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

ar ar and u pb ages of marble hosted ruby deposits from central and southeast asia to date the formation of ruby deposits and link it to the regional metamorphism associated with tertiary himalayan orogenesis 40ar 39ar stepwise heating experiments were performed on single grains of phlogopite syngenetic with ruby and zircon inclusions in ruby and spinel were dated with the u pb method by ion probe the ar ar ages of phlogopites associated with ruby are oligocene 24 7 0 3 ma at jegdalek in afghanistan miocene at mogok in myanmar 18 7 0 2 to 17 1 0 2 ma at hunza in pakistan 10 8 0 3 to 5 4 0 3 ma and chumar in nepal 5 6 0 4 ma and pliocene 4 6 0 1 ma at ruyil in nepal in vietnam a zircon included in a ruby from the quy chau deposit yielded a 238u 206pb age of 53 8 4 6 ma whereas in the red river shear zone ruby formed at around 40 36 ma during ductile deformation under peak metamorphic conditions the ages obtained in this study are in agreement with those previously published for the ruby bearing metamorphic belts and document extensional tectonics tha

mesozoic cenozoic tectonic evolution and metallogeny in myanmar evidence from zircon cassiterite u pb and molybdenite re os geochronology abstract it is well known that there are many sn w mo and cu au metal resources in myanmar however the absence of precise mineralization ages for these deposits significantly hinders to understand the close genetic relationship among metallogeny ore bearing intrusions and tectonic evolution in this study two groups of consistent molybdenite re os and zircon u pb ages indicate that the dapingba mo w deposit in northern myanmar tengchong terrane formed at early cretaceous 119 ma and 114 ma the dapingba ore bearing granitic magmas were mainly derived from melting of ancient tengchong crust on the basis of zircon hf isotopic compositions ehf t 9 3 to 2 5 moreover the first reported cassiterite u pb ages of 60 ma for the bawapin and kalonta sn w deposits in southern myanmar western sibumasu terrane suggest that the two deposits formed at paleocene whereas the precise molybdenite re os age for the shangalon porphyry cu au deposit in the west burma terrane indicates that this deposit formed at eocene 39 ma importantly combined with previous studies on tectonic evolution and magmatic petrogenesis in myanmar and southwest china a comprehensive mesozoic cenozoic tectono magmatic and metallogenic model are proposed two periods of early cretaceous 120 114 ma and late cretaceous 75 70 ma crust derived felsic melts and related mo sn w deposits from the tengchong and western sibumasu terranes likely formed in a continental arc during subduction of the meso and neo tethys oceanic lithosphere respectively subsequently paleocene eocene 60 50 ma sn w deposits and coeval ore bearing granites in the western sibumasu terrane possibly formed during roll back of the neo tethys oceanic slab after 50 ma india asia collision eocene 41 39 ma porphyry cu au west burma terrane and sn w deposits western sibumasu terrane likely formed during the neo tethys oceanic slab tear and break off in a collisional setting whereas miocene 19 14 ma high sulfidation epithermal cu deposit in the west burma terrane possibly formed in an arc setting during oblique subduction of the indian oceanic lithosphere

the modi taung nankwe gold district slate belt central myanmar mesothermal veins in a mesozoic orogen abstract the recently discovered quartz gold veins comprising the modi taung nankwe gold district in central myanmar are largely hosted by mudstones of the late palaeozoic slate belt mesozoic rocks of the paunglaung mawchi zone separate the slate belt from the shan scarp and shan plateau to the east at modi taung 5 km of exploration adits indicate that the veins within steeply dipping oblique reverse slip shear zones are displaced by movements along the shears intruded by late jurassic calc alkaline dykes and offset on conjugate cross faults drill intercepts show that mineralization extends vertically for more than 500 m coarse visible gold book and ribbon texture and stylolitic laminations and trace metal values are consistent with mineralization at mesothermal depths of several kilometres in the brittle ductile regime our field observations suggest that mineralization took place in the early jurassic following collision of myanmar on the passive western margin of a greater shan thai continental block with an oceanic arc on the overriding plate to the west collision generated intra continental thrusting in and east of the paunglaung mawchi zone metamorphism of plateau rocks thrust west beneath the slate belt to form the mogok metamorphics and ascent of mineralizing fluids expelled from dehydrating underthrust rocks reversal in orogenic polarity initiated late jurassic eastward subduction of oceanic crust beneath myanmar and generation of a magmatic arc with dykes cutting the quartz gold veins renewed east directed thrusting translated the slate belt over arc clastics and probably resulted in exhumation of the mogok metamorphics and offsets of the veins on conjugate faults young k ar rb 87 sr 86 and ar 40 ar 39 ages on the mogok metamorphic belt imply renewed tertiary uplift and possibly intrusion of mid tertiary or palaeogene granites

geochemical and sr nd isotopic characteristics of cretaceous to paleocene granitoids and volcanic rocks se tibet petrogenesis and tectonic implications abstract northward subduction of the neo tethyan oceanic lithosphere beneath south asia gave rise to an andean type convergent margin with arc magmatism starting since at least the early jurassic and lasting until the eocene this study reports geochemical and sr nd isotope data of the early cretaceous 133 110 ma to paleocene 60 ma magmatic belt that formed in the eastern lhasa terrane se tibet including three major transhimalayan batholiths namely azhagong demulha and chayu and an early cretaceous volcanic succession from ranwu area all these rocks show relative enrichments in lile and lree and depletions in hfse corresponding to the geochemical characteristics of arc magmas from modern subduction zones while the azhagong batholith consists typically of metaluminous i type granitoids that occasionally contain mafic enclaves highly fractionated peraluminous s type and a type granites are observed from the chayu and demulha batholiths respectively these granitoids as a whole show heterogeneous sr and nd isotope ratios with e nd t varying from 1 5 to 13 and i sr from 0 703 to 0 745 the ranwu volcanic rocks which range from basaltic to dacitic compositions are calc alkaline in nature they have e nd t from 3 to 6 and i sr from 0 705 to 0 707 overlapping the isotopic range of the azhagong mafic enclaves the overall geochemical and sr nd isotope data suggest three magma source components involved in the petrogenesis which are the mantle wedge and the lower and upper parts of the lhasa continental crust accordingly we propose a two stage petrogenetic model involving 1 deep level differentiation of the mantle wedge derived mafic magmas associated with assimilation by the lower continental crust of the lhasa terrane and 2 additional differentiation and upper crustal contamination of the evolved magmas as they rise and install in shallow level magma chambers while the first stage can explain how the ranwu volcanics and azhagong enclaves formed the second accounts for the emplacement of the azhagong and chayu batholiths the shallow intrusions moreover may have caused low pressure melting of existing calc alkaline rocks of paleoproterozoic nd isotope model age to produce the early cretaceous 125 ma a type granites in the demulha batholith a specific rock type that occurs rarely in subduction zones but echoes with the notion for an extension setting in the region this setting may have taken place after the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes and interacted with the back arc evolution in the neo tethyan subduction system

linking a prolonged neo tethyan magmatic arc in south asia zircon u pb and hf isotopic constraints from the lohit batholith ne india the neo tethyan subduction that operated before the india asia collision resulted in an andean type convergent margin in south asia and was associated with extensive arc magmatism that formed the transhimalayan batholiths magmatism in the gangdese batholith the largest batholith exposed in the lhasa terrane of southern tibet is considered to have lasted from the early jurassic to eocene however eastward correlation of the gangdese batholith is uncertain because it is truncated by the eastern himalayan syntaxis here we report new data from the lohit batholith ne india including i zircon u pb ages of five granitoids from ca 148 to 96 ma and ii zircon hf isotopes of these rocks that yield high and positive ehf t values we argue that the lohit batholith is the eastward extension of the gangdese batholith and can be correlated southward to the wuntho popa arc in west burma thus linking a prolonged neo tethyan magmatic arc system from southern tibet to southeast asia

transcurrent movements in the burma andaman sea region the drag produced by the northward movement of the indian plate has caused the indoburman ranges an accretionary prism to decouple from the burma plate along the kabaw fault and the burma plate itself has decoupled from the eastern highlands of burma along the sagaing fault the indoburman ranges have probably been dragged north slightly ahead of the burma plate although at times the two plates may have locked together to move as one unit it is suggested that the double arc formed by the indoburman ranges and the andaman nicobar sumatra islands was formerly one large single arc northward translation of this larger single arcuate structure has caused the tail end of the arc i e the andaman nicobar sumatra section to rotate into the burma plate causing a bending of the arc to form the present double arc and compression within the burma plate to form the pegu yoma folding northward movement of the burma plate has also resulted in offset by over 400 km of the irrawaddy river from its former connection through the channel of what is now the chindwin river

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

deciphering relationships between the nicobar and bengal submarine fans indian ocean abstract the nicobar fan and bengal fans can be considered as the eastern and western parts respectively of the largest submarine fan system in the world this study presents the integrated results of petrographic and provenance studies from the nicobar fan and evaluates these in the context of controls on sedimentation both fans were predominantly supplied by himalaya derived material from the main tectono stratigraphic sequences as well as the gangdese arc a lack of volcanic material in the nicobar fan rules out sources from the sumatra magmatic arc overall the petrographic data shows a progressive decrease in sedimentary detritus and corresponding increase of higher grade metamorphic detritus up section changes in sediment provenance and exhumation rates in the himalaya are seen to track changes in sediment accumulation rates high sediment accumulation rates in the bengal fan occurred at 13 5 8 3 ma and in the nicobar fan from 9 5 5 ma both fans show peak accumulation rates at 9 5 8 3 ma but with the nicobar fan being about twice as high and both record a sharp drop from 5 5 5 2 ma that coincided with a change in river drainage associated with the brahmaputra river diverting west of the uplifting shillong plateau at 5 ma the nicobar fan was supplied by an eastern drainage route that finally closed at 2 ma when sediment accumulation rates in the nicobar fan significantly decreased sediment provenance record these changes in routing whereby bengal fan deposits include granitoid sources from the namche barwa massif in the eastern syntaxis that are not seen in the nicobar fan likely due to a more localised eastern drainage that included material from the indo burman wedge prior to 3 ma source exhumation rates were rapid and constant and the short lag time rules out significant intermediate storage and mixing in terms of climate versus tectonic controls tectonically driven changes in the river network have had most influence on fan sedimentation

the crustal architecture of myanmar imaged through zircon u pb lu hf and o isotopes tectonic and metallogenic implications abstract the tethys margin in central and eastern asia is comprised of continental terranes separated by suture zones some of which remain cryptic determining the crustal architecture and therefore the geological history of the eastern tethyan margin remains challenging sited in the heart of this region myanmar is a highly prospective but poorly explored minerals jurisdiction a better understanding of myanmar s mineralization can only be realized through a better understanding of its tectonic history itself reflected in at least four major magmatic belts the eastern and the main range provinces are associated with the late permian to early triassic closure of palaeo tethys the mogok mandalay mergui belt and wuntho popa arc are a response to the eocene closure of neo tethys however magmatic ages outside these two orogenic events are also recorded we present new zircon u pb lu hf and o isotope data from magmatic rocks across myanmar which we append to the existing dataset to isotopically characterize myanmar s magmatic belts eastern province permian i type magmatism has evolved ehf 10 9 to 6 4 whilst main range province triassic s type magmatism also records evolved ehf 13 5 to 8 8 the mogok mandalay mergui belt is here divided into the tin province and the mogok metamorphic belt the tin province hosts ca 77 50 ma magmatism with evolved ehf 1 2 to 15 2 and 18o of 5 6 8 3 the mogok metamorphic belt exhibits a more complex magmatic and metamorphic history and granitoids record jurassic late cretaceous and eocene to miocene phases of magmatism all of which exhibit evolved ehf values between 4 6 and 17 6 and 18o between 6 3 and 9 2 from the tagaung myitkyina belt we report a magmatic age of 172 ma and ehf of 18 1 to 10 8 to accommodate the geological evidence we propose a tectonic model for myanmar involving a greater sibumasu where the documented zircon isotopic variations reflect compositional variations in magmatic source and invoke the role of a tengchong block the baoshan block and greater sibumasu were likely assembled on or before the triassic a former andean margin and suture which may lie across the northern shan plateau and reflected in isotopic differences between the northern and southern parts of the mogok metamorphic belt this contiguous sibumasu baoshan block then sutured onto the indochina margin in the late triassic we propose that a tengchong block within myanmar provides for a southerly termination of the meso tethys suture immediately north of the mogok area a discrete tengchong block may explain a discontinuous arc of late triassic to jurassic i type magmatism in central myanmar representing an andean type margin sited above a subducting meso tethys on the margin of sibumasu the tengchong block sutured onto greater sibumasu before the late cretaceous after which subduction of neo tethys drove the magmatism of the wuntho popa arc and ultimately that of the tin province the metallogenic character of granite belts in myanmar reflects the crustal architecture of the region which is remarkable for its prolific endowment of granite hosted sn w mineralization in two quite distinct granite belts related to sequential indosinian and himalayan orogenesis

structures uplift and magmatism of the western myanmar arc constraints to mid cretaceous paleogene tectonic evolution of the western myanmar continental margin abstract knowledge of trans himalayan tectono magmatic evolution is critical to understanding the complex pre collisional history of southern eurasia active continental margin it has been proposed that magmatic rocks of the trans himalayan batholith extending from southern tibet to southeast asia are now exposed as the western myanmar arc and central granite belt in myanmar yet origin emplacement and relationships of the two juxtaposed belts remain poorly constrained in this study 2d seismic and drilling data for the western myanmar arc zircon u pb age and hf isotope and whole rock geochemical data for magmatic rocks from the arc have been applied our seismic profiles borehole stratigraphic sequences and zircon u pb data show that a typical arc basin system was well developed along the western myanmar continental margin the magmatic arc has experienced at least three igneous events in the mid cretaceous 110 90 ma latest cretaceous early paleocene 69 64 5 ma and eocene 53 38 ma as well as three associated uplift processes in the late cretaceous eocene and late oligocene whole rock geochemical characteristics and zircons showing variable but predominately positive e hf t values suggest a significant juvenile mantle source involving a proportion of ancient subducted sediments and juvenile crustal materials for these typical arc related magmatic rocks the identification of mid cretaceous to paleogene magmatic rocks having positive e hf t values from the western myanmar arc 1 indicates that the magmatism can be correlated with the gangdese arc within the lhasa terrane of the southern tibetan plateau 2 provides evidence for the proximal derived model that paleogene sediments in the central myanmar basin were from the western myanmar arc but were not delivered by the paleo yarlung tsangpo irrawaddy river system from the gangdese arc and 3 enables a model of eastward subduction of the neo tethyan indian oceanic crust to reflect onset of the magmatism at the mid cretaceous and a long existed back arc extension in western myanmar

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

genesis of the xiaolonghe quartz vein type sn deposit sw china insights from cathodoluminescence textures and trace elements of quartz fluid inclusions and oxygen isotopes abstract quartz textures revealed by scanning electron microscope cathodoluminescence sem cl images suggest that quartz in the xiaolonghe sn deposit formed in at least three fluid episodes quartz q1 in the pre ore silicification zone has homogeneous texture high cl intensity and high ti content 19 53 ppm fluid inclusions hosted in q1 are vapor rich v1 type and homogenized as supercritical fluid at 570 c quartz q2 in the syn ore topaz cassiterite quartz veins has lower cl intensity and is characterized by euhedral growth zones with lower ti content 1 3 12 ppm fluid inclusions hosted in q2 topaz and cassiterite are liquid rich fluid inclusions of moderate salinity 15 wt nacl equiv l1 type which homogenized at 423 c the post ore quartz q3 closely associated with sericitization of topaz generally crosscuts q2 and has dark cl intensity and much lower ti concentration the upper limits of t p conditions of pre ore and syn ore stage are constrained by the intersection of nacl h2o fluid inclusion isochores and ti in quartz isopleths and the lower limits are based on microthermometry results of fluid inclusions combined with the 18ofluid value 8 3 of q1 it indicates that the pre ore supercritical fluid was directly exsolved from a granitic magma at t 570 600 c and p 0 70 0 77 kbars corresponding to a maximum depth of 2 8 km under lithostatic pressure the syn ore subcritical fluid 8 0 18ofluid 6 3 mixed with some meteoric water was under 423 450 c 0 32 0 45 kbars the transition from the pre ore supercritical fluid to the syn ore subcritical fluid indicates boiling condition probably at 512 c 0 62 kbars which was likely caused by hydraulic fracturing under high pressure both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in xiaolonghe sn deposit in the post ore stage the coexisting s type and v2 type fluid inclusions in q3 indicates a second fluid boiling at 269 c 0 05 kbars which was probably caused by decompression due to rapid denudation of the overlain strata the low salinity 5 5 wt nacl equiv l2 type fluid inclusions hosted in fluorite homogenized at 199 c and

rock relationships in the mogok metamorphic belt tatkon to mandalay central myanmar abstract the mogok metamorphic belt mmb over 1450 km long and up to 40 km wide consists of regionally metamorphosed rocks including kyanite and sillimanite schists and granites lying along the western margin of the shan plateau in central myanmar and continuing northwards to the eastern himalayan syntaxis exposures in quarries allow correlation of palaeozoic meta sedimentary early mesozoic meta igneous and late mesozoic intrusive rocks within a 230 km long northerly trending segment of the mmb from tatkon to kyanigan north of mandalay and with the mogok gemstone district 100 km to the northeast relationships among the metamorphic and intrusive rocks with sparse published radiometric age controls indicate at least two metamorphic events one before and one after the intrusion of late jurassic to early cretaceous calc alkaline rocks these relationships can be explained by either of two possible tectonic histories one constrained by correlation of mid permian limestones across myanmar requires early permian and early jurassic regional metamorphic events prior to an early tertiary metamorphism in the western part of but within a shan thai western myanmar block the second not compatible with a single laterally continuous permian limestone requires pre upper jurassic regional metamorphism and orogenic gold mineralization in the mergui group and western myanmar early cretaceous collision of an east facing mergui western myanmar island arc with the shan plateau and early tertiary metamorphism in the mmb related to reversal in tectonic polarity following the arc plateau collision

post permian events in the zangbo suture zone tibet the mesozoic geology of the zangbo zone in tibet is closely comparable to that of the zone9s continuation through western burma deposition of triassic turbidites and locally jurassic sediments on and immediately oceanward of the passive asian margin was followed by imbrication above subducting ocean floor in the early cretaceous the subducting slab became detached from the downgoing lithosphere and accreted to asia in the late lower cretaceous emplacement of the detached slab by southward thrusting over its triassic flysch cover to form the zangbo and western burma ophiolite took place respectively in or after the cenomanian and before the albian subsidence and deposition of albian limestones and mudstones in burma and of the xigatse flysch in a fore arc basin in tibet were followed in both regions by pre campanian uplift and campanian to early maastrichtian marine deposition maastrichtian olistostromes resulted from underthrusting and tectonic burial of poorly consolidated campanian sediments their extrusion together with blocks of adjacent older rock and downslope flow of the extruded melange collision of india with asia in the eocene was not associated with ophiolite emplacement and in the zangbo region resulted chiefly in northward directed thrusting of the triassic flysch and ophiolite over the xigatse flysch with consequent narrowing of the fore arc basin

genesis of a magmatic metamorphic hydrothermal system the sn w polymetallic deposits at pilok thailand cassiterite wolframite and base metal mineralization in the pilok area are hosted by veins and stockworks in the apical portion of leucocratic granite stocks close to their contacts with pelitic metasedimentary rocks a minimum pressure of emplacement of approximately 1 500 bars is indicated by the presence of two coexisting feldspars in the granites and a moderate depth is supported by a lack of coeval volcanism and absence of porphyritic textures that characterize hypabyssal intrusions a contact metamorphic metasomatic aureole in the surrounding pelitic metasediments consists of tourmaline biotite and muscovite zones that are superimposed on muscovite chlorite zone regional metamorphism whole rock carbon analyses demonstrate a volatilization of graphite in the metasediments as a function of distance from the intrusion and the presence of andalusite in the aureole constrains the maximum pressure to approximately 3 800 bars the earliest mineralization is late magmatic to early postmagmatic wolframite cassiterite intergrown with li and f rich muscovite in pegmatite pods the bulk of the wolframite mineralization was subsequently deposited in veins with potassic alteration which could have originated either by orthomagmatic or remobilization processes finally cassiterite and sulfides chalcopyrite sphalerite were deposited in association with greisen alteration and formed as a result of the remobilization of tin from the host granite fluid inclusion and stable isotope data indicate the involvement of at least four fluid types a moderately saline fluid of presumed magmatic origin aqueous carbonic metamorphic fluids low temperature and low salinity meteoric fluids and high salinity formational or metamorphic fluids the isotopic compositions of waters calculated from delta o 18 analyses of quartz muscovite and cassiterite and delta d analyses of muscovite range from 1 4 to 9 4 and 63 to 118 per mil respectively these are consistent with the mixing of magmatic and organic rich metamorphic fluids oxygen isotope thermometry indicates temperatures of 350 degrees to 500 degrees c for cassiterite mineralization the oldest preserved fluid inclusions are primary aqueous carbonic inclusions from wolframite and cassiterite mineralization both the homogenization of the carbonic phase and the bulk

diachronous cooling along the mogok metamorphic belt shan scarp myanmar the trace of the northward migration of the indian syntaxis abstract we present new observations and new mineral ages eight by the 40 ar 39 ar and nine by the 40 k 40 ar methods from high grade metamorphic and foliated intrusive rocks collected along the mogok metamorphic belt of central myanmar that complete preliminary results we previously published all 30 ages presented here confirm the oligocene to middle miocene age of the mogok metamorphism moreover the ages are young from the gulf of martaban in the south to the china myanmar border in the north showing a clear diachronism these results confirm a northward migration of the tectonic event responsible for the cooling of our samples at a velocity similar to the india relative to indochina velocity at the same period in addition intensive field work along a 800 km long section of the mogok metamorphic belt has revealed the numerous ductile structures that resulted from a strong nnw sse trending extension from the analogy between the present day local extrusion around the eastern indian syntaxis and the extension observed along the mogok metamorphic belt and from the diachronism we document we suggest that the central part of myanmar has recorded the northward passage of the eastern indian syntaxis with respect to indochina from oligocene to middle miocene

mid cenozoic fluvio deltaic to marine environments of the salin sub basin central myanmar abstract the salin sub basin is one of several basins within the wide elongate north south trending central basin in myanmar a field based campaign targeted the deposits of the reportedly oligocene shwezetaw padaung and okhmintaung formations which previously have been described only from spatially restricted and incomplete core records and limited field studies a minimum of 2 5 km thickness of these formations in the sub basin records a high sedimentation rate and long term subsidence which broadly kept pace with sediment input facies analysis based on sedimentary logs and panel diagram interpretation interprets these formations as deposits of large scale broadly southward flowing fluvial systems that interacted with deltaic and shallow marine environments in the southwestern parts of the basin a switch from south to southwest flowing rivers midway down the basin suggests these systems fed sediment to offshore basins in the west the overall environment was somewhat similar to the modern day irrawaddy river and delta despite the recorded high sedimentation rates and the coeval subsidence the depositional environment does not show much variation the main control is overall relative sea level rise associated with a northeastward marine transgression into the basin with contemporaneous smaller scale cycles of sea level rise and fall in terms of basin development this considerable thickness of clastic sediment indicates significant emergent sources palaeoenvironment reconstructions suggest that the south flowing fluvial systems sourced sediment from the northern margin of the basin but there were also some channels joining the main channel from the western margin of the basin and fewer channels from the northeast

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

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that

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

timing of syenite charnockite magmatism and ruby and sapphire metamorphism in the mogok valley region myanmar we thank the oxford burma aung san suu kyi trust for funding research and fieldwork visits to myanmarfor ms ng and lr geochronology was funded by ucsb and nsf grants ear 1348003and ear 1551054

the phuket supersuite southwest thailand fractionated i type granites associated with tin tantalum mineralization the phuket supersuite of southwestern thailand displays a transition from an i to s type character that may result from extensive crystal fractionation of an i type melt rather than implying a metasedimentary protolith for the latter the most evolved granites form large low grade tin tantalum deposits and are associated with the development of extensive mineralized pegmatite fields the less evolved members of the phuket supersuite including the khao prathiu suite consist of metaluminous granites asi 0 95 1 00 that contain hornblende allanite titanite and magnetite the kata beach suite granites asi 0 97 1 13 contain hornblende biotite in less evolved parts but only biotite in the more evolved parts minor minerals include allanite titanite ilmenite and tourmaline the lam pi suite consists of ilmenite series biotite muscovite granites asi 1 03 1 15 that contain ilmenite monazite and tourmaline among the minor mineral phases the lain pi suite is associated with the development of tin tantalum pegmatites the most evolved granites in the phuket supersuite include the khao tosae suite on phuket island and the nok hook granites that form part of the khao kata khwam batholith in the takua pa region the khao tosae suite consists of biotite muscovite granites asi 1 05 1 17 that contain garnet ilmenite monazite tourmaline and cassiterite and is associated with extensive tin tantalum pegmatites that range to a very high asi value 1 5 muscovite tourmaline and tourmaline muscovite granites in the nok hook area asi 1 13 1 26 contain topaz monazite rutile cassiterite and columbite and form large low grade tin tantalum deposits that are mined by hydraulic techniques consideration of existing isotopic data suggests that the phuket supersuite may have originated via partial melting of a mafic to intermediate meta igneous source of probable proterozoic age these source rocks had evolved to relatively high 87 sr 86 sr by the cretaceous and were capable of yielding partial melts with 86 sr 87 sr initial ratios 0 71 the high initial ratios interpreted for some of the mineralized phases of the phuket supersuite e g 87 sr 86 sr initial ratio 0 74 for the khao tosae suite probably originated through high level processes involving crystal fractionation hydrothermal alteration and or exchange of sr with the host metasediments

ion microprobe zircon u pb age and geochemistry of the myanmar jadeitite combined geochemistry and geochronology of the myanmar jadeitite were determined bulk rock trace element compositions display u shaped ree patterns with pronounced positive eu anomalies the total ree abundances are very low less than half chondritic and the high field strength elements and some large ion lithophile elements are moderately enriched these features indicate a metasomatic origin there are three groups of zircons with different interior characteristics cathodoluminescence mineral inclusions chemical compositions and sensitive high resolution ion microprobe u pb ages group i zircons with a mean age of 163 2 3 3 ma mostly have distinct oscillatory zoning highest u and th contents and na free mg rich mineral inclusions and thus indicate an igneous formation of oceanic crust or hydrothermal serpentinization and or rodingitization event in the middle jurassic group ii zircons with a mean age of 146 5 3 4 ma have bright luminescence without oscillatory zoning and include jadeite and jadeitic pyroxene inclusions suggesting that formation of the myanmar jadeitites as well as subduction of the eastern indian oceanic plate occurred in the late jurassic group iii zircons have an age of 122 2 4 8 ma which represents a later unknown thermal event discovery of the middle jurassic zircons provides geochronological constraint on the tectonic evolution of the eastern indo burman range

multiple alternating forearc and backarc ward migration of magmatism in the indo myanmar orogenic belt since the jurassic documentation of the orogenic architecture of eastern neotethys in se asia abstract we integrated our new data with a review of published work on the indo myanmar orogenic belt imob of the eastern neotethys in myanmar western yunnan china and naga hills india in order to better understand subduction accretion processes of the neotethys ocean in se asia and interactive relationships between the gondwana and laurasia supercontinents from east to west the imob is divided into three geographic units the shan thai plateau myanmar central basin and indo burma range the mogok metamorphic and slate belt is within the shan thai plateau the shan thai plateau and eastern myanmar central basin contain paleozoic sedimentary successions low grade to amphibolitic facies metamorphic rocks and the luxi ultramafic and myitkyina mogok ultramafic diorite belts unmetamorphosed and metamorphosed sediments have similar detrital zircon age peaks of 1000 ma and 700 ma or 500 ma and they are separated by the luxi ultramafic belt whose end 0 and 87sr 86sr i values are similar to surrounding granite diorite and migmatite and the os 4 8 8 8 is indicative of old sub continental lithospheric mantle rather than an oceanic suture zone these data and relations suggest that these regions belong to the cimmerian continental sliver derived from the gondwana supercontinent the myitkyina mogok ultramafic diorite belt located along the eastern margin of the myanmar central basin that was associated with the continental sliver contains peridotite andesite hornblende gabbro diorite granodiorite and plagiogranite all with arc geochemical signatures and ages of 177 166 ma the source region of some of these igneous rocks contains a component of em1 which is close to low 87sr 86sr i ratio of a migmatite in the cimmerian continental sliver as shown by sr nd isotopes values suggesting this belt developed as a jurassic continental margin arc the mogok metamorphic and slate belt contains granodiorite diorite tonalite granite and migmatite extending from the gongshan tengchong and luxi areas in western yunnan china to mandalay kalaw padatchaung and moulmein in myanmar these rocks have arc geochemical character and yield ages of 185 170 ma 128 112 ma 91 ma and 75 45 ma suggesting development of four episodes of arc magmatism along the central axis of the myanmar central basin there are magmatic arc related 106 94 ma diorite granodiorite and tonalite as well as eocene and neogene present 38 0 ma andesite dacite trachyte and rhyolite accretion took place along the central axis of the myanmar central basin towards the indo burma range and westward to the present trench axis on the margin of the indian ocean as shown by westward younging of accretionary complexes and trench slope basins a jurassic accretionary complex located in the hpakan area in the north of the myanmar central basin contains 189 147 ma high pressure metamorphic rocks such as jadeitite garnet mica schist and glaucophane schist in the eastern belt of the indo burma range early cretaceous 119 115 ma accretionary complexes consist of upper plate triassic unmetamorphosed and low grade metamorphic sediments and lower plate amphibolites high pressure metamorphic rocks and jurassic early cretaceous oceanic plate stratigraphy containing morb and oib type basalts and thin bedded radiolarian cherts late early cretaceous 100 ma and late cretaceous to middle eocene 75 45 ma trench slope basin deposits containing abundant fossil plants and shallow water sedimentary structures cover most of the indo burma range where sediments rest with an angular unconformity on older accretionary complexes the presence of earlier magmatic arcs accretionary complexes and trench slope basins suggests that the present trench on the margin of the indian ocean has evolved by continuous eastward subduction since the jurassic the magmatic arc axis migrated eastward landward during some time periods jurassic to early cretaceous and late cretaceous to middle eocene and westward seaward migration during others early cretaceous to late early cretaceous and middle eocene to present during continuous east dipping subduction

observations of laterally inhomogeneous anisotropy in the continental lithosphere elastic anisotropy may be an important factor when seismic data are used to determine the structure composition and dynamics of the earth s interior1 2 azimuthal anisotropy has been found in the oceanic and although less definitely in the continental lithosphere from field experiments where the pn wave velocity was observed to vary with direction3 5 these studies suggest a 180 periodicity in travel time variations as the only criterion of the presence of azimuthal anisotropy this criterion however may fail to distinguish between anisotropy and lateral inhomogeneity of the isotropic medium a new method for measuring azimuthal anisotropy has been described recently6 based on the phenomenon of shear wave splitting in anisotropic media which suggests three criteria instead of one to identify azimuthal anisotropy we have now applied this method to the records of permanent seismograph stations in southern germany our results provide strong evidence for the presence of azimuthal anisotropy in the lithosphere of the region and reveal pronounced lateral variations in the parameters of anisotropy on a scale of about 200 km

zircon upb age constraints on the mid cretaceous hkamti amber biota in northern myanmar abstract hkamti amber contains exquisite fossils but the age of the amber biota is unclear in this study we documented the characteristics of fossils hosted in the amber and we present zircon u pb ages of tuff layers from the kachin and hkamti sites i e the new mine we also present a compilation of arthropod and echinoderm syn inclusions from the mid cretaceous hkamti amber of myanmar indicating a humid tropical or subtropical forest paleo environment zircon analyses n 143 of four tuff samples that host the amber deposit in different pits yielded a weighted mean age of 109 7 0 4 ma zircon rare earth element data demonstrate the zircons are of igneous origin therefore the age of the cretaceous amber biota from hkamti is ca 110 ma this means that the hkamti assemblage should be treated as distinct from other burmese amber collections as it represents a significantly older source within a different depositional environment the commercial sources of burmese amber are variable and encompass multiple mining regions which makes maintaining distinctions between deposits important if their faunal contents are to be studied in a proper temporal or ecological context the refined understanding of amber deposits in myanmar highlights the importance of distinguishing sources but it also offers an opportunity to study a series of deposits from 110 to 72 ma instead of just one snapshot of terrestrial ecology around 99 ma

neo tethyan magmatism and metallogeny in myanmar an andean analogue abstract plate margin tectonism magmatic and hydrothermal processes and the genesis of mineral deposits are intricately linked in myanmar two near parallel magmatic belts that together contain a significant proportion of that country s mineral wealth have contrasting metallogenic endowments the mogok mandalay mergui belt hosts crustal melt s type granites with significant tin tungsten mineralization while the wuntho popa arc comprises i type granites and granodiorites with copper gold mineralization the spatial juxtaposition of the two belts and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the south american cordillera recent u pb age dating has shown the potential for the two belts to be near contemporary from the late cretaceous to eocene here we investigate whether an andean type setting during subduction of neo tethys could explain the observed magmatism and mineralization within these two belts

geochronological geochemical and sr nd hf isotopic constraints on the petrogenesis of late cretaceous a type granites from the sibumasu block southern myanmar se asia abstract the late cretaceous to paleogene granitoids occur widespread in the sibumasu block within myanmar se asia which show a close association with tin tungsten mineralization however the precise timing petrogenesis and tectonic significance of these granitoids are poorly constrained so far in this study we present a detailed study on geochronology elemental and sr nd hf isotopic geochemistry for the hermyingyi and taungphila granites in southern myanmar with the aim of determining their petrogenesis and tectonic implications la icp ms u pb dating of zircon grains from the two granites yield ages of 69 70 ma indicating a late cretaceous magmatic event these granitic rocks are weakly peraluminous and belong to the high k calc alkaline series they are both characterized by high sio2 k2o na2o feot feot mgo and ga al ratios and low al2o3 cao mgo p2o5 and tio2 contents enriched in rb th u and y but depleted in ba sr p and eu suggesting an a type granite affinity moreover they display prominent tetrad ree patterns and non charac trace element behavior which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration the granites belong to a2 type and probably formed at a high temperature and anhydrous condition they have zircon ehf t values from 12 4 to 10 0 and whole rock end t values from 11 3 to 10 6 with paleoproterozoic tdm2 ages 1741 1922 ma for both hf and nd isotopes geochemical and isotopic data suggest that these a type granites were derived from partial melting of the paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions without significant input of mantle derived magma and followed by subsequent fractional crystallization by integrating all available data for the regional tectonic evolution in se asia and adjacent regions we attribute the formation of the late cretaceous a type granites to a back arc extension in the hinterland behind the subduction zone which is induced by the rollback of the flat neo tethyan subducting slab around ca 70 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

the volcaniclastic series from the luang prabang basin laos a witness of a triassic magmatic arc abstract the paleogeographic evolution of south east asia sea during the early mesozoic is still poorly understood and a number of models have recently been put forward to account for the geodynamic evolution of sea the luang prabang basin north laos located in the core of a paleogeographic jigsaw in sea recorded a long lasting volcanism that spanned for 35 my from the earliest triassic up to late triassic as evidenced by combined stratigraphic and geochronological u pb zircon analyses performed on both volcanic and volcaniclastic series the volcanic rocks are arc tholeiites and calk alkaline andesites to dacites the volcaniclastic rocks contain in part volcaniclasts produced contemporaneously with sedimentation both the volcanic and volcaniclastic series display geochemical features characteristic of a subduction related volcanism therefore the luang prabang basin documents a magmatic arc in a good agreement with the recent recognition of neighboring ophiolitic rocks in the luang prabang area following a passive margin setting that prevailed from the late carboniferous to the late permian an active margin then initiated along the western margin of the indochina block this active magmatic arc developed as the result of an east dipping subduction below the indochina block during most of the triassic at least from ca 250 to 215 ma subsequently this oceanic subduction episode must have been followed by a continental collision of the indochina block with the eastern simao block at a period that remains to be defined

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

geochemistry mineralogy and mineral chemistry of the welatam cu mo bi au prospect northeast myanmar abstract the welatam prospect located in kachin state northeast myanmar is the first discovered bismuth gold locality within the tengchong lianghe tengliang metallogenic district two mineralization types identified in this area are related to three hydrothermal events the massive sulfide mineralization was formed during the hydrothermal activities of stage i and ii producing mainly iron sulfides e g pyrrhotite chalcopyrite pyrite arsenopyrite whereas the activity of stage iii resulted in quartz molybdenite mineralization which is characterized by the deposition of molybdenite galena and bi te au bearing phases the bi mineral assemblages suggest that at stage iii the prevailing temperatures were above 271 c fluid rock interaction that changed the ph fo2 fs2 and in particular temperature in hydrothermal fluids is important in causing the precipitation of liquid bismuth from bi3 the high correlation between bi and au r 0 782 demonstrates that liquid bismuth may have played a crucial role in gold enrichment here bi au bearing minerals commonly precipitate along the cleavages of molybdenite forming a distinctive mineral assemblage it may indicate that the cleavages besides providing spaces for the precipitation of liquid bismuth create local chemical conditions e g reducing and catalytic surfaces favorable for bi melt to scavenge au from ambient fluid the abundant bi minerals metal association e g cu bi mo au te w the restricted 34s values 7 3 to 1 9 of sulfides and the proximity with the welatam monzogranites suggest a magmatic contribution to the ore forming fluids

a palaeo tibet myanmar connection reconstructing the late eocene drainage system of central myanmar using a multi proxy approach strain resulting from the collision of india with asia has caused fundamental changes to asian drainage patterns but the timing and nature of these changes are poorly understood one frequently proposed hypothesis involves the connection of the palaeo tsangpo drainage to a precursor to the irrawaddy river of central myanmar in the palaeogene to test this hypothesis we studied the provenance of palaeogene fluvio clastic sedimentary rocks that crop out in central myanmar namely the late middle eocene early oligocene pondaung and yaw formations isotopic analysis on bulk rock and petrographic data indicate a primary magmatic arc source and a secondary source composed of recycled metamorphosed basement material although the exact location of both sources is hardly distinguishable because burmese and tibetan provinces share common lithological features the presence of low grade metamorphic fragments the heterogeneity in sr nd isotopic values of bulk sediments and westward directed palaeoflow orientations indicate a proximal source area located on the eastern asian margin central myanmar was the locus of westward prograding deltas opening into the indian ocean supplied by the unroofing of an andean type cordillera that extended along the burmese margin we found no evidence to support a palaeo tsangpo irrawaddy river at least during the late eocene supplementary material data locations and isotopic and petrographic results are available at www geolsoc org uk sup18655

granite related tin metallogenic events and key controlling factors in peninsular malaysia southeast asia new insights from cassiterite u pb dating and zircon geochemistry

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

burma terrane part of the trans tethyan arc during collision with india according to palaeomagnetic data convergence between the indian and asian plates has reshaped large parts of asia changing regional climate and biodiversity yet geodynamic models fundamentally diverge on how convergence was accommodated since the india asia collision here we report paleomagnetic data from the burma terrane at the eastern edge of the collision zone and famous for its cretaceous amber biota to better determine the evolution of the india asia collision the burma terrane was part of a trans tethyan island arc and stood at a near equatorial southern latitude at 95 ma suggesting island endemism for the burmese amber biota the burma terrane underwent significant clockwise rotation between 80 50 ma causing its subduction margin to become hyper oblique subsequently it was translated northward on the indian plate by an exceptional distance of at least 2000 km along a dextral strike slip fault system in the east our reconstructions are only compatible with geodynamic models involving a first collision of india with a near equatorial trans tethyan subduction system at 60 ma followed by a later collision with the asian margin

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

geology and tectonic history of the lohit valley eastern arunachal pradesh india abstract the lohit river section of eastern arunachal pradesh comprises four tectonic units from sw to ne these are the lesser himalayan rocks the mishmi crystallines the tidding suture zone and the lohit plutonic complex the mishmi thrust underlies the basal lesser himalayan unit while the mishmi crystallines are thrust over the lesser himalayan unit along the main central thrust the grade of metamorphism in the mishmi crystallines increases up the structural section from chlorite to staurolite kyanite zones exhibiting inverted metamorphism the relationship between deformation and metamorphism shows that the metamorphic peak was syn to post tectonic in relation to the main ductile shearing event continued deformation after the metamorphic peak was accommodated along millimetre scale shear zones developed throughout the sequence parallel to the regional schistosity movement along these shear zones has resulted in inversion of the metamorphic zones the rocks of the tidding suture represent an ophiolitic melange thrust over the mishmi crystallines which in turn are overthrust by the lohit plutonic complex along the lohit thrust the lohit plutonic complex is subdivided into western and eastern belts separated by the walong thrust the western belt consists of deformed quartz diorite diorite gabbro and trondhjemite intruded by basic and acid dykes the eastern belt comprises garnet sillimanite gneiss intercalated with crystalline marble bands followed by a complex zone of leucogranites aplites and pegmatites which intrude the early foliated quartz diorite soda rich granite and microdiorite the rocks of the eastern belt are the northward continuation of the mogok gneissic belt of central burma the occurrence of intrusive rocks in the eastern belt suggests that the magmatism related to subduction extended to the east far from the subduction zone the peraluminous leucogranites aplites and pegmatites are the products of crustal melting induced by crustal thickening related to the intracontinental walong thrust subsequent to metamorphism and shearing the whole sequence was folded into an antiform forming the eastern syntaxis and this deformation steeply tilted the earlier low angle thrusts and foliations later compression partitioned into right lateral strike slip motion producing a superimposed sub horizontal lineation observed mostly in the lohit plutonic complex

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

the exhumation of the indo burman ranges myanmar abstract the indo burman ranges ibr are a mountain range comprised of mesozoic cenozoic rocks which run the length of western myanmar extending into india and bangladesh to the west lies the indian ocean and to the east lies the central myanmar basin cmb along which the irrawaddy river flows the ibr are considered to be an accretionary prism developed at the juncture of the indian and sunda plates and a number of hypotheses have been proposed for their evolution however in order for these hypotheses to be evaluated the timing of ibr evolution needs to be determined we undertook a two pronged approach to determining the timing of uplift of the ibr 1 we present the first low temperature thermochronological age elevation profiles of the ibr using zft aft and zhe techniques our data show a major period of exhumation occurred around the time of the oligo miocene boundary we tentatively suggest subject to further verification an additional period of exhumation at or before the late eocene 2 we carried out a detailed multi technique provenance study of the sedimentary rocks of the ibr and arakan coastal region to their west and compared data to coeval rocks of the cmb we determined that during eocene times rocks of the cmb and ibr were derived from similar local provenance that of the myanmar arc to the east therefore at this time there was an open connection from arc to ocean by contrast by miocene times provenance diverged rocks of the cmb were deposited by a through flowing irrawaddy river with detritus derived from its upland source region of the mogok metamorphic belt and cretaceous paleogene granites to the north such a provenance is not recorded in coeval rocks of the ibr indicating that the ibr had uplifted by this time providing a barrier to transport of material to the west to the previously published list of viable proposals to explain the exhumation of the range we add a new suggestion the period of exhumation around the time of the oligo miocene boundary could have been governed by a change to wedge dynamics instigated by a major increase in the thickness of the incoming bengal fan sediment pile

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

collision of the ganges brahmaputra delta with the burma arc implications for earthquake hazard abstract we take a fresh look at the topography structure and seismicity of the ganges brahmaputra delta gbd burma arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential the gbd the world s largest delta has been built from sediments eroded from the himalayan collision these sediments prograded the continental margin of the indian subcontinent by 400 km forming a huge sediment pile that is now entering the burma arc subduction zone subduction of oceanic lithosphere with 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land the prism starts at an apex south of the gbd shelf edge at 18 n and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit the front of the prism is blind buried by the gbd sediments thus the deformation front extends 100 km west of the surface fold belt beneath the comilla tract which is uplifted by 3 4 m relative to the delta this accretionary prism has the lowest surface slope of any active subduction zone the gradient of the prism is only 0 1 rising to 0 5 in the forearc region to the east this low slope is consistent with the high level of overpressure found in the subsurface and indicates a very weak detachment since its onset the collision of the gbd and burma arc has expanded westward at 2 cm yr and propagated southwards at 5 cm yr seismic hazard in the gbd is largely unknown intermediate size earthquakes are associated with surface ruptures and fold growth in the external part of the prism however the possibility of large subduction ruptures has not been accounted for and may be higher than generally believed although sediment clogged systems are thought to not be able to sustain the stresses and strain weakening behavior required for great earthquakes some of the largest known earthquakes have occurred in heavily sedimented subduction zones a large earthquake in 1762 ruptured 250 km of the southern part of the gbd suggesting large earthquakes are possible there a large but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism and is the only known candidate for a rupture of the plate boundary along the subaerial part of the gbd burma arc collision zone

cenozoic metamorphism along the shan scarp myanmar evidences for ductile shear along the sagaing fault or the northward migration of the eastern himalayan syntaxis the mogok metamorphic belt exposed along the n s trending shan scarp and sagaing fault in the eastern part of myanmar has been regarded as paleozoic to precambrian for a long time new observations in the shan scarp area close to the sagaing fault from thaton in the south to mandalay in the north allowed us to collect samples of high grade metamorphic and intrusive rocks that have been analyzed by 40ar 39ar step heating method the 13 samples we analyzed provide oligocene to lower miocene ages for this metamorphism oriented thin sections and field observations suggest that this metamorphism was caused by a nnw sse to n s ductile extension therefore we suggest that this metamorphism is not directly related to the sagaing fault but could be instead related to the northward migration of the eastern himalayan syntaxis characterized by crustal thinning resulting from the india asia oblique collision

tectonic diapiric and sedimentary chaotic rocks of the rakhine coast western myanmar abstract the western margin of myanmar is the northern extension the active sunda india eurasia subduction zone coastal regions and offshore islands have remarkable exposures of chaotic rock terranes along wave cut terraces that allow characteristics of tectonic sedimentary and diapiric melanges to be recognized tectonic shear zones tectonic melanges contain fragments of cretaceous ophiolites chrome spinel bearing peridotites and radiolarian cherts that are in contact with thrust packets of eocene turbidite units broken formations the turbidites contain shale rich beds that have been sheared during soft sediment deformation sedimentary broken formations and are sandwiched between undeformed thick sandy beds these are mass transport deposits mtds that most likely formed during deposition of the initial detritus of the himalayan orogenic zone probably trench slope basins on the accretionary prism the ophiolitic and turbiditic thrust slices have been exhumed and are currently being intruded by active mud volcanoes that bring fragments of units up from depth to the surface forming diapiric melanges these diapiric melange bodies contain only small fragments

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

timing of metamorphism of the lansang gneiss and implications for left lateral motion along the mae ping wang chao strike slip fault thailand the mae ping fault mpf western thailand exhibits dominantly left lateral strike slip motion and stretches for 600 km reportedly branching off the right lateral sagaing fault in myanmar and extending southeast towards cambodia previous studies have suggested that the fault assisted the large scale extrusion of sundaland that occurred during the late eocene early oligocene with a geological offset of 120 150 km estimated from displaced high grade gneisses and granites of the chiang mai lincang belt exposures of high grade orthogneiss in the lansang national park part of this belt locally contain strong mylonitic textures and are bounded by strike slip ductile shear zones and brittle faults geochronological analysis of monazite from a sample of sheared biotite k feldspar orthogneiss suggests two episodes of crystallization with core regions documenting th pb ages between c 123 and c 114 ma and rim regions documenting a significantly younger age range between c 45 37 ma these data are interpreted to represent possible magmatic protolith emplacement for the lansang orthogneiss during the early cretaceous with a later episode of metamorphism occurring during the eocene textural relationships provided by in situ analysis suggest that ductile shearing along the mpf occurred during the latter stages of or after this metamorphic event in addition monazite analyzed from an undeformed garnet two mica granite dyke intruding metamorphic units at bhumipol lake outside of the mae ping shear zone produced a th pb age of 66 2 1 6 ma this age is interpreted to date the timing of dyke emplacement implying that the mpf cuts through earlier formed magmatic and high grade metamorphic rocks these new data when combined with regional mapping and earlier geochronological work show that neither metamorphism nor regional cooling was directly related to strike slip motion

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

late cenozoic to holocene deformation in southwestern sichuan and adjacent yunnan china and its role in formation of the southeastern part of the tibetan plateau from at least 2 4 ma to present crust in the southeastern part of the tibetan plateau west of the convex east xianshuihe xiaojiang fault system has deformed internally and rotated clockwise around the eastern himalayan syntaxis the northwest striking ganzi fault zone bounds the rotating crust on the north and has a total left slip of 78 100 km of which 60 km is transferred to the xianshuihe fault zone across a diffuse transfer zone and 22 40 km is absorbed by bending of older structures and crustal shortening crustal shortening is expressed along and east of the eastern end of the ganzi fault zone by mountains capped by permanent glaciers locally rising nearly 1000 m above the average elevation of the tibetan plateau a similar transfer of left slip into shortening occurs farther south across the xianshuihe fault in the high mountains around and east of gongga shan 7556 m the northwest striking convex east left lateral litang fault zone lies southwest of the ganzi xianshuihe xiaojiang fault zone and appears to be less well developed but otherwise similar to the ganzi fault zone the batang chenzhi and other northeast striking right lateral faults of small displacement occur within the rotating crustal fragment together with the left slip faults they accommodate east west shortening northeast of the eastern himalayan syntaxis south of this region of shortening the crust is extending to form grabens within the dali and southern xiaojiang fault systems and in the tengchong volcanic province the progressive change from shortening southward into extension is related to variations in strain that characterize the region from northeast to southeast of the eastern himalayan syntaxis the assemblage of structures in southwestern sichuan geometrically resembles structures of eocene to miocene age in southern yunnan that were positioned northeast of the eastern himalayan syntaxis similar to present day southwestern sichuan at the time of their development the similarity in the structural development in the two areas indicates that crust northeast of the syntaxis underwent a common evolution as the syntaxis migrated northward during the past 50 m y structures in sichuan are less fully developed than older structures in southwestern yunnan and can serve as a guide to reconstruct the progressive tectonic development in the region of the syntaxis deformation in these areas indicates that plateau formation has been complex inhomogeneous and diachronous at scales from 1000 km to less than 100 km

palaeodrainage evolution of the large rivers of east asia and himalayan tibet tectonics understanding the tectonics that gave rise to the formation of tibet is critical to our understanding of crustal deformation processes the unusual geomorphology of the drainage basins of east asia s major rivers has been proposed to be the result of either 1 distortion and attenuation of antecedent drainages as india indents into asia which can therefore be used as passive strain markers of horizontal shear or 2 due to fragmentation by river captures and flow reversals of an originally continental scale drainage in which the major east asian rivers once flowed into the palaeo red river if the latter hypothesis is correct then it has been proposed that dating the drainage fragmentation constrains the timing of uplift of tibet a number of sedimentary provenance studies have been undertaken in order to determine whether the palaeo red river was once a river of continental proportions into which the upper reaches of the yangtze salween mekong irrawaddy and yarlung drained we have assessed the evidence that the yarlung originally flowed into the palaeo red river and then sequentially into the irrawaddy and brahmaputra connecting to the latter first via the lohit and then the siang for this river system we have integrated our new data from the paleogene recent irrawaddy drainage basin detrital zircon u pb with hf and fission track rutile u pb mica ar ar bulk rock sr nd and petrography with previously published data to produce a palaeodrainage model that is consistent with all datasets in our model the yarlung never flowed into the irrawaddy drainage during the paleogene the yarlung suture zone was an internally drained basin and from neogene times onwards the yarlung drained into the brahmaputra in the bengal basin the central myanmar basin through which the irrawaddy river flows today received predominantly locally derived detritus until the middle eocene the irrawaddy initiated as a through going river draining the mogok metamorphic belt and bomi chayu granites to the north sometime in the late eocene to early oligocene and the river was dominated by a stable mmb dominated drainage throughout the neogene to present day existing evidence does not support any connection between the yarlung and the red river in the past but there is a paucity of suitable palaeo red river deposits with which to make a robust comparison we argue that this limitation also precludes a robust assessment of a palaeo connection between the yangtze salween mekong and the red river it is difficult to unequivocally interpret the recorded provenance changes as the result of specific drainage reorganisations we highlight the palaeo red river deposits of the hanoi basin as a potential location for future research focus in view of the near complete cenozoic record of palaeo red river deposits at this location a majority of previous studies consider that if a major continental scale drainage ever existed at all it fragmented early in the cenozoic such a viewpoint would agree with the growing body of evidence from palaeoaltitude studies that large parts of se tibet were uplifted by this period this then leads towards the intriguing question as to the mechanisms which caused the major period of river incision in the miocene in this region

deformation history and u pb zircon geochronology of the high grade metamorphic rocks within the klaeng fault zone eastern thailand abstract in eastern thailand the klaeng fault zone includes a high grade metamorphic rock assemblage named nong yai gneiss which extends about 30 km in a nw se direction along the fault zone the rocks of this brittle fault strand consist of amphibolite to granulite grade gneissic rocks structural analysis indicates that the rocks in this area experienced three distinct episodes of deformation d1 d3 the first d1 formed large scale nw se trending isoclinal folds f1 that were reworked by small scale tight to open folds f2 during the second deformation d2 d1 and d2 resulted from ne sw shortening during the triassic indosinian orogeny before being cross cut by leucogranites d1 and d2 fabrics were then reworked by d3 sinistral shearing including shear planes s3 and mineral stretching lineations l3 la mc icp ms u pb zircon dating suggested that the leucogranite intrusion and the magmatic crystallization took place at 78 6 0 7 ma followed by a second crystallization at 67 1 to 72 1 0 6 ma both crystallizations occurred in the late cretaceous and it is suggested were tectonically influenced by se asian region effects of the west burma and shan thai sibumasu collision or development of an andean type margin the sinistral ductile movement of d3 was coeval with the peak metamorphism that occurred in the eocene during the early phases of the india asia collision

geochronology geochemistry and sr nd hf isotopic compositions of late cretaceous eocene granites in southern myanmar petrogenetic tectonic and metallogenic implications abstract the geochronology petrogenesis and tectonic setting of granites associated with tin tungsten mineralization in southern myanmar remain unclear this work presents whole rock geochemical sr nd isotopic and zircon u pb and hf isotopic data for felsic intrusions in the sibusima terrane zircon u pb dating indicates formation in the late cretaceous early eocene 84 48 ma and suggests that these intrusions likely represent a southward extension of the coeval magmatic belt in the tengchong terrane primarily classified as high k calc alkaline the granites show strong enrichments in large ion lithophile elements e g cs rb and k depletions in nb ta p and ti and negative ba and sr anomalies on primitive mantle normalized diagrams p2o5 cao al2o3 mgo tio2 contents and nb ta ratios decrease with increasing sio2 contents possibly consistent with evolution trends in fractionated i type granitic magmas in addition these intrusions display a wide range of negative end t 14 6 5 5 and zircon ehf t values 22 7 5 7 suggesting a dominant sibusimacrustal source with a minor mantle contribution notably the eocene and a few paleocene granites show more contribution of mantle material based on higher end t 8 5 5 5 and zircon ehf t 11 0 3 2 values large variations in zircon hf isotopic compositions within an individual eocene granitic intrusion e g 15 2 5 7 and corresponding biotite rich enclave 17 8 0 2 likely indicate magma mixing considering the spatial temporal distribution of magmatism in the west burma and sibusima terranes the studied late cretaceous eocene felsic magmas likely formed in a continental arc setting during normal subduction 100 60 ma and subsequent roll back of the neo tethyan oceanic lithosphere 60 50 ma additionally most of granites have the elevated sn with increasing rb sr ratios and decreasing tio2 contents and nb ta ratios suggesting sn enrichment is primarily controlled by magmatic fractionation meanwhile sn and li depletions in some granites deviate from the magmatic evolution trend likely as a result of fluid exsolution the exsolved sn rich fluids could have made a genetic contribution to hydrothermal sn mineralization in southern myanmar

permian of myanmar abstract permo triassic carbonates with minor basal clastics cover extensive tracts of the shan plateau in the eastern part of myanmar these carbonates are grouped into the permian thitsipin limestone formation and the late permian early triassic nwabangyi dolomite formation the thitsipin formation occurs as isolated masses in many places faulted against older rocks it is now known that there is a regional unconformity between the thitsipin limestone formation and the underlying silici carbonates of devonian age in shan state and between the thitsipin limestone formation and carboniferous meta siliciclastics in kayah state mon state kayin state and tanintharyi division some of the thitsipin limestone is dolomitized and passes transitionally upward into the nwabangyi dolomite formation permian shelf carbonates occur within two different sequences the silici carbonate sequence of the shan thai block and the meta siliciclastic sequence of the mergui terrane suggesting that the permian limestones were deposited after the emplacement of the mergui terrane onto the southern margin of the shan thai block this event occurred when the shan thai block was in the southern hemisphere