multiple subduction processes of the proto tethyan ocean implication from cambrian intrusions along the north qilian suture zone abstract cambrian mafic to felsic intrusive rocks intruding precambrian rocks are recognized along the southern margin of the north qilian suture zone these intrusive rocks predate final closure of the north qilian ocean and consideration of these rocks is essential to any reconstruction of the tectonic framework of the qilian orogen they include 517 ma transitional i s type granite 510 ma i type calc alkaline diorite 509 505 ma calc alkaline gabbro and 498 ma shoshonitic monzonite as well as highly fractionated syenogranite distinctive geochemical signatures and sr nd hf isotopic compositions indicate derivation from multiple magma sources associated with subduction moreover tectonostratigraphic correlation indicates that the precambrian rocks along the southern margin of the north qilian suture zone were associated with the central qilian microcontinent these cambrian mafic to felsic intrusive rocks are likely to be magmatic products of a continental arc built on the northern margin of the central qilian microcontinent during the processes of southward subduction of the north qilian ocean together a cambrian andean type arc cambrian ordovician mariana type intra oceanic arc and multiple early paleozoic accretionary complexes within the north qilian suture zone attest to various subduction accretion processes that occurred within the proto tethyan ocean from cambrian to middle ordovician time prior to terminal continental collision

u pb and hf isotopic compositions of detrital zircons from the paragneisses of the quanji massif nw china implications for its early tectonic evolutionary history abstract the quanji massif is a cratonic fragment located on the northeastern margin of the qinghai tibetan plateau in western qinghai province northwest china fig 1 this massif consists of pre neoproterozoic crystalline basement unconformably overlain by mid to late neoproterozoic and cambrian strata the basement is dominantly made up of the delingha complex and the supracrustal dakendaban group the delingha complex is made up of 2 24 2 39 ga granitic gneisses with enclaves of dominant amphibolite and minor felsic gneisses as well as granulites the supracrustal dakendaban group is in tectonic contact with the delingha complex and can be divided into the lower and upper dakendaban sub groups data from detrital zircons show that the protolith rocks of these two sub groups were deposited after 2 32 ga and 2 11 ga respectively the detrital zircon age and hf isotopic data and geological correlations suggest that the quanji massif was possibly fragmented from the tarim craton and the delingha complex was probably uplifted to become the major sedimentary source for the upper dakendaban sub group at 2 11 ga our zircon hf isotope compositions demonstrate important crustal growth at 2 6 2 7 ga and 2 5 ga together with the important magmatic activity at 2 2 2 4 ga and geological data our results seem to suggest that the tarim craton was part of the north china craton in its early evolutionary history but rifted away and joined the yangtze craton prior to the neoproterozoic

differential compaction faults and their implications for fluid expulsion in the northern bozhong subbasin bohai bay basin china abstract a series of differential compaction faults was identified in the northern bozhong subbasin bohai bay basin china by using 3d seismic well log and lithology data the differential compaction faults display two obvious characteristics first they develop along a lithologic boundary which separates thick sandstone from underlying mudstones facies and thickness change such as an abrupt lithologic change between sandstone and mudstone a lateral thickness change of overlying sandstone are the basic controlling factors of these differential compaction faults second they have a definite strike direction according to the fault strike the differential compaction faults can be divided into three groups group a have an approximate orthogonal strike with the tectonic faults group b display a similar strike with the slope and group c show radial strikes on the circular basement uplift tectonic faults influence the planform patterns of differential compaction faults in their near vicinity and induce these faults displaying an approximate orthogonal intersection with the late period through going faults group a basin slope promote the formation of differential compaction faults by downslope gravity sliding and cause faults parallel to the strike of slope group b circular basement topography generates isotropic stress and leads the differential compaction faults above the basement dominated by radial strikes group c production and geochemistry data is an evidence of differential compaction faults developed in a late period when the strata reach a certain burial depth that the source rocks enter the oil generating window the presence of thermogenic fluid within shallow reservoirs represents as evidence of hydrocarbon drained and migrated through the differential compaction faults the differential compaction faults could serve as significant conduits for fluid expulsion and hydrocarbon accumulation in the bohai bay basin china

a revised layered model application to the bonney coast upwelling a conventional two layered model is revised to incorporate thermodynamics the interface between the first layer and the second layer is held at a constant height and across this interface mixing is allowed the thickness of the first layer is almost constant subject to free surface changes in comparison with the conventional layered model the new model has a longer integration time enabling examinations of the late stage of an upwelling event it also allows a temperature signal to be transmitted through the first layer producing a more realistic and complete simulation when the model is applied to the bonney coast upwelling system it not only assesses the role played by the thermodynamics but also resolves for the first time the relaxation phase of a well observed upwelling episode off the bonney coast sea level and current reversals are found to be poor indicators of upwelling termination

satellite investigations of a cyclonic gyre in the central tyrrhenian sea western mediterranean sea thermal satellite images related to surface temperature of the tyrrhenian sea western mediterranean sea show an elliptic cold patch suggesting the presence of a wind induced cyclonic gyre with well defined meanders of comparatively constant wavelength in order to gain insight into the dynamics of the gyre these data are compared with results of two classical linear models that of crepon and richez on wind induced upwellings and that of gill on currents due to a buoyancy discontinuity in rotating channels the large scale gyre meanders are analyzed using theoretical information on baroclinic instability models it results that the gyre is due to winds blowing eastward from the mouths of bonifacio and to the buoyancy due to a thermal front along 41 e with this general procedure from satellite images an estimate of the deep hydrologic quantities is obtained this technique is of interest also for other similar systems

offshore wind forcing in the gulf of tehuantepec mexico the asymmetric circulation since the early surveys carried out by the eastern tropical pacific eastropic and scripps tuna oceanographic research stor projects in the tropical pacific off mexico the northerly winds which blow over the gulf of tehuantepec were described as an important factor controlling the dynamics of this coastal ocean in january february 1989 an international team carried out the experiment tehuano designed to study the response of the gulf to these wind pulses the complete evolution of the coastal ocean after an event of moderate intensity was observed the forcing is characterized by a mostly symmetric fan shaped offshore wind jet which in turn produces a remarkably asymmetric upper ocean response while analytical results based on ekman theory forced by a symmetric offshore wind predict the formation of a symmetric dipolar circulation the observed flow consists mainly of a large 200 km in diameter anticyclonic warm core eddy in the western gulf with only a weak cyclonic counterpart in the eastern gulf intense surface cooling under the wind jet is caused by entrainment of subsurface water into the upper layer the thermocline in the west deepens with the development of the eddy which is formed initially by the advection of warm surface waters from west of the gulf east of the axis of the wind the mixed layer deepens due to wind induced entrainment while at the same time shoaling and compression of the deeper isotherms by curl induced upwelling ekman pumping strengthen the thermocline

u pb zircon geochronology of coesite bearing eclogites from the southern dulan area of the north qaidam uhp terrane northwestern china spatially and temporally extensive uhp metamorphism during continental subduction coesite bearing eclogites from 100 km 2 in the southern dulan area north qaidam mountains nqm of western china contain zircon that records protolith crystallization and ultra high pressure uhp metamorphism sensitive high resolution ion microprobe mass spectrometer and laser ablation inductively coupled plasma mass spectrometry u pb analyses from cathodoluminescence cl dark zircon cores in a coesite bearing eclogite yield an upper intercept age of 838 50 ma and oscillatory zoned cores in a kyanite bearing eclogite gave a weighted mean 206 pb 238 u age of 832 20 ma these zircon cores yield steep heavy rare earth element hree slopes and negative eu anomalies that suggest a magmatic origin thus c 835 ma is interpreted as the eclogite protolith age unzoned cl grey or bright zircon and zircon rims from four samples yield weighted mean ages of 430 4 438 2 446 10 and 446 3 ma flat hree patterns without eu anomalies and contain inclusions of garnet omphacite rutile phengite and rare coesite these ages are interpreted to record 16 5 myr of uhp metamorphism these new uhp ages overlap the age range of both eclogite and paragneiss from the northern dulan area suggesting that all uhp rock types in the dulan area belong to the same tectonic unit our results are consistent with slow continental subduction but do not match oceanic subduction and diapiric exhumation uhp model predictions these new data suggest that similar to eclogites in other hp uhp units of the nqm and south altyn tagh protoliths of the eclogites in the dulan area formed in a continental setting during the neoproterozoic and then subducted to mantle depth together with continental materials during the early palaeozoic

anatexis of ultrahigh pressure eclogite during exhumation in the north qaidam ultrahigh pressure terrane constraints from petrology zircon u pb dating and geochemistry plagioclase rich leucosomes and k feldspar rich veins are widely distributed within retrogressed eclogite in the xitieshan area of the north qaidam ultrahigh pressure metamorphic terrane western china in this contribution a combined study of petrology zircon internal structure zircon u pb age zircon trace element composition whole rock geochemistry and sr nd isotopes in plagioclase rich leucosomes and k feldspar rich veins provides insight into the nature and timing of partial melting in these rocks petrological evidence for partial melting is provided by elongated highly cuspate feldspars quartz along grain boundaries e g muscovite garnet and clinopyroxene and felsic veinlets composed of quartz and feldspar along the boundaries of garnet clinopyroxene and clinopyroxene plagioclase symplectite in the metabasite whole rock geochemistry suggests that the plagioclase rich leucosomes have lower contents of both rare earth elements rees and high field strength elements hfses but higher large ion lithophile elements liles e g rb ba k sr and pb than the metabasite hosts the plagioclase rich leucosomes may be divided into two subgroups according to their distinct ree patterns 1 higher total ree content with or without weak negative eu anomalies and 2 lower total ree content with conspicuous positive eu anomalies the eu rich group also shows higher sr content than those in the eu poor group however the k feldspar rich veins show higher ree hfse and lile concentrations than the plagioclase rich leucosomes and metabasites the inherited cores of k feldspar rich veins are of typical magmatic origin oscillatory zoning with high th u ratios enriched heavy h rees and negative eu anomalies yielding 206 pb 238 u ages ranging from 904 8 ma to 915 28 ma the zircon cores of plagioclase rich leucosomes and mantles of k feldspar rich veins exhibit no zoning or weak zoning with flat hree patterns and no negative eu anomalies and they contain mineral inclusions of garnet and clinopyroxene implying that these zircon domains were formed during an episode of eclogite facies metamorphism with 206 pb 238 u ages ranging from 444 10 ma to 452 9 ma internal textures and mineral inclusions quartz plagioclase and k feldspar and trace element systematics steep hree patterns with negative eu anomalies and low th u ratios of the zircon rims from plagioclase rich leucosomes and k feldspar rich veins are similar to anatectic zircon these anatectic zircon domains yielded 206 pb 238 u ages ranging from 430 10 ma to 440 12 ma and 406 12 ma to 430 13 ma respectively an integrated study of petrology geochronology and geochemistry demonstrated that the metabasites of the north qaidam ultrahigh pressure terrane likely experienced initial partial melting with plagioclase rich leucosome formation under eclogite facies conditions and partial melt crystallization during the granulite facies stage triggered by dehydration melting involving zoisite and rare muscovite the k feldspar rich veins within the metabasites may be the result of injected melts that were derived from partial melting of nearby gneisses

poleward coastal jets induced by westerlies in the bay of biscay 1 two hydrodynamic surveys based on acoustic doppler current profiler adcp and drift buoys measurements taken in summer 2008 and 2009 revealed poleward coastal jets of up to 32 cm s 1 that lasted up to 22 d along the aquitaine shelf in the southeastern area of the bay of biscay a strong increase in bottom temperature was associated with these currents up to 4 c in 5 d at 54 m depth these observations occurred after a few days of westerlies cross shore winds which were thought to have only a limited impact on longshore circulation here the mars3d hydrodynamic model was used with a schematic bathymetry of the southeastern area of the bay of biscay to reproduce and analyze these coastal jets simulations revealed that the triggering mechanism of the poleward currents is unequivocally due to downwelling circulation induced along the spanish coast this downwelling induces an external longshore pressure gradient which generates a high speed coastal trapped wave that propagates along the french coast with a phase velocity of about 3 to 4 m s 1 and an internal baroclinic kelvin wave with a phase velocity of about 1 m s 1 a sensitivity study of the role of stratification conditions wind strength and duration was then carried out to determine the periods that are the most sensitive to this wind induced circulation

wind forced setup of upwelling geographical origins and numerical models the role of bottom drag 1 an analysis is made to determine the properties and scales for the setup of upwelling driven by an impulsively started steady uniform wind of semi infinite fetch the backward edge of the wind field acts as a geographical origin for the generation of coastal trapped waves ctws a perturbation analysis is used to show that prior to the arrival of the nth mode ctw the alongshore velocity is shown to asymptote to a constant value set by bottom drag and over a timescale tn as this viscous limit is achieved the upwelling becomes increasingly confined to the bottom boundary layer and bottom stress balances wind stress interior upwelling is shut down the viscous limit may not be achieved since after the arrival of the nth ctw mode a gradient in the alongshore velocity is set up and its divergence acts to feed the offshore ekman transport and shut the upwelling down numerical results are used to show that the frictional length and timescales predicted by the perturbation analysis are unrealistically small due to an underestimation of thermal wind shear moreover the theory underpredicts the importance of the first ctw mode which is shown to largely determine the setup and shutdown of upwelling a simple first mode model for upwelling is developed and used to evaluate the validity of a numerical open boundary condition in determining the correct degree of upwelling a case study for the chilean shelf is presented

new style of honeycomb structures revealed on 3d seismic data indicate widespread diagenesis offshore great south basin new zealand abstract in the great south basin within the eocene section at time depths around 700 900 ms two way time below the seafloor unusual features are observed on 3d seismic data closely associated with polygonal faults the features referred to as honeycomb structures hs cover an area of 600 km 2 are packed circular oval to polygonal depressions 150 400 m across in plan view and several to 10 m in amplitude polygonal faults rapidly die out at the marshall paraconformity which is overlain by the oligocene penrod formation hence the polygonal faults are inferred to have formed prior to the marshall paraconformity and they cross cut hs features consequently the top of the hs probably formed at burial depths of around 375 500 m which is their decompacted depth below the paraconformity the interval containing hs is about 125 m vertical thick there are several possible origins for the hs the most probable is related to bulk contraction of the sediment volume accompanied by fluid expulsion which suggests a diagenetic origin in particular the opal a ct transition there are actually two polygonal fault systems pfs present in the area the southern tier 1 pfs lies laterally to the hs and overlaps with it the northern pfs tier 2 lies above the hs appears to be independent of the hs and formed in the upper 200 300 m of the sediment column the tier 1 pfs probably formed by shear failure related to the same diagenetic effects that caused the hs

geostatistical analysis of seafloor depressions on the southeast margin of new zealand s south island investigating the impact of dynamic near seafloor processes on geomorphology abstract seafloor depressions are widespread on the present day continental slope along the southeast coast of new zealand s south island the depressions appear to be bathymetrically constrained to depths below 500 m correlating to the top of the gas hydrate stability zone and above 1100 m similar depressions observed on the chatham rise are interpreted to have formed as a result of gas hydrate dissociation leading to the hypothesis that a similar origin can be applied for the depressions investigated in this study our investigation however has found limited geophysical or geochemical evidence to support this hypothesis the objective of this paper is to examine whether a causal relationship can be established between potential mechanisms of depression formation and the present day seafloor geomorphology geostatistical analysis methods applied to multibeam bathymetry and interpretation of 3d seismic data have been used to empirically describe the geomorphology of the seafloor depressions and investigate potential correlations between geomorphology and other processes such as current flow along the shelf and slope in this region and underlying polygonal fault systems although the results of our analysis do not preclude that the seafloor depressions formed as a result of gas hydrate dissociation neither does our geophysical or geochemical evidence support the theory therefore we propose an alternative mechanism that may have been responsible for the formation of these structures based on the evidence presented in this study the most likely mechanism responsible for the formation of these seafloor depressions is groundwater flux related to the interaction of current systems and the complex geomorphology of submarine canyons on the southeast coast of the south island

two contrasting accretion v collision orogenies insights from early paleozoic polyphase metamorphism in the altun qilian north qaidam orogenic system nw china

first record and timing of uhp metamorphism from zircon in the xitieshan terrane implications for the evolution of the entire north qaidam metamorphic belt the xitieshan terrane is one of four metamorphic terranes in the north qaidam metamorphic belt which is an early paleozoic high pressure to ultrahigh pressure hp uhp metamorphic belt in nw china however conclusive evidence and precise timing of uhp metamorphism in the xitieshan terrane have not been well documented in this study we report an integrated study of zircon grains from an amphibolite in the xitieshan terrane in terms of mineral inclusions trace elements and u pb age systematics the first record of coesite is reported as an inclusion in a metamorphic zircon which provides unambiguous evidence for the uhp metamorphism of the xitieshan terrane the metamorphic zircon domains have weak or no zoning very low th u ratios insignificant eu anomalies and flat hree patterns zircon grains contain inclusions of garnet omphacite and rutile in addition to the coesite inclusion these inclusions indicate that the metamorphic zircon grains formed under uhp metamorphic conditions the metamorphic zircon grains were dated by the sims and la icpms methods and yield weighted mean ages of 432 14 and 441 9 ma respectively combined with previous results the hp uhp metamorphism of the xitieshan terrane may have lasted 460 440 ma with the peak uhp metamorphism at 441 9 ma a compilation of the reported geochronological data reveals that all four terranes of the north qaidam metamorphic belt might have experienced coeval uhp metamorphism during the early paleozoic 420 450 ma and thus may have suffered a coherent subduction uhp metamorphism and exhumation cycle

kilometre scale polygonal seabed depressions in the hatton basin ne atlantic ocean constraints on the origin of polygonal faulting polygonal faulting is a widespread phenomenon in sedimentary basins worldwide it changes basin scale fluid flow patterns and alters the physical properties of the sediments making it important for hydrocarbon exploration and geohazard analysis it is generally accepted that polygonal fault patterns derive from dewatering and compaction of the host sediments but there is debate regarding the processes that control polygonal faulting new multibeam bathymetry data from the hatton basin ne atlantic show up to 10 m deep and 200 600 m wide troughs at the seabed they connect to each other forming polygons that are several hundred metres across i e of similar size as buried polygonal fault systems observed in 3d seismic data the troughs are symmetrical and resemble elongated pockmarks previously unpublished high resolution 2d seismic data from the same area show seismic disturbance zones similar to pipes observed under pockmarks elsewhere as well as faults that have all the characteristics of polygonal fault systems the observation of the wide disturbance zones is enigmatic as they appear to follow the polygonal seafloor pattern the observed extent of the polygonal sediment contraction system is substantial covering almost 37 000 km2 we calculate that some 2600 km3 of possibly carbon bearing fluids have been expelled from this system and we expect that this will affect the benthic ecosystems although so far there is only limited evidence for chemosynthetic habitats

remote sensing observation and numerical modeling of an upwelling jet in guangdong coastal water 1 an upwelling event that occurred in guangdong coastal water on july 14 16 2003 is observed by using satellite multisensor data including the moderate resolution imaging spectroradiometer modis sea surface temperature sst and quikscat ocean surface winds successive modis sst images reveal expansion process of a jet like upwelling cold water body in surface layer the regional ocean model system roms is used to explore the upwelling dynamics the modeling successfully reproduces the jet like shape of the surface upwelling water as well as the upwelling developing process analyses of modeling momentums reveal that the large offshore transport appeared on the west side of honghai bay as a result of high alongshore pressure gradient and nonlinear advections and the enhanced horizontal advection also played an important role in developing the prominent upwelling in honghai bay a numerical experiment is conducted to confirm that it was the wind driven upwelling rather than the wind induced vertical turbulent mixing that induced the surface cold water further numerical analyses suggest that strong internal tides occurred in honghai bay caused by the local bottom topography the interaction between the upwelling and internal tides enhances the bottom water uplifting the offshore expansion of the upwelling water is controlled by the cross shore topography slope a gentle and offshore extended slope helps the bottom water climbing up to the surface in a wide range in cross shore direction whereas a steep and narrow slope restricts the expansion of the upwelling water and confines the cold water in a narrow band along the shore

geochemistry of high grade supracrustal rocks from the kerala khondalite belt and adjacent massif charnockites south india abstract the kerala khondalite belt kkb comprises a suite of supracrustal rocks of probable proterozoic age that was metamorphosed to the granulite facies the kkb consists of an interlayered sequence of 1 garnet biotite orthopyroxene graphite gneisses 2 khondalites graphite garnet biotite sillimanite cordierite gneisses and 3 cordierite gneisses garnet biotite cordierite orthopyroxene as well as less abundant mafic granulites calc silicates and quartzites petrologic and geochemical data suggest that these rocks were originally arkosic and argillaceous sediments possibly accompanied by felsic volcanic rocks along with minor intercalations of basalts carbonates and quartz rich sandstones the ree patterns of the metasediments are typically lree enriched with large negative eu anomalies indicating a continental provenance the major and trace element compositions of some of the arkosic rocks of the kkb resemble those of the massif charnockites that bound the kkb to the north which suggests that the massif charnockites may have been the source of some of the kkb sediments modern day analogues of the pelite arkose lithologic association observed in the kkb occur in intracratonic rifts and rifted continental margins this association is clearly distinct from the graywacke mafic volcanic association found in the southern indian greenstone belts and many other lower grade archean sedimentary sequences the kkb supracrustals show both lithologic and chemical similarities to many proterozoic supracrustal successions

geochemistry and detrital zircon u pb and hf isotopes of the paragneiss suite from the quanji massif se tarim craton implications for paleoproterozoic tectonics in nw china abstract the delingha paragneiss suite in the quanji massif southeastern tarim craton is composed of mica schist paragneiss leptynite and quartzite similar to the khondalite suites described from elsewhere in the world the mica schist is rich in al2o3 up to 26 wt and contains graphite and diagnostic minerals including sillimanite and garnet with metamorphism under amphibolite facies to locally granulite facies conditions as manifested by association with amphibolite and granulite the detrital zircon u pb ages and geochemical data indicate that the protolith materials of the delingha paragneiss suite were mainly sourced from 2 20 to 2 45 ga granites felsic volcanic rocks and ttg and were deposited at 2 17 1 92 ga the detrital zircon hf and whole rock nd isotopes document important crustal growth at 2 5 2 7 ga the detrital zircon age spectra the whole rock nd and zircon hf model ages the low maturity of the protolith and short distance transportation suggest that the detritus were derived from the underlying delingha complex and the lower dakendaban sub group the timing of magmatic activities in the source region the depositional age and metamorphic histories of the delingha paragneiss suite are all comparable to those recorded in the khondalite belt along northern margin of the ordos block in the north china craton our study shows that the 2 2 2 45 ga magmatic rocks were generated in arc or active continental margin settings suggesting a prolonged subduction and accretion history prior to final amalgamation 2 5 1 8 ga to form the unified north china craton and the assembly of the tarim craton in nw china

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

contraction driven shear failure in compacting uncemented sediments shear failure in sediments is universally linked with active boundary conditions such as those imposed by tectonic stresses under conditions of no lateral strain and in the absence of tectonic stress soil mechanics theories predict a simple one dimensional compaction in which sediment particles displace vertically without shear failure during pressure diffusion conflicting with this theory shear failure planes are often found in sediments that formed under near horizontal burial conditions we investigated the effect of particle scale volume contraction as a potential cause of shear failure in uncemented particulate materials and found that loss of particle volume under confined conditions no external loading resulted in pronounced lateral stress reduction often reaching coulomb frictional failure conditions shear strain localization was analytically predicted and modeled numerically due entirely to volume loss at the grain scale we define this mode of internally driven shear failure as contractile to distinguish it from that caused by external loading and show that it can explain many natural fracture systems without invoking regional tectonics

reservoir rock chemo mechanical alteration quantified by triaxial tests and implications to fracture reactivation abstract co 2 injection into geological formations shifts the geochemical equilibrium between the minerals and resident brine the induced mineral brine co 2 reactions can alter the reservoir rock strength and deformational behavior which subsequently affects co 2 storage mechanical integrity this study attempts to investigate quantitatively the effect of mineral cement and particle dissolution through numerical modeling and validation of triaxial tests performed on unaltered and geologically altered entrada sandstone we utilize a numerical model that couples the discrete element method dem and the bonded particle model bpm to perform simulations of triaxial tests on synthetic rocks that mimic tested rock samples under various confining stresses numerical results in agreement with experimental evidence show that both cement and particle dissolution significantly contribute to rock weakening in sandstone samples with carbonate hematite cements and pore filling carbonate sensitivity analyses show that the brittleness of dem numerical samples is mostly conditioned by the cement bond size among all cement microscopic parameters an alteration path that mimics the mineral dissolution under subsurface boundary conditions leads to 1 vertical compaction and horizontal stress relaxation in the reservoir rock and 2 transfer of stresses to adjacent strata that results in bond breakage and potentially natural fracture reactivation at a large scale

eclogite facies metamorphism in impure marble from north qaidam orogenic belt geodynamic implications for early paleozoic continental arc collision abstract in the north qaidam ultrahigh pressure uhp metamorphic belt impure marble and interbedded eclogite represent a particular sedimentary provenance and tectonic setting which have important implications for a controversial problem the dynamic evolution of early paleozoic subduction collision complexes in this contribution detailed field work mineral chemistry and whole rock geochemistry are presented for impure marble to provide the first direct evidence for the recycling of carbonate sediments under ultrahigh pressures during subduction and collision in the yuka terrane in the north qaidam uhp metamorphic belt according to conventional geothermobarometry pre peak subduction to 0 8 1 3 gpa 485 569 c was followed by peak uhp metamorphism at 2 5 3 3 gpa 567 754 c and cooling to amphibolite facies conditions at 0 6 0 7 gpa 571 589 c u pb dating of zircons from impure marble reveals a large group with ages ranging from 441 to 458 ma peak at 450 ma a smaller group ranging from 770 to 1000 ma peak at 780 ma and minor 1 8 ga zircon aged ca 430 ma uhp metamorphism the youngest detrital zircons suggest a maximum depositional age of ca 442 ma and a burial rate of ca 1 0 1 1 cm yr when combined with p t conditions and uhp metamorphic age the ree and trace element patterns of impure marble with positive sr and u anomalies negative high field strength elements nb ta zr hf and ti and ce anomalies imply that the marble had a marine limestone precursor impure marble intercalated with micaschist and eclogite was similar to limestone and siltstone protoliths deposited in continental fore arc or arc setting with basic volcanic activity therefore the yuka terrane most likely evolved in a continental island arc setting during the paleozoic these data suggest that metasediments were derived from a mixture of proterozoic continental crust and juvenile early paleozoic oceanic and or island arc crust in addition their protoliths were likely deposited in a terrigenous dominated forearc marine basin rather than an intracontinental basin environment further evidence that some continental arc volcanic rock may have been the source of eclogite in the north qaidam these sediments formed in a forearc basin close to the qaidam block to the north were transported in the subduction zone to 100 110 km depth with uhp metamorphism prior to exhumation meanwhile the new results suggest that subduction erosion occurred along the active continental margin during the qaidam block with north dipping subduction indicating that the north qaidam uhp metamorphic belt may have formed during continental arc collision

geochemistry and trace element behaviors of eclogite during its exhumation in the xitieshan terrane north qaidam uhp belt nw china abstract the xitieshan terrane located in the central part of the north qaidam ultrahigh pressure uhp metamorphic belt china is mainly composed of orthogneiss and paragneiss and a few intercalated eclogite layers and boudins based on their bulk rock tio 2 contents the eclogites can be subdivided into a high ti group tio 2 2 and a low ti group tio 2 e nd t and restricted i sr values and therefore provide further evidence for the formation of the protoliths of the eclogites in an oceanic environment on the other hand the sr nd isotopes of high ti eclogites show mainly positive but also some negative e nd t values and relatively broadly distributed i sr values indicating minor crustal contamination of the ocean floor basalts considering available 750 877 ma protolith ages preserved in zircon cores it is inferred that some of the eclogites derived from neoproterozoic protoliths were emplaced onto the crust far ahead of the paleozoic deep subduction while the other eclogites originate from a different oceanic crust e g the paleo qilian ocean indicating multiple orogenies in the geological history of the xitieshan terrane china whole rock and in situ la icp ms mineral trace element analyses of eclogites revealed two stages of fluid behavior during retrogression that correspond to the two exhumation stages uncovered by phase equilibrium calculations the mineral scale trace element distributions and trace element inheritance of newly formed amphibole from its precursors indicate that at the peak metamorphic stage m1 and at the earlier eclogite facies overprint m2 the fluid was internally controlled by the rock itself within a mafic lens the amount of water soluble elements e g rb sr ba u pb and lree observed in the whole rock compositions as well as in amphiboles increases from the core phengite bearing eclogite to the rim amphibolite and implies an external fluid source for the amphibolite facies retrogression m3 which should be helpful for the final exhumation of uhp eclogite

petrogenesis of the early paleozoic low mg and high mg adakitic rocks in the north qilian orogenic belt nw china implications for transition from crustal thickening to extension thinning abstract the petrogenesis and geodynamic implications of the early paleozoic adakitic rocks in the north qilian orogenic belt remain topics of debate in this study petrology zircon u pb age and lu hf isotopic composition whole rock geochemistry and sr nd isotopes were carried on both low mg and high mg adakitic rocks from the north qilian orogenic belt these results will provide significant constraints on the evolution of the north qilian orogenic belt in general the low mg adakitic granites mainly consist of plagioclase 50 55 alkali feldspar 20 25 quartz 20 25 and biotite 5 in contrast the high mg adakitic granodiorites are generally composed of alkali feldspar 30 35 plagioclase 30 45 quartz 20 25 and amphibole 10 the low mg adakitic granitoids 446 457 ma are characterized by high sio2 69 72 wt low mg 39 42 and low cr and ni contents however the high mg adakitic granitoids 430 431 ma have relatively lower sio2 65 66 wt higher mg 50 59 and higher cr and ni contents the low mg adakitic rocks have high initial 87sr 86sr ratios 0 7068 0 7080 negative end t 2 3 to 3 3 and ehf t values 6 8 to 1 9 with old zircon hf model ages 1 2 1 6 ga however the high mg adakitic rocks show lower initial 87sr 86sr ratios 0 7044 0 7066 higher end t 1 8 to 3 0 and positive ehf t values 2 3 7 7 with younger zircon hf model ages 0 9 1 1 ga these results suggest that the low mg rocks were generated by partial melting of thickened crust whereas the high mg rocks were derived from anatexis of delaminated lower crust which subsequently interacted with mantle magma upon ascent the data obtained in this study provide significant information about the geological and tectonic processes after the closure of the qilian ocean the continent continent collision and thickening probably occurred during 440 467 ma with formation of low mg adakitic rocks and the transition of the tectonic regime from compression to extension probably occurred at 430 ma with formation of high mg adakitic rocks

modal and geochemical compositions of the lower silurian clastic rocks in north qilian nw china implications for provenance chemical weathering and tectonic setting abstract the north qilian orogenic belt records the transition from ordovician marine back arc basin to early devonian terrestrial molasse basin as the central qilian block was sutured to the north china craton the detrital framework and geochemical composition of lower silurian sedimentary rocks within the north qilian belt record the provenance tectonic setting and a variety of sedimentary processes that operated during transport from source to sink the petrological and geochemical characteristics of sandstones siltstones and shales in the western segment of the north qilian belt indicate a generally low degree of chemical weathering of source area s and limited sorting prior to deposition these characteristics suggest an active tectonic setting in contrast samples studied from the eastern part of the north qilian belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting such characteristics imply a more stable tectonic setting geochemical data including eu eu ti nb th sc and co th ratios suggest contrasting source regions for the western and eastern segments of the north qilian belt sources in the west included basement rocks of the central qilian block and the north china craton in addition western sources may have included mafic rocks located within the north qilian arc in contrast data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the central qilian block and the north china craton overall detrital and geochemical data combined with the regional geology suggest a foreland basin setting that formed during collision of the central qilian block with the north china craton

mineralogical and isotopic characterization of graphite deposits in the western part of the north qaidam orogen and east kunlun orogen northeast tibetan plateau china abstract medium to high grade metamorphic rocks comprising numerous graphite deposits are widely distributed in the periphery of the qaidam basin northern tibetan plateau china we present textural xrd and raman spectroscopy characteristics of graphite 13c results of graphite and cogenetic calcite and 18o results of calcite in three graphite occurrences located at the periphery of qaidam basin graphite displays hexagonal platy flaky irregular polygonal ovate morphologies with occasional spherulitic textures graphite morphologies combined with xrd and raman spectroscopy indicate that graphite has relatively high crystallinity raman microspectroscopy of graphite shows that peak metamorphic temperatures vary between 690 and 801 c graphite 13cv pdb values range between 26 3 and 21 6 indicating organic carbon as the major carbon source for graphite calcite 13cv pdb and calcite 18ov smow values range between 10 8 and 3 9 and between 6 6 and 29 5 respectively calcite 13cv pdb results show that organic carbon was mixed with inorganic carbon which resulted in an increase of 13cv pdb calcite 18ov smow values indicate that the graphite deposits experienced late stage water rock interaction the positive and negative anomalies of calcite 13cv pdb indicate that organic matter oxidation and recycling locally occurred during the final stage of the great oxidation event the wide distribution of regional metamorphic organogenic graphite deposits provides evidence for large scale paleoproterozoic biological activity in the periphery of the qaidam basin

zircon growth and ages of migmatites in the algoma type bif hosted iron deposits in qianxi group from eastern hebei province china timing of bif deposition and anatexis abstract algoma type bifs and associated volcanic suites of the qianxi group in eastern hebei province have undergone high grade metamorphism and anatexis the anatectic event is genetically related to high grade magnetite ores but the age of the anatectic melting has not been well constrained we present detailed textural relationship and internal structures of zircon grains and their age data from eight samples of migmatitic rocks representing the different algoma type bif hosted iron deposits to constrain the formation age of bif deposition and subsequent anatexis six continuous zircon growth stages are distinguished by a series of low cl and high cl zones outside from center to edge inherited magmatic zircon bright cl resorption domain dark cl recrystallization front dark gray cl diffusion domain light gray cl overgrowth and bright cl resorption edge the overgrowths are interpreted as a solid state diffusion of zr of primary zircon during interaction with anatectic melt which resulted in different stages of chemical re equilibration of primary domains and local re deposition of newly grown domains on the suitable isostructural substrate of residual magmatic zircon shrimp zircon u pb dating of inherited magmatic cores and discrete magmatic grains constrains the peak bif deposition age at 2520 ma which is different from the peak at 2 75 2 70 ga for algoma type bifs elsewhere in the world zircon u pb dating of light gray cl rims and newly grown homogeneous grains indicates that the anatectic event lasted from 2511 to 2485 ma at least immediately following the bif deposition the bif depositional event is consistent with widespread late neoarchean magmatism and the anatectic event is consistent with regional metamorphic events in the eastern part of the north china craton

transient upwelling generated by two dimensional atmospheric forcing and variability in the coastline abstract the present paper deals with two dimensional transient upwelling in a two layer ocean of constant depth motions generated by several two dimensional atmospheric forcings are investigated using asymptotic expansions in time it is shown that the component of the wind parallel to the coast generates an interface elevation which propagates along the coast as an internal kelvin wave front strong horizontal baroclinic motions are linked to this phenomenon the velocity within the deep layer is in the opposite direction to that of the wind on the surface it is found that the spin up time of mean motions is of the order of the coriolis period the motion generated by a wind blowing over a bay is then studied the bay is idealized by a right angle corner two independent cases are considered depending on whether or not the wind is parallel to one coast or the other

satellite images of upwellings and cold filament dynamics as transient effects of violent air sea interactions downstream from the island of sardinia western mediterranean sea a systematic analysis of thermal satellite images of upwellings and cold filament dynamics downstream from the island of sardinia western mediterranean sea covering the years 1984 1985 1989 1990 1993 and 1994 is discussed for this sea the main transient atmospheric forcing comes from bursts of the mistral a north western wind which downstream from sardinia affects a rather calm basin the tyrrhenian sea in early summer particularly clear effects of atmospheric forcings such as gyres upwellings and cold filaments can be observed our analysis provides not only a systematic insight into these phenomena but also some experimental evidence of a novel mechanism of cold filament formation and evolution indeed in july 1989 a nice set of satellite images shows a cold filament rooted to the shallowest part of the wide shelf off olbia which meanders offshore for a few days under the effect of the mistral and of the general circulation it is of interest to underline how stably the filament is rooted to the shelf so that in only one image it appears as an elongated straight segment also the filament s potential vorticity is discussed in order to gain some insight into shelf water fluxes detachment depths and velocities relative to such phenomena

coupled fluid flow and sediment deformation in margin scale salt tectonic systems 2 layered sediment models and application to the northwestern gulf of mexico 1 in paper 1 we described a methodology to model coupled fluid flow and deformation in composite salt and siliciclastic tectonic systems and investigated their compaction and overpressuring behavior prior to and during continental margin scale gravitational spreading compaction driven darcy fluid flow in clastic sediments is coupled through the effective pressure to their frictional plastic yield and mechanical deformation viscous flow of the underlying salt is independent of fluid pressure paper 1 presented prototype models that are limited to single uniform sediment lithologies either sandstone type or shale type that undergo mechanical and volumetric viscous compaction in this paper we present models with layered sandstone type and shale type lithologies designed to better approximate the more complex stratigraphy of the gulf of mexico our natural example a first set of models demonstrates that layered lithologies can produce fluid pressure regimes similar to those observed in sedimentary basins we then introduce an improved formulation of viscous compaction that includes a stronger dependence on porosity and depth used as proxy for temperature thereby more effectively self limiting viscous compaction a second set of models with the improved viscous compaction formulation demonstrates that the onset of gravity spreading is mainly controlled by overpressuring in the landward end of the salt basin and that resulting shortening in the distal part is partly accommodated by horizontal compaction models with moderately high fluid pressure best reproduce conditions considered to have been necessary for large scale gravitational spreading in the northwestern gulf of mexico which led to the formation of the perdido fold belt

inertial wind path and sea surface temperature patterns near the gulf of tehuantepec and gulf of papagayo during the northern hemisphere winter the surface atmospheric pressure on the gulf of mexico side of central america is often higher than that on the pacific side the resultant southward pressure gradient drives strong southward winds through a gap in the sierra madre mountain range at the isthmus of tehuantepec the atmospheric jet is narrow in comparison with the relevant radius of deformation so when it leaves the coast and flows out over the gulf of tehuantepec it is an inertial jet therefore the jet is expected to be deflected into a clockwise inertial circle by the coriolis force a similar process should also occur for central american atmospheric jets through mountain range gaps near the gulf of papagayo satellite measurements of sea surface temperature together with coastal wind data for the first 41 days of 1986 were examined to see if the expected wind path influenced sea surface temperature sst near the gulf of tehuantepec and the gulf of papagayo consecutive daily satellite images when the coastal southward tehuantepec wind increased suggest that the initial development of cold surface water in a clockwise loop is due to the wind mixing the shallow thermocline surface water along its inertial path a simple 1 layer analytical ocean model suggests in agreement with observations that the wind can drive surface quasi geostrophic currents of 1 m s 1 since the wind path is circular the wind actually generates a clockwise rotating ocean eddy with the approximate scale of the wind inertial circle the satellite sea surface temperature measurements also suggest that the wind driven surface ocean current is unstable in addition stronger gradients in sst to the right of the expected wind flow are consistent with advection of sea surface temperature by ocean surface ekman flow

late paleoproterozoic multiple metamorphic events in the quanji massif links with tarim and north china cratons and implications for assembly of the columbia supercontinent abstract the quanji massif preserves important records of late paleoproterozoic metamorphic events that provide insights into the tectonic history of the tarim craton and its relation with the north china craton here we investigate amphibolites from two regions in the quanji massif u pb ages from metamorphic zircons in the amphibolites combined with previously published ages from this region define distinct metamorphic events during paleoproterozoic the earlier medium p t type upper amphibolite facies metamorphic event occurred at ca 1 90 1 96 ga in a collisional setting the second event took place with low p t type amphibolite facies metamorphism in an arc setting at ca 1 82 1 85 ga with a subsequent medium p t type metamorphism during arc continental collision at ca 1 80 1 82 ga our data reveal for the first time that the late paleoproterozoic metamorphic events in the quanji massif are closely comparable with those documented from the khondalite belt within the inner mongolia suture zone and the trans north china orogen in the north china craton we therefore propose that the quanji massif and tarim craton probably shared similar tectonic histories with those of the north china craton in the late paleoproterozoic coinciding with the global assembly of the columbia supercontinent

petrology and geochronology of eclogites from the western segment of the altyn tagh northwestern china abstract the eclogites from the western segment of the altyn tagh occur as lens or boundins within quartzofeldspathic gneisses or pelitic gneisses characterized by amphibolite facies parageneses the petrographic features and reaction textures testify to three main metamorphic stages 1 the peak eclogite facies stage p 15 kbar t 665 880 c 2 the granulitic facies stage p 11 14 kbar t 670 800 c and 3 the amphibolite facies stage p 6 3 9 5 kbar t 619 738 c during decompression the trace element rare earth element and sm nd isotopic data suggest that most of the eclogites have protolith features resembling transitional type t type mid ocean ridge basalt morb the well preserved eclogite was selected for sm nd and u pb isotopic dating the sm nd isotopic data yield a whole rock garnet omphacite isochron of 500 10 ma age the u pb isotopic measurement of zircons from the same eclogite shows that the four grain populations are near concordant and are well plotted on concordia giving a weighted mean age of 503 9 5 3 ma the two different geochronological methods yield a similar age which is interpreted as the peak metamorphic age of eclogites and reflects the existence of a mountain root related to continental subduction during early paleozoic moreover based on the comparison with similar rocks in the northern margin of the qaidam basin a displacement of 350 400 km for the altyn tagh fault have been estimated

early paleozoic polyphase metamorphism in northern tibet china abstract the altun qilian kunlun orogenic system in the northern tibetan plateau is considered as the northernmost orogenic collage of the proto tethyan domain early paleozoic polyphase tectonothermal events related to the subduction of the proto tethyan ocean and subsequent collisional orogeny produced two dominant metamorphic belts the north altun nat north qilian nql hp lt metamorphic belt and south altun sat north qaidam nqd uhp metamorphic belt the nat nql hp lt metamorphic belt mainly consists of blueschist eclogite and hp metasediments eclogites record metamorphic conditions of 420 550 c and 21 25 kbar at 510 460 ma the hp lt metamorphic belt is associated with ophiolite subduction accretion complex and arc magmatic rocks suggesting that the nat nql is a typical early paleozoic accretionary orogenic belt in contrast the sat nqd uhp metamorphic belt is characterized by eclogite and garnet peridotite enclosed within continental orthogneiss and paragneiss these rocks record uhp metamorphism at t 700 c and p 27 kbar geochronology suggests that the uhp metamorphism occurred at 500 423 ma and eclogite protolith ages of 850 750 ma suggest that protoliths are related to neoproterozic continental rifting field relationships petrology and geochronology suggest that the sat nqd uhp metamorphic belt resulted from the deep subduction of continental crust moreover in the sat nqd uhp metamorphic belt two types of hp granulites have been recognized the first type of hp granulite was formed by overprinting of eclogites during exhumation the second type of hp granulite has a single metamorphic history and similar age to that of uhp eclogite penecontemporaneous metamorphic ages but different geothermal gradients between hp granulites and related uhp eclogite define a possible paired metamorphic belt which may be considered to be a diagnostic characteristic of collisional orogens high grade metamorphic rocks in the sat nqd commonly record barrovian type metamorphism although it remains unclear whether or not all of these rocks have an earlier u hp metamorphic history the low medium p barrovian metamorphism and associated magmatism are about 20 50 ma later than uhp metamorphism newly recognized eclogites in the northern part of the east kunlun mountains to the south of qaidam basin have a similar field relationship enclosed in continental gneiss and mineral assemblage to the nqd eclogites and a similar or slightly younger metamorphic age 410 430 ma the occurrence of similar continental type eclogites on two sides of the qaidam basin makes it necessary to reconsider the nature of the qaidam block the polyphase metamorphism in northern tibet can be linked to accretion and collisional orogenesis related to the evolution of prototethys through the early paleozoic

geochemistry of high grade metamorphic rocks of the north qaidam mountains and their geological significance the high grade metamorphic basement in the north qaidam mountains nqd is composed mainly of jinning age metasedimentary rocks and crustally derived granites possibly accompanied by minor paleoproterozoic and archaean material based on their geochemistry the metasedimentary rocks are divided into two groups type i which makes up the bulk of the high grade metamorphic basement in the nqd is characterized by high k2o low na2o relatively high total rare earth elements treez114 357 ppm and weak fractionation of light lree and heavy hree rare earth elements la yb nz8 27 these rocks also have strong negative eu anomalies eu eu z0 3 0 6 type ii rocks crop out mainly in the wulan area and are characterized by relatively high mgo 2 2 4 1 wt lower total ree and strong fractionation of lree and hree la yb nz29 48 both types of metasedimentary rocks have similar nd isotope compositions with tdmz1 9 2 2 ga and 3ndzk4 1 to k8 5 the granites are compositionally similar to the type i metasedimentary rocks the high grade metamorphic basement of the nqd is similar to that in the qilian orogenic belt and the yangtze platform the central qilian nqd terrane was separated from the dunhuang alxa terrane before the jinning period and the two terranes belong to the south china block and north china craton respectively q 2006 elsevier ltd all rights reserved

measurement of diagenetic compaction strain from quantitative analysis of fault plane dip we developed a new technique for quantifying the amount of porosity loss during diagenetic transformation of opal a to opal ct the technique is based on 3d seismic data from offshore norway where the widely developed biosiliceous sediments of the brygge formation are deformed by a polygonal fault system evidence is shown from two study areas that the dip of the polygonal fault planes reduces abruptly across the opal a to opal ct diagenetic boundary suggesting that the fault planes were passively rotated into shallower dips due to diagenesis the reduction of fault plane dip was used to quantify the vertical compaction strain due to diagenesis using an independent assessment of the magnitude of the porosity loss we are able to validate the method based on fault plane dips and also to evaluate whether the porosity loss results in an exclusively vertical strain additionally the impact of silica diagenesis on the shear strength of the sediments and fault growth is investigated we present evidence suggesting that deviations from classical mohr coulomb behaviour may be expected during the combined processes of diagenesis and porosity collapse and may indeed be sufficient to promote continued fault growth

precambrian evolution of the quanji block northeastern margin of tibet insights from zircon u pb and lu hf isotope compositions abstract the quanji block a cratonic fragment has been discovered between the north qaidam hp uhp metamorphic belt and the qilian orogenic belt in northwestern china this fragment has a pre neoproterozoic crystalline basement overlain unconformably by neoproterozoic paleozoic and mesozoic sedimentary strata pervasive anatexis of the basement produced extensive leucosomes in mafic and felsic migmatites zircons from the leucosomes yielded upper intercept and weighted mean 207 pb 206 pb ages of 1950 ma indicating that anatexis occurred in the late paleoproterozoic during regional high grade metamorphism hf model ages t dm2 for these zircons suggest that protoliths of the felsic and mafic migmatites had crustal residence time of 2 80 and 2 65 ga respectively the basement rocks of the quanji block are compositionally similar to those of the yangtze craton and may have been involved in assembly of the late paleoproterozoic global supercontinent columbia

analysis and modeling of contourite drifts and contour currents off promontories in the italian seas mediterranean sea the complex relationship between currents flowing around capes and their related contourite deposits is still an interesting topic to confront both from a sedimentologic and oceanographic perspective we analyze here recent observations of contourite drifts located at intermediate depths off promontories in the southern tyrrhenian and in the southern adriatic sea these contourites are located slightly upstream from the cape tip of cape vaticano while they occur both upstream and downstream in the lee wave region of the gargano promontory we therefore analyze and discuss tank and numerical simulations of contour following flows with particular attention to the presence of turbulent phenomena occurring in the lee region discussing the classical stream tube model i e a thin vein of dense water flowing around a cape we moreover provide physical justification for some aspects we recognized in the study experiments the comparison between bathymetric stratigraphic data and numerical tank and analytic results allows investigation of the possible occurrence of sediment drifts around capes we found that the presence of turbulence and thus of erosive conditions for sediments in the lee of a cape can be detected by using dimensionless numbers related to cape dimension and ocean current features this work can be seen as a new approach to bridge the gap between marine sedimentology and physical oceanography

proterozoic polymetamorphism in the quanji block northwestern china evidence from microtextures garnet compositions and monazite chime ages abstract the quanji block situated close to the triple junction of three major precambrian terranes in china i e the north china craton the yangtze block and the tarim block is composed of precambrian metamorphic crystalline basement and an unmetamorphosed mesozoic paleozoic sedimentary cover it has been interpreted as a remnant continental fragment microtextural relationships garnet trace element compositions and monazite chime ages in paragneisses schists and granitic leucosomes show two episodes of regional metamorphism in the quanji block basement the first regional metamorphism and accompaning anatexis took place at 1 93 ga the second regional metamorphism occurred between 1 75 and 1 71 ga mineral compositions of the first metamorphism including those of monazite were significantly disturbed by the second event these two regional metamorphic episodes were most likely linked to assembly and breakup of the supercontinent columbia respectively

east pacific ocean eddies and their relationship to subseasonal variability in central american wind jets subseasonal variability in sea surface height ssh over the east pacific warm pool off central america is investigated using satellite observations and an eddy resolving ocean general circulation model ssh variability is organized into two southwest tilted bands on the northwest flank of the tehuantepec and papagayo wind jets and collocated with the thermocline troughs eddy like features of wavelength similar to 600 km propagate southwestward along the high variance bands at a speed of 9 13 cm s wind fluctuations are important for eddy formation in the gulf of tehuantepec with a recurring interval of 40 90 days when forced by satellite wind observations the model reproduces the two high variance bands and the phase propagation of the tehuantepec eddies our observational analysis and model simulation suggest the following evolution of the tehuantepec eddies on the subseasonal timescale in response to the gap wind intensification a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks an energetics analysis based on the model simulation indicates that besides wind work barotropic and baroclinic instabilities of the mean flow are important for the eddy growth both observational and model results suggest a re intensification of the anticyclonic eddy in response to the subsequent wind jet event off papagayo ocean eddy formation is not well correlated with local wind jet variability in both the gulfs of tehuantepec and papagayo subseasonal ssh variability is preferentially excited on the northwest flank of the wind jet factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline 1 the role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments different scenarios include constant versus variable wind forcing and variations in bottom friction the three dimensional response of the shelf within the domain embayment enclosed by capes is associated with the generation of a velocity pycnocline disturbance at the upstream cape and its subsequent downstream advection this disturbance is more pronounced under variable wind conditions its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape when inertia dominates the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore the separation occurs at a low rossby number ro 0 15 which is attributed to the positive curvature of the coastline forming the cape when friction dominates the advection path is constrained along the coastline resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast isobaths simulations with spatially variable bottom friction with higher friction toward the coast result in the generation of eddy like features the numerical results are in agreement with both observations and surface temperature imagery from long bay south carolina an embayment enclosed by two capes and emphasize the role that coastline and associated shelf morphology can play in enhancing cross shelf transport and exchange

geochemistry zircon upb geochronology and luhf isotopic composition of eclogites and their host gneisses in the dulan area north qaidam uhp terrane new evidence for deep continental subduction abstract in this study we link zircon u pb shrimp and la icp ms geochronology and the lu hf isotopic composition of eclogites and their host gneisses schists with whole rock geochemistry of eclogites in the dulan area to constrain their protoliths and metamorphic relationships u pb dating suggests that the protolith of one of the eclogites was a neoproterozoic mafic intrusive rock 828 58 ma and the protolith of enclosing orthogneiss was an early neoproterozoic granitoid 923 12 ma detrital zircons from grt bearing mica schists yield ages of 0 9 2 5 ga with a dominant range of 1 0 1 8 ga indicating sedimentary sources from neoproterozoic to neoarchean crust and a depositional age 0 9 ga the matching metamorphic ages of eclogites 438 5 ma 436 4 ma and their country rocks grt bearing mica schists 438 4 ma 439 8 ma orthogneiss 427 8 ma indicate that all studied samples experienced coeval early paleozoic hp uhp metamorphism the u pb ages and hf isotopic compositions of the inherited magmatic zircon cores of an eclogite sample e hf 800 2 6 9 2 t dm1 1 0 1 3 ga t dm2 1 1 1 4 ga suggest that the protolith may be derived from neoproterozoic depleted mantle with variable proportions of an older crustal component the magmatic zircon cores of the orthogneiss e hf 900 7 3 to 0 2 t dm2 1 8 2 1 ga suggest that the parental magma was derived from a paleoproterozoic crustal source hf isotopic compositions of the detrital zircons from the metasediments e hf t 19 4 to 10 6 suggest three crust formation and reworking events 1 archean t dm2 2 7 2 9 ga juvenile crust reworked at 2 5 ga 2 early paleoproterozoic t dm2 2 3 2 5 ga juvenile crust reworked at 1 8 ga and 3 late paleoproterozoic t dm2 1 5 1 9 ga juvenile crust reworked in the neoproterozoic whole rock geochemical data suggest that the protoliths of the dulan eclogites were probably derived from a continental rift or an incipient oceanic basin rather than a large long lived ocean basin thus combined with field relationships petrology geochemistry zircon u pb dating and the lu hf isotopic analysis presented in this paper and reported from previous studies we suggest that the dulan eclogites and their country rocks experienced a common uhp metamorphism during late ordovician deep continental subduction

a comparison of mechanisms generating vertical transport in the brazilian coastal upwelling regions 1 several mechanisms can drive vertical velocities in the coastal ocean including wind forcing and through gradients in the vorticity field generated by flow topography interactions a two layer steady wind driven analytical model is applied to the major upwelling systems of brazil cabo frio cf and cabo de santa marta csm regions comparisons are made between the relative roles of wind and flow topography interaction in inducing upwelling over these regions ekman pumping is the weakest mechanism over the shelf but does influence the along shelf temperature in the cf area away from coastline irregularities wind driven upwelling ekman transport dominates over all mechanisms however in the vicinity of capes and coastal features topographically driven upwelling plays a significant role and its transports may vary from 43 to 94 of wind driven upwelling upstream of capes topographically driven vertical motions are downwelling favorable and act against the wind driven coastal upwelling while downstream of capes they are upwelling favorable where all mechanisms add up to create strong upwelling peaks in total upwelling in the cf region are about twice as large as those in the csm area because the cf region has stronger winds and larger coastline perturbations than in the csm region observed sea surface temperatures sst agree well with variability in the vertical transports where upwelling peaks are in phase with low temperature peaks along the coast results suggest that on larger scales the sst variability along the coast is mainly controlled by wind driven upwelling while upwelling due to flow topography interaction is responsible for the smaller scale sst variability

alongshore momentum balance analysis on a cuspate foreland 1 nearshore measurements of waves and currents off cape hatteras north carolina u s a are used to investigate depth averaged subtidal circulation and alongshore momentum balances in the surf and inner shelf region around a cuspate foreland data were collected on both sides of the cape representing shorefaces with contrasting shoreline orientation north south vs northwest southeast subjected to the same wind forcing in the nearshore the subtidal flow is aligned with the local coastline orientation while at the cape point the flow is along the existing submerged shoal suggesting that cape associated shoals may act as an extension of the coastline alongshore momentum balance analysis incorporating wave current interaction by including vortex and stokes coriolis forces reveals that in deep waters surface and bottom stress are almost in balance in shallower waters the balance is complex as nonlinear advection and vortex force become important furthermore linearized momentum balance analysis suggests that the vortex force can be of the same order as wind and wave forcing farther southwest of cape hatteras point wind and wave forcing alone fail to fully explain subtidal flow variability and it is shown that alongshore pressure gradient as a response to the wind forcing can close the momentum balance adjacent tide gauge data suggest that the magnitude of pressure gradient depends on the relative orientation of local coastline to the wind vector and in a depth averaged sense the pressure gradient generation due to change in coastline orientation even at km length scale is analogous to the effect of alongshore variable winds on a straight coastline

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

late mio pliocene landscape evolution around the chaka basin in the ne tibetan plateau insights from geochemical perspectives abstract the present ne tibetan plateau is characterized by a rugged mountain range and basin landforms knowledge of the landscape evolution as recorded by basin sediments will help to understand the growth history of the ne tibetan plateau our present contribution targeted the neogene chaka basin south of the qinghai nan shan and reports 40 geochemical sr nd trace element and rare earth element ree results of the sediments values of end vary from 15 6 to 11 6 for all samples but end is higher for samples younger than 5 5 ma 87sr 86sr ratios are all between 0 71441 and 0 71844 with the variation becoming less after 4 5 ma little variation in the sr nd isotopes and in the ree trend indicates that the source regions have very similar geochemical features the contribution of aeolian loess into the basin sediments after 3 5 ma is also speculated from the trace element and ree results these geochemical results reveal a change in the source region to the qinghai nan shan around 4 5 5 5 ma which is consistent with previous lithoface evidence since 3 5 ma landscape and topographic relief were further developed thus aeolian loess was deposited onto the fluvial fans south of the qinghai nan shan while global cooling and aridification began to dominate collectively our present geochemical study of the chaka basin sediments reveals stages of landscape evolution in ne tibet since the late miocene

sensitivity of the northern humboldt current system nearshore modeled circulation to initial and boundary conditions 1 the influence of the eastern pacific equatorial circulation on the dynamics of the northern humboldt current system is studied using an eddy resolving regional circulation model forced by boundary conditions from three distinct ocean general circulation models the seasonal variability of the modeled nearshore circulation and the mesoscale activity are contrasted in order to evaluate the role of the density forcing the seasonal variability of the surface and subsurface alongshore currents strongly depends on the amplitude and timing of the seasonal eastward propagating equatorial waves the equatorward flow and upwelling intensity are also impacted by nonlinear processes such as the seasonal generation of nearshore mesoscale eddies which create alongshore pressure gradients modulating the surface current boundary conditions affect differently the intensity and phase of the eddy kinetic energy as baroclinic instability is triggered by coastal waves during austral summer and fall whereas it is sustained by the wind driven upwelling during austral winter

kilometer scale chemical reaction boundary patterns and deformation in sedimentary rocks abstract we use three dimensional 3d seismic data to image patterns developed by kilometer scale chemical reaction boundaries to demonstrate that chemical patterns are scaleable phenomena the patterns develop in biosiliceous marine successions due to the dissolution of opal a biogenic silica and reprecipitation as opal ct crystobalite and tridymite during burial the reaction boundary patterns comprise roughly circular regions where the reaction boundary has preferentially advanced these regions are up to 2 7 km wide and c 50 200 m in height and are termed cells the cells form by amalgamation with adjacent juvenile cells they also form by the incorporation of much smaller regions surrounding the cells where the chemical change has already occurred that we term satellites 50 m wide the reaction results in enhanced rates of sediment compaction hence differential advancement of reaction boundaries causes differential subsidence of the overburden inducing folding and faulting of the overburden above the cellular promontories we propose three potential mechanisms for the development of kilometer scale reaction boundary patterns a mass transport of silica by advection b perturbation of isotherms as a result of convective or conductive heat transport or c establishment of a positive feedback loop between fluid production due to the reaction hydraulic fracturing and the upward and lateral transport of fluids this study provides the first insights into how strongly patterned diagenetic reaction boundaries evolve at a basin scale an initial conceptualization of the potential range of reaction boundary morphologies that could exist in this diagenetic system and the likely mechanisms that could control them furthermore it demonstrates that the discipline of seismic diagenesis could represent a completely new approach for the study of chemical diagenetic processes in sedimentary rocks

shallow water currents during hurricane andrew oceanographic measurements are used in combination with a numerical model to examine the influence of stratification on shallow water currents during the directly forced stage of a tropical cyclone hurricane andrew on the continental shelf the following stratification dependent coastal processes are examined 1 turbulent mixing 2 coastally trapped waves 3 near inertial oscillations and 4 upwelling and downwelling turbulent mixing was strong within 1 rw radius of maximum winds of the storm track and stratification was nearly destroyed turbulent mixing was weak at distances greater than 2 rw the dominant coastal wave was a barotropic kelvin wave generated as the storm surge relaxed after landfall baroclinic near inertial oscillations were dominant at the shelf break and occurred along with a barotropic response on the middle shelf downwelling favorable flow developed east of the track prior to the storm peak and upwelling favorable flow evolved west of the track as the eye crossed the shelf the idealized storm flow was modified by local barotropic and baroclinic pressure gradients on the shelf ocean circulation during hurricane andrew was hindcast using both stratified and unstratified three dimensional numerical models for areas within 1 rw of the storm track the unstratified model matched the observed currents better than the stratified model partly because of errors in the initial stratification at distances greater than 2 rw the influence of stratification increases and the unstratified model does not reproduce the observed upwelling favorable flow

reprint of comparison of modern fluid distribution pressure and flow in sediments associated with anticlines growing in deepwater brunei and continental environments iran abstract differences in fluids origin creation of overpressure and migration are compared for end member neogene fold and thrust environments the deepwater region offshore brunei shale detachment and the onshore arid central basin of iran salt detachment variations in overpressure mechanism arise from a the availability of water trapped in pore space during early burial deepwater marine environment vs arid continental environment and b the depth temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development chemical reactions associated with smectite rich mud rocks in iran occur shallow 1900 m smectite to illite transformation causing load transfer related moderate overpressures whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore brunei the basal detachment in deepwater brunei generally lies below temperatures of about 150 c where chemical processes and metagenesis are inferred to drive overpressure development overall the deepwater brunei system is very water rich and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines the result is a wide variety of fluid migration pathways and structures from deep to shallow levels particularly mud dykes sills laccoliths volcanoes and pipes fluid escape pipes crestal normal faults thrust faults and widespread inflationary type overpressure in the central basin the near surface environment is water limited mechanical and chemical compaction led to moderate overpressure development above the upper red formation evaporites only below thick early miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms fluid leakage episodes across the evaporites have either been very few or absent in most areas locations where leakage can episodically occur e g detaching thrusts deep normal faults salt welds are sparse however in both iran and brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds

petrology geochemistry zircon u pb dating and lu hf isotope of granitic leucosomes within felsic gneiss from the north qaidam uhp terrane constraints on the timing and nature of partial melting abstract granitic leucosomes are widely distributed within felsic gneiss in the north qaidam ultrahigh pressure uhp metamorphic terrane in western china which is crucial to understanding the relationships between partial melting metamorphic evolution and orogenic processes we have applied petrology whole rock geochemistry and sr nd isotope zircon u pb geochronology trace element composition and lu hf isotope of these granitic leucosomes to determine the nature and timing of partial melting of these rocks anatexis of the felsic gneiss is evidenced by 1 highly cuspate elongated feldspar grains along quartz quartz and quartz feldspar boundaries 2 cuspate wedge shaped pockets of k feldspar quartz plagioclase muscovite along the boundaries of quartz and or plagioclase and 3 felsic veinlets of k feldspar quartz plagioclase muscovite along grain boundaries major elements feo t mno mgo and tio 2 as well as lrees hrees and hfses are mainly retained in the melanosomes whereas the large ion lithophile elements liles e g rb ba k sr pb are preferentially partitioned into the granitic leucosomes three discrete u pb ages are recorded in the zoned zircons from the melanosomes and granitic leucosomes the inherited magmatic pre metamorphic zircon cores from melanosomes and granitic leucosomes contain quartz feldspar inclusions and record a neoproterozoic protolith age of approximately 950 ma the unzoned zircon mantles in the melanosomes and granitic leucosomes show characteristics similar to metamorphic zircons in terms of such as remarkably flat heavy rare earth element hree patterns an absence of obviously negative eu anomalies and low th u ratios these zircon mantles record an eclogite facies metamorphic age of 444 449 ma the last discrete age at 433 435 ma is preserved in anatectic zircon rims which display pronounced oscillatory zoning and contain felsic mineral inclusions of k feldspar plagioclase quartz the anatectic zircons have negative eu anomalies and pronounced positive ce anomalies and their low th u ratios and lu hf isotope features that are indistinguishable from those of the metamorphic domains the similarity in lu hf signatures indicates a closed system whereby no hf was added either from the outside via fluids or surprisingly from the pre metamorphic cores during partial melting muscovite relicts coexist with cuspate feldspars in the granitic leucosomes suggesting that the anatectic melts originate from dehydration melting due to breakdown of the muscovite in the felsic gneiss in conclusion an integrated study of the petrology geochronology and geochemistry demonstrates that partial melting of felsic gneiss in the nqd uhp terrane could mainly occurred during the initial retrogression stage and anatectic melt crystallized probably under granulite facies conditions

opening mode fracture in siliceous mudstone at high homologous temperature effect of surface forces in analogy to high temperature sintering of ceramics and metal powder compacts the formation of opening mode fractures in siliceous mudstone during natural in situ combustion of hydrocarbons is attributed to contractile surface forces between mineral grains and an interstitial melt phase a comparison between bulk density increase during sintering and created fracture space indicates that fracturing resulted from contraction of the rock matrix due to porosity reduction grain scale mass transfer and high temperature mineral formation it is suggested that contractile surface forces between mineral grains and between mineral grains and pore fluid contribute to subcritical fracture formation under a wide range of subsurface conditions

hualong complex south qilian terrane u pb and lu hf constraints on neoproterozoic micro continental fragments accreted to the northern proto tethyan margin abstract the neoproterozoic hualong complex dominates the south qilian terrane it contains mafic to felsic magmatic rocks cherts and turbiditic sediments some of which have been metamorphosed to amphibolite grade and is traditionally regarded as a pre cambrian micro continental block rifted from the south china plate new u pb geochronology of morphologically complex zircons sheds light on the history of the complex garnet bearing amphibolite and quartzite have detrital zircon u pb main peak ages of 1 47 1 78 ga with youngest u pb ages of 967 ma and 964 ma they are intruded by neoproterozoic orthogneisses that crystallized between ca 850 and 940 ma psammitic paragneisses are dominated by 940 780 ma detrital zircon populations with a youngest u pb weighted mean age of 721 3 ma and a main peak at 906 ma metamorphic overgrowths on older zircons record amphibolite facies metamorphism of the hualong complex and correspond to the emplacement of the younger plutonic rocks during the early paleozoic northward subduction of proto tethyan oceanic lithosphere 426 ma and 455 ma detrital zircon populations that originated from synkinematic granitoids dominate quartz mica schist negative to positive hf t values for both 940 850 ma granitic orthogneisses and intruding 460 410 ma granites suggest a crustal mantle mixture source hf t dm1 model ages and inherited zircon u pb ages are the same as those for garnet bearing amphibolites and psammitic gneiss indicating that late magmatic rocks were formed by melting of the accreted neoproterozoic rocks

provenance record of a foreland basin detrital zircon u pb ages from devonian strata in the north qilian orogenic belt china abstract devonian strata in the north qilian belt of the qilian orogen accumulated in a foreland basin formed through collision between the north china craton and the central qilian belt u pb age data for 393 detrital zircons from four sandstone samples from the lower to middle devonian laojunshan formation and upper devonian shaliushui formation range in age from 3 6 ga to 0 4 ga and indicate input from a multi component source detrital zircons older than the early mesoproterozoic 1 4 ga were likely derived from the north china craton whereas late mesoproterozoic to neoproterozoic zircons were derived from the central qilian belt early paleozoic zircons were derived from the north qilian continental arc and associated ophiolites the occurrence of neoproterozoic zircons indicates that their source the central qilian belt was likely once part of the yangtze block of the south china craton prior to its separation from the craton in the late neoproterozoic

lead isotope variability of fine grained river sediments in tibetan plateau water catchments implications for geochemical provinces and crustal evolution abstract the crustal structure of the tibetan plateau records the dynamic processes of several terranes that underwent disaggregation aggregation and amalgamation the dynamic evolution of continental crusts is best understood from these three processes however the detailed geochemical province division of the tibetan plateau and the palaeo tectonic affinity or evolution of terranes remains unclear in this paper the acid insoluble fraction of fine grained river sediments from catchments in the whole tibetan plateau was measured for lead isotopes and trace elements this study aims to reveal lead isotopic characteristics to delineate different lead isotope geochemical provinces and to trace and uncover the tectonic affinities of various terranes in the tibetan plateau results show that by weak acid chemical treatment the characteristics of the pb isotopes of fine grained river sediments can be utilized to represent and discriminate geochemical provinces the characteristics of pb isotopes enable the identification of different geochemical provinces and the palaeo affinity of various tectonic units constrained by tectonic evolution the tibetan plateau tectonic units can be divided into the following five pb isotope geochemical provinces 1 qilian terrane 2 northern tibetan plateau geochemical province including eastern kunlun qaidam songpan ganzi and eastern qiangtang terrane 3 northern lhasa terrane 4 southern lhasa terrane and 5 himalaya terrane in relation to the controversy concerning the palaeo affinity of the qilian and songpan ganzi terranes the pb isotopic compositions of fine grained river sediments suggest that they were much more likely separated from the yangtze craton than from the north china craton the characteristics of pb isotopes and trace elements of the eastern kunlun qaidam and eastern qiangtang terrane show some similarities with the songpan ganzi terrane which indicate that they also possibly originated from the disaggregation of the yangtze craton the various partial melting and contamination of the old himalaya continental crust from radiogenic pb isotopes and tethys mantle materials with low radiogenic pb isotopes caused different pb isotopes and trace elemental associations in the southern and northern lhasa terranes these factors also led to the evolution of the two different geochemical provinces

displacement field in contraction driven faults we investigate the distribution of strain and deformation in the host sediment that arises once a contraction driven shear fault has localized and propagated under a zero lateral strain condition numerical modeling of displacement distributions compares well with those measured using 3d seismic data the parameters that determine the displacement field for a single normal fault embedded in sediments are fault height overburden effective stress stiffness and residual friction angle or post peak strength proximity to the free boundary biases the displacement pattern which becomes asymmetric although the measured displacements and numerical predictions are similar the measured magnitude requires pronounced low stiffness of the sediment as well as low post peak shear strength this requirement suggests that sediments hosting contraction driven shear faults most likely have high porosity and high clay fraction and have undergone diagenetic reactions involving significant mineral dissolution the diagenetic evolution of the sediment and its current composition may explain the global scaling relationship between the measured displacement and fault height for polygonal fault systems

dissolution of randomly distributed soluble grains post dissolution k 0 loading and shear sediments experience mineral dissolution in most natural settings and as a result of engineered processes such as carbon dioxide injection the consequences of mineral dissolution are studied usin

comparison of isotopic and petrographic provenance indicators in sediments from tertiary continental basins of new mexico abstract isotopic variations of nd in sedimentary rocks provide a new tool for provenance determination we have compared the isotopic technique with classic petrographic indicators of provenance in sediments from two tertiary basins of the rio grande rift north central new mexico the siliciclastic sediments in these basins were derived from varying proportions of precambrian basement and oligocene volcanic rocks which are isotopically and petrographically distinct in the analyzed sediments a good correspondence exists between petrographic and isotopic provenance indicators the data also suggest that the isotopic tracer is more sensitive to minor detrital input from a second source than is the framework petrology the similar sm nd ratios for all analyzed sediments and the identical isot pic values of interlayered mudstone and sandstone indicate that no significant fractionation of sm and nd occurs during the formation of the sediments thus the nd model ages of the sediments preserve the crust formation age of the source the sr isotopic and concentration data show trends generally similar to the nd data but they do not indicate the sedimentary provenance as clearly this ambiguity is a consequence of strong rb sr source heterogeneities and rb sr fractionation during the sedimentary cycle

from subduction to collision in the northern tibetan plateau evidence from the early silurian clastic rocks northwestern china abstractthe qilian orogen records early paleozoic collisional suturing of the qaidam block and the central qilian block to the north china craton the composition and u pb age of detrital zircons and the composition of cr spinels from the early silurian lujiaogou and angzanggou formations in the northern part of orogen indicate derivation from evolving oceanic and continental source terranes heavy mineral chemistry indicates the incorporation of suprasubduction zone type ophiolitic detritus in addition to continent derived material integrating these chemical and age data with regional data on the duration of subduction related magmatic activity syn and postcollisional granitic rocks and high pressure metamorphic rocks constrains the transformation from oceanic subduction to continental collision to 450 440 ma the collision resulted in a flood of detritus into the northern part of the orogen from the central qilian block which masked input from the intervening magmatic arc implying rapid exposure o

seismic analysis of polygonal fault systems in the great south basin new zealand abstract polygonal fault systems pfs consisting of networks of layer bound normal faults are analyzed for eocene strata in the great south basin new zealand an advanced fault enhancement and skeletonization method is applied to delineate faults using 3d seismic data from the great south basin the process sharpens structural and stratigraphic discontinuities and smears the incoherent noise on coherence to obtain a skeletonized fault probability volume which can be directly used to extract and map fault geometries the characteristics of the polygonal faults in cross section planform and 3d space were studied the faults dip approximately 50 with displacements on a single fault ranging from tens of meters to a hundred meters the fault planform patterns are polygonal but also related to the regional horizontal stress anisotropy caused by slope changes of the basal unit the patterns vary from linear for high slopes rectangular for moderate slopes and polygonal for low slopes two preferred orientations may reflect the superposition of deep cretaceous trends on the polygonal system in the eocene strata a local concentric pattern with outward dipping normal faults is related to passive or active draping above a circular plutonic volcanic structure the genetic mechanism of the polygonal fault systems is interpreted to be related to volume loss and shear failure related to opal a ct transition within the sediments

corrigendum 146 sm 142 nd evidence from isua metamorphosed sediments for early differentiation of the earth s mantle nature 423 428 432 2003 in this letter the subscripts l and k were accidentally transposed so coefficient a in equation 4 should have read

record of multiple stage channelized fluid and melt activities in deeply subducted slab from zircon u pb age and hf o isotope compositions abstract geochemical features of island arc rocks require two slab derived components of a melt and a fluid added to their sources these two liquids may unite to an intermediate aqueous melt at the base of volcanic arc direct evidence of this process has been scarce yet here we present an integrated study of in situ u pb age trace element and o hf isotope for zircons from a suite of a quartz vein a felsic vein their host eclogite and surrounding gneiss at the xitieshan uhp terrane of the north qaidam metamorphic belt nqmb oscillatory zoned zircons from the quartz vein are enriched in u li nb and ree with a formation age of 442 6 ma consistent with the timing of the peak uhp metamorphism this demonstrates there is no temporal gap between the uhp metamorphism and fluid flow in the xitieshan terrane in particular the oscillatory zoned zircons of the quartz vein have similar hf isotope compositions to zircons from the surrounding gneiss but variable o isotope compositions between the host eclogite and surrounding gneiss the fluid from surrounded gneiss was thus an aqueous melt with high transport ability for lu and hf and o while the fluid from the host eclogite was an aqueous fluid only with the ability to transport o according to the similar behaviors of granitic rock and sediment it is inferred that a channelized hydrous melt can be formed in the downgoing sediment layer where an aqueous fluid can be formed from underlying basalt and or peridotite layers at the sub arc depth the two types of fluid are fed to the overlying mantle wedge from subducting slab to form island arc rock by contrast the zircons in the felsic vein yield a weighted mean 206pb 238u age of 420 4 ma which can be regard as the timing of partial melting during the exhumed stage for the xitieshan uhp rocks the zircon o and hf isotopic features of the felsic vein are between the country gneiss and host eclogite compatible with their emanating from hydrous melt of both the eclogite and gneiss during the exhumation stage of the uhp rocks this indicates that hydrous melt would be released from both the sediment and basalt or peridotite layers of the subducting slabs at relatively shallow depth

provenance of eclogitic metasediments in the north qilian hp lt metamorphic terrane western china geodynamic implications for early paleozoic subduction erosion abstract in this contribution we present new petrological geochemical zircon u pb and hf isotopic data for eclogitic metasediments from the north qilian orogenic belt in which early paleozoic ophiolitic sequences and hp lt metamorphic rocks have been previously recognized the studied metasediments contain eclogite facies assemblages reflecting p t conditions of 450 560 c and 1 9 2 4 gpa consistent with those of adjacent eclogites ree compositions of the eclogitic metasediments overlap those of average upper continental crust the shrimp and la mc icpms u pb data of zircons from metasediments demonstrate input from sources with major age components about 500 ma and 1600 1900 ma peak at 1800 ma with a smaller population at 660 800 ma peak at 750 ma and minor 1 9 ga zircon ages the youngest detrital zircons suggest a maximum depositional age of ca 475 ma and combined with p t conditions and previously determined metamorphic age suggest a burial rate of 0 6 0 7 cm yr zircon hf isotopic analyses show that 500 ma zircons have positive ehf t mainly between 8 and 16 by contrast meso to paleoproterozoic detrital zircons show a broad spectrum of ehf t mainly between 5 and 10 with t dm hf of 1800 2500 ma these data suggest that eclogitic metasediments are derived from a mixture of proterozoic continent crust and juvenile early paleozoic oceanic and or island arc crust and their protoliths likely were deposited in a terrigenous dominated continental margin basin rather than a pelagic oceanic crust environment the new results are consistent with subduction erosion of the active continental margin during south dipping subduction as these sediments formed in a fore arc environment close to the qilian block to the south were transported in the subduction zone to 60 70 km depth prior to their exhumation

melting of subducted continental crust during collision and exhumation insights from granitic rocks from the north qaidam uhp metamorphic belt nw china abstract the formation and reworking of continental crust have close connections with orogeny syn and post collisional magmatism is key to understanding crustal growth and reworking during continental collision and post collisional extension here we report a series of syn collisional felsic magmatic rocks intruded into migmatized gneiss and amphibolite eclogite in the north qaidam ultrahigh pressure uhp metamorphic belt to provide insights into melting reworking of uhp metamorphosed continental crust during continental collision and exhumation the syn collisional magmas are mainly tonalite trondhjemite and mica granite that occur as plutons and dykes and high potassium granite veins in migmatites they were formed by decompression melting of subducted oceanic and continental crust at different levels during exhumation without any discernible mantle contribution the tonalite trondhjemites show adakitic signatures of both oceanic crust and mafic continental crust with varying nd isotopic compositions the mica granite plutons have high silica and alkali contents are weakly to strongly peraluminous and have crustal sr nd isotope compositions these mica granites were formed by partial melting of previously subducted continental crust and formed mostly in high pressure conditions in the garnet stability field the protolith is predominantly granitic gneiss with minor meta sediment and metabasite a compilation of published ages and our results show that these syn collisional magmatic rocks formed between 437 and 397 ma overlapping with uhp metamorphic ages 440 420 ma and suggests that exhumation occurred synchronously with continental subduction individual zircon grains show metamorphic cores and magmatic rims with a 20 myr time interval interpreted as the time between peak uhp metamorphism and melting during exhumation such long lived and episodic melting of uhp metamorphic continental crust should result from periodic processes involving melt weakening and decompression by upward movement within the subduction channel rather than coherent motion of the entire uhp belt this process represents crustal reworking during collision and exhumation without input of mantle melts

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

the early paleozoic xitieshan syn collisional granite in the north qaidam ultrahigh pressure metamorphic belt nw china petrogenesis and implications for continental crust growth abstract syn collisional magmatism produced by partial melting of subducted oceanic and continental crust during the continental collision plays an important role in understanding the orogenic evolution and crustal growth this contribution reports zircon la icpms u pb ages and hf isotopic compositions whole rock major and trace elements and sr nd isotopic compositions of syn collisional xitieshan intrusion within the north qaidam ultrahigh pressure metamorphic uhpm belt to study its petrogenesis and contribution to continental crust growth la icpms zircon u pb dating of the xitieshan granite yields magmatic crystallization ages of 441 2 ma and 442 2 ma which are consistent with the peak age of ultrahigh pressure eclogite facies metamorphism in the xiteishan terrane the temporal correlation between them confirms that the xitieshan granite was products of syn collisional magmatism during the continental collision between qaidam and qilian blocks these granites show high k calc alkaline and slightly peraluminous signature low zirconium saturation temperatures and high contents of k2o with the s type characteristics they have rare earth element and trace element patterns resembling those of bulk continental crust with strong fractionation of light and heavy rare earth elements la yb n 19 26 moderately eu negative anomalies eu 0 65 0 71 and the obviously nb ta p and ti negative anomalies the xitieshan granite also exhibits remarkable sr nd isotopic differences initial 87sr 86sr 0 70920 0 71080 and end t 4 54 4 11 from the contemporaneous granites within north qaidam uhpm belt combined with the positive ehf t 0 5 5 3 and ages of inherited zircons 475 518 ma the magmatism is best explained as resulting from melting of subducted oceanic and continental crust during continental collision isotopic mixing calculations suggest that ca 28 35 ocean crust and ca 65 72 continental materials contribute to the origin of the xitieshan granite thus the syn collisional felsic magmatism represents juvenile crust with input of oceanic crustal materials derived from the depleted mantle and the hypothesis continental collision zones are primary sites for net continental crust growth is applicable in the north qaidam

post collisional magmatism consequences of uhpm terrane exhumation and orogen collapse n qaidam uhpm belt nw china exhumation of subducted slabs and extensional collapse of orogens are the main tectonic processes in ancient and modern continental collisional zones magmatism during these two processes may play important roles in understanding reworking and growth of the continental crust we report here that a series of plutonic magmas including intrusions of two mica granite tonalite granodiorite biotite monzogranite porphyritic biotite granite and diorite as well as contemporaneous mafic dykes have been recognized in dulan edogite bearing terrane the north qaidam ultra high pressure metamorphic uhpm belt the magmatism represented by these plutons is temporally similar to 20 30 million years mys younger than the uhpm age lasting for similar to 40 mys and derived from different sources with different mechanisms the magmatism was initiated by exhumation of uhpm terranes during which strongly peraluminous two mica granite and metaluminous tonalite were produced respectively by decompression melting of the exhumed uhpm upper and lower continental crust respectively the genesis of mafic magmatic enclave mme hosting granodiorite with a clear hybrid signature and coeval biotite monzogranite reflected the upwelling of asthenospheric mantle by extension of lithosphere during the orogen collapse it was induced by detachment of the subducted lithospheric mantle which then brought heat and mantle material into continental crust and triggered the partial melting of the exhumed uhpm continental crust and gave rise to mixing of crustal and mantle melts porphyritic biotite granite reflects a late melting event of continental crust diorite marked by high magnesium content represents mantle melts with slight crustal contamination which implies that the orogen has been unrooted and collapsed completely the post collisional magmatism of the north qaidam belt provides an improved understanding for the late thermal and tectonic evolution of a uhpm continental collision zone c 2014 elsevier b v all rights reserved

structural and stratigraphic controls on subsurface fluid flow at the veslemoy high sw barents sea abstract subsurface and seafloor fluid flow anomalies are gaining large interest after the finding of five new hydrocarbon discoveries and observation of large gas flares in the sw barents sea in the present study we have analysed structural and stratigraphic controls on fluid flow towards the seafloor using gravity cores selected based on subsurface gas anomalies observed on seismic data from the veslemoy high sw barents sea the subsurface fluid flow at the veslemoy high is observed to be controlled by 1 the morphology and orientation of regional faults structural highs and sedimentary basins 2 the presence of paleocene silica ooze deposits that changes microstructure with temperature thereby controlling fluid flow and 3 the location of regional and local open faults formed by glacial loading and unloading analysis of extractable organic matter in subsurface holocene sediments corroborates the active migration pathways inferred from seismic data micropalaeontological studies on benthic foraminifera reveal methane seep associated assemblages that confirm the interpretation of subsurface gas anomalies in seismic data we ultimately link these new results to the geological evolution history of the region to give a comprehensive model for the fluid flow system within the study area

smnd isotopic geochemistry of sediments from taiwan and implications for the tectonic evolution of southeast china abstract an isotopic and geochemical study on the miocene to late paleozoic sediments and metasediments of taiwan has been conducted in order to decipher the crustal evolution of se china with the exception of a few late paleozoic sediments most samples from taiwan have a narrow range in sr and nd isotopic ratios and sm nd crustal residence ages t dm assuming derivation from a depleted mantle source the isotopic characteristics are similar to those of suspended material from major rivers around the world in particular they closely resemble those reported for the yangtze river sediment and the pre cretaceous granitoids of se china no obvious trend in t dm or isotopic ratios has been found with respect to the depositional ages indicating no pronounced secular variation however a few late paleozoic samples might have been influenced by fresh mantle inputs to their provenance proterozoic t dm of the sediments combined with proterozoic pb components in zircons from taiwan s granitoids suggest that important crustal growth in se china took place in the middle proterozoic the isotopic and geochemical characteristics of the sediments suggest that their sources were primarily recycled pre existing continental crust ree contents of taiwan sediments measured in this study are similar to the suspended load in major rivers paas post archean average australia shale nasc north american shale composite and the continental shelf slope sediments from the east china sea off the mouth of the yangtze they seem to represent products derived from typical continental crust lower hree abundances in taiwan sediments suspended load in major rivers and surface sediments from the e china sea than those of paas suggest that the source of hree in paas is likely to be slightly different from that for these recent terrigenous sediments an alternative for the explanation of this hree discrepancy is that a certain proportion of hree in these recent sediments were left in the residue partially dissolution of heavy mineral in analysis procedures particularly zircon even in a teflon bomb might cause this hree discrepancy late yanshanian granitoids now widely exposed on the se china coast have higher nd and lower sr isotopic ratios than those for taiwan s sediments so these granitic intrusions were not a major source for the sediments indicating that they were not exposed to erosion until the miocene or later

the dynamics of the sicily strait a comprehensive study from observations and models abstract the dynamics of the sicily strait are investigated in a comprehensive study using recent in situ observations ocean general circulation model ogcm simulations and process model results in particular results of a very high resolution mediterranean model med16 developed in the context of the mercator project are described the circulation in the sicily strait can be described as a two layer exchange of atlantic water aw and eastern mediterranean outflow water eow the algerian current brings aw the upper layer eastwards and splits into two branches at the entrance to the sicily strait one flowing to the tyrrhenian sea the other into the sicily strait the later is composed of two streams referred to as the atlantic ionian stream ais and the atlantic tunisian current atc in winter the atc signature is more pronounced in summer the ais is associated with a number of well known semi permanent features including the intermittent northward extension of the ais called nais at the ionian shelf break which seems to be driven by the surface density contrast between waters of the sicilian and the ionian basins new intermittent patterns are shown by the med16 simulations for example an anticyclonic eddy called mca south of the malta channel and an anticyclonic gyre associated to the nais called naisa upwelling is well developed in august with temperature lower than 24 c along the western and southern coasts of sicily the seasonal transport of the aw through the strait has a maximum value 1 4 sv in winter and a minimum value at the end of summer 0 8 sv in the lower layer at the exit of the sicily strait the eow mainly composed of levantine intermediate water liw outflows into the tyrrhenian sea and veers to the right then as well known the liw flows along the northern coast of sicily before reaching the sardinia channel a new liw path from the sicily strait towards the sardinia channel is shown by the med16 model and is due to intermediate eddy shedding at the exit of the sicily strait the topography of the sill in the sicily strait plays a major role in the circulation a combination of barotropic baroclinic double kelvin waves on both side of the sill provides a mechanism for splitting the algerian current