genesis of fumarolic emissions as inferred by isotope mass balances co2 and water at vulcano island italy we have developed a quantitative model of co2 and h2o isotopic mixing between magmatic and hydrothermal gases for the fumarolic emissions of the la fossa crater vulcano island italy on the basis of isotope balance equations the model takes into account the isotope equilibrium between h2o and co2 and extends the recent model of chemical and energy two end member mixing by nuccio et al 1999 as a result the h2o and co2 content and the d 18o and 13c isotope compositions for both magmatic and hydrothermal end members have been assessed low contributions of meteoric steam added at a shallow depth have been also recognized and quantified in the fumaroles throughout the period from 1988 to 1998 nonequilibrium oxygen isotope exchange also seems to be occurring between ascending gases and wall rocks along some fumarolic conduits the 13cco2 of the magmatic gases varies around 3 to 1 vs peedee belemnite pdb following a perfect synchronism with the variations of the co2 concentration in the magmatic gases this suggests a process of isotope fractionation because of vapor exsolution caused by magma depressurization the hydrogen isotopes in the magmatic gases 1 to vs standard mean ocean water smow as well as the above 13cco2 value are coherent with a convergent tectonic setting of magma generation where the local mantle is widely contaminated by fluids released from the subducted slab magma contamination in the crust probably amplifies this effect the computed isotope composition of carbon and hydrogen in the hydrothermal vapors has been used to calculate the d and 13c of the entire hydrothermal system including mixed h2o co2 vapor liquid water and dissolved carbon we have computed values of about 10 vs smow for water and 2 to 6 5 vs pdb for co2 on these grounds we think that mediterranean marine water dh2o 10 feeds the hydrothermal system it infiltrates at depth throughout the local rocks reaching oxygen isotope equilibrium at high temperatures interaction processes between magmatic gases and the evolving seawater also seem to occur causing the dissolution of isotopically fractionated aqueous co2 and providing the source for hydrothermal carbon these results have important implications concerning fluid circulation beneath vulcano and address the more convenient routine of geochemical surveillance

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

origin of bedding parallel fibrous calcite veins in lacustrine black shale a case study from dongying depression bohai bay basin abstract the bedding parallel fibrous calcite veins in black shales are common in sedimentary basins and retain significant information about shale diagenesis and organic matter evolution however the origin of the bedding parallel fibrous calcite veins in black shales is still of great controversy carbonaceous black shales of es4s es3x interval are the main source rock in dongying depression bohai bay basin and fibrous calcite veins parallel to bedding are widely spread in these shales petrographic examination fluid inclusion microthermometry and isotopic analyses were conducted to study the timing diagenetic fluid conditions and formation mechanism of fibrous calcite veins the bedding parallel fibrous calcite veins include beef veins and cone in cone structures the beef veins occur as short lenses and are filled with sub vertical fibrous calcite they contain a median line defined with brown granular calcite scattered host rock fragment and pyrite framboids several adjacent beef veins may combine and grow together as a cone in cone structure and black shale laminas involved in it occur as sinusoidal solid inclusions in slices primary two phase inclusions in fibrous calcite have homogenization temperatures th between 86 4 c and 117 4 c the 13c composition of the micritic calcite in host shale ranges from 3 7 to 6 3 vpdb and that of granular calcite ranges from 0 2 to 1 4 vpdb but the fibrous calcite has a moderate 13c values ranging from 1 8 to 5 0 vpdb the 13c compositions of these calcite suggest an evolving carbon source at different burial stages the fibrous calcite likely precipitated from modified pore water at elevated temperature which is supported by its low 18o values 13 7 to 11 4 vpdb the veins formed over two stage and the fibrous calcite growth was continuous and at least partly driven by the force of crystallization the bicarbonate responsible for the fibrous calcite was derived from a mixed source including inorganic carbon from previous carbonate dissolution and organic carbon from both fermentation and thermal decarboxylation

recognition genesis and evolution of manganese ore deposits in southeastern china abstract manganese ore deposits are common in the falang formation of ladinian age middle triassic southeastern yunan china the deposits containing manganese oxide and manganese carbonate ores are not metamorphic in origin and they commonly contain bioclasts concentric ring structures are clearly observed in oolitic and pisolitic manganese ores an integrated approach using sedimentology and paleoenvironment analysis provides new insight into the genesis of these ores systematic research has been conducted on typical deposits dounan yanzijiao laowu tujichong using cathodoluminescence and scanning electron microscope techniques which allow elucidation of changes in laminated microtextures at the mm m scale preliminary results show that manganese enrichment in triassic deposits of this region may be related to microbial activity and mineralization was a consequence of bacterially mediated diagenetic reactions in addition findings of biodetritus in the manganese ore indicate that manganese ore is close to the redox level the concentration of manganese in solution and in precipitates in triassic is controlled by bacterial oxidation and redox conditions corresponding to sea level changes during the ladinian

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

the use of 36cl and chloride bromide ratios in discerning salinity sources and fluid mixing patterns a case study at saratoga springs abstract the well known saratoga springs of new york state are low temperature 10 19 c mildly acidic highly carbonated mineral springs which discharge along the many normal faults in the saratoga mcgregor fault system of eastern north america fifteen saline and moderately saline fluids collected from the saratoga springs system and its surroundings were measured for 36 cl cl ratios chloride concentrations and cl br ratios to determine the sources of salinity fluid mixing patterns and history of these waters the springs have total chloride concentrations between 300 and 6500 mg l far in excess of local freshwater and cl br ratios typically in the range of 100 140 36 cl cl ratios for these waters range from 3 22 10 15 markedly below both the modern rainwater 36 cl cl ratio of above 1500 10 15 and the expected pre nuclear rainwater 36 cl cl ratio for the region of 400 10 15 indicating that cl and 36 cl in these springs are primarily derived from subsurface non meteoric sources 36 cl concentrations and cl br ratios can be effectively used to eliminate the possibility of magmatic ancient marine porefluid and evaporite contributions to the springs 36 cl production rates and secular equilibrium 36 cl cl ratios were derived for different subsurface lithologies in the region based on estimated subsurface neutron fluxes for different rock types a comparison of 36 cl cl ratios and cl br ratios in the saratoga springs with secular equilibrium 36 cl cl ratios and with cl br ratios in potential host formations indicates water rock interactions in the subsurface to be the main source of 36 cl to the springs especially from the ordovician carbonates which make up the aquifer and the underlying cambrian clastic rocks the more dilute springs appear to be a mix of saline springs and a meteoric component probably due to the addition of rainwater as the springs rose to the surface along the fault zone the use of chloride bromide ratios was found to be an effective way to support and clarify the information yielded by 36 cl cl ratios and chloride concentrations in the study of brine history

mantle helium in ground waters of eastern north america time and space constraints on sources mantle helium in continental environments is generally considered to be the result of active volcanism and or active extension the latest episodes of volcanism in northeastern north america are the track of the new england hotspot 95 190 ma and the closure of the iapetus sea before 300 ma thus the identification of mantle helium in young ground waters of central new england is counter to the conventional wisdom on the basis of evaluation of helium evolution in emplaced magmas we postulate an aged mantle source for the excess helium component in ground waters of central new england that is either 1 a local near surface emplaced gas rich magma that has retained significant volatiles e g in fluid inclusions or 2 a deeply emplaced gas rich magma with high initial 2 he 4 he 10 5 and helium transport with dispersion through the crust over time this gas rich initial condition may support the concept of a volatile enriched mantle wedge and thus explain the increased buoyancy flux of the new england hotspot as it traversed eastern north america as has been suggested by others

distribution and mineral assemblages of bedded manganese deposits in shikoku southwest japan implications for accretion tectonics abstract numerous bedded manganese and manganese iron ore deposits occur in shikoku southwest japan the mineralogy wall rock characteristics and fossil age data of the deposits are synthesized in this paper their mineral assemblages correlate well with the progressive metamorphic grade of the accretionary complexes in shikoku based on the plate tectonic framework of subduction accretion process the deposits are considered to have formed by metamorphism of mn fe nodule bearing siliceous sediments on the ocean floor

isotopic geochemistry of the saratoga springs implications for the origin of solutes and source of carbon dioxide we report the results of an isotopic study designed to determine the source of solutes and carbon dioxide in the famed saratoga springs new york mineral waters these waters have thousands of milligrams per liter total dissolved solid concentrations and are highly charged with carbon dioxide gas the spring waters are cold 12 c and there is no local deep seated thermal anomaly they emerge through thick shale caprock along the surface expression of normal faults the 13c 5 8 to 0 8 vienna peedee belemnite of the dissolved inorganic carbon and elevated 3he 4he ratios suggest that the source of the co2 is the mantle or an ancient deep crystallized igneous melt the stable isotopic content of the spring waters defines a mixing line between modern local meteoric waters 70 and a component with heavier d but similar 18o values this trend and that of 87sr 86sr of dissolved strontium versus 1 sr are consistent with the hypothesis that canadian shield type brines contribute salinity to the springs these brines plausibly migrate from the adirondack mountains to the topographically low mcgregor fault system in the hudson river lowlands where the saratoga springs discharge

origin of calcite cements and their impact on reservoir heterogeneity in the triassic yanchang formation ordos basin china a combined petrological and geochemical study abstract calcite cement is a typical product of fluid rock interaction in petroleum reservoirs and its migration has a major impact on reservoir heterogeneity a case study of a closed diagenetic system was carried out on the upper triassic yanchang formation of ordos basin china the most successful exploration region for tight sandstone oil in china the investigated sandstones are mainly lithic arkoses q31f42l27 three occurrences of calcite cement are the most important diagenetic minerals affecting reservoir quality early calcite completely filling intergranular volumes late calcite filling pores after chlorite coating distributed in oil layers or locally replacing feldspar and crystal stock calcite typically distributed in dry layers 13c values of the sandstones are in the range 9 69 to 2 05 indicating that calcite is derived mainly from thermodynamic decarboxylation of organic matter dark mudstone interbedded with sandstone and hydrocarbon emplacement are the two crucial sources of organic fluid providing sufficient ca2 mn2 fe2 and mg2 for calcite precipitation through interaction with feldspar and other silicates such as dissolution and replacement together with transformation of smectite to illite manganese was continuously enriched in calcite during burial diagenesis driven by compaction of interbedded mudstone and fluid overpressure calcite migrated widely into calcite cemented zones cczs where fluid rock interaction was strong such as in the margins of sandstone bodies intrastratal sandstones with original high permeability zones and thin sandstones thereby forming an important organic co2 sink potential high quality reservoirs are distributed mainly in the central part of the closed system restricted by calcite cemented zones and are an exploration target our data suggest that frequently alternating sandstone and mudstone sequences comprise a complete organic co2 source sink system controlling the migration of calcite cement in a closed diagenetic system and reservoir heterogeneity by fluid rock interaction

fluid geochemistry of montserrat island west indies two geochemical surveys carried out in march 1991 and september 1992 revealed the existence of a hydrothermal system in the southern portion of montserrat island below soufriere hills volcano this conclusion is supported by the presence of a the thermal springs of plymouth which are fed by deep na cl waters cl concentration 25 000 mg kg temperature ca 250 c mixed with shallow steam heated waters b the four fumarolic fields of galway s soufriere gages upper soufriere gages lower soufriere and tar river soufriere where acid to neutral steam heated waters are present together with several fumarolic vents discharging vapors formed through boiling of hydrothermal aqueous solutions involvement of magmatic fluids in the recharge of the hydrothermal aquifers is suggested by a the high 3he 4he ratios of fumarolic fluids i e 8 2 ra at galway s soufriere and 5 9 ra at gages lower soufriere b the d and 18o values of na cl thermal springs and steam condensates indicating the involvement of arc type magmatic water in the formation of deep geothermal liquids and c the ch4 co2 ratios of fumarolic fluids which are lower than expected for equilibrium with the feo feo1 5 hydrothermal rock buffer but being shifted towards the so2 h2s magmatic gas buffer

mineralogy of low grade metamorphosed manganese sediments of the urals petrological and geological applications abstract the paper describes mineralogy of the low grade metamorphosed manganese sediments which occur in sedimentary complexes of the pai khoi ridge and the polar urals and volcanosedimentary complexes of the central and south urals the degree of metamorphism of the rocks studied corresponds to pt conditions of the prehnite pumpellyite deposits of pai khoi and polar and south urals and green schist deposits of the central urals facies one hundred and nine minerals were identified in the manganese bearing rocks on the basis of optical and electron microscopy x ray diffraction and microprobe analysis according to the variations in the amount of major minerals of the manganese rocks of the urals they are subdivided on carbonate i oxide carbonate silicate ii and oxide silicate iii types carbonates various mn 2 bearing silicates associated with oxides and carbonates and braunite mn 3 bearing silicate are the major mn hosts in types i ii and iii respectively because of the different oxidation state of mn the rocks of types i and ii are termed as reduced and the rocks of type iii as oxidized the formation of a certain mineralogical type of metamorphic assemblage is controlled by the content of organic matter in the primary sediments the sequence type i type ii type iii reflects the decrease in the amount of organic matter in metalliferous sediments mineralogical data indicate that manganese in the primary sediments accumulated in a silicate form mn si gel glass etc during diagenesis the mn si phase was transformed to neotokite with subsequent formation of caryopilite and further crystallization of pyroxmangite rhodonite tephroite and other silicates due to reactions involving caryopilite the hydrated mn silicates caryopilite and or friedelite and the spatially associated parsettensite stilpnomelane and other minerals are the index minerals of the low grade metamorphism under pt conditions of prehnite pumpellyite facies nearly 70 of silicate minerals are hydrous the metamorphosed mn bearing sediments are characterized by the low temperature caryopilite or tephroite caryopilite pyroxmangite rhodonite and the high temperature caryopilite free or tephroite pyroxmangite rhodonite facies their pt conditions correspond to zeolite and prehnite pumpellyite the low temperature and green schist and higher grade the high temperature facies

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

the influence of oxygen isotope exchange between co2 and h2o in natural co2 rich spring waters implications for geothermometry abstract oxygen isotope ratio 18o value deviations from the meteoric water line with no significant change in the hydrogen isotope 2h composition have been reported in naturally occurring co2 rich waters from around the world here we review the effects of oxygen isotope exchange with co2 high temperature equilibration with bedrock minerals and mineral dissolution and precipitation reactions on the co2 rich water isotopic composition we present two case studies from daylesford australia and pah tempe utah usa mineral springs where we use a numerical geochemical modelling approach to resolve the influence of low temperature water rock interactions and co2 equilibration to the oxygen isotope ranges observed in the mineral waters in both cases we find that mineral dissolution precipitation reactions are unlikely to have a significant effect on the groundwater isotopic compositions and that the observed 18o values in natural co2 springs can be simply explained by equilibrium fractionation between water and free phase co2 traditionally the interaction of co2 and water in a natural co2 rich groundwater setting has only been associated with water 18o depletion and this is the first study to consider 18o enrichment we establish that in a natural setting co2 and water equilibration can result in water 18o depletion or enrichment and that the change in the oxygen isotope composition ultimately depends on the initial co2 and water 18o values our new conceptual model therefore provides a mechanism to explain water 18o enrichment at ambient temperatures this finding is critical for the use of 18o in groundwater geothermometry and for the interpretation of natural water circulation depths we argue that in some cases natural waters previously interpreted as geothermal based on their oxygen isotope composition may actually have acquired their isotopic signature through interaction with co2 at ambient temperatures

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

determination of free co2 in emergent groundwaters using a commercial beverage carbonation meter summary dissolved co 2 in groundwater is frequently supersaturated relative to its equilibrium with atmospheric partial pressure and will degas when it is conveyed to the surface estimates of dissolved co 2 concentrations can vary widely between different hydrochemical facies because they have different sources of error e g rapid degassing low alkalinity non carbonate alkalinity we sampled 60 natural spring and mine waters using a beverage industry carbonation meter which measures dissolved co 2 based on temperature and pressure changes as the sample volume is expanded using a modified field protocol the meter was found to be highly accurate in the range 0 2 35 mm co 2 the meter provided rapid accurate and precise measurements of dissolved co 2 in natural waters for a range of hydrochemical facies dissolved co 2 concentrations measured in the field with the carbonation meter were similar to co 2 determined using the ph alkalinity approach but provided immediate results and avoided errors from alkalinity and ph determination the portability and ease of use of the carbonation meter in the field made it well suited to sampling in difficult terrain the carbonation meter has proven useful in the study of aquatic systems where co 2 degassing drives geochemical changes that result in surficial mineral precipitation and deposition such as tufa travertine and mine drainage deposits

seasonal evolution of upper ocean horizontal structure and the remnant mixed layer 1 we discuss the seasonal evolution of upper ocean thermohaline structure at small horizontal scales the upper 350 m of a 1000 km long section in the subtropical north pacific was observed in winter spring and summer with 3 14 km horizontal resolution four vertical regions had distinct density and salinity structure the mixed layer remnant mixed layer high stratification layer and permanent thermocline the remnant mixed layer consists of water from the winter mixed layer left over after restratification the remnant mixed layer was most similar to the mixed layer in winter and spring and most similar to the high stratification layer below in summer the high stratification layer had elevated stratification that varied seasonally the permanent thermocline varied little seasonally and was horizontally and vertically uniform in comparison in all seasons density ratios showed that mixed layer s differences tended to compensate in density with the strongest tendency toward compensation in winter density ratios were temperature dominated in the remnant mixed layer consistent with salt fingering salinity anomalies were largest at the surface and decayed with depth in all seasons spectra of isopycnal depth and s anomalies along isopycnals are compared between the three seasons and four vertical layers isopycnal depth variance at 30 46 km wavelengths decreased from winter to spring to summer by a factor of 2 10 in stratified regions by treating salinity anomalies as a tracer the effective isopycnal diffusivity in the remnant mixed layer was estimated to be 1 4 m2 s 1 over 30 46 km wavelengths

a large eddy in the central arctic ocean 1 long term moored measurements of temperature salinity and velocity over the abyssal plain near the north pole show a rich array of eddy like structures over a wide range of depths here we demonstrate an anticyclone that extends from the surface to at least 1700 m is about 60 km across and has a likely origin along the eurasian continental margin

geological and geochemical constraints on the cheshmeh frezi volcanogenic stratiform manganese deposit southwest sabzevar basin iran abstract the cheshmeh frezi mn deposit belongs to the southwest sabzevar basin to the north of the central iranian microcontinent this basin which hosts abundant mineral deposits including mn exhalative and besshi type cu zn volcanogenic massive sulfide deposits followed an evolution closely related to the subduction of the neo tethys oceanic crust beneath the central iranian microcontinent two major sedimentary sequences are recorded within this basin i the lower late cretaceous volcano sedimentary sequence llcvss and ii the upper late cretaceous sedimentary dominated sequence ulcss the cheshmeh frezi mn deposit is hosted within red tuff with interbeds of green tuffaceous sandstone of the llcvss mineralization occurs as stratiform blanket like and tabular orebodies psilomelane pyrolusite and braunite are the main minerals of the ore which display a variety of textures such as layered laminated disseminated massive replacement or open space fillings the footwall and hanging wall volcanic rocks are predominantly andesite and trachyandesite rocks footwall and hangingwall volcanic rocks at cheshmeh frezi are enriched in light rare earth elements lrees compared to chondrite have steep ree patterns and generally show ta and nb depletions relative to chondrite which are characteristic of back arc environments the significant geochemical characteristics of ore such as high mn content 12 41 33 14 wt average 19 41 wt low concentration of fe 0 64 2 27 wt average 1 63 wt high ba 49 7 9901 ppm average 2728 67 ppm lree hree and negative ce and eu anomalies reveal a primary distal hydrothermal exhalative source for mineralization cheshmeh frezi deposit in comparison with different types of volcanogenic manganese deposits shows broad similarities with the cuban type mn deposits such as tectonic host and associated rock types geometry textures structures mineralogy and lithogeochemistry

stable isotope geochemistry of cold co2 bearing mineral spring waters daylesford victoria australia sources of gas and water and links with waning volcanism abstract mineral springs in the victorian central highlands australia have high co 2 contents and naturally effervesce 13 c values of co 2 gas and dissolved inorganic carbon are 10 6 to 7 0 and 5 9 to 0 1 respectively with a net 13 c of 8 to 3 the carbon in these waters was derived from a mantle source associated with local pliocene to recent basaltic newer volcanic province rocks previously reported 3 he 4 he 1 2 3 1 relative to air and high he ne ratios are also consistent with the presence of magmatic volatiles silica contents imply that the waters were never heated above 130 c and that the system is not hydrothermal the occurrence of carbonated mineral springs in a relatively small region of the newer volcanics province where volcanic activity ceased several thousands of years ago may be due to the presence of late intrusions combined with deep circulation of water through deeply weathered and fractured ordovician basement a region of low seismic velocity under the daylesford area potentially images those intrusions most spring waters have 18 o and 2 h values of 8 to 6 and 45 to 35 respectively and lie to the left of the local and global meteoric water lines the anomalously low 18 o values results from co 2 exsolution at low temperatures which strongly partitions 18 o into the gas the lack of waters lying to the right of the local meteoric water line also implies that water rock interaction at elevated temperatures did not occur the 2 h values are lower than contemporary meteoric water suggesting that the waters may have recharged under colder climate conditions several thousand years ago the local ordovician rocks are gold bearing the present spring system is cold and would not efficiently transport au however volcanic is waning and the spring systems at the time of volcanism may have been hotter and able to redistribute au

towed thermistor chain observations of fronts in the subtropical north pacific a thermistor chain was towed 1400 km through the eastern north pacific subtropical frontal zone in january 1980 the observations resolve surface layer temperature features with horizontal wavelengths of 0 2 200 km and vertical scales of 10 70 m the dominant features which have horizontal wavelengths of 10 100 km amplitudes of 0 2 1 0 c and random orientation likely arise from baroclinic instability associated with them is a plateau below 0 1 cpkm in the horizontal temperature gradient spectrum strong temperature fronts o 1 2 c 3 10 km are observed near 33 n 31 n and 27 n temperature variability is partially density compensated by salinity with the fraction of compensation increasing northward there is evidence of vertical mixing during high winds temperature at 15 m depth is roughly normally distributed around the climatological surface mean with a standard deviation of approximately 0 5 c the standard deviation would correspond to an adiabatic meridional displacement of 80 100 km in the mean gradient horizontal temperature gradient at 15 m depth has maximum values in excess of 0 25 c 100 m and kurtosis near 80 in the band 0 10 1 cpkm the 15 m gradient spectrum is inversely proportional to wave number consistent with predictions from geostrophic turbulence theory while the spectrum at 70 m depth has additional variance that is consistent with garrett munk internal wave displacements

he ne ar and c isotope systematics of geothermal emanations in the lesser antilles islands arc the authors present he ne ar and c isotope analyses of hydrothermal brines and gases from fumaroles hot springs mofettes and hydrothermal exploration drillings on the major islands of the lesser antilles arc the origin of hydrothermal brines which have been analyzed also for o and h isotopes is essentially meteoric hydrothermal air corrected isotope compositions of helium 2 2 rc ra sup 3 he sup 4 he 8 6 rc ra and carbon minus 20 delta sup 13 c sub pdb 0 5 are variable and require a variety of crustal and magmatic sources the diversity of delta sup 13 c sub pdb and sup 3 he co sub 2 ratios within individual volcanic centers suggests that crustal sources e g limestone contaminate magmatic co sub 2 en route from high level magma reservoirs depth 15 km to the surface a similar contamination may be found for magmatic helium on distal springs the sup 3 he sup 4 he signature of summit fumaroles thought to reflect the sup 3 he sup 4 he signature of high level magmas shows a remarkable systematic variation along the arc in addition there is a correlation throughout the arc between published sr pb and nd isotope signatures of lavas and the sup 3 he sup 4 he signatures of summit fumaroles on the northern islands nevis montserrat guadeloupe and dominica summitmore fumaroles have the n morb signature sup 3 he sup 4 he 8 1 r ra and the isotope signature of lavas is not dissimilar from comparable intra oceanic arc tholeiites elsewhere variable enrichments in radiogenic sr and pb have been reported for lavas of individual volcanic centers of the southern islands martinique st lucia and grenada and summit fumaroles on these centers match these variations by variable radiogenic he enrichments i e lower sup 3 he sup 4 he ratios this correlation suggests that radiogenic sr and pb enrichments of lavas and low sup 3 he sup 4 he signatures on summit fumaroles have a common origin i e a terrigenous contaminant derived from the orinoco depositionary fan crustal assimilation is thought to decouple the he isotope system from any other radiogenic isotope system and therefore the authors argue that the observed correlation of he sr pb and nd isotope systems is related to a terrigenous contaminant derived from subducted sediments support for this scenario also comes from the matching of low sup 3 he sup 4 he ratios and tectonic features of the forearc thought to favor the subduction of forearc sediments the present study offers a first clue that under suitable conditions crustal helium from oceanic sediments might be subducted to the depth of arc magma sources and possibly even recycled into the deeper mantle less

pore fluid evolution distribution and water rock interactions of carbonate cements in red bed sandstone reservoirs in the dongying depression china the compositions distribution and its interaction with rocks of the evolving pore fluids controls the distribution of carbonate cements and reservoir storage spaces the reservoir quality of the red bed sandstone reservoirs in the dongying depression was investigated by an integrated and systematic analysis including carbonate cement petrology mineralogy carbon and oxygen isotope ratios and fluid inclusions the investigation was also facilitated by probing the mineral origins precipitation mechanisms pore fluid evolution and distribution and water rock interaction of carbonate cements and their influences on reservoir quality diagenetic evolving fluids in the interbedded mudstones are the main source for the precipitation of calcite cements that completely fill the intergranular volume cfiv calcite with heavier oxygen and carbon isotopes the ferro carbonate cements in the reservoir sandstone are enriched in lighter carbon and oxygen isotopes in addition to the cations released by the conversion of clay minerals in reservoirs products of organic acid decarboxylation and the associated feldspar dissolution process provide important sources for such carbonate cementation the carbon isotopes of co2 and the oxygen isotopic composition of fluids equilibrated with the cfiv calcite ferro calcite dolomite and ankerite cements indicate that the pore in the red bed reservoirs experienced high salinity fluids which evolved from the early formed interbedded mudstones through organic acid input and to organic acid decarboxylation pore fluids from nearby mudstones migrated from the edge to the centre of sandbodies causing strong calcite cementation along the sandbody boundaries and forming tight cementation zones pore fluids associated with organic co2 and acids and organic acid decarboxylation are mainly distributed in the internal portion of sandbodies causing feldspar dissolution and precipitation of ferro carbonate cements the distribution of pore fluids caused the zonal distribution of carbonate cements in sandbodies during different periods this may be advantageous to preserve the porosity of reservoirs as exemplified by the distribution of high quality reservoirs in the red bed sandbodies

adirondack appalachian crustal structure the cocorp northeast traverse reflection surveys from northeastern new york and central vermont the first elements of a cocorp seismic traverse of grenville and appalachian terranes in the northeastern united states indicate that an unusual zone of layered reflections characterizes the lower crust beneath the eastern adirondacks and that grenville age basement of the green mountains may actually be allochthonous perhaps thrust over paleozoic shelf rocks the top of the adirondack deep layered sequence is found at about 20 km beneath the marcy meta anorthosite massif it appears to dip about 10 northwestward and wedge out against more horizontal reflections at about 28 km this intracrustal sequence may correspond with a previously inferred increase in electrical conductivity possible interpretations range from its being a layered igneous complex to its representing a tectonically buried metasedimentary assemblage although graphitic schists and iron or sulfide segregations in such an assemblage might contribute to its electrical characteristics the problematical issue of water in the lower crust if and how it got there and remained is again raised if not resolved other intrabasement features include major east and west dipping reflections possibly corresponding to faults arched reflections that may represent folds a well defined lens shaped zone virtually devoid of reflections and possible moho reflections unequivocal sub moho reflections are absent superimposed at shallower levels on the eastern part of the traverse are appalachian structures reflections down to about 4 5 km beneath the taconic mountains are interpreted to represent paleozoic shelf sediments of the middlebury synclinorium underlying the taconic allochthons possibly correlative although less well defined reflections appear to extend in disrupted fashion beneath the precambrian rocks of the green mountains suggesting a major basement overthrust the inferred decollement for this overthrust steepens rapidly beneath the east flank of the green mountains east dipping reflections at the east side of the green mountains may represent another major thrust zone involving basement and overlying metasedimentary slices the basement overthrusting suggested by this study is similar in certain respects to the style if not the extent of that demonstrated by previous cocorp surveys in the southern appalachians

a geochemical constraint on the formation process of a manganese carbonate nodule in the siliceous mudstone of the jurassic accretionary complex in the mino belt japan abstract manganese mn carbonate nodules which differ from seafloor mn nodules mainly composed of mno 2 are occasionally embedded in the form of a lens shape in the jurassic accretionary complexes such as the mino belt in japan the interpretation of the formation process of mn carbonate is still controversial particularly concerning whether the mn carbonate was formed primarily or secondarily in this study a fresh mn carbonate nodule incorporated into the red siliceous mudstone was collected for geochemical and sedimentological analysis the optical observation of thin sections indicates that the mn carbonate nodules are composed of abraded grains of rhodochrosite spherule with radiolarians and are sedimentary embedded in siliceous mudstone microfossil radiolarians from the mn carbonate nodules and the host red siliceous mudstone are dated as the bajocian but the radiolarians in the nodules are somewhat older than those in the host red siliceous mudstone geochemical analysis using the x ray absorption near edge structure on ce indicates the dominance of trivalent ce at present despite the observation of a positive ce anomaly in the paas normalized ree pattern of mn carbonate the ree adsorption experiment on synthesized mnco 3 does not show any distinctive positive ce anomaly and a thermodynamic calculation suggests the possible coexistence of rhodochrosite and spontaneous oxidation of ce a leaching experiment that can selectively decompose the carbonate phase demonstrated no ce anomaly in the carbonate phase of the mn carbonate and a poor contribution to the bulk ree concentration the carbon isotope data of mn carbonate nodule implied the dominance of inorganic marine carbonate origin with small contribution of organic decomposition the most plausible account of all of the observational and geochemical results is that the rhodochrosite grains were primarily formed on the depositional site and subsequently transferred to a different site where siliceous mudstone was deposited

revisiting internal waves and mixing in the arctic ocean 1 to determine whether deep background mixing has increased with the diminishment of the arctic sea ice we compare recent internal wave energy and mixing observations with historical measurements since 2007 the north pole environmental observatory has launched expendable current probes xcps as a part of annual airborne hydrographic surveys in the central arctic ocean mixing in the upper 500 m is estimated from xcp shear variance and conductivity temperature depth ctd derived brunt vaisala frequency internal wave energy levels vary by an order of magnitude between surveys although all surveys are less energetic and show more vertical modes than typical midlatitude garrett munk gm model spectra survey averaged mixing estimates also vary by an order of magnitude among recent surveys comparisons between modern and historical data reanalyzed in identical fashion reveal no trend evident over the 30 year period in spite of drastic diminution of the sea ice turbulent heat fluxes are consistent with recent double diffusive estimates both mixing and internal wave energy in the beaufort sea are lower when compared to both the central and eastern arctic ocean and expanding the analysis to mooring data from the beaufort sea reveals little change in that area compared to historical results from arctic internal wave experiment we hypothesize that internal wave energy remains lowest in the beaufort sea in spite of dramatic declines in sea ice there because increased stratification amplifies the negative effect of boundary layer dissipation on internal wave energy

dissected hydrologic system at the grand canyon interaction between deeply derived fluids and plateau aquifer waters in modern springs and travertine geochemical study of water and gas discharging from the deeply incised aquifer system at the grand canyon arizona provides a paradigm for understanding complex groundwater mixing phenomena and quaternary travertines deposited from cool springs provide a paleohydrologic record of this mixing geochemical data show that springs have marked compositional variability those associated with active travertine accumulations deeply derived endogenic waters are more saline richer in co2 and elevated in 87sr 86sr relative to springs derived dominantly from surface recharge of plateau aquifers epigenic waters endogenic waters and associated travertine are preferentially located along basement penetrating faults we propose a model whereby deeply derived fluids are conveyed upward via both magmatism and seismicity our model is supported by 1 gas analyses from spring waters with high he ar and he n2 and 3he 4he ratios indicating the presence of mantle derived he 2 large volumes of travertine and co2 rich gases in springs recording high co2 fluxes and 3 87sr 86sr in these springs that indicate circulation of waters through precambrian basement geochemical trends are explained by mixing of epigenic waters of the colorado plateau aquifers with different endogenic end member waters in different tectonic subprovinces endogenic waters are volumetrically minor but have significant effects on water chemistry they are an important and largely unrecognized component of the hydrogeochemistry and neotectonics of the southwestern united states

characterizing horizontal variability and energy spectra in the arctic ocean halocline energy transfer from the atmosphere into the upper arctic ocean is expected to become more efficient as summer sea ice coverage decreases and multiyear ice thins due to recent atmospheric warming however relatively little is known about how energy is transferred within the ocean by turbulent processes from large to small scales in the presence of ice and how these pathways might change in future this study characterises horizontal variability in several regions of the eurasian arctic ocean under differing sea ice conditions historic along track ctd data collected by a royal navy submarine during summer 1996 allows a unique examination of horizontal variability and associated wavenumber spectra within the arctic ocean halocline spectral analysis indicates that potential energy variance under perennial sea ice in the amundsen basin is o 100 less than within the marginal ice zone miz of fram strait spectra from all regions show a transition in scaling at wavelengths of approximately 5 to 7 km at scales greater than the transition wavelength to 50 km energy spectra are consistent with a k 3 scaling where k is wavenumber and interior quasi geostrophic dynamics the scaling of spectra at these scales is extremely similar between regions suggesting similar dynamics and energy exchange pathways the k 3 scaling is steeper than typically found in regions of mid latitude open ocean at scales below the transition wavelength to 300 m spectra are close to a k 5 3 scaling or flatter indicating a change in dynamics which is potentially due to internal waves dominating variability at small scales this article is protected by copyright all rights reserved

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

thermohaline variability in the upper ocean the main goal of this exploratory study is to determine how the temperature salinity relationship changes with horizontal length scale and depth in the ocean temperature and salinity were measured on a range of scales from 4 m to 1000 km towing a seasoar along isobars and isopycnals in the subtropical gyre of the north pacific during the winter of 1997 the wavelet transform technique is used to compute the horizontal density ratio and thermohaline variability as a function of scale and location measurements along an isobar in the mixed layer show that the horizontal density ratio is 1 at all scales observed that is horizontal temperature and salinity gradients tend to cancel each other in their effect on density thermohaline variability at small scales is intermittent and clusters around large scale thermohaline anomalies below the base of the mixed layer horizontal gradients of temperature are only partially opposed by salinity and the density ratio is close to 2 in the thermocline the distribution of thermohaline variability is uniform along isobars but intermittent and colocated at different scales along isopycnals density compensated variability ubiquitous in the mixed layer is reduced along deeper isopycnals compensation of horizontal temperature and salinity gradients supports recent theoretical ideas that mixing in the winter mixed layer depends on horizontal density gradients

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

fossil brines preserved in the st lawrence lowlands quebec canada as revealed by their chemistry and noble gas isotopes abstract brines in cambrian sandstones and ordovician dolostones of the st lawrence lowlands at becancour quebec canada were sampled for analysis of all stable noble gases in order to trace their origin and migration path in addition to quantifying their residence time major ion chemistry indicates that the brines are of na ca cl type possibly derived from halite dissolution 87 sr 86 sr ratios and ca excess indicate prolonged interactions with silicate rocks of the proterozoic grenville basement or the cambrian potsdam sandstone the brines constrain a 2 3 contribution of mantle 3 he and large amounts of nucleogenic 21 ne and 38 ar and radiogenic 4 he and 40 ar 4 he 40 ar and 21 ne 40 ar ratios corrected for mass fractionation during incomplete brine degassing are identical to their production ratios in rocks the source of salinity halite dissolution plus the occurrence of large amounts of 40 ar in brines constrain the residence time of becancour brines as being older than the cretaceous evaporites in the st lawrence lowlands likely existed only during devonian silurian time brines might result from infiltration of devonian water leaching halite penetrating into or below the deeper cambrian ordovician aquifers during the devonian the basin reached temperatures higher than 250 c allowing for thermal maturation of local gas prone source rocks utica shales and possibly facilitating the release of radiogenic 40 ar into the brines the last thermal event that could have facilitated the liberation of 40 ar into fluids and contributed to mantle 3 he is the cretaceous monteregian hills magmatic episode for residence times younger than the cretaceous it is difficult to find an appropriate source of salinity and of nucleogenic radiogenic gases to the becancour brines

controls on chemistry during fracture hosted flow of cold co2 bearing mineral waters daylesford victoria australia implications for resource protection abstract mineral springs from daylesford australia discharge at ambient temperatures have high co2 contents and effervesce naturally mineral waters have high hco3 and na concentrations up to 4110 and 750 mg l respectively and co2 concentrations of 620 2520 mg l calcium and mg concentrations are 61 250 and 44 215 mg l respectively and si sr ba and li are the most abundant minor and trace elements the high pco2 of these waters promotes mineral dissolution while maintaining low ph values and geochemical modelling indicates that the co2 rich mineral water must have interacted with both sediments and basalts amorphous silica concentrations and silica geothermometry indicate that these waters are unlikely to have been heated above ambient temperatures and therefore reflect shallow circulation on the order of several hundreds of metres variations in minor and trace element composition from closely adjacent spring discharges indicate that groundwater flows within relatively isolated fracture networks the chemical consistency of individual spring discharges over at least 20 a indicates that flow within these fracture networks has remained isolated over long periods the mineral water resource is at risk from mixing with potentially contaminated surface water and shallow groundwater in the discharge areas increased 2h values and cl concentrations and lower na concentrations indicate those springs that are most at risk from surface contamination and overpumping elevated no3 concentrations in a few springs indicate that these springs have already been contaminated during discharge

observations of internal gravity waves under the arctic pack ice internal gravity waves measured under the arctic pack ice were strikingly different from measurements at lower latitudes the total wave energy integrated over the internal wave frequency band was lower by a factor of 0 03 0 07 and the spectral slope at high frequency was nearly 1 in contrast to the 2 observed at lower latitudes this result has implications for theoretical investigations of the generation evolution and destruction of internal waves and is also important for other processes such as the propagation of sound and the wave induced turbulent diffusion of heat plankton and chemical tracers

book review helium isotopes in nature developments in geochemistry 3 by b a mamyrin and i n tolstikhin elsevier amsterdam 1984 xiv 273 pp price u s 53 75 u s a and canada dfl 140 00 rest of world hardback

the influence of multiple stage oil emplacement on deeply buried marine sandstone diagenesis a case study on the devonian donghe sandstones tabei uplift tarim basin nw china abstract understanding the oil emplacement influence on diagenesis is one of the most key factors of reservoir quality prediction the devonian donghe sandstones are deeply buried to 5700 6000 m and they are important exploration target in the tarim basin additional the reservoirs experienced multi phase hydrocarbon accumulation and destruction the donghe sandstones contain various diagenetic minerals which are mainly composed of calcite cement a small amount of quartz overgrowth and pyrite trace ankerite and ferrocalctie the current study investigates the influence of multiple stage oil emplacement on the diagenesis with particular attention to calcite and quartz cementation of marine clastic reservoir interval of the donghe sandstones in the tarim basin the samples in the oil leg and water leg have been collected and a series of studies were performed including thin section petrography scanning electron microscopy sem carbon and oxygen isotopes and cathodoluminescence cl analysis the 13cv pdb values of calcite cement from the oil leg and water leg between 4 73 and 1 21 and 3 81 to 0 86 respectively the 18ov pdb values of calcite cement from the oil leg and water leg range from 15 59 to 6 61 and 14 97 to 7 76 respectively both of them display no obviously different in the oil leg and water leg all of the 13cv pdb values in the whole interval of the donghe sandstones show lightly depletion was explained mixing from marine carbon and carbon produced from bacterial sulfate reduction bsr that happens during petroleum degradation associated with sulfate reduced by hydrocarbons bacterially two dull luminescence zones trace fe and mn content and high fe accompanied by low mn content and orange red and bright orange yellow luminescence zones in oil leg indicate four generations of calcite occurred whereas two generations of calcite occurs in water leg which are dull and orange red luminescence zones two origins of calcite cement were clearly identified marine biogenic carbonates and hydrocarbon related from palaeo reservoir bsr during uplift the first generation of calcite cement originated from biogenic carbonate the second and third generations of calcite cement were mixing from predate carbonate cement dissolved and re precipitated and calcite precipitated by bsr directly some quartz grains and k feldspars were dissolved by residual organic acids that remained in the irreducible water and following replaced by the fourth generation of calcite cement some calcite cement in the oil leg precipitated in a temperature higher than the homogeneous temperature of fluid inclusion which indicates oil emplacement has no influence on calcite cementation the quartz overgrowth postdate the first hydrocarbon accumulation and predate the second hydrocarbon accumulation which originated from quartz grains dissolved by organic acids that produced from bsr and re precipitated at a low temperature the current study can promote the understanding of the influence of multiple stage hydrocarbon accumulation on diagenesis and it can also inspire the diagenesis process of other paleozoic hydrocarbon reservoirs in the tarim basin

plate tectonics radiogenic isotopic tracers and paleoceanography the case of the manganese crusts in the pacific abstract hydrogenous ferromanganese crust deposits on seafloor and volcanic seamounts are archives of past isotopic compositions of the ocean isotopic compositions of long life radiogenic isotopes that are dissolved in the ocean such as nd and pb are mixtures of different erosion products continents volcanics arcs ridges etc transported by oceanic currents or winds isotopic studies on mn crusts are thus potential paleogeographic and paleoceanographic tracers however global paleogeography can drastically evolve over the period of growth of crust as well as the latitude longitude and water depth of the mn crust thus each crust sampled a succession of geographic sites related to its spatial evolution through time for this reason valid information about the past ocean isotopic composition can only be extracted from mn crust under the condition that the successive paleogeographic and paleodepth positions can be reconstructed for each mn crust we followed this approach for six hydrogenous mn crusts from the pacific ocean that have recorded pb and nd isotopic signals for the past 80 myr the evolution of the isotopic data was considered within a proper geodynamical framework that takes into account the paleopositions of the pacific plate and surrounding continents of the hot spots and ridges as well as the paths of the six crusts the differences and similarities between the pb and nd revealed by our analysis emphasize their complementarity as paleoceanographic tracers the nd isotopes are strongly influenced by the exchange between indian and pacific waters specifically by the progressive closure of the indonesian gateway the closed central pacific characteristics are defined from the extrapolation of the isotopic trend this highlights the important role played by erosion of volcanic arcs in the nd isotopic value of seawater our approach also stresses the influence of local volcanic activity ridges or active hot spot for lead isotopes

the use of strontium and lead isotopes to identify sources of water beneath the fresh kills landfill staten island new york usa abstract a study was undertaken to explore whether the isotopic compositions of pb and sr are useful to distinguish mixtures of uncontaminated groundwater seawater and landfill leachate at the fresh kills landfill staten island new york ratios of 87sr 86sr ranged from 0 7088 to 0 7137 and could be used to distinguish sr that was derived from seawater from that in uncontaminated groundwater lead isotopic abundances did not vary systematically among the different water sources plots of 87sr 86sr versus dissolved organic c b and nh4 defined perpendicular trends documenting where leachate or sea water mixed with uncontaminated groundwater and demonstrating that leachate has not contaminated groundwater in aquifers beneath the landfill

mixing across the arctic ocean microstructure observations during the beringia 2005 expedition 1 turbulent scale temperature and conductivity were measured during the pan arctic beringia 2005 expedition the rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from alaska to the north pole across deep flat basins canada and makarov basins and steep ridges alpha mendeleev and lomonosov ridges the mixing rates are observed to be small relative to lower latitudes but also remarkably non uniform relatively elevated turbulence is found over deep topography confirming the dominant role of bottom generated internal waves measured patterns of mixing in the arctic are also associated with other mechanisms such as double diffusive structures and deep overflows a better knowledge of the distribution of mixing is essential to understand the dynamics of the changing arctic environment

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

contemporary doming of the adirondack mountains further evidence from releveling abstract the adirondack mountains constitute an anomalously large domical uplift on the appalachian foreland the dome has a nne ssw axis about 190 km long and an east west dimension of about 140 km it has a structural relief of at least 1600 m and a local topographic relief of up to 1200 m first order leveling in 1955 and again in 1973 along a north south line at the eastern margin of the adirondack shows an uplift rate of 2 2 mm yr at the latitude of the center of the dome and a subsidence rate of 2 8 mm yr at the northern end of the line near the canadian border the net amount of arching along this releveled line is 9 cm 2 cm isachsen 1975 to test the idea that this arching represented an edge effect of contemporary doming of the adirondacks as a whole the national geodetic survey was encouraged to relevel a 1931 north south line between utica and fort covington near the canadian border which crosses the center of the dome the releveling showed that the mountain mass is undergoing contemporary domical uplift at a rate which reaches 3 7 mm yr near the center of the dome compare with 1 mm yr for the swiss alps three other releveled lines in the area support this conclusion the domical configuration of the area undergoing uplift combined with subsidence along the northeastern perimeter of the dome argues for a geothermal rather than glacioisostatic origin a contemporary hot spot near the crust mantle boundary is proposed as the mechanism of doming based on analogy with uplifts of similar dimensions elsewhere in the world some of which have associated tertiary volcanics the lack of thermal springs in the area or high heat flow in drill holes up to 370 m deep indicates that the front of the inferred thermal pulse must be at some depth greater than 1 km the present adirondack dome did not come into existence until sometime after late devonian time based on isopach maps by rickard 1969 1973 strata younger than this which might provide further time stratigraphic refinement of this lower limit do not occur in the region however the consequent radial drainage pattern in the adirondacks indicates that the dome is a relatively young tectonic feature aligned with the long axis of the rising dome are prominent nne faults and lineaments the region is one of recurring low level seismic activity fault plane solutions indicate a wsw ene axis of compression aggarwal and sykes 1977 which indicates an anomalous relationship between doming and seismicity

strontium isotopic composition of some brines from the precambrian shield of canada abstract twenty four groundwater samples from seven operating mines at sudbury yellow knife and thompson ontario north west territories and manitoba resp all from depths greater than 1 km and ranging in total dissolved solids tds from 1900 to 250 000 mg l 1 were measured for their 87 sr 86 ar values each geographic location gives a limited range in values and each location is distinct from the others this is interpreted as the result of extensive water rock interaction on a local scale for most of the time these brines were isolated and only recently have been exposed to surface water as a result of the mining operations the extent of the isolation is shown by the contrasting isotopic values of two pockets of water 0 711 vs 0 716 located on opposite sides of the same fault system on the north range at sudbury the exchange at all sites probably has continued until the present as indicated by the close agreement between water and present day 87 sr 86 sr whole rock values if so it suggests that there is no single age for such brines but it may be possible to date stages in the water s evolution by determining the age of secondary minerals that equilibrated with the water

the central india tectonic zone a geophysical perspective on continental amalgamation along a mesoproterozoic suture abstract the central india tectonic zone citz is a prominent divide and a major suture zone between the north indian and south indian crustal blocks the resistive upper crust as modeled in the magnetotelluric data from citz suggests a dominant tonalite trdondhjemite granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components the highly conductive bodies in this zone might represent mafic ultramafic layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the cretaceous deccan flood basalts the uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of archaean and paleoproterozoic subducted slabs we redefine the nature of deep faults traversing the citz which were described as steep and penetrating the moho by previous workers and classify them as listric faults with gentle dips at depth seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the bhandara craton reflection data from the central part of the citz show northerly dip in the southern part suggesting northward subduction of the dharwar craton however an opposite trend is observed in the northern part of the suture with a southward dip of the bundelkhand craton based on these features and in conjunction with existing magnetotelluric models we propose a double sided subduction history along the citz this would be similar to the ongoing subduction accretion process in the western pacific region which possibly led to the development of paired collision type and pacific type orogens one important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust the high resistivity felsic domain suggests underplated sediments felsic crust that would have caused the doming our model also accounts for the extrusion of regional metamorphic belts at the orogenic core and the occurrence of high pressure ultrahigh temperature paired metamorphic belts within the suture

metallogeny and temporal spatial distribution of manganese mineralizations in iran implications for future exploration abstract there are a lot of manganese mn deposits and numerous mineral occurrences of this type of mineralization in iran the major tectonic structural zones of iran that host manganese deposits are 1 urumieh dokhtar magmatic assemblage udma 2 the central iran ci 3 the sabzevar zone sz 4 the alborz magmatic belt amb and 5 the cretaceous ophiolites these manganese deposits were formed during discrete time periods 1 late neoproterozoic early cambrian narigan and halab deposits in the ci 2 jurassic halalan deposit in the sz 3 cretaceous mn mineralizations in the late cretaceous volcano sedimentary sequence of southwest sabzevar basin in the sz nasirabad abadeh tashk alashtar sorkhvand esfandagheh benvid gugher kamar talar sardasht and safou manganese deposits in the southeast of birjand dehoo and north of sabzevar deposits which occur in the upper cretaceous ophiolites and 4 eocene miocene e g venarch jalal shahrestanak boznein garab menamin robat karim qaleh mohammad khan rabiei zarashlou narkan sarikand jokandy gharaeh tavaragh and barout aghaji deposits in the udma and amb magmatic arcs intra arc rifts and back arc basins are the principal plate tectonic settings for iranian manganese deposits all of the manganese deposits of the udma and amb formed within tertiary arc and back arcs respectively that developed during subduction of the neo tethyan crust beneath the iranian plate intra oceanic or continental back arc spreading settings are recognized in the neo tethys domain in iran and these host several manganese deposits in the sz and ophiolites the trace element content of all studied manganese deposits is generally low in concentrations and tends to enrichment in the assemblage of v cu pb zn and as with geochemical characteristics similar to hydrothermal deposits rare earth element ree patterns of the iranian manganese deposits support a hydrothermal origin the main time period of formation of manganese mineralization in iran was from cretaceous to miocene the udma and sz are the most favourable metallogenic provinces in iran for manganese exploration because these zones host the most and the largest manganese deposits including venarch and shahrestanak deposits in the udma and manganese mineralizations in the late cretaceous volcano sedimentary sequence of the southwest sabzevar in the sz

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

diagenetic constraints on the heterogeneity of tight sandstone reservoirs a case study on the upper triassic xujiahe formation in the sichuan basin southwest china abstract heterogeneity is an essential feature of tight sandstones because it is directly related to reservoir quality the upper triassic xujiahe formation in the sichuan basin was used as a case study to analyse the diagenetic constraints on the heterogeneity of tight sandstone reservoirs the three main diagenetic processes of interest are mechanical compaction cementation and dissolution a dissolution facies quartz cement facies and carbonate cement facies present sequentially from the centre to the margin of sand bodies abundant feldspars and rock fragments were dissolved to form secondary porosity or filled by carbonate cement authigenic chlorite coatings generated from eogenesis to the deep burial stage are thickest in high porosity samples the 13 c of carbonate cement ranges from 10 56 to 1 15 pdb suggesting multiple sources of carbon including carbonate fragments early inorganic carbonate cement and organically derived co 2 based on 18 o carbonate cementation occurred from 33 c to 110 c microthermometric data of aqueous inclusions indicate that quartz cement precipitated at a temperature range of 120 c 140 c a summary model of the diagenetic constraints on the heterogeneity of sandstones was constructed the spatial distribution of digenetic facies is controlled by differences in fluid flow velocity and ph fluids especially hydrocarbons migrated preferentially within the centre of sand bodies and caused dissolution dissolution generated secondary porosity and provided materials for authigenic mineral precipitation carbonate fragments were better preserved and superimposed with later carbonate cement along the sandstone mudstone boundary quartz overgrowths formed after carbonate cementation and developed in the transition zone between the intervals of carbonate cementation and dissolution consequently the reservoir quality of the xujiahe sandstones decreases gradually moving from the centre to the margin of the sand bodies

constraining paleo latitude of a biogeographic boundary in mid panthalassa fusuline province shift on the late guadalupian permian migrating seamount abstract the guadalupian paleo atoll limestone iwato formation in sw japan was primarily formed in low latitude mid panthalassa and was later tectonically accreted to south china japan margin during the jurassic the present biostratigraphic study clarified that the iwato formation consists of 5 biostratigraphical intervals i e four fusuline assemblage zones assemblage zones 1 to 4 and a barren interval on the top assemblage zones 1 to 4 correspond to the neoschwagerina craticulifera zone n margaritae zone yabeina globosa zone and lepidolina multiseptata zone of the conventional tethyan fusuline stratigraphy respectively the present study newly clarified the following significant aspects of paleobiogeography of the permian fusulines as to the extinction of large tested taxa in the latest guadalupian 1 the long unknown stratigraphic relationship was documented for the first time between the yabeina dominant interval and the overlying lepidolina dominant one within a single limestone unit 2 the occurrence of lepidolina cf kumaensis kanmera the unique last runner of large tested fusuine was detected for the first time in mid oceanic paleo atoll limestones 3 with respect to the northbound migration history of the paleo seamount capped by the iwato formation the development of the two coeval fusuline biogeographic territories in the low latitude panthalassa i e the yabeina territory on the south and the lepidolina territory on the north was confirmed 4 the paleo latitude of the biogeographic boundary between the yabeina and lepidolina territories is constrained around 12 in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone this new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo latitude data is applicable to other cases in different time space co ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past

arctic sea ice thickness characteristics in winter 2004 and 2007 from submarine sonar transects 1 a transect of the arctic ocean by the british submarine tireless in march 2007 enabled the thickness characteristics of the ice cover to be measured during the winter immediately preceding the exceptional retreat of summer 2007 in this paper we report on mean and modal drafts probability density functions of draft and the frequency and depth distribution of pressure ridges and we compare results with those from an earlier submarine cruise in winter 2004 which covered part of the same area in the region from north of fram strait to ellesmere island about 85 n 0 70 w we find no change in mean drafts between 2004 and 2007 though there is a change in ice composition with more ridging in 2007 but a lesser modal draft this agrees with the observations of younger ice being driven toward fram strait in 2007 the region north of ellesmere island continues to be a redoubt containing more thick deformed multiyear ice than any other part of the transect in the west the submarine profiled extensively under the sedna ice camp at 73 n 145 w this is in the same location as the 1976 aidjex ice camp and a sonar survey done by a u s submarine in april 1976 we found that a large decrease in mean draft had occurred 32 over 31 years and that in 2007 the sedna region contained the thinnest ice of any part of the arctic surveyed by the submarine this was a region from which the ice completely retreated during the subsequent summer of 2007

geochemistry and origin of piemontite quartz schists in the sanbagawa metamorphic belt central shikoku japan abstract in the sanbagawa metamorphic belt of central shikoku geochemical characteristics are used to demonstrate that piemontite quartz schists had a manganiferous sedimentary protolith the sanbagawa metamorphic belt was formed during a cretaceous regional intermediate high pressure type of metamorphism which is present throughout southwest japan based on a detailed mineralogical study of the asemi gawa and besshi areas in central shikoku the sanbagawa piemontite quartz schists can be divided into talc bearing and talc free types phlogopite occurs only in talc bearing assemblages and the modal percentage of piemontite in talc bearing types is higher than in talc free types plotting analyses of piemontites and garnets from talc bearing and talc free types in the al2o3 fe2o3 mn2o3 mno al fe3 mn3 mn2 diagram for the asemi gawa and besshi areas separately shows that the piemontite which accompanies talc is richer in mn3 and poorer in fe3 also garnets from talc bearing assemblage contain a slightly higher amount of mn2 and a lower amount of al than talc free types the al2o3 sio2 fe2o3 feo plot shows that sanbagawa piemontite quartz schists have a composition between deep sea pelagic clay and pure silica by the use of pearson s product moment correlation coefficient method and plotting elements against each other after removing silica and volatiles it is possible to distinguish four components which are able to explain the variance of the samples these components are first component al2o3 tio2 mgo na2o k2o zr rb y nb and to lesser degree fe2o3 feo ni th ba second component sio2 third component mno and fourth component cao al2o3 tio2 zr and other elements with positive coefficient relations with them have a detrital origin biogenic origins are considered for cao and sio2 and it was concluded that mno was derived from an hydrothermal source because the sanbagawa metamorphic belt has been subjected to much detailed research and also contains talc bearing and talc free piemontite quartz schists it provides the best opportunity to find an explanation for the occurrence of talc in some types of piemontite schist and its absence from others mineralogical and geochemical evidences show that the oxygen fugacity for talc bearing and talc free types is similar oxygen fugacity is so high that almost all of the iron is present as fe3 in hematite pressure and temperature is considered to have been constant for talc bearing and talc free types in each locality because the samples were collected from a known metamorphic context the talc absent present problem is discussed using phase relations of the samples with the greatest number of phases in each locality consideration of talc clinochlore piemontite and garnet in the system al2o3 mn2o3 mno mgo cao acmmn with excess phases albite quartz hematite phengite and water shows that talc coexists with piemontite and garnet which are richer in the piemontite and spessartine end members respectively

recognizing oib and morb in accretionary complexes a new approach based on ocean plate stratigraphy petrology and geochemistry abstract we present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy ops and on the petrology and geochemistry of basalts from mid oceanic ridges morb and oceanic islands oib using examples from four accretionary complexes ac in sw japan akiyoshi mino tamba chichibu and shimanto the key to the problem is the model of ops which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid oceanic ridge to a subduction zone we propose the reconstruction of the tectonic settings of basalts according to their relationships with associated ops sediments their petrogenesis and their geochemical features five types of ops are recognized in the accretionary complexes of sw japan 1 sandstone shale 2 sandstone shale and chert 3 sandstone shale chert and morb 4 sandstone shale chert morb and gabbro peridotite 5 seamount ops including oib cap carbonates slope clastics and basal shale chert the alkaline tholeiitic or calc alkaline composition of basaltic melts which are typical of oceanic islands mid oceanic ridges and island arcs respectively can be identified by the sequence in crystallization of their major phenocrysts i e olivine ol clinopyroxene cpx and plagioclase pl and by their compositions alkaline and calc alkaline mafic lavas are characterized by an ol cpx pl succession whereas tholeiitic melts by their ol pl cpx succession titanium rich minerals e g ti augite kaersutite ti biotite are typical of alkaline lavas the application of geochemistry based tectonic discrimination diagrams is also a powerful tool if not supported by geological and petrological data may result in confusion due to magma contamination post magmatic alteration and secular change of mantle thermal conditions we propose that a direct comparison of normalized multi element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination our ops petrology geochemistry method allows us to confirm the above conclusions that the lavas of the akiyoshi mino tamba and southern chichibu ac formed in oceanic islands because they are associated with seamount ops sediments crystallized from ol to cpx and pl contain ti augite and kaersutite and are enriched in tio2 lree and nb in this paper we present geochemical data from the inuyama basalts of the mino tamba ac and from the toba complex in the huge mikabu greenstone belt of the chichibu ac the inuyama basalts are in contact with jurassic pelagic cherts but their geochemical features are confusing they contain phenocrysts of ol ti augite and kaersutite and therefore probably formed in seamounts the toba volcanic rocks are a part of the huge ophiolite belt they have flat to slightly lree enriched ree patterns are characterized by an ol cpx succession of phenocrysts and they plot in the oib field in binary plots suggesting they formed in an oceanic plateau

geochemical evidence for the paleoproterozoic arc back arc basin association and its importance in understanding the evolution of the central indian tectonic zone abstract the central indian tectonic zone citz is considered to be one sector in a series of paleoproterozoic orogens that stitched together the supercontinent columbia the paleoproterozoic mahakoshal belt forms the foundation of the citz metabasalts and metaclastic rocks of the mahakoshal belt have been studied for major elements and trace elements including the rare earth elements ree metabasalts of the lower saleemanabad formation are grouped into two types however both types of metabasalt depict a back arc basalt character by showing enrichments in large ion lithophile elements liles like k rb cs and ba and light rare earth elements lrees but show depletions in high field strength elements hfses like nb ta y and ti and hree heavy rare earth elements in comparison to the n morb this is further supported by some key elemental ratios like ba nb nb ta la nb eu eu nb nb and ree patterns the geochemistry of the metaclastic rocks of the lower saleemanabad middle parsoi and upper dudhmaniya formations of the mahakoshal belt show an arc signature rather than the cratonic signature in the bundlekhand ttg and n morb normalised diagrams the arc signature calc alkaline series of metaclastic rocks is further supported by various tectonic discrimination diagrams the overall study indicates that the mahakoshal belt was formed as a back arc rift basin very close to continental arcs on the hinterland of the bundelkhand craton at the initial stage of subduction as a result of trench rollback followed by thermal relaxation and basin inversion the sediment supply started from the continental arcs lying south of the mahakoshal basin furthermore the present study strengthens the mechanism of subduction related outgrowth of columbia along its continental margins and implies that the citz is a major precambrian crustal boundary that began as a mahakoshal back arc rift by northward subduction

an approach for assessing engineering risk from shale gas wells in the united states in response to a series of energy crises in the 1970s the united states government began investigating the potential of unconventional domestic sources of energy to offset imported oil hydraulic fracturing applied to vertical tight sand and coal bed methane wells achieved some degree of success during a period of high energy prices in the early 1980s but shale gas remained largely untapped until the late 1990s with the application of directional drilling a mature technology adapted from deepwater offshore platforms that allowed horizontal wells to penetrate kilometers of organic rich shale and staged hydraulic fracturing which created high permeability flowpaths from the horizontal wells into a much greater volume of the target formations than previous completion methods these new engineering techniques opened up vast unconventional natural gas and oil reserves but also raised concerns about potential environmental impacts these include short term and long term impacts to air and water quality from rig operations potential migration of gas fluids and chemicals through the ground and effects on small watersheds and landscapes from roads pads and other surface structures engineering risk assessment commonly uses integrated assessment models iams which define sources of risk from features events and processes the risk from each system element is assessed using high fidelity models output from these is simplified into reduced order models so that a large integrated site performance assessment can be run using the iam the technique has been applied to engineered systems in geologic settings for sequestering carbon dioxide and it is also applicable to shale gas albeit with some modifications of the various system elements preliminary findings indicate that shale gas well drilling and hydraulic fracturing techniques are generally safe when properly applied incident reports recorded by state environmental agencies suggest that human error resulting from the disregard of prescribed practices is the greatest cause of environmental incidents this can only be addressed through education regulations and enforcement

biogenic signature and ultra microfossils in ferromanganese nodules of the central indian ocean basin abstract theories related to the precipitation mechanism of the metallic elements in marine manganese nodules have remained controversial between two schools of thoughts 1 chemical oxidation abiotic origin and 2 deposition of the metals through microbial enzymatic processes biogenic origin one of the most important evidence in support of the biogenic origin is the occurrence of fossilized microbes however well documented literature in this regard is either lacking or very scanty in case of indian ocean nodules using high resolution feg sem we have recorded various biogenic signatures and ultra microfossils in the ferromanganese nodule samples from central indian ocean basin ciob that are presented in this paper the microfossils are mostly protozoans belonging to varieties of bacteria diatoms and foraminifera some of the features recorded in this study have perhaps never been reported before from any manganese nodules the chemical compositions of these ultra microfossils indicate a high level of manganese precipitation in and around them in comparison to the distant surrounding areas while clumpy microbes are enriched with nickel the rod shaped bacteria are rich in copper up to 4 70 wt nickel and 5 31 wt cu have been recorded in the fossilized microbe bodies the high abundance of biogenic features as well as microfossils in the ferromanganese nodules and their chemical compositions support arguments in favor of a dominant role of the microorganisms in the construction of the nodules of the ciob

isotopic evolution of river water in the northern chile region two main northern chilean rivers the loa and tarapaca were investigated regarding their isotopic characteristics groundwater associated with various recharge zones and the input of tributaries along their courses mainly control their 180 2h isotopic composition of the rivers in the loa river carbon isotopic exchange between dissolved inorganic carbon dic and atmospheric coplays a minor role in the inorganic carbon cycle of the loa river the carbon isotopic composition 4 c 13 c of this river is probably controlled by carbon source associated with volcanic and geothermal activities and by the deposition of travertines for the tarapaca river the carbon isotope content of the dic reflects the input of recirculated water from irrigated areas along the river course and carbon isotopic exchange these findings imply that the input of volcanic and or geothermal co2 into the dic pool has to be evaluated in order to use carbon isotopes as a dating tool for groundwater in the loa basin and that modern conditions are not analogous to the paleohydrology of the tarapaca river

fluid rock interaction and its effects on the upper triassic tight sandstones in the sichuan basin china insights from petrographic and geochemical study of carbonate cements abstract tight sandstone gas is an important unconventional hydrocarbon resource but its exploration is made difficult by the compactness and heterogeneity of the sandstone fluid rock interaction and subsequent cementation play key roles in developing this heterogeneity we conducted a petrographic trace element and isotopic study of the upper triassic xujiahe sandstones from the sichuan basin to investigate fluid rock interactions and associated diagenetic effects carbonate fragments and cements are widespread in these sandstones and are the primary control on the nature of the xujiahe sandstone reservoirs the carbonate cements primarily comprise of calcite and are typically distributed around the margins of sandstone bodies and along fine grained beds carbonate minerals in the centre or at the margin of sandstone units have heavy 13ccarb values of ca 0 whereas 13ccarb is markedly depleted in the transition zone with values as low as 10 reflecting a contribution from organic carbon manganese strontium and barium generally become enriched in the carbonate cements with diagenesis and their concentrations correlate with porosity and 13ccarb redox sensitive mn and fluid mobile sr and ba were analysed to reveal the diagenetic processes and environment of carbonate precipitation we propose that fluids flowed preferentially along the central parts of sandstone units associated with mineral dissolution whereas cementations took place near the margins of the units fluid rock interaction especially that involving late hydrocarbon related fluids greatly enhances the heterogeneity of sandstones and can potentially create high quality reservoirs in the central parts of tight sandstone units

accreted oceanic materials in japan abstract the phanerozoic circum pacific orogenic belts contain numerous ocean derived materials accreted through plate converging processes japanese islands in particular display various kinds of oceanic materials of different origins including fragments of seamounts oceanic reef limestone morb like rocks and oceanic mantle and pelagic sediments the compilation of these rocks in many subduction complexes of late permian to the present led to following conclusions accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust i e layer 1 and layer 2 many fragments of seamount with alkali basalt 600 hot spot seamount 26 oceanic reef limestone 291 morb like basalt 200 and numerous cherts more than 1000 are recognized as ancient oceanic materials accreted to the japanese islands however gabbros and mantle materials of layer 3 and lower parts of the oceanic lithosphere scarcely occur in subduction accretion complexes except for a few examples of back arc basin or fore arc origin accretion occurs episodically in southwest japan oceanic materials were accreted intermittently in 1 a end permian 2 b middle late jurassic 3 c late cretaceous times 4 d at ca 50 ma and 5 e in miocene times while in northeast japan and hokkaido this occurred in b middle late jurassic c late cretaceous and f early cretaceous times in contrast to the general belief on accretion of younger oceanic plates the majority of japanese subduction accretion complexes were formed during the subduction of plates up to 160 ma old the accretionary events in end permian and middle late jurassic times coincide with northward collision of ancient island arcs oceanic rises or seamount chains of hot spot origin with the asian continent accretion relevant to subduction of older plates may be controlled by the collision subduction process of these topographic reliefs on an oceanic plate in addition the chronological coincidence with the continent collision amalgamation between the sino korean and siberian platforms and between the sino korean and yangtze blocks also implies collision induced voluminous supply of elastics from back arc regions and its contribution to the formation of huge accretionary complexes accreted fragments of ancient seamounts are much smaller than the average size of modern seamounts this implies that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels with respect to the metamorphic grades for japanese subduction complexes oceanic materials have less than 1 vol in the zeolite facies 15 20 in the prehnite pumpellyite metagraywacke facies and ca 30 in the greenschist glaucophane schist facies and albite epidote amphibolite fades this relationship indicates that the major process for landward accretion of oceanic materials is not off scraping or sedimentary mixing at the trench but underplating subcretion at much deeper levels of a subduction zone

manganese formations in the accretionary belts of japan implications for subduction accretion process in an active convergent margin abstract in the accretionary complexes of japan many bedded manganese and iron manganese ore deposits occur especially in the jurassic complexes such as the chichibu tamba mino ashio and northern kitakami belts the manganese ores in these jurassic accretionary complexes probably formed from manganese nodule crust bearing siliceous sediments on deep sea floor and were subsequently converted to the manganese ores by metamorphism during the subduction accretion process some of the deposits also show the signatures of younger granitic intrusions the manganese formations now incorporated within these belts are marker beds of accretionary tectonics associated with plate tectonic processes in convergent margins