post rift tectonic history of the songliao basin ne china cooling events and post rift unconformities driven by orogenic pulses from plate boundaries

intraplate extension prior to continental extrusion along the ailao shan red river shear zone left lateral movement of the ailao shan red river shear zone lends support to the hypothesis of continental extrusion resulting from the collision of india with asia our new observations from northwestern yunnan china and northwestern vietnam on different sides of the shear zone demonstrate that the sinistral offset was 600 km according to correlations of permian triassic flood basalt successions and late paleogene highly potassic mafic magmas we conclude that the shear was propagating on the south china continental margin and does not correspond to a suture between south china and indochina furthermore the highly potassic magmas were emplaced from ca 40 to 30 ma before the shear movement which was caused by the late oligocene to early miocene ca 27 22 ma extrusion activity this suggests that a late eocene to early oligocene intraplate extension possibly induced by delamination of thickened continental lithosphere took place in northwestern yunnan or eastern tibet as a response to the india asia collision this extension and sea floor spreading of the south china sea that began ca 30 ma could have accounted for the initiation of the ailao shan red river shear zone

deformation fabrics and strain localization mechanisms in graphitic carbon bearing rocks from the ailaoshan red river strike slip fault zone abstract graphitic carbon bearing rocks generally occur in low to high grade metamorphic units in many brittle faults graphitic carbon is often associated with gouge or low grade metamorphic rocks whereas in ductile faults graphitic carbon commonly occurs in marble schist or gneiss carbonaceous material gradually transforms from an amorphous into an ordered crystalline structure by increasing thermal metamorphism the degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock in this contribution based on detailed field observations the variably deformed and metamorphosed graphitic gneisses to phyllites located within the footwall and hangingwall unit of the cenozoic ailaoshan red river strike slip shear zone are studied according to lithological features and temperatures determined by raman spectra of carbonaceous material these graphitic rocks and deformation fabrics are divided into three types type i is represented by medium grade metamorphism and strongly deformed rocks with an average temperature of 509 c and a maximum temperature of 604 c type ii is affected by low grade metamorphism and deformed rocks with an average temperature of 420 c type iii is affected by lower grade metamorphism and occurs in weakly deformed undeformed rocks with an average temperature of 350 c slip localized micro shear zones and laterally continuous or discontinuous slip planes constituted by graphitic carbon aggregates are developed in types i and ii the electron back scattered diffraction ebsd lattice preferred orientation lpo patterns of graphitic carbon grains were firstly observed in comparison with lpo patterns of quartz and switch from basal rhomb to prism slip systems which indicate increasing deformation temperatures comparison of quartz and graphite lpos indicates that graphite lpos show higher temperature conditions according to the graphitic slip planes micro shear zones with grain size reduction and mylonitic foliation constituted by graphitic carbon minerals we also propose that the development of fine grained amorphous carbon plays an important role in rheological weakening of the whole rock during progressive ductile shearing

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

contrasting exhumation histories along a crustal scale strike slip fault zone the eocene to miocene ailao shan red river shear zone in southeastern tibet abstract four metamorphic massifs in southeastern tibet the xuelong shan xls diancang shan dcs ailao shan als and day nui con voi dncv have been suggested to constitute coherent parts of the ailao shan red river asrr shear zone this study details the cooling exhumation histories of the crustal scale shear zone by determining the cooling paths of the als massif and comparing these paths to those of the dcs massif we show that the different parts of the als massif have experienced two stages of diachronous cooling histories the two cooling stages of the als massif i e an early rapid cooling of ca 45 715 c myr and a late slow cooling of 10 17 c myr differ significantly from the cooling of the dcs massif along the same shear zone which featured an early slow cooling of 11 17 c myr and a late rapid cooling of 30 140 c myr this study confirms that differing cooling exhumation histories exist along the same crustal scale shear zone from the contrasting cooling exhumation histories we would argue that the als and dcs massifs are isolated units with different tectono thermal histories during the oligo miocene tectonic evolution of southeastern tibet

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

deformation partitioning shear zone development and the role of undeformable objects abstract the formation of a mylonite zone by homogeneous progressive simple shear is highly unlikely because heterogeneous strain of grains with different compositions causes deformation partitioning and results in progressive inhomogeneous simple shear or non coaxial progressive bulk inhomogeneous shortening however the presence of rigid bodies in a zone of rock undergoing bulk simple shear spreads and homogenizes the stress field such that the instantaneous displacement field is essentially homogeneous at a scale up to at least four times the diameter of the rigid object that is the portion of rock surrounding the rigid body deforms by homogeneous progressive simple shear and the rigid object is forced to rotate this has considerable implications for the rotation or lack thereof of unstrained porphyroclasts and porphyroblasts and hence the information such grains preserve about the sense of shear on their margins or through inclusion trails geometric relationships between porphyroclasts or porphyroblasts and the surrounding matrix that are superficially similar can indicate exactly the opposite sense of shear depending on whether the porphyroclasts or porphyroblasts have or have not rotated leading to considerable problems in interpretation of the bulk movement in a shear zone resolution of these relationships enables ready distinction of whether the deformation history involved progressive bulk inhomogeneous shortening or progressive simple shear in particular these results have considerable implications for the origin of blueschist minerals preserved in garnet porphyroblasts via the roles of strain softening and hardening during mylonitization due to the destruction of feldspar porphyroclasts and growth of garnet porphyroblasts respectively

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

neoproterozoic granitoids along the ailao shan red river belt zircon u pb geochronology hf isotope analysis and tectonic implications abstract the ailao shan red river belt asrrb is a complex tectonic collage of archean to miocene geological units located between two major tectonic domains i e the south china domain to the east and the tethys domain to the west although general agreements have been reached on that the ailao shan suture zone along the asrrb represents a silurian to middle triassic subsidiary ocean in the eastern paleo tethyan system and the ailao shan red river shear zone within the belt occurred as the northeastern boundary of the cenozoic extrusion of the indochina block during the indian eurasian collision the precambrian tectonic attributes of the belt remain controversial this study presents new zircon u pb ages whole rock geochemical and hf isotopic data of neoproterozoic granitoids along the asrrb neoproterozoic granitoids along the asrrb are located to the east of the jinshajiang ailao shan suture zone samples from the granitoids have zircon 206 u 238 pb ages between 799 ma and 724 ma implying the existence of extensive neoproterozoic granitic magmatism along the asrrb their basement rocks share similar characteristics e g paleo to meso proterozoic protolith ages to those of the western yangtze block evidences suggest that the neoproterozoic intrusions and their metamorphic basement rocks along the asrrb were derived from the southwest margin of the yangtze block zircon ehf t values of the granitoid samples range from 10 22 to 0 64 with hf crustal model ages of 1632 2 2335 9 ma it is suggested combining the present results and regional geology data that the neoproterozoic granitic magmatism along the asrrb is dominantly of crustal origin and contributions from mantle sources are common they are possibly attributed to partial melting of ancient lower crust and addition of mantle fluids related to oceanic subduction the results support a scenario that arc magmas were generated by continued oceanic subduction beneath the southwestern margin of the yangtze block instead of the northeastern margin of the indochina block lasted from 799 ma to 724 ma

the geometry of the north anatolian transform fault in the sea of marmara and its temporal evolution implications for the development of intracontinental transform faults the north anatolian fault is a 1200 km long strike slip fault system connecting the east anatolian convergent area with the hellenic subduction zone and as such represents an intracontinental transform fault it began forming some 13 11 ma ago within a keirogen called the north anatolian shear zone which becomes wider from east to west its width is maximum at the latitude of the sea of marmara where it is 100 km the marmara basin is unique in containing part of an active strike slip fault system in a submarine environment in which there has been active sedimentation in a paratethyan context where stratigraphic resolution is higher than elsewhere in the mediterranean it is also surrounded by a long civilised rim where historical records reach well into the second half of the first millennium bce before common era in this study we have used 210 multichannel seismic reflexion profiles adding up to 6210 km profile length and high resolution bathymetry and chirp profiles reported in the literature

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

nucleation and growth of myrmekite during ductile shear deformation in metagranites myrmekite is extensively developed along strain gradients of continuous lower amphibolite facies shear zones in metagranites of the gran paradiso unit western alps to evaluate the role of stress strain energy and fluid phase in the formation of myrmekite we studied a sample suite consisting of weakly deformed porphyric granites wdgs foliated granites fgs representative of intermediate strains and mylonitic granites mgs in the protolith most k feldspar is microcline with different sets of perthite lamellae and fractures in the wdgs abundant quartz oligoclase myrmekite developed inside k feldspar only along preexisting perthite lamellae and fractures oriented at a high angle to the incremental shortening direction in the wdgs stress played a direct role in the nucleation of myrmekites along interfaces already characterized by high stored elastic strain because of lattice mismatch between k feldspar and albite in the fgs and mgs k feldspar was progressively dismembered along the growing network of microshear zones exploiting the fine grained recrystallized myrmekite and perthite aggregates this was accompanied by a more pervasive fluid influx into the reaction surfaces and myrmekite occurs more or less pervasively along all the differently oriented internal perthites and fractures independently of the kinematic framework of the shear zone in the mgs myrmekite forms complete rims along the outer boundary of the small k feldspar porphyroclasts which are almost completely free of internal reaction interfaces therefore we infer that the role of fluid in the nucleation of myrmekite became increasingly important as deformation progressed and outweighed that of stress mass balance calculations indicate that in al si conservative conditions myrmekite growth was associated with a volume loss of 8 5 this resulted in microporosity within myrmekite that enhanced the diffusion of chemical components to the reaction sites and hence the further development of myrmekite

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

structural evolution of the day nui con voi metamorphic complex implications on the development of the red river shear zone northern vietnam the day nui con voi dncv metamorphic complex in north vietnam is the southernmost high grade metamorphic zone along the nw se trending red river shear zone rrsz in indochina the rrsz was considered as a classical large scale continental strike slip fault that had played a significant role in the continental extrusion of southeast asia since the collision of india and eurasia earlier ideas determined the rrsz as a steep shear zone that penetrated the entire lithosphere both metamorphism and structures within rocks along the dncv metamorphic complex have been previously thought to be formed syn tectonically by left lateral shearing of the rrsz during the oligocene miocene continental escape tectonics however our meso and microstructural re examination of this region shows that these metamorphic rocks were formed during earlier tectonic episodes unrelated to strike slip shearing high angle to near orthogonal overprinting fabrics indicated that this region recorded three episodes of ductile deformation followed by brittle faulting events with different intensity spanning from the triassic to the tertiary d1 is preserved as nw se striking upright folds under garnet grade regional metamorphism during the triassic indosinian orogeny as south china block amalgamated with the indochina block the large scale horizontal d2 folds with a dominant top to n nw bottom to s sw sense of shear and sub horizontal fold axial planes suggest that the dncv metamorphic complex remained at midcrustal depths since the indosinian orogeny the youngest ductile deformation event d3 refolded d2 recumbent folds into a dome and uplifted the dncv as lower temperature fabrics s3 indicated steep mylonite zones with left lateral kinematic indicators and brittle faulting were developed on both limbs of the dome along the steep song hong and song chay faults during left lateral movement of the rrsz our new spatial temporal and kinematic correlations of metamorphic fabrics within the dncv metamorphic complex support the suggestion that the rrsz developed after regional metamorphism and remained purely a crustal fault the complicated deformation history recorded within the dncv metamorphic complex provides an alternative interpretation and suggests that crustal scale strike slip faults such as the rrsz need not root from the mantle

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

late triassic paleomagnetic result from the baoshan terrane west yunnan of china implication for orientation of the east paleotethys suture zone and timing of the sibumasu indochina collision abstract in order to better understand the paleogeographic position of the baoshan terrane in the northernmost part of the sibumasu block during formation of the pangea supercontinent a paleomagnetic study has been conducted on late triassic basaltic lavas from the southern part of the baoshan terrane in the west yunnan region of southwest china following detailed rock magnetic investigations and progressive thermal demagnetization stable characteristic remanent magnetizations chrms were successfully isolated from late triassic niuhetang lava flows the chrms are of dual polarity and pass fold and reversal tests with magnetic carriers dominated by magnetite and subordinate oxidation induced hematite we thus interpret them as a primary remanence this new paleomagnetic result indicates that the baoshan terrane was located at low paleolatitudes of 15 n in the northern hemisphere during late triassic times together with available paleomagnetic data from the baoshan terrane and surrounding areas a wider paleomagnetic comparison supports the view that the east paleotethys ocean separated the sibumasu and indochina blocks and closed no later than late triassic times we argue that the currently approximately north to south directed changning menglian suture zone is very likely to have been oriented nearly east to west at the time of the sibumasu indochina collision

exhumation of the diancang shan metamorphic complex along the ailao shan red river belt southwestern yunnan china evidence from 40ar 39ar thermochronology abstract exhumation of the high grade metamorphic rocks from deep to shallow crustal levels in the diancang shan dcs massif is evident by the temporal transition from shearing and mylonitization at the amphibolite facies in the lower to middle crust through retrograde ductile brittle faulting at greenschist facies in the middle crust and brittle faulting near the surface new 40ar 39ar ages of amphibole muscovite biotite and k feldspar mostly from mylonitic rocks help constrain the thermal evolution of the massif during its exhumation the thermochronologic studies have shown at least three stages of exhumation and cooling from late oligocene to pliocene e g 28 13 ma 13 4 ma and 4 0 ma respectively the initiation of the unroofing history of the dcs massif resulted from ductile left lateral shearing along the ailao shan red river shear zone asrr since the late oligocene diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history of the massif the first stage of exhumation might have stopped due to the cessation of the left lateral shearing at ca 21 ma although cooling continued until 13 ma ago to relatively low temperature conditions the second and third stages of cooling started from 13 ma and lasted until the recent active faulting the diversity of cooling rates during the second stage from 13 to 4 ma suggests differences in exhumation rates at various localities ductile to brittle shearing along the eastern flank retrograde normal shear zone is the best explanation for the exhumation during this stage the inhomogeneous cooling and exhumation of the lower plate of the normal fault zone possibly resulted from the tilting of the lower plate or differential exhumation of slabs in the lower plate during the third stage cooling and exhumation of the dcs massif since 4 ma ago is recognized when higher temperature cooling paths are extended and plotted at a lower temperature of about 16 c the present day average surface temperature therefore the diachronous cooling and exhumation continuously spanned to the surface the tectonic exhumation of the dcs massif constitutes a part of the tectono thermal evolution and diachronous exhumation of the metamorphic complexes in the fan shaped area bounded broadly in se asia by the red river fault zone and sagaing fault zone since 36 ma extrusion induced strike slip shearing and rotation associated normal faulting played important roles in the diachronous cooling and exhumation of the dcs massif and other metamorphic complexes in se asia

ar ar and fission track ages in the song chay massif early triassic and cenozoic tectonics in northern vietnam the song chay massif is the northeasternmost metamorphic complex in vietnam to the east of the red river shear zone it shows a large antiformal structure involving orthogneisses and migmatites overlain on its northern flank by muscovite bearing marbles an e w striking fault bounds the dome to the south kinematic indicators along a s n section reveal top to the n shear sense along the interface between the orthogneissic core and the overlying metasediments radiometric ages were obtained by the 40ar 39ar method using purified mica separates across the dome ages range from 236 ma at the southern edge to 160 ma in the core attesting to a strong imprint in the early triassic time a clear difference is seen between these mesozoic ages and the eocene to miocene ages from 40 to 24 ma that obtained in the nearby red river shear zone using the same method these data show that the song chay massif was already high in the crust when the high temperature deformation of the red river shear zone took place the final exhumation of the song chay orthogneiss constrained by fission track analysis on samples along the same transect occurred during the early miocene and could be interpreted as the consequence of a first normal sense of motion along the fault which bounds the massif to the south timing is similar to that of exhumation in the red river shear zone

4 d evolution of se asia s mantle from geological reconstructions and seismic tomography abstract how the collision between india and asia is related to processes deeper in the mantle is unclear here we compare geological reconstructions of block motions within asia since 50 ma with the tomographically imaged three dimensional 3 d morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure past positions of the convergent margin show remarkable similarities with slab geometry at specific depths the striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision the slab contours match the progressive deformation of asia s margin including india s indentation and sundaland s extrusion ever since the onset of collision the indian plate appears to have overridden its own sinking mantle and it does not seem at present to underthrust tibet significantly north of the zangbo suture if correct this observation would provide further evidence against models of plateau build up involving indian lithosphere the tomographic images beneath india confirm that asian deformation has absorbed at least 1500 km of convergence since collision began from the match between the southeastward motion of sundaland between 40 and 20 ma and the principal change in slab structure between 700 and 1100 km depths we infer that lateral advection in the mantle is small and that the sinking rate beneath sunda was 2 cm yr in the lower mantle and 5 cm yr above the transition zone

thermochronological evidence for the movement of the ailao shan red river shear zone a perspective from vietnam in order to explore the timing of strike slip movement along the ailao shan red river shear zone an 40ar 39ar thermochronological study of the day nui con voi metamorphic massif in northern vietnam was undertaken the massif exposed in the southeastern segment of the ailao shan red river shear zone reveals a rapid cooling in the early miocene 25 21 ma after a very slow cooling ca 34 25 ma the slow cooling period most likely resulted from a geothermal perturbation in the lithosphere owing to the late paleogene 40 30 ma extension in eastern tibet and western yunnan china the rapid cooling consistent with evidence of a wider rapid cooling span from 27 to 17 ma compiled from the entire ailao shan red river shear zone constrains the duration of left lateral shearing which eventually offset indochina from south china by about 600 km the time constraints we have established reinforce the argument that the onset of the ailao shan red river shear zone postdates the opening of the south china sea that began ca 30 ma this result highlights the necessity for reevaluating the cenozoic tectonic models of southeast asia

miocene structural evolution and exhumation of the ximeng dome in yunnan southeastern tibet implications for intraplate deformation during extrusion of the sundaland block abstract the ximeng complex is located in the eastern shai thai block a part of the extruding sundaland block in southeastern tibet the complex is mainly composed of neoproterozoic medium grade metamorphic rocks and early paleozoic granite in the core surrounded by paleozoic low grade metamorphic rocks as a cover the two structural units are separated by a tectonic contact tdc detailed structural analysis reveals that the structural framework of the ximeng complex is a dome structure and the complex experienced a primary and progressive shearing during doming the rheological stratification led to the differential behavior of rocks from different stratigraphic and crustal levels during shearing zircon u pb ages of the laojiezi granites in the core range from 465 50 2 70 to 430 37 0 93 ma the cooling path from 40 ar 39 ar and apatite fission track data indicates that the complex experienced two stages of cenozoic cooling i e an early rapid cooling and a subsequent slow cooling the early rapid cooling and exhumation of the complex are attributed to doming and accompanied by middle to upper crustal flow from ca 23 to 20 ma shearing cooling and exhumation of the middle to lower crustal rocks are widely distributed along the boundary fault zones i e the ailao shan red river shear zone and the sagaing shear zone of the extruding sundaland block and within the triangular area between them the doming ductile shearing and exhumation of the ximeng complex highlight the importance of intraplate deformation coeval with indian eurasian collision localized crustal flow within the sundaland block is possibly an important process during the extrusion of the sundaland block

questions about myrmekite in deformed rocks abstract several questions about the development of myrmekite in deformed felsic and metapelitic rocks remain unanswered although a general relationship between deformation and myrmekite appears to be well established the fact that myrmekite grows into relatively non deformed k feldspar while being simultaneously deformed and recrystallized at the rear of the growing lobes suggests that strain energy may not be a major contributor to the advance of the growth interface of the myrmekite colony furthermore because myrmekite typically nucleates on existing plagioclase rather than in k feldspar strain energy may not contribute directly to nucleation of myrmekite either at least in many instances however strain energy probably contributes indirectly by facilitating access of fluids to growth sites thereby altering the local chemical environment and so promoting development of myrmekite because myrmekite recrystallizes readily in deformed felsic rocks it is one of the main contributors to the development of folia

a high resolution late neogene geochemical record of the southeastern margin of the tibetan plateau constraints on dali fault system activity and uplift of the diancang shan massif abstract the dali basin located northeast of the diancang shan massif is tectonically controlled by the dali fault system located along the southeastern margin of the tibetan plateau the sediments in the dali basin thus record the activity of the dali fault system and uplift of the diancang shan massif during the late neogene period in this study we present the chemical compositions and bulk mineralogical characteristics of fine grained sediment samples collected from the dasongping section in the dali basin spanning an interval from 7 6 to 1 8 ma mineral assemblages and geochemical data indicate that the sediment provenance in dali basin was a distally sourced weathered material from 7 6 to 4 2 ma and changed to a locally sourced bedrock after 4 2 ma this suggests that the dali basin was an open lake from 7 6 to 4 2 ma and changed to a closed lake at 4 2 ma the main reason for this change was intensified normal fault activity in the dali fault system at 4 2 ma that resulted in the isolation of the dali basin and the infilling of local bedrock around the diancang shan massif within the dali basin late pliocene global cooling marked by the expansion of northern hemisphere glaciation further intensified the uplift of the diancang shan massif at 3 6 ma which exposed paleogene conglomerates east of the dali basin since 2 7 ma the dali fault system has been dominated by normal extensional processes the enhanced reactivation resulted in the rapid uplift of the diancang shan massif and the rapid infill of the dali basin by coarse grained sediments

clockwise rotation of the red river fault inferred from paleomagnetic study of cretaceous rocks in the shan thai malay block of western yunnan china more than 150 samples were collected at 23 sites from the lower cretaceous jingxing formation near the city of yongping 25 5 n 99 5 e which is located on the west side of the red river fault sixteen sites have characteristic directions with a high temperature component above 500 c the high temperature component of magnetization from twelve sites is of pre fold origin and reveals clockwise deflection in declination d 42 0 i 51 1 and 95 15 7 the easterly declination of more than 40 at yongping is consistent with the cretaceous paleomagnetic direction d 45 of chuxiong 25 n 101 5 e which is located on the east side of the red river fault both areas were subjected to about 25 clockwise rotation with respect to the eastern part of the yangtze block since cretaceous time we conclude that the red river fault was rotated through25 16 with respect to the eastern part of the yangtze block associated with rotation of the yongping and chuxiong areas removal of the rotation from the red river fault indicates that the latter and the jinsha suture formed a straight line along n55 w s55 e within the asian continent from vietnam to the tibetan plateau in the present coordinate system during the cretaceous the linear feature of the red river fault and jinsha suture was probably deformed to the present curved shape as a result of collision of the indian continent with the asian continent

evolution of the miocene ailaoshan orogenic gold deposits southeastern tibet during a complex tectonic history of lithosphere crust interaction the orogenic gold deposits along the nnw trending ailaoshan shear zone are formed during miocene continental collision after a complex history of neoproterozoic subduction late triassic amalgamation between the indochina and south china blocks after closure of the paleo tethyan ocean and oligocene eocene continental scale shearing related to the indian eurasian continental collision as a result the eastern neoproterozoic basement with ductile shear zones was thrust over the western metasedimentary rocks and paleo tethyan ophiolites affected by brittle faulting these tectonically juxtaposed successions were underlain by lithosphere metasomatized in the neoproterozoic the gold hosting western succession is characterized by tightly folded silurian to permian metasedimentary rocks overlain by gently folded late triassic metasedimentary rocks and cut by secondary nw trending shear zones this crustal architecture controlled migration of ore fluid towards the cessation of regional ductile deformation at ca 22 ma with major ductile shear zones serving as the main conduit tight folds and jogs or intersections on subsidiary brittle shear zones as the fluid trap and late triassic rocks as the seal gold rich rims on disseminated gold poor sedimentary pyrite with a limited 34s range from 3 to 3 pyrite he ar isotope ratios and the timing of mineralization within retrograde metamorphism suggest an important metal contribution from mantle lithosphere the auriferous fluid derived from previously metasomatized mantle lithosphere is interpreted to have advected up the ailaoshan shear zone into the metasedimentary sequence during mantle upwelling clearly contrasting with widely accepted crustal metamorphic models for phanerozoic orogenic gold deposits

northwest trending middle cenozoic left lateral faults in southern yunnan china and their tectonic significance abstract the northwest striking jianshui qujiang and chuxiong faults and probably the zhongdian fault south china show evidence for different amounts of middle cenozoic pre pliocene and post early paleogene left lateral displacement that range from 6 to 25 km the age and orientation of the left lateral faults suggest that the faults are related to a regional deformational event associated with important left lateral shear on the ailao shan shear zone which lies 50 70 km to the south identification of these faults extends left lateral shear during this deformational event farther to the northeast than previously recognized unlike the ailao shan shear zone these faults do not appear to be part of a through going nw trending shear zone these faults are interpreted to be the northernmost part of a nw trending boundary whose main structure the left lateral ailao shan shear zone forms a broad zone of mylonitic rocks bounding a crustal fragment that rotated clockwise around the eastern himalayan syntaxis following middle cenozoic left lateral displacement only the jianshui and qujiang faults exhibited a reversal of displacement in post miocene time this reversal is interpreted to be the result of counterclockwise rotation within the broad n s striking left lateral xiaojiang fault zone none of the post miocene displacement on these two faults appears to be related to post miocene right lateral displacement on the red river fault system the chuxiong fault may have reversed its early left lateral displacement but evidence from surface geology for young and active right lateral displacement is not clear the zhongdian fault appears to have undergone only left lateral displacement some of which may be middle cenozoic in age and some post miocene in age active displacement on the zhongdian fault is interpreted to mark the eastern boundary for a small crustal fragment that rotates clockwise around the eastern himalayan syntaxis

onset timing of left lateral movement along the ailao shan red river shear zone 40ar 39ar dating constraint from the nam dinh area northeastern vietnam left lateral motion along the ailao shan red river asrr shear zone has been widely advocated to be the result of the collision between the indian and eurasian plates and to account for sea floor spreading in the south china sea our new 40 ar 39 ar data on the south easternmost outcrop of the day nui con voi metamorphic massif northern vietnam suggest that the exhumation of metamorphic massif by shearing along the asrr zone began 027 ma and lasted until 022 ma a perfect correlation between location and cooling path for the samples along the shear zone suggests that the transtensional deformation may have propagated northwestward at a rate of 0 6c m y 1 such a good correlation also indicates that the onset of the leftlateral movement of the shear zone may have occurred later than 027 5 ma this conclusion is consistent with our previous interpretation that collision induced southeastward extrusion of indochina along the asrr shear zone postdates the opening of the south china sea and that extrusion tectonics in se china may not be responsible for the opening of the south china sea 2000 elsevier science ltd all rights reserved

intraplate tectonics in asia a precise age for large scale miocene movement along the ailao shan red river shear zone china tertiary left lateral movement along the 1000 km long ailao shan red river shear zone appears to have played an important role in absorbing post collisional northward penetration of india into asia crustal strike slip shear along this zone caused the formation of a gneiss belt metamorphosed to amphibolite grade including anatectic melting both metamorphism and melting were induced by ductile deformation yielding the possibility to date the major tectonometamorphic event that shaped the ailao shan red river belt 17 u pb isotope analyses were performed on small size fractions of zircon monazite and xenotime extracted from two different leucogranitic layers the two samples are located about 50 km apart in the central segment of ailao shan in structurally well controlled settings where the melts crystallized within the strongly foliated gneisses during late stages of deformation all mineral u pb analyses had to be corrected for excess or deficit amounts of radiogenic 206 pb originating from initial 230 th disequilibrium in the 238 u decay series in monazite such disequilibrium 206 pb reaches 20 of total radiogenic 206 pb the corrected u pb ages of monazite and xenotime lie between 22 1 and 23 9 ma whereas zircon yields significantly discordant u pb ages between 30 5 and 33 9 ma pointing to precambrian material in the magma source region inherited components could also be detected in monazite the set of u pb data shows that monazite and xenotime formed simultaneously in both localities substantiating an early miocene age of 23 0 0 2ma for late kinematic crystallization of anatectic melts in the metamorphic belt of the ailao shan red river shear zone

an early miocene transition in deformation regime within the red river fault zone yunnan and its significance for indo asian tectonics recent work has tended to support the view that lateral extrusion of indochina along the red river fault zone was a significant factor in accommodating the convergence of india with asia to better understand the nature and timing of this feature 40ar 39 ar age spectrum analyses were undertaken on minerals from the ailao shan red river metamorphic belt in southern yunnan china interpreted using diffusion domain theory these results yield thermal histories in the temperature range 550 150 c discontinuities in cooling rates observed from these results suggest a transition in deformation style in the shear zone during the early miocene at least in the vicinity of our samples left lateral strike slip ductile deformation appears to have ceased by about 20 ma the mylonitic gneisses in the shear zone were subsequently obliquely unroofed probably due to a component of normal faulting along the eastern edge of the shear zone causing a brief locally 100 c m y cooling episode this transition may have resulted from a component of northeast southwest extension attributable to greater clockwise rotation of indochina relative to south china after 20 ma than that consistent with pure strike slip along the fault k ar ages on clay minerals from gouge within the normal faults bounding the ailao shan and diancang shan yield a range of ages between 20 and 185 ma but show a significant clustering at 20 25 ma these results suggest that early miocene movement on a precursor to the range front normal fault in the ailao shan caused oblique unroofing of the shear zone this early miocene event corresponds in time with a transition from low to very high denudation rates throughout the himalaya and southern tibet this coincidence may reflect that once left lateral strike slip motion on the red river fault zone slowed or was terminated accommodation of much of the continued northward convergence of india occurred on the main central thrust resulting in rapid uplift in the tethyan himalaya and gangdese belt

seismic sequence stratigraphy and hydrocarbon potential of the phu khanh basin offshore central vietnam south china sea the phu khanh basin offshore central vietnam is the only undrilled basin on the vietnam margin of the south china sea analysis of multichannel seismic data indicates that the phu khanh basin follows a typical rift margin development faulted basement synrift sedimentation a breakup unconformity and postrift sedimentation initial rifting probably began during the late cretaceous or paleogene rifting and uplift appear to have resumed or continued locally during the late oligocene and early miocene the later part of basin development was dominated by subsidence postrift sedimentation evolved from a transgressive ramp phase to a regressive shelf slope phase during the transgressive phase rising sea level provided favorable conditions for carbonate buildup development the regressive interval contains a number of sequences composed of seismically resolvable lowstand highstand and rarely transgressive systems tracts these sequences are interpreted as third order sequences superposed on second order eustatic cycles principal potential source rocks are believed to be synrift lacustrine sediments the synrift sediments may lie below the oil floor and probably are gas prone in the postrift section the transgressive interval and the starved basinward portion of transgressive and highstand systems tracts within the regressive interval also may have source rock potential carbonate complexes weathered basement shallow water sands and basin floor fans all have the potential to provide reservoirs potential traps include carbonate complexes basement hills and associated anticlines fault traps and coastal sand traps hydrocarbon indicators such as flat spots amplitude anomalies and gas chimneys with seeps occur at a number of locations

fabrics and 40ar 39ar ages of metamorphic rocks in the gaoligong tectonic belt implications for cenozoic metamorphism and deformation in the se tibetan plateau abstract as one of the major tectonic belts in the southeastern tibetan plateau the gaoligong tectonic belt plays important roles in accommodating the indian eurasian plate collision in this belt medium high grade metamorphic rocks are preserved in this study we selected three cross sections from the northern to the southern segment of the gaoligong tectonic belt for detailed structural macro and micro observations and quartz fabric analysis quartz c axis fabrics reflect three ranges of metamorphic temperature in the metamorphic rocks range 1 650 700 c corresponding to granulite facies range 2 550 650 c amphibolite facies and range 3 400 500 c greenschist facies mineral separates amphibole muscovite and biotite from five samples taken from the lushui pianma section were selected for 40ar 39ar study yielding plateau ages of 30 ma amphibole 17 ma biotite and 15 ma muscovite respectively combined with the previous geochronological data it is suggested that there are three stages of metamorphism deformation of the gaoligong tectonic belt during cenozoic the early stage of metamorphism occurred at high temperature conditions 650 700 c corresponding to granulite facies during 50 34 ma coeval with the cenozoic collision of the indian plate and tengchong block the subsequent stage of metamorphism occurred at medium to low temperatures 550 650 c 400 500 c respectively during 34 10 ma and is the result of a non coaxial progressive deformation showing dextral shear along the gaoligong strike slip fault the latest stage represents rapid exhumation and cooling during 10 3 ma

the lateral boundary of a metamorphic core complex the moutsounas shear zone on naxos cyclades greece we describe the structure microstructures texture and paleopiezometry of quartz rich phyllites and marbles along n trending moutsounas shear zone at the eastern margin of the naxos metamorphic core complex mcc fabrics consistently indicate a top to the nne non coaxial shear and formed during the main stage of updoming and exhumation between ca 14 and 11 ma of the naxos mcc the main stage of exhumation postdates the deposition of overlying miocene sedimentary successions and predates the overlying upper miocene pliocene conglomerates detailed microstructural and textural analysis reveals that the movement along the moutsounas shear zone is associated with a retrograde greenschist to subgreenschist facies overprint of the early higher temperature rocks paleopiezometry on recrystallized quartz and calcite yields differential stresses of 20 77 mpa and a strain rate of 10 15 10 13 s 1 at 350 c for quartz and ca 300 c for calcite chlorite geothermometry of the shear zone yields two temperature regimes 300 360 c and 200 250 c the lower temperature group is interpreted to result from late stage hydrothermal overprint

40ar 39ar ages of detrital white mica constrain the cenozoic development of the intracontinental qaidam basin china ar 39 ar dating of detrital white mica from cenozoic sediments from the nonmarine qaidam basin in western china yields several age groups these include 1 ca 350 450 ma 2 220 280 ma subordinate clusters with 3 122 140 ma and 4 a minor group ca 500 ma ages between 350 and 450 ma are the most common and dominating in the analyzed samples detrital mica in the western qaidam basin can be of a northern altyn mountains and or a southern qimantagh kunlun mountains provenance the main age group of 350 450 ma is well known from intrusions in the altyn mountains whereas the young ages 120 126 ma have been found within shear zones along the central kunlun and altyn tagh faults however hinterland sectors beyond the altyn tagh and central kunlun faults must be considered as potential source areas because the imbalance between the amount of basin fi ll to eroded basement material requires additional sources early paleozoic ages ca 500 ma have been documented so far only in the hongliugou suture zone north of the altyn tagh fault this suggests late or slow continuous uplift of the southern altyn range and because of sinistral slip along the altyn tagh fault further units of the same age are now exposed farther westward the age group of 220 280 ma has been documented only from the northern basin margin this age group may indicate recycling from triassic jurassic cover sequences of the altyn mountains or provenance from permian triassic granite bodies that possibly originated in the qilian mountains

age and origin of magmatism along the cenozoic red river shear belt china to decipher the geodynamic significance of cenozoic magmatism along the red river shear belt geochemical analyses u pb and rb sr dating and pb sr nd isotope tracing were undertaken zircon monazite titanite and a ti u oxide from foliated granitoid intrusions in the shear belt gneisses yield u pb emplacement ages of 33 1 0 2 2 31 9 0 3 25 8 0 2 and 24 7 0 2 ma and an age of 35 0 0 3 ma was obtained for the roughly 100 km long adjacent jinping phan si pang alkali granite together with our previous data the new ages suggest that magmatism and left lateral strike slip movements occurred coevally during latest eocene oligocene times from 33 to 22 ma the rb sr dating of muscovite and biotite from the northernmost gneisses indicates that cooling to 500 c occurred at 52 6 1 1 ma pre dating the onset of magmatism whereas further cooling to 300 c took place at 28 9 0 6 this shows that unroofing in the north took place almost 9 million years earlier than in the central gneiss segments of the shear zone geochemical data substantiate two types of magmas 1 amphibole bearing intrusions of alkaline trend which are derived from sources with isr 0 7065 0 7089 and i nd 3 7 to 6 6 2 leucogranitic layers and bodies having isr 0 7084 0 7354 and i nd 3 3 to 13 4 the former type of intrusion is found in both the gneisses and the adjacent unmetamorphosed cover rocks whereas leucogranites are restricted to the shear belt gneisses source signatures of the alkaline intrusions lie adjacent to the those of oib plotting at the lower end of the mantle array contamination of these melts by continental material seems to be very limited on the other hand the leucogranitic layers are essentially crustal derived but none of the them has country rock isotope signatures requiring melting of crust different from the actually exposed gneisses magma sources similar to those of ocean island basalt indicate magmatism to involve melting of light rare earth element and large ion lithophile element enriched mantle domains most likely present in the lithosphere underneath the region since lithospheric thickening or subduction can be ruled out to produce both types of magmas the presence of an important thermal anomaly is required which is coevally active with left lateral strike slip shear adiabatic decompression and melting within the rising anomaly is the most plausible mechanism to produce the mantle magmas which successively migrate through the crust to induce anatectic melting at 20 15 km crustal depth alkaline magmas largely dominate the volume of magmatism along the belt being continuously present in the shear zone for millions of years such lubrication potentially explains how very large amounts of displacement can be absorbed in surprisingly narrow shear zones such as the red river belt possibly also playing a role for where and when zones of plate scale lateral extrusion develop

duration of strike slip movements in large shear zones the red river belt china abstract sixty four size fractions of zircon monazite xenotime and titanite were dated by the u pb method to temporally and spatially constrain left lateral movements in the red river shear zone between the depths of 15 and 20 km the shearing led to the formation of the high grade metamorphic gneisses that form the bulk of the 4200 m high diancang shan and 3100 m high ailao shan mountain ranges the omnipresence of melt layers and pockets in these gneisses shows that temperatures associated with tectonometamorphism lie at and above the solidus of continental crust and deformation patterns are very homogeneous over the entire length of the belt north of the gneisses subvolcanic bodies intrude unmetamorphosed cover rocks in particular eocene red beds along the projected trend of the red river shear zone for a leucogranitic layer in the diancang shan gneisses an age of 24 2 0 2 ma 2 is obtained for monazite and 22 4 0 2 ma is obtained for xenotime whereas zircon formed through two growth stages at 24 23 ma these ages record solidification of the anatectic melts over a period of at least 1 8 0 4 ma during which left lateral shear was continuously active in the ailao shan gneisses zircon and titanite ages are 26 3 0 3 and 26 1 0 2 ma for two monzonitic bodies and 24 1 0 2 and 22 4 0 2 ma for two pegmatitic layers that occur within the monzonitic intrusions these results show that zircon monazite titanite and probably also xenotime are closed systems for u and pb under melting conditions 650 c therefore the ages date mineral formation in the melt rather than cooling below certain closure temperatures a significantly older age of 35 0 0 1 ma is obtained for a monzonitic subvolcanic intrusion north of the diancang shan gneisses because these intrusions follow the trend of the shear zone they most likely represent the surface expression of early activity along that zone indicating that strike slip movement had already occurred in latest eocene time the total set of u pb ages shows that magmatic and metamorphic activity occurred from 35 to 20 ma strengthening the idea that the red river shear zone absorbed most of the intraplate movements required to compensate the opening of the south china sea between 32 and 16 ma the existence of monzonitic syenitic intrusions along the red river zone implies that melting affected source rocks other than the diancang shan and ailao shan gneiss protoliths potential sources to produce such rocks lie in the deep crust possibly including melts from the mantle consequently the red river shear zone must be a deep rooted structure along which melts migrated to the surface moreover the contemporaneity of shear motion and magma generation suggests that melting occurred in direct relation to strike slip activity

indosinian nw trending shear zones within the truong son belt vietnam 40ar39ar triassic ages and cretaceous to cenozoic overprints abstract several nw trending ductile and partly mylonitic shear zones cross the truong son belt of central vietnam along the song ma and song ca valleys and north of the kontum block from da nang to aluoi and khe sanh high grade metamorphic rocks of amphibolite facies showing a retrograde evolution and consisting of ortho and paragneisses metavolcanics amphibolites marbles and quartzites are exposed along these structures they display a homogeneous deformation pattern characterized by a generally steeply dipping foliation and a near horizontal to gently plunging mineral stretching lineation indicating a strike slip tectonic regime of deformation along the southernmost fault zone at least various and consistent kinematic indicators including s c structures asymmetric tails of porphyroclasts prove that the strain and metamorphism have been generated by a phase of dominantly non coaxial deformation with a dextral sense of shear 40ar 39ar dating applied on the high grade metamorphic rocks minerals occurring along these zones provide plateau cooling ages closely around 245 ma establishing that this event took place in the lowermost triassic as an early phase of the indosinian orogeny the existence of indosinian movements in vietnam as they have been defined by previous authors during the early century is now accurately confirmed and this is the first insight in the occurrence of ductile strike slip tectonics of indosinian age along nw se fault zones well expressed in central vietnam is a cretaceous thermal and deformational overprint marked by epimetamorphism which took place between 90 and 120 ma as attested by low temperature degassing ages this cretaceous event is not found further north in the song ma zone where younger ages appear as a result of the influence of cenozoic shear movements along the red river fault which displays 20 30 ma ages on the northern flank of song ca in the bu khang phu hoat core complex comparable oligocene lower miocene ages 20 35 ma yielded by biotite and phlogopite reflect a strong overprinting and attest to a rapid uplift of the basement

geometry and timing of mesozoic deformation in the western part of the xuefeng tectonic belt south china implications for intra continental deformation abstract the xuefeng tectonic belt is an important intraplate structural system in the south china block its west margin is up to 1300 km away the present day continental margin and the mesozoic structural trends in this belt are perpendicular to and have no correlation with the triassic qinling dabie orogenic belt this belt provides important clues for understanding the mechanism of intraplate deformation and the tectonic history of south china we identified two generations of folding with different strike directions in the xuefeng tectonic belt based on the youngest folding involved strata and their overprinting relationship the early one is ne striking overprinted by the n s striking folds both during late jurassic and late cretaceous thrust faults in the xuefeng tectonic belt mainly show top to west thrust movement which is approximately coeval with the n s striking folding the thrust fault system can be divided into three zones the root zone with steep thrusts the middle zone characterized by imbricate thrusts and the frontal zone with a few shallow thrusts in addition two generations of strike slip faults with different structural trends have been identified e w striking strike slip faults showing dextral transpression and ne striking strike slip faults with sinistral offset and controlling the upper cretaceous basins according to regional geological relationship and structural overprinting we interpret that the e w trending strike slip faults formed in the first stage whereas the ne striking strike slip faults formed later during an e w oriented compressional event therefore the principal stress direction varies from nw se to e w

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

the origin of ribbon lineation within the southern adirondacks u s a abstract multiply deformed metamorphic rocks of the southern adirondacks exhibit a pronounced linear fabric consisting of elongate flat ribbons oriented parallel to early fold axes and lying within foliation planes the ribbons which are often monomineralic consist of quartz feldspar and mafic minerals as seen in transition from least to most deformed rocks these ribbons appear to be the result of elongation of grains or grain aggregates in response to a regional rotational strain which also rotated early fold axes into parallelism with the lineation a consistent sense of asymmetry of feldspar tails with respect to foliation suggests that simple shear was the dominant component of strain the long dimension of these ribbons is believed to mark the maximum elongation direction x of the finite strain ellipsoid

zircon u pb ages hf isotope data and tectonic implications of early middle triassic granitoids in the ailaoshan high grade metamorphic belt of southeast tibet the ailaoshan tectonic belt where the effects of the paleo tethyan ocean evolution and indian eurasian plate collision are superimposed is one of the most significant geological discontinuities in western yunnan province of southeast tibet an ailaoshan micro block within the belt is bounded by the ailaoshan suture zone to the west and the red river fault to the east and consists of low and high grade metamorphic belts late permian middle triassic granitoids that are widely distributed to the west of the ailaoshan suture zone and within the ailaoshan micro block may yield significant information on the tethyan tectonic evolution of the ailaoshan tectonic belt this study reports new la icp ms zircon u pb geochronology and hf isotope data of four granitoids from the ailaoshan high grade metamorphic belt zircon grains from the yinjie granitoid do not have inherited cores and yield a weighted mean u pb age of 247 1 2 0 ma the zircon e hf t values range from 7 8 to 12 1 and hf model ages from 775 to 546 ma indicating that the granitoid was derived from juvenile crust the rims of zircons from the majie and yuanjiang granitoids yield weighted mean u pb ages of 239 5 1 8 and 237 9 2 6 ma respectively whereas the cores yield ages of 1608 352 ma the e hf t values of zircon rims range from 20 4 to 5 3 yielding hf model ages from 2557 to 1606 ma and suggesting that the source magma of the majie and yuanjiang granitoids was derived from ancient crust an additional granitoid located near the majie village yields a zircon u pb age of 241 2 1 0 ma based on our geochronological and geochemical data combined with geological observations we propose that the ailaoshan micro block was derived from the western margin of the yangtze block and is comparable to the zhongzan and nam co micro blocks the presence of late permian mafic rocks with rift related geochemical characteristics within the ailaoshan micro block together with granitoids derived from partial melting of ancient juvenile crust indicates the presence of an ailaoshan rift this possible rift may correspond to the ganzi litang ocean to the northwest and the jinping song da rift to the southeast it is suggested that westward subduction of the jinshajiang ailaoshan song ma oceanic lithosphere triggered the separation of the zhongzan ailaoshan and nam co micro blocks from the western passive continental margin of the yangtze block through the opening of the ganzi litang ailaoshan jinping song da ocean rift this ocean rift may represent a subsidiary branch of the paleo tethyan ocean along the western margin of the yangtze block

characterizing a middle to upper crustal shear zone microstructures quartz c axis fabrics deformation temperatures and flow vorticity analysis of the northern ailao shan red river shear zone china abstract structural and microstructural characteristics deformation temperatures and flow vorticities of the northern ailao shan als high grade metamorphic belt provide significant information regarding the nature and tectonic evolution of the ailao shan red river asrr shear zone mineral deformation mechanisms quartz lattice preferred orientation lpo patterns and the opening angles of quartz c axis fabrics of samples from the gasa section indicate that the northern als high grade metamorphic belt has experienced progressive shear deformation the early stage shearing is characterized by a gradual decrease of deformation temperatures from 650 c at the northeastern unit to ca 300 c at the southwestern unit that results in the formation of migmatites mylonitic gneisses thin bedded mylonites mylonitic schists and phyllonites from the ne to sw across the strike of the shear zone the late stage low temperature 300 400 c shearing is superimposed on the early deformation throughout the belt with the formation of discrete small scale shear zones especially in the thin banded mylonitic rocks along both margins the kinematic vorticity values estimated by rotated rigid porphyroclast method and oblique grain shaped quartz c axis fabric method imply that the general shear dominated flow 0 49 0 77 progressively changed to a simple shear dominated flow 0 77 1 toward the late stage of ductile deformation the two stages of shearing are consistent with early shortening dominated and late extrusion controlled regional tectonic processes the transition between them occurred at ca 27 ma in the als high grade metamorphic belt along the asrr shear zone the large amount of strike slip displacement along the asrr shear zone is predominantly attributed to accelerated flow along the shear zone during the late extrusion controlled tectonic process

tectonic evolution of the hinterland of the zagros orogen revealed from the deformation of the golpaygan metamorphic complex iran in the southwestern part of the central iran zone the golpaygan metamorphic complex gmc was evolved during the zagros orogeny this complex is composed of different metamorphic rocks including schist marble slate gneiss and amphibolite the metamorphic complex is overlain by a cover sequence including permian carbonates jurassic clastic rocks cretaceous carbonates and eocene clastic rocks the internal structure of the gmc is characterized by four deformational stages the first stage d1 developed contemporaneously with the prograde regional metamorphism and resulted in formation of the first generation folds and prevailing axial plane foliation the second stage of deformation d2 was accompanied by deformation partitioning and formation of contractional shear zones these structures were overprinted by different scale folds of the third stage d3 the fourth stage of deformation d4 is characterized by generation of the extensional shear zones which gradually transformed into normal faults d1 and accompanied metamorphism may have resulted from steep subduction of the neotethys ocean beneath the active margin of the central iran zone during jurassic times d2 d3 structures and retrograde metamorphism may have been formed by a regional shortening and transpression deformation event which resulted in exposure of the metamorphic rocks in shallower levels during cretaceous flat slab subduction this condition lasted until paleocene time when the slab roll back caused extension and thinning of the overriding central iran plate the subsequent decompression and regional extension resulted in intrusion of magmatic rocks and generation of d4 which formed the gmc and related magmatism in paleocene eocene time

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

investigating tropical cyclone climate feedbacks using the trmm microwave imager and the quick scatterometer 1 sea surface temperature sst and near surface winds from the tropical rainfall measuring mission trmm microwave imager tmi and the quick scatterometer quikscat are used to calculate globally integrated tropical cyclone induced sst anomalies and power dissipation pd we estimate tropical cyclone induced upper ocean cooling to be 35 higher than our previous estimates based on reanalyzed era40 and ncep surface data annually averaged global pd estimates from tmi are 5 1019 j for the years 1998 to 2006 roughly 30 greater than era40 pd for overlapping years quikscat pd is estimated to be 1 7 1020 j for the years 2000 to 2006 on the basis of these results we conclude that the cyclone induced cooling signal appears to be underrepresented in era40 and ncep reanalysis as postulated in recent observational and modeling studies furthermore we observe a strong positive relationship between pd and ocean surface cooling providing further evidence for the likelihood of cyclone induced climatic feedbacks these results support the hypothesis that tropical cyclones play an active role in the tropical surface ocean heat budget by cooling the tropical upper oceans through enhanced vertical mixing which likely represents a net warming beneath the oceanic mixed layer thus to the degree that vertical mixing is important for regulating the ocean s meridional overturning circulation and poleward heat transport tropical cyclones may be an important contributor to earth s climate system this further confirms the results of emanuel 2001 2002 and sriver and huber 2007b that possible future changes in integrated cyclone intensity associated with warmer sst may provide possible climatic feedbacks through enhanced vertical mixing and increased ocean heat transport thus buffering the tropics to increased temperatures while amplifying the warming at higher latitudes

complex deformation within the crust and upper mantle beneath se tibet revealed by anisotropic rayleigh wave tomography abstract knowledge about rayleigh wave phase velocity azimuthal anisotropy can provide important insight into the dynamic processes and complex deformation mechanisms beneath southeastern se tibet in this study we imaged the azimuthal anisotropy of the rayleigh wave phase velocity in the period range of 10 60 s beneath se tibet the model provides seismological evidence for the existence of asthenospheric upwelling beneath the indo china block icb and east central tibet stratified anisotropy architectures around the eastern himalaya syntaxis ehs are observed and the upper boundary of the subducting indian slab at least extended to the center lhasa block lsb additionally our models also reveal the complex deformation pattern of different blocks in the crust and upper mantle beneath se tibet and the crustal deformation is much more complicated than that of the upper mantle the ehs and lsb are deformed in the whole crust which is affected by the subducting indian lithosphere the qiangtang block icb and songpan ganzi block deformation was mainly controlled by the strikes of the faults and the west east tectonic movement of the plateau materials the deformation of the sichuan yunnan diamond block is related to mid lower crustal flow in the upper mantle the fast propagation directions of most of the blocks match the fast polarization directions of sks and the absolute plate motion excluding the icb and east central tibet based on the combined results of the isotropic and anisotropic models and previous studies two dynamic models are proposed to shed new light on the complex deformation and dynamics processes in se tibet

the red river fault zone in the yinggehai basin south china sea abstract the red river fault a major strike slip fault of onshore southeast asia is suggested to be closely related to the formation of the south china sea and uplift of the tibetan plateau yet published documentation of the offshore segment of the red river fault is sparse high resolution seismic reflection and borehole data obtained by the petroleum industry along the northwestern margin of the south china sea permit mapping of the offshore segment of the red river fault in the yinggehai basin as well as demonstration of the timing of its shear movement and slip reversal two boundary faults and two basin center faults are mapped three successive deformation phases for the offshore red river fault zone include sinistral movement from 30 to16 ma slip reversal between 16 and 5 5 ma and dextral movement with low rates after 5 5 ma although no robust piecing points were observed for the sinistral movement period the horizontal displacement of dextral movement is estimated to be tens of kilometers this study supports a two stage model for the evolution of the india asia collisional orogen before the middle miocene sinistral movement of the red river fault likely was linked to spreading of the south china sea consistent with the concept of continental extrusion after the middle miocene distributed shortening better explains a low rate of dextral accommodation of the red river fault in response to the continuing india asia collision

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

midcrustal shearing and doming in a cenozoic compressive setting along the ailao shan red river shear zone the cenozoic xuelong shan antiformal dome is located along the northern segment of the ailao shan red river shear zone in yunnan china subhorizontal foliation in the gneiss core is recognized representing a broad top to ne shear initiated under amphibolite facies conditions and propagating into greenschist facies in the mantling schist and strike slip shear zone microfabrics of crystallographic preferred orientations cpos in quartz suggest that the deformation temperatures increased with increasing structural depth from the upper crust 300 500 c in the mantling schist to the midcrust 15 km or more 650 c in the gneissic core this trend is mirrored by variations in the metamorphic grade of the syn kinematic mineral assemblages and microstructures which range from garnet amphibole biotite sillimanite rutile feldspar in the core to garnet staurolite biotite epidote muscovite within the limb units the dome experienced the following deformation history 1 a broad top to ne shear in the subhorizontal foliation of the gneiss core during the first stage of deformation d1 2 opposing reverse sense shear along the two schist limbs of the dome during contraction related doming d2 d3 3 sinistral strike slip shearing within the eastern limb d4 and 4 extensional deformation d5 the structural thermal patterns suggest the antiformal dome formation was roughly coeval with top to ne ductile shearing in the midcrust of tibet at 32 ma or earlier a major implication is that there was a phase of contractional ductile deformation in the region prior to the initiation of strike slip deformation

p t t paths and post metamorphic exhumation of the day nui con voi shear zone in vietnam abstract the day nui con voi belt in vietnam is the southeasternmost part of the red river shear zone in asia it is a narrow high grade metamorphic core complex consisting of garnet sillimanite biotite gneisses mylonite bands amphibolite layers and migmatites geothermobarometric study of the complex revealed that the peak metamorphism took place under amphibolite facies conditions of 690 60 30 c and 0 65 0 15 gpa and the subsequent mylonitization occurred under greenschist facies conditions of 480 c and under 0 3 gpa fifteen synkinematic hornblende and biotite separates from gneisses amphibolites and mylonites were dated with the k ar method hornblende separates from the day nui con voi give k ar ages of 26 4 28 5 ma and the biotite separates do give 24 5 24 7 ma combination of thermobarometric and geochronological data yields the cooling history of 500 c at 28 ma and 300 c at 24 ma with a cooling rate of 70 110 c ma 1 and 23 km post metamorphic exhumation of the core complex the first 16 km exhumation from the peak of metamorphism at probably 31 ma to 28 ma was triggered by the left lateral strike slip displacement of the red river shear zone

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

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

first shrimp u pb zircon dating of granulites from the kontum massif vietnam and tectonothermal implications abstract the kontum massif in central vietnam represents the largest continuous exposure of crystalline basement of the indochina craton the central kontum massif is chiefly made of orthopyroxene granulites enderbite charnockite and associated rocks of the kannack complex mineral assemblages and geothermobarometric studies have shown that the kannack complex has severely metamorphosed under granulite facies corresponding to p t conditions of 800 850 c and 8 1 kbars twenty three shrimp ii u pb analyses of eighteen zircon grains separated from a granulite sample of the kannack complex yield ca 254 ma and one analysis gives ca 1400 ma concordant age for a zoned zircon core this result shows that granulites of the kannack complex in the kontum massif have formed from a high grade granulite facies tectonothermal event of indosinian age triassic the cooling history and subsequent exhumation of the kannack complex during indosinian times ranged from 850 c at ca 254 ma to 300 c at 242 ma with an average cooling rate of 45 c ma

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

oligocene miocene bu khang extensional gneiss dome in vietnam geodynamic implications a large oligocene miocene extensional gneiss dome in vietnam has implications for the kinematics of the ailao shan red river shear zone and rifting of the south china sea a major northeast dipping extensional shear zone separates the bu khang dome from less metamorphosed units above shearing deformation occurred during the exhumation of high pressure rocks 40 ar 39 ar ages on micas reveal oligocene miocene ages from 36 to 21 ma after a high pressure episode of probable oligocene age the area was subjected to northeast southwest extension during the opening of the south china sea a kinematic model involving left lateral shear and block rotation within a north south dextral shear zone integrates our observations in the bu khang dome with south china sea rifting

the xuelongshan high strain zone cenozoic structural evolution and implications for fault linkages and deformation along the ailao shan red river shear zone abstract new structural geometric petrographic and u pb zircon data constrain the kinematics of the xuelongshan high strain zone northermost parts of the ailao shan red river shear zone in the xuelongshan range mylonitic foliation mainly trends nw se on steep foliation and flatted foliation mineral stretching lineation is various from gentle to steep and ductile shear senses indicate a left lateral top to the northwest shear movement on the eastern limb and a left lateral top to the southeast shear on the western limb of the range these dome related ductile geometries and kinematics namely d1 deformation represent regional high temperature metamorphism due to crustal thickening the superimposed sinistral strike slip shearing of d2 deformation occurred locally along the earlier domal fabrics metamorphism migmatization and the emplacement of leucogranitic veins associated with partial melting were syntectonic with the regional scale upright antiform la icp ms u pb dating of zircons reveals the late permian triassic and oligocene thermal events the latter event ca 33 26 ma or possibly earlier from the leucogranitic veins corresponds to the regional metamorphism during crustal thickening along the xuelongshan these data indicate that the jiali xuelongshan diancangshan ailao shan high strain zones can belong to a system around the eastern himalayan syntaxis ehs and that the xuelongshan zone played a role in linking other segments between the tibet to indochina in cenozoic

high temperature metamorphism in a major strike slip shear zone the ailao shan red river people s republic of china abstract petrographic and thermobarometric analysis provides constraints on thept path of the mylonitic gneisses of the left lateral ailao shan red river shear zone which has accommodated the lateral extrusion of indochina during the tertiary two different paragenesis p1 and p2 are coeval with this deformation and correspond respectively to the amphibolite and greenschist facies microprobe analysis reveals that p1 garnets bear a chemical zonation from core to rim this zonation indicates a temperature increase during garnet growth conditions of formation of garnet rims p1b which are estimated using biotite garnet and plagioclase garnet thermobarometers are close to the granitic solidus 710 70 c and4 5 1 5 kbar p2 conditions are estimated to be approximately 500 c and

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

orientation related deformation mechanisms of naturally deformed amphibole in amphibolite mylonites from the diancang shan sw yunnan china abstract sheared amphibolite rocks from diancang shan high grade metamorphic complex along the ailao shan red river shear zone southwestern yunnan china show typical mylonitic microstructures the mylonites are characterized by porphyroclastic microstructures and the ultramylonites are highly lineated with alternating amphibole and quartzofeldspathic domains microstructural analysis and p t estimation suggest that the amphibole grains in the mylonitic rocks are deformed and dynamically recrystallized at amphibolite facies in the mylonitic amphibolites there are two types of amphibole porphyroclasts i e type i hard and type ii soft porphyroclasts they have their 001 crystallographic orientations subnormal and sub parallel to the stretching lineation of the rocks respectively the two types of porphyroclasts show distinct deformation microstructures and sub microstructures formed by various deformation mechanisms which contribute in different ways to the generation of the fine grained matrix shape preferred orientation analysis misorientation analysis of the two types of porphyroclasts and new fine grains around them further prove the generation of the fine grains in matrix from the type ii porphyroclasts the type i hard porphyroclasts are deformed mainly by mechanical rotation work hardening and intragranular microfracturing in contrast the deformation of the type ii soft porphyroclasts is mainly attributed to crystalline plasticity i e twinning dislocation creep and dynamic recrystallization during the deformation of the type ii porphyroclasts the 100 001 slip system plays a dominant role during deformation and grain size reduction of amphibole twinning along the active 100 slip system in combination with dislocation creep gliding and climbing governs the nucleation of subgrains and formation of dynamically recrystallized fine grains a process here named twinning nucleation recrystallization

evidence for cool extrusion of the north indochina block along the ailao shan red river shear zone a diancang shan perspective abstractmuch debate surrounds the temporal thermal structural evolution of the 1000 km nw se trending ailao shan red river asrr shear zone this mainly reflects the contradictory interpretations of the timing and p t conditions for the occurrence of left lateral shearing event due to a diverse data set of mineral ages our new microstructural petrological and geochronological data from the southern section of the diancang shan dcs block along the west wall of the asrr support slow cooling from 300 c to 150 c from the middle eocene to the late miocene accompanied by left lateral shearing activity this conclusion is based on the following 1 the lower greenschist facies assemblages of biotite replaced by muscovite or chlorite the albitized k feldspar and the stable association of k feldspar chlorite rather than muscovite biotite are universally observed for the synkinematic sn 1 and mylonitic s c fabrics from both quartzofeldspathic and amphibolite domains 2 new 40ar 39ar data for k fe

structures microfabrics and textures of the cordilleran type rechnitz metamorphic core complex eastern alps rechnitz window group represents a cordilleran style metamorphic core complex which is almost entirely located within nearly contemporaneous neogene sediments at the transition zone between the eastern alps and the neogene pannonian basin two tectonic units are distinguished within the rechnitz metamorphic core complex rmcc 1 a lower unit mainly composed of mesozoic metasediments and 2 an upper unit mainly composed of ophiolite remnants both units are metamorphosed within greenschist facies conditions during earliest miocene followed by exhumation and cooling the internal structure of the rmcc is characterized by the following succession of structure forming events 1 blueschist relics of paleocene eocene age formed as a result of subduction d1 2 ductile nappe stacking d2 of an ophiolite nappe over a distant passive margin succession ca e w to wnw ese oriented stretching lineation 3 greenschist facies grade metamorphism annealing dominant in the lower unit and 4 ductile low angle normal faulting d3 with mainly ne sw oriented stretching lineation and 5 ca e to ne vergent folding d4 the microfabrics are related to mostly ductile nappe stacking to ductile low angle normal faulting paleopiezometry in conjunction with p t estimates yield high strain rates of 10 11 to 10 13 s 1 depending on the temperature 400 350 c and choice of piezometer and flow law calibration progressive microstructures and texture analysis indicate an overprint of the high temperature fabrics d2 by the low temperature deformation d3 phengitic mica from the paleocene eocene high pressure metamorphism remained stable during d2 ductile deformation as well as preserved within late stages of final sub greenschist facies shearing chlorite geothermometry yields two temperature groups 376 328 c and 306 132 c chlorite is seemingly accessible to late stage resetting the rmcc underwent an earlier large scale coaxial deformation accommodated by a late non coaxial shear with ductile low angle normal faulting resulting in subvertical thinning in the extensional deformation regime the rmcc was rapidly exhumed during ca 23 18 ma

cenozoic exhumation of the ailaoshan red river shear zone new insights from low temperature thermochronology continental scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the ailaoshan red river shear zone asrrsz in the se tibetan plateau this study presents 13 apatite u th he 11 zircon u th he and three apatite fission track dates together with thermal modeling in the ailaoshan and xuelongshan segments alsz and xlsz of the shear zone to investigate its cenozoic exhumation history and mechanism which are critical for understanding its tectonic and landscape evolution our results combined with published chronologic data reveal that shear zone rocks along the alsz experienced prominent and rapid cooling from high temperature 500 c to 120 60 c at a rate of 75 100 c myr during 29 17 ma with northwestward younging onset a second lower magnitude accelerated cooling occurred at 14 10 ma along the alsz at a rate of 20 30 c myr with a later initiation on the xlsz at 5 ma and continuing to present with a cooling rate of 20 c myr thermal modeling reveals a single rapid cooling phase with a rate of 17 14 c myr in the eocene to early oligocene for samples outside the shear zones these three fast cooling episodes are directly related to deformation stages including crustal shortening across the se plateau sinistral ductile shearing along the asrrsz and dextral faulting with a dip slip component on the red river and weixi qiaohou faults along the shear zone flanks furthermore the northward migration of kinematic reversal and associated cooling along strike since the mid late miocene likely reflects the northward advance of the eastern himalayan syntaxis

linking paleogene rifting and inversion in the northern song hong and beibuwan basins vietnam with left lateral motion on the ailao shan red river shear zone

new tectono geochronological constraints on timing of shearing along the ailao shan red river shear zone implications for genesis of ailao shan gold mineralization abstract several world class gold deposits are located along the ailao shan als belt in eastern tibet china the genesis of gold mineralization along the belt however has been the subject of debates in the last decades which highlights the importance of dating shearing magmatism and mineralization along the ailao shan red river shear zone asrr through detailed field observations and microscopic analysis a group of leucocratic intrusions from within and outside the shear zone along the als belt are investigated in the present paper pre syn and post shearing intrusions are grouped based on structural and microstructural analysis la icp ms and sims dating of the intrusions revealed the existence of two age populations a group of ages older than 30 ma and the other younger than 28 ma the former are distributed both within and outside the shear zone and the latter in contrast occur only within the shear zone our new results show that the ductile shearing along the asrr shear zone initiated since ca 30 ma ago the dating results place major constraints on timing of shearing along the asrr shear zone and have profound implications on the genesis of gold mineralization along the als belt the present study reveals that ductile shearing along the asrr shear zone was resulted from extrusion of the indochina block late during the indian eurasian plate collision meanwhile we conclude that the gold mineralization took place prior to the shearing but in close relation to an early magmatism 30 ma ascribed to post collisional extension collapse involving mantle processes early during the plate collision

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

geodynamic significance of the kontum massif in central vietnam composite 40ar 39ar and u pb ages from paleozoic to triassic abstract the kontum massif of south central vietnam has long been classified as lower continental crust of precambrian archean age u pb zircon and 40ar 39ar biotite ages from charnockites and amphibolite facies rocks from this basement however yield much younger ages and imply at least two paleozoic thermal events syntectonic charnockites from the kannack complex and the southern kontum massif record permo triassic magmatism u pb documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 249 pm 2 end document 2 ma and docume

comment on onset timing of left lateral movement along the ailao shan red river shear zone 40ar 39ar dating constraint from the nam dinh area northeastern vietnam by wang et al 2000 journal of asian earth sciences 18 281 292

oligo miocene granitic magmatism in central vietnam and implications for continental deformation in indochina two granitoid intrusions within the bu khang extensional complex in central vietnam have been dated by u pb and rb sr geochronology a monazite u pb age of 26 0 0 2 2 myr was obtained for the bu khang pluton and 23 7 1 6 1 7 myr for monazite allanite and zircon from the dai loc intrusion these ages date crystallization of magmas previously assigned precambrian to devonian rb sr analyses of k feldspar and biotite fractions from the samples yield ages of 19 8 0 6 2 myr and 19 6 0 5 myr respectively the thermal history recorded by the different geochronometers implies an average exhumation rate of 2 mm yr 1 corresponding to 9 km of unroofing magmatism was either i induced passively by lithospheric thinning driven by changes in regional tectonic stresses or ii triggered actively by an ascending plume tertiary exhumation and magmatism documented elsewhere in indochina e g ailao shan red river and wang chao shear zones favours a regional tectonic cause for extension and granitoid magmatism in the bu khang complex on the other hand the presence of an upwelling thermal anomaly since at least 35 ma causing mantle melting below indochina is supported by shear wave velocity variations in the mantle and source geochemistry of both the bu khang plutons and the red river belt intrusions in either case tertiary exhumation of the bu khang complex can account for previously undocumented ne sw directed extension which is required in northern vietnam to account for structural changes related to the opening of the south china sea