polyphase deformation in a fore arc back arc basin salin subbasin myanmar burma the salin subbasin of myanmar part of the larger central basin is a fore arc back arc basin couplet situated between an oblique subduction zone to the west and a major right lateral strike slip fault to the east surface and subsurface expressions of folds and faults suggest that the basin experienced north northwest directed extensional deformation in the miocene followed by east northeast directed pliocene pleistocene transpressional deformation resulting in a variety of structural styles including thrust faults oblique reverse faults strike slip faults and normal faults fault propagation folds cored by west dipping thrust faults in the basin center are located above steps in the top of basement surface most likely fault controlled unconformities at the base of and within the pliocene pleistocene synorogenic section indicate that the thrust faults were active during the pliocene pleistocene the southeastern region contains broad north northwest trending uplifts and east northeast striking normal faults associated with thickened miocene synorogenic deposits pliocene pleistocene sedimentary rocks lie unconformably above the miocene section and are folded above the uplifts reflecting pliocene pleistocene compression in the southern part of the basin miocene sedimentary rocks thicken dramatically over the 20 n uplift and the yedwet uplift suggesting that the north northwest striking faults that bound them represent pliocene pleistocene inversion of miocene normal faults during the miocene the burma plate acted as a fore arc sliver coupled with the india plate subducting obliquely underneath it and moved northward relative to asia along the sagaing fault normal faulting and local basin formation took place at this time when the northern part of the burma plate collided with eastern asia in the pliocene transpressional deformation predominated creating thrust and reverse faults positive flower structures and inverted basins

density of dry peridotite magma at high pressure using an x ray absorption method the density of a peridotite magma was measured up to 2 5 gpa and 2300 k using an x ray absorption method the method allowed measurement of the density of a peridotite melt under seven different conditions and clarified the pressure and temperature dependence of the density a fit of the pressure density temperature data to the high temperature birch murnaghan equation of state yielded the isothermal bulk modulus k t 0 24 0 1 3 gpa its pressure derivative k 7 3 0 8 and the derivative of bulk modulus k t t p 0 0027 0 0017 gpa k at 2100 k the large bulk modulus and its pressure derivative of the peridotite melt compared with that of basaltic melt is consistent with previous results from sink float experiments

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

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

a composition independent quantitative determination of the water content in silicate glasses and silicate melt inclusions by confocal raman spectroscopy a new approach was developed to measure the water content of silicate glasses using raman spectros copy which is independent of the glass matrix compo sition and structure contrary to previous studies the compositional range of our studied silicate glasses was not restricted to rhyolites but included andesitic basaltic and phonolitic glasses we used 21 glasses with known water contents for calibration to reduce the uncertainties caused by the baseline removal and correct for the influence of the glass composition on the spectra we developed the following strategy 1 application of a frequency dependent intensity correction of the raman spectra 2 normalization of the water peak using the broad t o and t o t vibration band at 850 1250 cm 1 wavenumbers instead of the low wavenum ber t o t broad band which appeared to be highly sensitive to the feo content and the degree of poly merization of the melt 3 normalization of the inte grated si o band area by the total number of tetrahedral cations and the position of the band maximum the calibration line shows a 0 4 wt uncertainty at one relative standard deviation in the range of 0 8 9 5 wt water and a wide range of natural melt compositions this method provides a simple quick broadly available and cost effective way for a quantitative determination of the water content of silicate glasses application to silicate melt inclusions yielded data in good agreement with sims data

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

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

density of hydrous magma abstract magmas in the interior of the earth have been geophysically observed the generation of magmas is closely related to h2o because the water induced decrease in the melting temperature of mantle rocks is an essential process which forms hydrous magmas due to h2o incorporation into the molten rocks knowledge on physical properties of hydrous magmas such as density can give us better understanding of the magma behavior inside the earth the density of hydrous magma can be controlled by the partial molar volume of h2o v h 2 o and its pressure and temperature dependences the new compression behavior of v h 2 o using vinet equation of state is proposed based on compiled data since h2o is one of the most compressible oxides in the magma at lower pressure a rapid densification of hydrous magma can be observed at shallower mantle the dense hydrous magma can be gravitational stable above and below mantle transition zone

compressibility of molten apollo 17 orange glass and implications for density crossovers in the lunar mantle abstract we performed density measurements on a synthetic equivalent of lunar apollo 17 74 220 orange glass containing 9 1 wt tio2 at superliquidus conditions in the pressure range 0 5 8 5 gpa and temperature range 1723 2223 k using the sink float technique in the lunar pressure range two experiments containing pure forsterite fo100 spheres at 1 0 gpa and 1727 k and at 1 3 gpa 1739 k showed neutral buoyancies indicating that the density of molten orange glass was equal to the density of fo100 at these conditions 3 09 0 02 g cm 3 a third tight sink float bracket using fo90 spheres corresponds to a melt density of 3 25 0 02 g cm 3 at 2 8 gpa and 1838 k our data predict a density crossover for the molten orange glass composition with equilibrium orthopyroxene at 2 8 gpa equivalent to a depth of 600 km in the lunar mantle and a density of 3 25 g cm 3 this crossover depth is close to the orange glass multiple saturation point representing its minimum formation depth at the appropriate oxygen fugacity 2 8 2 9 gpa a density crossover with equilibrium olivine is predicted to fall outside the lunar pressure range 4 7 gpa indicating that molten orange glass is always less dense than its equilibrium olivines in the moon our data therefore suggest that that lunar liquids with orange glass composition are buoyant with respect to their source region at p fitting the density data to a birch murnaghan equation of state at 2173 k leads to an array of acceptable solutions ranging between 16 1 and 20 3 gpa for the isothermal bulk modulus k2173 and 3 6 8 for its pressure derivative k with best fit values k2173 18 8 gpa and k 4 4 when assuming a model 1 bar density value of 2 86 g cm 3 when assuming a slightly lower 1 bar density value of 2 84 g cm 3 we find a range for k2173 of 14 4 18 0 and k 3 7 8 7 with best fit values of 17 2 gpa and 4 5 respectively

static compression of hydrous silicate melt and the effect of water on planetary differentiation abstract high pressure experiments using the sink float method have bracketed the density of hydrous iron rich ultrabasic silicate melt from 1 35 to 10 0 gpa at temperatures from 1400 to 1860 c the silicate melt composition was a 50 50 mixture of natural komatiite and synthetic fayalite water was added in the form of brucite mg oh 2 and was present in the experimental run products at 2 wt and 5 wt levels as confirmed by microprobe analyses of total oxygen buoyancy marker spheres were olivines and garnets of known composition and density the density of the silicate melt with 5 wt water at 2 gpa and 1500 c is 0 192 g cm 3 less than the anhydrous form of this melt at the same p and t this density difference gives a partial molar volume of water in silicate melt of 7 cm 3 mol 1 which is similar to previous studies at high pressure the komatiite fayalite liquids with 0 and 2 wt h 2 o have extrapolated density crossovers with equilibrium liquidus olivine at 8 and 9 gpa respectively but there is no crossover for the liquid with 5 wt h 2 o these results are consistent with the hypothesis that dense hydrous melts could be gravitationally stable atop the 410 km discontinuity in the earth the results also support the notion that equilibrium liquidus olivine could float in an feo rich hydrous martian magma ocean extrapolation of the data suggests that feo rich hydrous melt could be negatively buoyant in the earth s d region or atop the core mantle boundary cmb although experiments at higher pressure are needed to confirm this prediction

aluminum coordination in rhyolite and andesite glasses and melts effect of temperature pressure composition and water content abstract the coordination state of the network formers si and al is one of the primary parameters describing the structure of silicate glasses and melts in this experimental study we use 27al mas nmr spectroscopy to investigate the effect of temperature pressure and composition on the coordination of al in dry and hydrous rhyolite and andesite glasses quenched from pressures of up to 3 5 gpa the spectra were collected at a high magnetic field of 20 tesla to increase spectral resolution and allow for a direct quantification of the different al coordinations the disorder around 4 al increases with increasing fictive temperature and pressure and with decreasing water content or peralkalinity al is predominantly 98 in fourfold coordination in all investigated samples nevertheless systematic trends in al coordination have been observed as a function of pressure composition and water content for the investigated pressure range the proportion of 5 al increases with increasing pressure but decreases with increasing water content and proximity to the metaluminous join for rhyolite glasses within analytical uncertainty the amount of 5 al is independent of fictive temperature the addition of water to andesite glasses does not decrease the amount of 5 al in contrast to the rhyolite glasses based on the glass data we conclude that the majority of al and si will be present in fourfold coordination in metaluminous dry and hydrous rhyolite magmas at the temperature and pressure conditions relevant for the crust and the subducting slab up to 3 5 gpa however consistent with previous predictions from model systems more higher coordinated al may be present in andesite and peralkaline or peraluminous rhyolite melts although the exact concentrations cannot be predicted accurately from the available data compared to more depolymerized melts rhyolite melts can accommodate a higher degree of densification without a significant increase in al coordination

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

density of high ti basalt magma at high pressure and origin of heterogeneities in the lunar mantle abstract the density of the apollo 14 black glass melt which has the highest tio 2 content of pristine mare glasses was measured to 4 8 gpa and 2100 k using an x ray absorption method a fit of the pressure density temperature data to the high temperature birch murnaghan equation of state yielded the isothermal bulk modulus k t 0 9 0 1 2 gpa its pressure derivative k 0 16 0 3 4 and the temperature derivative of the bulk modulus k t t p 0 0030 0 0008 gpa k at 1700 k the high ti basalt magma is less dense than the lunar mantle below about 1 0 gpa therefore the high ti basalt magma produced in the hybridized source 100 200 km can ascend to the lunar surface the basalt formed at the higher pressure could not ascend but move downwards and solidify in the lunar mantle the solidified high ti basalt components can create chemical heterogeneities in the lunar mantle and can cause the low velocity anomalies observed seismologically

u pb age and hf isotopic constraints of detrital zircons from the himalayan foreland subathu sub basin on the tertiary palaeogeography of the himalaya the subhimalaya of nw india exposes a well developed marine to continental foreland sequence preserving sediments shed from the tectonically evolving cenozoic himalayan orogen detrital zircon u pb ages and their hf isotopic compositions of seven samples were analyzed from the subathu sub basin foreland formations to constrain sediment provenance the detrital zircon u pb age spectra yielded a similar pattern for all foreland formations with major peaks clustered at 500 650 ma 900 1000 ma and 2500 ma corresponding to indistinguishable tethyan himalaya and higher himalayan crystalline sources and those at 1800 1900 ma corresponding to lower a lesser himalayan arc source comparison of the foreland detrital zircon u pb age spectra with himalayan lithotectonic source units in conjunction with their hf isotopes and previously determined sediment petrography and age constraints suggest that the sediments to the flysch marine subathu formation 65 to 41 ma were sourced from a positive relief area of the tethyan himalaya mixed with detritus from lower lesser himalaya and additional cratonic northern indian precambrian rocks no cretaceous to eocene aged detrital zircons contributed by eroding ladakh batholith north of the indus tsangpo suture zone were recorded in the palaeogene aged foreland samples the younger synorogenic continental dagshai formation 30 to 22 ma sediments were sourced from the very low grade tethyan himalaya whereas the alluvial facies kasauli formation 22 to 13 ma began to receive sediments additionally from erosion of the medium grade metamorphic rocks of the higher himalayan crystalline and the lower lesser himalaya the lower siwalik formation sediments 13 11 5 ma were derived from the low grade rocks of the tethyan himalaya both the upper and lower lesser himalaya and additionally from the eroding high grade migmatitic gneisses of the higher himalayan crystalline thus from the similar detrital zircon age spectra of the foreland formations we infer that differences in the continental sediment detritus into the foreland basin reflect a straightforward sediment mixture of variable proportions from fixed himalayan lithotectonic sources which progressively shifted towards the foreland with development of the orogen

density of phonolitic magmas and time scales of crystal fractionation in magma chambers abstract understanding magmatic processes and their evolution in the earth s interior requires a better knowledge of silicate melts and their physical properties among them density is one of the most important to constrain the residence or ascent time of magma in the upper mantle and crust however the volumetric properties of volatile bearing and highly polymerized silicate melts are still poorly constrained due to scarce experimental data in this study the density of dry and hydrous 4 35 wt h2o phonolitic melt was measured in situ using the x ray absorption method in a paris edinburgh press at 0 73 3 1 gpa and 1484 1855 k calculated melt densities range from 2 49 0 02 to 2 66 0 03 g cm 3 and from 2 31 0 02 to 2 52 0 02 g cm 3 for the dry and hydrous compositions at depths of 30 to 100 km the results are used to calibrate the equation of state eos of phonolitic liquids for crustal and upper mantle conditions and to derive the partial molar volume of water a least squares fit of the p t data to a third order birch murnaghan eos yields v 0 28 10 0 74 0 10 cm 3 mol k t 14 6 3 0 3 2 gpa k 8 9 2 6 3 3 and 47 30 28 10 6 k for the dry melts and v 0 20 6 0 8 7 5 cm 3 mol k t 4 6 3 0 2 3 gpa k 5 5 0 5 6 1 and 135 115 114 10 6 k for the hydrous component at 1673 k combined with literature data our eos for water indicates that v h 2 o does not depend strongly on the silicate liquid composition at the investigated conditions crystal settling velocities in phonolitic liquids were calculated from the eos to constrain the time scales of crystal fractionation in magma chambers the high compressibility of phonolitic melts results in a small density contrast between nepheline and sanidine crystals and melt neph phon 0 13 0 27 g cm 3 and san phon 0 05 0 21 g cm 3 with corresponding settling times of about 380 and 510 yr km respectively for crystal sizes of 2 cm because of their higher density similar sized magnetite and augite only require about 31 and 100 yr km respectively the observed phenocryst populations in phonolitic magmas indicate that the residence time was sufficiently long to fractionate augite and magnetite but not sanidine and nepheline thus our density data combined with the phenocryst populations of the erupted lavas point to a residence time in the crust between a few tens to hundreds of years consistent with estimates from u th ra isotope compositions

partial molar volume of water in phonolitic glasses and liquids the volumes and expansivities of four hydrous phonolite glasses and liquids have been measured by dilatometry from 300 k up to the glass transition and over a 50 k interval just above the glass transition the partial molar volume of water is independent of the water content for the glass and liquid phases with values of about 11 0 0 5 and 17 1 0 9 cm3 mol at 300 and 800 k respectively the partial molar thermal expansivity of water in phonolite glasses is about 8 10 5 k 1 a result similar to recently published values for different silicate compositions and about 36 5 10 5 k 1 in phonolite liquids the implications for melt density and water dissolution are discussed

stability of hydrous melt at the base of the earth s upper mantle seismological observations have revealed the existence of low velocity and high attenuation zones above the discontinuity at 410 km depth at the base of the earth s upper mantle1 2 it has been suggested that a small amount of melt could be responsible for such anomalies3 4 5 the density of silicate melt under dry conditions has been measured at high pressure4 6 7 8 9 10 11 12 13 and found to be denser than the surrounding solid thereby allowing the melt to remain at depth but no experimental investigation of the density of hydrous melt has yet been carried out here we present data constraining the density of hydrous basaltic melt under pressure to examine the stability of melt above the 410 km discontinuity we infer that hydrous magma formed by partial melting above the 410 km discontinuity may indeed be gravitationally stable thereby supporting the idea that low velocity or high attentuation regions just above the mantle transition zone may result from the presence of melt

zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet the first in situ hf and u pb isotope analyses of zircon separates from mesozoic granites in southern tibet identify a significant previously unknown stage of magmatism igneous zircons n 34 from a granite within the gangdese batholith show a weighted mean 206 pb 238 u age of 188 1 1 4 ma and e hf t the parts in 10 4 deviation of initial hf isotope ratios between the zircon sample and the chondritic reservoir values between 10 4 and 16 8 suggesting predominantly early jurassic intrusive activity with a juvenile mantle contribution of 40 inherited zircons from two cretaceous s type granites in the northern magmatic belt 23 delineate a slightly older 206 pb 238 u age cluster between 188 and 210 ma these zircons have e hf t values from 3 9 to 13 7 yielding crustal hf model ages from ca 1 4 to 2 1 ga suggesting a major episode of crustal growth in proterozoic time and remelting of this crust in early jurassic time combining these with literature data we interpret the jurassic gangdese magmatism as an early product of the neo tethyan subduction that played a long lasting role in the tectonic evolution of southern tibet prior to the india asia collision

pressure induced elastic and structural changes in hydrous basalt glasses the effect of h2o on the gravitational stability of basalt melts at the base of the upper mantle abstract to understand the effect of hydration on the elastic properties of silicate melts we conducted in situ high pressure brillouin scattering measurements on two hydrous basalt glasses with different water contents in diamond anvil cells second order phase transitions were observed in the hydrous basalt glasses and are due to the topological rearrangement of the silicate network to a high si al o coordination up to a pressure of 10 gpa at 300 k the extra 2 23 wt h2o lowers the elastic moduli of fx 2 basalt glass 2 69 wt h2o by 10 18 but does not affect the pressure derivatives of the elastic moduli compared with fx 1 0 46 wt h2o basalt glass the phase transition takes place at a higher pressure in fx 2 compared with fx 1 possibly because of the depolymerization of water to silicate glass water interacts with network forming cations and creates si oh and al oh groups and prohibits nonbridging oxygen ions from being connected to other nearby framework cations i e 5 6 si al resulting in the hysteresis of the second order phase transition the density contrasts of our hydrous basalt melts with previous mid ocean ridge basalt and preliminary reference earth model data indicate that basalt melts may need very low water content

provenance study on eocene miocene sandstones of the rakhine coastal belt indo burman ranges of myanmar geodynamic implications the indo burman ranges ibr represent an accretionary wedge which is the result of subduction of the indian plate beneath the asian plate in the rakhine coastal belt it comprises a thick stack of cretaceous to neogene turbiditic sediments and localized thrust sheets of oceanic plate mafics and pelagic sediments we investigate eocene miocene sandstones aiming to reveal the provenance of the detrital material using modal framework grain heavy mineral and detrital zircon analysis u pb laser ablation icp ms dating hf isotope geochemistry and typology the results show a predominant derivation of the clastic material from i late cretaceous to oligocene igneous rocks which are often bimodal with a low number of zircons spanning the cretaceous palaeogene boundary and ii recycled orogenic terrane sources comprising ophiolitic rocks age corrected hf isotope ratios confirm subduction related mixed mantle crust sources we also observe minor reworking of older magmatic zircons by comparing our obtained petrographic parameters and zircon characteristics with potential himalayan indian continent and burman margin sources we conclude a burman margin and arc origin provenance with regard to hydrocarbon exploration in the ibr a forearc and trench basin system model linked with the burman arc appears more appropriate for evaluating the petroleum system

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

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

solid liquid iron partitioning in earth s deep mantle iron in partially molten rocks under deep mantle conditions partitions into the melt phase less than previously reported suggesting that melt generated near the core mantle boundary should segregate upwards denis andrault et al investigate phase relationships in partially molten rocks under deep mantle conditions and find that iron in the rocks partitions into the melt phase to a lesser extent than has previously been reported the calculated densities of the solid and melt phases suggest that melt generated near the core mantle boundary should be buoyant and hence should segregate upwards melting processes in the deep mantle have important implications for the origin of the deep derived plumes believed to feed hotspot volcanoes such as those in hawaii1 they also provide insight into how the mantle has evolved geochemically and dynamically since the formation of earth2 melt production in the shallow mantle is quite well understood but deeper melting near the core mantle boundary remains controversial modelling the dynamic behaviour of deep partially molten mantle requires knowledge of the density contrast between solid and melt fractions although both positive and negative melt buoyancies can produce major chemical segregation between different geochemical reservoirs each type of buoyancy yields drastically different geodynamical models ascent or descent of liquids in a partially molten deep mantle should contribute to surface volcanism or production of a deep magma ocean respectively we investigated phase relations in a partially molten chondritic type material under deep mantle conditions here we show that the iron partition coefficient between aluminium bearing mg fe sio3 perovskite and liquid is between 0 45 and 0 6 so iron is not as incompatible with deep mantle minerals as has been reported previously3 calculated solid and melt density contrasts suggest that melt generated at the core mantle boundary should be buoyant and hence should segregate upwards in the framework of the magma oceans induced by large meteoritic impacts on early earth our results imply that the magma crystallization should push the liquids towards the surface and form a deep solid residue depleted in incompatible elements

ponded melt at the boundary between the lithosphere and asthenosphere the boundary between earth s rigid lithosphere and ductile asthenosphere is marked by a seismic discontinuity laboratory experiments on basaltic magmas show that melts should pond at pressures that correspond to the lithosphere asthenosphere boundary thus magma ponding could explain the observed seismic discontinuity

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

neutral buoyancy of titanium rich melts in the deep lunar interior the absence of very deep moonquakes implies that the lower mantle of the moon is partially molten an analysis of the density range of lunar melts at high pressures suggests that only titanium rich melt is neutrally buoyant deep within the moon

multiple pressure source model for ground inflation during the period of high explosivity at sakurajima volcano japan combination analysis of continuous gnss tilt and strain data abstract we herein propose a three pressure source model for ground inflation with highly eruptive activity at the showa crater of sakurajima volcano japan we applied a model of stacked spherical sources to continuous combined geodetic data from a global navigation satellite system tilt and strainmeters the data were recorded during ground inflation throughout an eruptive episode that began in october 2011 and ended in march 2012 using a genetic algorithm we obtained the locations and volumes of three sources a pressure source analysis of ground inflation during the period from october 2011 to march 2012 revealed inflation sources to be located at a depth of 9 6 km beneath aira caldera a source and 3 3 km beneath kita dake k source and a shallow deflation source is located at a depth of 0 7 km beneath minami dake m source the a source corresponds to the main magma reservoir at a depth of 10 km beneath the aira caldera inferred by previous geophysical studies the k source is a reservoir of sakurajima volcano where magma intrudes from the main magma reservoir beneath the aira caldera during the first stage of eruptive activity the m source is the uppermost part of a conduit from the k source to the summit and the showa crater magma injection into the a source started in mid november 2011 instantly triggering the migration of increased volumes of magma from the a source to the k source approximately one month later in mid december 2011 an increased volume of magma started migrating from the k source to the m source and finally erupted at the surface the accumulation rate for the a source is comparable to the magma supply rate for the past 100 years 0 8 to 1 6 10 7 m 3 the three pressure source model was applied to inflation events before the 2011 event in order to reconstruct the magma migration process applying our source model to earlier activity phases we found that injected magma from the a source remained at the k source and a small amount of magma began to move from the k source to the m source before the start of eruptive activity at the showa crater in june 2006 furthermore a large amount of magma was found to have moved toward the crater during this violent volcanic activity we also found that the magma injection rate into the a source sometimes reached the level of the average injection rate of the past 100 years during the ground inflation events

amorphous materials properties structure and durability compositional dependent compressibility of dissolved water in silicate glasses the sound velocities and elastic properties of a series of hydrous rhyolite andesite and basalt glasses have been determined by brillouin scattering spectroscopy at ambient conditions to elucidate the effect of glass composition on the compressibility of dissolved water both the adiabatic bulk k s and shear modulus of the dry glasses decrease with increasing silica content k s basalt k s andesite k s rhyolite and basalt andesite rhyolite for each composition the shear modulus systematically decreases with increasing water content although the addition of up to 14 mol water decreases the k s of andesite and basalt glasses by up to 6 there is no discernable effect of water on the k s of the rhyolite glasses the partial molar k s of dissolved water k s in rhyolite andesite and basalt glasses are 37 5 19 7 and 40 3 gpa corresponding to partial molar isothermal compressibilities t of 0 029 0 005 0 042 0 004 and 0 026 0 002 gpa 1 respectively these results indicate that the compressibility of dissolved water strongly depends on the bulk composition of the glass hence the partial molar volume of water cannot be independent of the bulk composition at elevated pressure if the compressibility of dissolved water also depends on composition in the analog melts at high temperature and pressure these observations will have important consequences for magmatic processes such as magma mixing unmixing and fractional crystallization

reconstruction of eastern gondwanaland substantial additions of large continental blocks to the smith et al 1 model of eastern gondwanaland are proposed here largely on the basis of the distribution of key land floras tropical and subtropical marine faunas lithofacies patterns and the identification of a triassic magmatic arc that characterized all the eastern margin of gondwanaland the continental fragments that must have been rifted from northern australia new guinea in the jurassic are identified as south tibet burma thailand malaya and sumatra the original site of deposition of the subtropical permian limestones and tropical late triassic limestones overthrust onto the northern margin of australia by the late cenozoic collision2 is located in this greater gondwanaland palaeomagnetic data except those from malaya3 support this reconstruction

nature of ophiolite occurrences along the eastern margin of the indian plate and their tectonic significance upper mesozoic to lower eocene ophiolitic rocks occur in two parallel belts along the eastern margin of the indian plate the eastern belt passes through central burma sumatra and java and coincides with a zone of gravity highs resulting from steeply dipping mafic rocks it denotes the locus of the subduction where these ophiolites were accreted just prior to middle eocene time in contrast the western belt which passes through nagaland manipur western burma and andaman is flanked to the east by a negative gravity anomaly zone in it the ophiolites occur as rootless subhorizontal bodies tectonically overlying eocene oligocene flysch sedimentary rocks they are inferred to be nappes that propagated westward from the eastern belt during late oligocene terminal collision of the indian and eurasian continental blocks ophiolite occurrences in andaman and mentawai islands belonging to the western belt are generally linked with active subduction west of the island arc this subduction began only in late miocene time and thus it could not have produced the ophiolites which had been emplaced on land much earlier

density of carbonated peridotite magma at high pressure using an x ray absorption method the density of carbonated peridotite magma was measured up to 3 8 gpa and 2100 k using an x ray absorption method a fit of the pressure density temperature data to the high temperature birch murnaghan equation of state yielded the isothermal bulk modulus k t0 22 9 1 4 gpa its pressure derivative k 0 7 4 1 4 and the temperature derivative of the bulk modulus k t t p 0 006 0 002 gpa k at 1800 k the bulk modulus of carbonated peridotite magma is larger than that of hydrous peridotite magma the partial molar volume of co 2 in magma under high pressure and temperature conditions was calculated and fit using the vinet equation of state the isothermal bulk modulus was k t0 8 1 1 7gpa and its pressure derivative was k 0 7 2 2 0 at 2000 k our results show that the partial molar volume of co 2 is less compressible than that of h 2 o suggesting that on an equal molar basis co 2 is more effective than h 2 o in reducing peridotite melt density at high pressure

provenance of the tertiary sedimentary rocks of the indo burman ranges burma myanmar burman arc or himalayan derived the indo burman ranges in western myanmar extend along the sunda arc subduction zone and may be divided into a western portion of neogene sedimentary rocks and an eastern portion of palaeogene sedimentary rocks separated by the kaladan fault both himalayan and burman sources have been proposed for these sediments our thermochronological analyses on detrital grains isotopic analyses on bulk rock and petrographic and heavy mineral data indicate that the palaeogene indo burman ranges contain a significant component of arc derived material interpreted as derived from the burmese portion of the mesozoic tertiary arc to the east and older crustal component is also identifiable which may have been sourced from the himalaya or the burmese margin by contrast the neogene indo burman ranges show dominant derivation from the himalaya a minor arc derived component may have been sourced from the trans himalaya or recycled from the arc derived paleogene indo burman ranges

an overview of the sedimentary geology of the bengal basin in relation to the regional tectonic framework and basin fill history abstract the bengal basin in the northeastern part of indian subcontinent between the indian shield and indo burman ranges comprises three geo tectonic provinces 1 the stable shelf 2 the central deep basin extending from the sylhet trough in the northeast towards the hatia trough in the south and 3 the chittagong tripura fold belt due to location of the basin at the juncture of three interacting plates viz the indian burma and tibetan eurasian plates the basin fill history of these geo tectonic provinces varied considerably precambrian metasediments and permian carboniferous rocks have been encountered only in drill holes in the stable shelf province after precambrian peneplanation of the indian shield sedimentation in the bengal basin started in isolated graben controlled basins on the basement with the breakup of gondwanaland in the jurassic and cretaceous and northward movement of the indian plate the basin started downwarping in the early cretaceous and sedimentation started on the stable shelf and deep basin and since then sedimentation has been continuous for most of the basin subsidence of the basin can be attributed to differential adjustments of the crust collision with the various elements of south asia and uplift of the eastern himalayas and the indo burman ranges movements along several well established faults were initiated following the breakup of gondwanaland and during downwarping in the cretaceous by eocene because of a major marine transgression the stable shelf came under a carbonate regime whereas the deep basinal area was dominated by deep water sedimentation a major switch in sedimentation pattern over the bengal basin occurred during the middle eocene to early miocene as a result of collision of india with the burma and tibetan blocks the influx of clastic sediment into the basin from the himalayas to the north and the indo burman ranges to the east rapidly increased at this time and this was followed by an increase in the rate of subsidence of the basin at this stage deep marine sedimentation dominated in the deep basinal part while deep to shallow marine conditions prevailed in the eastern part of the basin by middle miocene with continuing collision events between the plates and uplift in the himalayas and indo burman ranges a huge influx of clastic sediments came into the basin from the northeast and east throughout the miocene the depositional settings continued to vary from deep marine in the basin to shallow and coastal marine in the marginal parts of the basin from pliocene onwards large amounts of sediment were filling the bengal basin from the west and northwest and major delta building processes continued to develop the present day delta morphology since the cretaceous architecture of the bengal basin has been changing due to the collision pattern and movements of the major plates in the region however three notable changes in basin configuration can be recognized that occurred during early eocene middle miocene and plio pleistocene times when both the paleogeographic settings and source areas changed the present basin configuration with the ganges brahmaputra delta system on the north and the bengal deep sea fan on the south was established during the later part of pliocene and pleistocene and delta progradation since then has been strongly affected by orogeny in the eastern himalayas pleistocene glacial activities in the north accompanied sea level changes in the bay of bengal

the petrology and mineralogy of mt popa volcano and the nature of the late cenozoic burma volcanic arc mt popa is situated on a line of widely spaced calc alkaline volcanic centres in the central lowlands of burma latites rhyodacites and ignimbrites are interbedded with strongly folded arenaceous sediments of topmost miocene and pliocene age these are overlain unconformably by a composite cone of basalt and basaltic andesite lavas and pyroclastic deposits of pleistocene or early recent age the two groups of lavas are regarded as a single petrographic suite in which several continuous and discontinuous mineral reaction series are recognized phenocryst phases analysed by microprobe are olivine bronzite hypersthene biotite diopsidic augite salite magnesio hastingsite magnesio hornblende titaniferous magnetite bytownite oligoclase and sanidine whole rock analyses are characterized by relatively high k ba sr rb and zr high mg mg fe ratios of 0 85 to 0 65 in both phenocrysts and whole rock high k rb 767 and low sr 87 sr 86 0 70431 and rb sr 0 0155 ratios suggest that the basalts are relatively primitive mantle derived compositions modified slightly by fractionation with negligible crustal contamination the more siliceous lavas may have been derived by fractional crystallization of such magmas at crustal levels this high k calc alkaline suite is typical of a continental margin orogenic environment analyses of contemporaneous lavas from elsewhere in burma define three n s volcanic lines which become more alkaline from w to e the magmatism is attributed to the waning stages of orogeny as eastward subduction of the indian plate beneath china gave way to strike slip movement associated with the andaman sea spreading centre within this tectonic model magmas were probably generated by hydrous mantle melting above dehydrating oceanic crust of the subduction zone

measurement of hydrous peridotite magma density at high pressure using the x ray absorption method abstract the density of hydrous peridotite magma containing 5 wt h 2 o was measured at pressures and temperatures up to 4 3 gpa and 2073 k respectively using the x ray absorption method a fit of pressure density temperature data to the high temperature birch murnaghan equation of state yields isothermal bulk modulus k t 8 8 1 9 gpa its pressure derivative k 9 9 3 6 and the temperature derivative of the bulk modulus k t t p 0 0022 0 0015 gpa k at 1773 k the small bulk modulus of the hydrous peridotite magma compared with that of the dry peridotite magma reflects the effect of water which is more compressible than the silicate melt the partial molar volume of h 2 o in magma under high pressure conditions was calculated and fitted using the vinet equation of state the isothermal bulk modulus was k t 2 4 1 0 gpa and its pressure derivative was k 5 7 1 5 at 1973 k

the density of andesitic melts and the compressibility of dissolved water in silicate melts at crustal and upper mantle conditions abstract many magmatic processes including the extraction of partial melts fractional crystallization and buoyancy overpressure depend on the density of the silicate melt phase because of its low molecular weight water has a disproportionately large effect on melt density and accurate data on the effect of water on melt density is required to model density dependent processes however the volumetric properties of the hydrous component at crustal and mantle conditions remain debated in this study we determined the density of dry and hydrous 0 9 wt h2o haplo andesitic melts from 0 7 to 4 0 gpa and 1600 to 1930 k using the x ray absorption method in a paris edinburgh press to determine the partial molar volume of water at high pressure our in situ data were combined with atmospheric pressure data to derive the first experimental equation of state for andesitic melts valid for crustal and subduction zone conditions with k t 17 2 gpa and k 6 3 2 5 3 3 at 1273 k in addition the partial molar volume and compressibility of dissolved water in andesitic melts were derived from the in situ data with v 0 19 2 1 9 2 4 cm 3 mol k t 2 7 2 2 7 6 gpa and k 3 6 2 7 13 5 at 1273 k combined with available literature data for other melt compositions our results support a compositionally independent partial molar volume of water in silicate melts at least within the currently attainable precision of the in situ measurements this observation greatly simplifies the construction of future models for magma density

density of magmas at depth knowing the density of silicate liquids at high pressure is essential to answer questions relevant to the presence of magmas at depth whether that be in the present earth or in its earliest times during differentiation of the planet melts have unique physical and chemical properties which vary as a function pressure and chemical composition the focus here will be on in situ measurements of the density of magmas with a presentation of the available methods and of the main results obtained so far including why some magmas may be trapped at depth understanding the macroscopical physical properties of magmas requires an accurate microscopic structural description structural descriptions of compressed magmas are becoming more widely available from experiments and from theoretical calculations these structural inputs are used to understand the compression mechanisms at stake in the densification of magmas e g the collapse of voids coordination increase for the major cations and bond compressibility these densification processes profoundly affect not only the physical properties of the melt but also its chemical properties i e the way elements partition between the magma and a metallic melt or between the magma and crystals

collision related fore arc and back arc evolution of the northern sunda arc abstract comparison with other arc systems suggests that in the fore arc area of the northern sunda arc emplacement of chromite and jadeite bearing serpentinite melange diapirs and deposition of olistostromes were caused by campanian collision with a continental fragment since underthrust eastwards beneath the arc the age and position of east directed thrusts and associated tin granites in the continental back arc area implies that thrusting and generation of granites were genetically related to the collision and that the back thrusts were coupled to the fore arc thrusts by a decollement beneath the fore arc basin and magmatic arc subsidence and sedimentation in the fore arc basin succeeded collision and rise of the back arc shan plateau possibly resulted from late cenozoic relaxation of collision related compressive stress