submarine groundwater discharge sgd into the yellow sea revealed by 228ra and 226ra isotopes implications for global silicate fluxes abstract we estimated the magnitude of submarine groundwater discharge sgd into the yellow sea which is one of the largest continental shelves in the world using 226 ra and 228 ra isotopes on the basis of 228 ra and 226 ra mass balance models we estimated the advective flux of 226 ra through sgd to be 270 10 12 dpm yr 1 in the yellow sea using this 226 ra flux and the measured 226 ra activity in coastal groundwater the submarine discharge of groundwater mostly brackish groundwater was calculated to be at least 40 of the river water input 2 3 10 11 m 3 yr 1 then on the basis of the sgd and the concentration of si in coastal groundwater we estimated the flux of si through sgd to be 20 100 of that associated with river discharge 23 10 9 mol yr 1 this large sgd is likely to be due to the high tidal range up to 10 m and the wide distribution of sandy sediments in the yellow sea favorable for the recirculation of seawater through bottom sediments and rocks this result from such a large area implies that the si flux through sgd may be significant on a global scale

crustal accretion beneath the koyna coastal region india and late cretaceous geodynamics abstract in 1967 a major earthquake in the koyna region attracted attention to the hitherto considered stable indian shield the region is covered by a thick pile of deccan lava flows and characterized by several hidden tectonic features and complex geophysical signatures although deep seismic sounding studies have provided vital information regarding the crustal structure of the koyna region much remains unknown the two available dss profiles in the region have been combined along the trend of bouguer gravity anomalies unified 2 d density modelling of the koyna crust mantle suggests a ca 3 km thick and 40 km wide high velocity high density anomalous layer at the base of the crust along the coastline the thickness of this anomalous layer decreases gradually towards the east and ahead of the koyna gravity low the layer ceases to be visible based on the seismic and gravity data interpretation in the geodynamical rheological boundary conditions the anomalous layer is attributed to igneous crustal accretion at the base of the crust it is suggested that the underplated layer is the imprint of the magmatism caused by the deep mantle plume when the northward migrating indian plate passed over the reunion hotspot

anomalous seismic velocity drop in iron and biotite rich amphibolite to granulite facies transitional rocks from deccan volcanic covered 1993 killari earthquake region maharashtra india a case study 65 ma deccan volcanic province of western india forms one of the largest flood basaltic eruptions on the surface of the earth the nature of the concealed crust below this earthquake prone region which is marked by several low velocity zones at different depths has hardly been understood these low velocity zones have been invariably interpreted as fluid filled zones genetically connected to earthquake nucleation while carrying out detailed geological and petrophysical studies on the late archean basement cores obtained from a 617 m deep klr 1 borehole drilled in the epicentral zone of 1993 killari earthquake region of the southern deccan volcanic province we came across several instances where we observed remarkable drop in measured p wave velocity in a number of high density cores we provide detailed petrographic and geological data on 11 such anomalous samples which belong to mid crustal amphibolite to granulite facies transitional rocks they are associated with a mean p wave velocity of 6 02 km s range 5 82 6 22 km s conforming to granitic upper crust but in contrast have a high mean density of 2 91 g cm3 range 2 75 3 08 g cm3 which characterise mid to lower crust this velocity drop which is as much as 15 in some cores is primarily attributed to feot enrichment up to about 23 wt during the course of mantle fluid driven retrogressive metasomatic reactions caused by exhumation of deep seated mafic rocks presence of iron content mainly magnetite widely seen as opaques in thin sections of the rocks seems to have resulted into sharp increase in density as well as mean atomic weight our study indicates that the measured vp is inversely related to feot content as well as mean atomic weight of the rock

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

anomalous crustal and lithospheric mantle structure of southern part of the vindhyan basin and its geodynamic implications abstract tectonically active vindhyan intracratonic basin situated in central india forms one of the largest proterozoic sedimentary basins of the world possibility of hydrocarbon occurrences in thick sediments of the southern part of this basin has led to surge in geological and geophysical investigations by various agencies an attempt to synthesize such multiparametric data in an integrated manner has provided a new understanding to the prevailing crustal configuration thermal regime and nature of its geodynamic evolution apparently this region has been subjected to sustained uplift erosion and magmatism followed by crustal extension rifting and subsidence due to episodic thermal interaction of the crust with the hot underlying mantle almost 5 6 km thick sedimentation took place in the deep faulted jabera basin either directly over the bijawar mahakoshal group of mafic rocks or high velocity high density exhumed middle part of the crust detailed gravity observations indicate further extension of the basin probably beyond nsl rift in the south a high heat flow of about 78 mw m2 has also been estimated for this basin which is characterized by extremely high moho temperatures exceeding 1000 c and mantle heat flow 56 mw m2 besides a very thin lithospheric lid of only about 50 km many areas of this terrain are thickly underplated by infused magmas and from some segments granitic gneissic upper crust has either been completely eroded or now only a thin veneer of such rocks exists due to sustained exhumation of deep seated rocks a 5 8 km thick retrogressed metasomatized zone with significantly reduced velocities has also been identified around mid to lower crustal transition

fresh and saline groundwater discharge to the ocean a regional perspective 1 studies of groundwater flow in coastal aquifers often focus strongly on freshwater and investigate flow in a narrow 5 km zone surrounding the coastline this work was designed to place coastal flow in a regional context and to compare fresh and saline submarine groundwater discharge sgd for regional flow systems numerical flow and transport models were developed to estimate sgd associated with topography driven flow seawater recirculation and geothermal convection in a passive margin setting simulations were based on two cross sections of north carolina and sensitivity studies were used to explore the impact of varying hydraulic and transport parameters results suggest that saline flow associated with seawater recirculation and geothermal convection should be considered in studies of sgd studies limited to shallow topography driven flow may be justified in using small study areas but flow systems contributing to sgd may span at least 20 km surrounding the coast and continental slope

the ratio in the cenozoic bengal abyssal fan sediments and its use as a paleostream energy indicator abstract the tio 2 al 2 o 3 ratio in the cenozoic bengal abyssal fan sediments displays decisive potential as a paleostream velocity indicator the reason for this is that even in the finest fan suspendates hydrodynamic sorting determines the amounts of heavy tio2 rich minerals relative to lighter al2o3 rich clay minerals in five deep sea drilling project cores 213 217 which have been recovered in and south of the bay of bengal tio 2 al 2 o 3 ratios increase linearly with time from the late miocene to recent the increase reflects fan progradation and intensified bottom current activity on the southern bengal fan these processes are related to the himalayan elevation by factors such as the maturation of northern india river systems evolution of orographic monsoon rains and elevation attributed increases in denudation rates

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

sediment nutrient dynamics on the south atlantic bight continental shelf continental shelf sediments on the south atlantic bight sab consist of relict sands that at depths ranging from 14 45 m fall within the photic zone and are sites in which significant rates of benthic primary production are observed thus sab seafloor sediments are a source of organic matter to the shelf system and are possibly a sink for nutrients regenerated within the sediments we have investigated the nutrient dynamics in sab shelf sediments along two transects off the coasts of georgia and florida as part of a study that addresses the significance of benthic primary production in terms of overall shelf biogeochemistry sandy sediments were sampled with a newly designed corer that permits retention of pore water in highly permeable sands and thus avoids commonly encountered washout problems nutrient ammonium silicate nitrate nitrite and phosphate distributions from sediments along both transects show substantial variation in concentration magnitudes and profile shapes over short horizontal spatial scales meters laboratory experiments and numerical models of diagenetic processes in these sediments suggest that 1 pore water advection driven by current flows over wave ripples and bioturbational features is likely an important transport process in promoting nutrient exchange in these porous sands more so than irrigation and 2 reaction rates in sab sediments are rapid and are comparable to those in nearshore muddy habitats in spite of this variation and the apparently high rates of advective transport time series measurements show a gradual increase in depth integrated nutrient concentrations at one station along the georgia transect from the spring through the fall this increase is probably related to elevations in temperature and metabolic rates in sediments during the warmer summer months measured oxygen and nutrient fluxes across the sediment water interface in paired transparent light chambers and opaque dark chambers did not conform to trends observed in shallow water systems where oxygen is typically evolved and nutrients are consumed in the light versus oxygen that is consumed and nutrients that are evolved in the dark the absence of measurable or consistent fluxes on the sab shelf is likely the result of low concentrations of nutrients in both the water column and the upper sediment layers however rapid regeneration rates in sediments and generally higher nutrient concentrations in deeper sediment layers suggest that sediments are an important source of the nutrients that fuel benthic primary production although ammonium is rapidly produced in these oxic sands nitrate concentrations are uniformly low and measurable nitrate generally appears in the oxic sedimentary layers the absence of high nitrate concentrations in the suboxic or anoxic zone suggests that denitrification may not be an important process in sab shelf sediments

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust

importance of geochemical transformations in determining submarine groundwater discharge derived trace metal and nutrient fluxes abstract seasonal spring and summer 2002 concentrations of dissolved 3 po 4 si and doc were determined in groundwater samples from 5 wells aligned along a 30 m shore normal transect in west neck bay long island ny results show that significant systematic changes in groundwater trace metal and nutrient composition occur along the flowpath from land to sea while conservative mixing between west neck bay water and the groundwaters explains the behavior of si and doc non conservative inputs for co and ni were observed concentration increases of 10 and 2 fold respectively and removal of po 4 and no 3 decreases to about half along the transport pathway groundwater associated chemical fluxes from the aquifer to the embayment calculated for constituents not exhibiting conservative behavior can vary by orders of magnitude depending on sampling location and season e g co 3 4 10 2 8 2 10 3 mol d 1 using measured values from different wells as being representative of the true groundwater endmember chemical composition also results in calculation of very different fluxes e g cu 6 3 10 3 mol d 1 inland freshwater well vs 2 1 10 5 mol d 1 seaward well s 17 ppt this study suggests that seasonal variability and chemical changes occurring within the subterranean estuary must be taken into account when determining the groundwater flux of dissolved trace metals and nutrients to the coastal ocean

sulfate reduction related to the early diagenetic degradation of organic matter and black spot formation in tidal sandflats of the german wadden sea southern north sea stable isotope 13c 34s 18o and other geochemical results abstract a stable isotope geochemical investigation 34 s 32 s 13 c 12 c 18 o 16 o has been carried out to study the development of anoxic surface sediments black spots in the backbarrier tidal area of spiekeroog island southern north sea microbial sulfate reduction related to the degradation of mainly marine organic matter under anaerobic conditions led to the accumulation of hydrogen bisulfide up to 8 mm in the interstitial waters of the sandy sediments while the carbon isotopic composition of organic matter reflected the downcore preferential degradation of labile marine organic matter sulfur and oxygen isotope variations in the dissolved sulfur species provided information about the microbiologically mediated complex interactions between the sulfur carbon and oxygen cycles

the diffusive tortuosity of fine grained unlithified sediments abstract use of fick s first law to estimate solute fluxes is arguably the most common and important calculation related to the geochemistry and environmental chemistry of fine grained unlithified sediments in such porous media the diffusion coefficient in this law must be reduced by the square of the tortuosity to account for the longer diffusive paths experimental methods to estimate tortuosity are specialized or time consuming and not routinely done an analysis of available data shows that tortuosity is accurately correlated to readily measured porosity values through the simple relation 2 1 l n 2

ultrasonic p and s wave attenuation and petrophysical properties of deccan flood basalts india as revealed by borehole studies petrophysical properties and ultrasonic p and s wave attenuation measurements on 35 deccan basalt core specimens recovered from killari borehole site in western india provide unique reference data sets for a lesser studied deccan volcanic province these samples represent 338 m thick basaltic column consisting four lava flows each of ambenali and poladpur formations belonging to wai subgroup of the deccan volcanic sequence these basalt samples are found to be iron rich average feot 13 4 wt but relatively poor in silica content average sio2 47 8 wt the saturated massive basalt cores are characterized by a mean density of 2 91 g cm3 range 2 80 3 01 g cm3 and mean p and s wave velocities of 5 89 km s range 5 01 6 50 km s and 3 43 km s range 2 84 3 69 km s respectively in comparison saturated vesicular basalt cores show a wide range in density 2 40 2 79 g cm3 as well as p wave 3 28 4 78 km s and s wave 1 70 2 95 km s velocities based on the present study the deccan volcanic sequence can be assigned a weighted mean density of 2 74 g cm3 and a low vp and vs of 5 00 and 3 00 km s respectively such low velocities in deccan basalts can be attributed mainly to the presence of fine grained glassy material high iron contents and hydrothermally altered secondary mineral products besides higher porosity in vesicular samples the measured q values in saturated massive basalt cores vary enormously qp 33 1960 and qs 35 506 while saturated vesicular basalt samples exhibit somewhat lesser variation in qp 6 46 as well as qs 5 49 in general high porosity rocks exhibit high attenuation but we observed the high value of attenuation in some of the massive basalt core samples also in such cases energy loss is mainly due to the presence of fine grained glassy material as well as secondary alteration products like chlorophaeite that could contribute to intrinsic attenuation dominance of weekly bound secondary minerals might also be responsible for the generation of microcracks which may generate squirt flow in saturated samples hence we argue that the deccan basalts attenuate seismic energy significantly where its composition plays a major role

biogeochemical impact of submarine ground water discharge on coastal surface sands of the southern baltic sea this study evaluates the effect of submarine ground water discharge sgd on biogeochemical processes of sandy sediments of hel bight poland in the shallow southern baltic sea using stirred benthic chambers combined to seepage meters deep pore water profiles and a reactive transport model the main impacts of fresh anoxic groundwater seepage are due to 1 the efflux of methane 2 the efflux of phosphate and silicate 3 the efflux of dissolved organic carbon doc of aquifer origin methane from sgd is assumed to be only slightly oxidized within the sediments and potentially reach the atmosphere at a maximum rate of 30 mmol ch4 m 2 d 1 silicate and phosphate supplied by sgd promote a seep site net community production rate that is more than twice as compared to adjacent non seeping sites 70 and 30 mmol c m 2 d 1 respectively however oxygen uptake rates at the seep site during the night 30 mmol o2 m 2 d 1 are lower than those observed at the reference sites 50 mmol o2 m 2 d 1 we hypothesize that autogenic relatively labile doc is available at the reference site leading to higher oxygen uptake rates as compared to the seep sites where it is being replaced by less reactive doc originating from the ground water

solute flux in meltwaters draining from a glacierized basin in the karakoram mountains electrical conductivity of meltwaters in the batura river which drains from the portal of batura glacier in the karakoram mountains was recorded continuously together with stage throughout an ablation season with the aim of estimating the annual total solute flux from the 56 glacier covered basin through time variations of meltwater cationic concentration were obtained from the electrical conductivity record using a rating curve established between sums of cations determined in periodically collected samples of meltwater and electrical conductivity measured at the times of sampling hourly average cationic flux was then obtained as the product of cationic concentration and discharge error arising as a result of inaccuracy in river gauging and use of the rating relationship electrical conductivity varied diurnally inversely with discharge overall level decreasing as discharge increased in spring continuing subdued through july and august irrespective of episodic discharge fluctuations in contrast solute flux mimicked discharge variation low solute concentrations being offset by the volume of water flowing total annual cationic flux from batura basin was 1 03 meq 15 assuming almost all of the flux was derived subglacially the solute flux from beneath batura glacier was 2 64 0 40 eq m 2 a 1 these rates of cationic denudation substantially higher than the continental average are at the top end of the global range of reasonably reliable estimates for other smaller glacierized basins carbonate lithology high annual runoff high sediment concentration in meltwaters and long subglacial pathways account for the high solute flux from batura glacier through longer residence times of meltwater in transit under ice and higher discharges dissolution kinetics and flow couple to enhance solute fluxes from larger glaciers although subglacial chemical denudation in the karakoram mountains is significant in carbon cycling at the continental scale such carbonate dissolution probably contributes little to net consumption of carbon dioxide from the atmosphere

trace element rich brines in eclogitic veins implications for fluid composition and transport during subduction primary and pseudosecondary fluid inclusions occur in oscillatory and sector zoned omphacite in eclogitic veins from the monviso ophiolitic complex in the western alps the inclusions contain aqueous brines and daughter crystals of halite sylvite calcite dolomite albite anhydrite and or gypsum barite baddeleyite rutile sphene fe oxides pyrite and monazite this daughter mineral suite indicates high solubilites of na k ca mg fe zr ti p ba ce la th and s species and provides direct evidence for transport of high fieldstrenght large ion lithophile and light rare earth elements as dissolved species during subduction fluid inclusion heterogeneities preserved within and between adjacent grains in the veins however suggest that the scale of fluid equilibration was small a crack seal geometry in some of the veins implies that fluid release in pulses rather than steady flow controlled mineral deposition and growth in the veins from these observations we develop a model of fluid release and entrapment in which pulses of fluid are associated in time with increments of shear and tensile failure the rate of fluid release and the reduction in porosity both depend on the rate of plastic flow vein fluids may initially be derived from decreptitation of early fluid inclusions in the host eclogites small scale fluid heterogeneities implied by the fluid inclusions in the veins are best interpreted in terms of limited fluid flow and hence limited metasomatism we conclude that element recycling into the mantle wedge during subduction will depend at least as strongly on fluid transport mechanisms as on element solubilities in the fluid phase at monviso despite evidence for high trace element solubilities in saline brines the elements were not removed from the downgoing slab prior to teaching depths of 40 km

the glass transition in hydrous granitic melts abstract the influence of water on the glass transition temperature of hydrous granitic melts is estimated on the basis of a variety of available sources of data that provide phenomenological data for the liquid glass transition and for which the relaxation timescale can be accurately estimated these sources include a dilatometric micropenetration viscosity determinations b temperature dependent spectroscopic investigations of hydrous melts and c densities of synthetic fluid inclusions in glasses all available evidence on the glass transition temperature of hydrous granitic melts when corrected for equivalent timescales yields a single consistent trend of decreasing tg with increasing water content that has powerful applications in the rheology and kinetics of processes involving late stage silicic intrusives and eruptive products the brittle ductile transition in hydrous silicic liquids can be accurately predicted using this trend combination of the presently derived relationship for the influence of water on the glass transition of granitic melts with presently available data for the high temperature viscosities of such systems permits the estimation of the temperature dependence of the viscosity of hydrous melts over the entire range of temperature relevant to granite petrogenesis such a comparison reveals that the viscosity temperature relationships of hydrous granitic melts are not arrhenian as is assumed by most existing calculational schemes for the prediction of hydrous melt viscosities the increasing deviation of viscosity temperature relationships of hydrous granitic melts from arrhenian with increasing water content is broadly consistent with similar trends accompanying the addition of excess alkalies to metaluminous granitic melt base compositions in detail however the influence of water on the deviation of viscosity temperature relationships of hydrous granitic melts from arrhenian is not as strong as would be predicted from a molar comparison of the effects of h2o vs alkali oxide or alkaline earth oxide added to these melts the answer to this apparent discrepancy may lie in the incomplete dissociation of water in the melt structure

the rapid drift of the indian tectonic plate the breakup of the supercontinent gondwanaland into africa antarctica australia and india about 140 million years ago and consequently the opening of the indian ocean is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the marion kerguelen and reunion plumes plate reconstructions based on palaeomagnetic data suggest that the indian plate attained a very high speed 18 20 cm yr 1 during the late cretaceous period subsequent to its breakup from gondwanaland and then slowed to approximately 5 cm yr 1 after the continental collision with asia approximately 50 myr ago the australian and african plates moved comparatively less distance and at much lower speeds of 2 4 cm yr 1 refs 3 5 antarctica remained almost stationary this mobility makes india unique among the fragments of gondwanaland here we propose that when the fragments of gondwanaland were separated by the plume the penetration of their lithospheric roots into the asthenosphere were important in determining their speed we estimated the thickness of the lithospheric plates of the different fragments of gondwanaland around the indian ocean by using the shear wave receiver function technique we found that the fragment of gondwanaland with clearly the thinnest lithosphere is india the lithospheric roots in south africa australia and antarctica are between 180 and 300 km deep whereas the indian lithosphere extends only about 100 km deep we infer that the plume that partitioned gondwanaland may have also melted the lower half of the indian lithosphere thus permitting faster motion due to ridge push or slab pull

seismogenesis of the lower crustal intraplate earthquakes occurring in kachchh gujarat india abstract large intraplate continental earthquakes like the 1811 12 new madrid m w 8 0 and the 2001 bhuj mw7 7 were highly destructive because they occurred in strong crust but the mechanisms underlying their seismogenesis are not understood here we show using local earthquake velocity tomography and joint inversion of receiver functions and surface wave group velocity dispersion that the crust and uppermost mantle beneath the 2001 bhuj earthquake region of western india is far more complex than hitherto known through previous studies a new image of the crust and underlying mantle lithosphere indicates the presence of a 18 km thick high velocity vp 7 15 8 11 km s differentiated crustal and mantle magmatic layer above a hot and thin lithosphere only 70 km in the epicentral region of 2001 bhuj earthquake this magmatic layer begins at the depth of 24 km and continues down to 42 km depth below this region brittle ductile transition reaches as deep as the moho 34 km due to the possible presence of olivine rich mafic magma our 1 d velocity structure envisages an initial phase of plume activity deccan plume at 65 m y ago resulting in basaltic magma in the eclogitic layers at sub lithospheric levels wherein they were subjected to crystallization under ultra high pressure conditions our study also delineates an updoming of moho 4 7 km as well as asthenosphere 6 10 km below the kachchh rift zone relative to surrounding areas suggesting the presence of a confined body of partial melts below the lithosphere asthenosphere boundary restructuring of this warm and thin lithosphere may have been caused due to rifting at 184 and 88 m y ago and tholeiitic and alkalic volcanism related to the deccan traps k t boundary event at 65 m y ago recent study of isotopic ratios proposed that the alkalic basalts found in kachchh are generated from a co 2 rich lherzolite partial melts in the asthenosphere that ascended along deep lithospheric rift faults into the lithosphere it appears that such kind of crust mantle structure deepening of brittle ductile transition and a high input of volatiles containing co 2 emanating from mantle control the seismogenesis of lower crustal earthquakes in the kachchh continental rift zone

surface glaciochemistry of taylor valley southern victoria land antarctica and its relationship to stream chemistry we have analysed a series of surface samples from the alpine glaciers of taylor valley southern victoria land antarctica for their geochemical composition this was done to better establish the role of glaciochemical variation on the chemical composition of meltwater streams emanating from the glaciers the chemistry of the snow and ice changes with proximity to the ocean and with elevation of the glacier surface the aeolian transport of dry valley dust as indicated by both chemical and particulate matter variations is a major process affecting the overall glacier chemistry and the chemistry of the meltwaters streams originating on the western edges of the glaciers are more impacted by the aeolian input as they are in the direct path of the major regional wind direction our data strongly suggest that the variation in stream geochemistry in taylor valley is a result in part of the differences in chemical composition of glacier melt copyright 2003 john wiley sons ltd

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

upwarped high velocity mafic crust subsurface tectonics and causes of intraplate latur killari m 6 2 and koyna m 6 3 earthquakes india a comparative study abstract a unique attempt is made to understand the genesis of intraplate seismicity in the latur killari and koyna seismogenic regions of india through derived crustal structure by synthesizing active and passive seismic magnetotelluric gravity and heat flow data it has indicated presence of relatively high velocity density intermediate granulite and amphibolite facies rocks underneath the deccan volcanic cover caused mainly due to a continuous geodynamic process of uplift and erosion since precambrian times these findings have been independently confirmed by detailed borehole geological geochemical and mineralogical investigations the crystalline basement rock is found to contain 2 wt of carbon di oxide fluid components the presence of geodynamic process associated with thermal anomalies at subcrustal depths is supported by a high mantle heat flow 29 36 mw m2 beneath both regions although some structural and compositional variations may exist as evidenced by p and s wave seismic velocities we suggest that the stress caused by ongoing uplift and a high mantle heat flow is continuously accumulating in this denser and rheologically stronger mafic crust within which earthquakes tend to nucleate these stresses appear to dominate over and above those generated by the india eurasia collision the role of fluids in stress generation as advocated through earlier studies appears limited

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

benthic photosynthesis and oxygen consumption in permeable carbonate sediments at heron island great barrier reef australia abstract in order to investigate benthic photosynthesis and oxygen demand in permeable carbonate sands and the impact of benthic boundary layer flow on sedimentary oxygen consumption in situ and laboratory chamber experiments were carried out at heron island great barrier reef australia total photosynthesis net primary production and respiration were estimated to be 162 9 43 4 98 0 40 7 and 64 9 15 0 mmol c m 2 d 1 respectively din and dip fluxes for these sands reached 0 34 and 0 06 mmol m 2 d 1 respectively advective pore water exchange had a strong impact on oxygen consumption in the permeable sands consumption rates in the chamber with larger pressure gradient 20 rpm 1 2 pa between centre and rim simulating a friction velocity of 0 6 cm s 1 were approximately two fold higher than in the chambers with slow stirring 10 rpm 0 2 pa between centre and rim friction velocity of 0 3 cm s 1 in the laboratory chamber experiments with stagnant water column oxygen consumption was eight times lower than in the chamber with fast stirring laboratory chamber experiments with br tracer revealed solute exchange rates of 2 6 2 2 0 7 ml cm 2 d 1 at stirring rates of 20 10 and 0 rpm respectively in a laboratory experiment investigating the effect of sediment permeability on oxygen and dic fluxes a three fold higher permeability resulted in two to three fold higher oxygen consumption and dic release rates these experiments demonstrate the importance of boundary flow induced flushing of the upper layer of permeable carbonate sediment on oxygen uptake in the coral sands the high filtration and oxidation rates in the sub tropical permeable carbonate sediments and the subsequent release of nutrients and dic reveal the importance of these sands for the recycling of matter in this oligotrophic environment

seismic imaging of the proterozoic cuddapah basin south india and regional geodynamics abstract cuddapah basin has been believed to be one of the largest intra cratonic proterozoic sedimentary basins of india situated in the eastern part of the dharwar craton of the south indian shield which is magmatically infested and contain thick column of sediments its overall sedimentary thickness as well as the nature of crustal evolution has remained enigmatic based on deep seismic sounding and other geological studies in the past it was perceived that this basin may contain as much as 10 12 km thick sediments the results of our present analysis derived up to a depth of 12 km reveals five layered upper crust associated with velocities i 4 50 km s ii 5 20 5 30 km s iii 5 50 5 80 km s iv 5 85 6 00 km s and v 6 40 km s out of which second and third layers correspond to upper and lower cuddapah sediments the results suggest the presence of only 4 0 km thick sediments in the deepest part of the basin below the nallamalai fold belt which has its implications in the developmental history of the basin a thermal driving force was invoked by earlier workers to account for estimated 10 12 km thick sediments however the present estimate of only 4 km basement depth in the cuddapah basin shows that the role of the thermal driving force may be marginal particularly in the deeper eastern cuddapah as isostatic subsidence due to sedimentary accumulation alone is enough to explain the basin depth further a basement sag of about 10 km would have logically needed lateral extension of the order of several hundreds of kilometers however as our present estimate of the sediment thickness gets reduced from earlier 10 km to only 4 km the size of the basin 44 500 km 2 would be in conformity with isostatic subsidence due to sedimentary accumulation hypothesis the structural features derived from present analysis like maximum depth observed near the thrust suture on the basin margin from where it decreases away from it its association of shallow marine sediments the arcuate shape of the basin along with its areal dimension resembles foreland basin between continent continent collisions

glaciers show direct linkage between erosion rate and chemical weathering fluxes field studies suggest a linkage between high physical erosion rates and rates of chemical denudation mechanical erosion by temperate glaciers is commonly an order of magnitude higher than in mountainous fluvial catchments leading to an expectation that chemical weathering fluxes should also be high from glacierized basins yet solute fluxes from glaciers are not found to be higher than non glacierized catchments application of a model of silicate weathering from glaciers based on mineral surface area production and mineralogy shows that solute fluxes are consistent with the low temperatures dilute water chemistry and high mineral surface area production in these environments low temperatures reduce silicate weathering rates this effect explains the difference between silica fluxes from glaciers and from non glacierized basins as in laboratory flow through reactors glacial solute flux should depend on surface area production and mineral weathering rate constants the surface area production is significant a typical glacial erosion rate and grain size distribution produces on the order of 104 km2 of mineral surface area per square kilometer per year this new surface area is highly reactive because mineral weathering rates decline with surface age application of the reactor model yields results largely consistent with measured solute fluxes for the example of bench glacier alaska the model underpredicts potassium fluxes probably due to accelerated initial dissolution of biotite strained by abrasion the success of the model in predicting other silicate weathering fluxes reflects the far from equilibrium conditions in glacial runoff such that mineral weathering rate constants are not limited by saturation state in a small data set from glacial catchments both annual silica fluxes and mean concentrations increase with water discharge this suggests that mineral surface area increases with water discharge from glaciers an effect plausibly linked to erosion rates those glaciers for which both erosion rate and silica flux data are available support the idea that production of new reactive mineral surface area by glacial erosion drives silicate weathering fluxes

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

seafloor oxygen consumption fuelled by methane from cold seeps the leakage of cold methane rich fluids from subsurface reservoirs to the sea floor sustains some of the richest ecosystems on the sea bed these cold seep communities consume around two orders of magnitude more oxygen than the surrounding sea floor as a result of the microbial consumption of seep methane

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

flow induced uptake of particulate matter in permeable sediments we demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata z 2 x 10 l l m2 incubated in a laboratory flume increased pressure up and downstream of small mounds z 2 5 cm drove water 5 5 cm into the core carrying suspended particles 1 pm to 2 2 cm sediment depth within 10 h simultaneously decreased pressure at the downstream slope of the protrusions drew pore fluid from deeper layers z 5 10 cm to the surface in the sediment friction reduced the velocity of the particulate tracers resulting in size fractionation and layers of increased particle concentration ripple topography 0 8 2 8 cm high enhanced interfacial particle 1 pm flux by a factor 2 3 when compared to a level control core the pathways of the particle and solute tracers below a sediment ripple are explained with a source sink model that describes the pore flow velocity field our results suggest that bedform induced interfacial flows are important for the uptake of particulate organic matter into permeable shelf sediments

infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the woxi orogenic au sb w deposit western hunan south china abstract the woxi au sb w deposit hosted by the neoproterozoic low grade metamorphic clastic rocks is located in a brittle ductile shear zone within the xuefengshan range south china orebodies are predominantly banded quartz veins which are strictly controlled by bedding faults and display significant vertical extents up to 2 km without obvious vertical metal zoning fluid inclusions hosted in quartz scheelite and stibnite from quartz scheelite and quartz sulfide gold veins have been studied using conventional and infrared microscopy respectively four types of fluid inclusions were identified based on petrography including type i two phase liquid rich aqueous inclusions type ii two or three phase co 2 rich inclusions type iii two phase vapour rich aqueous inclusions and type iv single phase aqueous inclusions the fluid inclusions in ore minerals scheelite and stibnite and their coexisting quartz largely share similar characteristics in terms of their types homogenization temperatures and salinities this is consistent with the fact that these ore minerals are always intergrown with quartz microthermometric and laser raman data indicate a low to moderate temperature 140 240 c low salinity 2 rich n 2 bearing aqueous ore forming fluid such fluid is further identified as a deeply non magmatic crustal fluid rather than a mantle source fluid by the significantly low 3 he 4 he ratios 0 002 0 281 ra and a small amount of meteoric water or host rock buffered fluid could be involved w ore precipitation was probably associated with mixing between a deeply originated crustal fluid and host rock buffered fluid based on the fluid inclusion features in scheelite and quartz i however au and sb ore deposition probably resulted from boiling which was caused by the marked pressure drop geological features such as banded structure and crack sealing structure also indicate that fluid pressure fluctuation induced by fault valve mechanism occurred during ore precipitation these characteristics of the ore forming fluids in the woxi deposit are in good agreement with the definition of orogenic gold deposits and the woxi au sb w deposit is probably an atypical orogenic gold deposit for its unique ore forming element association

composition of fluids in the lower crust inferred from metamorphic salt in lower crustal rocks knowledge of the rheological properties of the lower crust and the metamorphic processes that operate there is important for our understanding of orogenic processes and granite genesis the rheological properties critically depend on whether fluids are present in the lower crust1 2 and if present on their composition3 4 5 6 fluid inclusion7 8 9 and phase equilibria4 10 studies of lower crustal granulites have shown that fluids with low water activities due to the presence of dissolved components such as ch4 n2 co co2 and chlorides 11 are present at least episodically in the lower crust here we report the occurrence of a solid salt solution nacl kcl found together with chlorine rich amphibole and biotite in lower crustal granulites a desiccation mechanism explains how salt and chlorine rich minerals formed from an originally water rich fluid through a short lived series of hydration reactions in the granulites during which chlorine was progressively enriched in the fluid consequently it would appear that fluid was present in the lower crust in only small amounts and was not stable over geologically long periods of time leading to the conclusion that the lower crust is devoid of a free fluid phase during most of its history

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

microbial methane turnover in different marine habitats microbial methanogenesis in the subsurface seafloor is responsible for the formation of large and dynamic gas reservoirs like the recently discovered gas hydrate deposits gas seepage occurs wherever methane builds up an overpressure outside the hydrate stability field illustrating the potential importance of ocean margins for the global methane budget however a variety of bacteria and archaea are capable of methane consumption and control the emission of methane to the hydrosphere unfortunately much less is known about the microbial methane turnover in the ocean than about methane turnover in freshwater or terrestrial habitats this investigation compares rates of methane production anaerobic and aerobic methane oxidation at different marine sites combining radiotracer on site and in vitro measurements samples were obtained from gas hydrate bearing sediments cold seeps organic rich and organic poor subsurface sediments all investigated subsurface sediments had the potential for methanogenesis as well as for methanotrophy the anaerobic oxidation of methane aom was highest in samples from gas hydrate areas and cold seeps aom was strongly influenced by methane partial pressure and temperature indicating a substantial underestimation of in situ activity with current ex situ measuring techniques a potential for aerobic methane oxidation was detected at all sites where the sediment had contact with oxic bottom water a first comparison of methane turnover rates in diverse marine habitats showed that microbial methane oxidation provides a very effective barrier for methane emissions from the subsurface seafloor d 2005 elsevier b v all rights reserved

metamorphic fluids in the deep crust evidence from the adirondacks unusual mineral assemblages of tremolitic hornblende diopside enstatite quartz have been examined to estimate the temperature t and water fugacity at the time of the granulite fades metamorphism in the adirondacks the pyroxenes are closely represented by the system cao mgo sio2 allowing application of experimental data1 with only small corrections for reduced values of activities tremolite equilibria2 buffered log 3 0 0 1 equivalent to 0 9 kbar of water pressure at 7 kbar 710 c nearby marbles contain wollastonite calcite quartz and buffered 1 1 kbar consistent with 5 9 kbar inferred local gradients in fluid compositions suggest that deep crustal fluid conditions are complex and heterogeneous indicating that fluid movements whether of mantle3 or deep crustal origin are channelized rather than pervasive thus some granulite facies rocks were wholly or partly closed systems with respect to externally derived fluids permitting localized buffering of fluid compositions recognition of restricted fluid mixing limits theories that call for massive amounts of pervasive fluid flow to facilitate melting cause metasomatism or to stabilize granulite facies mineralogy

high salinity fluids the result of retrograde metamorphism in thrust zones abstract highly saline fluid inclusions in vein quartz from caledonian thrust zones of northern norway are associated with late orogenic retrograde metamorphic reactions several retrograde reactions have been observed in pelitic lithologies and all involve the rehydration of earlier higher grade metamorphic assemblages the most common products of these reactions are chlorite and sericite which have formed at the expense of garnet kyanite staurolite and hornblende chlorite geothermometry suggests temperatures between 330 and 370 c for the formation of the retrograde chlorite a range of total fluid salinities has been determined by microthermometry between 27 and 50 wt these high fluid salinities result from relatively rapid rehydration reactions during limited infiltration of the thrust zones by aqueous fluids crush leach analyses show the fluids to be multi component fluids whose electrolyte contents are na and cl dominated but with appreciable contents of ca k fe and sr geochemical modelling of the fluid compositions suggests that the concentrations of the major elements in solution were buffered by the retrograde rehydration reactions the source of the infiltrating fluids which caused the retrogression is not identifiable from their major element chemistry surface derived meteoric sea or sedimentary formation waters fluids may have utilised pre existing thrust zones as fluid pathways and are considered to have been important in the retrogression in the structurally higher parts of the caledonian allochthon at deeper levels however metamorphic fluids produced by devolatilisation reactions in underthrust units may have migrated upwards into the thrust zones and resulted in the retrogression of the hangingwalls of overlying higher grade nappes

transport and degradation of phytoplankton in permeable sediment in flume and field experiments we demonstrate that interfacial water flows generated when bottom currents interact with sea bed topography provide a fast and efficient pathway for the transport of suspended phytoplankton into subsurface layers of permeable sandy sediments the advective transport associated with small mounds and ripples as commonly found on shelf sediments increased penetration depth of unicellular algae dunaliella spec into sandy sediment permeability k 5 4 3 10 211 m 2 up to a factor of 7 and flux up to a factor of 9 relative to a smooth control sediment the pore water flow field produced a distinct distribution pattern of particulate organic matter in the sediment with subsurface concentration maxima and zones depleted of algae flux chamber simulations of advective transport of algae into sands of different grain sizes revealed increasing fluxes algal penetration depths and degradation rates with increasing permeability of the sediment two experiments conducted in intertidal sand flats confirmed the importance of the advective interfacial transport of phytoplankton for natural settings showing permeability dependent penetration of planktonic algae into embedded sand cores of different grain sizes the significance of our results is discussed with respect to particulate organic matter flux and mineralization in shelf sands and we suggest the concept of a decomposition layer in contrast to muddy sea beds with low permeabilities where transport of solutes is mainly driven by diffusion water can flow through marine sands providing a fast carrier for the exchange of substances between the water column and the upper sediment layers surface gravity waves cause pressure oscillations that increase fluid exchange at the sediment water interface and dispersion of solutes within the

mantle derived fluids in the basement of the deccan trap evidence from stable carbon and oxygen isotopes of carbonates from the killari borehole basement maharashtra india we report here for the first time geochemical mineralogical and stable carbon and oxygen isotopic data on the crystalline basement rocks of the 1993 killari earthquake region of maharashtra india which is covered by a thick suite of deccan volcanics our results revealed the hitherto unknown amphibolite granulite nature of the 2 5 ga basement which contains 2 00 2 28 wt of co2 the stable carbon 13c and oxygen 18o isotopic measurements on carbonates separated from two basement samples kil 13 440 5 m depth and kil 20 499 6 m depth collected from the klr 1 borehole drilled in the epicentral region showed the respective values of 6 23 and 6 22 versus pdb for 13c and 7 94 and 8 11 versus smow for 18o the samples plot in the primary igneous carbonatite field indicating the mantle origin of the carbonates derived through the process of mantle metasomatism from the deep mantle carbon reservoir this would suggest large scale crust mantle thermal fluid interaction beneath the killari seismogenic region which is characterized by massive upwarping of the high velocity mafic crust and retrograde metamorphism

surface and deep water changes in the northeast indian ocean during the last 60 ka inferred from carbon and oxygen isotopes of planktonic and benthic foraminifera abstract stable carbon and oxygen isotopic records of planktonic globigerinoides ruber and benthic foraminifera mostly cibicidoides wuellerstorfi from a deep sea core in the northeast indian ocean are used to infer surface and deep water characteristics for the last 60 kyr the gravity core sk 157 14 studied here was retrieved from the ninetyeast ridge 5 11 n 90 05 e at a water depth of 3306 m chronology of the core was established using nine radiocarbon dates and oxygen isotope stratigraphy significant variations in 18o during the last 2 60 kyr bp are suggestive of large changes in monsoonal precipitation over the indian sub continent the last glacial maximum lgm to holocene shift in planktonic foraminifera 18o 1 64 is less than documented earlier from the bay of bengal cores two prominent negative 18o excursions at 8 7 and 20 18 kyr bp are attributed to the sudden influx of freshwater as a result of intensified monsoonal precipitation large fluctuations in 18o of g ruber during the holocene suggest variability in riverine input planktonic 18o values show a combined effect of increased sea surface salinity and decreased sea surface temperature sst during the lgm in contrast the planktonic 13c values are not linked to the glacial to holocene transition comparison of the benthic 18o and 13c time series with those of a pacific core rc13 110 suggests a similar glacial deep water evolution the lgm to holocene 18o shift in benthic foraminifera mostly c wuellerstorfi exceeds the ice volume effect by 0 5 indicating a glacial deep water cooling of 2 c assuming no salinity change variations in the distribution of 13c in the glacial northeast indian ocean neio are most likely the result of deep ocean circulation changes the glacial deep neio 13c characteristics clearly point to reduced north atlantic deep water nadw input consequently the contribution from the southern ocean deep water may have increased resulting in low 13c a positive shift in 13c during the early deglaciation is consistent with other records from this region deglacial 13c fluctuations appear to have been caused by the switch on and off of nadw production

pore water advection and solute fluxes in permeable marine sediments ii benthic respiration at three sandy sites with different permeabilities german bight north sea this contribution presents total oxygen uptake tou rates and nutrient fluxes of organically poor permeable shelf sands of the german bight measurements have been made in situ with the novel autonomous benthic chamber system sandy under controlled conditions of advective pore water exchange average oxygen consumption rates of 31 3 18 2 mmol m 2 d 1 measured in this study were relatively high as compared with rates reported from shelf sediments with much higher organic contents tou of highly permeable medium and coarse grained sands was substantially enhanced in the presence of advection this indicates that advective oxygen supply contributed significantly to respiration in these sediments and that advection has to be considered when assessing oxygen consumption and organic matter mineralization in shelf areas in fine grained less permeable sands no effect of advection could be measured a lower advective oxygen supply in these sediments is in agreement with a release of ammonium instead of nitrate and a shallower oxygen penetration depth scaled up to the entire german bight the results imply that in 40 of the area an effect of advection on benthic oxygen uptake and other advectionrelated processes can be largely excluded while in the remaining 60 significant pore water advection potentially takes place however because permeabilities of the sediments investigated in this study were widely spaced a significant effect on oxygen supply was only verified for highly permeable sands that are likely to cover approximately 3 of the area

cretaceous black shales as active bioreactors a biogeochemical model for the deep biosphere encountered during odp leg 207 demerara rise abstract a transport reaction model was designed to identify the combination and importance of biogeochemical processes operating in four sites drilled during odp leg 207 demerara rise equatorial atlantic almost 100 ma after their deposition deeply buried cretaceous black shales still act as active bioreactors in great sediment depths and control the biogeochemical reaction network of the whole sediment column according to a model calibrated at the four drill sites through inverse modeling techniques methanogenesis could be identified as a key process that dominates not only organic matter degradation but also sulfate availability through the anaerobic oxidation of methane above the black shales a complete depletion of sulfate within the black shale sequences promotes the remobilization of biogenic barium that reprecipitates as authigenic barite at the top of the sulfate depletion zone temporal dynamics of degradation processes caused continuous shifts of the barite precipitation zone during burial thus inhibiting the formation of an authigenic barite front or causing the dissolution of earlier formed fronts major deviations of pore water sulfate profiles from a linear gradient coincide with depths of decelerated or accelerated transport caused by local porosity minima or maxima model determined reaction rates are by far lower than those found in shallower sediments due to the low metabolic activities that are characteristic for the deep biosphere but even after almost 100 ma changing organic matter quality still influences the degradation within the black shale sequences as it is indicated by model results

magnitudes of submarine groundwater discharge from marine and terrestrial sources indian river lagoon florida 1 magnitudes of terrestrial fresh and marine saline sources of submarine groundwater discharge sgd are estimated for a transect across indian river lagoon florida two independent techniques seepage meters and pore water cl concentrations show terrestrial sgd decreases linearly to around 22 m offshore and these techniques together with a model based on the width of the outflow face indicate a cumulative discharge of between 0 02 and 0 9 m3 d per meter of shoreline seepage meters and models of the deficiencies in 222rn activity in shallow sediments indicate marine sgd discharges of roughly 117 m3 d per meter of shoreline across the entire 1800 m wide transect two surface streams nearest the transect have an average discharge of about 28 m3 d per meter of shoreline marine sgd is thus 4 times greater then surface water discharge and more than 2 orders of magnitude greater than terrestrial sgd the magnitude of the terrestrial sgd is limited by the amount of regional precipitation evaporation recharge and groundwater usage while marine sgd is limited only by processes circulating marine water into and out of the sediments the large magnitude of marine sgd means that it could be important for estuarine cycling of reactive components such as nutrients and metals with only slight modification from estuarine water compositions the small magnitude of terrestrial sgd means that large differences from estuarine water composition would be required to affect chemical cycling

controls on the major ion chemistry of the dokriani glacier meltwaters ganga basin garhwal himalaya india a detailed study of the major ion chemistry of the dokriani glacier meltwaters feeding the bhagirathi river ganga basin garhwal himalaya india has been carried out to assess the role of active glaciers in the higher chemical denudation rate cdr in this area the cdr of the dokriani glacier catchment is 321 6 t km a higher than in other glacierized catchments of the world indicating intense chemical erosion in the glacierized catchments of the himalaya the dominance of ca 2 hco 3 and so 4 2 in meltwaters throughout the 6 month may october ablation period suggests that the chemical weathering is dominated by coupled reactions involving sulphide oxidation and carbonate dissolution good positive correlation between so 4 2 and suspended sediment concentration during july and august r 2 0 72 and 0 67 respectively suggests that the southwest monsoonal rainfall enhances the weathering of supraglacial moraine and contributes significant amounts of sulphate to the high meltwater discharges the sulphate flux as a proportion of combined so 4 2 hco 3 flux also increased from 45 at 2 m 3 s 1 to 63 at 10 m 3 s 1

depth dependent dispersion coefficient for modeling of vertical solute exchange in a lake bed under surface waves variable pressure at the sediment water interface due to surface water waves can drive advective flows into or out of the lake bed thereby enhancing solute transfer between lake water and pore water in the lake bed to quantify this advective transfer the two dimensional 2d advection dispersion equation in a lake bed has been solved with spatially and temporally variable pressure at the bed surface this problem scales with two dimensionless parameters a dimensionless wave speed w and a relative dispersivity solutions of the 2d problem were used to determine a depth dependent vertically enhanced dispersion coefficient de that can be used in a 1d pore water quality model which in turn can be easily coupled with a lake water quality model results of this study include a relationship between de and the depth below the bed surface for w 50 and 0 1 the computational results are compared and validated against a set of laboratory measurements an application shows that surface waves m

thermal stability and spectroscopic studies of zemkorite a carbonate from the venkatampalle kimberlite of southern india while characterizing the mineralogy of the kimberlite at venkatampalle andhra pradesh india lat 14 56 00 n long 77 22 15 e we found the second occurrence of zemkorite na k 2 ca co 3 2 which was first reported in 1989 in the udachnaya kimberlite in siberia we also report the first fourier transform infrared spectroscopic ftir scanning electron microscopic thermo gravimetric and high temperature heat capacity measurements on this rare carbonate powder x ray diffraction xrd patterns show 24 well resolved diffraction lines all of which can be indexed with a hexagonal cell with a 10 038 5 a and c 12 726 5 a the vibrational spectrum of zemkorite at room temperature exhibits 13 distinct absorption bands in the frequency range 2000 to 400 cm 1 the ir bands of zemkorite indicate a structural similarity with shortite but are quite distinct from other alkali carbonates such as nyerereite butschiite and fairchildite the heat capacity of zemkorite has been measured up to 700 k by differential scanning calorimetric techniques the temperature dependence of the heat capacity of zemkorite was fitted with the polynomial c p 140 2 8 584 10 2 t 2 458 10 6 t 2 the upper thermal stability of zemkorite is 700 k which is similar to shortite zemkorite may have formed during the late stages of kimberlite genesis possibly as a result of metasomatism or by the breakdown of metasomatic natrocarbonatitic minerals or glass that segregated on decompression melting in the upper mantle

in situ evaluation of nearshore marine and fresh pore water transport into flamengo bay brazil abstract transport between pore waters and overlying surface waters of flamengo bay near ubatuba brazil was quantified using natural and artificial geochemical tracers 222rn cl and sf6 collected from multi level piezometers installed along a transect perpendicular to the shore eight sampling ports positioned along the length of the piezometers allowed sampling of pore waters at discrete depth intervals from 10 to 230 cmbsf centimeters below seafloor small volume samples were collected from the piezometers using a peristaltic pump to obtain pore water depth profiles pore water 222rn is deficient in shallow sediments allowing application of a diffusion corrected 222rn exchange rate this model estimates the magnitude of pore water exchange rates to be about 130 419 cm day an sf6 saturated fluorescein dye tracer was gently pumped into deep pore waters and exchange rates estimated from this method range from 29 to 185 cm day while absolute rates are higher using 222rn than sf6 rates are of similar magnitudes and the trends with distance from shore are the same flow is greatest 6 m from shore and decreases by more than 50 further offshore a cl mass balance indicates the greatest fraction of fresh sgd occurs along an apparent preferential flow path in sediments within 5 7 m of the shoreline 87 recirculating bay waters through sediments dominate pore water advection at 10 m offshore where only 4 of the flow can be attributed to a freshwater source both fresh and marine sources combine to make up submarine groundwater discharge to coastal water bodies the magnitude of fresh aquifer discharge is often a spatially variable and minor component of the total discharge

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

understanding conspicuous gravity low over the koyna warna seismogenic region maharashtra india and earthquake nucleation a paradigm shift the continued seismicity in koyna warna region of the western part of maharastra india and its relationship with subsurface structures concealed below thick volcanic sequences are studied in detail using gravity field along with newly available deep scientific drilling results this seismically active zone is marked by a large conspicuous negative gravity anomaly the causes of which are yet to be fully understood recent findings from the boreholes drilled in the koyna gupta et al in int j earth sci 104 1511 1522 2015 and killari seismic zones both of which penetrated the thick deccan volcanic cover and the underlying archean crystalline basement have motivated us to revisit the bouguer gravity field over this region using a newly developed finite element method of regional residual separation our study reveals the presence of two thick low density low velocity crustal zones below the koyna warna region the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the moho both of these zones appear to contain mantle metasomatised and fractionated magmatic material respectively interestingly the hypocenters of all m 5 koyna earthquakes occur within the upper low velocity low density zone we also suggest high order crustal exhumation below this region which led to the removal of the entire sedimentary and granitic upper crustal column this process has brought denser mid crustal lithological facies close to the surface quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing a paleo rift may have existed beneath this region below which moho temperatures 600 c and mantle heat flow 31 mw m2 are still high

elastic properties of amphibolite and granulite facies mid crustal basement rocks of the deccan volcanic covered 1993 latur killari earthquake region maharastra india and mantle metasomatism abstract present study provides a new data set of p and s wave velocities and density of metasomatized mid crustal amphibolite and granulite facies basement rocks of the 1993 latur killari earthquake region of maharashtra india which is concealed below a thick suite of deccan volcanics this includes laboratory tests geochemical analysis and petrographic examination on 29 fresh cored samples selected from the depths between 351 7 m and 616 8 m of the klr 1 borehole drilled in the earthquake epicentral zone these samples show a wide range in sio2 content from 52 2 to 70 0 wt majority of these samples are characterized by intermediate composition with a mean density of 2 85 g cm3 range 2 72 3 06 g cm3 and average p and s wave velocities of 6 23 km s 5 83 6 61 km s and 3 56 km s 3 21 3 96 respectively they also contain quite high amount of feot and cao with respective means of 9 76 and 6 59 wt average poisson s ratio is 0 25 together with respective values of young s bulk and rigidity modulus at 90 8 gpa 62 0 gpa and 36 3 gpa inspite of having higher densities some of the biotite and feo rich samples exhibit unusually low velocities consequent to metasomatic activity our study demonstrates that the mantle metasomatic alteration and retrogression of the underlying high velocity mafic crust under the latur killari earthquake region accompanied by geodynamic process of uplift and erosion during the geologic past has led to severe changes in the petrophysical and elastic properties of the studied rocks

hydrogeological characterization of southeast coastal plain aquifers and groundwater discharge to onslow bay north carolina usa summary the natural geochemical tracer 222 rn was used to quantify submarine groundwater discharge sgd onto the continental shelf of onslow bay north carolina water column samples were collected aboard the r v cape hatteras on july 21 26 2002 and an additional nearshore water column transect and groundwater samples were collected in 2005 2006 assessment of sgd was accomplished using a mass balance approach that quantified sources and sinks of radon including benthic flux exchange across the pycnocline or air sea interfaces horizontal transport into and out of the study area and a water column inventory four independent geochemical box models were developed to quantify sgd regionally and with distance from shore overall water column inventories and diffusion rates decreased with distance from shore average water column inventories were 8520 1310 7230 1190 and 760 510 dpm m 2 for three shore parallel boxes from nearshore to offshore and resulted in a regional average of 5800 1050 dpm m 2 for the regional box model diffusion rates of radon through the sediment water interface were 0 9 0 2 0 6 0 1 and 0 4 0 1 dpm m 2 min 1 for the near to offshore models and averaged 0 6 0 1 dpm m 2 min 1 for the regional box model sgd estimates were calculated using two end member 222 rn activities for the advecting fluids which allowed a distinction between terrestrially driven sgd and total sgd terrestrially driven and total sgd estimates averaged 0 2 and 0 7 cm d 1 respectively the calculated terrestrially driven sgd is as important in the delivery of fresh water as riverine sources to onslow bay and a significant contributor to the south atlantic bight

rates of chemical denudation and co2 drawdown in a glacier covered alpine catchment solute fluxes from a glacier covered alpine catchment are partitioned into components derived from sea salt acid aerosol dissolution of atmospheric co2 and crustal weathering the bulk of solute is crustally derived coupled sulfide oxidation and carbonate dissolution so cd and carbonation of carbonate minerals generate approximately equal amounts of solute chemical denudation constitutes 1 5 of solid denudation but is significantly higher than the continental average co2 drawdown by weathering reactions varies directly with discharge and suspended sediment load and inversely with meltwater p co2 if it is generally true that flushing rates control co2 drawdown in glacier covered catchments then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial interglacial time scales