the origin of jadeitite forming subduction zone fluids cl guided sims oxygen isotope and trace element evidence jadeitite a rare high p t rock is associated spatially with blueschist and or eclogite terranes scanning electron microscope sem and cathodoluminescence cl petrography of jadeitite samples from several major occurrences in burma myanmar guatemala japan kazakhstan and the u s a show that grains were deposited from s uids jadeite grain compositions indicate these s uid compositions changed with time cl imagery guided the acquisition of oxygen isotope and trace element analyses with the ion microprobe jadeite grains in each rock grew in cycles that began with red and or blue luminescent and ended with green luminescent zones the cl images were used to order the data into crystallization sequences these data and electron microprobe major element analyses document the association of green cl with increases in ca mg and cr 1 toward grain exteriors 2 in ne grained matrix around porphyroblasts 3 in shear zones that cut grains 4 in former open spaces now lled with jadeite or 5 in veins abundances of many trace elements are greater in green cl jadeitite compared with the red or blue cl zones some of these elements in particular li rb sr ti hf zr y and ree are unlikely to have been derived from serpentinite although crystal chemical effects may explain some of the trace element systematics e g preferential incorporation of ree into ca richer jadeite some kinetic control is suggested by sector zoned rhythmically zoned grains the oxygen isotope data suggest that jadeitite depositing s uids either had multiple sources or evolved in composition along their s ow paths or both

geochemical evolution of the massif type anorthosite complex at bolangir in the eastern ghats belt of india granulite facies recrystallization 750 800 c 7 8 kbar a h2o the bolangir massif type anorthosite in the eastern ghats belt of 0 25 during cooling from the igneous to the regional thermal india is composed of homogeneous anorthosite and subordinate regime volumes of schlieric leuconorite in its marginal parts the massif is separated from granulite grade country gneisses by coarse grained garnetiferous granitoids extremely iron rich ferrodiorites feo 39 30 wt sio2 36 43 wt do 7 7 8 0 occur

superimposed tectono metamorphic episodes of jurassic and eocene age in the jadeite uplift myanmar as revealed by 40ar 39ar dating abstract the myanmar jadeite uplift forms an important link between the indo burma range and the tagaung myitkyina belt two contrasting ages of jurassic 152 4 1 5 ma of glaucophane from blueschist and eocene 44 8 1 1 and 45 0 1 3 ma of phengitic muscovites from quartz schists in the uplift were yielded using 40 ar 39 ar dating the jurassic age of the glaucophane even older than the forming age of the jadeitite from recent relevant literatures and for the reason of possible excess argon involved is interpreted as the lower limit of the subduction age previous studies correlated this subduction with the woyla intra oceanic arc or the incertus arc to the west the eocene ages of phengitic muscovites are interpreted as the time of an intra continental shearing deformation event against the timing of hp lt metamorphism as previously suggested combined with other studies it is suggested that the tagaung myitkyina belt and the indo burma range belonged to a single belt which has been separated by the sagaing fault leaving the jadeite uplift straddling along the fault between the belt and the range we propose a rapid exhumation model for the myanmar jadeitite at 45 ma coeval with onset of the sagaing fault

geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part ii ree and the trapped liquid fraction rare earth elements in bulk cumulates and in separated minerals plagioclase apatite ca poor and ca rich pyroxenes ilmenite and magnetite from the bjerkreim sokndal layered intrusion rogaland anorthosite province sw norway are investigated to better define the proportion of trapped liquid and its influence on bulk cumulate composition in leuconoritic rocks made up of plagioclase ca poor pyroxene ilmenite fmagnetite folivine where apatite is an intercumulus phase even a small fraction of trapped liquid significantly affects the ree pattern of the bulk cumulate together with cumulus minerals proportion and composition contrastingly in gabbronoritic cumulates characterized by the presence of cumulus ca rich pyroxene and apatite cumulus apatite buffers the ree content la sm and eu eu vs p2o5 variations in leuconorites display mixing trends between a pure adcumulate and the composition of the trapped liquid assumed to be similar to the parental magma assessment of the trapped liquid fraction in leuconorites ranges from 2 to 25 and is systematically higher in the north eastern part of the intrusion the likely reason for this wide range of tlf is different cooling rates in different parts of the intrusion depending on the distance to the gneissic margins the ree patterns of liquids in equilibrium with primitive cumulates are calculated with mass balance equations major elements modelling duchesne j c charlier b 2005 geochemistry of cumulates from the bjerkreim sokndal layered intrusion s norway part i constraints from major elements on the mechanism of cumulate formation and on the jotunite liquid line of descent lithos 83 299 254 permits calculation of the ree content of melt in equilibrium with gabbronorites partition coefficients for ree between cumulus minerals and a jotunitic liquid are then calculated calculated liquids from the most primitive cumulates are similar to a primitive jotunite representing the parental magma of the intrusion taking into account the trapped liquid fraction calculated from the p2o5 content consistent results demonstrate the reliability of liquid compositions calculated from bulk cumulates and confirm the hypothesis that the trapped liquid has crystallized as a closed system without subsequent mobility of ree in a migrating interstitial liquid d 2005 elsevier b v all rights reserved

late cainozoic glaciation in western tasmania australia abstract four major quaternary glaciations with associated interglaciations and interstadials have been identified in tasmania for which some chronological cotrol is given by radiocarbon and amino acid assays pollen analysis and relative weathering characteristics the glaciations are known as the margaret henty moore and linda the margaret glaciations has two clear stadial intervals isotope stages 4 and 2 separated by the tullabardine interstadial dated at ca 50 25 ka bp an interglaciation corresponding to isotope stage 5 pieman interglaciation is characterised by sediments containing a pollen assemblage of a temperate rain forest weathered glacial deposits lying beneath the pieman sediments are inferred to be those of the penultimate glaciation three stadial moraines are identified a preceding interglaciation langdon contains wood that yielded an amino acid ratio equivalent to the age of marine isotope stage 7 the following moore glaciation had three stadial intervals two of which are separated by a clear interstadial baxter with organic sediments that have amino acid ages equivalent to isotope stage 10 the non glacial sediments have a drm of normal polarity and are inferred to be of mid quaternary age the oldest interglaciation regency is identified from organic rich sediments pollen assemblage of a temperate rain forest overlying intensely weathered glacial deposits that have a drm with reversed polarity i e 730 ka the linda glaciation is the most extensive of all in tasmania although dating is uncertain it has been assigned tentatively to the early quaternary

zircon hf isotope signature of the depleted mantle in the myanmar jadeitite implications for mesozoic intra oceanic subduction between the eastern indian plate and the burmese platelet article i nfo this study systematically investigated the lu hf isotope signatures of zircons in jadeitite from the north myanmar which was formed from jadeite forming hydrothermal fluids and is always sourced in serpentinite as a mark for the subduction zone results show that the three group zircons have positive ehf t values group i zircons 163 2 3 3 ma have relatively higher 176 lu 177 hf ratios n0 0004 and the corresponding ehf t values range from 15 5 to 20 0 at t 163 ma in contrast group ii zircons 146 5 3 4 ma exhibit highly variable 176 lu 177 hf ratios from 0 000027 to 0 001398 but still have ehf t values of 15 6 to 18 5 at t 147 ma which resemble to those of the group i zircons the group iii zircon 122 2 4 8 ma has a 176 lu 177 hf ratio of 0 000578 and a ehf t value of 15 8 at t 122 ma such highly positive ehf t values for all jadeitite zircons indicate that they were derived from rapid reworking of the very juvenile crust therefore zircon in jadeitite can be used as a valuable mineral to constrain the age of serpentinization rodingitization and even the age of formation of ultramafic rock within ophiolites the results also suggest the presence of the mesozoic intra oceanic subduction within the indo burman range and further suggest that the hydrothermal fluids were derived from dehydration of seawater altered oceanic juvenile crust that had been hydrated during and or after the formation of the oceanic crust and additionally from serpentine minerals at greater depth consequently the fluids carry the hf isotope signature of the depleted mantle that can be later imparted to the jadeitite zircons

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

tectonics of the western margin of the shan plateau central myanmar implication for the india indochina oblique convergence since the oligocene abstract we present new data and interpretations on the neogene tectonics of the shan scarp area central myanmar and its relationship with the india indochina oblique convergence we describe ductile and brittle fabrics associated with the major features in this area the mogok metamorphic belt mmb the shan scarp and the sagaing fault from these data we identify a succession of two tectonic regimes first a dominant nnw sse trending extension marked by ductile stretching that characterizes the mmb and associated n70e brittle normal faults later from middle or upper miocene to the present these structures were cross cut by brittle right lateral faults among which the most important are the n20w transpressive shan scarp fault zone and the n s sagaing fault to explain this transition from a dominant transtensive to a transpressive stress regime that occurred during miocene we place our data within a larger geodynamic context we suggest that like the intraplate deformation in the indian ocean the end of spreading in the south china sea the opening of the andaman basin or the end of subduction within the indo burma range the change in the tectonic regime in central myanmar could be in response to a major miocene regional plate kinematic reorganization

u pb dating of serpentinization hydrothermal zircon from a metasomatic rodingite shell sudetic ophiolite sw poland abundant zircon grains were found within a metasomatic chlorite corrensite trioctahedral regularly interstratified chlorite smectite shell that surrounds rodingite from the jordanow gogolow jg serpentinite massif sudetic ophiolite bohemian massif the zircon grains bear two types of primary fluid inclusions containing either liquid co2 or aqueous solutions the inclusions were used to assign the p t conditions of the zircon formation 270 300 c ca 1 kbar using the crossed isochore method abraded single zircon grains give a u pb age of 400 4 3 ma which is interpreted as the age of zircon crystallization this zircon formed during rodingitization i e a metasomatic process directly connected with the serpentinization and thus provides the opportunity of direct dating of the early serpentinization process the zircon age from the jordanow gogolow massif is consistent with the crystallization age of metagabbro protoliths from the sudetic ophiolite as determined by oliver et al j geol soc lond 150 1993 355 a ce anomaly combined with the mineralogical record of greenschist facies metamorphism of the mafic rocks from sudetic ophiolite suggests that the sm nd whole rock isotopic data of pin et al lithos 21 1988 195 353 21 ma possibly characterize the age of later metamorphic event

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

40ar 39ar geochronology constraints on the formation age of myanmar jadeitite abstract the jadeitite that occurs in myanmar is one of the largest and most important jadeite deposits in the world however the formation age of the myanmar jadeitite remains poorly constrained here we conduct an integrated study using petrology and 40 ar 39 ar geochronology to analyze the myanmar jadeitite petrological observations show that the studied jadeitite consists mainly of jadeite minor sodic calcic amphibole and analcime and that the jadeitite was cut by late amphibole rock consisting of sodic amphibole and minor chlorite 40 ar 39 ar laser stepwise heating dating of jadeite from the jadeitite yielded a plateau age of 123 9 3 4 ma the sodic calcic amphibole associated with jadeite yielded a plateau age of 134 8 1 4 ma and the sodic amphibole of late amphibole rock yielded a plateau age of 92 7 1 2 ma these results indicate that the studied jadeitite was formed during the early cretaceous from 135 ma high pressure hp metasomatism and then experienced a late cretaceous 93 ma hp metasomatism combining our results with previous studies using petrography and geochronology we suggest that the formation process of myanmar jadeitite involved multistages of metasomatism

mechanical twinning of jadeite an indication of synseismic loading beneath the brittle plastic transition the orientation distribution of mechanically twinned jadeite crystals in a metagranite from the sesia zone western alps is evaluated to derive the orientation of the principal stress directions for a prominent stage of ductile deformation at ca 300 to 350 c that has been interpreted to reflect synseismic loading and postseismic creep by kuster and stockhert 1999 it is tested whether the orientation distribution can be used to obtain information on the magnitude of differential stress if the critical shear stress for twinning is known assuming that the critical shear stress of 140 mpa determined by kolle and blacic 1982 for mechanical twinning of clinopyroxene in the 100 001 system holds true for jadeite and assuming a homogeneous stress field as a first approximation differential stresses of the order of 1 2 gpa are inferred for metagranites with ca 15 jadeite and of 0 5 gpa for jadeitite with 80 of jadeite notwithstanding the uncertainty for the critical resolved shear stress for jadeite these unexpectedly high values are suspected to be due to a combination of the following effects 1 an inhomogeneous stress field in the polyphase material with curved stress trajectories 2 stress concentration in jadeite due to load transfer from the quartz matrix and 3 minor reorientation of the jadeite crystals in the flowing quartz matrix hence absolute values of differential stress cannot be derived from the orientation distribution of twinned jadeite in polyphase rocks notwithstanding the failure in deriving reliable absolute values a short period with exceptionally high stress must have occurred and is fully consistent with the microstructural record of other minerals it is proposed that the mechanical twinning of jadeite was caused by a short lived stress peak and flow at laboratory strain rates related to quasi instantaneous loading of the uppermost level of the ductile lower crust during brittle failure of the brittle upper crust in a major seismic event

application of k feldspar jadeite quartz barometry to eclogite facies metagranites and metapelites in the sesia lanzo zone western alps italy the eclogite facies assemblage k feldspar jadeite quartz in metagranites and metapelites from the sesia lanzo zone western alps italy records the equilibration pressure by dilution of the reaction jadeite quartz albite the metapelites show partial transformation from a pre alpine assemblage of garnet alm 63 prp 26 grs 10 k feldspar plagioclase biotite sillimanite to the eo alpine high pressure assemblage garnet alm 50 prp 14 grs 35 jadeite jd 80 97 di 0 4 hd 0 8 acm 0 7 zoisite phengite plagioclase is replaced by jadeite zoisite kyanite k feldspar quartz and biotite is replaced by garnet phengite or omphacite kyanite phengite equilibrium was attained only in local domains in the metapelites and therefore the k feldspar jadeite quartz kjq barometer was applied only to the plagioclase pseudo morphs and k feldspar domains the albite content of k feldspar ranges from 4 to 11 mol in less equilibrated assemblages from val savenca and from 4 to 7 mol in the partially equilibrated samples from monte mucrone and the equilibrated samples from montestrutto and tavagnasco thermodynamic calculations on the stability of the assemblage k feldspar jadeite quartz using available mixing data for k feldspar and pyroxene indicate pressures of 15 21 kbar 1 6 1 9 kbar at 550 50 c this barometer yields direct pressure estimates in high pressure rocks where pressures are seldom otherwise fixed although it is sensitive to analytical precision and the choice of thermodynamic mixing model for k feldspar moreover the kjq barometer is independent of the ratio p h 2 o p t the inferred limiting a h 2 o for the assemblage jadeite kyanite in the metapelites from val savenca is low and varies from 0 2 to 0 6

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

zircon u pb dating of jadeitite from the syum keu ultramafic complex polar urals russia constraints for subduction initiation abstract high pressure low temperature metamorphic rocks record subduction of oceanic crust and sediments into the mantle but the timing of subduction initiation is commonly difficult to determine however the appearance of fluid activity in the mantle wedge above a subduction zone can be correlated with incipient subduction here we describe jadeitite veins up to 5 m wide which are hosted in serpentinites of the syum keu ultramafic complex polar urals russia the jadeitites consist of both jadeite 86 88 mol jd and omphacite 54 75 mol jd multi stage growth of the jadeite is indicated by variations in color and structure such as growth zoning and the distribution of fluid inclusions we consider that the jadeitite veins formed from na al si rich fluids under hp lt conditions during active subduction and that the source material was subducted ocean crust shrimp u pb dating of zircons from the jadeitite yielded a concordant weighted mean 206pb 238u age of 404 7 ma which we interpret as the age of peridotite serpentinization and jadeitite formation in the suprasubduction zone mantle this age indicates that subduction was initiated about 40 ma earlier than peak metamorphism 360 355 ma of eclogite in the polar urals

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

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

rare earth element variations resulting from inversion of pigeonite and subsolidus reequilibration in lunar ferroan anorthosites we present results of a secondary ion mass spectrometry study of the rare earth elements rees in the minerals of two samples of lunar ferroan anorthosite and the results are applicable to studies of rees in all igneous rocks no matter what their planet of origin our pyroxene analyses are used to determine solid solid ree distribution coefficients d cree in low ca pyroxene cree in augite in orthopyroxene augite pairs derived by inversion of pigeonite our data and predictions from crystal chemical considerations indicate that as primary pigeonite inverts to orthopyroxene plus augite and subsolidus reequilibration proceeds the solid solid ds for orthopyroxene augite pairs progressively decrease for all rees the decrease is greatest for the lrees the ree pattern of solid solid ds for inversion derived pyroxene pairs is close to a straight line for sm lu and turns upward for rees lighter than sm the shape of this pattern is predicted by the shapes of the ree patterns for the individual minerals equilibrium liquids calculated for one sample from the compositions of primary phases using measured or experimentally determined solid liquid ds have chondrite normalized ree patterns that are very slightly enriched in lrees the plagioclase equilibrium liquid is overall less rich in rees than pyroxene equilibrium liquids and the discrepancy probably arises because the calculated plagioclase equilibrium liquid represents a liquid earlier in the fractionation sequence than the pyroxene equilibrium liquids equilibrium liquids calculated from the compositions of inversion derived pyroxenes or orthopyroxene derived by reaction of olivine are lree depleted in some cases substantially in comparison with equilibrium liquids calculated from the compositions of primary phases these discrepancies arise because the inversion derived and reaction derived pyroxenes did not crystallize directly from liquid and the use of solid liquid ds is inappropriate the lree depletion of the calculated liquids is a relic of formation of these phases from primary lree depleted minerals thus if one attempts to calculate the compositions of equilibrium liquids from pyroxene compositions it is important to establish that the pyroxenes are primary in addition our data suggest that experimental studies have underestimated solid liquid ds for rees in pigeonite and that ree contents of liquids calculated using these ds are overestimates our results have implications for sm nd age studies our work shows that if pigeonite inversion and or subsolidus reequilibration between augite and orthopyroxene occurred significantly after crystallization and if pyroxene separates isolated for sm nd studies do not have the bulk composition of the primary pyroxenes then the sm nd isochron age and end will be in error

collisional emplacement history of the naga andaman ophiolites and the position of the eastern indian suture abstract dismembered late mesozoic ophiolites occur in two parallel belts along the eastern margin of the indian plate the eastern belt closely following the magmatic arc of the central burma basin coincides with a zone of high gravity it is considered to mark a zone of steeply dipping mafic ultramafic rocks and continental metamorphic rocks which are the locus of two closely juxtaposed sutures in contrast the western belt which follows the eastern margin of the indo burma range and the andaman outer island arc broadly follows a zone of negative gravity anomalies here the ophiolites occur mainly as rootless subhorizontal bodies overlying eocene oligocene flyschoid sediments two sets of ophiolites that were accreted during the early cretaceous and mid eocene are juxtaposed in this belt these are inferred to be westward propagated nappes from the eastern belt emplaced during the late oligocene collision between the burmese and indo burma andaman microcontinents ophiolite occurrences in the andaman islands belong to the western belt and are generally interpreted as upthrust oceanic crust accreted due to prolonged subduction activity to the west of the island arc this phase of subduction began only in the late miocene and thus could not have produced the ophiolitic rocks which were accreted in the late early eocene

ree controls in ultramafic hosted mor hydrothermal systems an experimental study at elevated temperature and pressure a hydrothermal experiment involving peridotite and a coexisting aqueous fluid was conducted to assess the role of dissolved cl and redox on ree mobility at 400 c 500 bars data show that the onset of reducing conditions enhances the stability of soluble eu 2 species moreover eu 2 forms strong aqueous complexes with dissolved cl at virtually all redox conditions thus high cl concentrations and reducing conditions can combine to reinforce eu mobility except for la trivalent ree are not greatly affected by fluid speciation under the chemical and physical condition considered suggesting control by secondary mineral fluid partitioning lree enrichment and positive eu anomalies observed in fluids from the experiment are remarkably similar to patterns of ree mobility in vent fluids issuing from basalt and peridotite hosted hydrothermal systems this suggests that the chondrite normalized ree patterns are influenced greatly by fluid speciation effects and secondary mineral formation processes accordingly caution must be exercised when using ree in hydrothermal vent fluids to infer ree sources in subseafloor reaction zones from which the fluids are derived although vent fluid patterns having lree enrichment and positive eu anomalies are typically interpreted to suggest plagioclase recrystallization reactions this need not always be the case

spherules with pure iron cores from myanmar jadeitite type i deep sea spherules abstract here we report spherules in myanmar jadeitite a rock forming from jadeitic fluids within mantle derived serpentinized rocks in subduction zones under high pressure conditions 1 0 gpa and rather low temperatures of about 250 370 c the spherules have off centre iron nuclei and dendritic wustite cortexes with tiny wustite crystals perpendicular to the surface of iron core within the spherules are vesicles occupied by calcite jadeite albite or mixtures of these phases and the cortexes contain about 10 wt sio 2 al 2 o 3 na 2 o filling materials within wustite the spherules are in direct contact with jadeite crystals contrasting patterns of some individual spherules are obvious between a front area with a crowd of hill like prominences and a rear zone with one or more rings on the surface such surface features and internal textures suggest that they experienced movement at high temperature and then rapid cooling chemical compositions of the nuclei are homogenous and consist of nearly pure iron with minor cr 56 fe and 57 fe in the core and cortex are 0 51and 0 78 respectively such features suggest that there is a very low possibility of origin associated with volcanic explosive eruption impact ejecta chemical reduction or oxidation of iron on seafloor since biological reduction processes are not significant under high p t condition in subduction zones this origin is excluded considering their low ni contents it is more likely that they belong to the minor type i deep sea cosmic spherules dusts of low isotope fractionation this discovery shows that such spherules could remain stable under low temperature and high pressure conditions during recycling processes and therefore could be found in rocks related to slab derived sediments within subduction zones this also suggests that subducted oceanic slab sediments contribute to the formation of jadeitite coupled with dehydration of sediments and altered oceanic crust

behaviour of saturated railway track foundation materials during undrained cyclic loading this paper presents results of a series of hollow cylinder tests carried out to investigate the undrained behaviour of saturated railway track foundation materials during cyclic loading involving p

geochemistry and petrogenesis of placer nephrite from hetian xinjiang northwest china article the yurungkash and karakash rivers also known respectively as the white jade and black jade rivers located in hetian xinjiang province northwest china are the two main sources in china of white green and black placer nephrite with a long history 5000 years of exploration and mining the twenty nine placer nephrite samples collected from both rivers and analyzed in the present study possess fine grained and compact microstructures the mineral assemblages in the samples provide clues to the metamorphic metasomatic processes that formed the nephrite which was the result of one of the following reactions dolomitic marble tremolite or dolomitic marble diopside tremolite white nephrite from the yurungkash river and green nephrite from the karakash river are predominantly tremolite based on electron probe microanalytical data backscattered electron images and raman spectra two kinds of black nephrite from the karakash river are identified one dominated by actinolite aggregates and another consisting of tremolite aggregates with graphite crystals up to 2 mm in length compared with black nephrite white and green nephrites contain fewer mineral inclusions and have lower feo and mno contents all the amphiboles in the nephrites have very low contents of cr2o3 0 00 0 07 wt and nio 0 00 0 05 wt relative to serpentinite related nephrite 0 07 0 43 wt cr2o3 0 08 0 36 wt nio most of the nephrite samples have low total rare earth element ree contents ranging from 12 22 to 49 40 ppm in two nephrite samples relatively high ree concentrations 161 and 190 ppm are related to the presence of ree bearing minerals whole rock ree chondrite normalized patterns of all samples are characterized by strong negative eu anomalies 0 16 0 48 moderate light ree enrichment la ndn 1 8 5 0 and nearly flat heavy ree distributions gd ybn 0 3 1 7 nephrite samples from both river locations have 18

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

petrology geochemistry and isotope data on a ultrahigh pressure jadeite quartzite from shuanghe dabie mountains east central china abstract in the dabie ultrahigh pressure terrane of east central china coesite bearing jadeite quartzites occur locally as intercalated layers with marble and mafic eclogite this rock assemblage is in turn enclosed within quartzofeldspathic gneisses metamorphic parageneses and kelyphitic textures reveal a multistage metamorphic evolution and complex exhumation history the primary peak metamorphic assemblage consists of jadeite garnet coesite rutile apatite minor coesite and coesite pseudomorphs occur as inclusions in jadeite and garnet three stages of retrograde assemblages are observed in the jadeite quartzites stage a is represented by the polymorphic transformation of coesite to quartz aggregates stage b is characterized by formation of coronas around jadeite porphyroblasts consisting of an inner layer of oligoclase amphibole and an outer layer of albite aegirine augite the last stage stage c involved total replacement of jadeite and most garnets by taramitic amphibole albite aegirine augite peak metamorphic p t conditions were 26 kbar at 660 c and are consistent with the estimates from the adjacent coesite bearing eclogites the jadeite quartzites display clockwise p t path that matches those of the adjacent eclogites major and trace element data suggest that the protolith of the jadeite quartzite could have been an albitized siltstone enriched in na and depleted in k and ca the highly negative present day end value 24 7 indicates a very old age for the protolith its late archean model age tdm of 2 58 ga is among the oldest so far identified for rocks from the dabie uhpm terrane concordant field relations and petrogenetic considerations suggest that all mafic politic carbonate and gneissic rocks have experienced in situ uhp metamorphism during triassic continental collision between the sino korean and yangtze cratons

early cretaceous wedge extrusion in the indo burma range accretionary complex implications for the mesozoic subduction of neotethys in se asia the indo burma range ibr of myanmar the eastern extension of the yarlung tsangpo neotethyan belt of tibet in china contains melanges with serpentinite greenschist facies basalt chert sericite schist silty slate and unmetamorphosed triassic sandstone mudstone and siltstone interbedded with chert in the east and farther north high pressure blueschist and eclogite blocks in the naga hills melange our detailed mapping of the mindat and magwe sections in the middle ibr revealed a major 18 km antiformal isocline in a melange in which greenschist facies rocks in the core decrease in grade eastwards and westwards symmetrically outwards to lower grade sericite schist and silty slate and at the margins to unmetamorphosed sediments and these metamorphic rocks are structurally repeated in small scale imbricated thrust stacks in the mindat section the lower western boundary of the isoclinal melange is a thrust on which the metamorphic rocks have been transported over unmetamorphosed sediments of the triassic pane chaung group and the upper eastern boundary is a normal fault these relations demonstrate that the ibr metamorphic rocks were exhumed by wedge extrusion in a subduction generated accretionary complex along strike to the north in the naga hills is a comparable isoclinal melange in which central eclogite lenses are succeeded outwards by layers of glaucophane schist and glaucophanite and to lower grade greenschist facies sericite schist and slate towards the margins in the natchaung area from west to east unmetamorphosed triassic sediments overlie quartzites sericite schists actinolite schists and meta volcanic amphibolites derived from morb type basalt which are in fault contact with peridotite olivine in the peridotite has undulatory extinction suggesting deformation at 600 700 c similar to the peak temperature of the amphibolite these relations suggest generation in a metamorphic sole the amphibolites have u pb zircon ages of 119 3 ma and 115 ma which are close to the zircon ages of nearby calc alkaline granite and diorite which belong to an active continental margin arc that extends along the western side of the shan thai block the ibr accretionary complex and the active continental margin arc were generated during early cretaceous 115 128 ma subduction of the neotethys ocean

age and isotope geochemistry of magmatic rocks of the lohit plutonic complex eastern himalaya implications for the evolution of transhimalayan arc magmatism we present integrated in situ zircon u pb and hf isotope data along with whole rock sr nd isotope and geochemical data for plutonic rocks of the lohit plutonic complex of eastern himalaya to understand the age distribution and petrogenetic tectonic evolution of the transhimalayan batholiths in the eastern himalaya the plutonic rocks are gabbro diorite and quartz diorite in composition have calc alkaline signatures with metaluminous character and have an affinity with gangdese i type granitoids of southern tibet the enrichment of large ion lithophile elements with highly depleted negative nb anomalies is consistent with their origin in a subduction related environment our laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages suggest that two major stages of magmatic emplacement took place at c 145 ma early cretaceous for gabbro and c 100 90 ma early late cretaceous for diorite and quartz diorite the zircon hf isotopes in both the gabbro and diorite samples show high positive ehf t values between 11 and 20 suggesting crystallization from juvenile crust or depleted mantle derived melts as also constrained by the low initial 87sr 86sr ratios 0 7038 0 7045 and high positive end t values 2 9 to 5 9 results of ree modelling indicate that the source of these rocks is garnet lherzolite field observations and mineralogical and geochemical characteristics in conjunction with the isotopic database suggest that the transhimalayan magmatic rocks in eastern himalaya were generated by partial melting of the lithospheric mantle wedge and emplaced into the lower crust c 25 30 km during at least two major magmatic events that took place in the cretaceous period supplementary material la icp ms zircon u pb and hf isotope data are available at https doi org 10 6084 m9 figshare c 4665305

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

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

geochemistry and petrology of nephrite from alamas xinjiang nw china abstract the hetian nephrite deposit is one of the largest nephrite deposits worldwide located within the hetian deposit xinjiang northwest china the alamas ore body occurs as veins on the contact between the late variscan granodiorite and precambrian dolomitic marble petrographic studies and electronic microprobe analyses reveal two possible nephrite formation processes 1 dolomitic marble tremolite and 2 dolomitic marble diopside tremolite nephrite veins show continuous coloration zones ranging from white and white green zones to a green zone towards the granodiorite with increasing concentrations of cr feo and tfe2o3 all these nephrite samples have quite low cr and ni contents 8 95 178 7 ppm and 0 05 3 95 ppm respectively relative to serpentinite related nephrite cr2o3 0 07 0 43 wt nio 0 08 0 36 wt their bulk rock ree patterns exhibit strong negative eu anomalies 0 03 0 21 with declined lree flat hree and low ree concentration 2 84 84 81 ppm similar to those of host dolomitic marble samples with negative eu anomalies 0 15 0 23 declined lree flat hree and lower ree concentration 8 48 11 1 ppm indicating a close genetic relationship between them homogenization temperatures analyses on the fluid inclusions in tremolite yield a minimum temperature 293 c for the nephrite formation nephrites have oxygen and hydrogen isotope compositions in the range from 3 2 to 6 2 per mil and 83 0 to 94 7 per mil respectively the corresponding equilibrated fluids have isotope compositions of 18o 3 1 to 6 1 293 c combined with field observation there are at least three possible fluid sources meteoric water magmatic water and co2 derived from decarbonation of dolomite and a metasomatic and dolomite related origin is suggested for the alamas ore body in the hetian nephrite deposit xinjiang nw china

the tectonic evolution of the kohistan karakoram collision belt along the karakoram highway transect north pakistan the kohistan arc terrane comprises an intra oceanic island arc of cretaceous age separating the indian plate to the south from the karakoram asian plate to the north within the indus suture zone of north pakistan the intra oceanic arc volcanics chalt dras group were built on a foundation of dominantly mid ocean ridge basalt morb related amphibolites of the kamila group the subarc magma chamber is represented by multiple intrusions of a huge gabbro norite complex chilas complex which includes some ultramafic assemblages of residual mantle harzburgite and dunite layered cumulates and hornblendites cut by late stage dikes of hornblende plagioclase pegmatites the chilas complex norites intrude the gilgit metasediments of lower amphibolite and greenschist facies in northern kohistan which also form xenolithic roof pendants within the top of the chilas complex along the southern margin of kohistan jijal and sapat complex ultramafics dunites harzburgites and websterites form remnant suprasubduction zone ophiolitic mantle rocks along the hanging wall of the main mantle thrust the cretaceous obduction plane along which kohistan was emplaced onto indian plate rocks garnet granulites of the jijal complex formed at 12 14 kbars represent original magmatic lower crustal rocks subducted to depths of at least 45 km and metamorphosed during high pressure and high temperature subduction of earlier arc related rocks obduction of the sapat ophiolite and kohistan arc occurred between 75 and 55 ma the closure of the shyok suture zone separating kohistan from the karakoram plate must have occurred prior to 75 ma the age of the jutal basic dikes which crosscut the closure related fabrics mainly late north directed backthrusting in the lower hunza valley andean type granitoid gabbrodiorite granodiorite granite emplacement along the kohistan ladakh batholith ended at the time of india asia collision 60 50 myr ago postcollisional crustal thickening along the karakoram led to multiple episodes of metamorphism from latest cretaceous and throughout the tertiary sillimanite grade metamorphism in hunza was actually pre india asia collision and may have resulted from the earlier kohistan collision localized and sporadic crustal melting episodes across northern kohistan indus confluence and parri granite sheets and the southern karakoram hunza dikes and sumayar and mango gusar leucogranites occurred from 51 to 9 ma and culminated in the huge baltoro monzogranite leucogranite intrusion 25 21 myr ago a vast network of leucogranitic and pegmatitite dikes containing gem quality aquamarine muscovite tourmaline garnet biotite quartz are younger than 5 ma and form the final phase of intrusion in the haramosh area and parts of the southern karakoram area

thermobaric structure of the franciscan complex in the pacheco pass region diablo range california examination of the thermobaric structure of jadeite glaucophane bearing franciscan rocks in the pacheco pass region of the diablo range show that they are subhorizontal and the structurally intermediate horizon has the highest metamorphic grade mineral parageneses of more than 700 metagraywackes plus 38 metagraywacke samples from up to 1200 vertical feet of drill core were examined modal compositions of about 100 metagraywackes were determined and more than 2600 microprobe analyses were completed to quantify compositions of jadeitic pyroxene from about 80 metagraywackes the jadeite jd zone is defined by the assemblage jadeitic clinopyroxene quartz pm albite lawsonite pm sodic amphibole pm aragonite this zone occurs at an intermediate structural position sandwiched between subhorizontal jadeitic clinopyroxene free albite ab zones transition zones occur both above and below the jd zone the jd zone covers an area 20 km wide and 400 m thick the nearly flat lying boundaries betwee

magmatic history of central myanmar and implications for the evolution of the burma terrane the burma terrane is a microplate at the eastern edge of the himalayan tibetan orogen the origin of which remains poorly understood its basement comprises metamorphic and igneous rocks forming the wuntho popa arc wpa and has been correlated with tibetan gondwana or transtethyan rocks yet little is known about the magmatic history of the wpa we report elemental and sr nd isotopic compositions of magmatic rocks crystallization zircon and apatite u pb and exhumation apatite fission track ages from rocks and river sands and structural measurements from the wuntho ranges central myanmar where the wpa is best exposed we show that the wpa in the wuntho ranges is characterized by two magmatic events at 108 90 ma and 46 32 ma magmatism is subduction related for both events characterized by depleted nd and sr isotopic compositions with more enriched values with time apatite fission track data suggest arc exhumation during the 39 22 ma time interval partly overlapping with the last magmatic event structural data indicate nw se striking tilting folding and thrusting that we associate with at least two phases of deformation in the cretaceous and the late paleogene correlating the wpa with tibetan gondwana or transtethyan rocks based on its magmatic history remains ambiguous however models arguing for a transtethyan origin for the wpa are most compatible with our results combined with available burmese geological data

the rainbow vent fluids 36 14 n mar the influence of ultramafic rocks and phase separation on trace metal content in mid atlantic ridge hydrothermal fluids fluids were collected from the rainbow vent field 36 14 n on the mid atlantic ridge mar during the 1997 diving flores cruise this vent field in ultramafic rocks at a depth of 2300 m is composed of 10 black smokers emitting acidic ph 2 8 fluids at 365 c the low ph of the hot temperature rainbow fluids likely results from seawater ultramafic rock interaction that releases h ions into reducing hydrothermal fluids fluid chemistry is strongly influenced by phase separation generating cl rich brines clem 750 mm strongly enriched with mn fe co ni cu zn ag cd cs pb y and rare earth elements ree ree and transition metal abundance particularly fe and mn in the rainbow fluids is dramatically higher than in other mar fluids the abundance of trace element and ree enrichment is due to the greater solubility of these elements that is strongly favored by cl complexation at low ph and high temperature conditions chondrite normalized ree patterns show strong lree enrichment with evidence of the typical eu anomaly this ree partitioning suggests that either 1 ultramafic rocks represent only a part of rocks leached during hydrothermal alteration and or 2 that the unique rainbow fluid temperature ph and redox state issued from the ultramafic character of leached substratum can produce unique ree partitioning

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

nested strike slip duplexes and other evidence for late cretaceous palaeogene transpressional tectonics before and during india eurasia collision in thailand myanmar and malaysia the late cretaceous palaeogene structural and tectonic events in the northern region of sundaland represent a poorly known but potentially important orogenic development in se asia extensive late cretaceous s type granites extending from malaysia through thailand to myanmar have long been used to infer an episode of crustal thickening an inference supported by the presence of late cretaceous eocene ophiolites in myanmar however structural evidence for a well developed associated fold and thrust belt has been lacking apatite and zircon fission track studies of thailand indicate a broad regional uplift from about 80 ma to 40 ma suggesting an episode of crustal thickening but the uplift amount is modest and not that expected for a major fold and thrust belt left lateral motion on major nw se trending strike slip fault zones mae ping and three pagodas faults in myanmar and thailand has been attributed to himalayan tibetan escape tectonics this paper demonstrates that the fault zones are considerably more complicated than just nw se trends they are a network of branching faults with important north south trends as well as nw se trends they form large scale nested strike slip duplex structures and affect a region over 1000 km long and up to 250 km wide this diffuse branching network of strike slip fault trends may represent a substantial late cretaceous palaeogene transpressional belt himalayan escape tectonics represent later increments of deformation with both oligocene sinistral and late oligocene recent dextral reactivation