temporal spatial distribution and tectonic implications of the batholiths in the gaoligong tengliang yingjiang area western yunnan constraints from zircon u pb ages and hf isotopes abstract considerable progress has recently been made regarding temporal and spatial distribution of magmatism in the lhasa terrane however the eastward and southeastward correlation of these tibetan magmatic suites in western yunnan and burma remains poorly constrained this paper reports zircon u pb dating and hf isotopic compositions of granites in the gaoligong tengliang yingjiang area west yunnan it reveals three episodes of plutonism and more importantly a southwestward magmatic migration the gaoligong batholiths in the northeast were mainly emplaced during early cretaceous 126 121 ma and comprised predominantly s type granites with negative zircon ehf values ehf 2 12 the tengliang granites situated southwest of the gaoligong belt were emplaced in late cretaceous 68 76 ma and also displayed a strong peraluminous affinity and negative ehf 5 14 indicating a provenance from a proterozoic sedimentary source with little mantle contribution the youngest phase of magmatism 52 66 ma occurred in yingjiang southwestmost of the study area it is composed of s type granites ehf 2 12 in east yingjiang and i type granites ehf 4 6 in west yingjiang near the china burma border the late cretaceous early cenozoic plutons in the tengliang and yingjiang area are thus considered as the northern continuation of the late cretaceous magmatic arc west which comprises i type granites and andesitic rocks and of the belt of predominant s type granites east in burma thailand and malaysia such a chemical polarity of the dual i type and s type granites is strongly reminiscent of the northern american cordillera indicating a cordilleran style continental margin during the late cretaceous early cenozoic while the magmatic arc was related to eastward subduction of the neo tethys beneath the asian continent the s type granites represented the melting products of thickened crust in the hinterland in response to subduction induced decrease in lithospheric strength and compressive plate convergence forces and to a less degree to the collision between burma and sundaland blocks the gaoligong early cretaceous granites which bear strong similarities in lithology geochemistry and emplacement age to those in the northern magmatic belt in the lhasa terrane are also the magmatic expression of crustal thickening this crustal thickening may have stemmed from the collision between the lhasa block and the qiangtang block in late jurassic and early cretaceous the magmatism in western yunnan thus recorded a long term subduction of the neo tethyan plate enhanced by continental collisions at different time

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

spreading structure of the troodos ophiolite cyprus some paleomagnetic constraints it has been suggested that grabens on the northern flank of the troodos ophiolite formed by listric faulting in an oceanic environment and represent axial valleys fossilized by ridge jumping this paleomagnetic survey of the solea graben was carried out to constrain the structural interpretation an analysis was devised which restores both the dikes sampled to vertical and the primary remanent magnetizations to a previously derived structurally corrected remanent magnetization direction typically two solutions for the original dike orientation and the pole and angle of net rotation are obtained for each dike sampled these solutions can be separated if a locally consistent original dike strike is assumed reasons are discussed for the selection of the solution that gives an original northwesterly dike strike results are consistent with a graben rotations are up to 78 at the sites studied rotation vectors are subhorizontal and subparallel to the original dike strike suggestive of an axial process for the development of the structure however on the basis of field observations an alternative mode of origin is proposed invoking ephemeral extreme upper crustal extension by listric faulting on the west flank of an intermediate to fast spreading axis the grabens being formed by antithetic faulting

first global positioning system results in northern myanmar constant and localized slip rate along the sagaing fault we present the first recorded global positioning system gps data from myanmar measured at the northern tip of the sagaing fault this area is in a very complex geodynamic context where rigid and semirigid plates interact the 12 gps sites measured in 2005 and 2008 in northern myanmar show that the slip rate is 18 mm yr and is localized along a single active narrow fault trace 20 km wide the same rate was previously demonstrated and remeasured 500 km southward in central myanmar despite the geodynamic regional complexity induced by interaction between the sunda and india plates the burma microplate and the highly deformable eastern himalayan syntaxis the slip rate remains surprisingly constant along this fault however the modeled locking depth varies from 20 km in central myanmar to 5 km in the north

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

strain and rotation rate from gps in tibet anatolia and the altiplano 1 deformation measured by regional gps networks in continental plateaus reflects the geologic and tectonic variability of the plateaus for two collisional plateaus tibet and anatolia and one noncollisional the altiplano we analyze the regional strain and rotation rate by inverting gps velocities to calculate the full two dimensional velocity gradient tensor to test the method we use gridded velocities determined from an elastic block model for the eastern mediterranean middle east region and show that to a first order the deformation calculated directly from the gps vectors provides an accurate description of regional deformation patterns principal shortening and extension rate axes vertical axis rotation and two dimensional 2 d volume strain dilatation are very consistent with long term geological features over large areas indicating that the gps velocity fields reflect processes responsible for the recent geologic evolution of the plateaus differences between geological and gps descriptions of deformation can be attributed either to gps networks that are too sparse to capture local interseismic deformation or to permanent deformation that accrues during strong earthquakes the altiplano has higher internal shortening magnitudes than the other two plateaus and negative 2 d dilatation everywhere vertical axis rotation changes sign across the topographic symmetry axis and is due to distributed deformation throughout the plateau in contrast the collisional plateaus have large regions of quasi rigid body rotation bounded by strike slip faults with the opposite rotation sense from the rotating blocks tibet and anatolia are the mirror images of each other both have regions of positive dilatation on the outboard sides of the rotating blocks positive dilatation in the aegean correlates with a region of crustal thinning whereas that in eastern tibet and yunnan province in china is associated with an area of vertical uplift rollback of the hellenic trench clearly facilitates the rotation of anatolia rollback of the sumatra burma trench probably also enables rotation about the eastern syntaxis of tibet

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

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

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

jurassic to miocene magmatism and metamorphism in the mogok metamorphic belt and the india eurasia collision in myanmar situated south of the eastern himalayan syntaxis at the western margin of the shan thai terrane the highgrade mogok metamorphic belt mmb in myanmar occupies a key position in the tectonic evolution of southeast asia the first sensitive high resolution ion microprobe u pb in zircon geochronology for the mmb shows that strongly deformed granitic orthogneisses near mandalay contain jurassic 170 ma zircons that have partly recrystallized during 43 ma high grade metamorphism a hornblende syenite from mandalay hill also contains jurassic zircons with evidence of eocene metamorphic recrystallization rimmed by thin zones of 30 9 plus or minus 0 7 ma magmatic zircon the relative abundance of jurassic zircons in these rocks is consistent with suggestions that southern eurasia had an andean type margin at that time mid cretaceous to earliest eocene 120 to 50 ma i type granitoids in the mmb myeik archipelago and western myanmar confirm that prior to the collision of india an up to 200 km wide magmatic belt extended along the eurasian margin from pakistan to sumatra metamorphic overgrowths to zircons in the orthogneiss near mandalay date a period of eocene 43 ma high grade metamorphism possibly during crustal thickening related to the initial collision between india and eurasia at 65 to 55 ma this was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 ma similar syntectonic syenites and leucogranites intruded the ailao shan red river shear belt in southern china and vietnam during the eocene oligocene to miocene and the wang chao and three pagodas faults in northern thailand that most likely link with the mmb were also active at this time the complex history of eocene to early miocene metamorphism deformation and magmatism in the mmb provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of india and resulting extrusion or rotation of indochina

crustal thickening of the early cretaceous paleo pacific gondwana margin abstract the cause of 7 to 25 km of early cretaceous thickening of parts of the new zealand gondwana margin has been argued to be due to tectonic or magmatic processes new insights into this event have been gained from examination of the grebe mylonite zone an extensive amphibolite facies early cretaceous ductile shear zone that separates volcanic arc rocks of the outboard median batholith from metasedimentary and intrusive rocks of the western province inboard median batholith at lake manapouri in southwest new zealand ar ar and u pb geochronology shows that here exhumation of the outboard median batholith began 128 ma syn kinematic magmatism was taking place at 121 ma and measurable displacement had ceased by 116 ma although the mylonite zone is currently subvertical a combination of thermochronological cooling profiles lineation orientations and back rotation of tilted tertiary unconformities indicate that it most likely formed as an oblique sinistral reverse fault that dipped 60 e and therefore displaced the outboard median batholith over the margin of the western province however the high original angle of this and other compressional shear zones in analogous structural positions the apparent absence of a regional thrust or nappe sheet s and the subtly different ages of thickening for different areas indicate that tectonic loading can have played only one part in the crustal thickening event another factor was the contemporaneous emplacement of 30 000 km 3 of mafic to felsic magma which was likely accommodated by vertical depression of the middle and lower crust tectonic and magmatic processes leading to crustal thickening were therefore not mutually exclusive

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

evidence for mechanical coupling and strong indian lower crust beneath southern tibet how surface deformation within mountain ranges relates to tectonic processes at depth is not well understood the upper crust of the tibetan plateau is generally thought to be poorly coupled to the underthrusting indian crust because of an intervening low viscosity channel here however we show that the contrast in tectonic regime between primarily strike slip faulting in northern tibet and dominantly normal faulting in southern tibet requires mechanical coupling between the upper crust of southern tibet and the underthrusting indian crust such coupling is inconsistent with the presence of active channel flow beneath southern tibet and suggests that the indian crust retains its strength as it underthrusts the plateau these results shed new light on the debates regarding the mechanical properties of the continental lithosphere and the deformation of tibet

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

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

paleomagnetic analysis of eastern tibet implications for the collisional and amalgamation history of the three rivers region sw china abstract a comparative analysis of paleolatitudes and latitudinal displacements was undertaken for the south china simao baoshan shan thai indochina qiangtang lhasa and himalayan blocks by using available paleomagnetic data to determine the collisional and amalgamation history of the main blocks in the three rivers region western yunnan the results show that 1 the simao block is a south china derived block 2 the baoshan and shan thai blocks were subjected to rapid northward drift during the period from late carboniferous to late permian 3 the baoshan block collided with the simao block in the late permian and continued to drift rapidly northwards together with the south china and shan thai blocks until the late triassic 4 the paleo tethys separating the baoshan and simao blocks was possibly opened in the early silurian 5 the meso tethys ranged in age from early permian time to early cretaceous time and reached its greatest width of about 42 latitude in the late triassic

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

low temperature magnetic behavior of titanomagnetites titanium substitution has a significant effect on the temperature dependence 5 300 k of low temperature saturation remanence and of initial susceptibility in synthetic and natural titanomagnetite fe3 xtixo4 0 x 0 4 and electronic and lattice relaxation phenomena over the entire titanomagnetite compositional range these features produce diagnostic magnetic behavior useful for titanomagnetite identification in natural samples moreover the apparent similarities between the thermal decay of low temperature remanence of titanomagnetite with pyrrhotite pure magnetite and superparamagnetic phases can lead to complications in interpreting low temperature remanence data when titanomagnetite is present

timing of india asia collision geological biostratigraphic and palaeomagnetic constraints 1 a range of ages have been proposed for the timing of india asia collision the range to some extent reflects different definitions of collision and methods used to date it in this paper we discuss three approaches that have been used to constrain the time of collision the time of cessation of marine facies the time of the first arrival of asian detritus on the indian plate and the determination of the relative positions of india and asia through time in the qumiba sedimentary section located south of the yarlung tsangpo suture in tibet a previous work has dated marine facies at middle to late eocene by far the youngest marine sediments recorded in the region by contrast our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50 6 52 8 ma in broad agreement with the timing of cessation of marine facies elsewhere throughout the region double dating of detrital zircons from this formation by u pb and fission track methods indicates an asian contribution to the rocks thus documenting the time of arrival of asian material onto the indian plate at this time and hence constraining the time of india asia collision our reconstruction of the positions of india and asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early eocene we conclude the paper with a discussion on the viability of a recent assertion that collision between india and asia could not have occurred prior to 35 ma

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

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

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

cretaceous tertiary geology of the gangdese arc in the linzhou area southern tibet abstract knowledge of the cretaceous tertiary history of upper crustal shortening and magmatism in tibet is fundamental to placing constraints on when and how the tibetan plateau formed in the lhasa terrane of southern tibet the widely exposed angular unconformity beneath uppermost cretaceous lower tertiary volcanic bearing strata of the linzizong formation provides an excellent geologic and time marker to distinguish between deformation that occurred before vs during the indo asian collision in the linzhou area located 30 km north of the city of lhasa a 3 km thick section of the linzizong formation lies unconformably on cretaceous and older rocks that were shortened by both northward and southward verging structures during the late cretaceous the linzizong formation dips northward in the footwall of a north dipping thrust system that involves triassic jurassic strata and a granite intrusion in the hanging wall u pb zircon geochronologic studies show that the linzizong formation ranges in age from 69 ma to at least 47 ma and that the hanging wall granite intrusion crystallized at 52 ma coeval with dike emplacement into footwall cretaceous strata 40ar 39ar thermochronologic studies suggest slow cooling of the granite between 49 and 42 ma followed by an episode of accelerated cooling to upper crustal levels beginning at 42 ma the onset of rapid cooling was coeval with the cessation of voluminous arc magmatism in southern tibet and is interpreted be a consequence of either 1 tertiary thrusting in this region or 2 regional rock uplift and erosion following removal of overthickened gangdese arc lower crust and upper mantle or break off of the neo tethyan oceanic slab

paleomagnetic results from the upper carboniferous of the shan thai malay block of western yunnan china the upper carboniferous basaltic woniusi formation was sampled at 21 sites from two limbs of a syncline near baoshan city 25 2 n 99 3 e and from a monocline near yongde county 23 9 n 99 2 e for paleomagnetic study the study area is generally thought to be part of the shan thai malay microplate thermal demagnetization reveals a single polarity characteristic remanent magnetization chrm which is carried by both magnetite and hematite with the former being the dominant mineral in basalt and the latter being the principal carrier in associated tuffaceous basalt and sandstone the tilt corrected formation mean from baoshan d 209 2 i 61 0 95 6 7 confirms the results reported by previous workers and a positive fold test constrains the chrm acquisition to be prefolding the paleomagnetic inclinations determined from this study are similar to that derived from the devonian rocks from the same area by other workers indicating a paleolatitude of about 42 for the baoshan area during the devono carboniferous time the paleomagnetic declinations however present a large difference between the two sampling localities for the upper carboniferous as well as between the sampling sites for the devonian and for the upper carboniferous the paleo declination difference can be partly explained by the apparent polar wander of gondwana if the shan thai malay microplate was rigidly attached to gondwanaland during this time interval the large part of it has to be ascribed to tectonic rotations between the sampling sites this fact suggests that extreme caution should be exerted when trying to establish an apparent polar wander path for and to reconstruct the paleo geographic position of the shan thai malay microplate

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

testing the influence of high voltage mineral liberation on grain size shape and yield and on fission track and 40ar 39ar dating mineral liberation and separation are fundamental for modern thermochronology the fragmentation of rocks by high voltage electrical pulses called electrical fragmentation is a new technology only available since the development of a lab sized machine a few years ago the proposed advantages e g disintegration along grain boundaries compete with suspected negative effects of the locally occurring high temperatures up to 104 k on the physical properties of the liberated minerals comparison of electrical fragmentation with conventional mechanical fragmentation jaw crusher revealed similar amounts of liberated apatite and zircon from the same quantity of granite but 45 production of fines 80 m for mechanical fragmentation versus 5 for electrical fragmentation electrical fragmentation yielded larger sized apatite grains 180 250 m compared to 80 125 m for mechanical liberation but no differences in shape factors elongation roundness compactness the liberation of idiomorphic crystals from coarse grained rocks is ameliorated by the new method as shown by the liberation of mm sized idiomorphic biotite crystals from granite degassing curves of 40ar from electrically and mechanically liberated biotites from the same sample are nearly identical maximum difference six percentage points 40ar 39ar ages of biotites from three samples two mechanically one electrically fragmented from the same intrusion are identical within 2 error length measurements of apatite fission tracks gave identical results within 2 error regardless of fragmentation method used in summary the positive aspects of electrical fragmentation have been confirmed in this study while effects negative for thermochronology are not observed

relative motion across the eastern tibetan plateau contributions from faulting internal strain and rotation rates abstract a kinematic model comprising 14 rotating elastic plastic blocks is used to represent the modern deformation of eastern tibet and neighboring regions block rotations fault slip rates and permanent strain rates within the blocks are constrained by inverting gps velocities slip vector azimuths derived from earthquakes and fault slip rates derived from geology the calculated internal strain rates of blocks in eastern tibet amounts to 10 to 30 10 9 yr in contrast to relatively low rates

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

new constraints to the onset of the india asia collision paleomagnetic reconnaissance on the linzizong group in the lhasa block china abstract to better understand the onset of the india asia collision a paleomagnetic study has been conducted on paleogene volcanic rocks and sediments of the linzizong group 64 44 ma from the linzhou and namling basins of the lhasa block at the southern margin of the asian continent following detailed rock magnetic investigations and progressive thermal or hybrid thermal and alternating field demagnetization stable characteristic remanent magnetizations chrms were successfully defined from the dianzhong 64 60 ma nianbo and pana 60 44 ma formations these chrms are of dual polarity and pass a fold test with some of them in volcanic rocks carried by oxidation induced hematite we thus interpret them as primary remanences paleomagnetic results from the bulk of the collection imply that the southern leading edge of asia i e the lhasa block remained essentially stationary in low latitudes at 10 n without paleomagnetically detectable tectonic rotation and latitudinal variation during the formation of the linzizong group consequently a large scale post collisional northward convergence in the tibetan plateau and central asia is very likely to have occurred after formation of the linzizong group and the definitive paleoposition of the lhasa block during the period embracing the interval between 64 and 44 ma provides further constraints on the latitudinal position of the initial contact between india and asia this evidence rules out the model for a younger 35 ma india asia collision and implies that the initial india asia collision occurred between 65 and 50 ma given that greater india comprised the present indian continent together with a 950 km extension beyond its northern margin prior to the rifting of gondwana in the middle jurassic we conclude that the initial india asia collision most probably occurred between 55 and 60 ma

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts