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

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

miocene jiali faulting and its implications for tibetan tectonic evolution the karakoram jiali fault zone kjfz comprises a series of right lateral shear zones that southerly bound the eastward extrusion of northern tibet relative to india and stable eurasia here we present new 40 ar 39 ar age data from the puqu and parlung faults two easternmost branches of the jiali fault zone which indicate a main phase of the kjfz shearing from v18 to 12 ma thus the tibetan eastward extrusion bounded by principal strike slip fault zones started and was probably most active around the middle miocene an interval marked also by active east west extension in southern tibet the coincidence of these two tectonic events strongly suggests a common causal mechanism which is best explained as oblique convergence between india and asia under the framework of this mechanism the extension in southern tibet is not a proxy for the plateau uplift the kjfz activity was furthermore coincident with right lateral displacements along the gaoligong and sagaing faults in southeast asia this defines a miocene deformation record for the regional dextral accommodation zone that in response to the continuing india asia collision may have accounted for the initiation and prolonged history of clockwise rotation of the tibetan extrusion around the eastern himalayan syntaxis 2002 elsevier science b v all rights reserved

tin metallogenesis associated with granitoids in the southwestern sanjiang tethyan domain nature deposit types and tectonic setting article i nfo tin mineralization in the southwestern sanjiang tethys sn metallogenic domain extends from the southeast asia tin belt in the south the eastern part of the domain does not contain significant sn deposits whereas the central part of the domain composed of the changning menglian sn belt and related to ca 239 178 ma s type granitoids generated by the collision between tengchong baoshan and simao blocks carries wide spread the hydrothermal vein type mineralization the western part of the domain composed of the tengchong baoshan sn metallogenic belt is related to both 136 113 ma and 89 52 ma s type granitoids the former granitoids resulted from the collision between western burma and tengchong baoshan blocks and generated skarn type tin deposits the younger groups correspond to the india asia continental collision and are associated with the xiaolonghe and lailishan greisen type sn deposits

the coupling of indian subduction and asian continental tectonics abstract in order to understand the potential controls on asian tectonics during the subduction of the tethys and indian lithospheres we reconstruct the coupled subduction continent deformation history using tomographic imaging kinematics constraints and numerical modeling the global p waves tomographic images of the mantle below the india asia collision zone provide constraints on the deep structure of continents and subduction history linking the slab positions in the mantle to the asian tectonics reconstructions and the indian plate kinematics we reconstruct the timing and location of successive subduction and breakoff events showing one major breakoff occurred between india and the tethys ocean 45 ma in the western syntax a vertical slab continuous to the continent is shown to override the deeper detached tethys slab in the central region similar structure is found with a detached slab yet closer to the tethys slab in the eastern syntax no slab is imaged it is inferred that after tethys slab had broke off subduction only resumed in the center of the margin while underthrusting took place at both extremities of the convergent margin during following convergence a second breakoff event detached the central indian slab from the margin 15 ma ago which renewed indian lithosphere underthrusting below asia this most probably occurred when the tibetan plateau was already uplifted implying that uplift is not a direct result of underthrusting numerical models of breakoff during subduction illustrate the controls of slab detachment on the complexities of the indian margin in these models the subduction of continental lithosphere resumes after breakoff only where this is entrained by the mantle flow associated with the long lasting oceanic slab sinking that is in the center of the margin while converging continent edges underthrusts the upper plate furthermore the breakoff during subduction has profound implications on the asian intra plate tectonics in the models the breakoff is rapidly followed by large stresses in the upper plate interiors propagating at large distance from the margin along a belt oriented at 45 from the trench the long term evolution of the asian continental tectonics shows drastic changes in the fault pattern with successive strike slip faulting across the asian continent which are in agreement with the mechanisms illustrated by the models transient large coupling at the trench caused by the breakoff events during india asia convergence offers an explanation for episodic nucleation of lithospheric faults within the asian continent and their link to deep processes

deciphering the origin of the tengchong block west yunnan evidence from detrital zircon u pb ages and hf isotopes of carboniferous strata article i nfo to constrain the paleoposition of the tengchong block within gondwana during the early paleozoic we per formed in situ u pb and hf isotope analyses on detrital zircons from carboniferous strata in the tengchong block the age distributions yield dominant neoarchean 2 5 ga mesoproterozoic 1 7 1 4 ga grenvillian 0 95 ga and pan african 0 65 0 5 ga age groups hf isotope compositions of mesoproterozoic grenvillian and pan african zircon age groups exhibit wide range of ehf t suggesting their diverse sources the oldest hf model agesindicate that thesource magma included reworked eoarchean 3 8 3 7 ga crustal materials the re markable resemblance of zircon age spectra and hf isotopes from the tengchong block with those from tethyan himalayan western qiangtang and indochina suggests that the tengchong block was located along the indian margin of gondwana during the early paleozoic in grenvillian and pan african crustal growth for the source areas was insignificant

eocene break off of the neo tethyan slab as inferred from intraplate type mafic dykes in the gaoligong orogenic belt eastern tibet article i nfo eocene 40 42 ma basaltic dykes in the gaoligong tengliang belt eastern tibet are characterized by high na2 o 2 4 in contrast with the widespread post collisional potassic and ultrapotassic rocks in the tibetan plateau despite the ubiquitous negative nb anomalies these dykes have relatively high nb and zr contents making them distinct significantly from the gangdese arc magmas all these together with the positive nb anomaly in some samples indicate an intraplate affinity for the gaoligong tengliang dykes specifically the gaoligong dykes represent the asthenosphere derived melts which has been contaminated to various degrees by the lithosphere mantle derived melts whereas the tengliang samples were directly derived from an enriched lithosphere mantle the thin lithosphere b80 km inferred from basalt geochemistry is unusual in tibet thus demanding a peculiar mechanism to thin lithosphere a slab break off model is preferred given the geochemical contrast between pre 40 ma and post 40 ma magmas in tibet and the temporal correlation among this intraplate magmatism the termination of gangdese arc magmatism and regional thermally driven metamorphism therefore the occurrence of intraplate type magmas in the gaoligong orogenic belt likely represents magmatic expression of the detachment of subducting neo tethyan slab from the indian continental plate during the eocene in the light of the slab break off concept and thermo mechanical modeling the eocene slab break off furthermore suggests the onset of the india asia collision between 52 and 57 ma

lower crustal granulite xenoliths from the pannonian basin hungary part 2 sr nd pb hf and o isotope evidence for formation of continental lower crust by tectonic emplacement of oceanic crust mafic granulite xenoliths from the lower crust of the pannonian basin are dominated by lree depleted bulk rock compositions many of these have morb like 143nd 144nd but 87sr 86sr is elevated relative to most morbs their 18o values cover a wide range from 3 8 to 9 5 a group of lree enriched mafic granulites have higher 87sr 86sr 0 704 0 708 and lower 143nd 144nd 0 5128 0 5124 with higher 18o values on average 7 8 to 10 6 than the lree depleted granulites the lree enriched granulites are however isotopically similar to newly discovered metasedimentary granulite xenoliths a sublinear correlation in ehf end isotope space has a shallower slope than the crust mantle array with the metasedimentary rocks forming the low ehf end member the radiogenic end is restricted to the lree depleted granulites and these overlap the field of morb pb isotopes for the lree depleted samples are less radiogenic on average than those of the lree enriched and metasedimentary xenoliths and metasedimentary granulites have consistently higher 208pb 204pb the wide range in 18o over a restricted range in nd and sr isotope values in combination with the predominance of lree depleted trace element compositions is consistent with an origin as a package of hydrothermally altered oceanic crust the existence of 18o values lower than average morb and or mantle peridotite requires that at least some of these rocks were hydrothermally altered at high temperature presumably in the oceanic lower crust the low 143nd 144nd of the lree enriched mafic granulites cannot be explained by simple mixing between a lree depleted melt and an enriched component represented by the recovered metasediments instead we interpret these rocks as the metamorphic equivalent of the shallowest levels of the ocean crust where pillow basalts are intimately intercalated with oceanic sediments a possible model is accretion of oceanic crustal slices during subduction and convergence followed by high grade metamorphism during the alpine orogeny

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

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

petrogenesis of metaluminous a type granitoids in the tengchong lianghe tin belt of southwestern china evidences from zircon u pb ages and hf o isotopes and whole rock sr nd isotopes abstract the tengchong lianghe tin belt is the most importantpart of the tin metallogenic belt in southwest china s sanjiang metallogenic province in this district two a type granite plutons that are spatially associated with the tin deposits have recently been discovered these granitoids are dominated by biotite granites with weakly peraluminous to metaluminous compositions high sio2 contents 73 3 76 2 wt and high alkali contents k2o na2o 8 3 9 17 wt trace element spider diagrams show that these granitoids are also clearly enriched with the large ion lithophile elements rb th u and k but are markedly depleted in ba and sr they are significantly depleted in the high field strength elements nb and ti but are enriched with zr and hf these rocks have relatively high zircon saturation temperatures 774 833 c high zr nb ce y contents 272 416 ppm and 10 000 ga al ratios almost 2 7 that are typical of a type granites they also have high total rare earth element ree contents 174 404 ppm and relatively flat chondrite normalized ree patterns with significantly negative eu anomalies la icp ms zircon u pb dating results indicate that the emplacement of these two granite plutons occurred during the early tertiary 52 7 0 3 53 0 0 4 ma and the late cretaceous 73 3 0 5 73 3 0 5 ma periods respectively isotopic compositions show that the granitoids have highly variable 87sr 86sr i ratios 0 7182 0 7457 relatively constant low end t values 11 2 to 12 4 and ancient nd and hf model ages 1 56 1 88 ga suggesting that they were derived from the partial melting of the paleoproterozoic continental crust their zircon 18o values 6 6 8 5 and ehf values from 8 6 to 11 3 also suggest that these granitoids mainly originated from the middle lower continental crust consisting of mafic and metasedimentary rocks such geochemical characteristics indicate that these two a type granite plutons were generated by the partial melting of paleoproterozoic mafic and the metasedimentary basement of the tengchong block in a post collisional or syn collisional extensional setting of the neo tethy anorogenic zone during the late cretaceous early cenozoic the late cretaceous granitoids were probably associated with the subduction of the neo tethyan plate under the post collisional extension of the western burma and tengchong microplates collision during the jurassic early cretaceous the early tertiary granitoids might be the syn collisional product of stretching relaxation during the middle and late main collisional period 55 41 ma between india and asia

s type granitic magmas petrogenetic issues models and evidence abstract despite a perception that it represents a perverse divergence it is perfectly possible to believe in the existence of s and i type granites and the implications for the nature of their protoliths and to disbelieve in the applicability of the restite unmixing model for chemical variation in granitic magmas white and chappell erected the s i classification with impeccable validity the isotopic evidence demands contrasting source reservoirs for s and i type granitic magmas however the major advance was not the classification but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas the restite unmixing model is commonly seen as a companion to the s i classification but it is really a separate issue this model implies that the compositions of granites image those of their source rocks in a simple way however there are other equally valid models that can explain the data and none of them represents a unique solution the most cogent explanation for the high grade metasedimentary enclaves in most s type granites is that they represent mid crustal xenoliths restitic enclaves are either rare or absent inherited zircons in s type rocks are certainly restitic however the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock zircon and zirconium behaviours are controlled by disequilibrium and kinetics and zr contents of granitic rocks can rarely be used to infer magma temperatures since the dominant ages among inherited zircons in lachlan fold belt lfb s type granites are ordovician and proterozoic it seems likely that crust of this age but geochemically different from the exposed rocks not only underlies much of the lfb but also forms a component in the granite magma sources the evidence is overwhelming that the dark microgranular enclaves that occur in both s and i type granites are igneous in origin they represent globules of quenched more mafic magma mingled and modified by exchange with the host granitic magma however magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas likewise the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and in some cases violate constraints from isotopic studies s and i type magmas commonly retain their distinct identities this suggests limited source mixing limited magma mixing and limited wall rock assimilation though intermediate types certainly exist they are probably relatively minor in volume crystal fractionation probably plays the major role in the differentiation of very many granitic magmas including most s types especially those emplaced at high crustal levels or in the volcanic environment minor mechanisms include magma mixing wall rock assimilation and restite unmixing isotopic variations within plutons and in granite suites could be caused by source heterogeneities magma mixing assimilation and even by isotopic disequilibrium however source heterogeneity coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust and crustal thickening likewise fails to provide sufficient heat generally the mantle must be the major heat source this might be provided through mantle upwelling and crustal thinning and possibly through the intra and underplating of mafic magmas upper crustal extension seems to have been common in regions undergoing granitic magmatism migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid present reactions granitic magmas are mostly formed by fluid absent processes where we do see rare evidence for arrested fluid absent partial melting the melt fraction is invariably concentrated into small shear zones veinlets and small dykes thus it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels however one major missing link in the chain is the mechanism by which melt fractions in small scale segregations occurring over a wide area can be gathered and focused to efficiently feed much wider spaced major magma conduits answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones self organization almost certainly plays a role

spur and groove morphology from a late devonian reef abstract spur and groove structures form on the windward side of modern coral reefs in response to wave action hitherto no examples have been confirmed in the palaeozoic record we confirm here ancient spur and groove morphology from the teichert hills an exhumed platform atoll from the upper devonian frasnian reef complex of the canning basin western australia oriented growth of the reef building metazoans laminar tabulate corals and stromatoporoid sponges proves an organic and constructional origin for the spurs grooves acted as sediment traps that filled with coarse bioclastic sand and winnowed brachiopods derived from the back reef and reef flat geometry and style of ancient spurs and grooves may provide indications of ancient synoptic hydrodynamic regimes on the basis of the relationship between modern coral reef spur orientation and incoming wave direction these ancient spurs are inferred to have formed normal to refracted waves the presence of these structures offers unequivocal evidence for the active growth of mid palaeozoic reefs in wave dominated hydrodynamic regimes and demonstrates that reef building biota can show a common morphological response to wave energy independent of taxonomic position

paleogene crustal anatexis and metamorphism in lhasa terrane eastern himalayan syntaxis evidence from u pb zircon ages and hf isotopic compositions of the nyingchi complex in the eastern himalayan syntaxis the southern lhasa terrane is dominated by middle to high grade metamorphic rocks nyingchi complex which are intruded by felsic melts u pb zircon dating and zircon hf isotopic composition of these metamorphic and magmatic rocks provide important constraints on the tectono thermal evolution of the lhasa terrane during convergent process between indian and asian continents u pb zircon data for an orthogneiss intruding the nyingchi complex yield a protolith magma crystallization age of 83 4 1 2 ma with metamorphic ages of 65 46 ma this orthogneiss is characterized by positive ehf t values of 8 3 and young hf model ages of 0 6 ga indicating a derivation primarily from a depleted mantle or juvenile crustal source zircons from a quartz diorite yield a magma crystallization age of 63 1 0 6 ma with ehf t values of 8 2 to 2 7 suggesting that this magma was sourced from partial melting of older crustal materials zircon cores from a foliated biotite granite show ages ranging from 347 to 2690 ma with age peaks at 347 403 ma 461 648 ma and 1013 1183 ma their zircon ehf t values range from 30 6 to 6 9 both the u pb ages and hf isotopic composition of the zircon cores are similar to those of detrital zircons from the nyingchi complex paragneiss implying that the granite was derived from anatexis of the nyingchi complex metasediments the zircon rims from the granite indicate crustal anatexis at 64 4 0 7 ma and subsequent metamorphism at 55 1 1 3 and 41 4 2 3 ma our results suggest that the late cretaceous magmatism in the southern lhasa terrane resulted from neo tethys oceanic slab subduction and we infer that paleocene crustal anatexis and metamorphism were related to the thermal perturbation caused by rollback of the northward subducted neo tethyan oceanic slab

a tectonic model reconciling evidence for the collisions between india eurasia and intra oceanic arcs of the central eastern tethys abstract despite several decades of investigations inferences on the timing and nature of collisions along the mesozoic cenozoic eurasian margin remain controversial we assimilate geological and geophysical evidence into a plate tectonic model for the india eurasia collision that includes continuously closing topological plate polygons constructed from a time dependent network of evolving plate boundaries with synthetic plates constructed for now subducted ocean floor including back arc basins that formed on the southern eurasian margin our model is regionally constrained and self consistent incorporating geophysical data from abyssal plains offshore west australia and east antarctica including jurassic age data from offshore northwest australia limiting much of northern greater india to a 1000 km long indenter originally reaching to the wallaby zenith fracture zone southern eurasia and southeast asia are riddled with dismembered oceanic arcs indicating long lived tethyan intra oceanic subduction this intra oceanic subduction system was well established from cretaceous time in the india eurasia convergence zone in the neotethys which was consumed during greater india s northward trajectory towards eurasia from the early cretaceous fragments of obducted oceanic crust within the yarlung tsangpo suture zone between india and eurasia predominantly date to the late jurassic or mid cretaceous barremian aptian the various ophiolites along strike and a hiatus in subduction related magmatism during the tithonian aptian suggest that there was at least one generation of intra oceanic arc formation whose plate boundary configuration remains uncertain paleomagnetic and magmatic studies suggest that the intra oceanic arc was at equatorial latitudes during the early cretaceous before subduction resumed further north beneath the eurasian margin lhasa terrane with another hiatus in subduction related magmatism along southern lhasa during 80 65 ma possibly as the back arc spreading centre approached the active andean style margin in our model greater india collided with the tethyan intra oceanic arc in paleocene eocene time finally closing the tethyan seaway from mid late eocene time which is consistent with the age of the youngest marine deposits found between india and eurasia geological evidence from the collision zone indicates an age of initial arc continent collision by 52 ma followed by the soft initial continent continent collision between india and eurasia by 44 2 ma this timing is supported by marine geophysical data where the spreading centres in the indian ocean record a drastic decline in seafloor spreading rates and changes in spreading directions first at 52 ma followed by another reorganisation at 43 ma the abandonment of spreading in the wharton basin and the onset of extrusion tectonics in asia by 36 ma are likely indicators of hard complete continent collision and highlight the multi stage collisional history of this margin our continuously evolving network of mid ocean ridge and subduction zone geometries and divergence convergence vectors through time provide a basis for future refinements to assimilate new data and or test alternative tectonic scenarios

40ar 39ar dating of the jiali and gaoligong shear zones implications for crustal deformation around the eastern himalayan syntaxis abstract we conducted a comprehensive 40ar 39ar geochronological study of the jiali and gaoligong shear zones to obtain a better understanding of crustal deformation and tectonic evolution around the eastern himalayan syntaxis ehs the new age data reveal that the main phase of deformation in the jiali and gaoligong shear zones occurred from 22 to 11 ma and from 18 to 13 ma respectively structural data collected during this study indicate that the jiali shear zone underwent a change in shear sense from sinistral to dextral during its movement history based on a comparison with the deformation histories of other major shear zones in the region we argue that the initial sinistral motion recorded by the jiali shear zone was coincident with that of the ailao shan red river shear zone which marked the northern boundary of the southeastward extrusion of the indochina block during the early miocene from the middle miocene 18 ma the jiali shear zone changed to dextral displacement becoming linked with the dextral gaoligong shear zone that developed as a consequence of continued northward indentation of the indian continent into asia since this time the jiali and gaoligong shear zones have been united defining the southwestern boundary of the ehs during clockwise rotation of the eastward extruding tibetan block as revealed by recent gps data the temporal change in regional deformation pattern from southeastward block extrusion to clockwise rotation of crustal fragments may have played an important role in the development of the eastern himalayan drainage system around the ehs

mesozoic and cenozoic volcanic rocks from central and southern tibet 39ar 40ar dating petrological characteristics and geodynamical significance field relations radiometric ages and mineralogical and chemical characteristics of the orogenic volcanic rocks from the lhasa block tibet are studied volcanic activity started before the deposition of the albian aptian sedimentary units takena formation and xigaze group volcanism is volumetrically limited in the northern part of the lhasa block basalts andesites and dacites are present while ignimbrites are scarce radiometric ages of these rocks range between 110 and 80 ma conversely in the southern part of the lhasa block volcanism is largely developed gangdese belt there paroxysmal activity occurred later than in the north between 60 and 50 ma lingzizong formation this volcanism is mainly represented by andesites and ignimbrites a younger episode at about 15 10 ma took place in this southern region the mineralogical and geochemical characteristics indicate that as a whole the volcanic rocks from the lhasa block belong to a calc alkaline continental margin series enriched in k20 and other incompatible elements subordinate potassic alkaline lavas are present in the northern margin of the gangdese belt some basalts exhibit a tholeiitic affinity daquin area southern region the geodynamic significance of these cenozoic volcanic rocks lies in the relative motion of india and the lhasa block after accretion of the latter to the northern qantang block a geodynamic model based on changes of the type of subduction of the indian oceanic crust beneath the lhasa block for the period 120 40 ma is proposed to account for the abundance age and magmatic affinity of the volcanic products

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

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

magmatic evolution of the western myanmar arc documented by u pb and hf isotopes in detrital zircon abstract the evolution of the magmatic arc formed along the asian margin of neo tethys is a key to understand india asia convergence in contrast to the well studied trans himalayan magmatic rocks in tibet the southeast extension of the arc is still poorly documented in myanmar where it is largely buried by sedimentary rocks this study investigates the magmatic evolution of the western myanmar arc and the potential along strike variation of subduction related magmatism by analyzing u pb and hf isotopes of detrital zircons from the chindwin basin in western myanmar our data indicate that the western myanmar arc wma experienced a long lasting magmatism since the early cretaceous with a main magmatic stage between 110 and 80 ma and a subordinate magmatic stage at 70 40 ma arc derived detrital zircons yield positive e hf t values and young model ages 0 1 1 2 ga indicating magma generation from a juvenile source such geochronologic and geochemical signatures compare well with those of the kohistan ladakh gangdese arc in tibet indicating uniform magmatic arc activity all along the asian margin of neo tethys

u pb zircon constraints on the tectonic evolution of southeastern tibet namche barwa area the eastern syntaxis of the himalayas is expressed in the crust as a pronounced southward bend in the orogen the change in strike of geologic features coincides with the high topography of the namche barwa region the exposure of granulite grade metamorphic rocks and a 180 degree bend in the yalu tsangpo we have conducted a geochronologic and geochemical investigation of several suites of granitoids collected from the namche barwa massif and subjacent terranes of southeastern tibet ranging from cm scale dikes and sills to larger outcrop scale intrusions u pb shrimp rg zircon ages establish at least five magmatic episodes 400 to 500 ma 120 ma 40 to 70 ma 18 to 25 ma and 3 to 10 ma these episodes broadly correlate to spatial patterns in sample localities as follows 400 to 500 ma ages occur in zircon cores collected from within the massif proper 120 ma granites related to early gangdese arc plutonism are primarily located northeast of namche barwa later 40 70 ma gangdese activity is expressed in granites west of namche barwa 18 to 25 ma granites occur both along the suture zone west of gyala peri and directly north of namche barwa along the area of the jiali fault zone and are attributed both to shearing within the jiali fault zone and to an early miocene gangdese thrust event exceptionally young 10 ma zircon ages are clustered near the core of the massif along the yalu tsangpo gorge trace element geochemical data indicates the presence of both fluid present and fluid absent melts with a fluid absent decompression melting regime dominating near the core of namche barwa

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

permian of west yunnan southwest china a biostratigraphic synthesis recent progress in the study of permian stratigraphy of western yunnan southwest china is reviewed with particular references to the tengchong and baoshan blocks and the changning menglian belt where confusion or controversy exists in stratigraphical nomenclature and or dating we attempt to clarify the situation based on our recent field observations and newly obtained research results the permian within the changning menglian belt embraces different stratigraphic successions suggesting different tectonic settings ranging from passive margin and active margin to oceanic basin and seamounts permo carboniferous faunas in the carbonate sequences of the changning menglian belt are of typical cathaysian affinity as demonstrated by abundant fusulinaceans and compound rugose corals the permian stratigraphy and faunas of the tenchong and baoshan blocks are markedly different from those of the changning menglian belt the baoshan block lacks upper carboniferous deposits and its subsequent lower permian sequence consists predominantly of siliciclastic strata yielding cool water faunas and possibly glaciogene diamictites overlain by thick basaltic lava and volcaniclastics of probably rift origin the upper part of the permian in the baoshan block is characterized by carbonates containing mixed cathaysian and gondwanan faunas the tengchong block has a similar evolutionary history to the baoshan block but completely lacks volcanic rocks

late cretaceous gangdese intrusions of adakitic geochemical characteristics se tibet petrogenesis and tectonic implications article i nfo the gangdese batholith emplaced from the cretaceous to eocene in southern tibet has been widely regarded as the major constituent of an andean type convergent margin resulting from northward subduction of the neo tethyan oceanic lithosphere under asia while the gangdese batholith consists predominantly of calc alkaline rocks we identify from the eastern part of the batholith a suite of epidote bearing granodiorites that shows adakitic geochemical characteristics marked with apparently higher la yb and sr y and lower y and hree than other gangdese rocks and common arc magmas shrimp zircon u pb analyses of two of the samples yielded 206 pb 238 u dates of 80 4 1 1 and 82 7 1 6 2 ma which constrain the emplacement ages of the adakitic rocks trace element modeling suggests that these rocks originated from partial melting of a garnet amphibolite source that on the basis of the sr and nd isotope data isr 0 7044 0 7048 end t 3 2 to 0 9 we interpret to be a newly underplated mafic lower crust rather than the subducted neo tethyan oceanic crust this juvenile crust was produced by cretaceous basaltic underplating above the mantle wedge and then thickened by the tectonic contraction owing to flattening of the neo tethyan subduction a process that also led to the adakitic magmatism our interpretation involving a late cretaceous flat slab subduction and related orogenesis in southern tibet is consistent with petrographic data such as the occurrence of magmatic epidote and muscovite rimmed with resorption texture in the granodiorites which indicate deep seated emplacement followed by rapid tectonic exhumation

exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone 1 the nordfjord sogn detachment zone nsdz is widely cited as one of the primary structures responsible for the exhumation of norwegian ultra high pressure uhp rocks here we review data from the considerable volume of research describing this shear zone and compile a strikeparallel cross section along the nsdz from the solund basin in the south to the soroyane uhp domain in the north this cross section highlights several previously unrecognized patterns revealing a shear zone with top to the west asymmetric fabrics that 1 initiated at amphibolite facies 2 overprints metamorphic breaks and tectonostratigraphic contacts and 3 has a gradational continuum of muscovite cooling ages these patterns constrain the kinematic evolution of the nsdz and suggest a new three step model for the exhumation of norwegian u hp rocks the initial stages of exhumation were characterized by the rise of crustal rocks from u hp depths to the base of the crust by buoyancydriven mechanisms not specified in this paper mantle exhumation was followed by top to thewest normal sense displacement within a broad noncoaxial ductile shear zone near the base of the crust that overprinted tectonostratigraphic contacts formed previously during mantle exhumation in the final stages of crustal exhumation top w brittleductile detachments soled into and partially excised this ductile shear zone dropping the devonian basins into contact with rocks of varying tectonostratigraphic levels this new interpretation of the nsdz is significant as it accounts for the extreme crustal excision observed in western norway using three sequentially overprinting structures active at different stages of uhp rock exhumation citation johnston s m b r hacker and t b andersen 2007 exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone tectonics 26 tc5001

neo tethyan evolution in southeastern extension of tibet constraints from early paleocene to early eocene granitic rocks with associated enclaves in tengchong block abstract the granite is one of most widely distribution rocks in crust and its petrogenesis is crucial to advance our knowledge of thermal condition in continental crust the long time tectonic evolution of crust in the active continental margin could be recorded by multi stages of granitic assemblage in order to reveal the subduction of neo tethys and initial collision of indian asian continents in eastern tibetan plateau we selected the early paleocene to early eocene granitic rocks with associated enclaves in tengchong block southeastern extension of gangdese magmatic belt to clarify their different derivation regimes using geochemical and isotopic compositions mineral compositional variation the zircon data show that early paleocene granites formed at 64 ma and early eocene granitic rocks formed at 54 ma combing with the field contact relationship the similar and enriched sr nd pb and zircon hf isotopic compositions indicate that the two stages of granitic rocks have a common and ancient lower crustal source the enclaves in early paleocene granites could represent crystallization of coeval and cognate magmas at margin of magmatic conduit but the enclaves in early eocene granitic rocks are products of magma mixing between mafic and felsic magma according to rock assemblages and geochemical signatures of granitic rocks during early paleocene to early eocene in tengchong block we propose that early paleocene granitic rocks are derived from partial melting of lower crustal rocks induced by long lived heat accumulation with no or minimal basalt flux during the neo tethyan subduction whereas early eocene granitic rocks are derived from melting of crustal materials resulted from high mafic magma flux during indian asian continental collision the initial collision occurred at ca 55 ma

tracing the transhimalayan magmatic belt and the lhasa block southward using zircon u pb lu hf isotopic and geochemical data cretaceous cenozoic granitoids in the tengchong block yunnan china abstract a number of cretaceous cenozoic granitoid bodies in the tengchong block were analyzed for their u pb zircon ages lu hf zircon isotopic compositions and whole rock geochemistry zircons from six different granite bodies in the central tengchong block have weighted mean 206 pb 238 u ages ranging from 76 to 65 ma and negative e hf t values ranging from 2 7 to 15 5 with t dm c ranging from 1312 to 1928 ma one dextrally sheared and gneissic granodiorite sample of the nabang shear zone in the western tengchong block yielded a weighted mean 206 pb 238 u age of 19 7 0 4 ma and positive e hf t values ranging from 0 2 to 10 7 with t dm c ranging from 418 to 1092 ma the late cretaceous granites have metaluminous and peraluminous affinities with strong enrichment of u and th and significant negative anomalies of eu ba sr nb p and ti the miocene granodiorite displays strong negative anomalies of nb ta p and ti and a weak negative eu anomaly the data suggest that the late cretaceous granites in the tengchong block were derived from partial melting of ancient most likely proterozoic continental crustal material whereas the miocene gneissic granodiorite was derived from partial melting of juvenile crustal material possibly within a supra subduction setting and intruded synkinematically into the active nabang shear zone lu hf isotopic data of late cretaceous paleocene granites are indistinguishable from those of granites of the central lhasa block thus we tentatively correlate the late cretaceous granites of the tengchong block with those of the central lhasa block the boundary between the south and central lhasa blocks in western tengchong may be exposed in the nne striking dextral nabang shear zone along the chinese myanmar border region which hosts early eocene granitoids with e hf t values 0 the lu hf data of the zircons from the gneissic miocene granodiorite indicate a juvenile crustal substrate in the western tengchong block as well the synkinematic miocene granodiorite provides an important age constraint for dextral shear at mid crustal levels which was active until at least c 19 20 ma in the nabang shear zone this miocene intrusion may be a first indication that active margin tectonics lasted 20 25 ma longer than in the gangdese belt and possibly was associated with deformation partitioning in the hinterland produced by increasing obliquity of subduction during clockwise rotation of sundaland during the india asia collision

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

u pb zircon chronology geochemical and sr nd isotopic composition of mesozoic cenozoic granitoids in the se lhasa terrane petrogenesis and tectonic implications abstract whole rock geochemistry sr nd isotope and zircon u pb isotope data are reported for seven granitoid intrusions from the eastern lhasa terrane our zircon u pb data exhibit three periods of magmatism 164 125 ma 83 ma and 71 45 ma granitoids from the middle jurassic to early cretaceous 164 125 ma display evolved nd isotope composition with end t 8 6 to 15 5 and t2dm 1 6 to 2 2 ga in contrast the late cretaceous 83 ma granitoids with adakitic characteristics high sr y ratios display less evolved nd isotopic composition with end t 0 3 to 3 0 and t2dm 0 9 to 1 1 ga geochemical and sr nd isotopic data indicate that the middle jurassic to early cretaceous granitoids were derived from partial melting of proterozoic crustal basement and the late cretaceous adakitic granitoids were derived from partial melting of over thickened lower crust geochemical and sr nd isotopic data of granitoids from the latest cretaceous to eocene period 71 45 ma reveal that they result from diverse magma sources including both juvenile and reworked mature crustal materials our compilation of new and published data from the eastern lhasa terrane show a marked variation in sr y ratios and a step change in sr nd isotope compositions during the late cretaceous we suggest that the middle jurassic to early cretaceous granitoids resulted from the northward neo tethyan ocean slab subduction the increasing sr y ratios from the middle jurassic to late cretaceous granitoids and northeastward migration of arc magmatism in the eastern lhasa terrane during the interval ca 125 95 ma are attributed to the shallowing angle of subduction of the neo tethyan ocean slab the late cretaceous magmatism in the eastern lhasa terrane probably resulted from the neo tethyan mid ocean ridge subduction and subsequent delamination of the arc root the latest cretaceous to eocene granitoids could be interpreted as a magmatic response to roll back and or break off of the subducted neo tethyan slab

permo carboniferous sequences of gondwana affinity in southwest china and their paleogeographic implications abstract in southwest china permo carboniferous depositional sequences of gondwana affinity were first discovered in the himalayan region by the expedition team of acadimia sinica in 1975 by 1983 gondwana affinity permo carboniferous sequences had been identified also in the lhasa block the south qiangtang block in tibet and the tengchong and baoshan blocks in yunnan these sequences are characterised by the presence of successions which are interpreted as glacio marine deposits and by the presence of gondwana affinity biota the distribution of gondwana affinity permo carboniferous indicates that basins whose remnants are now represented by the yarlung zangbo suture and the bangong nujiang suture did not exist at that time and the vast area south of the lungmu shuanghu jinshajiang zone in tibet and west of the changning menglian belt in yunnan formed a part of the northern margin of gondwana

zircon age and nd hf isotopic composition of the yunnan tethyan belt southwestern china the baoshan block of the tethyan yunnan southwestern china is considered as northern part of the sibumasu microcontinent basement of this block that comprises presumably greenschist facies neoproterozoic metamorphic rocks is covered by paleozoic to mesozoic low grade metamorphic sedimentary rocks this study presents zircon ages and nd hf isotopic composition of granites generated from crustal reworking to reveal geochemical feature of the underlying basement dating results obtained using the single zircon u pb isotopic dilution method show that granites exposed in the study area formed in early paleozoic about 470 ma pingdajie granite and in late yanshanian about 78 61 ma late cretaceous to early tertiary huataolin granite the early paleozoic granite contains archean to mesoproterozoic inherited zircons and the late yanshanian granite contains late proterozoic to early paleozoic zircon cores both granites have similar geochemical and nd hf isotopic charateristics indicating similar magma sources they have whole rock tdm nd values of around 2 000 ma and zircon tdm hf values clustering around 1 900 1 800 and 1 600 1 400 ma the nd hf isotopic data imply paleoproterozoic to mesoproterozoic crustal material as the major components of the underlying basement being consistent with a derivation from archean and paleoproterozoic terrains of india or nw australia both granites formed in two different tectonic events similarly originated from intra crustal reworking temporally the late yanshanian magmatism is probably related to the closure of the neotethys ocean the early paleozoic magmatism traced in the baoshan block indicates a comparable history of the basements during early paleozoic between the se asia and the western tethyan belt such as the basement outcrops in the alpine belt and probably in the european variscides that are considered as continental blocks drifting from gondwana prior to or simultaneously with those of the se asia

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

multi system geochronological and isotopic constraints on age and evolution of the gaoligongshan metamorphic belt and shear zone system in western yunnan china abstract the gaoligongshan metamorphic belt located east of the eastern himalayan syntaxis ehs in the yunnan province southwestern china is a compelling region in which to determine temporal constrains on crustal dynamic processes related to the himalayan orogeny we applied multi system geo and thermochronology 900 c to zircon u pb data reveal three magmatic events at 486 ma 136 ma and 76 ma similar ages are found in orthoderivative rocks of the neighboring tengchong and baoshan blocks and the gangdese batholith suggesting that the southern gaoligongshan is composed of an assemblage of lhasa and qiangtang terrane derived rocks muscovite rb sr ages of 35 21 ma are coeval with the onset of lateral crustal displacement along major shear zones in eastern tibet and indochina and with the post collision volcanic activity in western yunnan biotite rb sr and mica 40 ar 39 ar ages provide evidence that mylonitization along the gaoligongshan shear zone and crustal rotation of the tengchong and baoshan blocks proceeded during the miocene between 19 and 12 ma when the rocks rapidly cooled through the 350 280 c temperature range almost identical 40 ar 39 ar ages reported for the karakorum jiali parlung fault system in western tibet suggest that the gaoligongshan shear zone is the southeastern continuation of this fault recording the eastward extrusion of tibet and crustal movement around the ehs the final stage of exhumation of the gaoligongshan occurred between 8 and 5 ma at an average exhumation rate of 3 km ma as documented by apatite fission track and apatite u th sm he data this rapid exhumation was triggered by crustal root delamination and opening of the andaman sea our results clearly show that the complex tectonothermal evolution of the gaoligongshan was influenced by tibetan extrusion and escape tectonics associated with lower crustal flow around the ehs and the southeastward movement of indochina and back arc extension in response to andaman seafloor spreading

age and petrogenesis of a type granites in the middle segment of the bangonghu nujiang suture tibetan plateau abstract during geological investigations conducted over the past several years the authors found a group of a type granites in the middle segment of the bangonghu nujiang suture on the tibetan plateau these granitic plutons occur as stocks with exposed areas of less than 1 km 2 and lithologically include biotite granite and granodiorite porphyry which had intruded into cretaceous sedimentary rocks petrogeochemically the a type granites contain high sio 2 levels varying from 68 62 75 36 wt moreover they contain relatively high fe 2 o 3 t 0 86 5 39 wt and low al 2 o 3 12 76 15 54 wt levels and are weak peraluminous to metaluminous a trace element n morb normalized spider diagram showed apparent enrichment of the large ion lithophile elements lile rb th u k and pb with marked depletions of ba and sr the high field strength elements hfse nb ta and ti were sharply depleted with relative enrichment of zr and hf these signatures are characteristic of a type granite the granite samples had high rare earth element ree contents with ree 122 37 291 19 ppm light ree were rich relative to heavy ree with lree hree 4 89 9 58 and negative eu anomalies were sharp with eu varying from 0 14 0 5 and a mean value of 0 34 their chondrite normalized rare earth element distribution patterns appear as gently right dipping v types zircon u pb laicpms dating for three granitic plutons yielded weighted mean ages of 109 6 1 4 ma mswd 3 7 112 3 0 51 ma mswd 0 21 and 113 73 0 5 ma mswd 0 21 indicating that they formed in the late stage of the early cretaceous epoch the nd sr and pb isotopic results showed that the granites were rich in radiogenic isotopes the 87 sr 86 sr and i sr ratios varied from 0 719842 0 786395 and 0 706900 0 710378 respectively the 143 nd 144 nd ratios were from 0 512123 0 512392 with relatively large negative e nd values 3 37 to 10 34 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios ranged from 18 703 19 070 15 680 15 732 and 39 121 39 576 respectively exhibiting isotopic signatures typical of crustal sources all of the data demonstrated unanimously that these granites were derived from partial melting of arc basaltic rocks underplated in the lower crust during oceanic crust subduction the high temperature heat source for melting of anhydrous basaltic rocks of the lower crust was from upwelling asthenosphere through slab windows formed as a result of slab break off during post collisional extension of the orogenic zone

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

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

zircon u pb and hf isotopic constraints from eastern transhimalayan batholiths on the precollisional magmatic and tectonic evolution in southern tibet abstract before the indian collision with asia northward subduction of the neo tethyan oceanic lithosphere produced an andean type convergent margin in south asia characterized by arc magmatism starting from the early jurassic and lasting until the eocene the magmatic arc is now represented by widespread intrusive bodies or the so called transhimalayan batholiths in the lhasa terrane of southern tibet that have been divided into two main magmatic suites i e the northern plutonic belt and the southern gangdese batholith their temporal distribution concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern himalayan syntaxis however remains poorly constrained here we report the first combined zircon u pb and hf isotopic study of the transhimalayan batholiths from the eastern part of the lhasa terrane 95 97 5 e and 28 5 30 n se tibet zircon u pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the early cretaceous 133 110 ma and subordinately in the paleocene 66 57 ma long after an older granite intrusion in the earliest jurassic 198 ma the zircon ehf t values range from 5 to 20 yielding hf crustal model ages tdmc between 0 8 and 2 4 ga that peak at 1 7 ga suggesting a major episode of crustal growth in the proterozoic and a predominantly or even exclusively crustal source for the granitoid petrogenesis these zircon u pb and hf isotopic constraints together with whole rock geochemical characteristics allow us to correlate them to s type granitoids in the northern plutonic belt rather than to the i type gangdese batholith from the central part of the southern lhasa terrane in contrast to the gangdese magmatism that formed with a significant juvenile mantle input related to the neo tethyan subduction these s type granitoids show geochemical similarities to the north american cordilleran interior batholiths that did not form directly from a subduction setting thus we attribute the petrogenesis of the widespread early cretaceous granitoids in the northern belt and eastern himalayan batholiths to a postcollisional regime due to the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes under this framework the s type magmatism was generated in response to collision induced crustal thickening which may have capabilities of causing crustal anatexis by itself in the region however continued interplay with the neo tethyan subduction zone processes such as back arc extension could also have played a crucial and long lasting role in the magma generation

early late cretaceous ca 93 ma norites and hornblendites in the milin area eastern gangdese lithosphere asthenosphere interaction during slab roll back and an insight into early late cretaceous ca 100 80 ma magmatic flare up in southern lhasa tibet abstract at more than 500 km in length the mainly jurassic early eocene gangdese batholith is one of the most important constituents of the southern lhasa sub block and provides an ideal site for study of tibetan orogenesis recent studies on gangdese intermediate felsic intrusive rocks mainly granites demonstrate that remarkable crustal growth as well as an early late cretaceous ca 100 80 ma magmatic flare up event occurred in southern tibet however the mechanism that drove this magmatic event and its relationship to crustal growth event are not yet clear here we report detailed petrological geochronological geochemical and sr nd hf isotopic data for recently identified norites and hypersthene bearing hornblendites in the milin area southern lhasa sub block these mafic rocks are dated at early late cretaceous ca 93 ma and are characterized by relatively uniform sr nd hf isotopic compositions 87sr 86sr i 0 7042 to 0 7047 end t 2 9 to 3 6 and ehf t zircon 10 9 to 17 0 suggesting that they evolved from similar parental magmas the milin norites and hornblendites are likely to be the products of mineral fractionation and accumulation from a common parental magma during the early and late stages of the magma evolution respectively thermometric calculations indicate that pyroxenes from the milin norites have high crystallization temperatures 1240 1349 c the parental magmatic compositions calculated from pyroxene trace element compositions in the milin norites show slightly flat to enriched light rare earth element lree patterns la yb n 2 9 3 4 la gd n 2 1 2 9 with variable negative nb anomalies nb la n 0 18 0 81 indicating their dual or hybrid geochemical characteristics we suggest that their parental magmas may have been generated by the interaction of upwelling asthenospheric and metasomatized lithospheric mantle taking into account the spatial and temporal distribution of the mesozoic magmatic rocks and regional paleomagnetic data we further suggest that the early late cretaceous magmatic flare up in the southern lhasa sub block was also triggered by the asthenospheric upwelling which resulted from roll back of subducted tethyan oceanic slab

cenozoic volcanism in tibet evidence for a transition from oceanic to continental subduction geochronological k ar or ar ar major and trace element sr nd pb isotopic and mineral chemical data are presented for newly discovered cenozoic volcanic rocks in the western qiangtang and central lhasa terranes of tibet alkali basalts of 65 45ma occur in the western qiangtang terrane and represent primitive mantle melts as indicated by high mgnumbers 100 mg mg fe 54 65 cr 204 839 ppm and ni 94 218 ppm contents and relatively low ratios of sr sr 0 7046 0 7061 pb pb 18 21 18 89 pb pb 15 49 15 61 and pb pb 38 42 38 89 and high ratios of nd nd 0 5124 0 5127 in contrast younger volcanic rocks in the western qiangtang terrane 30ma and the central lhasa terrane 23 13 and 8ma are potassic to ultrapotassic and interpreted to have been derived from an enriched mantle source they are characterized by very high contents of incompatible trace elements negative ta nb and ti anomalies and radiogenic pb isotopic compositions pb pb 18 43 19 10 pb pb 15 64 15 83 pb pb 39 14 39 67 sr sr 0 7088 0 7092 and nd nd 0 5122 ratios of the western qiangtang terrane potassic lavas are similar to those of 45 29ma potassic volcanic rocks in the north central qiangtang terrane whereas sr sr 0 7167 0 7243 and nd nd 0 5119 ratios of central lhasa terrane lavas are similar to those of 25 16ma ultrapotassic volcanic rocks in the western lhasa terrane the 65 45ma alkali basalts in the western qiangtang terrane along with widespread calc alkaline volcanic rocks of this age in the lhasa terrane may be related to roll back of a previously shallow north dipping slab of tethyan oceanic lithosphere beneath tibet subduction as opposed to convective thinning of continental lithosphere is favored to explain potassic volcanism in tibet because of its occurrence in distinct east west trending belts 45 29ma in the qiangtang terrane 25 17ma in the northern lhasa terrane 16 8ma in the southern lhasa terrane and temporal and spatial relationships with major thrust systems

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

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

eureka peak fault afterslip following the 28 june 1992 landers earthquake abstract although surface ruptures of the principal landers faults apparently slipped co seismically surface slip on the 10 km long eureka peak fault has continued at a decreasing rate during the year following the mainshock three creepmeters installed on the fault as early as 4 days after the mainshock have recorded afterslip amplitudes of more than 8 cm on the northern half of the mapped fault the maximum observed slip 1 yr after the earthquake is 23 2 cm and an additional 1 to 3 cm of afterslip may occur on the fault in the next decade if the current rate of slip decrease remains steady should this occur it will bring surface slip amplitudes close to the 25 cm of slip inferred from geodetic data to have occurred at depth on the northern 4 km of the fault creepmeters on the fault record both episodic creep events and slow background slip but although changes in creep rate occur they do not correlate well with seismic moment release in volumes near the fault zone as is the case with many afterslip processes and other creeping faults in california the eureka peak fault cuts through sediments it is possible that such sedimentary layers and corresponding depths to which afterslip is occurring are relatively shallow or that the fault lacks a well developed gouge zone near sites where episodic creep is absent

geochemistry zircon u pb geochronology and hf isotopes of granites in the baoshan block western yunnan implications for early paleozoic evolution along the gondwana margin abstract the leucogranites in the baoshan block of the tethyan belt in western yunnan are composed mainly of two mica granite with subordinate muscovite granite here we present zircon u pb ages from four intrusions that show ages of 448 476 ma suggesting that these rocks were emplaced during the ordovician the leucogranites are high k calc alkaline and strongly peraluminous with k2o na2o 1 and a cnk 1 12 1 54 these rocks are enriched in large ion lithophile elements liles and light rare earth elements lrees la yb n 1 13 32 4 and pb and are depleted in high field strength elements hfses they show similar chondrite normalized ree patterns with negative eu anomalies eu eu 0 03 0 46 a wide range of zircon ehf t values 9 6 to 2 6 and varying hf isotope crustal model ages 2 1 1 6 ga are also observed the geochemical signatures indicate that the leucogranites are s type granites derived mainly from the anatexis of ancient crustal materials the ages geochemistry and tectonics in the baoshan block and the lhasa terrane are closely comparable suggesting that the baoshan block might represent part of an early paleozoic magmatic arc in the gondwana continental margin facing the proto tethyan ocean the pinghe granites of the early phase in the baoshan block which are coeval with the cambrian magmatism ca 492 ma identified in the central and southern lhasa subterranes can be interpreted as products of the slab break off associated with the subduction of proto tethyan oceanic lithosphere however the late leucogranite stocks are analogous to the north himalayan leucogranites which formed in a short lived extensional setting caused by the slab break off associated with the subduction collision system

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

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

geochemical investigation of early cretaceous igneous rocks along an east west traverse throughout the central lhasa terrane tibet article i nfo bulk rock major and trace element sr nd isotope zircon u pb and hf isotope data are reported for early cretaceous igneous rocks sampled along an east west traverse through the central lhasa subterrane e80 00 e89 in southern tibet these results offer new insights into the pre cenozoic geology and tectonomagmatic evolution of the lhasa terrane and provide boundary conditions for the origin and evolution of the tibetan plateau our new data together with data from the literature indicate that the early cretaceous magmatism in the central lhasa subterrane lasted for a long period 143 102 ma with a magmatic flare up at 110 ma the latter is accompanied by mafic magmatism in this terrane the silicic rocks are metaluminous to peraluminous and enrichedinrb th and u and depleted inba nb ta sr p and ti withvarying initial 87

zircon u pb ages in myanmar magmatic metamorphic events and the closure of a neo tethys ocean abstract previous isotopic age studies have concluded that the main metamorphism in the mogok metamorphic belt mmb in myanmar was tertiary and caused by collision with or underthrusting by india we present here results of zircon u pb age determinations on 18 samples from myanmar largely on intrusive rocks from the north trending 550 km long shan scarps segment of the sickle shaped mmb the oldest determination is 491 ma on orthogneiss north of mandalay interpreted as a protolith age and similar to the stratigraphic age of the bawdwin volcanics augen gneiss at kyaukse has a 114 ma protolith age our zircon u pb ages on undeformed intrusive rocks in the mmb range from cretaceous to miocene the oldest 128 ma on a diorite near yebokson implies an earliest cretaceous minimum age for regional metamorphism here younger ages on undeformed intrusions include 91 ma on diorite at mokpalin 72 ma on the weakly foliated garnet bearing nattaung granite 44 and 48 ma respectively on the mec and sedo granites and 17 20 ma on granite dykes for the 128 ma diorite sr and nd isotopes indicative of a continental crust component and mapped continuity of metamorphic host rocks suggest correlation with mid early cretaceous plutons in the eastern transhimalayas zircon u pb ages for the mec sedo and other granites within the mmb and slate belt help to define a late cretaceous to early eocene age range for mostly ilmenite series peraluminous granites within the western granite belt and more restricted western tin belt of myanmar and southern thailand in the wuntho popa arc west of the dextral sagaing fault our new u pb zircon age of 105 ma on diorite at salingyi supports previous k ar ages 106 93 ma for pre tertiary intrusions in the cretaceous this arc may have occupied the andaman sea and continued northwards through the mokpalin diorites and west of the mmb to the 103 80 ma i type plutons in the gandise batholith of southern tibet we interpret the mmb and slate belt as part of a western myanmar block separated in the jurassic from the shan plateau to the east by the southwestward continuation of the bangong nujiang luxi neo tethys i ocean we relate most intrusive and metamorphic events in and near the mmb to westward subduction of this ocean and end jurassic collision of the plateau with the overriding western myanmar slate belt block to orogenic polarity reversal and early cretaceous westward translation of the plateau sequence over the suture zone and to eastward subduction of the ancestral indian ocean or neo tethys ii beneath myanmar with generation of the wuntho popa arc beginning before the late cretaceous the mmb includes meta plateau rocks near mandalay but meta slate belt rocks to the north and south within the mmb previous monazite xenotime thorite ages of eocene oligocene and oligocene early miocene cooling ages on micas with no deformation in eocene granites suggest a high temperature thermal event related to intrusion of these and other granites during a previously proposed regional extension our data imply that the main fabric forming metamorphic event in the mmb pre dated the india asia collision