paleomagnetic versus gps determined tectonic rotation around eastern himalayan syntaxis in east asia abstract northward indentation of the indian plate has brought about significant tectonic deformation into east asia a record of long term tectonic deformation in this area for the past 50 m yr particularly the vertical axis rotation is available through paleomagnetic data in order to depict rotational deformation in this area with respect to eurasia we compiled reliable paleomagnetic data sets from 79 localities distributed around eastern himalayan syntaxis in east asia this record delineates that a zone affected by clockwise rotational deformation extends from the southern tip of the chuan dian fragment to as far as the northwestern part of the indochina peninsula a limited zone that experienced a significant amount of clockwise rotation after an initial india asia collision is now located at 23 5 n 101 e far away from an area 27 5 n 95 5 e where an intense rotational motion has been viewed by a snapshot of gps measurements this discrepancy in clockwise rotated positions is attributed to southeastward extrusion of the tectonic blocks within east asia as a result of ongoing indentation of the indian plate a quantitative comparison between the gps and paleomagnetically determined clockwise rotation further suggests that following an initial india asia collision the crust at 30 n 94 e paleoposition was subjected to southeastward displacement together with clockwise rotation which eventually reached to present day position of 23 5 n 101 e implying a crustal displacement of about 1000 km during the past 50 m yr

miocene to present activity along the red river fault china in the context of continental extrusion upper crustal rotation and lower crustal flow detailed mapping of field relationships along the red river fault reveals information about the distribution and magnitude of slip along the fault about its interactions with other regional fault systems and the relationship between river incision and growth of the eastern margin of the tibetan plateau the red river fault is complex consisting of up to four strands and is dominated by right lateral strike slip displacement evidence for an extensional component of displacement is strongest along the northern part of the fault and decreases to the southeast to zero southeast of a major bend in the fault results of this study indicate dextral displacement on the red river fault is probably at least 40 km 15 16 km of which predates incision of the red river in pliocene time or later and probably also predates plateau growth and development of other regional fault systems long term average slip rate on the red river fault is a minimum of 5 mm yr however regional active tectonics are characterized by rotation of the upper crust around the eastern himalayan syntaxis bounded to the east by the xianshuihe xiaojiang fault system which deflects but does not cut the red river fault the distributed nature of the xianshuihe xiaojiang fault system as it approaches the red river fault is important for accommodating shearing across the strong crustal anisotropy formed by the red river fault and ailao shan shear zone the red river fault appears to terminate in the extending dali fault system in northwest yunnan pliocene surface uplift river incision and rotation around the eastern himalayan syntaxis are inconsistent with the pre pliocene displacement on the red river fault and lateral extrusion along the ailao shan shear zone advocated by the extrusion model this suggests a significant change in crustal conditions on the southeast margin of the tibetan plateau in pliocene time possibly the result of lower crustal flow

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

paleomagnetic evidence for 25 15 ma crust fragmentation of north indochina 23 26 n consequence of collision with greater india ne corner

paleomagnetic constraints from the baoshan area on the deformation of the qiangtang sibumasu terrane around the eastern himalayan syntaxis the sibumasu block in se asia represents the eastward continuation of the qiangtang block here we report a detailed rock magnetic and paleomagnetic study on the middle jurassic and paleocene rocks from northern sibumasu to document the crustal deformation during the india asia collision since the paleocene and reconstruct the overall strike of the qiangtang sibumasu elements before the india asia collision although the fold test is inconclusive based solely on our data a positive reversal test a positive regional fold test with previous paleomagnetic results and a detrital origin of hematite in the red beds as indicated by scanning electron microscopy suggest that the magnetizations obtained from the jurassic and paleocene rocks are most likely primary showing an 80 clockwise rotation since paleocene these results together with previously published paleomagnetic data suggest that the northern sibumasu and northern simao elements experienced a 60 80 clockwise rotation since paleocene this large clockwise rotation is also consistent with the surface gps velocity field and ne sw fault networks suggesting a rotational motion of crustal material from southeastern tibet during late cenozoic we infer that the large clockwise rotation is a sum of rotation in the eocene to middle miocene time associated with indochina extrusion and rotation after the middle miocene associated with the e w extension in central tibet this suggests that the eastward motion of tibetan crustal material along the xianshuihe xiaojiang fault after middle miocene is transmitted to the southwest toward myanmar jurassic and cretaceous paleomagnetic results suggest that the qiangtang northern sibumasu was originally a curved structure with an orientation of n60 w in tibet and changes to n10 w in southern sibumasu

late cenozoic exhumation history of the luoji shan in the southeastern tibetan plateau insights from apatite fission track thermochronology denudational history inferred from bedrock low temperature thermochronological data provides significant constraint to tectonic models for explaining the growth of the tibetan plateau here we present new apatite fission track ages from the luoji shan bounded by the anninghe and zemuhe faults in the southeastern tibetan plateau cooling ages vary from c 5 to c 13 ma from the bottom to the top of a vertical profile the age elevation relationship can be interpreted as either 1 a phase of river incision at a rate of c 0 16 km ma 1 from c 13 to c 5 ma or 2 a phase of denudation of c 0 40 km ma 1 between c 13 and c 10 ma followed by a phase of extremely slow denudation c 0 03 km ma 1 the results suggest that initiation of river incision started before c 13 ma in the study area combined with previously published data from adjacent sites our results indicate that denudation in this region displayed substantial spatial variation this finding does not support the existing lower crustal flow model for tibetan plateau growth which predicts uniform denudation we further speculate that the vertical component of slip along the southern extension of the anninghe fault might have significantly declined since late miocene time explaining the decreased rate of erosion c 10 ma

paleoenvironmental implications of molecular and carbon isotopic distributions of n alkanes in the hominoid bearing upper miocene sediments from the zhaotong basin southwestern china abstract it is crucial to understand the relationship between hominoid primates and their living environment located at the southeastern margin of the tibetan plateau the shuitangba stb outcrop from the zhaotong basin is famous for bearing the remains of the youngest known ape fossil in the terminal miocene 6 2 ma in this study the molecular and carbon isotope compositions of n alkanes together with the loss on ignition and the bulk carbon isotope composition of total organic matter were investigated in the stb outcrop to infer the paleoenvironmental conditions in this uppermost miocene sedimentary sequence with the emphasis on the habitat of the stb hominoid in the hominoid bearing peaty clay layer and the surrounding lignite layers the n alkane molecular and carbon isotope compositions support a primary contribution from terrestrial higher plants in contrast n alkanes in the upper shallow lake sediments are derived from multiple origins mainly from aquatic plants and bacteria both carbon preference index cpi and average chain length acl vary closely with the lithology but the cpi record shows the larger amplitude of change than the acl and varies sharply during the lithological boundary it is notable that the changes of the molecular and carbon isotope compositions of long chain n alkanes do not parallel with the abrupt increase of poaceae pollen percentage during the stb hominoid appearing stage such an inconsistency between herb pollen percentage and n alkane ratios may result from the different sources our results clearly support that these organic matter based ratios have the potential to record the paleoenvironmental changes in ancient lacustrine sediments

paleomagnetic evidence for clockwise rotation of the simao region since the cretaceous a consequence of india asia collision samples were collected for paleomagnetic analysis from 36 sites from six formations west of the red river fault in southwestern yunnan province china on the simao block 23 4 n 100 8 e in an attempt to examine the effects of the india asia collision on the asian continent paleomagnetic results from rocks ranging from cretaceous to miocene in age indicate a large clockwise rotation of these sites with respect to stable eurasia since the late cretaceous the tectonic corrected data from cretaceous samples mean direction of two formations are d 112 6 i 34 7 95 7 5 k 9 1 n 45 for eocene samples the data are d 84 7 i 38 9 95 7 6 k 12 0 n 32 and for miocene samples they are d 21 1 i 35 5 95 7 1 k 15 3 n 29 the samples from the paleocene and pliocene are either remagnetized or too weak to provide stable directions the cretaceous sites were sampled from folded beds and these sites pass the fold test the amount of rotation seen in this study r 86 1 9 9 as a mean value for the cretaceous r 76 8 11 for the eocene and r 14 7 10 0 for the miocene is significantly larger than that documented in previous studies from the lower cretaceous of northwestern and central yunnan province and may indicate that differential rotation has taken place in the region this rotation can be explained by the northward motion and collision of india with asia in the paleocene which caused continuous deformation of southwestern china in the form of strike slip faulting and clockwise rotation it is concluded that the rotation and deformation resulting from this collision probably continued from the paleocene until at least the miocene

magnetostratigraphy of the miocene chiang muan formation northern thailand implication for revised chronology of the earliest miocene hominoid in southeast asia abstract a paleomagnetic study has been conducted on the miocene chiang muan formation in northern thailand in order to provide a chronology for the earliest large bodied miocene hominoid in southeast asia the chiang muan formation is mainly composed of clay silt and sand beds indicating lacustrine and fluvial environments paleomagnetic samples were collected from 124 horizons along an approximately 150 m thick section from the chiang muan formation at the opencast chiang muan mine rock magnetic experiments and stepwise thermal demagnetizations revealed that the main carrier of the magnetization of the sediments is magnetite and the samples have stable magnetization exceptionally stable magnetization is also carried by hematite which is represented by red colored sediments characteristic remanent magnetization chrm directions calculated by the principal component analysis revealed normal or reversed polarities of magnetization which allow the application of the reversal test of mcfadden and mcelhinny mcfadden p l mcelhinny m w 1990 classification of the reverse test in paleomagnetism geophys int 103 725 729 the mean paleomagnetic directions of the normal and reversed polarities passed the reversal test with a classification c indicating that the chiang muan formation preserved the primary magnetization in total five normal and four reversed polarity zones are recognized from the studied section based on paleontological age constraints this magnetostratigraphic column of the chiang muan formation correlates best with chron c5aan c5n of the geomagnetic polarity time scale gpts from the geological time scale gts2004 developed by gradstein et al gradstein f ogg j smith a eds 2004 a geological time scale 2004 cambridge univ press cambridge uk p 589 this correlation revealed that sedimentation of the chiang muan formation began approximately at 13 ma and continued until 9 8 ma with a mean sedimentation rate of approximately 4 2 cm ky the age of the earliest southeast asian hominoid is between 12 4 and 13 0 ma

magnetostratigraphy of the middle miocene continental sedimentary sequences of the mae moh basin in northern thailand evidence for counterclockwise block rotation abstract a magnetostratigraphic study has been performed on the mae moh basin well known for its lignite mining in the lampang province paleomagnetic samples were collected from 66 stratigraphic levels rock magnetic investigations indicate the presence of low coercivity minerals specimens subjected to progressive thermal or alternating field demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component and a high temperature characteristic component chrm with either positive or negative virtual geomagnetic pole latitudes and opposite polarity considered as the characteristic miocene magnetization the overall mean paleomagnetic direction incl 22 2 decl 358 3 15 95 4 documents a counterclockwise vertical axis rotation of about 13 1 32 with respect to the expected miocene direction derived from the eurasian polar wander curve incl 42 decl 11 our paleomagnetic results are not consistent with the previously reported paleomagnetic data the rotation observed in the mae moh basin can be the response to local tectonics a section sampled for magnetostratigraphy reveals a polarity sequence of nine magnetozones that can reliably be correlated to the geomagnetic polarity time scale according to biochronological constraints the magnetostratigraphic results from the mammal bearing succession correlate with chron c5abn c5an2n between 13 5 and 12 1 ma according to the mean sedimentation rate of about 17 5 cm ka ages of 12 5 and 12 8 ma are proposed for the fossiliferous levels j5 and k1 k2 lignite zones were the mammal remains were found

late cenozoic to recent transtensional deformation across the southern part of the gaoligong shear zone between the indian plate and se margin of the tibetan plateau and its tectonic origin abstract within the southeastern part of the tibetan plateau the gaoligong shan shear zone forms the boundary between the tengchong and baoshan blocks and is one of the main cenozoic strike slip fault systems of the eastern himalayan syntaxis the mountain ranges rise to a maximum elevation of 3623 m with a width of 20 km and a length of 400 km the core of the shear zone consists of a narrow belt of mylonitic rocks with right lateral strike slip fabrics formed during the northward movement of india relative to eurasia in oligocene and miocene time to the south the mountains decreases in elevation and end against the wanding fault the latter is one of a series of ne sw striking active left lateral strike slip faults within the southeastern part of the tibetan plateau the cause and timing for the change in elevation of the gaoligong shan is unknown but based on our recent structural and fission track geochronological work the decrease in elevation is the result of east west extension across the southern part of the gaoligong shear zone inferred from the late cenozoic and active normal faults along its eastern and western boundaries southward the eastern boundary fault system merges with a series of splays of the wanding strike slip fault while the western boundary fault system is bent into parallelism with the wanding fault this geometric relationship suggests that the normal faulting along the eastern and western boundary of the gaoligong shear zone was caused by transfer of the ne sw left lateral movement along the wanding fault into e w extension on faults to the northeast the resultant normal faulting caused the lowering of the topography in the southern part of the shear zone fission track data from 11 samples from the mylonitic rocks in the footwall of the ruili oblique slip fault left lateral thrust slip yielded ages between 8 4 and 0 9 ma coeval with volcanism within the jietou and mangbang basins the left lateral strike slip movement along the wanding and ruili faults is interpreted to have accommodated differential clockwise rotation of the gaoligong shear zone and its adjacent tectonic units during late cenozoic to recent time during the northward movement of the indian plate with respect to the southeastern margin of the tibetan plateau along the right lateral sagaing fault

paleomagnetic study of permian and mesozoic sedimentary rocks from northern thailand supports the extrusion model for indochina abstract the mode of deformation of southeast asia resulting from the indian collision is still controversial is convergence between stable india and siberia absorbed principally by crustal shortening and thickening and minor strike slip faulting or by a mechanism of extrusion involving crustal thickening and lateral escape of blocks along major strike slip zones in order to test these models we have carried out a paleomagnetic study of sedimentary rocks of jurassic to cretaceous age on the khorat plateau in thailand a large discrepancy between the poles of indochina presented in this paper and a compilation of south china block pole positions both at the triassic jurassic and the jurassic cretaceous boundary imply some 1500 800 km of post middle cretaceous left lateral slip along the red river and xian shui he fault zones and approximately 14 7 of clockwise rotation for the indochina block relative to the south china block such relative motions are in agreement with a model of lateral extrusion of indochina during the india asia collision additional data of permian upper triassic and lower jurassic age collected in indochina indicate a post late permian remagnetization for the upper permian limestones a comparison of these data with those from yunnan south china the north china block and the south china block shows that these blocks have probably been in contact at least since the late triassic

magnetostratigraphic dating of hominoid bearing sediments at zhupeng yuanmou basin southwestern china abstract the hominoid fossils found in the yuanmou basin southwestern china are among the key fossils for understanding the evolution of early hominoids in eastern asia and their relationship with coeval hominoids in europe and africa however their exact ages have not yet been well determined we provide a new high resolution magnetostratigraphy for the zhupeng profile which is one of the fossil bearing type sections in the region based on magnetostratigraphy of 227 remanent directions together with the age of micromammalian fauna indicate that the hominoid bearing layer is dated within polarity chron 3br 2r or 3br 1r i e within the interval 7 43 7 38 ma or 7 34 7 17 ma this unambiguously indicates that the yuanmou hominoid has a late miocene age which therefore makes it the youngest hominoid found in eurasia it is possible that the yuanmou basin provided a refuge for hominoids during a time of major environmental changes

palaeomagnetic study of eastern tibet deformation of the three rivers region summary a palaeomagnetic study was undertaken for cretaceous red beds and granitic rocks of three geological provinces the lhasa the qiangtang and the sichuan along a road between chengdu and lhasa in eastern tibet in an attempt to determine aspects of deformation of se asia high temperature characteristic directions were isolated from 20 sites the tilt corrected data from the qiangtang terrane at markam 29 7 n 98 6 e exhibit largely clockwise deflected declinations with steep inclinations d 48 2 i 49 0 a95 8 8 whereas the lhasa terrane at basu 3o l0n 96 9 e and the sichuan province at ya an 3o l0n 103 0 e have northerly directions with shallow inclinations d 3 9 i 23 4 a95 19 2 and d 2 lo z 30 7 ag5 11 3 respectively the palaeomagnetic data indicate that the qiangtang terrane was subjected to clockwise rotation through 50 with respect to the neighbouring provinces of the lhasa and sichuan since the cretaceous tectonic deformation occurred later than the cretaceous in the eastern part of the qiangtang terrane and formed the arcuate shape of the orogenic belt in the three rivers region

stable isotopes reveal high southeast tibetan plateau margin since the paleogene abstract the evolution of the topography of eastern tibet reflects the dynamic interaction between processes at earth s surface and the lower crust reconstruction of its spatio temporal development provides constraints for our understanding of the geodynamics of continental deformation this study examines the topographic evolution of the southeast margin of the tibetan plateau throughout the cenozoic using stable isotope paleoaltimetry of pedogenic carbonates preserved in cenozoic basins extending from the northern to the southern portions of the se margin of the tibetan plateau yunnan province china paleoelevations are calculated using a monte carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the isotopic value of pedogenic carbonate isotope elevation relationships are determined from a modern sampling transect along the modern lancang mekong river and an estimated eocene rayleigh fractionation model that was randomly resampled calculated elevations indicate the se margin of tibet was at its present elevation as early as the late eocene with elevations of 3 3 km as far south as the northern third of china s yunnan province this result expands the extent of the eocene tibetan plateau more than 1000 km east of that previously known and precludes surface uplift via lower crustal flow in the area of sw sichuan and northern yunnan as a driver for drainage reorganization and an observed middle to late miocene pulse of rapid exhumation elevation estimates from the southern two thirds of the study area parallel to the red river fault suggest approximately 1 km of post late miocene surface uplift consistent with estimates from previous studies

paleomagnetic study of cretaceous rocks from pu er western yunnan china evidence of internal deformation of the indochina block abstract cretaceous red sandstones and siltstones were collected at 31 sties for paleomagnetic investigation from the jingxing and nanxin formation around pu er 23 0 n 101 0 e western part of yunnan province china in order to examine quantitative amount of tectonic deformation of the simao terrane due to collision of india with asia after stepwise thermal demagnetization the high temperature component magnetization with unblocking temperature of around 680 c is isolated positive field tests show that the high temperature component magnetization from 25 sites is primary for the cretaceous formations a tilt corrected mean direction is d 59 9 i 45 2 with 95 5 1 corresponding to a paleopole at 35 8 n 173 1 e with a 95 5 6 comparison with cretaceous paleomagnetic pole of the whole china block indicates that amount of clockwise rotation in the pu er area is evaluated to be 46 9 with respect to the whole china block which is consistent with large amount of rotation in the mengla and jinggu areas 47 and 66 in the central part of the simao terrane clockwise rotation of the central part is larger by more than 20 compared to the yunlong and yongping areas of northern part of the simao terrane suggesting that the simao terrane experienced internal deformation the southward displacement of the pu er area expected from inclination data is 7 5 6 6 with respect to the chuan dian fragment which is a similar estimate to other areas in the simao terrane and the indochina block while the simao terrane displaced southward by 800 km together with clockwise rotation of 30 as a whole further clockwise rotation occurred in the central part

quantitative climate reconstructions of the late miocene xiaolongtan megaflora from yunnan southwest china the late miocene xiaolongtan megaflora from kaiyuan in southeast yunnan 23 degrees 48 45 n 103 degrees 11 52 e 1050 m a s l was chosen for palaeoclimatic reconstruction using three quantitative techniques i e the coexistence approach ca leaf margin analysis lma and the climate leaf analysis multivariate program clamp the reconstructed climatic parameters are also compared with those of the two adjacent miocene floras currently available in yunnan i e the early to middle miocene carpological mangdan flora 24 degrees 24 n 97 degrees 49 e 1620 m a s l and the late miocene luhe palynoflora 25 degrees 10 n 101 degrees 22 e 1930 m a s l quantitative analyses of the xiaolongtan flora supports the previous qualitative results of a southern humid subtropical climate being more humid and having a slightly higher mean annual temperature mat than today the mats calculated by ca lma and clamp overlap 16 7 19 2 degrees c 22 3 2 05 degrees c 18 1 1 2 degrees c respectively and are close to the present day value 19 7 degrees c the overlapping of temperatures derived using the three techniques is unusual and probably related to the low latitude of the xiaolongtan area and the southern subtropical nature of its vegetation both the mean temperatures of the warmest month wmt and of the coldest month cmt reconstructed by ca wmt 25 4 26 0 degrees c cmt 7 7 8 7 degrees c and clamp wmt 25 9 1 6 degrees c cmt 10 8 1 9 degrees c are similar to those of today wmt 24 3 degrees c cmt 12 8 degrees c but great changes appear in the mean annual precipitation map the clamp results suggest a higher precipitation 1964 335 9 mm than ca 1215 1639 mm but they are much higher than the present map 820 5 mm this is consistent with results from the luhe palynoflora which also developed under a warmer subtropical climate with higher precipitation 803 6 1254 7 mm than that of today 815 9 mm in contrast the mangdan flora situated in a more complicated topographic region to the west of xiaolongtan and near the sino myanmar border implies a slightly lower precipitation 1170 1300 mm than that of today 1300 1400 mm overall the wetter climate during the late miocene around the xiaolongtan area suggests that the himalayas had not yet uplifted to its present altitudes at that time c 2009 elsevier b v all rights reserved

yunnan a refuge for trilophodont proboscideans during the late miocene aridification of east asia fossil elephantimorph proboscideans are very common in miocene faunas of east asia however their evolution and migration associated with ecological pressure have been studied little especially in china in the present article analyses of the dynamics of the elephantimorph genera of northern and southern china were performed the results indicate considerable depression of elephantimorph proboscidean diversity in northern china and continuous success of this group in the yunnan region southern china during the late miocene notably all trilophodont elephantimorph proboscideans were extinct by the end of the middle miocene in northern china and did not recover until the latest miocene however trilophodont and tetralophodont elephantimorph proboscideans coexisted throughout the late miocene in the yunnan region therefore we interpret the yunnan region as a late miocene refuge for proboscideans especially trilophodonts from severe aridity in northern china caused by uplift of the tibetan plateau and retreat of the paratethys sea further analysis of the dynamics of coexisting genera indicates that the components of elephantimorph proboscidean assemblages in northern china display patterns distinct from those of yunnan southeast asia and siwalik therefore ecological barriers between northern china and siwalik and between northern china and yunnan southeast asia are hypothesized to have existed by as early as the middle miocene the latter barrier occasionally opened e g at the boundary between the middle and late miocene and thus provided a pathway for the survival of trilophodont proboscideans escaping from ecological pressures in northern china

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

crustal lithospheric structure and continental extrusion of tibet crustal shortening and thickening to c 70 85 km in the tibetan plateau occurred both before and mainly after the c 50 ma india asia collision potassic ultrapotassic shoshonitic and adakitic lavas erupted across the qiangtang c 50 29 ma and lhasa blocks c 30 10 ma indicate a hot mantle thick crust and eclogitic root during that period the progressive northward underthrusting of cold indian mantle lithosphere since collision shut off the source in the lhasa block at c 10 ma late miocene pleistocene shoshonitic volcanic rocks in northern tibet require hot mantle we review the major tectonic processes proposed for tibet including rigid block continuum and crustal flow as well as the geological history of the major strike slip faults we examine controversies concerning the cumulative geological offsets and the discrepancies between geological quaternary and geodetic slip rates low present day slip rates measured from global positioning system and insar along the karakoram and altyn tagh faults in addition to slow long term geological rates can only account for limited eastward extrusion of tibet since mid miocene time we conclude that despite being prominent geomorphological features sometimes with wide mylonite zones the faults cut earlier formed metamorphic and igneous rocks and show limited offsets concentrated strain at the surface is dissipated deeper into wide ductile shear zones

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

kinematics and ar 40 ar 39 geochronology of the gaoligong and chongshan shear systems western yunnan china implications for early oligocene tectonic extrusion of se asia the gaoligong and chongshan shear systems glss and csss in western yunnan china have similar tectonic significance to the ailaoshan red river shear system asrrss during the cenozoic tectonic development of the southeastern tibetan syntaxis to better understand their kinematics and the cenozoic tectonic evolution of se asia this paper presents new kinematic and 40 ar 39 ar geochronological data for these shear systems all the structural and microstructural evidence indicate that the glss is a dextral strike slip shear system while the csss is a sinistral strike slip shear system and both were developed under amphibolite to greenschist grade conditions the 40 ar 39 ar dating of synkinematic minerals revealed that the strike slip shearing on the glss and csss at least began at 32ma possibly coeval with the onset of other major shear systems in se asia the latestage shearing on the glss and csss is dated at 27 29ma by the biotite 40 ar 39 ar ages consistent with that of the wang chao shear zone wcsz but 10ma earlier than that of the asrrss the dextral gaoligong shear zone within the glss may have separated the india plate from the indochina block during early oligocene combined with other data in western yunnan we propose that the baoshan southern indochina block escaped faster southeastward along the csss to the east and the glss to the west than the northern indochina block along the asrrss accompanying with the obliquely northward motion of the india plate during early oligocene 28 36ma during 28 17ma the northern indochina block was rotationally extruded along the asrrss relative to the south china block as a result of continuously impinging of the india plate

a complete magnetic polarity stratigraphy of the miocene continental deposits of mae moh basin northern thailand and a reassessment of the age of hominoid bearing localities in northern thailand northern thailand comprises more than 40 tertiary intermontane basins these basins tectonically interpreted as grabens or half grabens have yielded hominoid fossils and rich neogene mammal faunas relative ages provided by biochronological studies are controversial and neither absolute ages nor correlations with marine deposits are available a precise temporal framework provided by magnetic polarity stratigraphy is therefore crucial to understand the evolution of these southeast asian mammalian faunas to estimate the timing and duration of basin formation and finally to allow correlations with other neogene hominoid localities of the old world a complete magnetostratigraphic study which significantly extends previous paleomagnetic investigations has been conducted in the miocene sequence of mae moh basin lampang province northern thailand based on the biostratigraphic constraints the 15 polarity zones recognized from the composite section have been correlated with chrons c5acr c5r 3r between 14 1 and 12 0 ma the present study provides a high resolution magnetostratigraphic reference for the continental middle miocene of all southeast asia by correlation with the miocene sequence of the nearby basin of chiang muan the large bodied hominoid khoratpithecus chiangmuanensis bearing levels can be precisely dated between 12 4 and 12 2 ma

propagation of surface uplift lower crustal flow and cenozoic tectonics of the southeast margin of the tibetan plateau surface uplift of the southeast margin of the tibetan plateau is interpreted to have progressed from the northwest near the tibetan border to the southeast in the red river region of the central yunnan province china this interpretation is based on existing thermochronologic data and new mapping and sedimentologic and paleobotanic data demonstrating incision in the headwaters of the red river in pliocene time or later together with previously published data demonstrating surface uplift and a gradient in crustal thickness in the absence of upper crustal shortening this is strong evidence for growth of the southeast margin of the tibetan plateau through lower crustal flow displacement along the ailao shan red river shear zone slowed or ceased in early pliocene time and the xianshuihe xiaojiang fault system initiated accommodating diffuse deformation and rotation around the eastern himalayan syntaxis we suggest a kinematic link between the change in mode of deformation and the introduction of a weak crustal layer through lower crustal flow

tectonic deformation of the indochina peninsula recorded in the mesozoic palaeomagnetic results summary in order to describe features of tectonic deformation in the indochina peninsula early jurassic to early cretaceous red sandstones were sampled at three localities in the shan thai and indochina blocks stepwise thermal treatment of most samples revealed the presence of characteristic remanent magnetization which is generally unblocked by 680 c this component from phong saly 21 6 n 101 9 e and borikhanxay 18 5 n 103 8 e localities yield positive fold tests with late jurassic early cretaceous directions of dec inc 28 8 32 1 ks 15 4 95 8 8 n 22 and dec inc 42 1 46 9 ks 20 1 95 7 9 n 18 respectively additionally a syn folding mid cretaceous characteristic magnetization is observed in the samples of muang phin locality 16 5 n 106 1 e which gave a mean direction of dec inc 30 8 39 9 k 102 6 95 3 0 n 23 this reliable late jurassic to mid cretaceous palaeomagnetic directions from three different localities are incorporated into a palaeomagnetic database for shan thai and indochina blocks based on these compilations tectonic deformation of the shan thai and indochina blocks is summarized as follows 1 the shan thai and indochina blocks experienced a clockwise rotation of about 10 as a composite unit in the early stage of india asia collision and 2 following this the shan thai block underwent an internal tectonic deformation whereas the indochina block behaved as a rigid tectonic unit during the same period comparison of our palaeomagnetic results with seismic tomographic images suggests that the strength of continental lithosphere beneath these blocks played an important role in the process of deformation rather than any other tectonic regime in contrast to the shan thai block an existence of continental roots beneath the indochina block prevented its internal deformation

paleomagnetic study of cretaceous rocks from the yangtze block central yunnan china implications for the india asia collision abstract more than 200 samples for this study were collected at 30 sites from the cretaceous matoushan and puchanghe formations around the city of chuxiong 25 n 101 5 e twenty four sites have characteristic directions with a high temperature component above 350 c paleomagnetic directions from 21 sites of the cretaceous formations reveal clockwise deflection in declination d 44 6 i 41 3 and 95 10 7 the reliability of the direction is ascertained through a positive fold test and the presence of normal and reversed polarities comparison with paleomagnetic data from other areas indicates that the chuxiong area was rotated clockwise through26 17 with respect to the eastern part of the yangtze block whereas it was subjected to more than 44 of clockwise rotation with respect to the neighboring blocks of lhasa 56 21 and western sichuan 44 16 since cretaceous time the clockwise rotation of chuxiong is a reflection of rotational motion of the large region including the southeastern qiangtang terrane and the jinsha suture red river fault paleomagnetic data and tectonic features suggest that the rotation occurred prior to the folding in the central yunnan province probably during the paleogene this large rotation is a spectacular example of the deformation in the southeastern part of the asian continent due to the collision of india

uplift of the hengduan mountains on the southeastern margin of the tibetan plateau in the late miocene and its paleoenvironmental impact on hominoid diversity abstract the southeastern margin of the tibetan plateau has a number of well known late miocene localities that have yielded fossil hominoids belonging to lufengpithecus and khoratpithecus these localities provide critical evidence about the evolutionary history of hominoids including their response to environmental changes associated with uplift of the tibetan plateau here we present magnetostratigraphic dating of the baoshan hominoid locality in yunnan southwestern china which based on preliminary biochronological evidence was previously assumed to be the youngest known miocene hominoid locality in eurasia paleomagnetic investigations yield three normal and three reversed magnetozones which can be best correlated in conjunction with biostratigraphic constraints to chrons c3n 4n to c3ar the baoshan hominoid is derived from a horizon correlated with the lowest part of c3r having an estimated age of 6 0 ma this indicates that the baoshan hominoid is slightly younger than l cf lufengensis from zhaotong dated to 6 2 ma and l lufengensis from lufeng dated to 6 9 6 2 ma our results coupled with previously published magnetochronology indicate that hominoids occurred in southeast asia from the latest middle miocene to the terminal miocene 13 6 ma the period after 6 ma coincides with the uplift of the hengduan mountains especially the gaoligong mountain we propose that the late miocene uplift of these n s oriented mountains on the southeastern margin of the tibetan plateau created a barrier to the warm and moist indian monsoon from the west and this led to a cooler and drier climate in the southeastern margin of the tibetan plateau this paleoenvironmental change potentially had a profound impact on the diversity of the hominoid community in southwestern china and southeast asia

rock magnetic properties related to thermal treatment of siderite behavior and interpretation detailed analyses of rock magnetic experiments were conducted on the oxidation products of high purity natural crystalline siderite that were thermally treated in air atmosphere susceptibilities increase sharply between 400 and 530 c indicative of some new ferrimagnetic mineral phase generation both a drop between 540 and 590 c on the heating cycle and a dramatic increase from 590 c to 520 c on the cooling cycle occurred and are well consistent with the characteristic of magnetite a distinct hopkinson type susceptibility peak indicates that hematite is the terminal product if siderite is heated to 700 c over and over it has been revealed in detail that the original inverse magnetic susceptibility fabric contributed by the crystalline anisotropy of siderite in siderite bearing specimens is changed to a normal magnetic fabric during incremental heating over 410 490 c this is a result of dominant contributions from the distribution anisotropy of newly transformed ferromagnetic minerals a strong chemical viscous remanent magnetization could be produced during siderite oxidation in an external field rock magnetic experimental results show that magnetite maghemite and hematite are the transformation products of high temperature oxidation of siderite in air maghemite was not completely inverted to hematite even at temperature as high as 690 c during incremental thermal treatments the mineral transformation processes were confirmed by conventional optical microscopic observation x ray diffractometry and mossbauer spectroscopic analyses these results indicate that the rock magnetic methods used here are reliable and highly sensitive in detecting very small magnetic phase changes in rocks we conclude that these temperaturedependent variations of magnetic properties can be used as criteria for identification of siderite in rocks and sediments furthermore it is clear that great care should be exercised in thermal demagnetization of siderite bearing rocks in paleomagnetic magnetic anisotropy and rock magnetic studies

lower middle jurassic paleomagnetic data from the mae sot area thailand paleogeographic evolution and deformation history of southeastern asia we have carried out a paleomagnetic study 12 sites 85 samples of early middle jurassic limestones and sandstones from the mae sot area of western thailand this area is part of the shan thai malay stm block and its geological characteristics have led some authors to suggest a late jurassic accretion of this region against the rest of indochina along the changning menglian zone the latter sometimes being interpreted as a mesozoic suture the high temperature or high coercivity component isolated yields a paleodirection at d 359 8 i 31 4 95 5 0 the primary nature of the magnetization acquisition is ascertained at a site with reversed polarity and a positive fold test at the 95 confidence level comparison of the mae sot paleolatitude and another one from the stm with those recently published for the simao and khorat blocks show no significant difference at the 95 level showing that the stm was situated close to or had already accreted with the simao or khorat blocks in the early middle jurassic comparison of the latitudes from these blocks with those from china indicates a relative southward motion of 8 4 of indochina as a single entity relative to china most rotations of these regions relative to china are found to be clockwise between 14 and 75 these rotations and most prominently the 1200 500 km post cretaceous left lateral motion inferred for the red river fault provide quantitative estimates of the large amount of extrusion of indochina with respect to the rest of asia

magnetostratigraphy of the dali basin in yunnan and implications for late neogene rotation of the southeast margin of the tibetan plateau 1 the rotation pattern and fault activity in the southeast margin of the tibetan plateau semtp provide meaningful constraints on the geodynamic evolution of the plateau however the lack of cenozoic paleomagnetic studies and accurate age constraints on neogene sediments prevents a better understanding of the late cenozoic tectonic activity in this area to clarify the tectonic rotation pattern and deformation history of the semtp we report new magnetostratigraphic data from a late neogene sedimentary sequence in the dali basin northwestern yunnan province china rock magnetic analyses indicate that both magnetite and hematite are the main carriers of the characteristic remanent magnetizations chrms magnetostratigraphic results show that the sedimentary profile spans from chron c4n 1r to chron c2n the age of the sedimentary sequence in the dali basin can thus be paleomagnetically constrained to an interval from late miocene to early pleistocene the basal age of the sediments is 7 6 ma which indicates that the unroofing of diancang shan and activation of the dali fault system were initiated at this time the appearance of conglomerates and syntectonic sediments suggests the reactivation of the dali fault system at 2 5 ma moreover the overall mean chrm direction suggests that the dali basin experienced significant 4 4 2 5 but minor post late miocene rotation this indicates that most of the clockwise rotation demonstrated by previous paleomagnetic studies in the semtp occurred prior to late miocene and may be concentrated between eocene and miocene which is contemporaneous with the sinistral slip of the ailao shan red river fault

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

paleomagnetism of the earliest cretaceous to early late cretaceous sandstones khorat group northeast thailand implications for tectonic plate movement of the indochina block abstract a total of 400 samples 33 sites were collected from the earliest cretaceous to early late cretaceous sandstones of the khorat group in the indochina block for paleomagnetic study to unravel the tectonic evolution of the region the sites were adopted from 3 traverses located in the northern edge of the khorat plateau northeastern thailand results indicate that almost all the sandstones exhibit similar magnetic values with an average declination d 31 7 inclination i 30 3 59 7 190 9 k 54 4 and a95 3 7 at reference point 17 30 n and 103 30 e the calculated paleolatitude points are inferred to deviate from the present latitude point by 1 2 2 3 only the lowermost part of the cretaceous sandstones can pass a positive fold test at 95 confidence level the relationship between the virtual geomagnetic poles vgps of cretaceous rocks of the indochina plate in thailand and those of the south china plate advocate that there is a major displacement of indochina along the northwest trending red river and associated faults by about 950 150 km with a 16 0 17 0 clockwise rotation relative to the south china plate during earliest cretaceous times paleomagnetic results of the early late cretaceous indochina plate point to a 20 25 clockwise rotation relative to the present occurring since very late cretaceous 65 myrs early neogene times which may be due to the collision between india and asia

tectonic deformation around the eastern himalayan syntaxis constraints from the cretaceous palaeomagnetic data of the shan thai block summary lower to middle cretaceous red sandstones were sampled at four localities in the lanpin simao fold belt of the shan thai block to describe its regional deformational features most of the samples revealed a characteristic remanent magnetization with unblocking temperatures around 680 c primary natures of magnetization are ascertained through positive fold test a tilt corrected formation mean direction for the jingdong 24 5 n 100 8 e locality which is located at a distance of 25 km from the ailaoshan red river fault revealed northerly declination with steep inclination dec inc 8 3 48 8 95 7 7 n 13 however mean directions obtained from the zhengyuan 24 0 n 101 1 e west zhengyuan 24 0 n 101 1 e and south mengla 21 4 n 101 6 e localities indicate an easterly deflection in declination such as dec inc 61 8 46 1 95 8 1 n 7 dec inc 324 2 49 4 95 6 4 n 4 and dec inc 51 2 46 4 95 5 6 n 13 respectively the palaeomagnetic directions obtained from these four localities are incorporated into a palaeomagnetic database for the shan thai block when combined with geological geochronological and gps data the processes of deformation in the shan thai block is described as follows subsequent to its rigid block clockwise rotation of about 20 in the early stage of india asia collision the shan thai block experienced a coherent but southward displacement along the red river fault prior to 32 ma this block was then subjected to a north south compressive stresses during the 32 27 ma period which played a key role in shaping the structure of chongshan lancang chiang mai belt following this some local clockwise rotational motion has occurred during the pliocene quaternary time in central part of the shan thai block as a result of internal block movements along the reactivated network of faults

diffuse deformation in the se tibetan plateau new insights from geodetic observations the southeastern tibetan plateau is a key component in the india eurasia collision zone which is characterized by spatially prevalent strike slip fault systems with devastating earthquakes however slip rates on some of these faults are still poorly constrained hindering an understanding of kinematic and dynamic processes in this region we analyze contemporary crustal deformation in the se tibetan plateau based on the latest dense geodetic observations slip rates on a set of dextral nw nnw striking faults are determined using a 3 d elastic half space dislocation model our results show that boundary faults such as the red river and lancangjiang faults yield dextral slip rates ranging from 1 to 3 mm a similar to those of other small scale sub parallel faults such as the chuxiong qujiang and wuliangshan faults additionally sinistral slip of the xiaojiang fault may have partly transferred to transpressional slip on the qujiang jianshui and central red river faults which increase seismicity on these faults new seismic relocation results geodetic measurements and existing structural observations show the geometry of this dextral fault system at the depth which may be restricted above or within the rheologically weak mid lower crust rather than cutting into the mantle results confirm that the se tibetan plateau is characterized by on going diffuse deformation between the sagaing and xianshuihe xiaojiang faults driven by the northward advance of the eastern himalayan syntaxis and southward crustal extrusion distributed right lateral movements occurred along the nw nnw striking fault system

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

magnetostratigraphy of the xiaolongtan formation bearing lufengpithecus keiyuanensis in yunnan southwestern china constraint on the initiation time of the southern segment of the xianshuihe xiaojiang fault the late cenozoic extensional basins in yunnan province southwestern china which are kinematically linked with the regional strike slip faults can provide meaningful constraints on the fault activity history and tectonic evolution of the southeast margin of the tibetan plateau semtp and further on the geodynamic evolution of the tibetan plateau however this has been severely impeded by the lack of precise age constraints on the timing of fault activity to better constrain the timing of fault activity and the tectonic rotation of semtp we undertook a high resolution magnetostratigraphic study on the xiaolongtan formation in the xiaolongtan basin which is located at the southern tip of the xianshuihe xiaojiang fault and is well known by the presence of hominoid lufengpithecus keiyuanensis rock magnetic experiments indicate that magnetite is the main remanence carrier correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and biostratigraphic data our correlation suggests that the xiaolongtan formation sedimentary sequence spans from chron c5ar 1r to chron c5n 2n which indicates that the age of the xiaolongtan formation ranges from 10 ma to 12 7 ma and that the ages of the two sedimentary layers possibly bearing the hominoid l keiyuanensis are 11 6 ma or 12 5 ma the basal age of the sediments is 12 7 ma which indicates that the activation of the southern xianshuihe xiaojiang fault was initiated at this time the overall mean paleomagnetic direction d 353 2 i 34 2 95 2 1 n 166 documents a counter clockwise vertical axis rotation of 8 3 with respect to eurasia which is the response to the activity of the left lateral xianshuihe xiaojiang fault

late miocene southwestern chinese floristic diversity shaped by the southeastern uplift of the tibetan plateau in southwestern china and southeast asia modern geology and topography have been influenced strongly by the collision between the indian and eurasian plates the southeastern margin of the tibetan plateau is well known for its high biodiversity and diverse vegetation types while the present diversity is explained by the geological history of this region to date no study has looked at how past vegetation was shaped by geological and topographical history in this study we focus on three coeval late miocene leaf assemblages from yunnan lincang xiaolongtan and xianfeng the palaeoelevation of these three sites is reconstructed using enthalpy as a palaeoaltimeter enthalpy at the fossil site is reconstructed based on leaf physiognomy the difference between this enthalpy and enthalpy at sea level is used as a proxy for altitude the palaeoaltitudes are resolved as 214 901 m asl for lincang 530 901 m asl for xiaolongtan and 1936 901 m asl for xianfeng the floristic components of these floras are analysed for their geographical elements there is a gradient in the percentage of tropical genera between the three floras from lincang at the lowest elevation to xianfeng at the highest level for lincang this percentage exceeds the threshold used to define present day tropical regions our results demonstrate that there as already a floristic differentiation in yunnan during the late miocene floras with tropical affinities were at low altitude whereas floras with temperate affinities were at high altitude with the later uplift of southern yunnan floras with tropical affinities retreated to the south where they are still present the uplift framework reconstructed in this paper gives a tectonic context for further studies on the impact of uplift on biodiversity c 2014 elsevier b v all rights reserved

finite strain calculations of continental deformation 1 method and general results for convergent zones a finite element method is used to calculate stresses and strain rates in a thin viscous sheet representing the continental lithosphere that is bordered in one part by an indenting boundary we calculate solutions for velocity fields crustal thickness distributions strain rates rotation time integrated vorticity and finite strain ellipsoids to show the dependence of these quantities on the controlling parameters the stress strain exponent n and the strength of the sheet relative to the gravitational forces which may be expressed as a dimensionless number the argand number ar for n 3 and ar between 1 and 10 a plateau of thickened crust is formed in front of the indenter the strain histories of individual elements within the viscous sheet may be quite complex and the finite strain at the end of deformation may bear no obvious relation to the principal stress orientations during the deformation the strain rate fields are interpreted in terms of the style of faulting that would be expected in the brittle upper crust if it were coupled to the ductile but stronger upper mantle in general the length scale of deformation increases with ar and time since the start of the collision and decreases with n for ar 3 the increase in length scale is accompanied by a change in the style of deformation from predominantly crustal thickening with thrust faulting in the brittle layer to predominantly transcurrent deformation strike slip faulting in the brittle layer

fibrous gypsum and fibrous anhydrite in veins fibrous calcium sulphate occurs in nature mainly as gypsum satinspar in extensional veins several mechanisms have been put forward to account for these veins and their fillings but a number of features remain unexplained or are not in accord with the interpretation s given this paper describes anhydrite as a fibrous vein precipitate which shows most features typical of satinspar subhorizontal attitude of the vein s vertical fibres a parting separating a lower from an upper seam and incorporated wall rock fragments new observations include the stacked nature of the fibres pressure shadows next to wall rock fragments and parabolic alignment of the latter these features suggest that the veins opened due to vertically oriented tensile stress the vein filling crystals grew centrifugally outwards from the initial plane of rupture which now forms the parting keeping pace with the dilation the mode of incorporation of wall rock fragments in the fibres requires repeated differential opening of the fissure thereby either wall rock fibre interface ruptured at a time and statistically the ruptures alternated so that trace element trends across the vein s are roughly symmetrical to the parting the source of the calcium and sulphate ions may have been adjacent evaporite beds but an external source is indicated where no evaporite beds are present in contrast to previous interpretations hydration of anhydrite to gypsum in the host rocks is not a prerequisite for the formation of satinspar veins the exact causes for the vertical dilation remain somewhat speculative and may have been different in various locations the vertically oriented tensile stress may have resulted from lateral tectonic compression or hydraulic overpressure or a combination of the two

internal deformation of the shan thai block inferred from paleomagnetism of jurassic sedimentary rocks in northern thailand abstract paleomagnetic samples of red sandstones were collected at 16 sites from the lower to upper jurassic phu kradung formation and the upper jurassic phra wihan formation around nan city 19 2 n 101 0 e in the southern region of the shan thai block after stepwise thermal demagnetization a high temperature component with an unblocking temperature of about 680 c is isolated from 11 sites we interpret this to be a prefold characteristic remanent magnetization because of a positive fold test at the 95 confidence level the tilt corrected mean paleomagnetic direction from 11 sites is d 32 3 i 33 3 95 12 2 k 15 0 which gives a paleomagnetic pole for this area of 60 1 n 186 5 e with a95 11 7 compared with a jurassic paleopole for the stable part of the yangtze block we observe a clockwise tectonic rotation of 12 8 which is similar to the observed rotation 18 28 of the northern region of the shan thai block this amount contrasts with a large rotation of more than 45 that is estimated from the narrow zone extending from luxi to mengla in the central region of this block this declination aspect suggests that a coherent whole block rotation by about 20 of the shan thai block took place in an earlier phase during indentation of india into asia and that an internal deformation with additional local rotation between 25 and 77 followed within a limited zone in the central part the internal deformation of the shan thai block absorbed the stress on the asian continent induced by indentation of india as well as its coherent whole block motions of clockwise rotation and southward displacement

paleomagnetism of the yuanmou basin near the southeastern margin of the tibetan plateau and its constraints on late neogene sedimentation and tectonic rotation abstract new paleomagnetic investigation was carried out on the late neogene fluviolacustrine sequence of the yuanmou basin located near the southeastern margin of the tibetan plateau magnetostratigraphic results indicate nine reverse magnetozones r1 to r9 and eight normal magnetozones n1 to n8 in the sedimentary profile which can be correlated to the geomagnetic polarity timescale from c3n 3r to c1r 1r the age of the sedimentary sequence of the yuanmou basin can thus be paleomagnetically constrained to an interval from early pliocene to pleistocene with sedimentation rates varying from 12 5 to 55 cm kyr in addition to its highly resolved magnetostratigraphic sequence the yuanmou basin provides a record of plio pleistocene tectono and climato sedimentary processes the mean declinations of the seventeen polarity units excluding samples with transitional directions can be grouped into three distinct directional intervals group i 2 58 1 37 ma group ii 4 29 2 58 ma and group iii 4 91 4 29 ma these directions indicate that the yuanmou basin has probably experienced vertical axis clockwise rotation of about 12 from 1 4 ma to 4 9 ma which may be related to slip activity of the red river fault to the southwest and the xianshuihe xiaojiang fault to the east

paleomagnetic study of middle cretaceous rocks from yunlong western yunnan china evidence of southward displacement of indochina middle cretaceous red sandstones and siltstones were collected at 20 sites for paleomagnetic study from the nanxin formation around yunlong 25 8 n 99 4 e western part of yunnan province china after stepwise thermal demagnetization high temperature component magnetization with unblocking temperature of about 675 c is isolated a positive fold test at the 99 confidence limit shows that the high temperature component magnetization is primary for the middle cretaceous nanxin formation a tilt corrected formation mean direction is d 40 2 i 49 9 with 95 3 9 corresponding to a paleopole at 54 6 n 171 8 e with a95 4 4 comparison with previously reported cretaceous paleomagnetic directions indicates that the yunlong area has been subjected to southward displacement by 11 9 7 5 corresponding to 1300 800 km with respect to the stable yangtze craton since cretaceous time as well as clockwise rotation through 36 3 13 6 this study elucidates that indochina was squeezed out of the asian continent due to collision of india accompanied with clockwise rotation

quantitative reconstruction of the late miocene monsoon climates of southwest china a case study of the lincang flora from yunnan province the miocene lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern yunnan sw china and the evolution of monsoon intensity three quantitative methods were chosen for this reconstruction i e leaf margin analysis lma climate leaf analysis multivariate program clamp and the coexistence approach ca these methods however yield inconsistent results particularly for the precipitation as also shown in european and other east asian cenozoic floras the wide range of the reconstructed climatic parameters includes the mean annual temperature mat of 18 5 24 7 degrees c and the mean annual precipitation map of 1213 3711 mm compared with the modem lincang climate mat 17 3 degrees c map 1178 7 mm the miocene climate is slightly warmer wetter and has a higher temperature seasonality a detailed comparison on the palaeoclimatic variables with the coeval late miocene xiaolongtan flora from the eastern part of yunnan allows us to investigate the development and interactions of both south asian and east asian monsoons during the late miocene in southwest china now under strong influence of these monsoon systems our results suggest that the monsoon climate has already been established in southwest yunnan during the late miocene furthermore our results support that both southeast asian and east asian monsoons co occurred in yunnan during the late miocene c 2010 elsevier b v all rights reserved

paleomagnetism of cretaceous rocks from eastern qiangtang terrane of tibet thermal demagnetization has successfully isolated high unblocking temperature characteristic directions from paleomagnetic samples of lower and middle cretaceous redbed formations from eastern qiangtang terrane tibet the tilt corrected mean direction for the lower cretaceous is d i 57 7 50 2 with 95 10 9 and n 12 sites and that for the middle cretaceous is d i 39 7 51 6 with 95 8 5 and n 11 sites both formations pass the fold test and the latter possesses two polarities the magnetization predates the eocene and was probably acquired during cretaceous time comparison of the mean directions with expected directions from the stable interior of eurasia indicates significant clockwise rotation but little paleolatitudinal change for the sampling area deformation and rotation of these rocks are presumably related to the collision of india with asia and its subsequent northward indentation into asia existing paleomagnetic data from tibet and its environs seems to be compatible with a crustal shortening thickening model dewey et al 1988 in that the continental crust directly north of the indian indenter was substantially shortened north south whereas in the vicinity of the western and eastern syntaxes latitudinal displacement was minimal but tectonic rotation was very important more data are needed to further differentiate between this model and the lateral eastward crustal extrusion model molnar and tapponier 1975

chronological sequence and subdivision of chinese neogene mammalian faunas six land mammal ages are recognized for the neogene of east asia the ages are based upon updated large and small mammal faunas and replace or redefine the land mammal stages erected by li et al 1984 comparisons and correlations are made to faunas in europe northern and southern asia and north america in addition methods of utilizing mammalian faunal data to define and recognize geochronologic ages are discussed

tectonic deformation of the southwestern part of the yangtze craton inferred from paleomagnetism abstract upper cretaceous red sandstones have been sampled at 21 sites from the jiangdihe formation in yuanmou 25 9 n 101 7 e the northern part of yunnan china characteristic directions with unblocking temperature of 680 c have been isolated from all the sites and provide a positive fold test which is significant at the 99 probability level remanent magnetization of the prefolding origin represents a characteristic direction of the jiangdihe formation d 26 9 i 35 6 and 95 3 6 this paleomagnetic direction confirms the fairly large easterly declination of the cretaceous time for the southern part of the yangtze craton incorporating this result into previous data from the areas along the longitude of 102 e in the southwestern part of yangtze craton the declination value in the cretaceous paleomagnetic direction monotonously decreases from 45 to 2 as latitude increases from 25 0 to 30 1 n the tectonic rotation expected from the apparent polar wander path of eurasia shows that the clockwise rotation decreases gradually from 30 to 10 whilst increasing in latitude the systematically differential rotation along the longitude in the southwestern part of the yangtze craton is a part of the deformation mode of the asian continent due to the collision with india the yangtze craton behaved as a unit continuum material with a ductile nature during deformation

paleomagnetic evidence for post cretaceous internal deformation of the chuan dian fragment in the yangtze block a consequence of indentation of india into asia abstract paleomagnetic samples of paleocene eocene red sandstones were collected at 36 sites from the jiangdihe 4 and zhaojiadian formations around the yongren 26 1 n 101 7 e and dayao areas 25 7 n 101 3 e these areas are located in the chuxiong basin of the chuan dian fragment southwestern part of the yangtze block after stepwise thermal demagnetization a high temperature component with unblocking temperature of about 680 c is isolated from 26 sites the primary nature of this magnetization is ascertained through positive fold and reversal tests at 95 confidence level the tilt corrected mean paleomagnetic directions for the yongren and dayao areas are d 17 2 i 26 6 with 95 5 8 and d 16 5 i 31 1 with 95 4 8 respectively easterly deflected declinations from this study are consistent with those reported from other areas of the chuxiong basin indicating its wide presence in the cretaceous eocene formations of the said basin comparison with declination values expected from the cretaceous eocene apwp of eurasia indicates that the magnitude of clockwise rotation systematically increases toward the southeast within the chuxiong basin as well as in the chuan dian fragment this trend of the differential tectonic rotation in the chuan dian fragment is consistent with curvature of the xianshuihe xiojiang fault system deformation of the chuxiong basin can fairly be associated with the formation of eastward bulge in the southern part of the chuan dian fragment during southward displacement the chuan dian fragment was probably subjected to tectonic stresses as a result interaction with the yangtze and indochina blocks which resulted into east west extension and north south shortening

mineral magnetic variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability 1 to retrieve reliable long term paleoclimatic signals from the chinese loess paleosol sequences deposited over the past 2 6 myr multiparameter mineral magnetic investigations have been conducted on the jiaodao section on the chinese central loess plateau first the lithogenic magnetic components and the pedogenic overprinting were chemically separated by the citrate bicarbonate dithionite cbd method the magnetic properties of the least pedogenically altered loess units and post cbd loess paleosols are dominated by coarse grained lithogenic magnetite increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite maghemite long term changes of the pre cbd magnetic properties suggest a long term decrease in summer monsoon intensity and a long term increase in winter monsoon intensity from the late pliocene to the late pleistocene long term variations of the post cbd magnetic properties suggest an increase in both concentration and grain size of coarse grained lithogenic psd md magnetite grains and hence indicate a long term increase in winter monsoon intensity over that period the coercivity decrease of the lithogenic component for the loess unit l15 may be related to the accelerated uplift of the tibetan plateau and its adjacent regions during the period of l15 deposition from paleosol s5 to loess l1 higher values of coercivity of the lithogenic component occur in typical loess and paleosols and lower values are found at the loess paleosol transition these coercivity variations are thought to be related to significant changes in the source region as well as dust deposition in the loess plateau caused by changes in ice snow or vegetational cover these new results lead to a better understanding of the relationships between the effects of tectonic paleoclimatic and paleoenvironmental processes in northwestern china

widespread cenozoic remagnetization in thailand and its implications for the india asia collision abstract paleomagnetic study of 13 sites from the khorat plateau in thailand spanning ages from the devonian to the jurassic and reappraisal of published results from the triassic to the cretaceous show that most of the indochina block suffered complete remagnetization after the triassic and possibly after the cretaceous most likely at the time of the collision of india and eurasia the paleodirection associated with this remagnetization is consistent with the contention that thailand was a part of eurasia at that time and that it has suffered some 20 of clockwise rotation subsequently also consistent is the observed azimuthal difference of mesozoic fold axes on either side of the red river fault as is the early geometry of and sense of motion on this fault re interpretation of late neogene data suggests that rotation may have continued into the neogene the remagnetization event prevents the determination of paleopositions of thailand prior to the cenozoic but carries great interest in the frame of the extrusion tectonics concept

pollen evidence of the palaeoenvironments of lufengpithecus lufengensis in the zhaotong basin southeastern margin of the tibetan plateau evolutionary processes in hominoid primates were closely related to global and or regional environmental changes and therefore palaeoenvironmental reconstruction is fundamental for understanding how environmental changes shaped their evolution here we present pollen data from the 16 m thick shuitangba stb section yunnan province southwestern china bearing remains of the hominoid lufengpithecus lufengensis of the terminal miocene and use principal component analysis to reconstruct the palaeovegetation and palaeodimate during the key period when the hominoid lived our results show that before the stb hominoid appeared zone a the vegetation was dominated by subtropical evergreen broad leaved taxa with a few temperate deciduous taxa e g quercus castanea castanopsis alnus the development of aquatic plants commencing at the similar to 12 m depth is a prominent feature indicating a warm and humid climate during the time when the hominoid lived zone b evergreen broad leaved forests with evergreen quercus were predominant while grasses including poaceae began to expand and simultaneously conifers decreased indicating a warm climate the significant presence of aquatic pollen taxa in subzone a 2 and zone b suggests the occurrence of lacustrine or swampy environments in contrast in zone c the vegetation changed to coniferous forest indicating cooler and drier conditions these results provide substantive evidence of the vegetation conditions when the hominoid lived suggesting that the greater diversity of vegetation and the warm humid climate compared to the present day would have favoured its survival c 2015 elsevier b v all rights reserved

oligo miocene magnetostratigraphy and rock magnetism of the xishuigou section subei gansu province western china and implications for shallow inclinations in central asia magnetostratigraphy of 222 remanent directions together with late oligocene to early miocene mammal and charophyte paleontology suggest that 2179 m of the xishuigou section subei gansu province china were deposited from 26 to 19 ma stratigraphic patterns of bulk susceptibility anisotropy of magnetic susceptibility parameters and natural and anhysteretic remanent magnetization intensities demonstrate that 1 faulting does not significantly affect the record 2 sediment deposition was relatively continuous 3 sediment source changed around 23 ma and 4 rapid uplift near subei occurred at 21 ma subei rotated 27 5 counterclockwise with respect to the 20 ma pole from the eurasian synthetic apparent polar wander path folding and rotation of the section took place after 19 ma the paleolatitude of subei is 14 less than at present and 19 3 less than predicted from the reference pole both rock magnetic and paleomagnetic data sets suggest that the unusually low paleolatitude is the result of synsedimentary inclination shallowing a phenomenon which has likely affected other paleomagnetic data from central asia

internal crustal deformation in the northern part of shan thai block new evidence from paleomagnetic results of cretaceous and paleogene redbeds in order to describe the internal deformation of the northeast part of the shan thai block resulting from the penetration of the indian plate into asia a paleomagnetic study was carried out on the cretaceous and paleogene strata in the southern part of the simao terrane high temperature magnetic components with unblocking temperatures around 680 degrees c were isolated and positive fold test shows its primary nature of magnetization the tilt corrected site mean directions of the lower cretaceous and upper cretaceous from the menglun area are d s 46 2 degrees i s 45 9 degrees k 11 0 alpha 95 10 6 degrees and d s 33 2 degrees i s 30 9 degrees k 68 4 alpha 95 8 2 degrees respectively the site mean directions of the upper cretaceous and lower paleogene for the mengban area are d s 50 5 degrees i s 31 0 degrees k 207 6 alpha 95 6 4 degrees and d s 43 5 degrees i s 23 0 degrees k 26 1 alpha 95 13 4 degrees respectively the results of the lower cretaceous and upper paleogene from the mengla area are d s 46 9 degrees i s 42 2 degrees k 27 3 alpha 95 7 7 degrees and d s 41 8 degrees i s 23 8 degrees k 38 9 degrees alpha 95 5 8 degrees respectively in comparison with previous paleomagnetic data of the simao terrane the rotational deformation can be divided into four stages the cretaceous and paleocene sediments of the simao terrane experienced intensive folding before the early oligocene during the early oligocene to early miocene the shan thai and indochina blocks experienced southeastward extrusion with similar to 20 degrees clockwise rotation relative to the south china block during the middle to late miocene the shan thai blocks experienced more 15 degrees clockwise rotation since the late miocene the activity of strike slip faults surrounding the simao terrane enhanced the internal differential rotations of the terrane these deformation processes finally resulted in a complex internal deformation of the simao terrane c 2013 elsevier b v all rights reserved

oroclinal origin of the simao arc in the shan thai block inferred from the cretaceous palaeomagnetic data summary an active oroclinal bending is discovered in the shan thai block to the south of the eastern himalayan syntaxis to investigate the evolution of the simao arc using palaeomagnetic techniques the middle cretaceous red beds of the nanxin formation were sampled at the zhengwan 22 8 n 100 9 e and dadugang 22 4 n 101 0 e localities in the southern simao basin most of the studied samples revealed the presence of characteristic remnant magnetization with unblocking temperatures around 680 c a primary nature for this magnetization is interpreted on the basis of a positive fold and reversal test tilt corrected mean directions calculated for zhengwan and dadugang localities are characterized by large easterly deflected declination d 51 8 i 47 9 ks 45 0 95 6 9 n 11 and d 64 1 i 48 1 ks 36 0 95 7 3 n 12 respectively steep inclination values at both these localities with respect to those expected are in the range previously reported from the shan thai block confirming their southward displacement by 6 2 1 7 as part of the shan thai block combination of the present data two localities with those previously reported from simao basin seven localities reveals a positive palaeomagnetic oroclinal test indicating that the present day arc like geometry of the simao basin was formed by oroclinal bending comparison with recent gps and structural data suggest that formation of the simao curvature started after the early pliocene after 4 ma and continuing until the present origin of the simao arc is ascribed to southwestward movement of the crustal material across the ailao shan red river fault around the eastern himalaya syntaxis which was formed by westward movement of the decollement with progressive eastward deepening of the lanping simao basin decoupling between the upper and the middle lower crusts is a requisite condition for the arc formation on the continent

discrepant cretaceous paleomagnetic poles between eastern china and indochina a consequence of the extrusion of indochina abstract a paleomagnetic study of cretaceous and paleocene red beds has been carried out in the yunlong area yunnan province of china of the northern indochina block a high temperature component with dual polarities was isolated from both lower cretaceous and paleocene rocks and of solely polarity for upper early cretaceous and lower late cretaceous rocks thirteen magnetic polarity zones are found along the pijiang section the primary nature of cretaceous magnetic remanence is ascertained by positive and reversal fold tests these results combined with previous cretaceous results from the yunlong and yongping areas of the lanping basin indicate that these areas behaved as a relatively rigid block and rotated 37 2 17 clockwise relative to eurasia since the paleocene comparing available early cretaceous paleomagnetic results obtained both from indochina and eastern china a statistically significant paleolatitude difference of 9 6 5 7 is inferred this difference is consistent with an estimated 1000 400 km extrusion of indochina relative to south china through a counter clockwise rotation of 14 of indochina around a finite rotation pole inferred from the stage poles of rotation derived from the magnetic isochrons in the south china sea the reconstruction is fully consistent between the cretaceous pole obtained from the khorat basin of the stable core of the indochina block and the coeval pole of eastern china

miocene emplacement and deformation of the konga shan granite xianshui he fault zone west sichuan china geodynamic implications the presently active sinistral xianshui he strike slip fault xsh is a lithospheric scale strike slip fault in the eastern himalaya in the study area this fault affects the eastern edge of the konga shan granitic massif where it has caused both brittle and ductile deformation a rbsr isochron and nd and pb isotope study of three samples and a upb zircon study of a single sample were completed on the granite upb data indicate a granite emplacement age of 12 8 1 4 ma the rbsr isochrons show that the granite emplacement and the deformational event were synchronous at around 12 10 ma minimum age for deformation the nd and pb isotope compositions of whole rocks and k feldspars indicate the involvement of proterozoic continental crust which is confirmed by upb systematics indicating inherited zircons sinistral faulting along the xsh began at the latest at 12 ma and marks the extrusion toward the east of the west sichuan and south china blocks following their extrusion along the red river fault zone between 50 and 21 ma

paleomagnetic results from cretaceous and jurassic rocks of south and southwest yunnan evidence for large clockwise rotations in the indochina and shan thai malay terranes abstract cretaceous and jurassic redbeds have been sampled from south and southwest yunnan china for paleomagnetic study the paleomagnetic directions resolved from the cretaceous rocks indicate that the xiaguan area which is located on the red river fault has not been rotated with respect to stable eurasia since at least late cretaceous times and that the jinggu mengla area 200 400 km farther south has been rotated by 46 65 clockwise the jurassic results reveal the same rotation pattern at face value the differences between the observed cretaceous paleolatitudes and those predicted from the eurasian apparent polar wander path apwp indicate a southward extrusion of the region but the amount of extrusion is not large enough to be resolved by paleomagnetic methods comparison with mesozoic paleomagnetic data from central yunnan northern thailand and northwestern borneo suggests that the red river fault is not a demarcation between unrotated and significantly rotated regions and that sundaland did not respond to the india asia collision as a single coherent unit the existing paleomagnetic data from east asia appear to indicate that the crust in central tibet and tien shan north of tarim directly in front of the indian indentor has been substantially shortened and thickened whereas the crust in the syntaxial areas has probably been largely squeezed out to further evaluate the relative importance of crustal thickening and extrusion in the tectonic evolution of the tibetan plateau paleomagnetic investigation should be intensified in the bounding zones to the indian indentor and be expanded into the cenozoic sedimentary rocks in tibet and surrounding regions

oligocene deformation of the chuandian terrane in the se margin of the tibetan plateau related to the extrusion of indochina mechanisms driving the tectonic evolution of the southeast se margin of tibet include the paleogene extrusion of the coherent indochina lithospheric block and the continuous deformation caused by lower crustal flow since the middle miocene the timing and style of regional deformations are key to determining the role of each mechanism fault bounded and controlled cenozoic basins within the se margin of tibet record regional deformation surface uplift and variations in paleoclimate but often are poorly dated new magnetostratigraphy and 40ar 39ar dating of volcanic ashes constrain precisely the timing of sedimentation within the luhe basin to between 35 and 26 5 ma the basin is located in the chuandian terrane along the chuxiong fault which lies 70 km north of and parallel to the ailao shan red river fault the asymmetric syncline of the luhe basin suggests syn contractional sedimentation and the basal age of the basin represents the initiation of the chuxiong fault and crustal shortening at 35 ma this is coincident with the onset of the ailao shan red river fault and supports a kinematic link between them our study suggests that like the ailao shan red river fault the chuxiong fault is a paleogene transpressional structure that developed during the extrusion and clockwise rotation of indochina around the eastern himalayan syntaxis which caused the late paleogene deformation and surface uplift of the chuandian terrane and indochina our revised chronostratigraphy of the luhe basin provides further evidence that many of the neogene sedimentary basins in the se margin of tibet may be much older than previously thought

new paleomagnetic constraints on the extrusion of indochina late cretaceous results from the song da terrane northern vietnam abstract samples were collected for paleomagnetic investigations from the upper cretaceous yen chau formation in the song da terrane 21 7 n 103 9 e bounded by the ailao shan red river fault system and song ma fault in an attempt to examine extrusion tectonics of east asia primary nature of the high temperature 600 690 c component of magnetization from 13 sites is supported by a positive fold test the tectonic corrected data provides the characteristic late cretaceous paleomagnetic direction for the song da terrane d 6 4 i 32 0 with 95 8 5 n 13 sites corresponding to a paleopole lying at 82 9 n 220 7 e a95 6 9 comparison with coeval paleomagnetic poles for the neighboring tectonic blocks indicates no latitudinal translation of the son da terrane with respect to the south china block whereas the shan thai block and the southern part of the indochina block revealed a southward displacement of 10 5 9 5 in latitude with respect to the song da terrane we conclude that the southeastern segment of the ailao shan red river fault system to the east of the dien bien phu fault is not a demarcation of the extruded indochina peninsula the indochina block extruded probably along some faults between the song da terrane and the khorat plateau

palaeomagnetic evidence for southward displacement of the chuan dian fragment of the yangtze block summary cretaceous red sandstones of the feitianshan formation and the xiaoba formation were sampled at 33 sites from the dadeli and mishi synclines of xichang 27 9 n 102 3 e the study area is a part of the chuan dian fragment bounded by the xianshuihe xiaojiang and the red river fault systems which in turn constitute the southwestern part of the yangtze block almost all the samples give a characteristic palaeomagnetic direction with unblocking temperatures up to 680 c the primary nature of magnetization is ascertained by a positive fold test with a 99 per cent confidence level for the dadeli syncline the tilt corrected overall mean direction of the 33 sites is d 3 7 i 41 5 95 3 4 with a corresponding palaeopole at 85 2 n 241 7 e a95 3 5 this pole occupies the near sided position with respect to the estimate of the cretaceous pole of the sichuan basin indicating that the xichang area experienced a significant southward displacement combined with earlier reported palaeomagnetic data from the chuan dian fragment a significant southward displacement of 6 7 3 5 in latitude is estimated for the whole fragment with respect to the sichuan basin since the late cretaceous extrusion dynamics in the asian continent due to its collision with india brought about the southward displacement of the chuan dian fragment declination data indicate that the southern part of the chuan dian fragment was subjected to clockwise sense rotation of up to 45 this significantly large tectonic rotation probably occurred during extrusion of this

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

paleoclimatic estimation reveals a weak winter monsoon in southwestern china during the late miocene evidence from plant macrofossils the late miocene xianfeng flora of yunnan province southwestern china was chosen to reconstruct the paleoclimate and the intensity of the asian monsoon three available quantitative climate reconstruction methods from fossil plants i e leaf margin analysis lma the climate leaf analysis multivariate program clamp and the coexistence approach ca were used in this study mats mean annual temperatures resulting from these three approaches i e lma 17 2 2 38 degrees c clamp 15 43 1 25 degrees c ca 17 2 21 7 degrees c appear to have been higher than the present 14 9 degrees c suggesting a much warmer climate in the late miocene both the growing season precipitation gsp from clamp 1908 7 217 7 mm and mean annual precipitation map from ca 1206 0 1613 0 mm estimates are higher than modern values 1003 2 mm gsp and 1038 mm map respectively indicating a more humid climate during the late miocene by comparing these with climates reconstructed from neighboring late miocene floras we conclude that the general late miocene climate appears warmer and more humid than present conditions in southwestern china furthermore the evident differences in estimated monthly temperatures between the summer and winter and precipitations between the humid and dry seasons indicate the existence of seasonality though not as strong as that of today difference in precipitation of dry season indicates a marked strengthening in the winter monsoon since the late miocene a new monsoon intensity index has also been defined based on precipitation seasonality to investigate the intensity of the asian monsoon c 2012 elsevier b v all rights reserved

tertiary paleomagnetic data from northwestern yunnan china further evidence for large clockwise rotation of the indochina block and its tectonic implications abstract eocene red sandstones were collected at 15 sites for paleomagnetic study from two areas lanping and yunlong of the western part of yunnan province china in the northern part of indochina the high temperature magnetization component with an unblocking temperature of around 680 c is isolated after stepwise thermal demagnetization characteristic directions from nine accepted sites reveal a positive fold test at the 99 confidence limit indicating that the high temperature magnetization component is possibly of eocene age a tilt corrected mean direction from nine accepted sites is d 266 1 i 39 8 with 95 11 2 corresponding to a paleopole at 14 5 n 169 7 e with a95 10 9 a comparison with previously reported tertiary paleomagnetic data indicates that the lanping basin of the northern part of the indochina block rotated clockwise through 91 15 with respect to the yangtze craton this large magnitude clockwise rotation is probably caused by the superimposition of regional and local rotations our previous middle cretaceous paleomagnetic results from the yunlong area indicate that about 40 of clockwise rotation out of 90 is explained by tectonic rotation due to a relatively rigid body rotation of the simao terrane during indentation of india the remaining component of rotation is probably ascribed to further eocene post eocene rotational motion of the tectonically independent small blocks within the lanping basin associated with fault movement

role of the red river shear zone yunnan and vietnam in the continental extrusion of se asia the 1000 km long nw se striking left lateral ailao shan red river shear zone runs from the southeastern corner of tibet to the gulf of tonkin and the south china sea it has been used as the prime example of a lithospheric scale strike slip fault that has accommodated between 500 and 1000 km of southeastwards extrusion of indo china away from the indian plate indentor central to the model of continental extrusion is that such faults cut through the entire lithosphere that shear heating resulted in high grade metamorphism and local anatexis and that the ages of sheared granites along the fault also date the timing of strike slip shearing however structural data from the red river shear zone clearly show that vertical strike slip faulting post dated metamorphism and granite emplacement most granites along the shear zone are mantle related granodiorites or within plate alkali granites formed prior to shearing along the red river shear zone left lateral kinematic indicators are ubiquitous within the red river mylonites but they are always lower temperature fabrics formed after peak sillimanite metamorphism and after granite crystallization it is suggested that left lateral strike slip shearing along the red river shear zone started after 21 ma not at 35 ma as previously thought and the fault was purely a crustal structure none of the geological features used to propose the 500 1000 km offsets are robust and the total finite offset remains unknown

structure kinematics and ages of transpression during strain partitioning in the chongshan shear zone western yunnan china abstract the chongshan shear zone extends from the eastern himalayan syntaxis to the lincang granitic pluton in yunnan province china the structure and kinematics show that the shear zone comprises mainly of mylonitic gneiss migmatite and schist with a dextral dominated strike slip motion in an n s trending northern segment and a sinistral strike slip shear in nw se trending middle and southern segments both were developed under a bulk regional scale sinistral transpression shrimp and la icpms u pb and 40 ar 39 ar dating reveal two tertiary magmatic events along the zone followed by younger sinistral strike slip shear the eocene magmatic event c 55 38 ma followed by metamorphism at c 36 ma happened before the strike slip motion the strike slip shear along the zone began c 32 ma which generated shear heating from 32 to 22 ma the 40 ar 39 ar ages of syn kinematic micas range from 19 to 14 ma and indicate that the strike slip shear continued to this time with coeval transpressional exhumation and uplift of the metamorphic rocks along the biluoxueshan chongshan chain the chongshan zone is thus a cenozoic shear zone which was contemporaneous with motion on the left lateral ailao shan red river shear zone and the right lateral gaoligong shear zone and should be important in accommodating the northwards movement of india during collision during oligocene to miocene times the continental block that was extruded between the ailao shan red river and gaoligong shear zones was dismembered into at least two major fragments by the chongshan shear zone

paleoecologies and paleoclimates of late cenozoic mammals from southwest china evidence from stable carbon and oxygen isotopes abstract to examine paleodiets and habitats of extinct taxa and to understand long term regional climate change we determined the carbon and oxygen isotopic compositions of fossil herbivore teeth and soil samples from six localities in yunnan province southwest china ranging in age from 10 ma to the present although limited in spatial and temporal coverage these initial results reveal significant changes in the environments and diets of mammalian taxa over the last 10 million years prior to 2 3 ma while most mammals examined had pure or nearly pure c 3 diets some individuals consumed a small amount of c 4 grasses up to 20 c 4 since then c 4 grasses became a significant dietary component for most herbivores as indicated by higher enamel 13 c values in the pleistocene yuanmou formation and at shangri la most likely reflecting an increased c 4 biomass in the region the carbon isotope results show that the diets of mammals of 2 5 1 75 ma from shangri la ranged from pure c 3 to pure c 4 while 1 7 ma horses from yuanmou had 0 70 c 4 grasses in their diets mammals living at 8 7 ma in the yuanmou and lufeng region had very similar diets and habitats with similar climatic conditions increased c 4 biomass after 3 4 ma suggests a significant change in certain aspects of regional climate such as increased seasonality of rainfall or an increase in seasonal drought and fires as these factors are important to modern grasslands the data also show that unlike the siwalik fauna in the indian subcontinent mammals in yunnan on the southeast side of the himalayan tibetan plateau lived in an environment dominated by dense forests until 3 4 ma nonetheless both 13 c values of paleosol carbonates and fossil enamels indicate that c 4 grasses were present in the yuanmou region in the latest miocene and pliocene 8 3 5 ma likely in greatly dispersed small patches of open habitats where the forest canopy was broken or on flood plains and the c 4 biomass increased significantly after 3 5 ma the oxygen isotope results from yuanmou xiaohe formation show a positive shift after 8 5 ma which is similar in timing and magnitude to 18 o shifts observed in horses and rhinos from the linxia basin and in fossils and paleosols from pakistan and nepal suggesting a shift toward a drier climate at the northeast southeast and southern borders of the tibetan plateau during the late miocene taken together the carbon and oxygen isotope data indicate a general drying of the local climate over time and a change from a largely dense forest environment at 8 ma to a more open environment with a mosaic of forests and grasslands after 3 4 ma in the yuanmou region intra tooth 13 c and 18 o variations within individual fossil teeth from yuanmou suggest a stronger seasonality of rainfall at 1 7 ma than in the late miocene the spatial and temporal 13 c and 18 o variations observed in mammalian teeth from yunnan likely reflect changes in regional climate and or tectonics but more data are needed to fully explore the significance of the regional patterns in the 18 o and 13 c data in relation to climate and tectonic evolution of the region

the intensification of the east asian winter monsoon contributed to the disappearance of cedrus pinaceae in southwestern china climate change during the quaternary played an important role in the distribution of extant plants herein cone scales of cedrus pinaceae were uncovered from the upper pliocene sanying formation longmen village yongping county of yunnan province in southwestern china detailed comparisons show that these fossils all belong to the genus cedrus pinaceae and a new species is proposed cedrus angusta sp nov this find expands the known distribution of cedrus during the late pliocene to yunnan where the genus no longer exists in natural forests based on the analysis of reconstructed neogene climate data we suggest that the intensification of the east asian winter monsoon during the quaternary may have dramatically increased seasonality and given rise to a much drier winter in yunnan combined with information on cedrus fossil records and its seed physiology we conclude that the intensification of a drier climate after the late pliocene may have prevented the survival of cedrus seedlings leading to the eventual disappearance of cedrus in western yunnan this study indicates that the topography in southwestern china acted as a vital refuge for many plants during the quaternary but that other species gradually disappeared due to the intensification of the monsoonal climate