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

should sibumasu be renamed sibuma the case for a discrete gondwana derived block embracing western myanmar upper peninsular thailand and ne sumatra the luxi nujiang suture which extends from yunnan into myanmar is shown to continue into thailand and the malacca strait it forms the eastern boundary of a discrete block here called the irrawaddy block which was formerly considered to be part of gondwana derived sibumasu it has a distinct palaeozoic succession with thick lower permian glacially influenced diamictite bearing marine mass flow intervals deposited at the gondwana margin the rest of sibumasu east of the suture also has local thin lower permian diamictite units however they have been interpreted as ice rafted deposits laid down at a greater distance from the gondwana margin in ne sumatra a diamictite bearing carboniferous lower permian succession has also been described as of mass flow origin and it is suggested that it is also part of the irrawaddy block it requires that the bounding suture is aligned se beneath the malacca strait in the late cretaceous palaeogene the dextral india australia oceanic transform propagated onshore as a strike slip fault bounding on the east the north going india plate it disrupted the irrawaddy block and for much of its length coincided with the line of the earlier suture insofar as the acronym sibumasu was coined to include sumatra consideration should be given to renaming this block sibuma

new insights into the cenozoic lateral extrusion of crustal blocks on the southeastern edge of tibetan plateau evidence from paleomagnetic results from paleogene sedimentary strata of the baoshan terrane in order to characterize the lateral extrusion of crustal material during the cenozoic we conducted a paleomagnetic study of the eocene oligocene zhushan formation and paleocene muguahe formation in the central part of the baoshan terrane bst on the southeastern edge of tibetan plateau a primary magnetic component and a remagentized component with the miocene acquisition age were isolated from the muguahe formation and zhushan formation respectively these data indicate that the bst did not commence clockwise rotation in the period of the paleocene and the oligocene and that the bst experienced 80 clockwise rotation relative to east asia since the miocene combining with the documented history of crustal boundary strike slip faults on the southeastern edge of the tibetan plateau shows that the bst and tengchong terrane tct firstly underwent latitudinal crustal shortening in the oligocene and the eastward extension was the main type of motion of the crustal material during this period which induced the initial strike slip movement of their boundary faults since the miocene the main form of crustal motion of bst tct and simao terrane was gradually transformed into clockwise rotation which possibly indicates that the fold and thrusting fault systems induced crustal shortening and thickening in the southeastern edge of the tibetan plateau have reached extremity and the southeastern part of the tibetan plateau have already been uplifted to the similar elevation with today s elevation in the miocene

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

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

mica dominated seismic properties of mid crust beneath west yunnan china and geodynamic implications abstract measurements of crystallographic preferred orientations cpo and calculations of p and s wave velocities v p and v s and anisotropy were conducted on three quartz mica schists and one felsic mylonite which are representative of typical metamorphic rocks deformed in the middle crust beneath the southeastern tibetan plateau results show that the schists have v p anisotropy av p ranging from 16 4 to 25 5 and maximum v s anisotropy av s max between 21 6 and 37 8 the mylonite has lower av p and av s max but slightly higher foliation anisotropy which are 13 2 18 5 and 3 07 respectively due to the lower content and cpo strength of mica with increasing mica content the deformed rocks tend to form transverse isotropy ti with fast velocities in the foliation plane and slow velocities normal to the foliation however the presence of prismatic minerals e g amphibole and sillimanite forces the overall symmetry to deviate from ti an increase in feldspar content reduces the bulk anisotropy caused by mica or quartz because the fast axis of feldspar aligns parallel to the slow axis of mica and or quartz the effect of quartz on seismic properties of mica bearing rocks is complex depending on its content and prevailing slip system the greatest shear wave splitting and fastest v p both occur for propagation directions within the foliation plane consistent with the fast pms s wave converted from p wave at the moho polarization directions in the west yunnan where mica amphibole bearing rocks have developed pervasive subvertical foliation and subhorizontal lineation the fast pms directions are perpendicular to the approximately e w orienting fast sks s wave traversing the core as p wave directions indicating a decoupling at the moho interface between the crust and mantle beneath the region the seismic data are inconsistent with the model of crustal channel flow as the latter should produce a subhorizontal foliation where vertically incident shear waves suffer little splitting

direct dating of left lateral deformation along the red river shear zone china and vietnam 1 exposures of high grade midcrustal rocks within the red river shear zone rrsz which separates the indochina and south china blocks exhibit clear evidence of left lateral ductile deformation assuming that the south china sea represents a pull apart basin formed at the southeastern termination of the rrsz it has been argued that seafloor magnetic anomalies constrain the timing of sinistral slip accommodated by the rrsz between 32 and 17 ma at a rate of 4 cm yr while 40ar 39ar thermochronometry indicates that left lateral slip occurred along the rrsz between 25 and 17 ma the timing of earlier high temperature deformation has not been directly constrained in situ th pb ion microprobe dating of monazite inclusions in garnets allows direct assessment of the timing of amphibolite grade metamorphism and synchronous left lateral shearing results from northern segments of the rrsz in yunnan china indicate that synkinematic garnet growth occurred between 34 and 21 ma and are the first to document late oligocene metamorphism and left lateral shearing data from the southern rrsz within vietnam are complicated by tertiary overprinting of rocks that experienced amphibolite facies metamorphism during the indosinian orogeny 220 ma the period during which sinistral deformation is now constrained to have occurred along the rrsz i e 34 17 ma is essentially coincident with spreading of the south china seafloor 32 17 ma this temporal and kinematic link between left lateral shearing along the rrsz and opening of the south china sea supports the view that indochina was extruded from asia as a block along lithospheric scale strike slip faults

late cenozoic tectonic evolution of the ailao shan red river fault se tibet implications for kinematic change during plateau growth surface uplift river incision shear zone exhumation and displacement along active faults have all interacted to shape the modern landscape in the southeastern margin of the tibetan plateau the ailao shan red river fault a major structure in the tectonic evolution of southeastern asia is an excellent recorder of these processes we present new stratigraphic structural and low temperature thermochronologic data to explore its late cenozoic tectonic and geomorphic evolution the stratigraphic and structural observations indicate that the major bend in the fault was a releasing bend with significant miocene sedimentation in the early middle miocene but became a restraining bend with abundant shortening structures developed after the late miocene reversal of displacement we also document exhumation of the shear zone from two low temperature thermochronologic transects new apatite u th he ahe data and published thermochronologic results reveal two accelerated cooling episodes backed by stratigraphic and geomorphic observations the first rapid cooling phase occurred from ca 27 to 17 ma with removal of cover rocks and exhumation of the shear zone the second accelerated cooling episode revealed by our ahe data commenced at 14 13 ma lasting 2 3 myr the ailao shan range may have risen to its modern elevation with high relief topography developing due to river incision we interpret the onset of this rapid exhumation to reflect renewed plateau growth associated with lower crustal flow

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

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

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

magnitude and symmetry of seismic anisotropy in mica and amphibole bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast tibetan plateau we calibrated the magnitude and symmetry of seismic anisotropy for 132 mica or amphibole bearing metamorphic rocks to constrain their departures from transverse isotropy ti which is usually assumed in the interpretation of seismic data the average bulk vp anisotropy at 600 mpa for the chlorite schists mica schists phyllites sillimanite mica schists and amphibole schists examined is 12 0 12 8 12 8 17 0 and 12 9 respectively most of the schists show vp anisotropy in the foliation plane which averages 2 4 for phyllites 3 3 for mica schists 4 1 for chlorite schists 6 8 for sillimanite mica schists and 5 2 for amphibole schists this departure from ti is due to the presence of amphibole sillimanite and quartz amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation forming orthorhombic anisotropy with vp x vp y vp z effects of quartz are complicated depending on its volume fraction and prevailing slip system most of the mica or amphibole bearing schists and mylonites are approximately transversely isotropic in terms of s wave velocities and splitting although their p wave properties may display orthorhombic symmetry the results provide insight for the interpretation of seismic data from the southeast tibetan plateau the n s to nw se polarized crustal anisotropy in the sibumasu and indochina blocks is caused by subvertically foliated mica and amphibole bearing rocks deformed by predominantly compressional folding and subordinate strike slip shear these blocks have been rotated clockwise 70 90 around the east himalayan syntaxis without finite eastward or southeastward extrusion in responding to progressive indentation of india into asia

tectonic amalgamation of the gaoligong shear zone and lancangjiang shear zone southeast of eastern himalayan syntaxis abstract the gaoligong shear zone glgsz and lancangjiang shear zone lcjsz are two major large scale shear zones southeast of eastern himalayan syntaxis ehs and play important roles in the accommodation of the intracontinental deformation in southeast asia the two shear zones which are mainly composed of high grade metamorphic rocks and have long been regarded as the precambrian basement of this area are gradually merged northward and become tectonically amalgamated from fugong to gongshan area structural and kinematic analyses reveal that the amalgamation area has experienced strongly partitioned dextral transpression n s trending tight to isoclinal folds sub vertical foliation and sub horizontal lineation are ubiquitously developed both within the shear zones and the carboniferous flysch sediments of baoshan block in between micro and macro kinematic indicators such as cs structures rotated porphyroclasts asymmetric shear folds sheath folds domino and boudin structures suggest that the shear sense of the glgsz and lcjsz is dextral in the amalgamation area comparative analyses of strata reveal that the baoshan block is aligned with south qiangtang block and the lanping simao block was aligned with north qiangtang block prior to the cenozoic large scale tectonic extrusion and rotation the amalgamation area which has progressively switched positions from northeast of ehs to east and southeast of ehs is just located at the neck of the large scale boudin of south qiangtang baoshan block a boudin model is proposed for the tectonic amalgamation of the glgsz and lcjsz from fugong to gongshan area in response to the continued northward convergence between indian plate and eurasian plate since early eocene resistance of south china block southeastward extrusion and clockwise rotation of baoshan block around ehs

paleomagnetism of eocene red beds in the eastern part of the qiangtang terrane and its implications for uplift and southward crustal extrusion in the southeastern edge of the tibetan plateau abstract a primary magnetic component with the acquisition time of 56 0 43 2 ma was isolated between 580 c and 685 c from the eocene gonjo and ranmugou formations in the eastern part of the qiangtang terrane tibetan plateau the tilt corrected site mean direction is d s 35 5 i s 29 3 k 45 9 95 3 2 the site mean inclination increased from 29 3 to 41 6 after multiple inclination shallowing corrections giving a paleopole of 57 9 n 192 1 e a 95 2 9 comparison of the paleogene paleomagnetic data for the qiangtang terrane and lhasa terrane reveals that both terranes experienced latitudinal crustal shortening before 54 43 ma indicating the uplift of southern and central tibet in the early eocene subsequently since 35 4 2 4 ma the north of the qiangtang terrane experienced 1300 410 km of crustal shortening indicating the uplift of the northern tibetan plateau the lhasa terrane and qiangtang terrane have not experienced further crustal shortening since the late eocene and the southeastern part of tibet cannot have provided abundant crustal material to accommodate the significant crustal southward extrusion in the southeastern edge of the tibetan plateau the crust of the tengchong terrane and shan thai block did not experience significant southward extrusion since the late oligocene early miocene the indochina block was situated in the north of the qiangtang terrane before the oligocene and since the early oligocene the indochina block began to experience southward extrusion from the north of the qiangtang terrane which absorbed part of the crustal shortening in the north of the qiangtang terrane

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

polystage deformation of the gaoligong metamorphic zone structures 40ar 39ar mica ages and tectonic implications abstract the gaoligong metamorphic zone is located southeast of the eastern himalayan syntaxis in western yunnan china the zone is characterized by four stages of deformation d1 d4 d1 structures record early compressive deformation during the indosinian orogeny which formed tight to isoclinal f1 folds of bedding with a penetrative s1 foliation developed parallel to fold axial planes mid crustal horizontal shearing during d2 resulted in overprinting of d1 structures d1 and d2 structures are associated with granulite facies metamorphism d3 doming resulted in late crustal thickening and the development of a regional nw se trending f3 antiform synchronous with or slightly subsequent to d3 deformation the zone experienced d4 ductile strike slip shearing resulting in its exhumation to shallow crustal levels and retrograde metamorphism granitic d4 mylonites predominantly yield 40 ar 39 ar mica ages of 15 16 ma indicating that d4 dextral strike slip shearing occurred in the miocene weakly deformed leucogranite and protomylonite yield 40 ar 39 ar ages of 10 11 ma suggesting that ductile strike slip shearing continued to the late miocene the new 40 ar 39 ar data indicate that escape related deformation along the gaoligong strike slip shear zone occurred in the miocene in association with recent geophysical studies and on the basis of the structural crystal preferred orientation cpo and geochronological data presented in this paper we suggest that the gaoligong metamorphic zone formed in response to intracontinental transpression in the southeast of tibet characterized as intense deformation and metamorphism at middle upper crustal levels

dynamics of the tengchong volcanic region in the southeastern tibetan plateau a numerical study abstract the constraints of surface heat flow and lithospheric structure were used to investigate the dynamics of the tengchong volcanic region based on thermal mechanical modeling three different boundary conditions representing three types of tectonic movements were modeled to discuss the thermal state and lithospheric deformation the compressive model shows that the subduction of the indian plate causes the upwelling of asthenosphere beneath the tengchong block in this process upwelling of the asthenosphere causes thinning of the lithosphere beneath the tengchong block however the surface heat flow of this model is not consistent with the observations the regional extension model shows that under the extension the asthenosphere upwells along the preexisting weak suture zone in the southeastern tibetan plateau the thickness of lithosphere is the thinnest along the suture zone and the surface heat flow is the highest however the extension time was found to generally need 10 15 myr to conform to the surface heat flow however this is not consistent with accepted geochronological data when a boundary condition from compression to extension is imposed both the surface heat flow and the lithospheric structure fit well with the observations the results show that the subduction of the indian plate leads to the upwelling of the asthenosphere which causes a thinned lithosphere beneath the tengchong block since the late miocene 8 5 ma the extension or extrusion has been predominant the thermal erosion of the lithosphere caused by upwelling of the asthenosphere renders the lithosphere even thinner along the bangong nujiang suture zone the upwelling of the asthenosphere provides an upward driving force and high temperature environment for the tengchong volcanic region these findings suggest that the origin of the tengchong volcanic region is caused by both the subduction of the indian plate and regional extension across the bangong nujiang suture zone

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

tectono magmatic evolution of the gaoligong belt southeastern margin of the tibetan plateau constraints from granitic gneisses and granitoid intrusions abstract the gaoligong belt is located in the southeastern margin of the tibetan plateau and is bound by the tengchong and baoshan blocks this paper presents new data from zircon geochronology geochemistry and whole rock sr nd pb hf isotopes to evaluate the tectonic evolution of the gaoligong belt the major rock types analysed in the present study are granitic gneiss granodiorite and granite they are metaluminous to peraluminous and belong to high k calc alkaline series laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of zircons from nine granitic rocks yielded crystallization ages of 495 487 ma 121 ma 89 ma and 70 63 ma the granitoids can be subdivided into the following four groups 1 early paleozoic granitic gneisses with high e nd t and e hf t values of 1 06 to 3 45 and 1 16 to 2 09 and model ages of 1 16 ga to 1 33 ga and 1 47 ga to 1 63 ga respectively their variable 87 sr 86 sr and pb values resemble the characteristics of the early paleozoic pinghe granite in the baoshan block our data suggest that the rocks were derived from the break off of the proto tethyan oceanic slab between the outboard continent and the baoshan block which induced the partial melting of mesoproterozoic pelitic sources mixed with depleted mantle materials 2 early cretaceous granodiorites with low e nd t and e hf t values of 8 92 and 4 91 with nd and hf model ages of 1 41 ga and 1 49 ga respectively these rocks have high initial 87 sr 86 sr 0 711992 and lower crustal pb values suggesting that they were derived from mesoproterozoic amphibolites with tholeiitic signature leaving behind granulite residue at the lower crust 3 early late cretaceous granites with low e nd t and e hf t values of 9 58 and 4 61 with nd and hf model ages of 1 43 ga and 1 57 ga respectively these rocks have high initial 87 sr 86 sr 0 713045 and lower crustal pb isotopic values these rocks were generated from the partial melting of mesoproterozoic metapelitic sources resulting from the delamination of thickened lithosphere following the closure of the bangong nujiang ocean and collision of the lhasa qiangtang blocks 4 late cretaceous to paleogene granitic gneisses with low e nd t and e hf t values of 4 41 to 10 and 5 95 to 8 71 nd model ages ranging from 1 08 ga to 1 43 ga and hf model ages from 1 53 ga to 1 67 ga respectively these rocks show high initial 87 sr 86 sr 0 713201 and 714662 and lower crustal pb values the data suggest that these rocks are likely related to the eastward subduction of the neo tethyan oceanic slab which induced partial melting of mesoproterozoic lower crustal metagreywacke the results presented in this study from the gaoligong belt offer important insights on the evolution of the proto tethyan bangong nujiang and neo tethyan oceans in the southeastern margin of the tibetan plateau

gas geochemistry of hot springs at the tengchong field southwest china controlled by the spatial distribution of magmatic chamber abstract the tengchong volcanic field located at the collision zone between the indian and eurasian plates is well known for its large scale holocene volcanic eruptions and extensive hydrothermal activities bubbling gases from eight geothermal springs at the tengchong field were collected and analyzed for their chemical and isotopic compositions 3he 4he 20ne n2 ar 13cch4 and 13cco2 the results show that the gas samples could be categorized into a group i dominated by n2 and a group ii with co2 as major component the air corrected 3he 4he ratios ranged from 0 17 ra to 4 76 ra and the calculated mantle contributions dramatically varied from 1 9 to 77 9 for group ii by contrast an invariant air corrected 3he 4he ratio of about 0 30 ra and a relatively constant mantle contribution of 4 0 to 5 0 was obtained for group i the sampling sites just on top of the magma chamber received significant mantle derived helium and magmatic gas components at the proximal site of the magma chamber 95 magmatic gas contributions the calculated n2 ar ratio of the hydrothermal endmember for group ii sample sites close to the magma chamber was 61 7 66 2 suggesting that the reaction zone temperature is between 223 c and 252 c the influence of the magma chamber decreases with increasing distance of the sampling sites from the chamber apex the sampling sites group i at the marginal area discharge gases with relatively low 3he 4he ratios and magmatic contributions 19 24 the temperature of the reaction zone for this group was estimated to be 74 c based on the n2 ar ratio of 42 this study provided important constraints to relate hydrothermal gas geochemistry directly with the spatial distribution of the underlying magma chamber plain language summary geochemical characteristics of gases discharged from hydrothermal systems are usually affected by deep magmatic processes shallow hot fluids circulation and water rock interactions in the reaction zone in this study we analyzed the gas abundances and isotopic compositions of hydrothermal gas discharged from the yunnan tibet geothermal belt we used a gas mixing model to quantify the contributions of mantle derived magmatic endmember and hydrothermal endmember the 3he 4he ratios magmatic contribution and temperature of the reaction zone decreased significantly with increasing distance from the magma chamber underneath the tengchong field highlighting the intimate relationships between gas transport hydrothermal circulation and the extent of the magma chamber

cenozoic clockwise rotation of the tengchong block southeastern tibetan plateau a paleomagnetic and geochronologic study abstract paleomagnetic data from 50 35 ma likely 40 ma mafic dykes in yunnan southeastern tibetan plateau cutting 115 ma granitoids record the rotation of the tengchong lhasa block around the east himalayan syntaxis ehs ti rich titanomagnetite and magnetite carry a primary magnetic component group1 a magnetic overprint resides in magnetite group2 likely induced by low grade metamorphism between 30 and 10 ma the tilt corrected overall mean directions are d i 89 8 35 1 for group1 and d i 33 3 41 4 for group2 these data imply a clockwise rotation of 87 87 3 12 5 of the tengchong block since remanence acquisition at 40 ma with respect to stable eurasia the average rotation rate of 2 18 0 31 myr is at the upper limit of the present day rotation rates around the ehs obtained from gps velocities and quaternary strain rates the remagnetized group2 indicates a poorly defined rotation of 31 31 2 32 9 our key results the detection of 87 clockwise rotation with high rotation rates following the india asia collision and a decrease in rotation rates during the miocene suggest that first the tengchong block rotated rapidly around the ehs synchronous with eastward tectonic escape of lithospheric blocks the later slower clockwise rotation similar to those recorded geodetically may be related to viscous flow of tibetan crust

flow directions in ash flow tuffs a comparison of geological and magnetic susceptibility measurements tshirege member upper bandelier tuff valles caldera new mexico usa this study concludes that the elongation axis k 1 of the ellipsoid of anisotropic magnetic susceptibility ams is a suitable proxy for flow axis in ashflow tuffs 153 oriented samples 176 specimens were studied from 18 sites in the 1 1 ma tshirege member of the bandelier tuff these sites are distributed around the valles caldera at distances of 5 25 km outside of the rim k 1 axes correlate well with postulated radial flow axes at 13 sites k 1 also agrees with measured geological flow indicators mainly imbricated larger clasts at 7 sites at 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredk 1 axes thek 1 axes correspond well with geological flow indicators indicating that the divergence of flow from the predicted radial flow pattern is real two major topographic buttresses are suggested as the cause of flow divergence for the tshirege ash flows the san pedro buttress northwest of the caldera and the san miguel buttress in the southeast in situk 1 axes plunge about 7 toward the source at two thirds of the sites therefore the plunge ofk 1 is a plausible in situ indicator for thedirection of flow multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash flow emplacement these observations raisre the question of how best to represent mean flow directions in ash flow sheets by eigenvector methods by vector sum methods or by modes a method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined imbrication determined in this way at one third of the sites dips toward the source i e up flow the minimum k 3 axis of the ams ellipsoid correlates with the flow foliation rather than with the larger clast imbrication the flow axes of ash flows correspond with thek 1 axes not with the declination ofk 3 axes as suggested by some authors initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction which is reversed with a mean ofd 173 5 i 38 4 95 3 4 n 18 this mean is not different at the 95 confidence level from that of earlier workers the mean pole at 098 0 e 74 8 n a 95 3 3 n 18 is about 15 far sided relative to the expected time averaged geomagnetic pole suggesting a history of emplacement too short to adequately average secular variation

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

seismic structure of the tengchong volcanic area southwest china from local earthquake tomography article i nfo weperformedalocalearthquaketomographytoimagethecrustofthetengchongvolcanicareainsouthwestern china using p wave arrival data from a temporary network and permanent stations the objective is to deter mine the magma sources of the volcanic area and the seismic structure of two m 7 earthquakes in the longling area south of tengchong the result reveals a correlation between the velocity structures and the volcanic activ ities from late miocene to holocene a prominent low velocity zone is observed beneath the central volcanic area that is cored at 10 20 km depths and extends down to 30 km depth with a lateral extent of 20 30 km we infer that this unusual low velocity zone represents a magma source of the heat flows for the volcanic erup tion during pleistocene and holocene close to it a high velocity zone appears beneath the eastern volcanic area and itislikelyto reflect solidifiedmagma intrusionsand high densityremnants withinthe cooled volcanicchan nel prior topleistocene in the m 7 earthquake area theuppercrustalstructureshows evidentvariationsacross the longling fault and the nu river fault bounded by the two fault zones the gaoligong metamorphic belt and the baoshan block are imaged by high velocities that are consistent with their high strength in the structures on the contrary low velocities are imaged in the area between the longling fault and the nu river fault implying a decreaseof the strength probably caused byigneous intrusions itwas thelateral variation intherheologic struc ture that led to the uneven stress accumulations across these fault zones and created tectonic conditions for the seismic ruptures of the two m 7 earthquakes in the longling area

the active tectonics of the eastern himalayan syntaxis and surrounding regions source parameters of 53 moderate sized earthquakes obtained from the joint inversion of regional and teleseismic distance long period body waves provide the data set for an analysis of the style of deformation and kinematics in the region of the eastern himalayan syntaxis focal mechanisms of eastern himalayan events show oblique thrust consistent with the n ne directed movement of the indian plate as it underthrusts a boundary that strikes at an oblique angle to the direction of convergence earthquakes near the sagaing fault show strike slip mechanisms with right lateral slip earthquakes on its northern splays however indicate predominant thrusting evidence that the dextral motion on the sagaing fault which accommodates a portion of the lateral motion between india and southeast asia terminates in a zone of thrust faulting at the eastern himalayan syntaxis remaining motion between india and southeast asia is accommodated in a zone of distributed shear in east burma and yunnan manifested by strike slip and oblique normal faulting east west extension crustal thinning and clockwise rotation of crustal blocks we determined strain rates throughout the region with a moment tensor summation using 25 years modern and 85 years modern and historic of earthquake data we matched the observed strains with a fifth order polynomial function and from this we determined both the velocity field and rotations with respect to a specified region velocities calculated relative to south china stationary show that the entire area extending from 20 n 36 n within deforming asia yunnan western sichuan and east tibet constitutes a distributed dextral shear zone with clockwise rotations up to 1 7 m y maximum in the region of the eastern syntaxis proper integrated strains across this zone relative to south china stationary show 38 mm yr 12mm yr of north directed motion at the himalaya remaining plate motion relative to south china fixed must be taken up by the underthrusting of india beneath the lesser himalaya strike slip motion on the sagaing fault and intraplate ne directed shortening within ne india as well as ne directed shortening within the eastern syntaxis proper 10 mm yr 2 mm yr of relative right lateral motion between india and southeast asia is absorbed in the region between the sagaing and red river faults 94 e 100 e it is the clockwise vorticity relative to south china associated with the deformation in yunnan east tibet and western sichuan that provides the relative north directed motion of 38 12 mm yr at the himalaya not all of the deformation is accommodated in right lateral shear between india and south china and between east tibet and south china velocity gradients exist that are parallel to the trend of the shear zone relative to a point within western sichuan 32 n 100 e the velocity field shows that the yunnan crust is moving s se at rates of 8 10 mm yr relative to south china there is no eastward expulsion of crustal material beyond the eastern margin of the tibetan plateau

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

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

amount and style of late cenozoic deformation in the liupan shan area ningxia autonomous region china the structures of the liupan shan area are characterized by numerous active thrust and strike slip faults that suggest thin skinned deformation the structural history of this area can be divided into three phases that probably overlap one another in time and are parts of a single protracted deformation the oldest cenozoic deformational phase occurred probably between late pliocene and early quaternary time and produced some of the folds and thrust faults in the liupan shan and yueliang shan during this phase deformation was the result of approximately n50 e shortening and the amount of shortening seems to have been about 1 2 km the second phase of deformation was dominated by left lateral strike slip faulting left slip on the n60 w striking haiyuan fault zone and shortening on north south trending structures shortening was associated with a transfer of the left slip displacement on the haiyuan fault zone to shortening in areas farther east shortening occurred by thrust faulting in the liupan shan and xiaoquan shan and by folding in the madong shan during this phase the orientation of shortening changed to n60 w the average amount of shortening on the north south trending folds in the madong shan is about 6 3 7 8 km most of the shortening on the liupan shan and xiaoguan shan thrust faults also occurred during this phase and amounted to a minimum of 4 8 6 3 km and 6 6 7 6 km respectively also with an orientation of n60 w during the third phase of deformation about 1 1 5 km of late pleistocene to recent left slip occurred on the xiaokou fault which was transferred into oblique left slip thrusting in the liupan shan at this time deformation in the madong shan and xiaoguan shan ceased or was reduced to a very slow rate the present active left slip on the haiyuan fault zone is accommodated by shortening in the liupan shan area the total displacement along the haiyuan fault is essentially the same as the total amount of shortening in the liupan shan area the sequence and interaction of strike slip and thrust faults in the liupan shan area seem to apply to the folds and thrust faults farther north in the southern ningxia region thus the northeastern margin of the tibetan plateau appears to grow by shortening oriented northeast and by left slip faulting that transfers material from farther to the west the total left slip in the entire southern ningxia region probably is less than 20 25 km and may be absorbed by shortening within this region thus the eastward translation of crustal fragments in the northern part of the tibetan plateau may not extend east of southern ningxia and if large scale eastward displacement has occurred it must lie farther south

cenozoic deformation in western yunnan china myanmar border in the present paper we describe ductile and brittle deformation styles in western yunnan and ne myanmar using field data and landsat 7 imagery we show that this complex area located at the northern termination of sunda plate three rivers area was wedged during the tertiary between the left lateral ailao shan chong shan metamorphic belts to the east and the right lateral shan scarp gaoligong metamorphic belt in west this triangular region therefore underwent the effects of these continental size ductile strike slip faults separating major blocks with a dominant ew to ene compression since the late miocene date of the reversal of motion along the rrf the incipient eastward motion of the sunda block and the persisting right lateral motion along its western boundary sagaing fault created n s compression and e w to wnw extension underlined by left lateral transtension along the wanding nanting fault zones at the same time the diangcan shan situated along strike the ailao shan metamorphic belt was slightly impinged by the blocks extruded from the syntaxis and exhumed again from the early pliocene in accordance with this late and still active state of stress q 2004 elsevier ltd all rights reserved

fault slip and gps velocities across the shan plateau define a curved southwestward crustal motion around the eastern himalayan syntaxis characterizing the 700 km wide system of active faults on the shan plateau southeast of the eastern himalayan syntaxis ehs is critical to understanding the geodynamics and seismic hazard of the large region that straddles neighboring china myanmar thailand laos and vietnam here we evaluate the fault styles and slip rates over multi timescales reanalyze previously published short term gps velocities and evaluate slip rate gradients to interpret the regional kinematics and geodynamics that drive the crustal motion relative to the sunda plate gps velocities across the shan plateau define a broad arcuate tongue like crustal motion with a progressively northwestward increase in sinistral shear over a distance of 700 km followed by a decrease over the final 100 km to the syntaxis the cumulative gps slip rate across the entire sinistral slip fault system on the shan plateau is 12 mm yr our observations of the fault geometry slip rates and arcuate southwesterly directed tongue like patterns of gps velocities across the region suggest that the fault kinematics is characterized by a regional southwestward distributed shear across the shan plateau compared to more block like rotation and indentation north of the red river fault the fault geometry kinematics and regional gps velocities are difficulty to reconcile with regional bookshelf faulting between the red river and sagaing faults or localized lower crustal channel flows beneath this region the crustal motion and fault kinematics can be driven by a combination of basal traction of a clockwise southwestward asthenospheric flow around the ehs and gravitation or shear driven indentation from north of the shan plateau

tectonics and paleomagnetic rotation pattern of yunnan 24 n 25 n china gaoligong fault shear versus megablock drift

improving curvature analyses of deformed horizons using scale dependent filtering techniques fractures which are common structural heterogeneities in geological folds and domes impact the charge seal and trapping potential of hydrocarbon reservoirs because of their effects on reservoir quality the numerical prediction of fractures has recently been the focus of petroleum geoscientists a horizon s curvature is commonly used to infer the state of deformation in those strata it is assumed that areas of elevated calculated curvatures underwent elevated deformation resulting in a concentration of fractures and faults there usually curvatures are calculated from spatial data after sampling the continuous horizon at discrete points this sampled geometry of the horizon includes surface undulations of all scales which are then also included in the calculated curvatures including surface undulations of all scales in the curvature analysis leads to noisy and questionable results we argue that the source data must be filtered prior to curvature analysis to separate different spatial scales of surface undulations such as broad structures faults and sedimentary features only those surface undulations that scale with the problem under consideration should then be used in a curvature analysis for the scale dependent decomposition of spatial data we test the suitability of four numerical techniques fourier spectral analysis wavelet transform filtering singular value decomposition factorial kriging on a seismically mapped horizon in the north sea for surfaces sampled over a regular grid e g seismic data fourier spectral analysis extracts meaningful curvatures on the scale of broad horizon features such as structural domes and basins

late cenozoic geological evolution of the foreland basin bordering the west kunlun range in pulu area constraints on timing of uplift of northern margin of the tibetan plateau 1 with an average elevation of 5000 m the west kunlun range marks northwestern margin of the tibetan plateau and formed as an orogen in response to the collision of india and asia 50 ma ago its history of uplift and erosion in the late cenozoic is recorded in a unique sedimentary sequence exposed through the highest terrace along the southern margin of the tarim basin in pulu area the terrace is composed of coarse grain conglomerate at the bottom alkaline enriched volcanic rocks in the middle and eolian sediments on the top the underlying basement rocks are formed by neogene rocks and paleozoic granite named the xiyu conglomerate the coarse grained conglomerate is assigned a depositional age in the late pliocene and the early pleistocene 3 4 1 6 ma and generally considered to be the products of rapid uplift of the tibetan plateau to reveal the relations between uplift erosion and sedimentation we have collected samples of granite overlain by the xiyu conglomerate for dating the fission track age of apatite the fission track ages date the absolute time of cooling through the track retention temperature of the granite within the west kunlun range to be miocene to early pliocene 20 4 8 ma the cooling event was coeval with the north verging thrusting along the northern boundary fault and the associated foreland basin deposition suggesting that the west kunlun range once underwent significant tectonic uplift in the neogene in contrast to the underlying tertiary foreland basin strata the xiyu conglomerate thins toward the west kunlun range and contains granite pebbles of cooling ages of 93 18 and 12 ma our study suggests that the primary cause for accumulation of the xiyu conglomerate and the correspondent sediments is the increase of erosion and sedimentation rates after the main pulse of tectonic uplift due to quaternary climate change

exhumation of west sundaland a record of the path of india abstract the indian plate commenced its northward migration towards eurasia in the early cretaceous the lateral effect of this migration on the western edge of the sunda plate in southeast asia still remains equivocal in order to assess this effect we evaluate several key sectors characterized by deep crustal exhumation along a n s transect from the southern malay peninsula to the east himalayan syntaxis the evaluation is aided by a structural analysis of vertical movements and basin development five major metamorphic domes with similar geodynamic evolution maximum p t burial conditions and exhumation are studied exhumation of these domes migrated with time between late cretaceous in the stong complex north malaysia in the south and late miocene in the gaoligong shear zone south china in the north as documented by published work and our new fission track data presented herein deformation is characterized by a n s oriented extension that followed the more regional e w oriented plate tectonic shortening creating local core complexes and syn kinematic magmatism in the footwall of crustal scale detachments which displays a consistent temporal northward migration the n s extension was associated with the onset of hanging wall deposition in the sedimentary basins of western sundaland e g malay sumatra and thai basins during continuous exhumation of the footwall to upper brittle levels our multifaceted analysis of structural and thermochronological data shows a similar succession of tectonic thermal and sedimentary events in west sundaland that was driven by the gradual northward migration of india starting from cretaceous times we infer that the principal mechanism was driven by the subduction of an excess topography of greater india rifted continental margin during its underplating resulting in uplift thermal anomalies extensional exhumation and associated subsidence