new age constraints on the lan sang gneiss complex thailand and the timing of activity of the mae ping shear zone from in situ and depth profile zircon and monazite u th pb geochronology abstract the mae ping shear zone mpsz is one of four major strike slip systems in thailand and a key structural element in some models of the cenozoic tectonic evolution of southeast asia in northwestern thailand the mpsz exposes a 5 km wide core of intensely deformed high grade metamorphic and minor undeformed magmatic rocks the lan sang gneiss complex lsgc despite previous efforts to determine the chronology of the lsgc and ultimately the mpsz the evolution of this gneiss complex remains incompletely resolved here we present new zircon and monazite u th pb la mc icp ms ages and whole rock geochemical analyses from three peraluminous high k meta igneous granitic rocks augen gneiss sheared granodiorite undeformed subvolcanic dike of the lsgc our zircon u pb dating suggests that the granitic protolith of the augen gneiss intruded metasedimentary basement of sibumasu as early as 235 220 ma zircon rim and monazite u th pb ages from the same sample attest to periods of metamorphic recrystallization and overgrowth in the late triassic early jurassic early cretaceous and eocene the latter event had started by 45 ma and culminated in partial melting of the basement gneisses and the intrusion of granodiorite magma into the lsgc at 35 ma contemporaneous with ductile deformation along the mpsz a late undeformed subvolcanic dike that crosscuts the mylonitic fabric of the calc silicate and marble core of the mpsz dated in this study at 22 ma may indicate that ductile shearing had ceased by that time thus our study provides the first evidence for late eocene early miocene magmatism in the lsgc

distribution of anthropogenic co2 in the pacific ocean 1 this work presents an estimate of anthropogenic co2 in the pacific ocean based on measurements from the woce jgofs oaces global co2 survey these estimates used a modified version of the c technique modifications include a revised preformed alkalinity term a correction for denitrification and an evaluation of the disequilibrium terms using an optimum multiparameter analysis the total anthropogenic co2 inventory over an area from 120 e to 70 w and 70 s to 65 n excluding the south china sea the yellow sea the japan east sea and the sea of okhotsk was 44 5 5 pg c in 1994 approximately 28 pg c was located in the southern hemisphere and 16 5 pg c was located north of the equator the deepest penetration of anthropogenic co2 is found at about 50 s the shallowest penetration is found just north of the equator very shallow anthropogenic co2 penetration is also generally observed in the high latitude southern ocean one exception to this is found in the far southwestern pacific where there is evidence of anthropogenic co2 in the northward moving bottom waters in the north pacific a strong zonal gradient is observed in the anthropogenic co2 penetration depth with the deepest penetration in the western pacific the pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area the lack of deep and bottom water formation in the north pacific means that the north pacific inventories are smaller than the north atlantic

revisiting the tectonic evolution of the triassic palaeo tethys convergence zone in northern thailand inferred from detrital zircon u pb ages

the role of strike slip faults in the displacement of the palaeotethys suture zone in southeast thailand abstract six n s tectono stratigraphic belts can be recognized in southeast thailand each with a distinct stratigraphy and igneous history the westernmost belt i is thought to be part of the sibumasu block and the easternmost v to include part of the indochina block between those belt iii comprises acid volcanic rocks volcaniclastics and carboniferous to triassic sedimentary rocks with distinctive faunas interpreted to be a volcanic arc belt iv comprises triassic rocks of back arc basin origin belt v is interpreted as a permian accretionary complex on the western flank of indochina and vi is an unconformable cover of jurassic cretaceous red beds correlating with the khorat group a history of the triassic indosinian orogeny is proposed leading to the cratonization of southeast thailand by the end triassic the apparent absence in southeast thailand of rocks from the devonian triassic palaeotethys ocean the inthanon zone of northern thailand is suggested to have resulted from a phase of post indosinian oblique to longitudinal sinistral strike slip faulting that phase is thought to have included displacement on the mae yuam fault which bounds the inthanon zone in northern thailand then followed a phase of transverse sinistral strike slip faulting which offset the tectono stratigraphic belts and faults of the earlier phase

u pb zircon dating of granitoid plutons from the west coast province of peninsular malaysia u pb zircon dating of granitoid plutons from the west coast province of peninsular malaysia yields precise and unambiguous ages of 198 220 ma late triassic these ages are considerably older than previously reported k ar mica ages which have been largely reset but agree with or are younger than rb sr whole rock apparent ages the u pb zircon ages are considered to represent the best estimate of the intrusive ages of the plutons some of the problems associated with the interpretations of the pre triassic rb sr whole rock apparent ages are discussed here and alternative ways to explain these ages in the light of recent work are considered reversely discordant patterns displayed by zircon populations from a number of plutons yield consistent upper intersection ages of 1500 1700 ma that approximately date source derived inherited zircon components the precambrian ages of these inherited zircon components suggest that the west coast province s type granitoids are derived from sedimentary sources recycled at least in part from mid proterozoic crystalline basement sources

rb sr sm nd and u pb geochronology of the rocks within the khlong marui shear zone southern thailand abstract in southern thailand the khlong marui shear zone is dominated by a nne ssw striking high topographic lozenge shaped area of ca 40 km long and 6 km wide between the khlong marui fault and the bang kram fault the geology within this strike slip zone consists of strongly deformed layers of mylonitic meta sedimentary rocks associated with orthogneisses mylonitic granites and pegmatitic veins with a steeply dipping foliation the strike slip deformation is characterized by dextral ductile deformation under amphibolite facies and low to medium greenschist facies in situ u pb ages of inherited zircon cores from all zircons in the khlong marui shear zone indicate that they have the same material from the archean late triassic to late cretaceous ages obtained for zircon outer cores of the mylonitic granite are probably related to a period of magmatic activity that was significantly influenced by the west burma and shan thai collision and the subduction along the sunda trench the early dextral ductile deformation phase of the khlong marui shear zone in the early eocene suggested by u pb ages of zircon rims and the later dextral transpressional deformation in the late eocene indicated by mica rb sr ages rb sr sm nd and u pb dating correlation implies that the major exhumation period of the ductile lens was in the eocene this period was tectonically influenced in the se asia region by the early india asia collision

probing into thailand s basement new insights from u pb geochronology sr sm nd pb and lu hf isotopic systems from granitoids

zircon u pb dating and the petrological and geochemical constraints on lincang granite in western yunnan china implications for the closure of the paleo tethys ocean abstract lincang granite is a batholith located in the sanjiang region and is an important research subject for understanding subduction and collision during the paleo tethyan period it is widely exposed in the lincang terrane and extends south into burma based on various petrological and geochemical investigations performed from south to north across the lincang granite a new set of data which includes zircon chronological and hf isotopic data is presented to discuss the origin of the lincang granite and its tectonic significance the lincang granite is a peraluminous high k calc alkaline body with sub parallel ree patterns and a strong negative eu anomaly this anomaly is characteristic of a post collision peraluminous s type granitic batholith the 200 230 ma formation age of the lincang granite was determined using la icp ms zircon u pb dating thus it has been confirmed that the granite formed during the late triassic period and the formation process lasted for approximately 30 ma geochemical and isotopic compositions indicate that the primary magma of lincang granite most likely originated from a crustal source and possibly underwent an assimilation fractionation crystallization afc process during its emplacement the lincang granite formed during the continental collision between the baoshan gengma terrane and the lanping simao terrane after the northeast subduction of the paleo tethyan oceanic plate therefore the late triassic lincang granite is important evidence for the closure of the paleo tethyan ocean

u pb zircon and chime monazite dating of granitoids and high grade metamorphic rocks from the eastern and peninsular thailand a new report of early paleozoic granite abstract in order to understand the age and tectonic framework of eastern to peninsular thailand from the viewpoint of basement metamorphic and plutonic geology the la icp ms u pb zircon dating and the chemical th u total pb isochron method chime monazite dating were performed in the khao chao hub kapong to pran buri and khanom areas in eastern to peninsular thailand the la icp ms u pb zircon dating of the garnet hornblende gneiss from the khao chao area gave 229 3 ma representing the crystallization age of the gabbro and that of the garnet biotite gneisses gave 193 4 ma representing the timing of an upper amphibolite facies metamorphism the chime monazite dating of pelitic gneiss from the khao chao gneiss gave scattered result of 68 22 ma due to low pbo content and rejuvenation of older monazite grains during another metamorphism in the late cretaceous to tertiary time the u pb ages of zircon from the hua hin gneissic granite in the hub kapong to pran buri area scatter from 250 ma to 170 ma on the concordia granite crystallization was at 219 2 ma followed by the sillimanite grade regional metamorphism at 185 2 ma monazite in the pelitic gneiss from this area also preserves early to middle jurassic metamorphism and rejuvenation by later contact metamorphism by non foliated granite or by another fluid infiltration event in the late cretaceous to tertiary time the khao dat fa granite from the khanom area of peninsular thailand gave a u pb zircon age of 477 7 ma this is the second oldest granite pluton ever reported from thailand and is a clear evidence for the sibumasu block having a crystalline basement that was formed during the pan african orogeny the khao pret granite gives u pb zircon concordia age of 67 5 1 3 ma which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite grade contact metamorphism against surrounding metapelites and gneisses metamorphic rocks in the doi inthanon area also share the similar plutono metamorphic history with the khanom and the hub kapong to pran buri areas this suggests that these three areas belong to the sibumasu block and the sibumasu block records similar plutono metamorphic history from northern to peninsular thailand relative abundance of oceanic components in the khao chao gneiss their late triassic magmatic ages and the early jurassic metamorphic ages prefer the interpretation that the khao chao gneiss belongs to the sukhothai arc

in situ characterization of dolomite crystals evaluation of dolomitization process and its effect on zoning dolomitization is a dissolution re precipitation process which proceeds via micrometre scale interface reaction horizons however the effect of this fundamental local medium of replacement process on precipitated dolomite crystals is rarely investigated for this purpose dolomite samples of ordovician boat harbour formation carbonates newfoundland canada from main brook and daniel s harbour about 150 km apart were studied the investigation used high resolution approaches to carry out imaging and elemental analyses of individual dolomite crystals including scanning electron microscopy scanning electron microscopy based cathodoluminescence secondary ion mass spectrometry and electron microprobe analysis the purpose was to better understand geochemical variations across the crystal traverses and their association with dolomite replacement processes and conditions the scanning electron microscopy based cathodoluminescence zoning character reveals three major crystal facies distinctly planar boundaries zoned core and indistinctly zoned core are zoned dolomite crystal facies in burial dolomite from main brook relatively unzoned crystal facies was identified in that of daniel s harbour compositionally zoned dolomite crystals are characterized by decreasing sr na y and ree but increasing mn and fe from core to rim sections core to rim zoning was not found for major mg and ca elements the zoning exhibited by the replacive dolomite crystals is interpreted to be principally a result of limited exchange between solutes of the bulk pore fluid and those of dissolving precursor marine carbonate in tandem with petrographic features the systematic compositional zoning character demonstrates that the effectiveness of the dolomitization process grades from indistinctly zoned core to relatively unzoned crystal facies via interface reaction horizons homogenization of major elements of core and rim sections seen in distinctly zoned core crystal facies and to a much greater extent in relatively unzoned crystal facies via a secondary reaction interface is the first recognized stage of the maturation process followed by homogenization of the trace elements seen largely in relatively unzoned crystal facies

tectonic setting of the permo triassic chiang khong volcanic rocks northern thailand based on petrochemical characteristics abstract the inferred permo triassic chiang khong volcanic belt is composed of felsic to mafic volcanic rocks and their pyroclastic equivalents almost all the least altered mafic volcanic rocks are lava flows a few might have occurred as dykes these mafic volcanic rocks are non foliated to weakly foliated and mostly have porphyritic textures the phenocrysts microphenocrysts in porphyritic samples are commonly plagioclase and may include clinopyroxene olivine fe ti oxide apatite and amphibole the matrix of lava flows ranges texturally from felty to trachytic but a few samples show felty to ophitic subophitic and glassy textures whereas that of possible dyke samples is holocrystalline the primary matrix constituents are largely plagioclase and variable proportions of clinopyroxene fe ti oxide amphibole olivine apatite quartz alkali feldspar and or glass all the studied samples have been subjected to greenschist facies regional metamorphism chemically the samples show narrow ranges of least mobile incompatible element ratios and range compositionally from dacite to basalt of tholeiitic series these samples are chemically analogous to those of the tertiary andesite from sardinian rift sardinia italy particularly in terms of least mobile incompatible element ratios accordingly the studied mafic volcanic rocks are interpreted to have formed in a continental volcanic arc however the problem related to the geometry of plate convergence giving rise to the continental volcanic arc still exists

kinetics of dolomitization dolomitization of caco3 in the laboratory at 175 c demonstrates that the transformation has two distinct stages an induction stage during which no detectable products form and a nucleation growth stage during which dolomite forms at the expense of the reactant caco3 experiments at 218 c demonstrate that as the mg ca ratio of the solution increases the length of the induction stage decreases addition of co2 to the solution decreases the induction stage and also changes the overall transformation mechanism previously published data show that the induction stage is affected by the temperature of the reaction and the surface area and mineralogy of the reactant the induction stage is often the slowest part of the overall transformation characteristics of natural dolomites that are consistent with the experimental results include the following 1 dolomite selectively replaces fine crystalline caco3 2 most carbonate rocks are 100 dolomite or 100 calcite 3 limestone dolomite contacts are usually sharp and involve a decrease in the number of dolomite rhombs but the size of the rhombs remains constant 4 dolomite in completely dolomitized rocks is more stoichiometric than dolomite in partially dolomitized rocks 5 aragonite is selectively dolomitized in modern sabkha sediments and 6 modern dolomite is most abundant in areas of elevated mg ca ratio or hco3

mn2 activated luminescence in dolomite calcite and magnesite quantitative determination of manganese and site distribution by epr and cl spectroscopy abstract dolomite calcite and magnesite were studied by epr and cl spectroscopy mn2 activated luminescence in calcite and magnesite is characterized by single gaussian peaks at 16 250 cm 1 615 nm and at 15 300 cm 1 654 nm respectively in calcite the mn2 content and the normalized epr area are linearly correlated when the mn2 content is deconvolution of corrected cl spectra from dolomite shows two overlapping peaks at 17 315 cm 1 578 nm and 15 270 cm 1 655 nm in rare cases only the 15 270 cm 1 655 nm gaussian peak is present the cl peak at 17 315 cm 1 578 nm ia is due to mn2 in the ca site and the peak at 15 270 cm 1 655 nm ib to mn2 in the mg position the mn2 content in dolomite is linearly correlated with the normalized epr areas of the two sites the distribution ratio kd of mn2 in the two sites of dolomite i e the ca and the mg position was determined by epr and cl spectroscopy a linear correlation exists between kd from epr and the intensity ratio i b i a from cl cl spectroscopy is thus an appropriate method to determine kd in dolomite evaporitic dolomites may be differentiated from non evaporitic dolomites by their kd values

the permian fusulinoidean faunas of the sibumasu and baoshan blocks their implications for the paleogeographic and paleoclimatologic reconstruction of the cimmerian continent abstract permian fusulinoidean faunas occur in mainly four stratigraphic levels in the baoshan block of west yunnan and the sibumasu block of southeast asia which constituted part of the eastern cimmerian continent the oldest fauna from the upper part of the dingjiazhai formation in the baoshan block consists of pseudofusulina eoparafusulina and a new boultoniid genus and is assignable to the yakhtashian artinskian the second one which occurs in the basal part of the ratburi limestone and its equivalent strata in the sibumasu block is represented by monodiexodina and is probably referable to the bolorian kungurian the third fauna composed of eopolydiexodina rugososchwagerina yangchienia chusenella jinzhangia and several other genera is dated to the murgabian wordian and occurs in the lower part of the shazipo and daaozi formations in the baoshan block and the main part of the ratburi limestone in the sibumasu block the youngest fauna of probably dzhulfian wuchiapingian age is found in the upper part of the ratburi limestone and contains nanlingella reichelina codonofusiella and a few staffellid genera a smaller foraminiferal genus shanita found from the upper part of the ratburi limestone and the upper part of the shazipo formation is also an important element of the foraminiferal assemblage near the midian dzhulfian capitanian wuchiapingian boundary in the baoshan and sibumasu blocks in the eastern cimmerian continent low generic diversity throughout the permian and the paucity of tethys characterizing neoschwagerinid and verbeekinid genera during middle permian time are two remarkable features of the permian fusulinoidean faunas in the cimmerian continent the generic diversity of permian fusulinoidean faunas in space and time gradually increases from the early permian to late middle permian as well as from the eastern cimmerian areas to western ones the temporal increase of the generic diversity can be explained by the northward drift of the cimmerian continent during permian time in contrast the lower generic diversity of the eastern cimmerian permian fusulinoidean faunas against western ones is possibly due to an oblique arrangement of the continent to paleolatitude thus the western cimmerian continent was more proximal to the tropical tethyan domain than its eastern part in addition the middle permian cimmerian paleobiogeographic region is likely to be subdivided into two subregions the western tethyan cimmerian and the eastern gondwanan cimmerian based on the distribution pattern of verbeekinid and neoschwagerinid fusulinoideans and overall generic diversity the scarce occurrence or total absence of these essentially tethys indicating fusulinoideans in the baoshan and sibumasu blocks suggests that the eastern cimmerian continent was still far from the equatoro tropical cathaysian domain and was probably in a warm temperate or subtropical zone until the end of the permian the eastern cimmerian areas finally migrated into a tropical zone by the late triassic judging from well developed carnian sponge coral buildups in the chaiburi formation in the sibumasu block

zircon u pb geochronology and elemental and sr nd hf o isotopic geochemistry of post collisional rhyolite in the chiang khong area nw thailand and implications for the melting of juvenile crust volcanic rocks are widely exposed within the chiang khong lampang tak igneous zone in nw thailand a representative rhyolite sample from the chiang khong area yielded a zircon u pb age of 230 7 1 1 ma n 20 mswd 0 98 the chiang khong rhyolites are characterized by low tio2 0 29 0 62 wt and mgo 0 04 0 82 wt with a cnk values of 0 95 1 06 one outlier at 1 47 and can be classified as highly fractionated i type rhyolites they are enriched in liles and lrees and depleted in hfses two representative samples have 87sr 86sr i ratios of 0 70497 and 0 70527 and the end t values fall at 1 1 and 1 3 respectively ehf t and 18o in zircon are between 4 7 to 12 0 and 5 3 to 5 9 respectively our geochemical data suggest that the chiang khong rhyolites formed by partial melting of juvenile mafic lower crust in a post collisional setting deep crustal anatexis was probably induced by upwelling asthenospheric mantle shortly after slab detachment subsequent to closure of the paleo tethys

influence of riverine alkalinity on carbonate species in the okhotsk sea 1 comparing data set of carbonate species and other hydrographic chemical properties in 1999 2000 and 2006 in the okhotsk sea we found that salinity normalized alkalinity in the subsurface water has shown a rate of increase by 2 6 0 1 mol kg 1 y 1 while the increase in salinity normalized dissolved inorganic carbon corrected by aou was almost half of that in alkalinity therefore ph has increased by 0 013 0 001 ph unit y 1 in the subsurface water 26 5 27 3 which is the origin of the north pacific intermediate water this increase in ph could be explained by the increase in alkalinity in the amur river in the last decade suggesting a possibility that could mitigate one fifth of recent ocean acidification in the north pacific

crystal chemistry and thermodynamic and kinetic properties of calcite dolomite apatite and biogenic silica applications to petrologic problems abstract sedimentary minerals are generally metastable phases that given time and changing environmental conditions recrystallize to more stable phases the actual pathway of stabilization is governed by a host of kinetic factors unfortunately much of the theoretical and experimental work on thermodynamic and kinetic behavior of sedimentary minerals either has not reached field practitioners in sedimentary petrology or has been conducted under conditions that are difficult to extrapolate to natural sedimentary environments in this paper we review and present new data on the basic crystal chemistry thermodynamic and kinetic properties of calcite dolomite apatite and biogenic silica and discuss the relevance of these data to the solution of geological and geochemical problems the crystal chemistry and structure of a given magnesian calcite exert a fundamental control on its solubility and solid solution behavior and this control can be seen most clearly through comparison of synthetic and biogenic phases thus variations in crystal chemistry and structure through solubility control during diagenesis yield a range of possible stabilization pathways whose documentation is the domain of much field based study experimental work involving dolomite has focused on delineation of phase relations in dry and aqueous systems at moderate to high temperatures determination of reaction pathways followed during dolomitization of calcium carbonate and measurement of reaction rate uncertainties reside in the relevance of these data to the classic problem of low temperature dolomite formation we suggest that the effort must now focus on designing experimental systems that effectively mimic natural environments and yield reaction rate data as a function of temperature and solution composition such an example is presented a primary goal in experimental work involving carbonate fluorapatite has been an understanding of the mechanism of formation of this mineral we review the state of this knowledge and also present the results of ongoing dissolution rate experiments the importance of this work is that it bears directly on the understanding of the role carbonate fluorapatite plays in the biogeochemical cycle of p in the oceans many factors influence the solubilities of opaline silica and the silica polymorphs and solubility plays an important role in controlling silica diagenesis a model is presented that relates changes in sediment properties including density and acoustic velocity to the stages of silica diagenesis the model is applied to sediments of deep sea drilling project leg 63 the discussions of the sedimentary phases calcite dolomite apatite and biogenic silica in this paper point to several directions for future experimental research on sedimentary mineral solution reactions these include emphasis on 1 experimental studies of synthetic sedimentary mineral solution reactions to form a foundation for an understanding of natural mineral solution reactions 2 experimental investigations of mineral reactions in aqueous solutions under conditions of composition temperature and pressure similar to the natural conditions of mineral formation and 3 studies of the surface as opposed to bulk properties of sedimentary minerals in aqueous solutions and their role in reactions governing precipitation and dissolution of sedimentary phases

did oligocene crustal thickening precede basin development in northern thailand a geochronological reassessment of doi inthanon and doi suthep the doi inthanon and doi suthep metamorphic core complexes in northern thailand are comprised of amphibolite grade migmatitic gneisses mantled by lower grade mylonites and metasedimentary sequences thought to represent cordilleran style core complexes exhumed through the mobilization of a low angle detachment fault previous studies have interpreted two metamorphic events late triassic and late cretaceous followed by ductile extension between the late eocene and late oligocene a model which infers movement on the detachment at ca 40 ma and which culminates in a rapid unroofing of the complexes in the early miocene the chiang mai basin the largest such cenozoic basin in the region lies immediately to the east its development is related to the extension observed at doi inthanon and doi suthep however it is not definitively dated and models for its development have difficulty reconciling miocene cooling ages with eocene detachment movement here we present new in situ la icp ms and sims u pb age data of zircon and monazite grains from gneiss and leucogranite samples taken from doi inthanon and doi suthep our new zircon data exhibit an older age range of 221 210 ma with younger ages of ca 72 ma and 32 26 ma our monazite data imply an older age cluster at 83 67 ma and a younger age cluster of 34 24 ma while our data support the view of indosinian basement being reworked in the cretaceous they also indicate a late eocene oligocene tectonothermal event resulting in prograde metamorphism and anatexis we suggest that this later event is related to localized transpressional thickening associated with sinistral movement on the mae ping fault coupled with thickening at the restraining bend of the mae yuan fault to the immediate west of doi inthanon further this upper oligocene age limit from our zircon and monazite data would imply a younger miocene constraint on movement of the detachment which when combined with the previously recorded miocene cooling ages has implications for a model for the onset of extension and subsequent development of the chiang mai basin in the early mid miocene

geochronological elemental and sr nd hf o isotopic constraints on the petrogenesis of the triassic post collisional granitic rocks in nw thailand and its paleotethyan implications abstract new u pb geochronological petrologic elemental and sr nd hf o isotopic data for the granites from the inthanon and sukhothai zones in nw thailand in conjunction with correlations with sw china are presented to constrain the age and position of the paleotethys ocean in this region and the associated assembly of southeast asia the geochronological data show that the granitic rocks in the inthanon and sukhothai zones herein named group 1 and group 2 granites respectively yield similar crystallization ages of 230 200 ma group 1 samples are characterized by monzogranite and granite with i and s type geochemical affinity and group 2 samples by i type monzogranite and granodiorite they have generally similar chondrite normalized ree and pm normalized multi element patterns but distinct sr nd hf o isotopic compositions group 1 samples have slightly higher initial 87sr 86sr ratios 0 7111 0 7293 but lower end t values 11 1 to 14 1 than those of group 2 samples 87sr 86sr i 0 7073 0 7278 and end t 8 3 to 11 0 group 1 samples show the lower ehf t values 5 4 to 18 2 older tdm 1 62 2 40 ga and higher 18o values 7 95 to 9 94 than those of group 2 samples ehf t of 11 1 to 4 80 tdm of 0 96 1 95 ga and 18o of 4 95 to 7 98 for the triassic crystallization zircons these geochemical signatures are similar to the kwangsian and indosinian granites in the south china and indochina blocks but distinct from those of the gangdese i type granite and sibumasu paleozoic granite our data suggest that group 1 samples mainly originated from the early paleozoic supracrustal rocks containing metapelite and metavolcanic components which had previously experienced the surface weathering group 2 samples were derived from a hybridized source of an old metamorphic and a newly underplated mafic component synthesis of our data with available regional observations indicates that the inthanon zone represents the main suture zone of the eastern paleotethyan ocean in nw thailand and links with the changning menglian suture zone in sw yunnan sw china in nw thailand a switch from the eastward subduction of the paleotethyan oceanic plate to the collision of the sibumasu with indochina blocks occurred at 237 ma and syn and post collisional time being at 237 230 ma and 200 230 ma respectively the late triassic granites in the inthanon and sukhothai zones are representative of the post collisional magmatic products

preface for the special issue geology geodynamics and mineral resources of se asia insights from geosea xv congress hanoi 2018 se asia is an assembly of gondwana derived crustal blocks and an important piece for the geodynamic understanding of the asian continent since the phanerozoic this area experienced several significant geodynamic events the separation of many continents and microcontinents from gondwana through rifting lead to the opening of oceanic domains the closure of these oceanic basins and the subsequent continental collision is attested by subduction related magmatism accretionary complexes high pressure and high temperature metamorphisms crustal melting and magmatism including volcanism and plutonism the mesozoic tectono magmatism the cenozoic intracontinental tectonics related to the india collision and the recent magmatism and tectonics are also significant events recognized in se asia these geodynamic events represent the general framework for the numerous ore deposits recognized in the area

p t t constraints on the development of the doi inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt northern thailand abstract the western gneiss belt in northern thailand is exposed within two overlapping cenozoic structural domains the extensional doi inthanon metamorphic core complex domain located west of the chiang mai basin and the mae ping strike slip fault domain located west of the tak batholith new p t estimates and u pb and 40ar 39ar age determinations from the doi inthanon domain show that the gneiss there records a complex multi stage history that can be represented by a clockwise p t t path u pb zircon and titanite dating of mylonitic calc silicate gneiss from the mae wang area of the complex indicates that the paragneissic sequence experienced high grade medium pressure metamorphism m1 in the late triassic early jurassic ca 210 ma in good agreement with previously determined zircon ages from the underlying core orthogneiss exposed on doi inthanon late cretaceous monazite ages of 84 and 72 ma reported previously from the core orthogneiss are attributed to a thermal overprint m2 to upper amphibolite facies in the sillimanite field u pb zircon and monazite dating of granitic mylonite from the doi suthep area of the complex provides an upper age limit of 40 ma late eocene for the early stage s of development of the actual core complex by initially ductile low angle extensional shearing under lower amphibolite facies conditions m3 accompanied by near isothermal diapiric rise and decompression melting 40ar 39ar laserprobe dating of muscovite from both doi suthep and doi inthanon provided miocene ages of ca 26 15 ma representing cooling through the ca 350 c isotherm and marking late stage development of the core complex by detachment faulting of the cover rocks and isostatic uplift of the sheared core zone and mantling gneisses in the footwall similarities in the thermochronology of high grade gneisses exposed in the core complex and shear zone domains in the western gneiss belt of northern thailand and also in northern vietnam laos yunnan and central myanmar suggest a complex regional response to indentation of southeast asia by india

dating multiple generation of zircons from granites and gneiss from thailand implication for the crustal evolution of the sibumasu terrane abstract the widespread granitic rocks of the sibumasu terrane were emplaced during the collision of the sibumasu and indochina in the triassic previous studies have suggested that each granite had a simple single step magmatic evolution in situ la mc icp ms u pb zircon dating of granites and gneiss from thailand revealed the evolution of these rocks inherited zircon core ages 515 130 ma from a granite of the chonburi pluton in the central granitoid belt are coeval with an orthogneiss protolith age 513 6 9 2 ma from hua hin area similar cambrian ages were also reported from the khao tao area in southern thailand moreover there are a series of inherited zircon core ages from neo proterozoic 1017 43 and 984 56 ma ordovician 449 26 ma devonian 385 15 ma carboniferous 316 12 ma to permian 276 31 and 266 12 ma taken together these neo proterozoic to permian protolith ages are interpreted to represent the basement of the sibumasu terrane in thailand two magmatic zircon growth events can be distinguished at approximately a 241 8 8 2 to 235 12 ma and b 230 6 3 4 to 213 4 3 0 ma we concluded that the sibumasu and indochina collision during the triassic caused a two step magmatic evolution of the granites of the sibumasu terrane the first magmatic crystallization during the middle triassic corresponded to the sibumasu and indochina collision and the second magmatic crystallization during the late triassic was related to the late collisional stage

the granites of the southeast asian tin belt four granite provinces have been delineated each with its own distinctive pattern of mineralization 1 the main range province endogenous greisen bordered vein swarms of cassiterite and wolframite 2 the eastern province magnetite cassiterite skarns base metal sulphides with antimony in thailand 3 the western peninsular thailand burma province endogenous greisen bordered vein swarms and pegmatites of cassiterite and wolframite 4 the north thailand migmatitic province endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony in all provinces but particularly in the main range granitoids designated as two phase variants have been recognized where xenocrysts and xenoliths of coarse primary texture granite are enclosed in and corroded by an invasive equigranular quartzo feldspathic matrix these rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids whole rock geochemistry from peninsular malaysia shows that the granites from the main range and eastern provinces comprise two contrasted suites which correspond approximately to the i and s type categories advocated by chappell white 1974 in addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters variation diagrams of plutons having the intrusive sequence primary texture granite two phase granite microgranite show linear trends with increasing sio 2 na 2 o rb w sn and u and decreasing sr ba th and all other major elements

petrochemistry u pb zircon age and palaeotectonic setting of the lampang volcanic belt northern thailand two ne trending belts of mainly subaerial dacitic to rhyolitic flows and tuffs occur in the area between the towns of lampang and denchai in northern thailand in the western belt doi ton the rocks have been pervasively altered to quartz keratophyre rocks in the eastern belt doi luang are generally less altered mobile chemical components such as na 2 o and k 2 o show wide variation particularly in samples from the doi ton belt however low zr tio 2 ratios and low nb and ta contents support an origin at a convergent plate margin a positive epsilon nd value of 4 9 for rhyolite from the doi luang belt supports derivation from a primitive crustal source a rhyolite sample from the doi luang belt yielded a u pb zircon age of 240 1 ma early mid triassic the doi ton and doi luang belts are part of the lampang volcanic belt which can be traced to the north into the lincang jinghong volcanic belt in southern china comparison with published petrological data from the lincang jinghong belt shows strong similarity including the widespread development of keratophyric mineralogy and chemistry the lampang lincang jinghong belt formed at an early mid triassic convergent plate margin and is similar in age and tectonic setting to the more mafic phetchabun volcanic belt on the east side of the nan river suture zone these data constrain the timing of final amalgamation between the indochina and shan thai terranes to mid triassic or younger

the 18 6 year period moon tidal cycle in pacific decadal oscillation reconstructed from tree rings in western north america 1 time series of pacific decadal oscillation pdo reconstructed from tree rings in western north america is found to have a statistically significant periodicity of 18 6 year period lunar nodal tidal cycle negative positive pdo tends to occur in the period of strong weak diurnal tide in the 3rd and 5th 10th 11th and 13rd year after the maximum diurnal tide mean pdo takes significant negative positive value suggesting that the aleutian low is weak strong western central north pacific in 30 50 n is warm cool and equator eastern rim of the pacific is cool warm this contributes to climate predictability with a time table from the astronomical tidal cycle

recent change in the oceanic uptake rate of anthropogenic carbon in the north pacific subpolar region determined by using a carbon 13 time series 1 applying the 13c approach to time series of observations in the north pacific subpolar region station knot 44 00 n 155 00 e we demonstrated time series of vertical distributions of oceanic anthropogenic carbon we found that the vertical distributions of oceanic anthropogenic carbon during 1999 2006 were almost consistent with those estimated by the other carbon based quasi conservative tracer approach c comparing the oceanic anthropogenic carbon contents and the water column inventories among 1999 2000 and 2006 we found the recent oceanic uptake rate of anthropogenic carbon above 27 3 to be 0 86 0 12 mol kg 1 yr 1 which was 1 2 times higher than the expected value derived from oceanic equilibration with increasing atmospheric co2 considering the strengthened ocean stratification with a bidecadal oscillation and the recent increase in alkalinity from the sea of okhotsk it was possible to explain the difference in the recent oceanic uptake rate of anthropogenic carbon between our result and the expected one

development of the khao khwang fold and thrust belt implications for the geodynamic setting of thailand and cambodia during the indosinian orogeny abstract the indosinian orogeny in thailand is often viewed as having developed between strongly linear terranes which today trend approximately n s the terranes were subsequently disrupted by later tectonics particularly nw se trending cenozoic strike slip faults the ene wsw to ne sw striking thrusts and folds in the khao khwang platform area of the saraburi group on the sw margin of the indochina terrane are not easily explained in the context of this traditional view reversal of the clockwise rotation shown to have affected the block north of the mae ping fault zone only enhances the e w orientation of structures in the fold and thrust belt and moves the belt further east towards cambodia one solution for the trend that fits better with regional understanding from hydrocarbon exploration of the khorat plateau is that the indochina terrane was actually a series of continental blocks separated by permian rifting during the early triassic the early stages of collision south china cathaysian terrane collision with vietnam indochina resulted in the amalgamation of disparate blocks that now form the indochina terrane by closure along the rifts at the same time or following on from the collision there was closure of the back arc area between indochina and the sukhothai zone the rift basins were thrusted and inverted during the early stages of the indosinian orogeny and only underwent minor reactivated when later sibumasu collided with sukhothai zone indochina terrane margin during the late triassic the scenario described above requires the presence of a minor e w trending suture in nw cambodia evidence for this suture is suggested by the presence of permo triassic calc alkaline volcanism

dolomite thermometry by electron spin resonance spectroscopy abstract electron spin resonance esr spectroscopy has been used to distinguish different genetic types of dolomite in the complex metamorphic terrain of the ballachullish area of nw scotland by measuring the esr signals of mn2 from the two inequivalent sites in dolomite the partition coefficient can be determined and related to temperature a systematic one hundred fold increase in the partition coefficient from the highest grade of contact metamorphic skarn to supergene dolomites was found the use of this partition coefficient complements fluid inclusion and gross chemical data and is a useful aid in geothermometry

age tectonic setting and regional implications of the chiang khong volcanic suite northern thailand the chiang khong volcanic suite forms the northeastern part of the tak chiang khong volcanic belt in the sukhothai terrane of northern thailand it consists mainly of subaerial andesitic to rhyolitic tuffaceous rocks a rhyolitic tuff yielded a middle triassic u pb zircon age of 232 9 0 4 ma the suite displays calc alkalic chemical trends and nb p and ti depletion characteristic of subduction related magmatism based on petrological similarities the suite is correlated with the c 240 ma lampang volcanic rocks located farther to the sw in the tak chiang khong belt and with volcanic rocks of similar age in the lincang jinghong belt in yunnan in the western part of the simao block these correlations support the placement of the palaeo tethyan suture to the west of the sukhothai terrane

temperature and bulk composition control on the growth of monazite and zircon during low pressure anatexis mount stafford central australia the formation age and trace element composition of zircon and monazite were investigated across the prograde low pressure metamorphic sequence at mount stafford central australia three pairs of inter layered metapelites and metapsammites were sampled in migmatites from amphibolite facies t 600 c to granulite facies conditions t 800 c sensitive high resolution ion microprobe u pb dating on metamorphic zircon rims and on monazite indicates that granulite facies metamorphism occurred between 1795 and 1805ma the intrusion of an associated granite was coeval with metamorphism at 1802 3ma and is unlikely to be the heat source for the prograde metamorphism metamorphic growth of zircon started at t 750 c well above the pelite solidus zircon is more abundant in the metapelites which experienced higher degrees of partial melting compared with the associated metapsammites in contrast monazite growth initiated under sub solidus prograde conditions at granulite facies conditions two distinct metamorphic domains were observed in monazite textural observations petrology and the trace element composition of monazite and garnet provide evidence that the first metamorphic monazite domain grew prior to garnet during prograde conditions and the second in equilibrium with garnet and zircon close to the metamorphic peak ages from sub solidus prograde and peak metamorphic monazite and zircon are not distinguishable within error indicating that heating took place in less than 20 myr

mineralogy and mn geochemistry of laboratory synthesized dolomite abstract dolomite was synthesized in hydrothermal bombs to assess influences on mn partitioning into the mg and ca sites calcite was added to magnesium chloride solutions doped with 0 10 20 or 50 ppm mn runs were made for 8 to 241 hr at 192 and 224 c the calcium content of dolomite increased to 60 64 after 75 hr at 192 c and reverted to stoichiometry thereafter increases in the mn content of the starter solution progressively retarded formation of dolomite for dolomites formed without added mn or formed in less than 40 hr with 10 ppm added mn the esr signals were too broad to permit determination of mn site distribution ratios measurable ratios of mn in the mg site to mn in the ca site vary as a linear function of time from 0 3 to 7 for samples prepared at 192 c and from 3 to 16 for those prepared at 224 c stoichiometric dolomites have higher mn partitioning ratios than nonstoichiometric dolomites as observed in natural systems dolomites formed in supratidal sabkha early groundwater and dorag conditions may differ in their mn signature from those formed during burial diagenesis

the closure of palaeo tethys in eastern myanmar and northern thailand new insights from zircon u pb and hf isotope data abstract two of the major granite belts of southeast asia are the main range and eastern province together these are interpreted to represent the magmatic expression of the closure of palaeo tethys during late palaeozoic to early mesozoic times recent geochronological and geochemical work has better delineated these belts within peninsular malaysia thereby providing important constraints on the timing of palaeo tethys suturing however the northern extension of this palaeo tethyan suture is less well understood here we present new ion microprobe u pb zircon age data from northern thailand and eastern myanmar measured ages of 219 and 220 ma from the kyaing tong granite imply northern extension of the main range province into eastern myanmar the tachileik granite in far eastern myanmar yields an age of 266 ma consistent with published eastern province ages and this therefore constrains the northern extension of the palaeo tethys suture in eastern myanmar we further discuss how this suture may extend northwards into yunnan a late cretaceous age 70 ma measured in thailand represents later magmatic activity and is similar to published magmatic ages from central myanmar this younger magmatism is interpreted to be related to the subduction of neo tethys prior to india asia collision further we present new laser ablation zircon hf isotope data from eastern myanmar which suggest that palaeoproterozoic crust underlies both the main range and eastern province granites our ehf model age of ca 1750 ma from sibumasu the basement underlying eastern myanmar lies within the range of other model ages reported thus far for the baoshan block north in yunnan interpreted by some to be the northern extension of sibumasu

the early triassic indosinian orogeny in vietnam truong son belt and kontum massif implications for the geodynamic evolution of indochina new structural field data at various scale and 40ar 39ar geochronological results from the basement rocks in the truong son belt and kontum massif of vietnam confirm that ductile deformation and high temperature metamorphism were caused by the early triassic event of the indosinian orogeny in the range of 250 240 ma a compilation of isotopic data obtained in other countries along the sibumasu indochina boundary broadly indicates same interval of ages this tectonothermal event is interpreted as the result of a synchronous oblique collision of indochina with both sibumasu and south china inducing dextral and sinistral shearing along e w to nw se and n s fault zones respectively the collision along song ma follows the northwards subduction of indochina beneath south china and the subsequent development of the song da zone which in turn was affected by the late triassic indosinian phase of shortening within the indochina plate internal collisions occurred coevally in the early triassic as along the poko suture at the western border of the kontum massif

the origin of the north pacific intermediate water possible source regions of the north pacific intermediate water npiw were investigated with synoptic conductivity temperature depth surveys in the okhotsk sea kuril basin a pycnostad referred to as the okhotsk sea mode water osmw was found in the density range of 26 6 27 the pycnostad is not seen in the western subarctic gyre wsag thus it is an indicative water peculiar to the okhotsk sea the maximum thickness is at 26 7 26 9 centered at 26 8 which coincides with the npiw density range in the north pacific subtropical gyre in the oyashio area east of the southern kuril islands and hokkaido waters that have intermediate temperature salinity and potential vorticity between the osmw and the wsag water were distributed suggesting a following transport route of the npiw source water the thick thus low q q is potential vorticity and low salinity water mass outflowing from the okhotsk sea mixes with the relatively warm saline and high q wsag water to form the oyashio water a coastal part of the oyashio water flows southwestward along the east coast of the southern kuril islands and hokkaido retaining the pycnostad q minimum a large part of the low q oyashio water flows further southward and merges with the kuroshio extension and then flows eastward forming new npiw in this process a salinity minimum develops and the q minimum disappears because of the mixing with a saline kuroshio water old npiw without a pycnostad in the npiw density range these results suggest that the origin of npiw is the water mass in the okhotsk sea osmw and the density of the water mass primarily determines the npiw density centered at around 26 8

possible explanation linking 18 6 year period nodal tidal cycle with bi decadal variations of ocean and climate in the north pacific 1 bi decadal climate variation is dominant over the north pacific on inter decadal timescale however the mechanism has not been fully understood we here find that the bi decadal variations in the north pacific climate and intermediate waters possibly relate to the 18 6 year period modulation of diurnal tide in the period of strong diurnal tide tide induced diapycnal mixing makes surface salinity and density higher and the upper layer shallower along the kuril islands and the east coast of japan simple model results suggest that the coastal depth adjustment by baroclinic kelvin waves enhances the thermohaline circulation the upper layer poleward western boundary current and associated heat transport by about 0 05pw this could also explain the warmer sst in the kuroshio oyashio extension regions where positive feedback with aleutian low might amplify the bidecadal variations the 18 6 year tidal cycle hence could play a role as a basic forcing for the bi decadal ocean and climate variations

mn ii partitioning between calcium and magnesium sites in studies of dolomite origin abstract in an electron spin resonance esr study of over 30 dolomites representing a variety of probable sedimentary origins we observed a mg site to ca site ratio in the mn distribution that suggests two groups of dolomite in one group the dolomites have a mn distribution ratio near 5 0 and an excess of ca in the other group the dolomites are near stoichiometric but have a mn distribution ratio that varies from near 5 to near 70 we suggest that these two groups reflect different origins for the dolomites the wide variation in the manganese distribution ratio for the near stoichiometric dolomites supplies a parameter against which other variables can be plotted in studies of dolomite origin

highly 13c enriched carbonate and organic matter in the neoproterozoic sediments of the bambuigroup brazil abstract paleontological and radiometric dating methods rb sr k ar and pb pb suggest neoproterozoic ages for sedimentary carbonate rocks of the bambuigroup in the southern part of the sa o francisco basin of central brazil the 13c values for carbonates fall within two ranges 2 to 2 and 10 to 16 for both groups coexisting organic carbon is depleted in 13c by 28 2 relative to the carbonates similar to numerous neoproterozoic examples worldwide secular variations in 13c in the bambuigroup show a significant positive excursion beginning with values near 0 in carbonates immediately above a diamictite and rising to values as high as 16 upsection the sr isotope data for carbonates from the bambuigroup agree with the age inferred from the secular variation in oceanic 13c values the striking feature in this study is that both the carbonate and total organic carbon are considerably more enriched in 13c than previously reported for neoproterozoic carbonates elsewhere it is not clear if these unusual 13c values are caused by primary or secondary processes

bidecadal variability in the intermediate waters of the northwestern subarctic pacific and the okhotsk sea in relation to 18 6 year period nodal tidal cycle 1 on the basis of historical oceanographic data we investigated the long term variations of the intermediate waters in the four regions in the northwestern subarctic pacific oyashio okhotsk sea mode water upstream oyashio and east kamchatka current we found bidecadal oscillations in these water properties that are synchronized with the 18 6 year period nodal cycle in periods when the diurnal tide is strong the following characteristics are found apparent oxygen utilization and phosphate are low in oyashio and okhotsk sea mode water the thickness of the intermediate layers is large and thus potential vorticity is correspondingly low in oyashio okhotsk sea mode water and upstream oyashio around the mesothermal temperature maximum water isopycnal potential temperature are low in the areas on the pacific side and high in the intermediate layer of okhotsk sea mode water the mixing ratio of okhotsk sea mode water in the upstream oyashio water is high these bidecadal oscillations can be explained by changes in the vertical mixing around the kuril straits induced by the diurnal tide whose amplitude is modulated with the 18 6 year nodal cycle higher sea surface salinity water around the kuril straits caused by stronger tidal mixing is possibly transported northward along the cyclonic okhotsk sea gyre and possibly enhances the formation of the dense shelf water this makes apparent oxygen utilization phosphate and potential vorticity lower in okhotsk sea mode water and oyashio

does carbon 13 track anthropogenic co2 in the southern ocean a multiparametric linear regression technique was used for waters in the southern ocean to estimate the change in both 13 c dic 13 c dic and dissolved inorganic carbon dic dic between 1978 and 1998 due to the accumulation of anthropogenic co 2 the observed decrease in 13 c dic at the surface the suess effect was 0 015 0 003 yr 1 in the sub antarctic zone and 0 005 0 003 yr 1 in the antarctic zone similar to values reported for the southern indian ocean gruber et al 1999 sonnerup et al 2000 to compare the 13 c dic with adic we used the ratio of these two anomalies rc 13 c dic dic mol kg 1 1 along the section arc ranged from 0 015 0 005 at 42 s to 0 007 0 005 mol kg 1 1 at 54 s the spatial variability in arc in the southern ocean reflects different timescales for processes controlling the uptake of 13 c from those controlling the uptake of 12 c and indicates that 13 c dic decouples from adic poleward of the sub antarctic zone the variations of arc along the section suggest that the 13 c dic anomaly is not a good predictor of the anthropogenic co 2 inventory in the southern ocean some methods for determining anthropogenic co 2 uptake both on the global and regional scale assume the penetration depths of 13 c dic to be the same as adic which implies a constant value for arc in the ocean at 0 016 mol kg 1 1 heimann and maier reimer 1996 ortiz et al 2000 bauch et al 2000 the use of a constant arc and the observed 13 c dic to estimate anthropogenic co 2 could lead to an underestimate in the inventory of anthropogenic co 2 for the southern ocean by 50

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

anthropogenic co2 accumulation rates in the north atlantic ocean from changes in the 13c 12c of dissolved inorganic carbon 1 the anthropogenic co2 accumulation rate for the north atlantic ocean was estimated on the basis of the decrease in the 13c of the dissolved inorganic carbon measured between cruises in 1981 transient tracers in the north atlantic 1993 oaces and 2003 repeat hydrography a mean depth integrated 13c change of 15 0 3 8 m yr 1 was estimated by applying a multiple linear regression approach to determine the anthropogenic 13c decrease at 22 stations where 13c depth profiles were compared the largest and deepest anthropogenic 13c decreases occurred in the subpolar ocean and in contrast the smallest and shallowest decreases occurred in the tropical ocean a mean anthropogenic co2 accumulation rate of 0 63 0 16 mol c m 2 yr 1 0 32 0 08 pg c yr 1 in the north atlantic ocean over the last 20 years was determined from the mean depth integrated 13c change and a ratio of anthropogenic 13c to dic change of 0 024 mol kg 1 1 only half of the accumulated anthropogenic co2 in the north atlantic during the last 20 years was the result of air sea co2 uptake based on a comparison of the air sea 13co2 flux to the dic13 inventory change with the other half likely a result of northward advective transport

recrystallization of dolomite evidence from the monterey formation miocene california dolomites from the upper calcareous siliceous member of the miocene monterey formation exposed west of santa barbara california were analysed for geochemical isotopic and crystallographic variation the data clearly document the progressive recrystallization of dolomite during burial diagenesis in marine pore fluids recrystallization is recognized by the following compositional and crystallographic variations dolomites have decreasing 18o and 13c compositions decreasing sr contents and increasing mg contents with increasing burial depths and temperatures from east to west in the study area 18o values vary from 5 3 in the east to 5 5 pdb in the west and are interpreted to reflect the greater extent and higher temperature of dolomite recrystallization in the west 13c values correlate with 18o and decrease from 13 6 in the east to 8 7 pdb in the west sr concentrations correlate positively with 18o values and decrease from a mean of 750 ppm in the east to a mean of 250 ppm in the west mol mgco3 values inversely correlate with 18o values and increase from a minimum of 41 0 in the east to a maximum of 51 4 in the west rietveld refinements of powder x ray diffraction data indicate that the more recrystallized dolomites have more contracted unit cells and increased cation ordering the fraction of the ca sites in the dolomites that are occupied by ca atoms increases slightly with the approach to stoichiometry the fraction of the mg sites occupied by mg atoms strongly correlates with mol mgco3 even in early diagenetic non stoichiometric dolomites there is little substitution of mg in ca sites during recrystallization the amount of mg substituting for ca in ca sites decreases even further most of the disorder in the least recrystallized non stoichiometric dolomites is related to substitution of excess ca on mg sites

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

first evidence of the cambrian basement in upper peninsula of thailand and its implication for crustal and tectonic evolution of the sibumasu terrane abstract although the sibumasu terrane in asia was previously considered to be composed of phanerozoic rocks with cambrian crystalline basement no reliable or direct radiometric dating evidences of such crystalline basement was ever reported our new in situ zircon u pb dating of the khao tao orthogneiss yields a concordant age of 501 5 7 5 ma 2 which provides the first robust evidence for the cambrian crust in upper peninsula of thailand the zircon ehf t values range from 3 7 to 6 1 with model ages tcdm of 1244 1827 ma suggests a mixed crust mantle source the chemical similarity and spatial continuity of the khao tao orthogneiss with other pre neotethys marginal eurasian and sibumasu granitoids indicate the linear paleogeographic association under a similar magmatic arc related regime along the gondwana india australia margin as part of the pan african orogeny system

relationship between paleotemperatures of metamorphic dolomites and esr determined mn ii partitioning ratios abstract an electron spin resonance esr study of the distribution of mn ii between mg sites and ca sites in 28 contact metamorphic dolomite samples suggests that the distribution is temperature sensitive the data can be modelled by alternative interpretations in the first a polynomial equation approximates the trend of the data suggesting an exponential relation with mn ii ratios decreasing to a stable value of 10 with increasing temperature to near 900 c the second suggests two groups of dolomites one group close to the intrusion

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

trace element zoning in dolomite proton microprobe data and thermodynamic constraints on fluid compositions abstract lower cretaceous euhedral dolomite crystals from the gargano peninsula italy have been analyzed by scanning proton microprobe spm for the trace elements sr zn fe mn cu ni y and rb intricate decoupled zoning patterns for fe mn and zn are a ubiquitous feature of the outer 55 microns of the dolomite crystals differences between peak and baseline concentrations are on the order of several hundred parts per million in contrast sr concentrations are nearly constant at 110 ppm the concentrations of the other cations are all low cu 20 ppm y 10 ppm and ni and rb 5 ppm in order to investigate the origin of the gargano dolomite we have used the method of tardy and garrels to estimate equilibrium partition coefficients for divalent cations between aqueous fluids and the dolomite structure 18o measurements on gargano dolomites show that they formed at a maximum temperature of 75 c 7 c estimated equilibrium constants for substitution of the cation m into dolomite calculated baseline molar cation ratios for fluids in equilibrium with gargano dolomite and measured cation ratios for seawater and marine sediment pore fluids at 75 c are as follows m n k eq log10 calculated ratio log10m n measured ratio in seawater log10m n measured ratio marine pore fluids mn mg 1 27 4 62 7 17 2 75 fe mg 12 66 4 77 6 57 3 81 zn mg 6 85 5 27 6 72 4 84 sr ca 0 17 2 94 1 92 1 83 cation ratios of fluids in equilibrium with the baseline concentrations of mn fe and zn in the gargano dolomite samples are bracketed by the cation ratios measured in seawater and in marine sediment pore fluids the factor often discrepancy for sr in the predicted fluid compared with seawater is probably due to nonideal mixing of sr on the ca site the decoupled fluctuations of the mn and fe concentrations in these samples can be explained by eh fluctuations in the reactant fluid zn fluctuations may be a product of ph dependent oxide surface reactions to test this hypothesis of origin unzoned tertiary dolomites from enewetak atoll and from the bahama bank have also been analyzed the homogeneous sr concentration in the gargano dolomite is similar to the sr concentrations measured in the enewetak atoll 175 ppm and bahama bank 150 ppm dolomites samples which in both cases almost certainly grew in equilibrium with seawater gargano baseline mn 20 ppm and fe 80 ppm concentrations are also much the same as the bahama bank dolomite mn 15 ppm and fe 140 ppm concentrations the lack of sr zoning in the gargano samples and the similarity of their sr mn and fe content to dolomite that formed in equilibrium with seawater indicates that the dolomitizing fluid was most likely seawater or a seawater type brine low sr concentrations 12 ppm in pore filling calcite from the gargano suggests that in contrast to the dolomite the calcite precipitated from meteoric fluids

zircon and monazite upb dating of the doi inthanon core complex northern thailand implications for extension within the indosinian orogen abstract the doi inthanon metamorphic core complex occupies a prominent central position within the northwestern thai gneiss belt which has been inferred to be as old as precambrian and as young as permo triassic u pb dating of zircon from core orthogneisses of the complex suggests that the orthogneisses were derived from granitic protoliths with essentially the same late triassic early jurassic age as the mae cham pluton 205 3 4 ma to the west of the doi inthanon complex monazite ages from the orthogneisses indicate that low pressure and high temperature metamorphism and migmatitization occurred in the late cretaceous 84 72 ma limited published radiometric age data from elsewhere in the migmatitic gneiss belt suggest that widespread minor plutonism accompanied this thermal event a younger u pb data of 26 8 0 5 ma for zircon and monazite from the mae klang granite which intruded mylonitic gneisses on the eastern side of the doi inthanon complex indicates that there was also significant plutonism in the late oligocene these u pb ages constrain the development of the complex and hence of the migmatitic gneiss belt as a whole to an interval between late cretaceous and early miocene ductile shearing uplift and tectonic denudation via detachment faulting chronologically overlap the initiation of extensional basin development to the east and southeast of the gneiss belt and imply a genetic connection thus oligocene early miocene thermal rifting from the gulf of thailand northward into mainland thailand may have been the direct product of crustal extension rather than the transtensional product of regional strike slip faulting

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

u pb zircon geochronology of early permian to late triassic rocks from singapore and johor a plate tectonic reinterpretation article i nfo the results of u pb zircon geochronology of permian to middle triassic granitoids from singapore and neighbouring johor are presented rhyolite from pulau sibu is 276 5 ma gabbros from singapore give ages of 260 2 to 249 2 ma granites from singapore give ages from 249 2 to 230 6 ma and rhyolite from telkuma gives an age of 238 2 ma u pb detrital zircon age spectra from a late triassic conglomerate from singapore show carboniferous mid dle triassic and late triassic spikes at 350 245 and 217 ma respectively these new data when combined with published u pb zircon ages allow a revision of the plate tectonic evolution of the malaysian peninsula region a tin bearing magmatic arc evolved in the eastern malaysian peninsula part of indochina from the early permian to the middle triassic when the palaeo tethys ocean was subducted and sibumasu continental lithosphere was rifted from pangea this opened up the neo tethys ocean that the granitoid ages show a progressive decrease in age from pulau sibu 276 5 ma to singapore 230 6 ma suggests that during this andean type orogenic phase the subduction zone rolled back and steepened causing the locus of mainly i type magmatism to migrate from east to west in present day coordinates across the eastern and central belts and stretch the lithosphere as it did so in the late triassic sibumasu collided with indochina causing the western belt sibumasu to over thrust the central belt indochina along the bentong raub suture the lower half of the thickened crust formally the tin bearing indochina plate was partially melted and pre dominantly s type tin bearing granites were intruded into the upper crust formally sibumasu this late triassic collisional phase is the indosinian orogeny in peninsular malaysia

tectonic evolution of the sibumasu indochina terrane collision zone in thailand and malaysia constraints from new u pb zircon chronology of se asian tin granitoids three principal granite provinces are defined across se asia as follows 1 the western thailand myanmar burma province consists of hornblende biotite i type granodiorite granites and felsic biotite k feldspar garnet tourmaline granites associated with abundant tin mineralization in greisen type veins new ion microprobe u pb dating results from phuket island show zircon core ages of 212 2 and 214 2 ma and a thermal overprint with rims of 81 2 1 2 and 85 75 ma 2 the north thailand west malaya main range province has mainly s type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the sibumasu plate with indochina during the mid triassic biotite granites around kuala lumpur contain extremely u rich zircons up to 38000 ppm that yield ages of 215 7 and 210 7 ma 3 the east malaya province consists of dominantly permian triassic i type hornblende biotite granites but with subordinate s type plutons and a type syenite gabbros biotite k feldspar granites from tioman island off the east coast of malaysia also yield a zircon age of 80 1 ma showing cretaceous magmatism in common with province 1 geological and u pb geochronological data suggest that two east dipping in present day coordinates subduction zones are required during the triassic one along the bentong raub palaeo tethyan suture and the other west of the phuket burma province 1 belt supplementary material a full description of u pb analytical methods used and data tables are available at www geolsoc org uk sup18523

late triassic post collisional granites related to paleotethyan evolution in se thailand geochronological and geochemical constraints abstract a set of new u pb geochronological elemental and sr nd hf isotopic data is presented to constrain the formation age and petrogenesis of granites in se thailand which are significant for understanding eastern paleotethyan tectonic evolution and regional correlation in se asia six granite samples from the chonburi rayong bang lamung and chanthaburi plutons yielded similar crystallization ages of 222 218 ma these granites can be geochemically classified into s type group 1 and i type group 2 granites both groups have similar chondrite normalized ree and primitive mantle normalized multi element patterns but distinctly different sr nd hf isotopic compositions group 1 is characterized by more enriched initial 87sr 86sr i ratios 0 7101 0 7272 and lower end t values 12 0 to 13 2 compared with those of group 2 with 87sr 86sr i of 0 7027 0 7053 and end t of 0 6 to 1 2 consistently zircons from group 1 yield negative ehf t values of 7 3 to 27 4 and mesoproterozoic or older hf model ages tdm 1 53 2 63 ga distinct from those of group 2 with positive ehf t values 5 0 11 3 and younger tdm 0 42 0 67 ga group 1 granites mainly originated from ancient greywackes but group 2 from juvenile mafic crust with the input of meta sedimentary component these data along with available observations synthetically indicate that these granites formed in the post collisional gravitational collapse setting of the thickened crust in response to the assemblage of the indochina with sibumasu blocks they linked northerly and easterly to the late triassic granitoids in nw thailand and east malay peninsula related to the paleotethyan tectonic regime respectively

seasonal variability of δ18o and δ13c of planktic foraminifera in the bering sea and central subarctic pacific during 1990 2000 we evaluated a 10 year time series of 18o and 13c records from three planktic foraminifers neogloboquadrina pachyderma globigerina umbilicata and globigerinita glutinata in the bering sea and central subarctic pacific with a focus on their responses to environmental changes foraminiferal 18o followed the equilibrium equation for inorganic calcite with species specific equilibrium offsets ranging from nearly zero 0 02 for n pachyderma and 0 01 for g umbilicata to 0 16 g glutinata equilibrium offsets in our sediment trap samples were smaller than those from plankton tow studies implying that foraminiferal 18o was modified by encrustation during settling habitat calcification depths varied from 35 55 m n pachyderma and g umbilicata or 25 45 m g glutinata during warm stratified seasons to around 100 m during winter when the mixed layer depth increases unlike 18o foraminiferal 13c showed species specific responses to environmental changes we found a dependency of 13c in g umbilicata on co32 concentrations in ambient seawater that agreed reasonably well with published laboratory results suggesting that 13c of g umbilicata is subject to vital effects in contrast 13c of n pachyderma and g glutinata are likely affected by other species specific biological activities seasonal flux patterns reveal that fossil records of n pachyderma and g glutinata represent annual mean conditions whereas that of g umbilicata most likely indicates those of a specific season because none of these three taxa was abundant from december to february their fossil records likely do not reflect isotope signals from cold seasons

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