geothermometry and geochemistry of aqueous and oil bearing fluid inclusions from fateh field dubai abstract the production of oil from fateh field dubai is principally from the cretaceous mishrif formation porosity in the reservoir facies is partly occluded by late coarse grained calcite cement this cement contains both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry was used to determine the temperature of that cement precipitation and calculate its timing relative to basin burial history these data were related to source rock maturation and from that the timing of oil migration was inferred to be oligocene to mid miocene which is geologically contemporaneous with early petroleum generation r 0 0 5 0 6 in the khatiyah source rock the fluid inclusions were analyzed by a thermal decrepitation gas chromatography technique benzene and low molecular weight paraffins were present and a series of normal alkenes was tentatively identified in the aqueous inclusions fresh oil inclusions consisted of c 1 n c 25 compounds whose light hydrocarbon composition was consistent with derivation from an early mature source rock altered petroleum residues detected in many mishrif samples are contained either in inclusions or along crystal cleavages these materials are the subject of an ongoing geochemical study of fateh field

beryllium geochemistry constraints on the hydraulic behavior of mud volcanoes the trinidad island case to constrain trinidad mud volcanoes hydraulic behavior both cosmogenic 10be t1 2 1 5 myr and 9be concentrations have been measured in fluid and associated expelled mud as previously evidenced a n dia m castrec j boulegue p comeau trinidad mud volcanoes where do the expelled fluids come from geochim cosmochim acta 63 1999 1023 1038 from 18o values and cl concentrations 9be concentrations in the fluids mostly reflect the mixing of two deep components rem i and rem ii rem i 18o 10 5 cl 275 mm and 9be 0 05 nm has characteristics of a continental fluid while rem ii 18o 3 cl 350 mm and 9be 1 nm results from seawater volcanogenic derived sediment interaction although 10be concentrations in the fluid samples are close to the detection limit the distribution of both beryllium isotopes between the hydroxylamine leachable and residual phases indicates exchange reaction with fluid younger than 15 myr comparison between the lowest rem i 10be 9be ratio in fluid recorded by the hydroxylamine leachable phase td5 mud sample and the 10be 9be ratio representative of meteoric contribution in the recharge area td8 fluid sample yields a circulation rate of rem i fluid in the trinidad mud volcanoes of several 10 1 m yr

new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault 1 zircons and monazites from 6 samples of the north ayilari dextral shear zone nasz part of the karakorum fault zone kfz have been dated with the u th pb method using both id tims and sims techniques the ages reveal 1 inheritance from several events spanning a long period between the late archean and the jurassic 2 an eocene oligocene magmatic event similar to 35 32 ma 3 an oligo miocene magmatic event similar to 25 22 ma at least partly synkinematic to the right lateral deformation and 4 a period of metamorphism metasomatism similar to 22 14 ma interpreted as thermal and fluid advection in the shear zone the labhar kangri granite located similar to 375 km farther southeast along the kfz is dated at 21 1 0 3 ma such occurrence of several oligo miocene granites along the kfz some of which show evidence for synkinematic emplacement suggests that the fault zone played an important role in the genesis and or collection of crustal melts we discuss several scenarios for the onset and propagation of the kfz and offset estimates based on the main sutures zones our preferred scenario is an oligo miocene initiation of the fault close to the na range and propagation along most of its length prior to similar to 19 ma in its southern half the averaged long term fault rate of the kfz is greater than 8 to 10 mm a in good agreement with some shorter term estimates based on the indus river course or quaternary moraines and geodesy our results show the kfz cannot be considered as a small transient fault but played a major role in the collision history

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

petrogenesis of calc alkaline shoshonitic and associated ultrapotassic oligocene volcanic rocks from the northwestern alps italy along the western alps there is geological evidence of late alpine oligocene magmatic activity which clearly postdates the lepontine eocene early oligocene metamorphism and related deformation of the alpine nappe pile this magmatic activity was notably delayed in relation to the most important convergent processes and may be related to buoyancy of lithosphere tensional tectonics and thermal updoming subsequent to the collision between the eurasian and african plates the geochemical features of the rocks and the geophysical characteristics of the alpine chain suggest that a shoshonitic and calcalkaline melts may have been generated by partial melting of metasomatized peridotitic material and subsequent fractional crystallization and crustal contamination silicic andesites and latites however could have been also derived from metasomatized eclogite or deep continental crust material b the ultrapotassic lamprophyres with high k p lree th zr u and high 87sr 86sr ratios were generated by partial melting of strongly metasomatized mantle the varied sr isotopic ratios may partially also reflect additional radiogenic component from the continental crust following magma segregation from the source

beryllium 10 in hydrothermal vent deposits from the east pacific ridges role of sediments in the hydrothermal processes beryllium 10 concentrations were determined for 31 handpicked hydrothermal sulfides six oxyhydroxides seven basalts and five sediments collected from the hydrothermally active areas of the east pacific ridges the samples include specimens from the east pacific rise epr at 21 n and 13 n the galapagos rift the guaymas basin and the gorda and the juan de fuca ridges additional samples from massive sulfides associated with the oman ophiolites were studied in all samples we obtained values ranging from 0 04 106 atoms g to 125 106 atoms g with the lowest values being very close to our blank 0 015 106 atoms g the data show systematic variations with sample location and type the 10be concentrations measured for the mid ocean basalts are of the order of 0 3 10 atoms g and reach 3800 106 atoms g for the pelagic deep sea sediments collected near the epr 21 n based on their 10be concentrations we can clearly distinguish two categories of sulfides sulfides containing low 10be concentration 106 atoms g located atop of a thick pile of young sediments guaymas basin or gorda ridge the oxy hydroxides collected on some of the juan de fuca chimneys are always very rich in 10be with concentrations reaching 125 106 atoms g we propose three mechanisms to explain these data 1 mechanical entrapment of sediments in the hydrothermal chimneys as observed in the gorda ridge sulfides 2 leaching of 10be from the ocean crust sediments transport by hydrothermal fluids and coprecipitation with heavy metals as hypothesized to explain the be concentrations observed in the guaymas basin and 3 passive adsorption of 10be from seawater preferred hypothesis oxy hydroxides of the areas with no sediment cover

upper oligocene lacustrine source rocks and petroleum systems of the northern qaidam basin northwest china our organic geochemical study of oils from the northern qaidam basin defines a family of genetically related oils that contain biomarkers indicative of source rocks deposited in tertiary hypersaline anoxic lacustrine settings although cenozoic outcrop samples from northern qaidam are too organic lean to be of source quality dark laminated upper oligocene mudstones containing gypsum crystals and pyrite from the shi 28 well yield total organic carbon toc and rock eval data indicative of fair to good source rocks organic matter is derived from algae and bacteria and there apparently was little contribution from terrestrial material biomarker data provide a good correlation between the produced oils and the upper oligocene shi 28 core samples hydrocarbons derived from these source rocks are contained in upper oligocene miocene and pliocene reservoirs although eight of the oil samples are from the northwest corner of the basin one sample in this genetic family of hypersaline oils comes from northeast qaidam an area previously believed to only produce oils derived from jurassic freshwater lacustrine source rocks this sample thus indicates the presence of an unidentified and undocumented source rock in the northeast part of the basin hypersaline oils and the associated source rocks have low biomarker maturity parameters thermal modeling indicates that hydrocarbon generation probably occurred in northwestern qaidam within the last 3 million years

early cretaceous subvolcanic calc alkaline granitoid magmatism in the nubra shyok valley of the shyok suture zone ladakh himalaya india evidence from geochemistry and u pb shrimp zircon geochronology abstract the lithounits constituting the ladakh himalaya are exposed along the indus and shyok sutures zones of northwest himalaya the shyok suture zone ssz in northern ladakh represents a highly tectonized zone of a back arc basin which is mainly composed of volcano sedimentary formations shyok and khardung formations intimately associated with intrusive granitoids in the nubra shyok valley of the ssz calc alkaline granitoids of batholithic dimension are exposed in the tirit region referred herein as the tirit granitoids which are intrusive evidently into the shyok volcanic rhyolite rocks belonging to the shyok formation in this valley the northern margins of granitoids of the ladakh batholith can also be found intrusive into the metasediments shale slate and metavolcanics of the shyok formation the compositions and crystallization pressures 66 to 91 mpa of amphiboles in the intrusive tirit granitoid corroborate a calc alkaline nature and solidification of tirit granitoid melt at subvolcanic level equivalent to a minimum of 2 5 km to a maximum of 3 5 km thick overburden of shyok volcanics u pb shrimp zircons from the tirit granitoids have yielded mean crystallization ages of 109 4 1 1 ma and 105 30 0 80 ma which strengthen the idea of early cretaceous subduction beneath the karakoram terrain inherited older zircon cores 278 393 ma 476 519 713 952 ma and 1933 ma suggest a contribution from heterogeneous palaeozoic and proterozoic sources in the generation of the tirit granitoids similar to those observed elsewhere in the karakoram kohistan region a mean crystallization age 105 30 0 80 of zircons in the tirit granitoid hosting xenoliths of porphyritic volcanics places a minimum eruption age of ca 105 ma for the shyok volcanics the ladakh granitoid tirit granitoids and porphyritic volcanic xenolith belong to a calc alkaline series a mean crystallization age 67 32 0 66 ma for zircon in the ladakh granitoid implies that the shyok metasediments shale slate were deposited and metamorphosed prior to ca 68 ma present and earlier determined ages on tirit granitoids revealed that the subduction related calc alkaline magmatism in the nubra shyok valley of the ssz prevailed between 110 and 68 ma and hence a minimum age of early cretaceous can be suggested for development of the ssz

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

210pb 230th and 10be in central indian basin seamount sediments signatures of degassing and hydrothermal alteration of recent origin 1 isotopic 210pb 238u 230th 10be major and trace elements and micromorphological and microchemical data were used to identify recent 100 yrs hydrothermal alteration of a 200 kyr sedimentary record from the flank of a seamount in the central indian basin located at the edge of the 75 30 e fracture zone alteration effects are also reflected in 1 the depleted sedimentary organic carbon 2 dissolution features of radiolarian skeletons 3 the presence of altered minerals such as smectite and zeolites and 4 distinctly different magnetic properties in the altered sediments we interpret a predominant influence of neutral chloride type hydrothermal fluids this is the first report of recently occurring sediment alteration by shallow circulating sub surface fluids along the indian ocean intra plate seamount environment

zircon fission track ages from the gasherbrum diorite karakoram range northern pakistan the gasherbrum peaks in the himalaya of pakistan reach elevations of 8000 m the relief between the peaks and the adjacent valley baltoro glacier is in excess of 3000 m eight samples of the early cretaceous gasherbrum diorite at elevations between 4880 and 7165 m on gasherbrum iv were collected for fission track dating zircon fission track ages from the gasherbrum diorite vary from early cretaceous to middle tertiary in age there is no consistent pattern between age and elevation the cretaceous ages indicate that these rocks were never deeply buried i e heated to temperatures in excess of 175 c to reset the zircons during cenozoic time these results also indicate that the uplift of this part of the himalaya has been either very rapid and recent or very slow since early cretaceous time this latter possibility is not consistent with the high relief at gasherbrum and what is known about regional tectonics gasherbrum iv zircons currently at approximately 4880 m have never been at depths greater than 6 km and less than 3 km of material has been removed from the top of the range by erosion since the early cretaceous rapid uplift has occurred very recently and erosion rates have notmore been able to keep pace with this uplift less

microstructural evidence for magma confluence and reusage of magma pathways implications for magma hybridization karakoram shear zone in nw india in the karakoram shear zone ladakh nw india miocene leucogranitic dykes form an extensive varied and complex network linking an anatectic terrane exposed in the pangong range with leucogranites of the karakoram batholith mineral paragenesis of the heterogeneous anatectic source rocks suggests melting has resulted from water influx into rocks at upper amphibolite facies conditions and microstructures suggest anatexis was contemporaneous with shearing the network is characterized by continuous and interconnected dykes with only rare cross cutting relationships forming swarms and chaotic injection complexes where magmatic rocks cover up to 50 of the outcrop area despite this volume of magma the system did not lose continuity suggesting that it did not flow en masse and that the magma network was not all liquid simultaneously leucogranites in this network including leucosomes in migmatites carry an isotopic signature intermediate between the two main anatectic rocks in the source suggesting efficient homogenization of the magmatic products here we describe a number of microscopic features of these magmatic rocks which suggests that several pulses of magma used the same pathways giving rise to textural and chemical disequilibrium features these include i narrow tortuous corridors of fine grained minerals cutting across or lining the boundaries of larger grains interpreted to be remnants of magma filled cracks cutting across a pre existing magmatic rock ii corrosion of early formed grains at the contact with fine grained material iii compositional zoning of early formed plagioclase and k feldspar grains and quartz overgrowths documented by cathodoluminescence imaging iv incipient development of rapakivi and anti rapakivi textures and iv different crystallographic preferred orientation of early formed quartz and fine grained quartz mapping of the fine grained corridors interpreted to represent late melt channels reveal an interlinked network broadly following the s c fabric defined by pre existing magmatic grains we conclude that early formed dykes provided a pathway exploited intermittently or continuously by new magma batches new influxes of magma opened narrow channels and migrated through a microscopic network following predominantly grain boundaries along an s c fabric related to syn magmatic shearing a mixed isotopic signature resulted not from the mixing of magmas but from the micro scale interaction between new magma batches and previously crystallized magmatic rocks through local equilibration

boron geochemistry of the central american volcanic arc constraints on the genesis of subduction related magmas boron contents were measured in representative quaternary lavas from the central american volcanic arc to evaluate along strike variations in subduction processes despite the significant range in b concentrations 2 37 ppm in the mafic lavas b la ratios vary in a systematic fashion along the arc higher values 1 are typical between guatemala and northern costa rica whereas low values most 0 5 typify central costa rica and western panama b la is highly correlated with 10be 9be r2 0 94 excluding one sample and appears to be a useful indicator of subduction contributions to the magma sources if enrichments of both b and 10be are proportional to the flux of subducted sediment along strike variations in b la suggest at least a twofold variation in this flux with maximum values below western nicaragua and minimum values below costa rica and western panama where the cocos ridge is being subducted these data may also reflect significant differences in thermal state of the descending slab which in turn differentially affects release patterns of fluids and fluid mobile trace elements and possibly melting processes beneath different parts of the arc the following scenario is suggested to explain the geochemical results beneath the northwestern part of the arc steep subduction of older relatively cold slab favors more efficient subduction of fluid components to depths beneath the volcanic front the released fluids carry fluid mobile elements to the overlying mantle which upon melting produces calcalkalic magmas shallow subduction of warmer slab beneath the southeastern part of the arc favors shallow release of fluids and limits fluid related metasomatism of sub arc mantle beneath the volcanic front under such conditions b la and ba la ratios in the sub arc mantle vary little from values seen in oceanic island basalts magmas in this part of the arc nevertheless display the highest la yb and lowest ba la and b la ratios which are consistent with prior light rare earth element enrichment in the source significantly lower degrees of melting or a combination thereof because some of the largest volcanoes occur in costa rica and magma flux there is nearly an order of magnitude higher than elsewhere in the arc source enrichment is considered to be the more plausible explanation it is proposed that quaternary magma production below costa rica involved lithospheric sources containing trapped or stored melt components but this enrichment process is unlikely to have involved typical arc magmas or subduction fluids because we see no b enrichment

tectonics of the southern asian plate margin along the karakoram shear zone constraints from field observations and u pb shrimp ages abstract new geological observations recent published data and u pb shrimp zircon dating from the karakoram mountains along the nubra and shyok rivers reveal that the initial subduction of the tethyan oceanic lithosphere took place 110 ma beneath the paleozoic mesozoic platform of the southern edge of the asian plate this has produced the i type plutons within the karakoram batholith complex well before the juxtaposition of the asian plate along the karakoram shear zone within this shear zone u pb zircon crystallisation ages of 75 ma from mylonitised granitoids and 68 ma from undeformed tirit granodiorite constrain the timing of suturing of the karakoram terrain with the trans himalaya between 75 and 68 ma post shearing leucogranite was episodically generated within frontal migmatised karakoram metamorphic belt and emplaced between 20 and 13 ma within the shear zone presence of a low resistivity zone as a possible indication of mid crustal partial molten crust underneath the higher himalaya ladakh karakoram terrains manifests the impingement of the indian plate along the main himalayan thrust at depth physical continuity of the baltoro granite belt into the karakoram batholith is established as well as the continuity of the shyok suture as the shiquanhe suture zone in western tibet through the chushul dungti sector the karakoram shear zone therefore displays a complex geological history of movements since 75 ma and plays a very significant role in the overall india asia convergence rather than merely being a strike slip fault for eastward extrusion of a segment of asia in tibet

a mid cretaceous change from fast to slow exhumation of the western chinese altai mountains a climate driven exhumation signal abstract the chinese altai mountains in western china are bound by cenozoic transpressional strike slip faults many of which show quaternary activity to better understand how mesozoic cenozoic deformation has affected the history of exhumation and uplift of the chinese altai mountains we collected paleozoic granitoid samples for apatite fission track and apatite u th sm he thermochronology central apatite fission track ages for n 6 samples range from 68 to 104 ma whereas apatite u th sm he ages range from 56 to 272 ma for n 23 samples n 80 individual analyses across four transects in the western chinese altai our results indicate fast cooling during the late early cretaceous followed by slow cooling since thermal modeling results suggests

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

enhanced cosmic ray production of 10be coincident with the mono lake and laschamp geomagnetic excursions the cosmogenic isotope 10 be total be and al were measured in partly varved sediments from the upper 50 m of core 480 leg 64 dsdp gulf of california the concentration of 10 be from 1 to 50 kyr is in general agreement with estimates of the geomagnetic dipole moment obtained from archaeomagnetic and marine core research 10 be anomalies were also found at 32 kyr and 43 kyr contemporaneous with the mono lake and laschamp excursions respectively the production of 10 be required to explain these anomalies is too high particularly for the mono lake excursion to be produced by a combination of decreased geomagnetic field and unprecedented long term solar activity we conclude that the cause is a change in the galactic cosmic ray flux consistent with a supernova event the coincidence with the two excursions remains a paradox

tectono metamorphic evolution of the karakorum metamorphic complex dassu askole area ne pakistan exhumation of mid crustal ht mp gneisses in a convergent context the south karakorum margin east of the himalayan syntaxis consist of an e w elongated zone of young 10 3 ma high grade metamorphic rocks m2 and related migmatitic domes this late tectono metamorphic event post dates the palaeogene 55 37 ma phase of thickening of the belt featured by nw se structures and associated m1 amphibolite facies metamorphism 0 7 gpa 700 c this m2 metamorphism is characterised by low pressure high temperature conditions coeval with migmatite formation in response to a thermal increase of c 150 c compared to m1 culminating at a temperature of c 770 c and a pressure of 0 5 0 6 gpa rapid exhumation of migmatitic domes at a rate of 5 mm yr 1 was accommodated by vertical extrusion in the core of e w crustal scale folds these crustal scale folds formed in response to n s syn collisional shortening and were enhanced by thermal weakening of the migmatised continental crust m2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid crustal level such relationships between a mantle related magmatism and a high temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted indian slab since 20 ma

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

a time series of vent fluid compositions from 21 n east pacific rise 1979 1981 1985 and the guaymas basin gulf of california 1982 1985 a time series study of four hot spring fields at 21 n on the east pacific rise demonstrates that the solution compositions of mid ocean ridge hydrothermal vents are stable on a decadal time scale the ocean bottom seismometer obs national geographic smoker ngs and south west sw vents show no significant changes in the major element composition of their end member fluids since 1979 two of the vents obs and sw have maintained exit temperatures near 350 c since 1979 the ngs vent has remained close to 270 c since 1981 after cooling from 350 c in 1979 only one vent hanging gardens shows important changes in solution chemistry from 1981 to 1985 in 1985 this vent appears to have cooled 10 c relative to the other vents the depth of the reaction zone as determined by quartz geobarometry has increased by about 1 km at this vent the large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances rather the constancy of small interfield variations in solution composition is more consistent with control by rock buffering a 4 year time series study of hydrothermal vents in the guaymas basin also shows no significant changes in the major element composition of the end member fluids interfield differences in solution chemistry have been maintained from 1982 to 1985 this phenomenon is best explained in terms of an equilibrium model

beryllium 10 thorium 230 and protactinium 231 in galapagos microplate sediments implications of hydrothermal activity and paleoproductivity changes during the last 100 000 years biogenic particle fluxes from highly productive surface waters boundary scavenging and hydrothermal activity are the main factors influencing the deposition of radionuclides in the area of the galapagos microplate eastern equatorial pacific in order to evaluate the importance of these three processes throughout the last 100 kyr concentrations of the radionuclides 10be 230th and 231pa and of mn and fe were measured at high resolution in sediment samples from two gravity cores klh 068 and klh 093 high biological productivity in the surface waters overlying the investigated area has led to 10be and 231pa fluxes exceeding production during at least the last 30 kyr and probably the last 100 kyr however during periods of high productivity at the up welling centers off peru and extension of the equatorial high productivity zone a relative loss of 10be and 231pa may have occurred in these sediment cores because of boundary scavenging the effects of hydrothermal activity were investigated by comparing the 230thex concentrations to the mn fe ratios and by comparing the fluxes of 230th and 10be which exceed production the results suggest an enhanced hydrothermal influence during isotope stages 4 and 5 and to a lesser extent during isotope stage 1 in core klh 093 during isotope stages 2 and 3 the hydrothermal supply of mn was deposited elsewhere probably because of changes in current regime or deep water oxygenation a strong increase of the mn fe ratio at the beginning of climatic stage 1 which is not accompanied by an increase of the 230thex concentration is interpreted to be an effect of mn remobilization and reprecipitation in the sediment

shyok suture zone n pakistan late mesozoic tertiary evolution of a critical suture separating the oceanic ladakh arc from the asian continental margin abstract the shyok suture zone northern suture of north pakistan is an important cretaceous tertiary suture separating the asian continent karakoram from the cretaceous kohistan ladakh oceanic arc to the south in previously published interpretations the shyok suture zone marks either the site of subduction of a wide tethyan ocean or represents an early cretaceous intra continental marginal basin along the southern margin of asia to shed light on alternative hypotheses a sedimentological structural and igneous geochemical study was made of a well exposed traverse in north pakistan in the skardu area baltistan to the south of the shyok suture zone in this area is the ladakh arc and its late cretaceous mainly volcanogenic sedimentary cover burje la formation the shyok suture zone extends northwards ca 30 km to the late tertiary main karakoram thrust that transported asian mainly high grade metamorphic rocks southwards over the suture zone the shyok suture zone is dominated by four contrasting units separated by thrusts as follows 1 the lowermost askore amphibolite is mainly amphibolite facies meta basites and turbiditic meta sediments interpreted as early marginal basin rift products or trapped tethyan oceanic crust metamorphosed during later arc rifting 2 the overlying pakora formation is a very thick ca 7 km in outcrop succession of greenschist facies volcaniclastic sandstones redeposited limestones and subordinate basaltic andesitic extrusives and flow breccias of at least partly early cretaceous age the pakora formation lacks terrigenous continental detritus and is interpreted as a proximal base of slope apron related to rifting of the oceanic ladakh arc 3 the tectonic melange reconnaissance further east north of the shyok river indicates the presence of redeposited volcaniclastic sediments and thick acid tuffs derived from nearby volcanic centres presumed to lie within the ladakh arc in addition comparison with lower cretaceous clastic sediments maium unit within the northern suture zone west of the nanga parbat syntaxis hunza river reveals notable differences including the presence of terrigenous quartz rich conglomerates serpentinite debris flow deposits and a contrasting structural history the shyok suture zone in the skardu area is interpreted to preserve the remnants of a rifted oceanic back arc basin and components of the asian continental margin in the west hunza river a mixed volcanogenic and terrigenous succession maium unit is interpreted to record syn deformational infilling of a remnant back arc basin foreland basin prior to suturing of the kohistan arc with asia 75 90 ma

oxygen isotopes in mantle related and geothermally altered magmatites of the transhimalayan gangdese ranges in closed magma systems sio2 approximately measures differentiation progress and oxygen isotopes can seem to obey rayleigh fractionation only as a consequence of the behaviour of sio2 the main role of 18o is as a sensitive indicator of contamination either at the start of differentiation 18oinit or as a proportion of fractionation in afc plots of 18o vs sio2 allow to determine initial 18o values for different sequences for source comparison for nbs 28 9 60 the 18o at 48 sio2 varies between a high 6 4 for kiglapait kalamarides 1984 5 9 for transhimalaya 5 8 for hachijo jima matsuhisa 1979 5 6 for koloula chivas et al 1982 and a low 5 3 for the darran complex new zealand the transhimalayan batholiths gangdese belt were emplaced in the ladakh lhasa terrane between the present day banggong nujiang and indus yarlung tsangbo suture zones after its accretion to eurasia the gradient of the least contaminated continuous 18o vs sio2 igneous trend line is similar to that of koloula and afc calculations suggest a low secondary assimilation rate of less than 0 05 times the rate of crystallisation outliers enriched in 18o are frequent in the lhasa and apparently rare in the ladakh transsect low 18o 5 0 0 granitoids and andesites on the lhasa yangbajain axis are the result of present day or recent near surface geothermal activity their quartzes still trace the granitoids to the transhimalaya 18o trend line but the distribution of low total rock or feldspar 18o values could be a guide to more recent heat flow and thermally marked tectonic lineaments two ignimbrites from maqiang show hardly any 18o contamination by crustal material

examination of hydrothermal influences on oceanic beryllium using fluids plume particles and sediments from the tag hydrothermal field we have carried out a comprehensive study of the distributions of9be and the cosmogenic radionuclide10be in fluids nearfield sediments and neutrally buoyant plume particles associated with the tag hydrothermal field these results coupled with previously published uranium decay series radionuclide distributions 1 2 suggest that the level of mno2 in iron oxide rich sediments and particles may play a role in be scavenging in addition the data are used to quantify the net effects of nearfield coprecipitation with fes and of scavenging by iron oxyhydroxide plume particles on the oceanic balance of the be isotopes these calculations suggest that hydrothermal input of9be is nearly balanced by nearfield and plume removal processes and that hydrothermally induced scavenging has a negligible effect on the oceanic10be budget

cretaceous tertiary structural evolution of the north central lhasa terrane tibet 1 in the north central lhasa terrane of tibet two distinct structural levels of an east west striking thrust system are exposed along the north trending late cenozoic xiagangjiang rift upper paleozoic strata deformed by the south directed langgadong la thrust and cretaceous strata involved in variably north and south directed thrusting characterize these lower and upper structural levels respectively these two structural levels are separated by the tagua ri passive roof thrust balanced cross section restoration suggests that the thrust system accommodated 103 km 53 shortening the 40ar 39ar results together with an interpretation of synthrust deposition of upper cretaceous strata suggest that the majority of shortening occurred during the late cretaceous paleocene cretaceous strata lie unconformable on permian rocks volcanic tuffs directly above the unconformity yield u pb zircon ages of 131 ma upper cretaceous strata record a change from shallow marine to nonmarine deposition indicating uplift above sea level during this time the overall south directed vergence of the thrust belt is consistent with substantial crustal thickening in central tibet by large scale northward underthrusting of lhasa terrane basement beneath the qiantang terrane prior to the indo asian collision the documented decoupling of contractional deformation at shallow crustal levels appears to be a regional characteristic of tibet from at least the bangong suture in the north to the tethyan himalaya to the south this style of deformation explains the absence of basement exposures and major denudation in this region despite substantial crustal shortening

petroleum hydrogeology of the cooper and eromanga basins australia some insights from mathematical modeling and fluid inclusion data mathematical modeling and fluid inclusion data analysis are used to reconstruct the petroleum hydrogeology of the australian cooper and eromanga basins our analysis focuses on the development of topography and compaction driven groundwater flow systems and their role in heat redistribution petroleum generation and oil and brine migration during basin evolution finite element models of basin transport processes are constructed along northeast southwest aa and northwest southeast bb cross sections that generally follow the present day groundwater flow patterns through these basins numerical results are presented in the copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received september 19 1995 revised manuscript received july 3 1996 final acceptance november 11 1996 2independent consultant 12 rinzee road dracut massachusetts 01826 3csiro division of petroleum exploration 51 delhi road north ryde nsw 2113 australia 4department of geology and geophysics university of minnesota 310 pillsbury drive se minneapolis minnesota 55455 e mail mperson darcy geo umn edu 5gza geoenvironmental inc 380 harvey road manchester new hampshire 03103 6santos ltd 101 grenfell street adelaide sa 7000 australia this research is supported by a grant from the petroleum research fund administered by the american chemical society prf 24184 ac8 we would also like to acknowledge the orpha and george gibson hydrogeology endowment and the mcknight land grant professorship program at the university of minnesota we thank the csiro division of exploration geosciences for providing support for travel costs within australia data provided by santos ltd and the department of mines and energy south australia are also gratefully acknowledged computational work performed on this project was done at the gibson computational hydrogeology laboratory at the university of minnesota which is supported by the national science foundation under ear 94 05807 special thanks go to m a habermehl of the australian geological survey organization david gravestock of the south australia bureau of mines and mineral resources and mike congreves of santos ltd for their assistance on interpreting the petroleum geology and hydrogeology of the cooper and eromanga basins the review comments of joseph toth stefan bachu and michelle walvoord as well as discussions with ward sanford greatly improved the quality of this manuscript three dimensional model results presented in this paper are available in animated form on vhs videocassette and can be obtained by contacting mark person at the address listed for him as the corresponding author

evidence for resetting of fluid inclusion temperatures from quartz cements in oilfields abstract quartz is a major pore occluding cement in north sea oilfield reservoir sandstones fluid inclusions yield homogenization temperatures t h which have been thought to represent growth temperatures for the host quartz however early diagenetic inclusions from the detrital grain overgrowth boundary yield excessively high palaeotemperatures which do not match the growth temperatures calculated from the depth of cementation the temperatures of these inclusions increase with present day depth of burial and approach present day reservoir temperatures this suggests that the inclusions have begun to reset towards present day pressure temperature conditions the t h of the inclusions hence represent burial temperatures rather than growth temperatures for the quartz experimental studies indicate that the amount of resetting undergone by an inclusion varies depending on its size shape and fluid composition a relationship between inclusion t h and these variables has been observed in inclusions from deeply buried quartz cements in the north sea

the karakorum block in central asia from ordovician to cretaceous abstract the karakorum block records a predominantly marine ordovician to cretaceous sedimentary history six major sedimentary cycles are recognised the oldest sediments early ordovician transgress over a crystalline basement the 1 km thick ordovician silurian mostly shaly succession contains rare carbonate intercalations in the early devonian a wide peritidal platform spread over the craton sedimentation rates were low 10 20 m ma and upper devonian probable lower carboniferous carbonates and clastics rest unconformably on the early devonian carbonates no evidence has been found for either late carboniferous or glaciogenic deposits sedimentation rates increased during the permian up to 50 m ma with thicknesses between 1 and 2 5 km three steps are identified 1 a huge alluvial to marginal marine terrigenous prism aggraded during the asselian sakmarian 2 the artinskian murgabian is characterised by local emergence and erosion linked to extension with block rotations 3 greater differentiation occurred from late permian to middle triassic when a peritidal carbonate flat developed in the southwest facing a deeper basin to the northeast carbonate sediments prevailed throughout the carnian norian the permo triassic evolution is interpreted as the passive margin stage of the karakorum block which previously belonged to the perigondwanian fringe when like mega lhasa it drifted northward on the tethyan transit plate mega lhasa is considered as a collage of blocks possibly separated by thinned crust or short lived seas with ocean crust quartzo lithic sandstones with grains of mafic volcanics and serpentinite overlain with gentle unconformity by pliensbachian toarcian red sandstones with sedimentary and metasedimentary clasts record the eo cimmerian deformation in the karakorum this orogenic episode was over by the aalenian when a shallow water carbonate ramp aggraded onto the previously emergent area the pre barremian upper jurassic and lower cretaceous are poorly documented in post barremian times the sedimentary succession of n karakorum was severely deformed in huge thrust sheets including slabs of crystalline basement a coarse conglomerate of mid cretaceous age sealed the thrust sheet edifice finally isolated campanian pelagic mudstones are recorded anticlockwise rotation of mega lhasa followed the late triassic docking of the iranian spur using the latter as pivot the rotation was completed during the middle jurassic when se pamir shaksgam and karakorum joined the qiangtang more closely assembling mega lhasa as it approached the asian margin

a slab breakoff model for the neogene thermal evolution of south karakorum and south tibet on the south karakorum margin neogene high temperature medium pressure ht mp gneisses define an east west trending thermal anomaly these rocks have been heated from 600 to 750 c during a slight pressure drop from 0 7 to 0 5 gpa their retrogressive path cross cuts the relaxed geotherm of tectonically thickened crust such a p t evolution occurs only if an advective source of heat is involved involvement of an advective heat source is also implied by the occurrence of neogene granitoids and lamprophyres within the ht mp gneiss area these rocks are strongly enriched in large ion lithophile elements relative to primitive mantle and show negative high field strength element anomalies we interpret these geochemical characteristics to be the result of melting of metasomatized asian lithospheric mantle the nd and sr isotopic compositions of the south karakorum neogene magmatic rocks nd 12 to 7 and 87sr 86sr 0 705 0 725 further suggest they could have originated from mixing between asian variously metasomatized mantle and precambrian crust by contrast the origin of the youngest magmatic rocks 10 myr here exemplified by the hemasil syenite and associated lamprophyres requires involvement of a depleted mantle the combined hf nd signature of these rocks hf 10 4 11 5 and nd 3 4 4 3 suggests that the source of the hemasil syenite could have been depleted mantle contaminated by oceanic sediments likely during the earlier subduction of the tethyan ocean neogene magmatic rocks with the same geochemical characteristics and evolution as those of south karakorum have previously been described in south tibet based on their location and the geochemical evolution of their source region we here propose that the neogene magmatic and metamorphic evolution of the south asian margin was controlled by slab breakoff of the subducting indian continental margin starting at about 25 ma this model is supported by available geophysical data from south karakorum and south tibet

utility of rb sr geochronology in constraining miocene and cretaceous events in the eastern karakoram ladakh india abstract multiple magmatic and deformational events resulting from accretion of gondwanan terranes to the northern margin of india and followed by post accretion tectonics have been recognized from the eastern karakoram the time resolution of these events is important for understanding the geodynamic evolution of the region to constrain certain major events conventional rb sr geochronology was applied to the various phases of granitoids and their mineral separates from mainly within the pangong transpressional zone of the dextral karakoram fault kf in order to show that this technique can date such young events calcalkaline gneissic granodiorite from within the transpression zone and calcalkaline tonalite enclaves within the karakoram batholith kb at skyangpoche yield a whole rock date of 118 15 ma mswd 1 5 sr i of 0 7045 0 0002 and whole rock biotite age of 115 18 ma with sr i of 0 7061 0 0002 and mswd 1 5 respectively four samples of a mesocratic foliated granite within the pangong migmatite near the ne strand of the kf yielded an errorchron corresponding to an age of 72 8 ma mswd of 39 and sr i of 0 7041 0 0008 phenocrysts of phlogopite from an ultrapotassic lamprophyre dyke within the ladakh batholith near leh yield an age of 24 3 2 2 ma with sr i of 0 7083 0 0001 a muscovite whole rock isochron age of 13 3 0 6 ma with sr i of 0 7249 0 0001 and mswd 1 5 was measured from the darbuk leucogranite on the sw strand of the kf a foliated granite proximal to muglib on the ne strand of the kf yields a whole rock biotite age of 12 4 0 7 ma and sr i of 0 7056 0 0001 the early cretaceous ages of the granitoids comprising early pre miocene plutonic components of the kb are consistent with an u pb shrimp age of 106 ma and can be spatially correlated with the k2 gneiss 115 120 ma and the hunza plutonic unit 106 ma of the kb in northern pakistan the late cretaceous age of foliated granite along the kf confirms that calcalkaline plutonism extended from tirit near the confluence of nubra and shyok rivers to rutog in western tibet and was probably related to plutonism in the ladakh magmatic arc the earliest miocene magmatism in se ladakh is represented by the ultrapotassic lamprophyre dyke at 24 ma and spatially represents the westernmost extension of the voluminous ultrapotassic and potassic lavas in sw tibet at this time 17 25 ma following the intrusion of the main kb forming leucogranite at 15 ma u pb shrimp crystallization age from zircon rims the time of shearing on the sw strand of the kf is recorded by the age of muscovite from the darbuk leucogranite at 13 3 ma comparable to that measured by ar isotopic systematics 13 9 ma on mica aggregates from a granodiorite deformed by the kf in the nubra valley the biotite cooling age of the foliated granite within the pangong migmatite is consistent with its cooling following high grade migmatization previously measured as having occurred between 17 and 14 ma

anatomy age and evolution of a collisional mountain belt the baltoro granite batholith and karakoram metamorphic complex pakistani karakoram abstract geological mapping and u th pb geochronology from the karakoram metamorphic complex and baltoro granite batholith has resulted in more detailed timing constraints on tectonic evolution of asian crust during and following collision and accretion of the kohistan arc and the indian plate to the southern margin of asia crustal thickening along the karakoram resulted in polyphase deformation metamorphism and melting u pb zircon and monazite ages show that kyanite and sillimanite grade metamorphism in the baltoro region peaked during oligocene early miocene c 28 22 ma times at structurally deeper levels sillimanite grade migmatites of the dassu dome have pliocene c 5 4 3 5 ma ages new u pb ages from crustal melt biotite muscovite garnet leucogranites from the trango towers cathedral peak and paiyu peak across the baltoro batholith range from 19 8 0 5 ma to perhaps as young as 14 ma using data from both the hunza and baltoro regions we suggest that regional high grade metamorphism was diachronous in space and time and could have lasted continuously for at least 37 ma c 50 13 ma or as much as 50 ma c 63 13 ma along the southern margin of the asian plate in the karakoram crustal melting along the baltoro granite batholith spanned at least 13 ma 26 4 13 ma supplementary material analytical methods and description of u th pb data of samples are available at http www geolsoc org uk sup18382

mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet 1 in the shiquanhe area of far western tibet mid cretaceous strata lie unconformable on ophiolitic melange and jurassic flysch associated with the bangong nujiang suture zone on the basis of our mapping and geochronologic studies we suggest that these cretaceous strata were shortened by 57 over a north south distance of 50 km during late cretaceous early tertiary time the late cretaceous narangjiapo thrust placed permian strata 20 km over ophiolitic melange and cretaceous strata north of the narangjiapo thrust 40 km of shortening was accommodated by the late cretaceous early tertiary south directed jaggang thrust system that involves jurassic flysch and cretaceous strata and roots into a decollement within ophiolitic melange the most recent shortening was accommodated to the south of the narangjiapo thrust along the north dipping shiquanhe thrust the shiquanhe thrust cuts flat lying 22 6 0 3 ma volcanic rocks and underlying folded tertiary nonmarine strata in its footwall and was likely active during slip along the oligocene gangdese thrust system of southern tibet ophiolitic melange and structurally overlying jurassic flysch near shiquanhe are interpreted to represent remnants of a subduction accretion complex and forearc basin respectively that were obducted southward onto the margin of the lhasa terrane during late jurassic early cretaceous closure of the bangong nujiang ocean subsequent imbrication of the obducted sheet could have produced the two east west trending belts of ophiolitic melanges separated by 100 km in western tibet late cretaceous early tertiary thin skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of lhasa terrane rocks beneath the obducted ophiolitic melange and the qiangtang terrane to the north

syn kinematic emplacement of the pangong metamorphic and magmatic complex along the karakorum fault n ladakh this paper investigates the age p t conditions and kinematics of karakorum fault kf zone rocks in the nw part of the himalaya karakorum belt granulite to greenschist facies assemblages were developed within the kf zone during strike slip shearing the granulites were formed at high temperature 800 c 5 5 kbar were subsequently retromorphosed into the amphibolite facies 700 750 c 4 5 kbar and the greenschist facies 350 400 c 3 4 kbar the tangtse granite emplaced syn kinematically at the contact between a lt and the ht granulite facies intrusion occurred during the juxtaposition of the two units under amphibolite conditions microstructures observed within the tangtse granite exhibit a syn magmatic dextral s c fabric compiled u pb and ar ar data show that in the central kf segment granulite facies metamorphism occurred at a minimum age of 32 ma subsequent amphibolite facies metamorphism at 20 18 ma further shearing under amphibolite facies 650 500 c was recorded at 13 6 0 9 ma and greenschist facies mica growth at 11 ma these data give further constrains to the age of initiation and depth of the karakorum fault the granulite facies conditions suggest that the kf accommodating the lateral extrusion of tibet could be at least a crustal or even a lithosphere scale shear zone comparable to other peri himalayan faults

40ar 39ar dating of volcanic rocks of the shyok suture zone in north west trans himalaya implications for the post collision evolution of the shyok suture zone abstract 40 ar 39 ar geochronological studies carried out on the khardung volcanics of ladakh india and our earlier ar ar results from the volcanics of the shyok suture along with the available geological and geochemical data provide good constraints for post collision evolution of the shyok suture zone whole rock samples from the shyok volcanics yielded disturbed age spectra and we have demonstrated earlier that the youngest tectonic event in the shyok suture zone responsible for the thermal disturbance of these samples is karakoram fault activation at 14 ma contrastingly whole rock samples from the khardung volcanics which are in tectonic contact with these shyok volcanics and are exposed in the form of thick rhyolitic and ignimbritic flows yielded undisturbed age spectra and good plateau ages the whole rock plateau ages of two rhyolite samples are 52 8 0 9 and 56 4 0 4 ma we interpret these ages to be the time and duration of emplacement of these volcanics over thickened margin of the continental crust which appears to be coeval with the initiation of the collision between the indian and asian plate the lesser extent of post emplacement isotopic re equilibration in these samples unlike the shyok volcanics indicate that these samples were present in different tectonic settings away from the karakoram fault at the time of deformation in the shyok suture zone we propose that the two volcanic belts of contrasting nature were brought together in juxtaposition by the karakoram strike slip faulting at 14 ma

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

mineral chemistry and k ar ages of plutons across the karakoram fault in the shyok nubra confluence of northern ladakh himalaya india abstract petrographic analyses of plutons across the karakoram fault in the shyok nubra confluence of northern ladakh area revealed that the rocks consist of diorite granodiorite granite and leucogranite pyroxene and biotite chemistries by epma indicate that most of the diorite granodiorite and granite are calc alkaline and formed in an arc related tectonic setting these calc alkaline plutons yield k ar biotite ages from 49 3 1 1 to 51 2 1 1 for ladakh batholith in khardung la and from 60 8 1 3 to 65 8 1 4 ma for granites and diorites in hundar area the k ar ages of the hundar igneous complex are within the age range of 46 70 ma of the ladakh batholith near leh town and the neighbor sites indicating the hundar igneous complex as a part of the ladakh arc their ages are also coincident with the khardung volcanics 67 4 and 60 5 ma the calc alkaline granites from panamik of karakoram block yield k ar biotite ages of 95 7 2 1 and 96 7 2 1 ma suggesting that the granites are member of the plutons 90 120 ma occurring in northern pakistan tangtse in ladakh and western tibet that emplaced during subduction of the neo tethyan oceanic plate under the karakoram block the leucogranite and granodiorite in the panamik region yield k ar biotite and muscovite ages ranging from 9 18 0 21 to 9 45 0 21 ma the leucogranites are the s type related to post collision tectonic setting and are considered to have emplaced in relating to activation of the karakoram fault

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

shoshonitic and ultrapotassic post collisional dykes from northern karakorum sinkiang china abstract high k calc alkaline shoshonitic and ultrapotassic post collisional dykes of neogene age have been found in the remote and little known region of northern karakorum located around the shaksgam valley north of the k2 gasherbrum range china the dykes derive from more or less comparable basic magma s and display rather unusual petrographic and geochemical characters with respect to the other k rich rocks the geochemical data are consistent with derivation of the basic magma s from small degrees of partial melting of garnet lherzolites previously enriched in incompatible elements of crustal origin possibly during the subduction of the indian plate beneath karakorum the spectrum of compositions reflects fractional crystallization governed by an early removal of clinopyroxene phlogopite plagioclase garnet amphibole followed by the precipitation of abundant alkali feldspar amphibole apatite quartz additionally assimilation of crustal rocks during magma ascent contributed to the unusual compositional characteristics and is suggested by the abundance of corroded quartz plagioclase xenocrysts and by the occasional presence of granitic xenoliths an apparent connection exists between magmatism and tectonism in the complex karakorum fault zone kfz it is suggested that during the neogene the strike slip kfz and some adjacent post metamorphic faults transiently behaved as extensional fault systems down to deep levels triggering ascent and emplacement of the k rich magma the subsequent re activation of a compressive and transcurrent regime determined the rapid and recent uplift of the more primitive lamprophyres occurring in the plutonites and metamorphites of the upper baltoro glacier and k2 gasherbrum range relative to the more fractionated and contaminated lamprophyres injecting the shallower rocks of the shaksgam valley area

a geological transect from kun lun to karakorum sinkiang china the western termination of the tibetan plateau preliminary note a geological geophysical expedition ev k2 cnr 1988 visited the area from west kun lun to karakorum k2 gasherbrum seven tectonic units including sedimentary magmatic and metamorphic rocks were distinguished in this area the northernmost are suggested to belong to the kun lun and qiangtang microplates the sedimentary sequence of shaksgam is proved to extend from the permian to the jurassic with carboniferous and cretaceous ages more doubtful this sequence shows intermediate affinities between the karakorum and the qiangtang the two southernmost units belong to the karakorum microplate the karakorum fault zone comprises a complex pattern of faults and thrusts with brittle deformation and uplifting of granitoid bodies

beryllium systematics in young volcanic rocks implications for 10 be beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior be analyses conducted on well characterized oceanic and arc volcanic rock suites as well as on marine sediments suggest a bulk solid liquid distribution coefficient of 0 03 0 06 for melting of the mantle and crystallization of basalts the be nd ratio for many volcanic rocks from diverse tectonic environments is approximately 05 similar to the ratio in chondrites be data for samples from volcanic arcs show that there are significant variations in 10be 9be among different arcs and that variations in 10be are not due to variations in be concentration alone for at least one volcano bogoslof the 10be 9be ratio is constant for samples that vary by a factor of three in both their be and 10be concentrations suggesting that 10be is an inherited magmatic signature and not simply a result of contamination near the surface in addition the be nd and pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the bogoslof source region provided the mantle wedge has the isotopic characteristics of depleted morb since 10be exists only in the uppermost tens of meters of oceanic sediments the data suggest an efficient return flux of sediment to the mantle at subduction zones

timing and origin of migmatitic gneisses in south karakoram insights from u pb hf and o isotopic record of zircons abstract the timing and origin of partial melting in collision belts is crucial to understand the thermotectonic evolution and the relationship between ht metamorphism and magmatism in over thickened crust in the present study we used the in situ isotopic hf o and u pb record of zircons to investigate the timing and origin of migmatitic gneisses exposed in the core of the dassu dome in south karakoram the new u pb zircon dating identified the proterozoic inherited cores 1 8 1 9 ga and 2 3 2 5 ga surrounded by a neogene overgrowth with ages ranging from 6 to 20 ma these ages imply that the partial melting in the karakoram metamorphic complex lasted from 20 ma to 6 ma and can be correlated with the miocene magmatism in the adjacent baltoro region oxygen isotopic data from proterozoic inherited cores 1 8 1 9 ga and neogene overgrowths are indistinguishable and generally vary from 8 to 9 5 these values are slightly higher than the most igneous zircons 6 5 8 valley et al 2005 indicating an igneous precursor with heavy initial o composition that later might have equilibrated with low temperature environment or some involvement of supracrustal material is likely however a few low u th relatively old inherited cores 2 3 2 5 ga showed mantle like 18o 5 3 0 6 valley et al 2005 values of 18o 5 5 2 7 the present day weighted mean ehf 0 of the proterozoic inherited cores ranges from 50 1 0 to 44 3 1 2 in contrast the neogene rims are 15 20 e units higher than the inherited core with present day ehf 0 30 6 0 9 this implies that the hf composition of the neogene overgrowth is not controlled exclusively by the dissolution of the inherited cores and that contamination by external melts is likely we suggest a contribution from the neogene less evolved magmatism in the baltoro region ehf 0 4 to 10 the elevated oxygen composition is not consistent with the contribution from pristine mantle derived magmas the observed homogeneous and uniform hf o isotopic composition of the proterozoic inherited cores suggest their derivation from mildly evolved infracrustal sources with minor input from supracrustal material the older inherited zircons 2 3 2 5 ga were precipitated from juvenile mantle derived magmas

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

the north karakorum side of the central asia geopuzzle an italian geological team visited a remote and in part never studied area in the northern hunza region pakistan which represents the link between the karakorum and pamir ranges the north karakorum sequence commences in the permian with terrigenous sediments followed by shallow to deep marine carbonates deposited on a newly formed passive margin deep water sedimentation continued till the end of the middle triassic when carbonate platform conditions resumed an episode of deltaic red sandstones with orogenic provenance is interbedded in the liassic and it is transgressed by a middle to upper jurassic shallow water marine unit eventually all of the sequence was faulted and folded with weak metamorphic imprint before fluviatile red polygenic conglomerates sealed the succession in a spectacular unconformity the north karakorum provides an example of a microplate that rifted away from gondwana in the permian reached deep marine conditions in the early triassic and marginally recorded compressive movements in the liassic a subsequent orogenic episode points to a reorganization of the southern asian margin possibly around middle cretaceous time finally the north karakorum was affected by strong fold thrust deformation and low to very low grade metamorphism in the cainozoic related to the india asia collision

india asia collision implications from the geology of the eastern karakoram the shyok tectonic belt of ladakh northwest india bridges the important geologic gap between the kohistan block of pakistan and the lhasa block of tibet the geology of the shyok tectonic belt supports the model of successive collision and accretion of gondwana fragments along the southern margin of the asian plate tectonic continuity is established between gondwana fragments of afghanistan kohistan shyok and tibet on the basis of new geologic data from the shyok tectonic belt and various plate tectonic models for the india asia collision are discussed 24 references 3 figures 1 table

10be and 9be in marine sediments and their potential for dating using sequential leaching experiments we have measured the fraction of the cosmogenic isotope 10be half life 1 5 my and its stable isotope 9be co extracted with the following phases in marine sediments exchangeable calcium carbonate fe and mn oxyhydroxides organic opal and detrital the extraction of the authigenic phases typically release 70 of the 10be but only 40 of the 9be in order to test its potential for dating marine sediments we have measured the authigeniccally associated 10be 9be in 17 surface sediment samples from different ocean basins the observed spatial variability which appears to be influenced by proximity to continental input of 9be precludes the general and precise applications of leached 10be 9be for dating however the relatively constant value observed in surface sediments over large areas of the pacific indian and southern atlantic oceans shows considerable promise for approximate dating of open oceans sediments in order to test temporal variability a profile of the authigenically associated 10be 9be ratio has been measured in the independently dated central pacific core rc12 65 the observed variation in 10be 9be over the past nine my is approximately twice that expected on the basis of 10be decay alone several possible explanations for such behavior and their potential consequences for the use of leached 10be 9be for dating are discussed

age and petrogenesis of a type granites in the middle segment of the bangonghu nujiang suture tibetan plateau abstract during geological investigations conducted over the past several years the authors found a group of a type granites in the middle segment of the bangonghu nujiang suture on the tibetan plateau these granitic plutons occur as stocks with exposed areas of less than 1 km 2 and lithologically include biotite granite and granodiorite porphyry which had intruded into cretaceous sedimentary rocks petrogeochemically the a type granites contain high sio 2 levels varying from 68 62 75 36 wt moreover they contain relatively high fe 2 o 3 t 0 86 5 39 wt and low al 2 o 3 12 76 15 54 wt levels and are weak peraluminous to metaluminous a trace element n morb normalized spider diagram showed apparent enrichment of the large ion lithophile elements lile rb th u k and pb with marked depletions of ba and sr the high field strength elements hfse nb ta and ti were sharply depleted with relative enrichment of zr and hf these signatures are characteristic of a type granite the granite samples had high rare earth element ree contents with ree 122 37 291 19 ppm light ree were rich relative to heavy ree with lree hree 4 89 9 58 and negative eu anomalies were sharp with eu varying from 0 14 0 5 and a mean value of 0 34 their chondrite normalized rare earth element distribution patterns appear as gently right dipping v types zircon u pb laicpms dating for three granitic plutons yielded weighted mean ages of 109 6 1 4 ma mswd 3 7 112 3 0 51 ma mswd 0 21 and 113 73 0 5 ma mswd 0 21 indicating that they formed in the late stage of the early cretaceous epoch the nd sr and pb isotopic results showed that the granites were rich in radiogenic isotopes the 87 sr 86 sr and i sr ratios varied from 0 719842 0 786395 and 0 706900 0 710378 respectively the 143 nd 144 nd ratios were from 0 512123 0 512392 with relatively large negative e nd values 3 37 to 10 34 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios ranged from 18 703 19 070 15 680 15 732 and 39 121 39 576 respectively exhibiting isotopic signatures typical of crustal sources all of the data demonstrated unanimously that these granites were derived from partial melting of arc basaltic rocks underplated in the lower crust during oceanic crust subduction the high temperature heat source for melting of anhydrous basaltic rocks of the lower crust was from upwelling asthenosphere through slab windows formed as a result of slab break off during post collisional extension of the orogenic zone

zircon u pb and hf isotopic constraints on petrogenesis of the cretaceous tertiary granites in eastern karakoram and ladakh india abstract multiple subduction events occurred preceding the collision of greater india with the karakoram terrane that consumed the neotethyan ocean between early cretaceous and eocene time zircon u pb dating and hf isotope analyses of granitic rocks collected from the karakoram terrane and ladakh batholith have been conducted to constrain these geological processes undeformed ladakh batholith granodiorite yielded zircon u pb ages of 68 and 64 ma with ehf t values of 6 4 and 10 3 and three diorites near leh and darbuk gave zircon u pb ages of 50 4 51 0 ma and ehf t values of 7 4 to 8 9 indicating that the paleocene eocene was the most important period of granitic magmatism that derived from a juvenile source three tonalite granodiorite enclaves at skyangpoche within the karakoram batholith have zircon u pb ages of 101 103 ma with ehf t values of 2 3 to 3 7 indicating generation of granitic rocks by partial melting of the karakoram basement three samples of the miocene karakoram batholith from around darbuk yielded ages of 16 6 19 1 ma with ehf t values of 8 5 and 10 5 that indicate an input of ancient crust from the indian plate granodiorite within the karakoram metasedimentary sequence zircon u pb age 74 ma ehf t of 5 4 from the tangtse gorge and granite around muglib zircon u pb age of 63 and 56 ma ehf t of 6 8 and 6 0 indicate similar geochronological and isotopic characteristics to those of the ladakh batholith thus the time resolved hf isotopic compositions of magmatic zircons from the granites in the karakoram and ladakh batholith show a large variation that indicate their derivation from both ancient and juvenile continental crusts in active continental margin since at least the mid cretaceous

beryllium isotope systematics of submarine hydrothermal systems abstract both 10 be and 9 be concentrations have been measured in a hydrothermal fluid from the sediment starved east pacific rise at 21 n as well as in fluids and associated sediments from the sediment covered guaymas basin and escanaba trough hydrothermal systems the results show that while the 9 be concentrations in fluids from both types of systems are comparable about three orders of magnitude higher than that of the seawater supplying the systems their 10 be concentrations are significantly different the 10 be concentration in the solution emanating from the studied sediment starved hydrothermal system is at least two times lower than that of the pacific bottom water by contrast the 10 be concentration in hydrothermal solutions from sediment hosted environments are enriched over ambient seawater and are at least one order of magnitude higher than that measured in the 21 n fluid the sedimentary cover being the only available source of 10 be in these systems these data demonstrate that 10 be is an unambiguous tracer of interactions between hydrothermal fluids and recent sediments as an example this study examines hydrothermal solutions from the sediment starved mariana trough back arc basin which have compositions similar in many respects to those from sediment hosted environments however these fluids are depleted in 10 be relative to ambient seawater which precludes interaction with recent sediment as the cause of their peculiar chemical composition

siliceous sediments of the guaymas basin the effect of high thermal gradients on diagenesis recent siliceous sediments of the guaymas basin a rapid spreading center in the gulf of california are intruded by basaltic sills which induced significant diagenetic and metamorphic changes in the sediments the transformation from opal a to opal ct opal ct to quartz and opal a directly to quartz in these sediments cored on dsdp leg 64 can be used to infer the temperature history and order of emplacement of intrusives at or near contacts with sills of 30 m or greater average thickness opal a inverts directly to authigenic quartz but there is less quartz than would be expected from the amount of opal a dissolution opal ct forms in sediments sandwiched between adjacent sills based on high rates of quartz nucleation and growth at high temperatures 150 c and on considerations of convective solution transfer opal ct is thought to form only where temperatures were lower or at positions between sills an environment which prevents rapid convective dissipation of silica in solution where temper

granites of western karakorum and northern kohistan pakistan a composite mid cretaceous to upper cenozoic magmatism abstract the petrography the chemical mineralogical typology and the ages of six plutonic units four from the karakorum axial batholith darkot pass ghamu bar batura and hunza units and two of northern kohistan gindai and nomal plutons are defined and compared based on field data and analyses of up to 78 samples major elements ree rb s sbnd sr and k ar isotopes the karakorum axial batholith is a composite body three major intrusive stages occurred 1 around mid cretaceous times ca 110 95 ma with the emplacement of subalkaline i e monzonitic darkot pass and calc alkaline hunza ghamu bar units 2 during palaeogene maybe up to 43 ma batura subalkaline unit a strong tectonommetamorphic event recorded in the gneissification of the cretaceous intrusives occurred between these two stages it may be of palaeocene age p t estimates of the highest metamorphic grade rocks of the hunza unit have yielded values of 580 640 c and 5 0 5 kbar and 3 during upper miocene ca 9 ma baltoro subalkaline unit debon et al 1986c in addition a conspicuous network of aplo pegmatitic dykes emplaced into the hunza area possibly from the eocene up to the upper cenozoic with a maximum during the middle miocene ca 15 ma most of these major magmatic stages are met again among the acidic intrusives and dykes of northern kohistan the first one as blastomylonitic tholeiitic plutons nomal ca 102 ma petterson and windley 1985 the second one as subalkaline plutons gindai ca 59 ma and a third one as leucocratic dykes of oligocene age ca 30 ma petterson and windley 1985 these data may be related to the geodynamic evolution of the nw part of the india eurasia suture zone thus allowing better constraints on the major steps of this evolution the partly synchronous closures by n dipping subduction of the two tethys branches which are assumed to have encircled the kohistan arc in upper mesozoic times may have generated both the karakorum and the kohistan intrusives of cretaceous and palaeogene ages the northern branch very likely closed before the southern one at the time of the second intrusive stage palaeogene a kohistan and karakorum had already collided were welded and had suffered the same major tectonometamorphic event b subduction of the southern tethys floor beneath the welded kohistan karakorum was still active c however collision between india and kohistan karakorum may have already begun particularly at the level of the nanga parbat promontory finally it is emphasized that the intrusive processes continued in the karakorum long after the collision e g baltoro granite

beryllium isotope geochemistry of hydrothermally altered sediments profiles of both10be and9be concentrations have been measured in sediments from the dsdp leg 64 site 477 core established in the deep guaymas basin in an area of high heat flow this site offers the opportunity of studying hydrothermal alteration induced by two distinct hydrothermal systems those caused i by the intrusion of hot sills into porous sediments and ii by heat associated with a magma chamber the results show that the distribution of both beryllium isotopes between two operationally defined sedimentary phases material susceptible to hydroxylamine leaching and residual material changes with the degree of hydrothermal alteration a decrease in10be 9be in the leachable phase of altered sediments relative to unaltered sediments indicates that hydrothermal alteration is not limited to a simple chemical leaching but involves redistribution of the beryllium isotopes between metamorphosed sedimentary phases in addition the similarity of the mean10be 9be ratios associated with the leachable and the residual phases in the part of the core which has experienced greenschist facies metamorphism suggests that this process leads in the prevailing geophysical conditions to isotopic homogenization a close relationship exists between10be and mgo concentrations in altered sediments from this core this supports earlier observations that beryllium is not easily removed from the sedimentary column and indicates that this remains the case even under the conditions encountered in submarine hydrothermal systems

using petroleum inclusions to trace petroleum systems a review abstract petroleum bearing fluid inclusions are small encapsulations of oil and gas that offer an invaluable opportunity to better constrain the evolution of petroleum systems insights into palaeo fluid compositions complement observations on present day fluid compositions which represent only the end point of complex cumulative processes throughout basin history in this contribution we review a wide range of approaches used to extract geochemical information from petroleum inclusions and how these can be used to better constrain petroleum systems these techniques can be grouped into optical spectrographic and thermometric non destructive methods or destructive chemical analyses of bulk samples or individual inclusions typically optical methods documenting the distribution and visual properties of petroleum inclusions are used to provide petrographic context for subsequent specialised geochemical analyses of petroleum inclusions additional non destructive techniques such as raman spectroscopy can then be applied to provide some further insights into the composition of the trapped fluids although the complex nature of petroleum generally requires direct access to the fluid for a more complete understanding of geochemical aspects a variety of destructive techniques have been developed initially to analyse bulk samples released by mechanical crushing and more recently through ablation type techniques that allow the composition of individual inclusions to be characterised screening geochemical techniques that utilise mechanical crushing of bulk samples to analyse petroleum inclusions using mass spectrometry without prior chromatographic separation have become routine analyses other geochemical techniques more geared towards detailed molecular information such as biomarkers utilise chromatographic separation prior to mass spectrometry evaluation of the isotopic composition of petroleum inclusions is also possible for both bulk samples and compound specific analyses the use of lasers to open individual inclusions allows the released contents to be analysed by thermal extraction gas chromatography mass spectrometry gc ms or mass spectrometric mapping of minerals using time of flight secondary ion mass spectrometry tof sims a surface sensitive analytical method that uses ion beams to ablate into minerals the continued evolution of techniques to analyse the incredibly small volume of hydrocarbons trapped within fluid inclusions has progressed to a point where there is little that can be done to evaluate a live oil or gas sample that cannot be achieved for a fluid inclusion sample the full power for tracing petroleum systems is however only realised where there is an effective integration of fluid inclusion data with a more conventional approach to petroleum systems analysis

volcanic rocks of the 1985 tibet geotraverse lhasa to golmud volcanic rocks encountered during the tibet geotraverse have been studied in the field in thin section and by major and trace element geochemistry in order to determine their most probable original eruptive environment rocks from a total of eleven distinct volcanic provinces were studied in this way they provide evidence for an active continental margin or post collision province of probable devonian early carboniferous age in the northern kunlun mountains an active continental margin of late carboniferous age in the southern lhasa terrane permian continental rifts in the central qiangtang and central kunlun terranes triassic volcanic arcs in the southern lhasa and northern qiangtang terranes a triassic active continental margin dyke swarm in the northern kunlun mountains a jurassic post collision or back arc rifting province in the southern qiangtang terrane a jurassic island arc in the northern lhasa terrane a cretaceous post collision province in the northern lhasa terrane possibly extending into the southern qiangtang terrane and a palaeogene active continental margin in the southern lhasa terrane an oligocene trachyte plug in the northern qiangtang terrane was the only evidence encountered during the geotraverse of volcanism post dating the palaeogene india eurasia collision however the composition of this plug coupled with new and published analyses from miocene volcanics in the southern lhasa terrane and from the pliocene recent volcanic province of northwest tibet places important constraints on models for post collision underplating of tibet by continental lithosphere any underplating is likely to have been a much later than the start of collision b directed beneath tibet from the north as well as the south and c limited in extent

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

hydrothermal scavenging on the juan de fuca ridge 23othxs 10be and rees in ridge flank sediments abstract we have investigated the geochemistry of a hydrothermally enriched sediment core recovered from the western flank of the n cleft segment juan de fuca ridge 8km west of the megaplume area previously identified near 45 n the core contains varying biogenic lithogenic and hydrothermal components as reflected in caco3 al and fe contents respectively horizons of pronounced hydrothermal input in core top sediments and at depth exhibit increased concentrations of fe cu zn and pb and shifts in pb isotopic compositions toward nonradiogenic morb hydrothermal values ree concentrations co vary with hydrothermal fe down core and shale normalised ree distribution patterns exhibit both negative ce anomalies and positive eu anomalies indicative of input from plume particle fall out unsupported 230thxs activities down core are consistent with continuous slow sediment accumulation rates of 0 54 cm ky for 200 ky since the deposition of the deeper fe rich horizon 10be 0 and 9be isotope concentrations also co vary with hydrothermal fe down core and exhibit 10 be o 9 be ratios which approach that of pacific ocean deep water indicative of a seawater scavenging source 10 be 0 230 oth xs 0 ratios throughout most of core gc88 6 are greater than mean pacific ocean values indicating that hydrothermal scavenging can lead to significant net removal of dissolved 10be into ridge flank sediments

tectonic inferences from oxygen isotopes in volcano plutonic complexes of the india asia collision zone nw india the india asia collision zone in ladakh nw india is characterized by two major granitic batholiths the northern karakoram granitic complex and the southern ladakh granitic complex are separated by thrust bound belts of ophiolites flysch and calc alkaline volcanics khardung volcanics of late paleozoic to tertiary age oxygen isotope analyses of whole rock and coexisting mineral separates indicate that a the ladakh granitic complex belongs to an i type suite with 18o 5 6 to 6 1 and b the karakoram granitic complex comprises two contrasting suites of granitoids an older predominantly i type with 18o 6 2 to 7 7 and a younger s type with 18o 9 5 to 10 7 the khardung volcanics show wide variation in 18o values ranging from 0 75 to 10 7 indicating isotopic exchange with a meteoric hydrothermal convective system we suggest that the older i type suite of the karakoram batholith represents jurassic to early cretaceous arc magmatism along the bangong nujiang north saltoro suture this implies a continental collision between the lhasa shyok kohistan block and the asian plate prior to the tertiary collision between india and asia india asia collision resulted in the rejuvenation of the north saltoro suture with the emplacement of the younger anatectic granite of the karakoram batholith

submarine hydrothermal venting related to volcanism in the lesser antilles evidence from ferromanganese precipitates 1 radiogenic isotope compositions sr nd pb hf and os of sediment hosted seafloor ferromanganese crusts and sediments incrusted with ferromanganese oxyhydroxides from the lesser antilles island arc were measured to distinguish between hydrogenous seawater derived and hydrothermal metal sources the ages of the precipitates range between recent last few thousand years and a few 100 kyr as deduced from 10be and co concentrations evidence from the presence of bladed todorokite and nontronite together with the major element and ree composition suggests that a significant proportion of these sediment hosted precipitates formed at relatively low temperatures from a mixture of seawater and hydrothermal fluids associated with island arc volcanism the radiogenic isotope compositions of all metals mentioned above except pb show large differences in hydrothermal versus hydrogenous contributions over space and time in contrast to precipitates of high temperature fluids which mainly scavenge their ree contents from seawater the crusts of this study show 143nd 144nd of up to 0 512817 nd 3 5 this is close to the signature of the nearby island arc rocks and far above the expected local seawater ratio of 0 51209 nd 10 7 these crusts also show high 176hf 177hf up to 0 283102 low 87sr 86sr up to 0 7069 and low 187os 188os up to 0 16 compared with local seawater as expected from hydrothermal island arc derived metal contributions in contrast the pb isotope signatures of the crusts cannot be explained by mixing between seawater and hydrothermal sources it is suggested that pb was either removed from the ascending fluids within the sediment column before they reached seawater or the temperatures were too low to leach significant amounts of pb from the rocks or sediments external sources such as saharan dust particulate inputs from the orinoco river or even incongruent release of pb isotopes from the island arc rock derived particles must have contributed to the observed pb isotope variability our results suggest that submarine hydrothermalism originating from intraoceanic island arc volcanism creates distinct geochemical environments for the dispersion of hydrothermal fluids and may be an important mechanism to supply metals of hydrothermal origin to seawater

last glacial to post glacial 10be fluctuations in a sediment core from the academician ridge lake baikal 10be concentrations sediment composition and sediment accumulation rates were determined in a sediment core from the academician ridge of lake baikal the 10be concentrations vary from 5 07 108 atoms g in the last glacial section to 11 25 108 atoms g in the section representing the post glacial climate stage 10be fluxes on the other hand increase toward the last glacial stage coinciding with an increase of the sediment accumulation rate these facts imply that climate related sedimentation is related to both flux and concentration of the nuclide in the sediment core during the last glacial stage arid conditions in the lake s watershed caused a marked increase in flux of clay particles with low 10be content to the lake resulting in an increased flux but lowered concentration of 10be in the sediments it is suggested that the 10be record of the bottom sediments of lake baikal can be used as a proxy indicator of climate change in central asia

investigation of oil pool formation from the homogenization temperatures of fluid inclusions and biomarkers in reservoir rocks a genetic model for the deng 2 oil pool in the jiyuan depression abstract the jiyuan depression is a frontier area for oil and gas exploration in henan province china in recent years oil was discovered in the deng 2 well in the lower tertiary though the tectonics and petroleum geology of the depression are very complex a series of experiments on fluid inclusions in the oil bearing sandstones from the deng 2 well were made that included measurement of the homogenization temperatures of gas liquid inclusions and gc ms analysis of biomarkers either in the sandstone pores or in the fluid inclusions the deng 2 oil reservoir was formed at about 78 c corresponding to a burial depth of about 2200 m the present burial depth is about 700 m because of erosion and fault block uplift in oligocene time although oil in the sandstone pores is now heavily biodegraded the biomarkers in the inclusions show slight biodegradation representing a watering and biodegradation process that did not occur before formation of the deng 2 oil pool having investigated the structural evolution of the deng 2 trap it is concluded that the oil discovered in the tertiary reservoir of deng 2 well migrated from mesozoic reservoirs through active faults around the deng 2 trap as the oil migrated from the mesozoic to the tertiary reservoir the deng 2 trap was uplifted close to the depth of active biodegradation subsurface temperature lower than 80 c and to a burial depth shallower than 2250 m from the thermal gradient of 3 1 c 100 m so that the oil in the inclusions shows a slight biodegradation because of the continuous uplift of the deng 2 trap during the tertiary and quaternary the reservoired oil has been more heavily biodegraded compared to that in the inclusions

genetic features of petroleum systems in rift basins of eastern china abstract most oil bearing basins in eastern china are mesozoic cenozoic continental rifts which have played a habitat for oil and gas in china investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins of the essential elements of the petroleum system the source rock is the most important in rift basins however rift tectonic evolution controls all the essential elements and processes necessary for a petroleum system a four stage evolution model is suggested for the controls in the rift basin a rift basin may consist of sub basins depressions and sub depressions and major moderate and minor uplifts a depression or sub depression has its own depocentre mainly occupied by source rock and all kinds of lacustrine sediments and thus has all the essential elements of a petroleum system however only those depressions or sub depressions which are rich in organic matter and deeply buried to generate oil and gas form petroleum systems immature oil another characteristic complicates the petroleum system in the rift basins three types of oil and gas habitats are described as a result of this analysis of the petroleum systems of the 26 largest oil and gas fields discovered in eastern china rift basins uplifts between oil source centres are the most prospective areas for oil and gas accumulations slopes connecting oil source centres and uplifts are the second and the third type is subtle traps in the oil source centre

mobilization of beryllium in the sedimentary column at convergent margins studies of be distributions in subduction zone sediments will help to understand questions regarding the enrichments of cosmogenic be 10 in arc volcanic rocks analyses of be 10 and be 9 in sediments of ocean drilling program site 808 nankai trough and be 9 in porewaters of site 808 and sites 671 and 672 barbados ridge complex show significant decreases in solid phase be 10 and large increases of porewater be 9 at the location of the decollement zone and below or at potential flow conduits these data imply the potential mobilization of be during pore fluid expulsion upon sediment burial experiments involving reaction between a decollement sediment and a synthetic nacl cacl2 solution at elevated pressure and temperatures were conducted in an attempt to mimic early subduction zone processes the results demonstrate that be is mobilized under elevated pressure and temperature with a strong ph dependence the be mobilization provides an explanation of be 10 enrichment in arc volcanic rocks and supports the argument of the importance of the fluid processes in subduction zones at convergent margins