unconformity of red sandstones in north vietnam field evidence for indosinian orogeny in northern indochina we re examine several unconformity sites in northwestern vietnam where the indosinian orogenesis has been defined field observations in the black river song da region near son la demonstrate that red sandtones and conglomerates reportedly of cretaceous age occur unconformably above schistosed epimetamorphic middle triassic sediments a mesozoic unconformity thus really exists in this region though the age of deformation is poorly contrained upper triassic to upper cretaceous in most places however the unconformity is strongly deformed folded triassic limestones are often thrusted onto the cretaceous rocks this implies that tertiary deformations probably due to the india asia collision have been strong in the northern part of the indochina block

a deforming plate tectonic model of the south china block since the jurassic abstract the south china block has experienced multiple phases of tectonic deformation since the middle jurassic understanding this deformation history helps reveal the driving mechanisms responsible and sheds light on the associated magmatism and mineralization here we construct deformable plate tectonic reconstructions for the south china block from 170 ma to the present using gplates the deformation starts with a nw se oriented shortening phase from 170 to 136 ma subsequently south china experienced two episodes of extension in the cretaceous during 136 118 ma and 100 80 ma respectively the cenozoic extension occurred mostly along the southeast continental margin including the east china sea shelf basin and rift basins in the northern south china sea margin and the taiwan margin segment the rifting was initiated nearly simultaneously along the continental margin at 65 ma and ceased at 34 30 ma the northern portion of the okinawa trough started rifting at 15 ma while the southern portion rifted in the last few million years the luzon volcanic arc thrusting onto the southeasternmost south china block since 6 5 ma caused the still active taiwan orogeny the predicted accumulated deformation at present day is characterized by overall shortening onshore with contraction factors mostly between 0 8 and 1 and extension offshore with stretching factors generally between 1 and 2 the central china orogen and taiwan orogen experienced more intense shortening relative to the interior south china by factors down to 0 6 the okinawa trough experienced intense stretching by factors up to 2 5 in its central part the intraplate deformation in the south china block is closely related to the subduction of the izanagi and pacific plates the jurassic and earliest cretaceous shortening was likely induced by trench advance and the extension during the cretaceous and the cenozoic was mostly driven by subduction retreat

terrestrial shallow water hydrothermal outflow characterized from out of space abstract we investigate the potential of satellite imagery to map and monitor the activity of shallow water hydrothermal systems which are often found around volcanic islands for this study we used publicly available data and proprietary worldview 2 satellites images with spectral bands that can penetrate up to water depths of 30 m shallow water hydrothermal sites are visible on satellite imagery primarily with publicly available data demonstrating the potential of satellite imagery to study and monitor shallow water hydrothermal activity we focus our work on volcanic islands showing intense near shore shallow water hydrothermal activity and distinct styles of hydrothermal venting satellite imagery constrains regional outflow geometry and the temporal variability or stability of these systems milos island shows hydrothermal outflow associated with reflective mineral precipitates and or bacterial mats which are stable over time 2010 2014 these outflows locally define polygonal patterns likely associated with hydrothermal convection in porous media in kueishantao island individual hydrothermal plumes charged with particles are visible at the sea surface and display great variability in intensity and distribution of plume sources 2002 2019 worldwide we have identified 15 shallow water hydrothermal sites with satellite imagery that are similar to either the milos system e g vulcano and panarea italy or the kueishantao system numerous sites in pacific volcanic islands this study demonstrates that satellite imagery can be used to map and monitor different types of shallow water hydrothermal systems at regional scale and monitor their evolution satellite data provide not only regional and temporal information on these systems unavailable to date but also the regional context for follow up in situ field data and observations e g instrumental monitoring sampling observations and mapping with divers or auvs to understand both the nature and dynamics of these systems and ultimately the associated fluxes

zircon hf isotopic constraints on the sources of the indus molasse ladakh himalaya india 1 india asia collision has resulted in the largest orogenic event on earth since at least 500 ma and this has had a profound influence on the drainage patterns of asia on the asian monsoon climate on global oceanography as well as on faunal extinctions despite this importance understanding of the paleogene evolution of this system is limited u pb and lu hf isotopic analyses of detrital zircons from the clastic sedimentary rocks of the indus molasse located within the indus suture of the ladakh himalaya india show that most have mesozoic cenozoic ages and juvenile hf isotopic compositions this suggests that the main source of these sediments is the transhimalayan batholith with minor flux from the lhasa karakoram terrane and indian plate the lower indus molasse chogdo formation is inferred to have been deposited at 60 49 ma whereas the upper choksti formation was deposited later than 45 41 ma and contains a greater contribution from the lhasa terrane the transhimalayan batholith was eroded throughout indus molasse sedimentation but increasing exhumation of lhasa karakoram terrane indicates its progressive uplift after initial collision and requires formation of apaleo indus river shortly after collision

a new model for the indochina and south china collision during the late permian to the middle triassic article i nfo a comparative analysis of indochina and south china during the early paleozoic indicates the former may be extended to include north vietnam part of the qinzhou tectonic zone and southern hainan island these three regions were traditionally regarded as parts of south china separated from indochina by the song ma suture in central north vietnam a new suture called the dian qiong suture is proposed here approximately along the southern margin of the present nanpanjiang basin this suture is linked to its eastern counterpart in hainan island through a nne trending dextral transform fault zone along the eastern margin of the nanpanjiang basin the conventional song ma suture originally constitutes its western extension and was translated to its present location by sinistral displacement along the red river fault zone during the tertiary upper paleozoic deep water turbidites and associated mid oceanic ridge basalts along the suture in the nanpanjiang basin illustrate a coeval ocean between indochina and south china the ocean was consumed by south directed subduction beneath indochina during the late permian to the middle triassic this suture zone was finally re shaped by the indentation between the active margin of indochina and the irregular passive continental margin of south china during the late triassic as well as displacement along the red river fault zone during the cenozoic

temporal variations of gas compositions of fumaroles in the tatun volcano group northern taiwan article i nfo he 4 he geochemical monitoring hydrothermal activity is common in the tatun volcano group of northern taiwan helium isotopic compositions of fumarolic samples show that mantle component occupies more than 60 in the previous study along with recent seismic results a magma reservoir is inferred to have existed beneath the area of da you keng where fumarolic venting is the most active in tatun volcano group progressive increases of hcl concentrations and so2 h2s ratio in fumaroles from da you keng have been observed since august 2004 the hcl concentration changed from almost the detection limit to thousands of ppm even up to 30 000 ppm so2 h2s ratios varied from almost 0 to 3 hence so2 became the dominated s species in this area these variations were accompanied by rising temperature of fumaroles in the tatun volcano group especially in the area of da you keng from boiling point to 131 c meanwhile 3

geochemical characteristics speciation and size fractionation of iron fe in two marine shallow water hydrothermal systems dominica lesser antilles abstract marine shallow water hydrothermal systems have so far largely been neglected with respect to trace metal fluxes and possible stabilizing complexation processes even though they emit their fluids directly into the photic zone the impact of stabilized dissolved metal input by shallow vents into surface waters as well as the effect on the transport and bioavailability of bioactive trace metals within the area of highest primary production rates in the world oceans is therefore at present mostly unknown in this study we investigated the concentration size fraction distribution colloidal and soluble as well as redox speciation and labile concentrations of the limiting micronutrient iron fe at two marine shallow water hydrothermal systems champagne hot springs and soufriere off the coast of dominica lesser antilles island arc caribbean geochemical characterization of the two different vent sites showed that both are affected by meteoric and seawater influence with a stronger meteoric influence at soufriere than at champagne hot springs measurements of soluble and labile fe were performed using a modified competitive ligand exchange adsorptive cathodic stripping voltammetry cle adcsv with salicylaldoxime sa as the artificial ligand our results show that focused fluids discharging at the seafloor as well as hydrothermal pore fluids are despite a calculated theoretical oxidation half life of only 6 4 min highly enriched in fe ii indicating a strong complexation of fe ii strong enough to prevent fe ii from oxidation and precipitation since these fluids show enriched dissolved organic carbon doc concentrations and very low fractions of chemically labile fe complexation may occur by organic carbon which was recently suggested to also be a factor in stabilizing particulate fe ii in deep sea hydrothermal non buoyant plumes our results indicate that shallow water hydrothermalism off the coast of dominica releases high concentrations of stabilized bioavailable fe ii into the photic zone which influences the biogeochemical cycle of fe in surface waters considering the abundance of marine shallow water hydrothermal systems in many regions such processes may even play a role in the global oceanic dfe cycle

s wave velocities and anisotropy of typical rocks from yunkai metamorphic complex and constraints on the composition of the crust beneath southern china abstract in order to constrain the interpretation of seismic data from receiver functions and deep profiles of the crust beneath southern china cathaysia and yangtze blocks we have measured s wave velocities v s and splitting as a function of hydrostatic confining pressure up to 650 mpa for 22 representative samples i e granite diorite felsic gneiss and mylonite amphibolite schist and marble from the yunkai metamorphic complex china that represent the crystalline basement beneath the region the experimental data were combined with electron backscattering diffraction ebsd analysis of rock forming minerals to constrain variations of v p v s ratios and understand the origin of seismic anisotropy the crusts beneath the yangtze and cathaysia blocks have different average thicknesses h 35 4 6 3 km and 29 8 1 8 km respectively but display almost the same v p v s values 1 73 0 08 and 1 74 0 04 respectively these ratios correspond to an average of bimodally distributed granitic and gabbroic lithologies which are dominant respectively in the upper and lower crusts instead a homogeneous andesitic composition of the overall crust positive and negative correlations between h and v p v s occur in west and east parts of southern china respectively the negative correlation indicates basaltic underplating from a partially molten mantle wedge above the subducting pacific plate into the southern china crust whereas the positive correlation implies that much larger thinning strain has taken place in the high temperature mafic lower crust high temperature than in the low temperature felsic upper crust during mesozoic cenozoic tectonic extension

the structural setting of the song ma region vietnam and the indochina south china plate boundary problem abstract the song ma song da region of northern vietnam contains the song ma anticlinorium a polydeformed polymetamorphosed early palaeozoic island arc forearc terrane accreted to the south china plate in siluro devonian times the song ma anticlinorium is not an indosinian subduction zone and nor is the post triassic post cretaceous song ma fault the song ma fault is one of many northwest trending post cretaceous high angle reverse oblique slip faults and thrusts responsible for shortening and strike slip transposition of northern vietnam folds penecontemporaneous with this faulting include the song ma anticlinorium which is formed probably of thrust ramp folds the faulting and penecontemporaneous folding developed during oligocene sinistral strike slip on the song hong fault and was reactivated during pliocene quaternary times we conclude that the present plate boundary is a broad deformation zone between da nang and the song hong and that parts of the south china plate extend well to the south of the song hong fault

origin of native sulfur ball from the kueishantao hydrothermal field offshore northeast taiwan evidence from trace and rare earth element composition we first report the trace and rare earth element compositions of native sulfur ball with sulfur contents varying from 97 08 wt to 99 85 wt from the kueishantao hydrothermal field off ne taiwan we then discuss the sources of trace and rare earth elements incorporated into the native sulfur ball during formation comparison of our results with native sulfur from crater lakes and other volcanic areas shows the sulfur content of native sulfur ball from the kueishantao hydrothermal field is very high and that the rare earth element ree and trace element constituents of the native sulfur balls are very low sigma ree 35 ppb in the native sulfur ball v cr co ni nb rb cs ba pb th u al ti and ree are mostly derived from andesite mg k and mn are mostly derived from seawater and fe cu zn and ni are partly derived from magma based on the sulfur contents trace and rare earth element compositions and local environment we suggest that the growth of the native sulfur ball is significantly slower than that of native sulfur chimneys which results in the relatively higher contents of trace and rare earth element contents in the native sulfur ball than in the native sulfur chimneys from the kueishantao hydrothermal field finally we suggest a glue pudding growth model for understanding the origin of the native sulfur ball in the kueishantao hydrothermal field whereby the native sulfur ball forms from a mixture of oxygenated seawater and acidic low temperature hydrothermal fluid with h 2 s and so 2 gases and is subsequently shaped by tidal and or bottom currents c 2010 elsevier ltd all rights reserved

north and south china collision along the eastern and southern north china margins abstract lithofacies distribution and petrography and intracontinental deformation in the north china block ncb and the south china block scb show an active continental margin flanked by the eastern ncb and a passive continental margin was present along the west side of the scb both margins initially trending n ne the tanlu fault possibly initiated as part of the subduction zone during paleozoic time along the eastern margin on the ncb the ncb and the scb were divided along the eastern southern north china margin by the qinling dabie tanlu sulu imjingang yanji zone from southwest to northeast these two continental blocks made contact first in the northeast during late early permian time finally in the southeast at late triassic time and the clockwise collision probably lasted to middle jurassic time the eastern suture the yanji imjingang sulu tanlu zone was dominated by contractional deformation the southern suture the qinling dabie zone was a transpression belt dominated by right lateral strike slip

the typical large scale superposed folds in the central south china implications for mesozoic intracontinental deformation of the south china block abstract the south china block has experienced polyphase intensive intracontinental deformation in the mesozoic time large scale superposed folds in central south china document the mesozoic tectonic events within the south china block here we present new structural data related to synfolding deformation coupling with chronological data to reconstruct the deformation sequence and tectonic regime during crustal shortening these data indicate that the superposed folds dominated by a two stage tectonic compressive regime experienced two phases of superposed buckle folding leading to the orthogonal superposition of ne sw trending folds onto wnw ese trending folds between the late middle jurassic and the earliest early cretaceous our structural analysis together with geochronological data for this area suggests that the south china block predominately underwent two phases of intracontinental deformation during the mesozoic the early phase of tectonism d1 is characterized by a late middle triassic to earliest early jurassic ne sw compression causing the occurrence of an orogeny perpendicular shortening accompanying with evident magmatism this tectonic event was most likely associated with progressive clockwise collision of the south china block toward the north in the indosinian event subsequent tectonic activity d2 between the late middle jurassic and the earliest early cretaceous contributed to a phase of nw se contraction that overprinted the early ne sw shortening in the interior of the south china block generating a large scale nw convex fold belt and the typical large scale superposed folds within the central south china block the later tectonism was probably driven by the nw directed subduction of the paleo pacific plate beneath the eastern part of the asian continent

late permian to middle triassic sedimentary records in shiwandashan basin implication for the indosinian yunkai orogenic belt south china abstract the shiwandashan basin is an elongate region of the late permian middle triassic potential sediment accommodation that formed on continental crust between the yunkai orogen and the adjacent yangtze craton block south china several terms such as remanent marine trough structural window rift and pull apart basin have been proposed studies of the late permian middle triassic sedimentary sequences and the tectonics lithofacies and paleogeography of the shiwandashan basin indicate that the late permian middle triassic succession is composed of thick coarse molasse deposits and fine clastics organized into coarsening upward and fining upward stratigraphic sequences the shiwandashan basin went through the process of growth and disappearance from molasse to turbidite deposition and finally to volcanic eruption during late permian middle triassic to some extent the facies evolution reflects the tectonic controls on the sedimentation of the foreland basin the coarsening upward sequences hundreds to thousands of metres scale occurring immediately adjacent to the thrust front demonstrate that important episodic thrusting orogenesis and piedmont flexuring subsidence with low velocity took place in the northwestern part of the yunkai orogen whereas fining upward sequences are the indicator of continued deformation with high thrust velocity the following four facts have been demonstrated 1 a foreland basin existed in late permian middle triassic 2 the development of the foreland basin was controlled by the evolution the yunkai orogen 3 the basin and mountains continuously changed and migrated 4 the shiwandashan basin was a key demarcation between an active region in southeastern south china cathaysian block and a relatively stable region in northwestern yangtze block it was a convergent boundary in late permian middle triassic and its tectonic nature changed in the wake of the tectonic evolution of the surrounding area

reversed spatial asymmetries between el nino and la nina and their linkage to decadal enso modulation in cmip3 models abstractthis study examines preindustrial simulations from coupled model intercomparison project phase 3 cmip3 models to show that a tendency exists for el nino sea surface temperature anomalies to be located farther eastward than la nina anomalies during strong el nino southern oscillation enso events but farther westward than la nina anomalies during weak enso events such reversed spatial asymmetries are shown to force a slow change in the tropical pacific ocean mean state that in return modulates enso amplitude cmip3 models that produce strong reversed asymmetries experience cyclic modulations of enso intensity in which strong and weak events occur during opposite phases of a decadal variability mode associated with the residual effects of the reversed asymmetries it is concluded that the reversed spatial asymmetries enable an enso tropical pacific mean state interaction mechanism that gives rise to a decadal modulation of enso intensity and that at least three cmip3 models realistically simu

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

tide influenced acidic hydrothermal system offshore ne taiwan elemental sulfur and hydrogen sulfide emitted offshore of northeastern taiwan known to local fishermen for generations but never studied until recently are found to have originated from a cluster of shallow 92 with small amounts of h2s helium isotopic ratios 7 5 times that of air indicate that these gases originate from the mantle high temperature hydrothermal fluids have measured temperatures of 78 116 degrees c and ph 25 degrees c values as low as 1 52 likely the lowest to be found in world records low temperature vents 30 65 degrees c have higher ph values continuous temperature records from one vent show a close correlation with diumal tides suggesting rapid circulation of the hydrothermal fluids c 2005 elsevier b v all rights reserved

the hengshan low angle normal fault zone structural and geochronological constraints on the late mesozoic crustal extension in south china abstract we document in this paper a significant low angle normal fault namely the hengshan detachment fault which extends more than 150 km long in nne orientation and bounds an elongated early cretaceous basin in hunan province central south china detailed structural and geochronological analyses have been conducted along its southern segment where a well exposed 3 km thick flat ductile shear zone develops along the western margin of the hengshan granitic massif this zone is featured by shallow dipping foliations of varied trend from ne to nw which bear penetrative stretching lineations varying from nw to sw trend shear sense criteria indicate top to the nw and top to the sw motions along its northern and southern parts respectively quartz c axis orientations of mylonitic rocks from the shear zone exhibit asymmetric single or crossed girdle patterns and the distributions of fabric point maxima suggest a simultaneous operation of basal and prism slips indicating a deformation temperature ranging from 400 c to 550 c one zircon u pb age of the sheared albitite and three muscovite 40 ar 39 ar ages of the mylonitic rocks indicate that the ductile shearing initiated at 136 ma and lasted till 97 ma the zircon u pb dating results of five granitic samples from the hengshan granitic pluton yield two phases of crystallization ages of 232 228 ma and 150 151 ma respectively indicating two preceding magmatic events prior to the ductile shearing in the lower plate our structural and geochronological data allow defining the hengshan massif as an extensional dome rather than a metamorphic core complex as previously predicted due to the lack of syn tectonic plutonism and the origin of detachment fault associated with the reactivation of the inherited thrust this study provides crucial evidence for understanding how the mid upper crust deformed during the process of extension which testifies to a coeval occurrence of non coaxial deformation of the ductile flow in the middle crust and brittle faulting in the upper crust it also sheds new insights into the timing of the regional crustal extension in south china and permits to constrain its onset time to be ca 136 ma

nitrogen as the carrier gas for helium emission along an active fault in nw taiwan variations of he gas concentration are widely applied in studies devoted to the location of faults and to monitor seismic activities up to now its migration mechanism in soil is not fully understood a systematic soil gas survey across an active fault in nw taiwan provides the opportunity to closely examine the mechanism of he migration in the fault zone significant spatial and temporal correlations observed between soil n2 and he gas support the hypothesis that n2 is the probable carrier gas for he emission in the studied area based on n2 ar ratios and n2 isotopic results the excess soil n2 in this study is considered to be largely derived from ancient atmospheric air which was dissolved in groundwater furthermore observations rule out the possibility of co2 being the dominant carrier gas for he in the studied area based on the c and he isotopic compositions and the relationship between concentrations of these gases at least two soil gas sources a and b can be identified in the studied area source a is an abiogenic gas source characterized by excess n2 and he and very low o2 and co2 content source b on the other hand is a mixture of biogenic gas and atmospheric air the development of the fault system is an important factor affecting the degree of mixture between sources a and b therefore variations of soil gas composition in particular those derived from source a could be a useful proxy for tracing faults in the area

a tidal influenced hydrothermal system temporarily cooled by a tropical storm abstract the lutao hydrothermal field is an intertidal arc volcanic system located offshore southeast taiwan hosting a zhudanqu zdq vent and a huwaichi hwc spring with strongly contrasting fluid chemistry low mg moderately enriched cl and h with respect to seawater indicate that the zdq endmember was derived from the brine phase that was formed during low degree subcritical phase separation in contrast the endmember for the hwc vent fluids is related to the vapor phase temperature and pressure of the phase separation were estimated as 150 c and 7 bar respectively the water rock ratio was roughly calculated as about 2 the lutao hydrothermal system was slightly affected by semi diurnal tides by some combination of tidal loading and tidal currents the time delay between tides and the response of the hydrothermal system was about 3 h while freshwater was almost absent in the hwc vent fluids at normal conditions the typhoon fung wong on sep 21st 2014 led to intrusions of freshwater into the vent fluids with a percentage of 16 both the zdq and the hwc endmember compositions showed some changes after the typhoon event suggesting a cooling of the reaction zone after the typhoon passed by the hydrothermal system began to recover evidenced by increasing percentages of the hwc endmember and decreasing freshwater contributions the flux of the hwc endmember was estimated as 460 560 l h 1 based on these observations this study for the first time reports a shallow depth tidal influenced hydrothermal system that was temporarily cooled by a tropical storm

acidic and sulfate rich hydrothermal fluids from the manus back arc basin papua new guinea hot 88 120 c and acidic ph 2 1 hydrothermal fluids rich in sulfate were discovered venting in the desmos caldera depth 1926 m eastern manus back arc basin bismarck sea surrounded by papua new guinea the abundant sulfate 32 8 m m higher than the seawater value of 28 m m with elemental sulfur deposition around the vents and remarkably low d h 2 o and 34 s h 2 s values 8 1 and 5 6 respectively are suggestive of the incorporation of a magmatic fluid and the disproportionation of the exsolved so 2 from a magma body the desmos fluid may be similar in origin to the acidic sulfate chloride hot springs associated with subaerial volcanic activity in contrast to the typical hydrothermal end member mg concentration of 0 the desmos fluids are rich in mg 46 52 m m probably because of mg dissolution by acid attack upon magnesium silicate minerals

nanpanjiang basin a window on the tectonic development of south china during triassic assembly of the southeastern and eastern asia abstract as the largest siliciclastic sink in the south china block the triassic nanpanjiang basin is generally thought of as a foreland basin related to indosinian collision between the south china and indochina blocks our basin analysis spanning an eight years period provides details of lopingian to middle triassic stratigraphic fill and tectonic subsidence of the basin field observation and sedimentological analyses reveal that the basin was not filled by a monotonous turbidite system and suggest instead the development of five primary depositional units constituted by deep water turbidite systems mass transport deposits condensed drapes shallow water isolated carbonate platforms and volcano volcaniclastic rocks the stratigraphic completeness of the basin the coexistence of widespread but localized carbonate platforms within axially filled deep water basin tectonically generated cyclothems of transverse mass transport deposits along intrabasinal faults and basin fill of extrusive rocks of bimodal composition together apparently call in question the claim that crustal shortening prevailed during the late permian to pre norian triassic patterns of basin fill differential tectonic subsidence and very high subsidence rate of the region adjacent to master fault are more closely match the pattern expected for extensional to transtensional basin in a back arc setting the crustal extension in the southwestern south china was not consistent with hypothesized indosinian collision between south china and indochina blocks but more likely developed in response to northwestward subduction of the paleo pacific plate our results combined with regional considerations lead to a new model for the triassic tectonic evolution of south china during triassic assembly of the southeastern and eastern asia

drivers for late paleozoic to early mesozoic orogenesis in south china constraints from the sedimentary record abstract unconformity bound permo triassic successions in the qinfang basin south china craton reflect tectonic processes associated with tectonothermal activity along the margins of the craton the provenance record of these successions based on modal analysis geochemical composition detrital zircon u pb ages and paleocurrent data indicate derivation from the adjoining precambrian yunkai massif and surrounding paleozoic sedimentary units the quartz dominated nature of the siliciclastic units along with their high th sc and zr sc ratios indicate a recycled orogen source detrital zircons from late permian to early triassic samples display major age groups at 1100 800 ma 650 500 ma 480 420 ma with subordinate age groups at 2800 2400 ma 1900 1600 ma and 1400 1200 ma late triassic sandstones show a similar detrital zircon age pattern as well as a 300 250 ma age group integration of this provenance data with regional geological information suggests that the unconformity at the base of the permian succession is related to subduction of the paleo tethys ocean to the south of the craton whereas the major driver for triassic tectonic activity corresponds with terrane accretion and the termination of paleo tethys ocean subduction along the southwest margin of the craton

seafloor hydrothermal clay alteration at jade in the back arc okinawa trough mineralogy geochemistry and isotope characteristics seafloor hydrothermal activity at jade has resulted in extensive alteration of the host epiclastic sediments and pumiceous tuffs forming mica kaolins kaolinite and halloysite mg rich chlorite talc montmorillonite and a mixed layer mineral of dioctahedral chlorite and montmorillonite chl mont clay mineral assemblages show a vertical variation which reflects variable amounts of cold seawater incorporated into hot hydrothermal fluids in subsurface sediments and tuff however mixing alone cannot explain the occurrence of abundant kaolin minerals at jade the formation of kaolin minerals requires much more acidic fluid than expected from simple mixing of hydrothermal fluids and cold seawater low ph values are likely attained by oxidation of h2s either dissolved in the hydrothermal fluid or released from the fluid during decompression the fluid reaching the seafloor is discharged into cold seawater which caused precipitation of sulfides close to vents and native sulfur and barite at the margins of the vent areas halloysite barite and anhydrite show sr isotope compositions similar to marine sr indicating the derivation of marine sr directly from seawater or by the dissolution of calcareous nannoplanktons the isotopic compositions of kaolinite 18o 7 4 d 23 chl mont 18o 7 0 d 32 and mica 18o 5 4 to 9 9 d 30 to 26 suggest fluids of a heated seawater origin the o isotopic data yielded formation temperatures of 170 c for kaolinite 61 to 110 c for halloysite and 145 to 238 c for mica barite 34s values 21 0 to 22 5 are very similar to the marine sulfate value confirming that the barite formation took place due to mixing of ba bearing hydrothermal fluids and sulfate rich seawater native sulfur shows a large variation in 34s in one hand specimen probably because of rapid disequilibrium precipitation of s during fluid exhalation on the seafloor sulfur in hydrothermal fluids is usually consumed to form metal sulfides therefore abundant native sulfur at jade suggests high h2s metals ratios of the hydrothermal fluids the alteration assemblages and isotopic data of hydrothermal minerals from jade are very similar to those of kuroko type barite deposits of middle miocene age which formed from fluids of high s metals ratios at less than 200 c at jade there is only one black smoker actively discharging high temperature 320 c fluid but there are many fossil sulfide chimneys and mounds in the area the mineralogy and high au and cu in these precipitates suggest highly metalliferous hydrothermal activity in the past these activities likely resulted in discharge of hydrothermal plumes and fall outs of sulfides and sulfates on the seafloor these fall outs were incorporated in sediments far from the vent areas they are now recorded as high metal contents in sediments with no petrographic and mineralogical evidence of in situ hydrothermal activity some are high as 8 100 ppm for cu 12 500 ppm for zn 1 000 ppm for as 100 ppm for ag and 21 000 ppm for pb detrital grains of montmorillonite in such sediments are coated with fe oxyhydroxides during the suspension in seawater before settling on the seafloor the depths of such metal anomalies in sediments suggest high levels of metalliferous hydrothermal activities from 1 800 to 300 ybp

a date for volcanic eruption inferred from a siltstone xenolith we present a tl age determination of a heated siltstone xenolith found at kueishantao a volcanic island 10 km o the northeastern shoreline of taiwan before this study no reliable numeric age determination had been obtained for the volcanic rocks its age has long been desired due to its active tectonic environment previous studies of the other radiometric dating methods indicate a very young age for the eruption of this volcano possibly later than 10 ka however reliable age is not allowed because it is younger than the lower dating limit our result shows a tl age of 7 0 7 ka for the lower part of the volcanic sequence indicating that other volcanic eruptions occurred later than 7 ka this nding suggests that the volcanic island kueishantao has not ceased its igneous activity and is still active geologically 2000 elsevier science ltd all rights reserved

eco geochemical dynamics of a shallow water hydrothermal vent system at milos island aegean sea eastern mediterranean shallow water hydrothermal vents are extreme environments that share many characteristics with their deep sea analogs however despite ease of access much less is known about the geochemical dynamics of these ecosystems here we report on the spatial and temporal geochemical dynamics of a shallow water vent system at paleochori bay milos island greece our multi analyte voltammetric profiles of dissolved o2 and hydrothermal tracers e g fe2 fesaq mn2 on sediment cores taken along a transection in hydrothermally affected sediments indicate three different areas the central vent area highest temperature with a deeper penetration of oxygen into the sediment and a lack of dissolved fe2 and mn2 a middle area 0 5 m away rich in dissolved fe2 and mn2 exceeding 2 mm and high free sulfide with potential for microbial sulfide oxidation as suggested by the presence of white mats at the sediment surface and finally an outer rim area 1 1 5 m away with lower concentrations of fe2 and mn2 and higher signals of fesaq indicating an aged hydrothermal fluid contribution in addition high frequency temperature series and continuous in situ h2s measurements with voltammetric sensors over a 6 day time period at a distance 0 5 m away from the vent center showed substantial variability in temperature 31 6 to 46 4 c and total sulfide 488 to 1329 m in the upper sediment layer the analysis of these data suggests that tidal and wind forcing and abrupt geodynamic events generate intermittent mixing conditions lasting for several hours to days despite substantial variability the concentration of sulfide available for chemoautotrophic microbes remained high however the availability of electron acceptors originating from seawater might be more intermittent which in turn has an effect on the reestablishment of the white mats after wave induced disturbances our results emphasize the importance of transient events in the development of chemoautotrophic communities in the hydrothermally influenced sediments of paleochori bay

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

ne sw trending hepu hetai dextral shear zone in southern china penetration of the yunkai promontory of south china into indochina abstract the ne sw trending hepu hetai shear zone extends for about 480 km along the boundary between guangdong and guangxi provinces in the southern part of south china field mapping and kinematic analyses indicate that the zone is characterized by dextral ductile strike slip deformation with an estimated displacement along the fault zone in excess of 500 km studies of synkinematic phengite and gas liquid inclusions in quartz within mylonite suggest that the ductile shear deformation occurred under medium temperature pressure conditions of the greenschist facies and 40ar 39ar analyses of muscovite yield ages of 213 195 ma based on these data and late paleozoic mesozoic paleogeographic data for southern china we propose that the hepu hetai shear zone originated via the penetration of the yunkai promontory of south china into indochina during the triassic

biogeochemistry and dynamics of particulate organic matter in a shallow water hydrothermal field kueishantao islet ne taiwan abstract the particulate organic matter pom of shallow water hydrothermal fields has been studied in the context of food web reconstruction but the processes governing its biogeochemistry and dynamics are poorly explored here we investigate the pom in the kueishantao hydrothermal field using chemical and hydrodynamic approaches the depletion of total suspended matter lower c n ratios and higher carbon isotopic values of particulate organic carbon 13cpoc in the vertical plumes relative to values derived from si based models were attributed to the hydraulic sorting of the vented particles which tend to have more n and 13c in the fine fraction the particulate organic carbon poc unlike the total suspended matter was enriched in the vertical plumes and explained by physicochemical processes rather than biological addition the poc enriched plume top water was found to be a better endmember than the vent fluids to explain particle mixing in the lateral plume physical mixing played a steering role in shaping the particle chemistry of the lateral plumes but markedly 13c enriched poc was still observable in several near vent low to intermediate si plume waters implying locally enhanced primary production of at least 0 1 0 4 mg c m3 h the presence of eddies confirmed by flow field measurements should have contributed to the detection of biogeochemical anomalies via extending the retention time of plume water to 1 2 h the dominating mixing process resulted in decoupling between the 13cpoc signatures and carbonate chemistry in this shallow water hydrothermal plume

sedimentary hosted polymetallic massive sulfide deposits of the kebrit and shaban deeps red sea massive sulfides recovered from the kebrit deep carbonaceous sedimentary succession represent black smoker fragments novel to any red sea brine pool deposit chimneys which were also observed in situ near the seawater brine interface of the kebrit deep pool are primarily comprised of fe zn and pb bearing phases and are often tar and asphalt impregnated cu sulfides are virtually absent from parageneses contrasting rift related smoker and red sea metalliferous sediment deposits concentration of nickel in discrete bravoite points to a basalt seawater leaching process as a source for most metals the sedimentary package which probably hosts cu mineralization in lower stockworks of the smoker deposit is considered the major source of lead prevention of boiling of hydrothermal fluids passing through a succession of organic rich carbonate and clay horizons prior to discharge is essential for smoker formation shaban deep sedimentary hosted massive sulfides are less frequent with pyrite being the dominant ore mineral sulfur isotope data indicate both high temperature inorganic as well as biogenic sulfate seawater and or evaporite reduction in sulfide forming processes cogenetic sulfates formed from residual bacteriogenically reduced seawater sulfate rather low sulfide sulfate precipitation temperatures of 110 130 c for the kebrit brine pool and 100 c for shaban deep massive sulfides are evident

observed changes in baroclinic wave activity during the life cycles of low frequency circulation anomalies abstract anomalous baroclinic wave activity during the onset and decay of blocking patterns in the northern hemisphere winter is investigated based upon a 30 year record of 500 mb height and sea level pressure a slowly varying envelope function is defined at each gridpoint in order to represent the modulation of the amplitude of baroclinic wave activity by the low frequency circulation anomalies related to blocking the envelope function fields and the low frequency circulation fields are composited relative to the onset and decay times of four persistent dipole patterns in low frequency circulation anomalies located downstream of the climatological mean stormtracks one polarity of the anomaly patterns corresponds to dipole or modon like blocking patterns over the eastern oceans and the other to strong zonal flow patterns each of the eight composites is comprised of more than 50 persistent blocking or zonal flow episodes the most striking common feature observed during the onset of blocking over th

indosinian high strain deformation for the yunkaidashan tectonic belt south china kinematics and 40ar 39ar geochronological constraints 1 structural and 40ar 39ar data from the yunkaidashan belt document kinematic and tectonothermal characteristics of early mesozoic indosinian orogenesis in the southern part of the south china block the yunkaidashan belt is tectonically divided from east to west into the wuchuang sihui shear zone xinyi gaozhou block and the fengshan qinxi shear zone indosinian structural elements ascribed to the indosinian orogeny include d2 and d3 deformation the early d2 phase is characterized by folding and thrusting with associated foliation and lineation development related to nw se transpression under amphibolite to greenschist facies conditions this event is heterogeneously overprinted by d3 deformation characterized by a gentle dipping s3 foliation subhorizontally to shallowly plunging l3 lineation some reactived d2 folds and low angle normal faults the d3 fabrics suggest a sinistral transtensional regime under greenschist facies metamorphism the timing of the d2 and d3 events have been constrained to the early to middle triassic 248 220 ma and late triassic 220 200 ma respectively on the basis of 40ar 39ar geochronology and regional geological relations the change from oblique thrusting d2 to sinistral transtension d3 may reflect oblique convergence and crustal thickening followed by relaxation of the overthickened crust in combination with the regional relations from xuefengshan to yunkaidashan and on to wuyishan the early phase of the indosinian orogeny constituted a large scale positive flower structure and is related to the intracontinental convergence during the assembly of pangea in which the less competent south china orogen was squeezed between the more competent north china and indosinian blocks

constraints on water depth of massive sulfide formation evidence from modern seafloor hydrothermal systems in arc related settings the results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment the shallowest hydrothermal systems in subduction related settings are hosted by arc volcanoes these shallow vent sites have a number of features in common with subaerial epithermal systems massive sulfide occurrences in arc related rifts the most likely setting for many ancient analogs are generally restricted to water depths from 700 to 2 000 m with rifts developing within old arc crust at the deeper end of this range back arc spreading centers proximal to arcs host massive sulfide deposits at depths of 1 500 to 2 000 m the deepest hydrothermal systems occur along mature back arc spreading centers distal to volcanic arcs where water depths range from 2 000 to 3 700 m these deeper vent sites probably represent the best modern analogues of ophiolite hosted massive sulfide deposits boiling of the hydrothermal fluids is common at volcanic arcs and in arc related rifts in these environments elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss by contrast the high ambient pressures in deep marine hydrothermal systems along mature back arc spreading centers prevent fluids from boiling during their ascent to the seafloor boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and therefore influences the metal content of seafloor sulfide deposits copper rich massive sulfides typically occur at water depths exceeding 1 000 m whereas zn and pb rich occurrences may form at any water depth boiling can be an important control on ag and au grades but is not the only factor controlling precious metal enrichment in massive sulfides shallow marine hot spring deposits can be highly enriched in trace metals such as as hg and sb submarine volcanic arc and back arc settings are geologically complex and significant variations in water depth can occur over short distances paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth the relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic hosted massive sulfide deposits

aulacogen formation in response to opening the ailaoshan ocean origin of the qin fang trough south china abstractthe qin fang trough south china trends northeast southwest orthogonal to the adjoining southern margin of the craton the devonian strata within the trough are unconformable on late neoproterozoic units of the yunkai massif indicating that strata within the trough are autochthonous u pb ages and hf isotope compositions of detrital zircons from the silurian to devonian succession are consistent with derivation from the massif in comparisons of our data with those from equivalent units in the ailaoshan belt and hainan island detrital zircons from the silurian strata show similar age distributions and hf isotope compositions indicating that the three areas shared a common source and were adjacent to each other during the silurian in contrast the age distributions of detrital zircons preserved in devonian strata in the qin fang area are different from those of equivalent units in the ailaoshan belt this along with the absence of devonian strata on hainan island suggests that the qin fang

tracing submarine hydrothermal inputs into a coastal bay in baja california using radon abstract hydrothermal fluid fluxes into deep ocean environments can be obtained from heat balance approaches however in shallow systems hydrothermal heat fluxes can be masked by solar heating in this paper we use radon 222rn as a naturally occurring geochemical tracer to map the location of hydrothermal fluid inputs as well as low temperature groundwater discharges and quantify fluxes into concepcion bay baja california mexico this fault bound bay contains intertidal seeps with salinities ranging from 5 3 to 25 6 temperatures reaching 64 c and nitrate reaching 900 m the bay is subject to natural eutrophication and frequent red tide events a detailed 222rn survey around the 100 km perimeter of concepcion bay allowed us to map the location of enhanced submarine groundwater inputs moorings at three contrasting coastal sites indicated that radon concentrations were higher at low tide and during the winter modeled hydrothermal fluid inputs ranged between 0 4 cm day in the middle of the bay and 43 9 cm day at the largest hydrothermal coastal seep site apparently faults allow meteoric water to be heated and serve as conduits for its subsequent discharge through permeable marine sediments when conservatively extrapolated to the entire bay using weighted distributions these fluxes are estimated at 17 5 m3 s a flow much higher than local ephemeral rivers about 42 of the fluxes described consisted of fresh groundwater with the remaining made up of recirculated seawater new nitrogen inputs associated with groundwater pathways are estimated to directly account for at least 15 of the local primary productivity our combined spatial survey time series strategy can be very useful to quantify hydrothermal fluid inputs in particular at vent sites where a temperature signal in shallow surface waters is difficult to be observed

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

detrital provenance of early mesozoic basins in the jiangnan domain south china paleogeographic and geodynamic implications abstract detrital provenance analysis is an effective way to understand paleogeographic change and geodynamics in this paper we present petrological whole rock geochemical and detrital zircon u pb geochronological analysis of early and middle jurassic terrestrial clastic rocks in the jingdezhen basin and the huangshan basin in the jiangnan domain south china petrology and whole rock geochemistry show that the source rocks are dominated by intermediate to acid component the chemical index of alteration ranges from 69 to 86 suggesting a moderate weathering history for the source rocks the early middle jurassic sediments in the jingdezhen and huangshan basins were mostly sourced from magmatogenic greywackes and felsic magmatic rocks respectively detrital zircons have seven age peaks at 240 ma 430 ma 1390 ma 1880 ma 2500 ma 3200 ma and 788 999 ma a wide peak provenance analysis indicates that the source rocks are in the jiangnan domain the northwest zhejiang basin and the wuyishan domain combining these with previous results and paleocurrent directions we infer that the ne trending wuyishan and xuefengshan domains and the nearly e w jiangnan domain and nanling tectonic belt were orogenic uplifts and watersheds during the late triassic to middle jurassic the early mesozoic geodynamics in the south china block was related to the westward subduction of the paleo pacific plate and the northward continent continent collision following the closure of the paleo tethys ocean

new insights into phanerozoic tectonics of south china early paleozoic sinistral and triassic dextral transpression in the east wuyishan and chencai domains ne cathaysia the northeast cathaysia area is characterized by an archetypical transpressional system with widespread strike slip shear zones whose geometries kinematics and ages are critical for deciphering the phanerozoic tectonic evolution of south china we present new structural geochronological and thermochronological data from the shear zones in the east wuyishan and chencai domains which record two phases of deformation the first phase corresponds to sinistral oblique shearing along arrays of nne oriented steep dipping zones under amphibolite facies conditions the sinistral oblique shearing commenced at 451 ma concurrently with regional nw se directed thrust shearing and folding the coexistence of sinistral and thrust structures indicates nw se transpressive shortening deformation dating by 40ar 39ar shows that such deformation terminated before 400 ma and was followed by cooling through 450 350 c at 400 370 ma our results merged with published data aid in tracing an early paleozoic orogen that extends through the jiangnan domain into the northeast cathaysia with the southeast yangtze acting as a foreland belt the synorogenic shortening was interpreted as resulting from underthrusting of the cathaysia beneath the east yangtze the second phase involved dextral oblique shearing associated with nne ssw transpression under greenschist to amphibolite facies conditions at 245 228 ma which was followed by postkinematic magmatism and cooling at 221 200 ma in the cathaysia similar middle triassic dextral shear zones were widespread and operated with approximately east striking thrusts as mutually complementary structures their kinematic coupling can be explained by a contractional termination model geodynamically we attributed middle triassic dextral transpression to the collisions of south china with north china and indochina

detrital zircon u pb ages and hf isotopes of lower middle devonian to middle jurassic sandstones in the qinfang basin southern south china block constraints on provenance and tectonic setting abstract the affinity and tectonic setting of the qinfang basin have long been an enigma here we conduct detrital zircon u pb geochronology and hf isotope analysis of lower middle devonian to middle jurassic samples from the basin along with published age data and paleontology from the basin and its east and west sides this study constrains the sediment provenance and tectonic setting of the basin sandstones of devonian jurassic exhibit an age distribution with major age groups at 2700 2300 ma absence for jurassic 1200 800 ma 600 400 ma and 334 246 ma for jurassic alone zircons peak 2500 ma were sourced from the yangtze block while 1200 800 ma grains may originate from the yunkai massif and jiangnan orogen 600 400 ma zircons came from yunkai massif and or cambrian to silurian sediments in the basin carboniferous early triassic 334 246 ma zircons were probably supplied by an older sequence in the great youjiang basin and the darongshan shiwandashan igneous rocks the qinfang basin and its two sides are considered to share a common east gondwana source in silurian the similarity in age spectra between silurian devonian samples in the basin and ailaoshan belt suggests that the basin is a remnant of the paleo tethyan ailaoshan ocean however the distinct age distribution between the basin and indochina block shows that the basin is not a part of the indochina block by middle jurassic following the final closure of the ailaoshan ocean in the late triassic the adjacent western area may be still tectonically active thereby feeding the basin with detritus of early permian

death in guizhou late triassic drowning of the yangtze carbonate platform abstract the yangtze platform in south china formed a stable palaeogeographic element from the late proterozoic to the end of the middle triassic with deposition of shallow water carbonates during much of this time a portion of the yangtze platform in south central guizhou drowned at the transition from permian to triassic as the south adjacent nanpanjiang basin encroached about 100 km northward but a new stable platform margin was established that persisted through the early and middle triassic this long history as a stable carbonate platform ended at the transition from the ladinian to the carnian the latest ladinian rocks the yangliujing formation are 490 m of shoaling upward carbonate cycles of grapestone and bioclastic grainstone fenestral limestone and stromatolitic dolomudstone commonly overprinted by extensive subaerial diagenesis the beginning of the carnian is marked by a rapid transition to medium dark grey nodular lime mudstones containing ammonoids conodonts and thin shelled bivalves the zhuganpo formation the upper part of this thin pelagic limestone contains many muddy intraclasts some slightly bored and encrusted indicating incipient cementation the overlying wayao formation is a condensed black shale with thin interbeds of dark grey manganiferous lime mudstone near the base ammonoids conodonts thin shelled bivalves and articulated crinoid stems are abundant fine grained greywacke with sole marks forms prominent bundles within grey calcareous shale in the overlying laishike formation ammonoids and thin shelled bivalves occur sporadically in this 810 m thick unit calcareous shale with thicker shelled bivalves and packages of cleaner coarser grained sandstone characterize the banan formation 460 m thick the sandstone units generally coarsen and thicken upward with ripples medium scale trough cross beds and rare u tube burrows quartzose coal bearing siliciclastics 690 m thick form the overlying huobachong formation thick bedded cross stratified sandstone and conglomerates are amalgamated into thinning and fining upward intervals separated by blocky mudstones this fining upward motif continues into the overlying erqiao formation but coals are lacking at the beginning of the late triassic carnian the previously stable yangtze platform on which peritidal limestones were forming was drowned and covered by dark lime mud that was cemented into intraclasts and nodular lime mudstone black shale and manganiferous pelagic limestone formed a condensed interval recording maximum submergence turbidite sandstone and shale of the laishike flysch filled the accommodation space of 800 m created during drowning of the yangtze platform leading to deposition of shoaling upward shelf and paralic sandstones and shales but without significant carbonate production the succeeding fining upward siliciclastics are interpreted as braided stream deposits with coals that mark minor marine incursions the shallow shelf and braided stream deposits form a molasse 1500 m thick it was apparently derived from the west in contrast to the underlying flysch where palaeocurrent directions are from the north or northeast the entire yangtze platform became emergent during the late triassic and was never submerged again subtle local differences in the drowning sequences indicate differential subsidence and suggest that tectonics played a role in the death of the yangtze platform

thermal evolution of the hengshan extensional dome in central south china and its tectonic implications new insights into low angle detachment formation abstract the hengshan massif is an exhumed mid crustal plutonic metamorphic dome formed during cretaceous crustal extension in the jiangnan orogenic belt central south china multiple thermochronometers mica 40ar 39ar apatite fission track and zircon u th he are applied to its footwall along a slip parallel transect to quantify its thermal history and cooling rate and the slip magnitude rate initial geometry and kinematic evolution of the low angle hengshan detachment fault our thermochronological data in conjunction with previous ages indicate that 1 footwall rocks cooled from 700 c to 60 c in less than 60 myr 136 80 ma at variable rates ranging from 50 c myr to 13 c myr 2 the hengshan detachment fault accommodated 8 12 km of total slip at variable slip rates from 0 14 to 1 mm yr during tectonic exhumation 3 the footwall has been tilted 26 50 to the east since slip began indicating that the low angle hengshan detachment fault initiated at a steep dip and was passively rotated to a more gentle orientation during subsequent normal slip this study provides compelling evidence supporting that the low angle detachment fault in the extensional dome can be generated by the reactivation and passive rotation of an initially steep reverse fault during normal slip in addition our thermochronological data constrain the time of extension in the hengshan dome between 136 and 80 ma which implies that the back arc extension within south china associated with the rollback of the paleo pacific slab might have lasted until at least 80 ma

excess dissolved ca in the deep ocean a hydrothermal hypothesis abstract variations in seawater alkalinity and dissolved calcium provide information essential to establishing the integrated deep ocean calcium carbonate dissolution flux high precision ca measurements reported here confirm earlier suggestions that the deep ocean contains higher levels of dissolved ca than expected from calcium carbonate dissolution only i propose that the mid depth ca excess is a manifestation of the circulation of seawater through hydrothermal systems at mid ocean ridges qualitative agreement with 3 he distributions and evidence for deep water mg depletions support this hypothesis the magnitude of the mid depth ca excess implies a total hydrothermal flux larger than expected from the corresponding excess in 3 he and points to the relative importance of low temperature diffuse fluxes versus high temperature discrete fluxes for elements such as ca the implied total hydrothermal flux for ca is consistent with its oceanic mass balance requirements and resolves several long standing problems associated with our understanding of the chemical evolution of the ocean and in particular its low alkaline content

geochronological and mineralogical constraints on mineralization of the hetai goldfield in guangdong province south china abstract the hetai goldfield located in the southern segment of the qinzhou bay hangzhou bay juncture orogenic belt qhjb is the largest concentration of gold deposits in guangdong province south china the gold mineralization is hosted within the late neoproterozoic to early paleozoic yunkai group and strictly confined to mylonite ductile shear zones the nature of the structural control of mineralization in particular the role of ductile versus brittle deformation and their ages which remain unclear despite numerous previous studies are examined in this paper through an integrated study of geochronology and mineralogy lamellar and filament structures shown by pyrite and pyrrhotite in the ores suggest that sulfidation took place during ductile deformation and syntectonic metamorphism but the majority of the ores are associated with brittle deformation features in combination with macroscopic and microscopy observations on shear fabrics la icp ms u pb dating on zircons of hydrothermal origin from mylonites suggests that the hetai goldfield was subjected to two shearing events an early sinistral ductile shearing at ca 240 ma and a late dextral ductile brittle shearing at ca 204 ma indosinian these ages are ca 90 30 ma older than the previously published gold mineralizing ages of ca 175 152 ma yanshanian suggesting that the main gold mineralization and related brittle deformation significantly postdate the ductile deformation this inference is supported by the mineralization temperatures estimated from geothermometers of arsenopyrite ca 350 290 c chlorite ca 260 230 c and sphalerite ca 230 170 c intergrown with native gold which are considerably lower than that for the ductile deformation 500 300 c or higher based on these data we propose that the gold mineralization in the hetai goldfield predominantly occurred during the yanshanian event and only minor gold mineralization and associated sulfidation took place during the earlier indosinian ductile deformation

evidence of tectonic control on active arc volcanism the panarea stromboli tectonic link inferred by submarine hydrothermal vents monitoring aeolian arc italy 1 the combination of the latest geophysical instruments and geochemical methods applied to the arc volcanism aeolian islands italy has given new insights on the role of active tectonics on fluids migration a continuous monitoring of the hydrothermal system off the island of panarea has shown contemporaneous modifications of the vented fluids and the seismic activity of the nearby stromboli volcano the almost contemporary start of the last volcanic crisis at panarea and stromboli in 2002 besides the contemporary variation of the 3 he 4 he ratios at both the islands and the large number of submarine crater shaped structures at panarea bears testimony to interconnections between the volcanic edifices to confirm a tectonic drive of magmatic fluids over volcanic arcs implies that episodes of volcanic unrest can be triggered by the tectonic activity increasing the volcanic risk for the whole area and this might be the case of the stromboli panarea volcanic complex

geochemistry of hydrothermal fluids from an intraplate ocean island everman volcano socorro island mexico abstract socorro island mexico still volcanically active is an alkaline and peralkaline volcanic island in the eastern pacific ocean located on a mid ocean ridge spreading center that was abandoned at 3 5 ma gas and water samples collected on the island in 1999 from the dome fumaroles and hot springs of everman volcano have been analyzed for major components h o c s he and ar isotopic composition and noble gas abundances the boiling point temperature steam vents and low salinity thermal springs discharge cl free meteoric water and are typical surface manifestations of a high temperature hydrothermal system high h 2 and ch 4 contents up to 14 and 3 5 vol in dry gas respectively and an enrichment of ch 4 in 13 c 13 c ch 4 18 may suggest that these reduced gases were at least partially produced by the interaction of ultramafic rocks with water inside volcanic edifice due to serpentinization of olivine the 3 he 4 he ratios 6 0 6 6 r a which are lower than the morb values and the high he ne ratios 4000 and he ar ratios up to 4 indicate a contribution of radiogenic he from the oceanic crust or shallow magma chamber like at a low 3 he hot spot the maximum of the 40 ar 36 ar values 311 is close to the maximum value found in the socorro volcanic rocks noble gas abundances are close to values for the partially degassed air saturated water however with some excess ne concentrations an enrichment in 132 xe or depletion in 84 kr of the least air contaminated gas sample he ne 4000 relative to air saturated water can be related to the contribution of noble gases from a non atmospheric source probably oceanic crustal component assimilated in a shallow magma reservoir

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

enargite luzonite hydrothermal vents in manus back arc basin submarine analogues of high sulfidation epithermal mineralization abstract active and inactive hydrothermal chimneys composed almost entirely of enargite and luzonite rare minerals in seafloor hydrothermal deposits were found at the summits of two submarine volcanoes north su and kaia natai in the manus back arc basin detailed mineralogical and geochemical studies revealed that most probably these deposits precipitated at t 200 330 c and high fs2 the negative 34s values 8 58 to 3 70 of the enargite luzonite are best explained by disproportionation reactions of magmatic so2 and suggest that the high fs2 is likely provided by direct magmatic input of so2 into the hydrothermal system fractionation of cu stable isotopes during the precipitation of enargite luzonite 65cu ranges from 0 20 to 0 35 is inferred to be associated with either rayleigh type fractionation or redox processes cu oxidation to cu2 and the mass balance of dissolved cu and cu2 species in the hydrothermal fluid the trace element composition of enargite and luzonite indicates a temporal fluctuation of the chemistry of the ore forming fluid with an increase of fe ga tl au hg pb and ag and decrease of sb sn te ge and v concentrations with time and points out that this type of deposits is the richest in au average 11 9 ppm and te average 169 ppm among all other types of seafloor metal deposits in addition to the widespread inorganic precipitation of enargite and luzonite in this setting there is evidence that this mineralization may be biogenically mediated on the external surfaces of the active vents fungi like filaments mineralized by luzonite imply that the fungi dikarya subkingdom may be implicated in a mechanism of bio sequestration of as s and cu and provide the initial substrate for luzonite precipitation the studied enargite luzonite deposits have characteristics similar to those of subaerial high sulfidation epithermal mineralization back arc basin setting acid sulfate and boiling ore forming fluids altered advanced argillic stage dacitic host rocks major enargite luzonite and minor pyrite barite and s0 34s au mineralization at depth

geochemistry of limestones deposited in various plate tectonic settings abstract limestone a major part of the global sedimentary succession susceptible to post depositional diagenesis studies of limestone geochemistry are essential in the discrimination of tectonic settings of basins in which the limestones were deposited six late mesozoic and one tertiary limestone successions of tibet western china that were deposited in oceanic plateau passive continental margin active continental margin fore arc basin back arc basin and foreland basin and continental inland freshwater basins were analyzed for their major trace and rare earth element ree composition this geochemical dataset in combination with the deep sea drilling project and ocean drilling program dsdp and odp literature geochemical data regarding limestones deposited in open ocean environments permitted delineation of the geochemical characteristics of limestones accumulated in these various plate tectonic settings major elements e g fe2o3 and mno except for cao of these limestone successions show large variations but are positively correlated with al2o3 the ree and trace element abundances for the inland and margin limestones show a distinct positive correlation with al2o3 whereas rees and trace elements of the open ocean limestones are positively correlated with mno there is a systematic increase in the magnitude of ce anomalies of open ocean floor limestones away from spreading ridges to open ocean highs to passive margins and to active margins and inland freshwater basins open ocean limestones display a narrow range of la sm n 0 46 0 96 sm yb n 0 25 1 96 and la yb n 0 23 1 38 but high la ce n 1 5 whereas the inland margins limestones display a much larger range la sm n 0 43 2 18 sm yb n 0 6 2 98 and la yb n 0 7 2 25 but low la ce n

permo triassic structural evolution of the shiwandashan and youjiang structural belts south china abstract we conducted field mapping coupled with radiometric dating across the shiwandashan and youjiang structural belts swsb and yjsb to investigate how southwest south china evolved and to better understand its links to plate boundary dynamics during the late permian to middle triassic our results reveal an episodic tectono magmatic evolutionary history of the swsb and yjsb the swsb underwent significant nw se shortening punctuated by 250 240 ma s type pluton emplacement during the late permian to middle triassic the shortening was expressed by thin skinned nw verging thrusts and folds and conjugate sets of n trending sinistral and e trending dextral faults the nw se shortening overlapped with and was succeeded by triassic ne sw shortening in the yjsb the ne sw shortening was expressed by ne verging thrusts and folds which documented a northeastward propagation of foreland deformation the ne verging folds overprinted older nw verging folds forming superimposed folds at the juncture of the yjsb and swsb in the long an area our results combined with regional considerations support a model of the nw se shortening as an andean type orogeny that developed in response to westward subduction of the paleo pacific plate and the ne sw shortening as a product of the indochina south china collision the subduction of the paleo pacific plate assisted in westward motion of the south china oceanic lithosphere which may have facilitated the closure of the paleo tethys ocean and subsequent collisions of south china with north china and indochina

impact of differential tectonic subsidence on isolated carbonate platform evolution triassic of the nanpanjiang basin south china the nanpanjiang basin of south china contains four exceptionally well exposed isolated triassic carbonate platforms detailed mapping of two dimensional transects and description of stratigraphic sections allow the reconstruction of facies architecture sequence stratigraphy and evolution of the platforms biostratigraphy magnetic susceptibility profiles and volcanic ash horizons allow chronostratigraphic correlation and thus a basinwide evaluation of mechanisms controlling platform evolution a comparison of platform architecture demonstrates that southerly platforms have substantially greater thickness backstepping geometry pinnacle development and earlier drowning that resulted from greater tectonic subsidence proximal to a probable convergent margin along the southern perimeter of the basin felsic volcanics thicken southward and contributed to the termination of the southernmost platform indicating the development of a volcanic arc along the southern margin of the south china tectonic block the northernmost isolated platform had greater longevity and lesser accumulation and lacks backstepping and pinnacle phases of development basin margin intertonguing relationships or lack thereof demonstrate that earlier siliciclastic influx into the basin to the south and concurrent starved basin conditions to the north impacted the evolution of platform margin geometries comparative analysis of platform evolution shows that the timing and rates of tectonic subsidence controlled the timing of platform termination by drowning backstep geometries pinnacle development and overall platform thickness the timing of siliciclastic basin fill dictated differences in platform margin geometries such as slope angle relief above basin floor and the presence or absence of basinward platform progradation despite the dramatic differences in platform architecture eustatic sea level fluctuations imparted a basinwide sequence stratigraphic signal

cretaceous tectonic evolution of south china a preliminary synthesis abstract the cretaceous tectonic evolution of south china is characterized by widespread extensional basin and dome generation voluminous magma intrusion eruption and associated polymetallic mineralization all of which are of world wide interests that have stimulated the attention of geologists for more than half a century due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of south china many controversies regarding the nature and origin of these features remain this paper attempts to make a review by synthesizing existing structural petrological geochronological and geochemical data of the cretaceous structures and magmas which guides us to propose a three stage tectono thermal evolutionary history of south china during the cretaceous period the earliest cretaceous 145 137 ma tectonic stage was characterized by syn orogenic shortening deformation and metamorphism under a nw se compressional setting which generated voluminous porphyry cu au ore bearing adakitic rocks in the lower yangtze river belt and gneissic granites in the coastal area its geodynamic origin was interpreted as combined effects of the pacific izanagi ridge subduction beneath the lower yangtze river belt and the pacific subduction beneath the cathaysia block this syn orogenic shortening stage was followed by a post orogenic stage 136 86 ma comprising two episodes of alternate extensional and shortening events the extension 136 118 ma in the earlier episode was dominated by a nw se extensional regime it led to significant taphrogenesis manifested by large scale extensional basins and voluminous magma intrusion eruption this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted pacific slab the subsequent nw se transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins this transpression lasted from 117 ma to 108 ma and its driving mechanism was attributed to the collision between the eastern asian margin and the west philippine block the extension 107 86 ma in the later episode was dominated by a wnw ese extensional regime which led to a second phase of basin subsidence and produced numerous a and i type granites and bimodal volcanoes the tectonic regime then changed at ca 85 ma to wnw ese oriented transpression causing inversion of the late cretaceous rift basins and cessation of extension related magmatism the change of stress field from wnw ese extension to wnw ese transpression was related to the variations of the subducted slab dynamics i e the transition from either the ese ward retreat to wnw ward subduction of the pacific slab or the alternate stress during slab break off during the latest cretaceous a drastic change of regional tectonic stress orientation from wnw ese to n s occurred in south china the third stage predominated by n s extension was developed which caused a new phase of regional crustal subsidence along the youngest e w trending extensional structures

gas discharges from the kueishantao hydrothermal vents offshore northeast taiwan implications for drastic variations of magmatic hydrothermal activities abstract the chemical compositions of gas discharges from the kueishantao kst hydrothermal field changed dramatically from 2000 to 2014 in this study we established a gas mixing model for the kst gases the n2 ar and co2 contents were mixed from a magmatic endmember with co2 of about 990 mmol mol a hydrothermal and an atmospheric endmember enriched in n2 and ar more than 71 kst gas components were mantle derived magmatic the calculated endmember n2 ar ratio and ar contents of the hydrothermal endmember percolated fluid are about 140 and 5 28 5 52 mmol mol respectively this relatively elevated n2 ar ratio was probably caused by the thermogenic addition of n2 the log ch4 co2 values of the kst gas samples correlate well with the mixing temperature that estimated from the mixing ratio between the percolated fluid and the magmatic endmember it is indicated that the kst ch4 and co2 may have attained chemical equilibrium the temporal variations of the kst gas compositions are determined by the mixing ratio which is dependent on the magmatic activity underneath the kst field with the decreasing of magmatic activity since 2005 the proportion of the hydrothermal endmember increased along with the increasing of n2 ar and ch4 contents this study proposed an effective model to quantitatively assess the sources of gas components discharged from submarine hydrothermal vents in addition it is suggested that the mixing between a magmatic and a hydrothermal endmember may play an important role in the concentrations of co2 and ch4 in hydrothermal gas discharges

linking paleogene rifting and inversion in the northern song hong and beibuwan basins vietnam with left lateral motion on the ailao shan red river shear zone

reprint of p wave velocities and anisotropy of typical rocks from the yunkai mts guangdong and guangxi china and constraints on the composition of the crust beneath the south china sea abstract in order to provide constraints on the interpretation of seismic data of the crust beneath the south china sea scs and its continental margins we have measured p wave velocities and anisotropy as a function of hydrostatic confining pressure up to 650 mpa for 31 representative samples i e granite diorite felsic gneiss mylonite and ultramylonite amphibolite schist and marble from the yunkai mts guangdong and guangxi provinces china that represent the crystalline basement beneath the continental margins of the scs the intrinsic velocity of each crack free rock increases with increasing density which is linearly dependent on the chemical composition increases with increasing mgo cao feo fe 2 o 3 and al 2 o 3 contents but decreases with increasing contents of sio 2 and na 2 o k 2 o most of the rocks have small m f of 41 43 and the ratio shows a general increase from the continental margin to the central basin the high velocity 7 0 7 6 km s materials in the lower crust could be either the former lower crustal mafic rocks that were present before rifting which have experienced less extensional thinning than the felsic upper crust or the materials crystallized from mafic magma which underplated the lower crust from the partially molten upper mantle during rifting

evaluation of results from the fourth and fifth iavcei field workshops on volcanic gases vulcano island italy and java indonesia abstract the major purpose of field workshops on volcanic gases organized by the iavcei commission on the chemistry of volcanic gases is the collection and analysis of volcanic gas discharges with the aim to develop and improve techniques for the geochemical surveillance of active volcanoes the fourth and fifth workshops were held at vulcano island italy in 1991 and on java island indonesia in 1994 respectively gas samples were collected from four gas vents by nine groups at vulcano and from eight gas vents by eight groups on java the quality e g scatter of the data of most of the results reported from these two workshops is sufficient to permit a broad chemical classification of the discharge and meaningful thermodynamic interpretation in most cases the majority of the data for individual gas vents cluster closely around the median values suggesting that the median values are the best estimates of chemical composition there is however also a considerable scatter of the analytical data and this scatter warns us to not rely too heavily on a single analytical value in particular on a value for ch4 and co because analytical data for these species often show a wide scatter this warning is particularly relevant for chemical monitoring of volcanic activity further improvement of the sampling and analytical techniques as well as more detailed comparison of the techniques is required to reduce such uncertainty in order to interpret the volcanic activity and hydrothermal conditions

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

changhsingian late permian conodonts from son la northwest vietnam and their stratigraphic and tectonic implications abstract late permian conodonts are for the first time reported from vietnam pa sa sb sc and m elements of the changhsingian conodont species hindeodus julfensis sweet are reported from a 40 cm thick limestone in the middle part of the yenduyet formation near son la nw vietnam the occurrence of h julfensis indicates a changhsingian age that is consistent with an interpreted early changhsingian age for a brachiopod fauna slightly higher in the sampled section the son la section is located in the song da rift zone and overlies basaltic volcanics considered equivalent to the emeishan large igneous province basalts that are plume related the permian triassic boundary in vietnam is yet to be precisely located biostratigraphically but proxy chemostratigraphic data indicate its likely position in sections at nhi tao and lung cam n vietnam and correlation with the global stratotype section and point at meishan south china the recovered conodonts have a conodont colour alteration index of 5 and have been heated to c 600 c but they do not show any evidence of textural alteration due to regional metamorphism such as micro folding or stretching that would indicate any direct effects of the compressional indosinian orogeny