mesozoic geology of southwestern china indosinian foreland overthrusting and subsequent deformation abstract the southwestern part of the south china block scb records triassic and subsequent deformations and is a key region that provides evidence of the post amalgamation tectonic evolution of southeast asia here we outline the tectonothermal evolution of early mesozoic orogenesis in this region using structural analysis and fission track thermochronology this region is divided into three tectonic units south to north the youjiang fold and thrust belt yftb the qianzhong massif qzm and the thin skinned thrust belt ttb of the southeastern sichuan basin all three of which record three deformation events here termed d 1 d 2 and d 3 d 1 deformation is represented by triassic top to the north thrusts f 1 and fault related folds f 1 that are indicative of n s shortening the intensity of deformation decreases toward the north the subsequent d 2 and d 3 deformations are marked by cretaceous top to the nw thrusting and fault propagation folding and cenozoic ne sw trending normal faults f 3 respectively the temperature time t t path obtained by apatite fission track modeling of samples from the yftb qzm and ttb areas provides evidence of uplift and denudation the d 1 deformation at 230 210 ma is characterized by buried thrusts within the relatively stable yftb and qzm and an increase in depth of the ttb this was coeval with the late triassic northward migration of uplift and denudation that is evidenced by a late triassic stratigraphic gap within the yftb a thin layer of coarse grained continental clastics within the qzm and a thick layer of clastic rocks within the ttb the study area records a triassic thrust system d 1 that progressively migrated northwards and represents a foreland fold and thrust belt that formed during the indochina scb collision this initial deformation was subsequently overprinted by late jurassic to cretaceous nw se thrusting d 2 and the development of cenozoic nw se extensional structures d 3

concurrent evolution of 3he 4he ratio in the earth s mantle reservoirs for the first 2 ga the differences in 3he 4he ratios between mid oceanic ridge basalts morbs and ocean island basalts oibs require the existence of at least two distinct mantle reservoirs that have been preserved over long periods of the earth s history however it is unclear how the 3he 4he ratios have evolved in the mantle over time and when these reservoirs acquired their present day signatures here we report the results of our model calculation for helium evolution in the mantle and show that from the time of the earth s formation to the late archean 2 ga the 3he 4he ratios in both the morb and oib mantle reservoirs evolved in a rather homogeneous fashion in contrast to previous models our model suggests that the distinction in 3he 4he ratios between the morb type source and the plume type source is a relatively recent characteristic of the earth s mantle

in situ sulfur isotope analysis of sulfide minerals by sims precision and accuracy with application to thermometry of 3 5 ga pilbara cherts abstract secondary ion mass spectrometry sims measurement of sulfur isotope ratios is a potentially powerful technique for in situ studies in many areas of earth and planetary science tests were performed to evaluate the accuracy and precision of sulfur isotope analysis by sims in a set of seven well characterized isotopically homogeneous natural sulfide standards the spot to spot and grain to grain precision for 34 s is 0 3 for chalcopyrite and pyrrhotite and 0 2 for pyrite 2sd using a 1 6 na primary beam that was focused to 10 m diameter with a gaussian beam density distribution likewise multiple 34 s measurements within single grains of sphalerite are within 0 3 however between individual sphalerite grains 34 s varies by up to 3 4 and the grain to grain precision is poor 1 7 n 20 measured values of 34 s correspond with analysis pit microstructures ranging from smooth surfaces for grains with high 34 s values to pronounced ripples and terraces in analysis pits from grains featuring low 34 s values electron backscatter diffraction ebsd shows that individual sphalerite grains are single crystals whereas crystal orientation varies from grain to grain the 3 4 variation in measured 34 s between individual grains of sphalerite is attributed to changes in instrumental bias caused by different crystal orientations with respect to the incident primary cs beam high 34 s values in sphalerite correlate to when the cs beam is parallel to the set of directions uuw from 111 to 110 which are preferred directions for channeling and focusing in diamond centered cubic crystals crystal orientation effects on instrumental bias were further detected in galena however as a result of the perfect cleavage along 100 crushed chips of galena are typically cube shaped and likely to be preferentially oriented thus crystal orientation effects on instrumental bias may be obscured test were made to improve the analytical precision of 34 s in sphalerite and the best results were achieved by either reducing the depth of the analysis pits using a kohler illuminated primary beam or by lowering the total impact energy from 20 kev to 13 kev the resulting grain to grain precision in 34 s improves from 1 7 to better than 0 6 2sd in both procedures with careful use of appropriate analytical conditions the accuracy of sims analysis for 34 s approaches 0 3 2sd for chalcopyrite pyrite and pyrrhotite and 0 6 for sphalerite measurements of 34 s in sub 20 m grains of pyrite and sphalerite in 3 5 ga cherts from the pilbara craton western australia show that this analytical technique is suitable for in situ sulfur isotope thermometry with 50 c accuracy in appropriate samples however sulfides are not isotopically equilibrated in analyzed samples

the primordial noble gases in the earth a key constraint on earth evolution models abstract we made an extensive compilation of noble gas data obtained from morb oceanic island basalts oib and diamonds on the basis of this data base we discuss the primordial noble gases in the earth and its implications on mantle evolution we conclude that in the contrary to a common assumption the primordial ne ar kr and xe in the earth are distinctly different from the solar noble gases the primordial noble gases were derived from the solar noble gas through rayleigh distillation like mass dependent fractionation the primordial ar kr xe are identical with the atmospheric components but ne observed in the mantle derived materials differs significantly from the atmospheric ne we suggest that ne was further fractionated in the atmosphere while the abundances of ar kr and xe in the mantle derived materials are well correlated to each other he and ne in morb is totally uncorrelated with the heavier noble gases this indicates that he and ne in morb is decoupled from the heavier noble gases in the mantle source he ne ar systematics indicate that he was open to the morb and oib mantle sources and ne in the morb mantle source while he is excess in the morb mantle source it is deficient in the oib mantle source relative to the closed system values however it is not known whether this apparent complementary characteristic corresponds to some fundamental mantle dynamics or accidental coincidence

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

on the role of infiltration and exfiltration in swash zone boundary layer dynamics boundary layer dynamics are investigated using a 2 d numerical model that solves the volume averaged reynolds averaged navier stokes equations with a vof tracking scheme and a k turbulence closure the model is validated with highly resolved data of dam break driven swash flows over gravel impermeable and permeable beds the spatial gradients of the velocity bed shear stress and turbulence intensity terms are investigated with reference to bottom boundary layer bl dynamics numerical results show that the mean vorticity responds to flow divergence convergence at the surface that result from accelerating decelerating portions of the flow bed shear stress and sinking injection of turbulence due to infiltration exfiltration hence the zero up crossing of the vorticity is employed as a proxy of the bl thickness inside the shallow swash zone flows during the uprush phase the bl develops almost instantaneously with bore arrival and fluctuates below the surface due to flow instabilities and related horizontal straining in contrast during the backwash phase the bl grows quasi linearly with less influence of surface induced forces however the infiltration produces a reduction of the maximum excursion and duration of the swash event these effects have important implications for the bl development the numerical results suggest that the bl growth rate deviates rapidly from a quasi linear trend if the infiltration is dominant during the initial backwash phase and the flat plate boundary layer theory may no longer be applicable under these conditions

multiple sulfur isotope constraints on sulfate driven anaerobic oxidation of methane evidence from authigenic pyrite in seepage areas of the south china sea abstract multiple sulfur isotope signatures and secondary ion mass spectroscopy sims sulfur isotope compositions of pyrite from two seafloor sites dh cl11 and hd109 in seepage areas of the south china sea were measured in order to study isotope effects of sulfate driven anaerobic oxidation of methane so 4 aom the multiple sulfur isotopes of pyrite reveal variable ranges for both sites 34 s between 44 1 and 2 9 for dh cl11 and between 43 8 and 1 6 for hd109 33 s between 0 02 and 0 17 for dh cl11 and between 0 03 and 0 14 for hd109 sims analysis reveals an extreme variability of 34 s values between 50 3 and 2 7 in dh cl11 between 50 1 and 52 4 in hd109 for three types of pyrite 1 framboids 2 zoned aggregates with radial overgrowth surrounding a framboidal core and 3 euhedral pyrite crystals the synchronous changes of geochemical proxies sulfate and methane concentrations 34 s sulfate and 18 o sulfate 34 s pyrite and pyrite content at the sulfate methane transition zone smtz at site dh cl11 are interpreted to be induced by so 4 aom under steady state conditions in contrast pyrite content and 34 s value fluctuations throughout core hd109 suggest that the sediment at this site was affected by multiple pyritization events during diagenesis multiple sulfur isotope signatures of early diagenetic pyrite i e with low and high 34 s values the latter above 315 cmbsf in dh cl11 above 70 cmbsf in hd109 in the upper sediment column suggest that organoclastic sulfate reduction osr and sulfur disproportionation generated the observed isotopic signatures in contrast to the early diagenetic 34 s depleted framboids the higher sims 34 s values of overgrowth and euhedral crystals suggest a late diagenetic 34 s enriched pool of dissolved sulfide derived from so 4 aom at the current and paleo smtzs interestingly pyrite resulting from so 4 aom in the smtz at site dh cl11 reveals a distinct pattern with higher 33 s values different from pyrite resulting from osr and sulfur disproportionation therefore paired 34 s and 33 s values may allow to differentiate osr and so 4 aom although a full understanding of the isotope effects associated with so 4 aom is hampered by uncertainties on the actual electron transfer mechanism in the syntrophic so 4 aom consortium

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

the early cambrian chahmir shale hosted zn pb deposit central iran an example of vent proximal sedex mineralization the chahmir zinc lead deposit 1 5 mt 6 zn 2 pb in central iran is one among several sedimentary exhalative zn pb deposits in the early cambrian zarigan chahmir basin e g koushk darreh dehu and zarigan the deposit is hosted by carbonaceous fine grained black siltstones and shales interlayered with volcaniclastic sandstone beds it corresponds to the upper part of the early cambrian volcano sedimentary sequence ecvss which was deposited on the posht e badam block during back arc rifting of the continental margin of central iran based on crosscutting relationships mineralogy and texture of sulfide mineralization four different facies can be distinguished stockwork feeder zone massive ore bedded ore and distal facies exhalites with barite silicification carbonatization sericitization and chloritization are the main wall rock alteration styles alteration intensity increases toward the proximal feeder zone fluid inclusion microthermometry was carried out on quartz associated with sulfides of the massive ore homogenization temperatures are in the range of 170 226 c and salinity is around 9 wt nacl eq the size distribution of pyrite framboids of the bedded ore facies suggests anoxic to locally suboxic event for the host basin 34s v cdt values of pyrite sphalerite and galena range from 10 9 to 29 8 the highest 34s values correspond to the bedded ore 28 6 to 29 8 and the lowest to the massive ore 10 9 to 14 7 and the feeder zone 11 3 and 12 1 the overall range of 34s is consistent with a sedimentary environment where sulfide sulfur was derived from two sources one of them was corresponding to early ore stage sulfides in bedded ore and distal facies consistent with bacterial reduction from coeval seawater sulfate in a closed or semiclosed basin however the 34s values of late ore stage sulfides observed mainly in massive ore interpreted as a hydrothermal sulfur component leached from the lower part of the ecvss sulfur isotopes along with the sedimentological textural mineralogical fluid inclusion and geochemical characteristics of the chahmir deposit are in agreement with a vent proximal selwyn type sedex ore deposit model

middle upper ordovician radiolarians in hunan and jiangxi provinces south china implications for the sedimentary environment and nature of the nanhua basin abstract the yanxi and duiershi formations of the middle upper ordovician in south china are composed of black grayish black and dark gray thin bedded cherts and siliceous slates rich in carbonaceous materials and pyrite horizontal beddings are developed the strata contain randomly distributed fossils radiolarians are discovered in the loudi yongzhou hengyang ji an and ganzhou sections the radiolaria from two sections are identified as protoentactinia sp abundances of radiolarian in the central area of hunan and jiangxi provinces are higher than in the southern area the strata become thickened while the amounts of siliceous materials are decreased and argillaceous contents are increased from northwest to southwest for the yanxi and duiershi formations the lithology gradually changes from carbonate rocks in the north to clastic rocks in the south 30si values of chert and siliceous slate range from 0 6 to 1 18 with al2o3 al2o3 fe2o3 mno tio2 lan cen ce ce and la yb n ratios of 0 65 0 97 0 01 0 16 0 99 1 27 0 85 1 10 and 0 91 1 66 respectively the sio2 and tio2 average contents are 89 08 and 0 27 the sio2 contents decrease while the tio2 increase from northwest to southeast they have similar the ree concentration with no obvious eu anomalies the yanxi and duiershi formations were deposited predominately in a bathyal environment on the continental slope basin and the seawater was stagnant in the middle early late ordovician the nanhua basin occupied a rather large area and sedimentary rocks in the region around hengyang ji an were deposited in the basin center with terrigenous source derived from the southeast

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

in situ sulfur isotope analysis by laser ablation mc icpms and a case study of the erlihe zn pb ore deposit qinling orogenic belt central china abstract sulfur isotopic composition is useful for tracing sources of ore forming materials in situ sulfur isotope analysis by laser ablation coupled with multi collector inductively coupled plasma mass spectrometry la mc icpms has an advantage over traditional bulk analysis in tracing sources of sulfur in an ore deposit that has complex mineral types and multiple ore forming processes however in using this method matrix effects exist widely for sulfides from ore deposits in this work matrix effects of different sulfides were examined by matrix unmatched tests in which the 34s values of different types of sulfides were calibrated against a laboratory pyrite standard the results show that the 34s values of pyrrhotite chalcopyrite molybdenite sphalerite and arsenopyrite are in agreement with the reference values suggesting that the matrix effect was negligible however a significant matrix effect occurred in the analyses of ag2s and galena leading to significant deviations in 34s values of up to 1 2 and 3 2 respectively the matrix effect occurred not only during the laser ablation stage but also during the transition of ions into the mass spectrometer resulting in significant space charge effects caused by heavy mass elements thus pyrite can be used as an external bracketing standard for sulfides that do not have a heavy mass matrix based on our matrix effect study the following available external standards were selected for the in situ sulfur isotope analysis of complex type minerals from the erlihe zn pb deposit the coarse grained sphalerite grains sph1 and euhedral to subhedral pyrite grains py1 from massive ores have 34s values ranging from 9 2 to 18 1 such heavy sulfur isotopic compositions indicate the derivation of sulfur from the deposits of seawater sulfate related to a thermochemical reducing process fine grained sphalerite sph2 and pyrite py2 from vein and disseminated ores coexist with pyrrhotite and chalcopyrite and have relatively light sulfur isotopic compositions with 34s values of about 7 the slightly positive 34s values are similar to those of sulfides from sulfide rich quartz veins which contain 34s values of about 4 and granodiorite rocks with 34s values of about 6 based on previous studies the light sulfur of the late stage sulfides may have resulted from a metamorphic or magmatic hydrothermal event during the indosinian orogeny in situ sulfur analysis by la mc icpms provides new evidence for sources of sulfur from each stage of mineralization in the erlihe deposit suggesting that this is a promising method for studying complex ore deposits

numerical modelling of the flow and bed evolution of a single bore driven swash event on a coarse sand beach abstract this paper examines the numerical prediction of the sediment transport and bed evolution for a single swash event on a coarse sediment beach in these conditions bed load is the dominant mode of sediment transport laboratory experiments of a single bore driven swash event are simulated numerically using a fully coupled model that solves the system of non linear shallow water equations and the exner sediment conservation formula the analysis focuses on two aspects the optimal choice of parameters for the meyer peter and muller sediment transport formula and the model used for computing the shear stress the methods tested for the bed shear stress are the momentum integral method and the chezy formulation in which the friction factor is computed using two different formulae infiltration into the beach and its effects on the shear stress and sediment transport are also modelled results show that the basic meyer peter and muller sediment transport formula provides good results in the run up on the other hand the sediment transport in the early stage of the backwash is overestimated a reduction of the sediment mobility constant in the formula in the backwash marginally improves the results however the causes of the overestimation of the sediment transport at the early stage of the backwash is the overestimation of the shear stress while at later stages there are several contributions that are identified i e modelling of the sediment transport and infiltration it is also suggested that the meyer peter and muller sediment transport formula might not capture the complexity of the processes involved during the backwash the comparison of the methods for the estimate of the bed shear stress show that comparable results can be obtained using the momentum integral method and the chezy formulation with time and space varying friction factor the resulting bed evolution is also described in the predicted final profile deposition is found in the upper part of the beach and erosion in the lower part a bed step is formed just below the position of the initial shoreline this feature is determined by the onset of a hydraulic jump during the backwash

rapid water table fluctuations within the beach face implications for swash zone sediment mobility abstract to incorporate groundwater infiltration exfiltration in the description of swash zone sediment transport it is required that the details of groundwater dynamics within the beach face be clarified field measurements of the vertical pore pressure structure within the bed identify capillarity effects as the primary mechanism driving rapid and relatively large magnitude water table fluctuations within the swash zone when the upper extent of the fully saturated capillary fringe coincides with the beach face surface wave runup produces near instantaneous increase in pore pressures across the capillary fringe corresponding to a rapid rise of the phreatic surface i e the surface where pore pressure atmospheric pressure to the sand surface therefore counter to previous conclusions in the literature the rapid rise and fall of the water table under the swash zone do not equate to regions of the beach face alternating between states that favor sediment deposition unsaturated and erosion saturated similar reports that rapid fluctuations of the water table within the beach face correspond to rapid rates of vertical flow and hence bed fluidization are also a misinterpretation field measurements and a careful consideration of saturation and pore pressure characteristics within the beach face demonstrate that rapid water table rise is associated with minute downwards swash infiltration rather than rapid upwards groundwater exfiltration the cause of the pressure fluctuations and phreatic surface oscillations is the alternating appearance and disappearance of meniscuses at the sand surface which generate pressure head fluctuations of decimeters due to the addition of millimeters of water

late paleozoic sedex deposits in south china formed in a carbonate platform at the northern margin of gondwana abstract sedex sulfide deposits hosted in black shale and carbonate are common in the south china block the dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 ma pyrite from the orebodies has a re os isochron age of 389 62 ma indicative of formation of the hosting strata and syngenetic pyrite ores in the mid late devonian the hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part the ore hosting black shales have high toc total organic carbon mo as pb zn and cd indicating an anoxic euxinic deep basin origin the high redox proxies v v ni 0 6 and v cr 1 and the positive correlations of toc with mo and v in black shales are also consistent with an anoxic depositional environment the dajiangping deposit is located close to the ne trending wuchuan sihui fault which was active during the devonian the mid late devonian mineralization age and the anoxic euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault bounded basin that developed in a carbonate platform of the south china block the regional distribution of many devonian stratiform carbonaceous sediment hosted sulfide deposits along the ne trending fault bounded basins in south china similar to the dajiangping deposit indicates that these deposits formed at a basin developed in the passive margin setting of the south china block during the devonian this environment was caused by the break up and northward migration of the south china block from gandwana

the paleoproterozoic mcarthur river hyc pb zn ag deposit of northern australia organic geochemistry and ore genesis polycyclic aromatic hydrocarbons pahs in ore and mudstone within the mcarthur river ore deposit show compound distribution patterns similar to those of hydrothermally generated petroleum in the guaymas basin and significantly different from those found in conventional oil pah abundances and their isomer distributions result from a temperature gradient between the source of mineralizing fluids and the sediments fringing the ore system during ore formation along with other geochemical geological paleobiological and mineralogical lines of evidence these data provide strong evidence that the ore formed within partially lithified sediments under marine conditions given that the mcarthur river ore body is an exquisitely preserved example of a sediment hosted base metal deposit these results may be widely applicable the mcarthur deposit is also a rich repository of paleobiological information allowing studies of the microbiology of ore formation and the paleobiology of an ancient hydrothermal system as is discussed elsewhere

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

distinctive features of late palaeozoic massive sulphide deposits in south china abstract more than 20 sediment hosted massive sulphide deposits occur in late palaeozoic basins in south china these deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their cu pb zn au and ag reserves the deposits and their host strata were commonly intruded by mesozoic granitoids remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein skarn and porphyry type orebodies in the same region or within a single deposit the ore containing basins occur in different tectonic settings the lower yangtze basin occurs on a passive continental margin where the deposits are high in cu and au with minor pb and zn and recoverable ag co and mo the ores have a lower concentration of radiogenic lead and 34s values close to zero fluid inclusions are highly saline and na rich fluids and metals of the lower yangtze region are interpreted to have been derived essentially from deep sources including the precambrian basement by contrast basins of the nanling region formed in an intracontinental setting developed on a folded caledonian basement these deposits are higher in pb zn sn and w as well as cu with recoverable ag sb hg u bi tl and mo the ores are characterised by a higher concentration of radiogenic lead and a wide variation of 34s composition fluid inclusions have lower salinities and higher k na ratios fluids are considered to have been sourced substantially from seawater by convection metals for the nanling deposits were essentially derived from the caledonian basement by leaching the contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore forming basins

noble gas constraints on the evolution of the atmosphere mantle system abstract we present a model on the evolution of atmosphere mantle system assuming a significant degassing from the less depleted mantle based on the recent results of the he ar systematics proposed by matsuda and marty 1995 the degassing fluxes of noble gases are represented by the concentrations in the mass flow which follows the model of porcelli and wasserburg 1995a porcelli and wasserburg 1995b however we have not assumed the steady state and have assumed the mass transfer as an exponential function of time the degassed amount from the less depleted mantle is related to the mixed amount of mass between the less depleted mantle and the depleted mantle the amount of mixing is constrained from the k abundances in each mantle reservoir consequently the degassed amount from the less depleted mantle is also constrained the following conclusions are obtained from this model the initial elemental ratio 3 he 36 ar is likely to be in cosmic abundances and the initial concentration of 36 ar in the earth is constrained to be 1 10 12 atoms g the present fraction of 36 ar in the depleted mantle reservoir is calculated to be at most 2 4 10 3 of the initial inventory the 40 ar 36 ar ratio in this reservoir is estimated to be less than 1 3 1 4 10 5 the less depleted mantle reservoir also degassed and the present amount of 36 ar is calculated to be at most 1 3 10 1 of the initial inventory the 40 ar 36 ar ratio in the less depleted mantle reservoir is estimated to be less than 3 7 10 4 to explain the difference between the neon isotopic ratios in the atmosphere and those observed in the mantle rocks isotopic fractionation during the escape from the atmosphere and or significant contribution of late accreted materials possessing planetary ne is necessary in our model ne degassing from both mantle reservoirs would have provided at least 50 90 times the amount of 22 ne in the present atmosphere therefore the fraction supplied by late accreted material would be negligible which is contrary to the model proposed by porcelli and wasserburg 1995b we conclude that isotopic fractionation model during escape from the atmosphere provides the best fit to the observations

megacusps on rip channel bathymetry observations and modeling abstract the formation of beach megacusps along the shoreline of southern monterey bay ca is investigated using time averaged video and simulated with xbeach a recently developed coastal sediment transport model investigations focus on the hydrodynamic role played by the bay s ever present rip channels a review of four years of video and wave data from sand city ca indicates that megacusps most often form shoreward of rip channels under larger waves significant wave height hs 1 5 2 0 m however they also occasionally appear shoreward of shoals when waves are smaller hs 1 m and the mean water level is higher on the beach after calibration to the sand city site xbeach is shown to hindcast measured shoreline change moderately well skill 0 41 but to overpredict the erosion of the swash region and beach face simulations with small to moderate waves hs 0 5 1 2 m suggest similar to field data that megacusps will form shoreward of either rip channels or shoals depending on mean daily water level and pre existing beach shape a frequency based analysis of sediment transport forcing is performed decomposing transport processes to the mean infragravity and very low frequency vlf contributions for two highlighted cases results indicate that the mean flow plays the dominant role in both types of megacusp formation but that vlf oscillations in sediment concentration and advective flow are also significant

modelling gravel beach dynamics with xbeach abstract numerical cross shore profile evolution models have been good at predicting beach erosion during storm conditions but have difficulty in predicting the accretion of the beach during calm periods this paper describes the progress made in modifying and applying the public domain xbeach code to the prediction and explanation of the observed behaviour of coarse grained beaches in the laboratory and the field under accretive conditions the paper outlines in details the changes made to the original code version 12 including the introduction of a new morphological module based upon soulsby s sediment transport equation for waves and currents and the incorporation of packwood s infiltration approach in the unsaturated area of the swash region the competence of this modified model during calm conditions for describing the steepening of the profile and the growth of the beach berm is demonstrated preliminary results on the behaviour of the beach subject to both waves and tides are presented good agreement is found between the model simulations and large scale laboratory measurements as well as field observations from a composite beach in the uk the reasons for the model s capabilities are discussed

efficacy of beach dewatering alassio italy abstract the goal of this study is to estimate the efficiency of dewatering operations in alassio beach north italy by following an integrated approach which included beach volume calculations daily mapping of the shoreline position examination of specific beach widening events and daily comparisons of morphodynamic characteristics of the drained beach versus a control section which included wave run up bar patterns rip migration evolution of the berm and cusp morphology alassio beach was documented by a daily time lapse photography by repeated dgps profile measurements and by an hourly wave and sea level monitoring following one year of draining the shoreline position and the beach volume of the drained beach and the control section showed little differences i e accumulation of 0 28 m 3 m 2 and a shoreline advance of 1 1 m on the drained beach whereas on the control beach the volume change was 0 03 m 3 m 2 and the shoreline retreated 1 2 m short episodes of beach widening 1 7 days long which coincided with onshore bar movement and a relative low sea level occurred simultaneously on the drained and the control sector this data indicated the inefficiency of the draining operation an improved resolution for determining the draining effect was attained by the sequential snap shot photography which showed many systematic morphological differences between the drained beach and the reference segment the drained beach developed a berm crest and a linear often scarped foreshore with a narrow swash zone no such cumulative morphologies were observed on the non drained control beach which commonly displayed cusps that were usually absent on the drained foreshore the wave data showed recurrent medium wave events of hs 1 2 m which repeatedly interrupted the calms thus cutting off the beach evolution the draining in alassio was unable to promote beach accumulation by counteracting the erosive effect of the medium interrupting storms

geology and in situ sulfur and lead isotope analyses of the jinlongshan carlin type gold deposit in the southern qinling orogen china implications for metal sources and ore genesis abstract the jinlongshan gold deposit shaanxi province central china is a large deposit 150 t au in the southern qinling orogen gold mineralization is hosted in upper devonian to lower carboniferous carbonaceous clastic carbonate sequences four stages of pyrite and paragenetic sulfides have been identified based on morphology and paragenesis laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were conducted to determine the chemical and s pb isotopic composition of the sulfides pre ore stage pyrites py1 and py2 contain relatively high concentrations of mn co ni cu zn sb and pb exhibiting a wide range of 34s values ranging from 29 9 to 48 4 these two pyrites were formed by bacterial and thermochemical sulfate reduction of upper devonian marine sulfate respectively main ore stage pyrite py3 and arsenopyrite apy contain high concentrations of au as cu sb hg and tl with restricted ranges of 34s values from 9 6 to 15 3 which is interpreted as resulting from the underlying low grade metamorphic paleozoic sedimentary rocks by the decomposition of pyrite and or inorganic reduction of sulfate late or post ore stage pyrite py4 is characterized by low concentrations of au ag sn hg and bi and exhibited variable 34s values ranging from 4 4 to 27 7 that may reflect the mixing of metamorphic fluids with meteoric water similarly the pb isotope composition of ore stage sulfides resembles those of underlying low grade metamorphic paleozoic sedimentary rocks whereas differs from precambrian metamorphic basement rocks and granitoids around the basin indicating that the metals of the jinlongshan gold deposit were sourced from the underlying paleozoic sedimentary rocks detailed fieldwork revealed that the deposit has mainly undergone four deformation events the ore bodies developed in ne trending dextral oblique slip reverse faults of d3 that crosscut wnw trending shear zones of d2 the timing and corresponding stress regimes of the d3 event suggest that it formed in a local extensional environment of yanshanian intracontinental orogeny of qinling orogenic belt gold metallogenesis of the jinlongshan gold deposit occurred during the transition of tectonic setting from compression to extension which reactivated the shear zones and migrated deep ore bearing fluids to ne trending brittle faults the geological and geochemical features of the jinlongshan gold deposit are more analogous to the carlin type deposits than other orogenic gold deposits worldwide therefore we propose it is a typical carlin type gold deposit in south qinling orogen

are 34s enriched authigenic sulfide minerals a proxy for elevated methane flux and gas hydrates in the geologic record abstract the sulfate methane transition smt zone is a diagenetic transition within anoxic marine sediments created by the metabolic activity of a consortium of sulfate reducing bacteria and methane oxidizing archaea as interstitial dissolved sulfate is consumed by microbially mediated sulfate reduction of sedimentary organic matter som and anaerobic oxidation of methane aom large enrichments of 34 s occur in the interstitial sulfate pool these isotopic enrichments are transmitted to the dissolved sulfide pool hs and subsequently into sulfide minerals so fes fes 2 we investigate the sulfur isotopic composition of pore water sulfate and sulfide minerals at three sites underlain by gas hydrates at the blake ridge the isotopic composition of sulfate sulfur is most positive at the smt showing maximum values of 29 1 49 6 51 6 vcdt at each of the respective sites 34 s values of bulk sulfide minerals tend to be more enriched in 34 s at and below the smt ranging from 12 7 to 23 6 corresponding to enrichments of 26 7 62 4 relative to the mean value of 38 8 in the sulfate reduction zone both enhanced delivery of methane to the smt and non steady state sedimentation appear necessary to create large 34 s enrichments in sulfide minerals similar associations of aom and large 34 s enrichments 0 occur in other gas hydrate terranes cascadia margin but their exact origin is equivocal at present an analysis of 34 s data from freshwater and marine sedimentary environments reveals that 34 s enrichments within sulfide minerals occur under a range of conditions but are statistically associated with aom and systems not limited by dissolved interstitial iron in methane rich sediments methane delivery to the smt increases the role of aom in sulfate depletion that impacts the formation and isotopic composition of authigenic sulfide minerals we hypothesize that under certain diagenetic conditions large 34 s enrichments within sulfide minerals in the geologic record potentially identify 1 the former occurrence of aom 2 present day and fossil locations of the sulfate methane transition zone and 3 a diagenetic terrane today characteristic of deep water methane rich marine sediments conducive to gas hydrate formation thus 34 s enriched sulfide minerals preserved in modern and ancient continental margin sediments may allow for the identification of aom related processes that occur in methane rich sediments

large scale laboratory investigation into the effect of varying back barrier lagoon water levels on gravel beach morphology and swash zone sediment transport abstract it is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea specifically a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion while the reverse is thought to hold for a high beach groundwater table here we use the results of a carefully designed series of tests conducted in the delta flume the netherlands as part of the barrier dynamics experiment bardex to unequivocally demonstrate the validity of this assertion during the experiment a 4 m high and 50 m long gravel barrier d 50 11 mm was constructed within the central region of the 250 m long and 7 m deep wave flume enabling a back barrier lagoon to be located at its landward side the groundwater table in the beach was manipulated by lowering and raising the lagoon level and the gravel beach was subjected to variable wave conditions and sea lagoon levels using as the initial beach profile the morphology resulting from 90 min of wave forcing with the sea and lagoon at the same level the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion the divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the bulk swash hydrodynamics i e based on single point velocity measurements arising from a difference in the amount of swash infiltration into the unsaturated beach instead application of a sediment transport model that accounts for the effects of in exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface due to the large hydraulic conductivity of gravel k o 0 1 m s 1 the effect of altered shear stresses due to in exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches

stratabound skarn pb zn mineralization in the yunkai domain south china the fozichong case abstract the fozichong pb zn ore district located in the yunkai domain southern section of the qin hang metallogenic belt qhmb in south china consists of several large size stratabound ore deposits the ore bodies are mainly stratiform and stratoid bounded within the ordovician and silurian strata that are intruded by the yanshanian porphyries these deposits are debated between syngenetic sedimentary exhalative sedex and epigenetic skarn type since the occurrence of ore bodies is accompanied by the green color stratiform rock gsr the gsr origin may play an important role to resolve the controversy this motivates us to conduct a set of petrographic investigations whole rock and mineral chemistry analyses of the gsr coupled with zircon u pb geochronology of the intrusions detailed petrographic observations reveal that the gsr is mainly composed of a mineral assemblage of garnet pyroxene epidote amphibole and chlorite in analogy with that of traditional skarns in addition the concentrations of ore related pb zn cu and ba consistently decrease from rim to core of an individual gsr layer supporting an origin of hydrothermal fluid replacement rather than comparatively homogeneous sedimentation therefore the fozichong gsr is referred to as the stratiform skarn in literature the mn poor and ca rich andradite diopside hedenbergite and calcic amphibole in the skarn provide robust evidence for the magmatic hydrothermal origin the skarn is believed to be formed by the infiltration of magmatic hydrothermal fluids since it is not confined in the intrusion contact zone where the hydrothermal fluids derived from is complicated due to the multi stages magmatic intrusions present in the district detailed investigations indicate that the late yanshanian porphyries zircon u pb dated at 100 ma including dacite porphyry and granite porphyry have a genetic link with the fozichong skarn mineralization while the indosinian dachong pluton and the early yanshanian guangping pluton exhibit insignificant correlation with the mineralization the redox state of the skarn system changes from oxidation prograde and retrograde stages to reduction late retrograde and quartz sulfide stages as recorded by the fe2 fe3 ratios in skarn minerals i e 0 05 for garnet 0 01 0 23 for amphibole and 55 6 178 1 for chlorite respectively during the redox transition the mineralization has been developed with the precipitation of chlorite at moderate temperatures 255 to 278 c in combined with the above analyses the fozichong is representative of a stratabound skarn pb zn mineralization system in the yunkai domain south china

the role of evaporites in the formation of gems during metamorphism of carbonate platforms a review the mineral and fluid inclusions trapped by gemstones during the metamorphism of carbonate platform successions are precious markers for the understanding of gem genesis the nature and chemical composition of inclusions highlight the major contribution of evaporites through dissolution or fusion depending on the temperature of formation from greenschist to granulite facies the fluids are highly saline nacl brines circulating either in an open system in the greenschist facies colombian and afghan emeralds and with huge fluid rock metasomatic interactions or sulphurous fluids ruby garnet tsavorite zoisite tanzanite and lapis lazuli or molten salts formed in a closed system with a low fluid mobility ruby in marble in the conditions of the amphibolite to granulite facies these chloride fluoride sulphate carbonate rich fluids scavenged the metals essential for gem formation at high temperature the anions so42 no3 bo3 and f are powerful fluxes which lower the temperature of chloride and fluoride rich ionic liquids they provided transport over a very short distance of aluminium and or silica and transition metals which are necessary for gem growth in summary the genetic models proposed for these high value and ornamental gems underline the importance of the metamorphism of evaporites formed on continental carbonate shelves and emphasise the chemical power accompanying metamorphism at moderate to high temperatures of evaporite rich and organic matter rich protoliths to form gem minerals

infiltration effects on sediment mobility under waves sediment mobility measurements with a horizontal sand bed under non breaking waves are reported conditions include no seepage and steady downward seepage corresponding to head gradients up to 2 5 the results indicate that infiltration tends to inhibit sediment mobility for a horizontal bcd of 0 2 mm quartz sand exposed to moderated wave induced bed shear stresses the effect is weak for the parameter range of the present study the two opposing effects of shear stress increase due to boundary layer thinning and the stabilizing downward drag are successfully accounted for through the modified shields parameter of nielsen nielsen p 1997 coastal groundwater dynamics proc coastal dynamics 97 plymouth asce dp 546 555 using coefficients derived from independent studies that is from the shear stress experiments of conley conley d c 1993 ventilated oscillatory boundary layers phd thesis university of california san diego 74 pp and the slope stability experiments of martin and aral martin c s and m m aral 1971 seepage force on interfacial bed particles j hydraulics div proc asce vol 97 no hy7 pp 1081 1100 c 2001 elsevier science b v all rights reserved

an important source of4he and3he in diamonds a large data base has recently accumulated on the concentrations of helium isotopes in diamonds mined from various regions it was noted earlier ozima et al 1985 1 lal et al 1989 2 that the frequency distribution of the4he concentrations is a fairly narrow one whereas that of3he concentrations is a broad one with no pronounced peaks the ratios 3he 4he on the other hand show a broad maximum around 2 ra ra equals atmospheric 3he 4he ratio 1 40 10 6 with a slow decrease over two orders of magnitude on either side does this imply that the diamonds sample a wide variety of helium reservoirs having a range of 3he 4he ratios but somehow attain similar4he concentrations we propose that in a majority of the diamonds studied 4he is primarily due to implantation of radiogenic alpha particles from the host material after emplacement in the crust usually kimberlite and that the concentrations of4he in diamonds often get appreciably altered by this process thus the4he trapped in the diamond at the time of its crystallization is usually overwhelmed by the implanted helium and the measured 3he 4he ratios do not generally correspond to any sources in the mantle however the implanted4he resides in the outer 16 m of the diamond and the intrinsic4he and 3he 4he ratios in the diamond can be studied if its outer layers are removed the wider implications of diamond being the target material for nuclear reaction products from the host material are discussed radiogenic3he produced in the host material is also implanted in the diamond but this contribution is small on a gross basis however since the depth of implantation of3he is greater than that of4he some of the very high 3he 4he ratios observed in diamonds could be due to the implantation of radiogenic3he the radiogenic reactions in the host material can also contribute to appreciable21ne in diamonds

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

peeling oceanic crust in subduction zones thin slabs of oceanic pillow basalt formed at ridge axes with associated pelagic sediments are common features in ancient accretionary complexes estimates of the average thicknesses of scraped off basaltic sections of oceanic crust in accretionary prisms vary from a few tens of metres to 300 m with a mean thickness of 80 100 m in the complexes studied the permeability contrast within the uppermost part of the oceanic crust is an important factor governing the thickness of delaminated oceanic crust this mechanism is an effective means of separating oceanic crust altered at low temperatures from the remainder of the downgoing slab and thus controlling geochemical budgets in subduction zones

influence of infiltration on suspended sediment under waves the effect of percolation through a permeable bed on sediment suspension under regular waves was examined in a laboratory wave tank 28 in x i in x 1 in using acoustic backscatter sensors to make rapid 3 hz suspended sand profile measurements 0 005 m vertical resolution waves of 1 7 s period and heights ranging from 0 14 to 0 185 m were used over sand with a d 50 of 255 mum infiltration velocities of 0 5 0 x 10 4 m s 1 were used with percolation through an initially flat bed ripple development was suppressed particularly at lower wave heights ripples took longer to form and were more three dimensional suspension was also suppressed the total suspended load was correlated with shields number at the 1 significance level when the shields number was modified to take account of both the infiltration nielsen p 1997 coastal groundwater dynamics proceedings of coastal dynamics american society of civil engineers pp 546 555 and ripple steepness coastal eng 1986 23 the ripple steepness was found to be the most important factor relating to the reduction in the total suspended loads the influence of infiltration on time averaged concentration profiles over equilibrium ripples was investigated by switching the percolation on and off for 5 min periods the total suspended loads were reduced by up to 50 with percolation on these results suggest that fluctuation of the water table and drainage within a beach will affect sediment transport and ripple dynamics and that for sand of 0 25 mm percolation will tend to reduce suspension and transport c 2002 elsevier science b v all rights reserved

using argon as a temporal tracer of large scale geologic processes abstract argon ar has proven to be one of the most useful elements in understanding the timing and duration of geological processes because of its chemical and physical properties ar is a particularly sensitive indicator of temperature variations associated with large scale geological events ar mobility in minerals is commonly described using solid state diffusion theory volume diffusion which has been used extensively to model diffusion profiles and closure temperatures in minerals because 40 ar is the radiogenic daughter product of radioactive 40 k and therefore occurs in many common rock forming minerals ar has been used effectively as a temporal tracer to understand a wide variety of geological phenomena ar isotopes have been applied with great success in three broad fields of earth science the origin and evolution of the earth s atmosphere the tectonothermal history of geologic terranes and the timing and duration of large scale tectonic events from ar isotopic data the earth s atmosphere is now known to be mainly secondary in nature although evolutionary models have undergone a recent paradigm shift due to geophysical evidence moving away from the earlier notion of a chemically layered upper and lower mantle to a whole earth mantle structure that may be chemically inhomogeneous although recent models are growing in sophistication by integrating additional information and measurements reflecting the behaviour of other noble gases through time the temporal evolution of the earth s atmosphere still remains ambiguous because measured compositions of ancient atmosphere are sparse and remain difficult to obtain 40 ar 39 ar thermochronology is one of the most commonly used tools in tectonothermal investigations because of the large range of ar closure temperatures recorded by various common k bearing minerals although more recent thermochronological models such as multidiffusion domain mdd modelling remain controversial the combination of 40 ar 39 ar thermochronology with both higher and lower temperature thermochronological methods utilizing other isotopic systems makes this an extremely versatile method of understanding the temperature time evolution of geologic regions recent developments involving the numerical modelling of ar diffusion coupled with the geodynamic modelling of orogens have led to new ways of estimating the timing and duration of a complete tectonic cycle of subduction and exhumation by applying these new methods to rocks from the bergen arcs in norway studies have shown that this cycle can be so rapid that the subducted and exhumed crust can remain relatively cool never achieving thermal equilibrium with its ambient environment throughout the entire process in summary the versatility of the 40 ar 39 ar dating method combined with the effective application of various techniques e g laser spot dating and step heating and a detailed understanding of the diffusional behaviour of ar has proven to be a powerful research tool in elucidating the timing and duration of many large scale earth system processes

surface groundwater flow numerical model for barrier beach with exfiltration incorporated bottom boundary layer model abstract a surface groundwater flow model is developed for the swash flow on a barrier beach the non linear shallow water equations are used to simulate the surface flow laplace s equation is used to describe the groundwater flow and is solved using the boundary integral equation method to provide potential heads and normal potential derivatives at and within the boundaries of the barrier an exfiltration incorporated bottom boundary layer sub model is used to obtain bed shear stress the groundwater model is verified against the numerical test results in kazemzadeh parsi and daneshmand 2012 for the groundwater flow through a rectangular dam the coupled surface groundwater model is validated against the prototype scale bardex ii experimental results turner et al 2016 the steady state groundwater flow comparisons show excellent agreement in phreatic surfaces the comparisons of groundwater flow under the action of waves show reasonably good agreement with experimental results in phreatic surfaces the simulated time averaged pore velocities for the runs with and without waves are in satisfactory agreement with experimental results in general and certain discrepancies are observed near the beach side the bed shear stress variation due to exfiltration is investigated by incorporating the modified logarithmic bottom boundary layer model of cheng and chiew 1998 in the coupled surface groundwater flow model the results confirm that as exfiltration increases bed shear stress decreases as a result of thickening of the bottom boundary layer

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

argon solubility in sio2 melt under high pressures a new experimental result using laser heated diamond anvil cell abstract we have measured the solubility of argon in sio2 melt under high pressure by melting a sio2 crystal at the argon pressure as high as 19 gpa using laser heated diamond anvil cell lhdac sio2 was successfully melted at the pressure of about 12 gpa and recovered with a completely glassy phase above 15 gpa the sample contained a large amount of crystalline sio2 although it was completely melted and spherical due to the surface tension this may arise from the change in the coordination number of si in sio2 melt at around 12 15 gpa which is close to the triple point of coesite stishovite and liquid sio2 argon content in the recovered sio2 was measured by energy dispersive spectroscopy and mass spectrometry it increased at pressures up to approximately 5 7 gpa and exhibited a constant value up to at least 12 gpa this implies that at these conditions the noble gas behaves as an incompatible element the result is completely different from those of previous lhdac studies which claimed that the increased solubility then dramatically drops above the pressure of about 5 gpa here we report the new details of experimentally determined pressure dependence of noble gas solubility by lhdac and discuss the experimental difficulties and the structure change of silicate melt under high pressures

suction effects on bridge pier scour under clear water conditions abstractthe experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear water conditions the results show that suction has a profound effect on pier scour development and the extent of the influence is related to the location of the suction source when the suction source is located at or upstream of the pier the equilibrium scour depth is reduced by up to 50 with qs qo 2 where qs and qo suction flow rate and undisturbed approach flow rate respectively the data also show that for the suction source that is located downstream of the pier the equilibrium scour depth is reduced by up to 30 with the same suction flow rate the extent of pier scour depth reduction at different locations from the suction source is closely associated with changes to the local effective shear and critical shear velocity results of this study show that bed suction may be used as an effective pier scour countermeasure

the importance of siliceous radiolarian bearing mudstones in the formation of sediment hosted zn pb ba mineralization in the selwyn basin yukon canada sediment hosted massive sulfide shms mineralization occurred in three main episodes during the evolution of the selwyn basin yukon and northwest territories canada in the macmillan pass district tom and jason deposits the upper devonian strata of the earn group host the youngest least deformed examples of shms mineralization the earn group comprises gray to black homogeneous mudstones which have been deformed in the cordilleran fold and thrust belt are weathered and poorly exposed this makes stratigraphic correlations and the recognition of prospective units very challenging the host rock siliceous mudstone and mineralized intervals at the tom and jason zn pb ba deposits have been sampled from drill core major element chemistry and total organic carbon toc data are presented for the host rock samples from two drill holes tyk 5 n 18 76 17 n 19 all mudstones contain between 2 and 5 wt toc and 67 to 83 wt sio2 subtle alteration marked by potassium loss k2o al2o3 50 radiolarians by volume within the mineralized horizons and in barren time equivalent strata and therefore are a useful stratigraphic marker unit in otherwise homogeneous featureless fine grained mudstones the presence of highly siliceous carbonaceous mudstone units with preserved radiolarians suggests that in the late devonian there is a link between biological productivity in the water column the resultant sedimentation and the shms deposits these biosiliceous lithologies may be particularly favorable host rocks to shms mineralization for the following reasons 1 high porosities during early diagenesis preserve volume and enhance permeabilities in partially lithified sediments which are important parameters for subseafloor replacement mineralization 2 these units are rich in organic materials due to their deposition in productive settings and have a high capacity for the generation of sulfide via sulfate reduction therefore we suggest there is a link between times of high biological activity and productivity in oceans sediments derived from those processes and shms deposits

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

swash infiltration exfiltration and sediment transport field measurements of vertical pore pressure gradients within the bed are used to quantify instantaneous 8 hz rates of swash infiltration exfiltration across the beach face cyclic infiltration exfiltration is associated with individual swash events with observed vertical flow rates o 10 3 m s rates of net swash groundwater exchange i e through bed flow integrated over several swash cycles are two orders of magnitude smaller at the timescale of individual swashes vertical pore pressure gradients within the beach face are much greater than horizontal pore pressure gradients this permits application of the numerical solution of darcy s law for one dimensional vertical flow to model fluctuating pore pressures and hence vertical through bed flow vertical flow through a porous bed modifies sediment mobility in at least two ways 1 seepage forces change the effective weight of surficial sediments and 2 boundary layer thickening or thinning result in altered bed shear stresses by considering these two opposing effects separately a new shields parameter is derived that incorporates terms for through bed flow simulation of time varying seepage force and bed stress effects over an uprush backwash cycle suggests that the effect of altered bed stresses dominates over the change in effective weight and that infiltration exfiltration effects are most important during uprush simulated transport rates are increased by up to 40 of the peak transport rate during uprush and reduced by 10 during backrush in summary swash infiltration exfiltration across a saturated beach face enhances the net upslope transport of sediment

high isotope fractionations during sulfate reduction in a low sulfate euxinic ocean analog a detailed record of the early earth sulfur s cycle is chronicled by the s isotope values of sulfide and sulfate preserved in the rock record interpretation of this record rests on our understanding of sulfur cycling in modern systems experiments and the resulting isotopic signatures very large fractionations in 34s of 70 are commonly measured between sulfide and sulfate in modern systems and in ancient sediments theoretical calculations suggest that sulfate reducing prokaryotes are capable of producing such large fractionations during the reduction of sulfate to sulfide although they have only been demonstrated to generate fractionations up to 48 here we report the first direct determination of 60 70 fractionations by natural populations of sulfate reducers these high fractionations occur under the relatively low sulfate conditions 1 1 2 mm of meromictic lago di cadagno in switzerland the major and minor isotopic composition of sulfide and sulfate in the lake water is consistent with sulfide produced by sulfate reduction with little evidence for modification by further oxidative sulfur cycling these observations help us to constrain the evolution of seawater sulfate concentrations

hydro and morpho dynamic modeling of breaking solitary waves over a fine sand beach part ii numerical simulation abstract a comprehensive numerical model is developed to predict the transient wave propagation sediment transport morphological change and the elastodynamic responses of seabed due to breaking solitary waves runup and drawdown over a sloping beach the individual components of the numerical model are first validated against previous analytical numerical and experimental results the validated numerical model is then used to simulate breaking solitary wave runup and drawdown over a fine sand beach where the experimental results are presented in young et al 2010b hydro and morpho dynamic modeling of breaking solitary waves over a fine sand beach part i experimental study the strengths and weaknesses of the model are assessed through comparisons with the experimental data based on the results sediment transport mechanisms and wave seabed interactions in the nearshore region are discussed

noble gas constraints on the layered structure of the mantle several chemical models of mantle structure have been proposed1 6 based on isotopic data such as sr nd hf and pb in volcanic rocks from both oceanic and continental areas the most popular of these are two chemical models of the vertically layered mantle 1 that it is a depleted mantle from which mid oceanic ridge basalt morb is derived and 2 that it is a fertile mantle from which a mantle plume may arise1 5 however these models are almost always based on solid elements such as sr nd hf and pb isotopes and do not fully reflect the noble gas data because noble gases are liable to be lost from the solid earth when a mantle differentiation occurs on a global scale in the upper mantle the data on noble gas isotopes could give constraints on the structure of the mantle that differ from those by solid element isotopes based on a consideration 3he 4he and 40ar 36ar ratios of recent samples i argue here that the observed data suggest that mixing occurs between the source materials of a mantle plume and of morb the data seem to favour the model which assumes that the source of a typical mantle plume is deeper than that of morb