle triassic to middle jurassic sediment composition of the kuqa subbasin reflects arc orogen and mixed orogenic sand types with extensive planation of the ancestral tian shan and the development of relatively stable coal bearing depositional environments 3 renewed compression uplift of the tian shan occurred in late mesozoic especially in cretaceous with most detrital modes of the kuqa subbasin indicating provenance attributes akin to the south tian shan 4 further intensive compression uplift and probably southward basinward propagation of the south tian shan occurred during miocene and 5 supracrustal gravity gliding and collapse occurred in the tian shan kuqa subbasin probably due to intensive deep compression with rejuvenated uplift and probable southward basinward structural propagation of the south tian shan developing since pliocene observed changes in sediment composition and depositional environment since pliocene time were also controlled by frequent and abrupt climate changes in addition to intensive uplift of the tian shan moreover all depositional records in the kuqa subbasin seem to reflect west to east differences in provenance along the tian shan probably indicating greater exhumation depth in the western tian shan than that in the eastern tian shan since early cretaceous

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

paleomagnetism of late paleozoic rocks in the tianshan northwestern china a paleomagnetic study of late paleozoic rocks in two areas of northwestern china helps to constrain the timing of collision between tarim and the junggar part of eurasia along tianshan a primary late permian direction d i 198 59 k 24 a95 12 6 is derived from seven sites 53 samples from the heavenly lake tianzhi section in northern tianshan that has both normal and reversed polarities and passes a fold test at the 99 confidence level this result gives a latitude of 39 n in the late permian for southern junggar twenty two sites 144 samples from the devonian and carboniferous rocks across tianshan reveal postfolding remagnetizations some of which are interpreted as being acquired in the permian due to the tarim eurasia collision the late permian paleomagnetic pole from the heavenly lake section is statistically indistinguishable from three published late permian poles from tarim indicating closure of the tianshan ocean and suturing of tarim and junggar before that time these paleomagnetic poles from northwestern china are however significantly different from those of stable eurasia suggesting substantial later relative motion that can be partly accounted for by the progressive closure of the mongolo okhotsk ocean and associated tectonic rotations the absence of a discernable permian ocean record west of the khangay highland in central mongolia requires that the rotations be accommodated within a diffusive plate boundary in the eurasian continent a late permian continental plate reconstruction is presented that takes into consideration these new paleomagnetic results and other geological constraints

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

the neogene xiyu formation a diachronous prograding gravel wedge at front of the tianshan climatic and tectonic implications the tarim and junggar basins in central asia are capped by a thick pile of conglomerates called the xiyu formation that are commonly linked to a change in climate and or accelerated uplift near the plio pleistocene boundary in order to better understand their origin and significance we carried out a combined structural and magnetostratigraphic study in the quilitage syncline southern tianshan where the base of the xiyu conglomerates is observed at both sides of the syncline a balanced cross section shows that even at a local scale the base of the xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer on the southern flank of the quilitage syncline we collected 172 samples collected for magnetostratigraphic dating identify 17 polarity chrons that date the new section from 5 2 to 1 7 ma and constrain the base of the xiyu conglomerate here at 1 7 ma this is 4 2 ma younger than the age of the xiyu previously found on the northern limb of the same syncline together with other magnetostratigraphic studies carried out around the tianshan our study unambiguously demonstrates that the onset of deposition of the xiyu conglomerates is diachronous and that the conglomerates are systematically younger toward the basin consequently the xiyu formation should not be considered as a chronostratigraphic marker related to any particular tectonic or climatic event but is instead a prograding gravel wedge that has prograded over the underthrusting forelands a synthesis of chronologic and structural results yields progradation rates over the last 10 ma on the order of 2 0 mm yr and 3 9 mm yr south and north of the tianshan mountains respectively these rates are comparable to the shortening rate across the tianshan range suggesting that underthrusting is the main factor governing the progradation rate of the xiyu formation

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

postglacial land uplift in estonia based on four precise levelings abstract the vertical velocities of the fundamental benchmarks of estonian 1st order leveling network were estimated based on the four precise leveling campaigns from 1933 to 2010 the kinematic least squares adjustment of the network was used where heights and velocities were introduced as unknown parameters for detection of outliers baarda s data snooping method was applied estimation of variance components by the helmert s and the iaue methods provided realistic weights in the network adjustment and revealed also that the observation errors of the first three levelings are up to 3 times larger than was assumed a priori to obtain apparent uplift rates and fix velocity in kinematic adjustment the velocity value 2 1 mm yr of the ristna tide gauge on island hiiumaa was transferred to the nearest stable benchmark by using precise levelings from tide gauge to the national height network average standard deviation of velocities at benchmarks was estimated to be 0 5 mm yr based on apparent vertical velocities of the benchmarks an interpolated land uplift surface was created using kriging and minimum curvature gridding methods although the two methods gave similar surfaces rms of differences was below 0 1 mm yr the kriging solution was used in comparison with the results of the earlier studies the uncertainty of new velocity surface was estimated to be 0 5 to 0 7 mm yr the new land uplift model fits well with the fennoscandian land uplift model nkg2005lu the rms of the differences was 0 2 mm yr good agreement was also confirmed with the earlier land uplift maps of estonia rms of differences 0 6 mm yr however clear disagreement was noticed when tide gauge observations from several studies were used in comparison rms of differences up to 1 0 mm yr apparently different velocity solutions of estonian tide gauges are systematically biased the reasons for these biases need further investigation

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

geochemical sr nd and zircon u pb hf isotopic studies of late carboniferous magmatism in the west junggar xinjiang implications for ridge subduction abstract voluminous granitic intrusions are distributed in the west junggar nw china and they can be classified as the dioritic rocks charnockite and alkali feldspar granite groups the dioritic rocks sio 2 50 4 63 8 wt are calc alkaline and mg enriched average mgo 4 54 wt mg 0 39 0 64 with high sr y ratios average 21 2 weak negative eu average eu eu 0 80 and pronounced negative nb ta anomalies their sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7035 0 7042 e nd t 4 5 7 9 e hf t 14 1 14 5 show a depleted mantle like signature these features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials the charnockites sio 2 60 0 65 3 wt show transitional geochemical characteristics from calc alkaline to alkaline with weak negative eu average eu eu 0 75 but pronounced negative nb ta anomalies sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7037 0 7039 e nd t 5 2 8 0 e hf t 13 9 14 7 also indicate a depleted source suggesting melts from a hot juvenile lower crust alkali feldspar granites sio 2 70 0 78 4 wt are alkali and fe enriched and have distinct negative eu and nb ta anomalies average eu eu 0 26 low sr y ratios average 2 11 and depleted sr nd and zircon hf isotopic compositions 87 sr 86 sr i 0 7024 0 7045 e nd t 5 1 8 9 e hf t 13 7 14 2 these characteristics are also comparable with those of rocks derived from juvenile lower crust despite of the differences in petrology geochemistry and possibly different origins zircon ages indicate that these three groups of rocks were coevally emplaced at 305 ma a ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks as the slab window opened upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms partial melting of the subducting slab formed the dioritic rocks partial melting of the hot juvenile lower crust produced charnockite and alkali feldspar granite and partial melting in the mantle wedge generated mafic rocks in the region these results suggest that subduction was ongoing in the late carboniferous and thus support that the accretion and collision in the central asian orogenic belt took place in north xinjiang after 305 ma and possibly in the permian

from oblique accretion to transpression in the evolution of the altaid collage new insights from west junggar northwestern china abstract along active margins tectonic features that develop in response to plate convergence are strongly controlled by subduction zone geometry in west junggar a segment of the giant palaeozoic collage of central asia the west karamay unit represents a carboniferous accretionary complex composed of fore arc sedimentary rocks and ophiolitic melanges the occurrence of quasi synchronous upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the west junggar latest carboniferous ca 300 ma alkaline plutons postdate this early phase of folding which was synchronous with accretion of the carboniferous complex the permian dalabute sinistral fault overprints carboniferous ductile shearing and split the west karamay unit ca 100 km apart oblique convergence may have been provoked by the buckling of the kazakh orocline and relative rotations between its segments depending upon the shape of the convergence zone either upright folds and fold with vertical axes or alternatively strike slip brittle faults developed in response to strain partitioning sinistral brittle faulting may account for the lateral imbrication of units in the west junggar accretionary complex

junggar basin northwest china trapped late paleozoic ocean abstract the junggar basin originated during the late paleozoic as either a remnant lower to mid paleozoic ocean basin or a mid carboniferous back arc intra or inter arc basin bounded by emergent volcanic arcs south of the siberian craton the retreating junggar sea left behind a regressive sedimentary section comprising at least 3 4 km of marine volcaniclastics in the southern junggar area sandstones deposited in the junggar basin since the devonian are exclusively volcaniclastic demonstrating that precambrian basement rocks have never been exposed in the basin and supporting the hypothesis that the junggar is underlain by oceanic crustal materials the mid carboniferous junggar ocean may have been a remnant ocean basin of early to mid paleozoic age or alternatively may have been an extending intra or inter arc basin formed behind an emergent volcanic arc in the northern turpan region subsequent strike slip deformation and the general sparsity of geologic and geophysical data from the junggar area make it difficult to distinguish between these models late early permian through triassic sediments of the junggar basin are exclusively non marine deposited in a flexurally subsiding foreland basin during initial uplift of the ancestral tian shan mountains the sedimentary section deposited during the late permian early triassic appears to be inconsistent with a proposed rifting episode during this period

geochronological and geochemical study of the darbut ophiolitic complex in the west junggar nw china implications for petrogenesis and tectonic evolution abstract the darbut ophiolitic complex consists of ultramafic rocks cumulates pillow lavas and abyssal radiolarian cherts and occurs in the sartuohai suluqiaoke area which is situated in the eastern part of the west junggar nw china southern altaids in the present study we report new geochronological and geochemical data obtained for gabbro and basalt blocks embedded in the darbut ophiolitic complex zircon u pb analyses from one representative gabbro sample by la icp ms yielded a weighted mean age of 391 6 ma showing that it was emplaced in the middle devonian the samples bear n morb e morb and arc like geochemical signatures they are tholeiitic in composition with low concentrations of na 2 o k 2 o varying from 1 36 to 4 09 wt mg and ti depleted large ion lithophile elements liles enriched with insignificant negative eu they also show negative nb ta anomalies and high positive e nd t values with relative high la nb ba nb ba la ba th and zr nb ratios we interpret that these volcanic rocks were derived from a slightly metasomatized depleted mantle source in a back arc basin setting which corresponds to 10 30 partial melting of a depleted spinel lherzolite mantle the data presented here in combination with previously published data suggest a northwestward subduction model for the west junggar during the period of the early devonian to early carboniferous the west junggar was dominated by normal northwestward subduction and the ridge subduction commenced in the late carboniferous

late paleozoic paleomagnetic results from the junggar block northwestern china we have obtained middle carboniferous to permian paleomagnetic results from the junggar block in order to test its tectonic coherence and to reconstruct its late paleozoic position from hoboksar on the northwestern margin of junggar a paleomagnetic pole from basic silicic flows yields p 299 e p 70 n n 15 sites k a95 36 6 4 in the same general area a pole from lava flows plutons and as well as from remagnetized limestones sandstones is at p 350 e p 69 n n 26 site k a95 15 7 5 farther to the southwest in keramayi a pole from late paleozoic dike swarms lies at p 230 e p 80 n n 23 sites k a 95 16 7 8 in the southern margin near urumqi from sedimentary rocks and volcaniclastics of the middle to upper carboniferous qijiagou and aoertu formations a pole is produced at p 7 e p 72 n n 15 sites k a95 28 7 4 from the middle carboniferous liushugou formation and dike swarms intruding into the formation two poles are located at p 231 e p 69 n n 4 sites k a95 46 13 7 and p 172 e p 55 n n 7 sites k a95 17 15 1 respectively though reliabilities of these two poles are in question magnetic polarities of all the poles in our study are exclusively reversed based on positive fold tests and a baked contact test we believe that these magnetizations were acquired during the kiaman reversed interval 250 320 ma more accurate ages of the magnetizations cannot be resolved at present despite widely separate locations the pole positions are roughly located on a small circle segment around the junggar block similar inclinations suggest a coherent junggar block since permian time based on the results of this study and other published paleomagnetic data a mean middle carboniferous to permian paleomagnetic pole is calculated at p 329 e p 82 n n 6 poles k a95 26 13 4 recognition of late paleozoic apparent polar wander for junggar is obscured by a lack of detailed geochronologic data and possible relative horizontal rotations around vertical axis the paleolatitude for the southern junggar predicted by this pole is only 4 south of the present latitude difference exists between the mean pole from junggar and permian poles from other tectonic units in asia tarim siberia kazakhstan and north and south china indicating post permian relative motions at the boundary between tarim and junggar this motion is likely to have a left lateral sense

geochemical and geochronological study of early carboniferous volcanic rocks from the west junggar petrogenesis and tectonic implications abstract a series of early carboniferous volcanic rocks i e basalt andesite and dacite occur in the west junggar zircon u pb isotopic data indicate that these rocks coevally erupted at 331 344 ma these volcanic rocks have comparable trace element patterns characterized by the enrichment of large ion lithophile elements lile and the depletion of high field strength elements hfse isotopically they display consistently depleted sr nd isotopic compositions initial 87sr 86sr ratios 0 7034 0 7054 end t 4 2 7 7 these rocks are interpreted to be derived from a slightly metasomatized depleted mantle in a normal subduction environment in the context of a previously proposed ridge subduction model this study constrains that ridge subduction if it indeed occurred commenced between 331 and 310 ma in the central west junggar

first triassic palaeomagnetic constraints from junggar nw china and their implications for the mesozoic tectonics in central asia northwestern china belts result from the palaeozoic collage of central asia and the subsequent reactivations due to far field effects of the mesozoic tibetan and the cenozoic himalayan collisions triassic is a crucial period to understand and decipher the tectonics related to these two episodes about 250 oriented palaeomagnetic cores from 43 sites were collected from six sections of upper permian to late triassic sandstone in south and west junggar northwestern china thermomagnetic irm and hysteresis measurements reveal magnetite as the main carrier of the magnetic remanence with minor hematite and maghemite stepwise thermal demagnetisation has generally isolated two components the low temperature component up to 300 350 c displays a direction consistent with the present day geomagnetic field the locality mean directions related to the high temperature component above 350 c were also calculated two out of six sections display intense viscous magnetisation and the occurrence of maghemite reveals a possible cenozoic chemical remagnetisation for these two localities for the other four localities we assume that the magnetisation is primary because 1 ams measurements reveal a primary fabric 2 there are local occurrences of antipodal polarities and 3 palaeolatitudes of tilt corrected poles are compatible with previous studies the consistency between the early triassic poles of west and south junggar indicates that junggar evolved as a rigid block only since early mesozoic the comparison of the late palaeozoic and the early mesozoic poles of junggar and those of siberia and tarim shows major rotations between the late permian and the late jurassic early cretaceous these periods of discrete rotations are characterized by strike slip faulting in tianshan and altai and they may correlate with the major episodes of coarse grained detrital sedimentation and uplift of the range especially the counter clockwise rotations of junggar relative to tarim and siberia which occurred between the early and the late triassic and between the late triassic and the late jurassic are accommodated by transpressive tectonics in the tianshan and the altai belts this reactivation is a far field effect of tibetan blocks diachronous collisions therefore these first triassic palaeomagnetic results from junggar infer that post carboniferous rotations were due to the combined effect of the post orogenic transcurrent movement and the mesozoic oblique reactivation

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

upper permian lacustrine organic facies evolution southern junggar basin nw china abstract the jingjingzigou lucaogou and hongyanchi formations of the southern junggar basin together comprise over 1000 m of organic rich lacustrine facies they record an overall evolution from relatively shallow evaporative lakes to freshwater lakes associated with fluvial systems the jingjingzigou formation is characterized by low toc and hi and biomarker features such as abundant carotane consistent with a specialized saline or hypersaline biota biomarker distributions in jingjingzigou formation extracts most closely resemble oils from the giant karamay oilfield the lucaogou formation represents one of the richest and thickest lacustrine source rock intervals in the world yet it contradicts conventional lacustrine source rock models in at least two important aspects first deposition occurred at middle paleolatitudes 39 43 n rather than in the tropics second limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20 toc and hi near 800 the overlying hongyanchi formation has 1 5 toc but low hi and was deposited in freshwater oxic to sub oxic lakes

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

the mesozoic palaeorelief of the northern tian shan china terra nova 23 195 205 2011 abstract the tian shan range offers a natural laboratory to study orogenic processes most of the previous studies focused on either the palaeozoic evolution of the range or its cenozoic intracontinental evolution linked with the india asia collision in this study it is shown that detailed field investigations on the relationship between sedimentary cover and basement constrain the mesozoic evolution of the northern tian shan sedimentological observations argue for a limited transport distance for lower and uppermost jurassic deposits geological sections presented in this paper show that in preserved locations triassic to jurassic sedimentary series present a continuous onlap type sedimentary unconformity on the top of the basement at different scales observations clearly evidence the existence of major palaeorelief during the mesozoic according to the present study the topography of the current tian shan range and the associated movements along its northern front structures cannot be considered as the consequence of cenozoic reactivation alone

primary carboniferous and permian paleomagnetic results from the yili block nw china and their implications on the geodynamic evolution of chinese tianshan belt in order to better understand the tectonic role of the yili block on the paleozoic evolution of the chinese tianshan belt we performed a primary paleomagnetic study on carboniferous and permian rocks from different areas in the yili block nw of china more than 320 sedimentary and volcanic samples were collected from 39 sites except for the ordovician samples showing a weak and unstable magnetic remanence the majority of this collection presents characteristic remanent magnetization carried by magnetite and hematite in the study area though positive fold test has been observed on the early carboniferous rocks a general remagnetization of these rocks has been identified and attributed to the late carboniferous magmatism moreover all early and late carboniferous samples from the interior of the yili block yield stable and coherent magnetic directions with exhaustively reverse magnetic polarity the late carboniferous c2 is considered as the magnetic remanence age since these rocks are covered or intruded by synchronous magmatic rocks of the yili arc which lasted until to 310 ma the c2 paleomagnetic pole is therefore calculated at 68 6 n 290 6 e with 95 6 4 and n 15 the late carboniferous rocks located close to a deformation zone present a consistentmagnetic inclination but significant different declination with respect to other areas and are suspected to have probably experienced a local rotation although no fold test can be performed due to the monoclinal bedding stable magnetic components are isolated from late permian p2 red beds in the interior of the yili block with also a solo reverse magnetic polarity the p2 paleomagnetic pole of the yili block has been therefore calculated from the characteristic remanent magnetization 79 7 n 172 0 e with 95 11 3 and n 5 keeping important uncertainties in mind comparisons of the c2 and p2 paleomagnetic poles of the yili block with available coeval poles of junggar tarim and siberia indicate 1 no significant relative motion between the yili and junggar blocks since the late carboniferous 2 no significant or weak latitudinal relative motion occurred since the late carboniferous among these blocks but 3 the 46 2 15 1 and the 31 6 15 1 counterclockwise rotations of the yili junggar blocks with respect to tarim and siberia took place during c2 to p2 these rotations are accommodated by the permian dextral strike slip faults along the northern and southern sides of tianshan belt and sinistral strike slip faulting along the erqishi fault of altay belt resulting in about 1000 km and 600 km lateral displacements in the tianshan and altay belts respectively

middle paleozoic paleomagnetism of east kazakhstan post middle devonian rotations in a large scale orocline in the central ural mongol belt abstract in order to test different hypotheses concerning the paleozoic evolution of the ural mongol belt umb and the amalgamation of eurasia we studied middle devonian basalts from two localities 11 sites and lower silurian volcanics redbeds and intra formational conglomerates from three localities 20 sites in the chingiz range of east kazakhstan the devonian rocks prove to be heavily overprinted in the late paleozoic and a high temperature presumably primary southerly and down component is isolated at only four sites from a homoclinal section most silurian redbeds are found to be remagnetized in the late paleozoic in contrast a bipolar near horizontal remanence isolated from silurian volcanics is most probably primary as indicated by positive tilt and conglomerate tests analysis of paleomagnetic data from the chingiz range shows that southward pointing directions in ordovician silurian and devonian rocks are of normal polarity and hence indicate large scale rotations after the middle devonian the chingiz paleomagnetic directions can be compared with paleozoic data from the north tien shan and with the horseshoe shaped distribution of subduction related volcanic complexes in kazakhstan both paleomagnetic and geological data support the idea that today s strongly curved volcanic belts of kazakhstan are an orocline deformed mostly before mid permian time despite the determination of nearly a dozen new paleozoic paleopoles in this study and other recent publications by our team significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late paleozoic however the paleomagnetic results from the chingiz range and the north tien shan indicate that these areas show generally coherent motions with siberia and baltica respectively

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

paleomagnetic investigation of upper permian sediments in the south junggar basin china lacustrine organic rich mudstones of the upper permian lucaogou formation are a significant petroleum source bed throughout most of the junggar basin in northwest china and paleomagnetic data may provide insight into tectonic conditions prevalent during their deposition secondary magnetizations were removed from 180 samples from 29 sites within the south junggar basin characteristic magnetizations of these samples were either revealed directly during thermal demagnetization or were calculated from great circle trajectories the primary nature of the characteristic magnetization is attested to by a positive fold test by exclusively reversed magnetizations which are consistent with the mid carboniferous to late permian kiaman reversed interval for the geomagnetic field and by relatively low levels of thermal maturity found in the mudstones tectonically corrected remagnetization circles and direct observations combined give a steep direction i 61 9 d 163 0 k 17 n 78 specimens the steep mean inclination recorded within the lacustrine organic rich mudstones suggests that junggar was situated near its present day latitude during deposition of the mudstones in late permian times consistent with the marginal ocean basin origin for junggar that has been proposed based upon stratigraphic relationships our data suggest that junggar may always have been associated with the northern continents of laurasia initially as a pre permian marginal ocean basin north of the tethys and subsequently as a permian mesozoic and cenozoic nonmarine foreland basin

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

late paleozoic paleogeographic reconstruction of western central asia based upon paleomagnetic data and its geodynamic implications abstract carboniferous to permian volcanoclastic rocks have been collected from south junggar and west junggar primary magnetizations have been observed from the characteristic components of 10 sites of early permian p1 and late permian p2 red beds of south junggar area the 14 early carboniferous sites from west junggar mountains expose post folding secondary magnetizations and according to their spatial distribution 9 remagnetized sites are related to late carboniferous early permian granite emplacement whereas 5 sites are located at the vicinity of late permian mafic dykes two new paleomagnetic poles have been consequently calculated for the periods of p1 at 79 5 n 36 6 e and of p2 at 60 4 n 4 7 e with a95 of 6 8 and 5 4 respectively they yield two paleomagnetic poles at 65 3 n 329 7 e with a95 of 6 3 and 64 8 n 179 5 e with a95 of 6 9 respectively compilation of available data shows stationary and consistent poles for south junggar area during the carboniferous and permian whereas nw junggar underwent a significant anticlockwise rotation between the late carboniferous early permian and the late permian indicating that junggar was not a rigid block up to the end of the paleozoic west junggar and south junggar may have experienced contrasting tectonic evolutions comparisons of late paleozoic poles of central asia blocks show 1 counterclockwise rotation of west junggar with respect to siberia contrasting with the clockwise rotation of north kazakhstan with respect to siberia 2 no significant movements between west junggar north kazakhstan and siberia since late permian indicating that they were rigidly welded since that time and 3 anticlockwise rotations of tarim yili and south junggar with respect to the welded siberia kazakhstan west junggar block such rotations may have been accommodated by late permian to early triassic strike slip faults with an estimation of the displacements of 1570 280 km along the irtysh gornotsaev shear zone 410 380 km along the nikolaiev nalati tectonic line and 490 250 km along the chingiz alakol north tian shan fault since late permian time

late paleozoic strike slip shear zones in eastern central asia nw china new structural and geochronological data 1 new structural studies and 40ar 39ar dating in northwest china provide information about late paleozoic strike slip motions subsequent to accretional events which built eastern central asia during the paleozoic two principal areas were affected by these large transcurrent motions first in the tianshan range main east west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism associated biotites give ages ranging from 290 ma to 245 ma the earlier n110 shearing occurred in western tianshan while the last one dextral in whole tianshan occurred 250 245 myr ago second in the chinese altay region several nw se shear zones structured the area the main motion is sinistral and occurred along the erqishi zone at 280 290 ma it is followed by a complex succession of dextral and sinistral shearing episodes leading to the northwestward structuring dated at 245 ma of a metamorphic zone that was folded during a compressive event

resolving the problem of shallow magnetizations of tertiary age in asia insights from paleomagnetic data from the qiangtang kunlun and qaidam blocks tibet china and a new hypothesis we present new paleomagnetic results obtained at 39 sampling sites from five sections of tertiary red bed formations two eocene formations from the qiangtang block of tibet xialaxiu locality 32 8 n 96 6 e and the xining basin of qaidam xining locality 36 5 n 102 0 e and three neogene formations from the xining basin jungong locality 34 7 n 100 7 e and the kunlun block tuoluo lake and west yushu localities 35 3 n 98 6 e and 33 2 n 96 7 e respectively thermal demagnetization of the rocks isolated a high temperature component that we interpret as the primary magnetization in four localities the paleopoles lie at 52 6 n 352 e dp dm 6 0 10 7 for xialaxiu 61 6 n 211 3 e dp dm 9 7 16 1 for xining 66 0 n 228 6 e dp dm 3 6 6 9 for jungong and 53 9 n 205 4 e dp dm 5 6 10 0 for west yushu as in previous studies of tertiary formations from asia the inclinations we obtained are shallower by 18 to 26 than the magnetic field computed from the eurasian apparent polar wander path apwp at 10 and 20 ma for neogene rocks and at 40 and 60 ma for eocene rocks on the basis of a compilation of eocene data from the south china block tibet central asia and kyrgyzstan we conclude that this inclination anomaly reflects erroneous predictions of positions of the siberian craton when based on the apwp of eurasia the main reason for this discrepancy might be nonrigid behavior of the eurasian plate in the tertiary combination of this with intracontinental shortening of asia under the penetration of india provides a full explanation for the anomaly verification of this new interpretation of the inclination anomaly will require new geologic and paleomagnetic data from the northern parts of these remote regions in mongolia and siberia

a new paleogeographic configuration of the eurasian landmass resolves a paleomagnetic paradox of the tarim basin china 1 new paleomagnetic data from permian red beds and middle jurassic limestones from the tarim basin pose a paradox their declinations are similar to upper carboniferous to neogene rocks collected from the same sections and their inclinations parallel present values when assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects then the paleolatitudes of all upper carboniferous to present rocks from tarim are indistinguishable local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin our middle jurassic data positions tarim 23 6 8 4 farther south than that predicted from the coeval reference pole for eurasia however no geologic argument exists to support the closure of a large ocean basin between tarim and siberia since the middle jurassic thus the paradox are the rocks from tarim totally overprinted or is the middle mesozoic part of the reference eurasian apparent polar wander path erroneous several lines of evidence suggest the tarim rocks are not remagnetized we conclude that tarim has experienced little or no apparent polar wander since the carboniferous moreover our middle mesozoic reconstruction of eurasia using the new middle jurassic pole from tarim results in a more geologically compatible solution for the eastern asian blocks over previous reconstructions

annual to sub annual resolution of multiple trace element trends in speleothems this study aims to establish evidence for the widespread existence of preserved high resolution trace element variations in speleothems that may have climatic significance ion microprobe analysis of speleothems reveals that annual to sub annual variations in element chemistry exist at five shallow western european cave sites crag cave county kerry and ballynamintra county waterford ireland uamh an tartair sutherland scotland grotte pere noel belgium grotta di ernesto ne italy with widely varying climatic geomorphic and geological settings the variations are not restricted to species mg sr and ba known to substitute directly for ca in the calcite lattice but include h f na and p phosphorus as phosphate displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element the technique allows estimation of growth rate of speleothems at any interval of interest which is one of several possible uses in palaeoclimatology

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial