zn sr isotope records of the ediacaran doushantuo formation in south china diagenesis assessment and implications abstract recent studies show that zinc isotopes could provide valuable clues to environmental change and biogeochemical cycle of the past oceans this study reports a modified procedure for leaching the carbonate fractions in sedimentary rocks a thorough evaluation of diagenetic effects and systematic variations of zn and sr isotope ratios in lower part of the ediacaran stratigraphic unit deposited in the aftermath of the marinoan glaciation in south china the influence of post depositional diagenesis on zn isotope compositions of the studied samples is assessed by comparing 66zn to other geochemical indexes 87sr 86sr 13c 18o and mn sr ratios in the five studied cap carbonate sections member i of the doushantuo formation dolostones from four sections have 66zn values positively correlated with 18o values and negatively correlated with 87sr 86sr ratios 0 7081 0 7204 these correlations suggest that these cap dolostone samples have been modified by post depositional diagenesis the light 66zn value 0 02 suggests that initial zn isotope ratios of cap dolostones could have been reset by hydrothermal fluids with relatively high zn concentration and low 66zn values by contrast carbonates from member ii of the doushantuo formation above cap dolostones are relatively pristine based on their low 87sr 86sr ratios 0 7079 0 7086 being indistinct from the proposed early ediacaran seawater 87sr 86sr values chemical and isotopic variations in these samples are interpreted to reflect primary signals that record paleo environmental changes of the early ediacaran ocean a rapid increase of 66zn from 0 3 to 1 1 occurs in the middle part of member ii accompanying by relatively invariant 87sr 86sr ratios that imply insignificant changes in input from continental weathering considering the limited change in atmospheric oxygen during this period the rapid 66zn raise indicates an increase in buried organic matters which is consistent with the coupled positive shift of 13ccarb as well as the fossil records found in the same strata these results provide insights into zn cycling in the post marinoan oceans and facilitate the application of zn isotopes in carbonates as a proxy for the fate of marine organic matter

building an island arc crustal section time constraints from a la icp ms zircon study geochronological studies of samples from continuous crustal sections of fossil intra oceanic arcs are paramount for determining the precise timing of major processes that took place during the building of an oceanic island arc crust in this study laser ablation icp ms u pb zircon and conventional rb sr analyses pinpoint the timing of major events responsible for crustal growth of the kohistan paleo island arc northern pakistan inheritance in magmatic rocks is evidence for recycling of intra arc material and indicates that the kohistan arc may have formed as early as 135 4 ma one older inherited grain indicates that the arc developed on a young oceanic lithosphere whose remnants include a c 175 ma old component an interesting consequence is that intra oceanic arc magmas can yield inherited zircons which can be much older than the arc system itself without requiring recycling back into the mantle by subduction processes in the case of the kohistan arc ante arc neotethys oceanic lithosphere was tapped by arc magmas during their way upward into the arc crust the oldest magmatic ages measured in this study fall in the range 101 102 ma 100 9 0 6 and 102 1 0 4 ma this period corresponds to arc build up and thickening of the arc crust leucogranitic melts dated at 89 9 0 4 ma and 90 9 1 0 ma are considered as produced by dehydration melting reaction accompanying granulitisation of the thickened lower arc crust a maximum age for this event is 97 7 0 7 ma the age of emplacement of a garnet meta tonalite affected by granulite facies metamorphism magmatic activity was still ongoing during and after the granulitisation as testified by emplacement of a diorite and a gabbro dated at 89 1 0 6 and 88 2 0 9 ma respectively the upper part of the metaplutonic sequence contains diorite samples dated at 84 6 0 5 ma and 84 3 0 5 ma and as young as 81 1 0 7 ma during this period and based on the present day outcropping sequences the mean crustal growth rate varied from 32 to 65 km 3 km ma volume per unit width along the strike of the arc which is comparable to the range for present day arcs of the western pacific region the correspondence of crustal growth rates observed for present day island arcs and the good preservation of the crustal section in the kohistan arc make this area an exceptional natural laboratory to study arc related processes and to check models of continental crust formation by arc accretion

progressive localization of deformation during exhumation of a major strike slip shear zone norumbega fault zone south central maine usa detailed structural studies along with 40ar 39ar thermochronology provide important constraints on the temporal spatial and structural evolution of a major orogen parallel strike slip shear zone the norumbega fault zone in maine detailed structural analysis in south central maine reveals two very different styles of dextral noncoaxial deformation a wide zone 25 km of heterogeneously distributed ductile shear structures and a relatively narrow zone 1 km of lower greenschist facies high strain mylonitization 40ar 39ar thermochronology indicates that these two zones of deformation developed during a prolonged period of regional exhumation following middle devonian amphibolite facies metamorphism the wide zone of dextral shear is interpreted to reflect a major episode of moderate temperature post amphibolite facies metamorphism but pre regional cooling below 320 c late devonian to early carboniferous transcurrent tectonism the narrow zone of dextral shear represents both a younger latest carboniferous and significantly cooler 320 c deformational event occurring at much higher structural levels a general model of increasingly narrow but more highly focused noncoaxial deformation during progressive regional exhumation is supported by the observations

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

high temperature and pressure seismic properties of a lower crustal prograde shear zone from the kohistan arc pakistan anastomosing shear zones exposed in the lower crust of the kohistan palaeoisland arc in pakistan have parageneses indicating increasing pressure during deformation therefore they represent a rare example of strain localization during crustal thickening we investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones the compressional wave velocity was measured at confining pressures of up to 0 5 gpa and temperatures of up to 600 8c the density the average vp compressional p wave velocity and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite the seismic anisotropy is largest for the strain gradient the vp dependence of the velocities on temperature is much higher in the mylonite than in the protolith the acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures but not at high temperatures this suggests that the seismic reflectivity may also depend on the temperature consequently ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients and may be transparent in crusts with high geothermal gradients

a role for scavenging in the marine biogeochemical cycling of zinc and zinc isotopes zinc zn and cadmium cd are important biologically active trace metals in the ocean to date the marine distributions of these elements have been understood primarily in terms of biological assimilation by growing phytoplankton and regeneration of sinking biological material initial studies of zn and cd concentrations and stable isotope ratios 66zn and 114cd have therefore focused on their use as simple tracers of assimilation and regeneration in the oceans however these two processes are insufficient to explain new data on the marine distribution of zn and 66zn here using the first high resolution paired marine depth profiles of zn cd 66zn and 114cd we suggest that scavenging of zn onto organic matter plays a major yet largely unconsidered role in the marine cycling of zn this hypothesis is supported by culture experiments which show that zn released from degrading phytoplankton is rapidly scavenged back onto organic matter and that adsorbed zn is isotopically heavier than the dissolved phase by 0 58 in contrast very little cd or phosphate was scavenged and cd isotopes were not significantly fractionated during degradation our hypothesis is further supported by one dimensional modeling which reproduces observed marine 66zn profiles with 1 of zn adsorbed to particles understanding how zn cycling in the oceans is a balance between assimilation scavenging and regeneration is necessary in order to investigate 66zn as a tracer of marine productivity we anticipate that paired analyses of 66zn and 114cd will prove to be valuable new tools in constraining patterns of global primary productivity providing key information for the marine carbon cycle during periods of past and present global climate change

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

mechanisms of shear localization in the continental lithosphere inference from the deformation microstructures of peridotites from the ivrea zone northwestern italy the ultramafic massif of balmuccia northwestern italy shows a variety of deformation fabrics including some localized shear zones that resulted in nearly complete melting pseudotachylyte a series of peridotite specimens were collected near one of the pseudotachylyte fault veins to investigate the mechanisms of shear localization the microstructural analyses show at least three deformation stages the first stage i is nearly homogeneous deformation at low stress 3 mpa and high temperature 1300 1500 k followed by localized deformation stage ii at a higher stress 60 mpa and moderate temperature 1000 1150 k and finally semi brittle deformation stage iii at a very high stress 400 mpa that resulted in the formation of pseudotachylyte the stage ii deformation resulted in relatively small strains in most areas but significant localized deformation leading to dynamic recrystallization occurred the degree of which increases systematically toward the fault zone based on this observation together with the observation that the brittle deformation post dated dynamic recrystallization we conclude that the shear localization in this locality occurred as a result of ductile deformation rather than brittle deformation various mechanisms of shear localization in the ductile regime are examined and we conclude that the grain size reduction due to dynamic recrystallization at relatively high stresses and moderate temperatures is a probable mechanism of shear localization the intermediate regime between dislocation and diffusion creep where rheology is grain size sensitive yet continuous recrystallization occurs due to dislocation creep is suggested to play an important role in shear localization in the upper mantle the conditions of shear localization due to this mechanism are examined based on the laboratory data on creep and dynamic recrystallization it is shown that shear localization occurs at relatively low temperatures and or high stresses localized deformation in the continental lithosphere will occur well below the brittle ductile transition 10 km depth down to 40 80 km depth depending upon the geothermal gradient and water fugacity

quasi adiabatic instabilities associated with necking processes of an elasto viscoplastic lithosphere abstract necking of the lithosphere involves complex nonlinear thermal mechanical feedback mechanisms in an elasto viscoplastic plate the mode of extension of such plates relies on the mechanical properties of the upper part of the mantle and on the nucleation of ductile faults within the lithosphere our numerical model addresses the key problem of controls of ductile failure of the strongest part in the lithosphere it is found that a small heterogeneity within this strong part can nucleate quasi adiabatic shear bands these develop spasmodically with time as finite amplitude instabilities with increasing temporal and length scales the largest shear zone takes about 100 000 years to propagate through the entire lithosphere and can lead to a thermal instability for an ambient mantle temperature larger than 900 k in our numerical model thermal runaway occurs when the plate is severed the temperature rise of the thermal instability is a function of the creep law exponent n and can be quenched for a lower n and smaller activation energy the model is applicable to the problem of onset of continental break up and holds the key to ductile instabilities in the earth s lithosphere the changing hot surface temperature on venus might also have precipitated lithospheric instabilities in the past

physical and biogeochemical controls on the distribution of dissolved cadmium and its isotopes in the southwest pacific ocean abstract cadmium stable isotope ratios 114cd have become a useful tool for oceanographers investigating the biogeochemical and physical processes that affect the nutrient like distribution of the bioactive trace metal cadmium cd throughout the oceans here we present a meridional transect of dissolved cd and 114cd from japanese geotraces section gp19 along 170 w from 64 s in the southern ocean to the equatorial pacific along the gp19 section the deep ocean 1500 m shows small variability in dissolved cd 0 75 0 9 nmol kg 1 and a homogeneous 114cd signature 0 26 0 06 2sd n 60 relative to nist srm 3108 adding these data to previously published work allows us to calculate a deep pacific and southern ocean 1500 m mean 114cd of 0 26 0 10 2sd n 436 higher in the water column depth profiles of cd along the gp19 section exhibit a strong vertical gradient from a maximum up to 0 9 nmol kg 1 at 1500 2000 m up to depleted surface waters overall the distribution of cd and 114cd along the gp19 section is remarkably well explained by large scale mixing of water mass endmembers with defined 114cd signatures emphasizing the importance of surface southern ocean processes for the distribution of trace metals such as cd in the subsurface southwest pacific at the regional scale however two other processes may overprint this mixing relationship first by comparison with the nearby southeast pacific gp16 section we find that the 114cd signature of equatorial intermediate water masses shows little zonal variation across the equatorial pacific despite becoming enriched in dissolved cd due to remineralization we propose that this uniformity is explained by complete utilization of cd in the surface tropical pacific and remineralization of cd with an isotopic signature similar to intermediate waters therefore conserving the southern sourced isotopic signature similarly the observed increase of about 30 in deep ocean cd concentrations from the south to the north pacific is associated with a near constant 114cd signal these observations enable us to constrain the net 114cd of cd added by remineralization to the deep ocean with the caveat that such a signal is integrated over the entire pacific and that remineralization under different oceanic regimes such as hnlc areas may add cd with different isotopic compositions to deep waters second at gp19 stations close to the equator subtle cd depletion relative to phosphate is observed associated with low oxygen subsurface waters consistent with other studies from the north pacific discerning the effects of such processes on cd isotopic distributions is an important step to a more detailed understanding of the biogeochemical cycling of cd in the modern ocean and the application of 114cd as a tracer of past deep water circulation this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

complex flow in lowest crustal anastomosing mylonites strain gradients in a kohistan gabbro northern pakistan 1 strain localization in near paleo moho metagabbros of the kohistan arc northern pakistan produced anastomosing shear zones the two dimensional 2 d analysis of strain gradients in planes parallel to the general flow direction reveals simple shear strain 7 combined with about 50 surface loss the pargasite garnet assemblage of the mylonite has a density 2 8 higher than the protolith which is insufficient to account for the measured surface loss furthermore major and trace element compositions of the gabbro and the mylonite indicate isochemical deformation average vp and acoustic impedance measured at room temperature and up to 300 mpa increase from gabbro through the gradient zone to mylonite they are consistent with density measurements the three dimensional analysis of shape preferred orientation and lattice preferred orientation of sheared and synkinematic minerals indicates that the 2 d surface loss reflects sideways and lengthwise material transfer sideways and lengthwise material transfers take place in widening and lengthening mylonites respectively the anastomosing shear zone pattern impels this complexity of the regional flow we conclude that shear zones with a thinning component are likely representative of deep crustal flow in other tectonic environments

the cycling of iron zinc and cadmium in the north east pacific ocean insights from stable isotopes abstract dissolved stable isotope ratios of the transition metals provide useful information both for understanding the cycling of these bioactive trace elements through the oceans and tracing their marine sources and sinks here we present seawater dissolved fe zn and cd concentration and stable isotope ratio 56fe 66zn and 114cd profiles from two stations in the pacific ocean the safe station 30 n 140 w in the subtropical north east pacific from the geotraces ic2 cruise and the marginal san pedro basin 33 8 n 118 4 w within the south california bight these data represent to our knowledge the first full water column profiles for 66zn and 56fe from the open ocean north pacific and the first observations of dissolved 66zn and 114cd in a low oxygen marginal basin at the safe station 56fe is isotopically lighter throughout the water column 0 6 to 0 1 relative to irrm 014 compared to the north atlantic suggesting significant differences in fe sources or fe cycling between these two ocean basins a broad minimum in 56fe associated with the north pacific oxygen minimum zone omz

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

contrasting metamorphic p t time paths of the kohistan granulites and tectonics of the western himalayas in the swat indus kohistan area lower crustal rocks of the kohistan arc including amphibolites granulites and ultramafic rocks are widely exposed detailed petrological structural studies reveal that the chilas jijal metamorphic complex comprises essentially intermediate to high pressure granulites with a granulite amphibolite transition controlled by extensive retrograde metamorphism and ductile deformation contrasting patterns of compositional zoning in garnet and orthopyroxene suggest complicated p t paths in the granulites geothermobarometry based on garnet bearing granulites identify two distinct p t time paths a high pressure anticlockwise path of the jijal complex and a low pressure retrograde path of the chilas complex these p t time paths represent the evolution of middle to lower crustal rocks of the kohistan arc the anticlockwise p t time path combined with published isotopic ages reveals that i the high pressure granulitefacies metamorphism is related to the kohistan asia collision and ii the crust of the kohistan arc had been thickened at least 55 km before the india asia collision

superposition of replacements in the mafic granulites of the jijal complex of the kohistan arc northern pakistan dehydration and rehydration within deep arc crust abstract a deep level crustal section of the cretaceous kohistan arc is exposed in the northern part of the jijal complex the occurrence of mafic to ultramafic granulite facies rocks exhibits the nature and metamorphic evolution of the lower crust mafic granulites are divided into two rock types two pyroxene granulite orthopyroxene clinopyroxene plagioclase quartz 1 and garnet clinopyroxene granulite garnet clinopyroxene plagioclase quartz 2 two pyroxene granulite occurs in the northeastern part of the jijal complex as a relict host rock of garnet clinopyroxene granulite where the orthopyroxene rich host is transected by elongated patches and bands of garnet clinopyroxene granulite garnet clinopyroxene granulite together with two pyroxene granulite has been partly replaced by amphibolite hornblende garnet plagioclase quartz 3 the garnet bearing assemblage 2 is expressed by a compression dehydration reaction hornblende orthopyroxene plagioclase garnet clinopyroxene quartz h 2 o subsequent amphibolitization to form the assemblage 3 is expressed by two hydration reactions garnet clinopyroxene plagioclase h 2 o hornblende quartz and plagioclase hornblende h 2 o zoisite chlorite quartz the mafic granulites include pod and lens shaped bodies of ultramafic granulites which consist of garnet hornblendite garnet hornblende clinopyroxene 4 associated with garnet clinopyroxenite garnetite and hornblendite field relation and comparisons in modal chemical compositions between the mafic and ultramafic granulites indicate that the ultramafic granulites were originally intrusive rocks which dissected the protoliths of the mafic granulites and then have been metamorphosed simultaneously with the formation of garnet clinopyroxene granulite the results combined with isotopic ages reported elsewhere give the following tectonic constraints 1 crustal thickening through the development of the kohistan arc and the subsequent kohistan asia collision caused the high pressure granulite facies metamorphism in the jijal complex 2 local amphibolitization of the mafic granulites occurred after the collision

sources and ore forming fluid pathways of carbonate hosted pb zn deposits in southwest china implications of pb zn s cd isotopic compositions the sichuan yunnan guizhou metallogenic province of southwest china contains more than 200 mt of pb zn ore in carbonate hosted pb zn deposits representing 27 of the total pb and zn resources of china sources of metals and pathways of ore forming fluids were elucidated through a study of the pb zn s cd isotopic compositions of sphalerite from the tianbaoshan fusheng maozu jinshachang and daliangzi carbonate hosted pb zn deposits 34s values indicate that s in the deposits is derived mainly from evaporites in cambrian to triassic sedimentary strata sulfates coexisting with sulfides and meso neoproterozoic folded basement 66zn values and pb isotopic ratios indicate that these metals originate mainly from sinian to lower permian sedimentary rocks and proterozoic basement there is a trend towards isotopically heavier cd and zn compositions of sphalerite from maozu to daliangzi jinshachang and tianbaoshan which are all hosted in the upper sinian dengying formation previous studies showed that there would be a trend of enrichment in heavier zn and cd isotopes following the migration of fluids and precipitation of minerals the above observations suggest that the ore forming fluids of these deposits are probably derived from the same hydrothermal fluid system the fluids most likely flowed through maozu first migrating along the xiaojiang and anninghe fault belts and their branch faults to daliangzi jinshachang and tianbaoshan respectively zn and cd isotopes could be useful tools in tracing the pathways of ore forming fluids in this district and heavier zn and cd isotopic compositions could provide a geochemical fingerprint for detecting remote orebodies in large hydrothermal fluid systems

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

synthetic seismic reflection profile through the ivrea zone serie dei laghi continental crustal section northwestern italy a geologic cross section restored to its original horizontal orientation in permian triassic time has been constructed for the middle and lower continental crustal rocks of the ivrea verbano zone and the adjacent serie dei laghi of northwestern italy seismic p wave velocities of a representative suite of rock samples were measured to high pressure and high temperature conditions a synthetic seismic reflection profile 76 km long and 30 km thick was computed to compare what can be deduced from the seismic profile with what is known in much more detail from geologic mapping imaged features correspond closely to those seen on many present day profiles and the broad features of the tectonic evolution would be correctly interpreted but important recumbent fold structures would be missed and relationships between intrusive bodies and their country rocks would be unclear

shear criteria in granite and migmatite deformed in the magmatic and solid states microstructural criteria for the determination of the sense of shear in rocks homogeneously deformed in the partially melted state are similar to those which apply to solid state deformation sense of shear determination is either direct deduced from the sense of rotation of markers or indirect involving the obliquity between the shear and foliation planes or between the successive foliations imprinted at different stages of progressive deformation this study is a by product of the detailed structural and microstructural investigation of a high grade metamorphic rock pile variscan vosges massif france which underwent subhorizontal shearing during partial melting and further solidification depending on the rock chemistry on the position in the pile and the relative timing of progressive deformation layered migmatites and homogeneous granites were variously deformed in the partially melted and solid states the sense of shear obtained from these rock types using the criteria presented here consistently gives a top to sw direction

controls on trace metal authigenic enrichment in reducing sediments insights from modern oxygen deficient settings any effort to reconstruct earth history using variations in authigenic enrichments of redox sensitive and biogeochemically important trace metals must rest on a fundamental understanding of their modern oceanic and sedimentary geochemistry further unravelling the multiple controls on sedimentary enrichments requires a multi element approach of the range of metals studied most is known about the behavior of fe mn and mo in this study we compare the authigenic enrichment patterns of these elements with a group whose behavior is not as well defined cd cu zn and ni in three oxygen poor settings the black sea the cariaco basin venezuela and the peru margin these three settings span a range of biogeochemical environments allowing us to isolate the different controls on sedimentary enrichment our approach relying on the covariation of elemental enrichment factors ef defined for element x as efx x al sample x al lithogenic has previously been applied to mo and u to elucidate paleoenvironmental information on for example benthic redox conditions the particulate shuttle and the evolution of water mass chemistry we find two key controls on trace metal enrichment first the concentration of an element in the lithogenic background sediment used in calculating efx controls the magnitude of potential enrichment maximum enrichment factors of 376 and 800 are calculated for mo 1 ppm in detrital sediments and cd 0 3 ppm respectively compared to values not greater than 17 in any setting for the other five metals 45 ppm to 4 5 wt in detrital sediments second there is a relationship between the aqueous concentration of the element in overlying seawater and its degree of enrichment in the sediment we further identify four important processes for delivery of trace metals to the sediment these are 1 cellular uptake especially important for zn and cd 2 interaction co precipitation with sulfide mo cu and cd 3 passive scavenging via the traditional particulate shuttle mo ni and cu and 4 an association with the benthic fe redox shuttle mn ni finally we summarize the oceanic mass balance of cd and mo and place the first constraints on the contribution of reducing sediments to the oceanic mass balance of cu zn and ni we show that reducing sediments are the ultimate repository for up to half the total output flux of these elements from the oceanic dissolved pool

superimposed variscan caledonian and proterozoic features inferred from deep seismic profiles recorded between southern ireland southwestern britain and western france abstract from southern ireland to the northern bay of biscay subduction was active from the proterozoic to the late palaeozoic they led to the cadomian caledonian and variscan collisions features characterizing these three orogenies have been crossed by the winch swat wam and bay of biscay deep seismic profiles recorded by the birps and ecors groups in the celtic sea the variscan front is characterized by a s dipping ramp rising directly from the middle crust with much less northward flattening than shown by the front in the northern france and west germany profiles south of the variscan front other s dipping reflections occur above a possible deep detachment the lizard ophiolitic suture marks s dipping events traversing the entire crust and the present moho in the english channel several sets of prominent n dipping reflections occurring in the celtic sea and south irish sea are interpreted as caledonian features running parallel to the caledonian iapetus suture and the pattern of folds and faults recognized in wales and southeastern ireland proterozoic s dipping subduction is recorded by geological data in northern wales and the english channel related crustal structures correspond to deep seismic events cutting across the lower crust and the moho and show the same apparent dip as the variscan features parallelism between dips and or strikes of structural features with different ages suggests a tectonic heritage the crust thus appears to be characterized by n and s dipping features which cut across large parts of it and may be assigned to variscan caledonian or candomian thrusts or shear zones the lower part of the crust shows a band of high amplitude subhorizontal reflections and a flat moho reflection which seem to have overprinted the above mentioned dipping features in a later period the lack of evidence of any shallow detachment in the caledonian and variscan belts together with the presence of dipping crustal thrust like features suggest that the region may have reached the very latest collisional stage the end of both of these orogenies

zinc and strontium isotope evidence for climate cooling and constraints on the frasnian famennian 372 ma mass extinction abstract the frasnian famennian f f mass extinction is one of the big five biotic crises during the phanerozoic whereas the cause of this catastrophic event still remains debated here we present for the first time high resolution zn and sr isotope data obtained by a sequential leaching procedure for carbonate rocks across the f f boundary from the fuhe section in south china both 66zn and 87sr 86sr values rapidly increase in the lower and upper kellwasser horizons and palmatolepis delicatula platys to p minuta minuta conodont zones and the positive isotope shifts are exactly located in the same horizons characterized by low 13c values equivalent to low atmospheric pco2 level reflecting climate cooling and sea level fall stages the strong temporal coupling of 66zn values raise with elevated 87sr 86sr ratios is most likely to have been caused by input of isotopically heavy zn and radiogenic sr from carbonate dominated weathering and or uptake of isotopically light zn into primary producers during climate cooling climate cooling could cause relative sea level falls resulting in widespread exposure of carbonate platform enhance carbonate influx proportion through differential weathering of carbonate and silicate rocks and cause greater productivity by promoting oceanic thermohaline circulation and enhancing upwelling of bio limiting nutrients all of these processes would have contributed to the positive shifts of 66zn as observed this proposed scenario is in accordance with the fact that the f f mass extinction was almost limited to the shallow water tropical stenothermal faunas whereas the high latitude and deep water faunas were less affected our data support and represent the composite effect of a series of events linked to climate cooling which may have induced this catastrophic event

isotopic constraints on the evolution of metamorphic conditions in the jijal patan complex and the kamila belt of the kohistan arc pakistan himalaya

tectonic stacking of back arc formations in the thelichi section indus valley of the kohistan arc northern pakistan abstract metamorphosed volcanic and sedimentary rocks of the jaglot group are exposed along the west bank of the indus river near thelichi the structural bottom unit the thelichi formation is composed of metavolcaniclastic metavolcanic metapelitic and metacalcareous rocks bedding planes of the thelichi formation trend e w or nw se and dip steeply to the n the middle unit gashu confluence volcanics is composed of metavolcaniclastic metavolcanic and metacalcareous rocks bedding planes trend nw se and dip moderately to the n the top unit the gilgit formation is composed of interlayered metapsammitic and metapelitic rocks graded bedding cross bedding and pillow structures are preserved in these metamorphic rocks of the jaglot group those indicate clastic sedimentary and volcanic origins there is no major repetition of layers due to folding so called the jaglot syncline as is evidenced by the consistent northward younging of the beds the three lithological units constitute a north dipping tectonic stack the tectonic stack was provably caused by the northward subduction of the back arc basin under the asian margin and subsequent collision between the asia and the kohistan the closure of back arc basin

copper zinc chromium and osmium isotopic compositions of the tepla barrandian unit black shales and implications for the composition and oxygenation of the neoproterozoic cambrian ocean abstract two neoproterozoic cambrian shale suites that consist of normal nbs and metal rich hmbs black shales from the tepla barrandian unit bohemian massif czech republic are studied in terms of their cu zn cr and re os isotopic compositions to improve our knowledge of elemental and isotopic mass balance of these elements in earth s oceans in the past and the extent of surface oxygenation at the neoproterozoic cambrian boundary the rock compositions indicate that the inputs of cu and zn have been controlled by variable proportions of metal rich authigenic and low metal terrigenous sources the latter having exceptionally low 65cu and partially 66zn in this respect our data confirm previous studies conclusions that organic rich sediments with high a terrigenous flux play an important role in the sinking of light zn in the oceans and provide new evidence that these types of rocks also represent the currently unidentified burial of very light cu in the ocean the chromium isotopic composition reveals a complex history of cr uptake and fractionation through the dominant cr input from different terrigenous sources with variable 53cr followed by cr fractionation that was controlled by redox states nbs on the other hand mixing and or continuous equilibrium isotopic exchange between seawater and hydrothermal cr was the dominant process for the hmbs the re os contents of the nbs were controlled by hydrogenous components which yield a poorly defined re os age for the least disturbed samples of 555 60 ma indicating an open system behavior while the hmbs re os composition was largely influenced by hydrothermal fluids during deposition the calculated authigenic 65cu which is similar to that in the present day ocean and highly positive 53cr values of the hmbs suggest high levels of surface oxygenation during the neoproterozoic cambrian transition furthermore the authigenic 66zn which is indistinguishable from that in the present day ocean may imply a constant zn isotopic composition of the oceans from the neoproterozoic because of the well balanced cycle of phosphates which were strongly adsorbed by fe hydroxides the radiogenic nature of the initial 187os 188os 0 6 although with a high associated error seems to not confirm previous indications of an abrupt increase of seawater 187os 188os during the late neoproterozoic due to the large scale radiogenic os flux into the ocean

crustal thickening of the lower crust of the kohistan arc n pakistan deduced from al zoning in clinopyroxene and plagioclase the lower crustal rocks of the kohistan complex northern pakistan are mostly composed of metabasic rocks such as pyroxene granulites garnet granulites and amphibolites we have investigated p t trajectories of the relic two pyroxene granulites which are the protolith of the amphibolites within the kamila amphibolite belt aluminous pyroxene retains igneous textures such as exsolution lamellae developed in the core the significant amount of al in clinopyroxene is buffered by breakdown reactions of plagioclase accompanied by film like quartz as a product at grain boundaries between plagioclase and clinopyroxene distinct al zoning profiles are preserved in pyroxene with exsolution lamellae in the core and in plagioclase adjacent to clinopyroxene in pyroxene granulites in the northern part of the kamila amphibolite belt al in clinopyroxene increases towards the rim and abruptly decreases at the outer rim and anorthite in plagioclase decreases towards the rim and abruptly increases near the grain boundary between plagioclase and clinopyroxene in the southern part of the kamila amphibolite belt al in clinopyroxene and anorthite in plagioclase simply increase towards the margins of the grains the anorthite zoning in plagioclase is in agreement with the zoning profiles of ca tschermaks and jadeite components inferred from variations of al na ti and fe3 in clinopyroxene assuming that the growth surface between them was in equilibrium geothermobarometry based on al zoning in clinopyroxene coexisting with plagioclase indicates that metamorphic pressures significantly increased with increasing temperature under granulite facies metamorphism the peak of granulite facies metamorphism occurred at conditions of about 800 c and 800 1100 mpa these prograde p t paths represent a crustal thickening process of the kohistan arc during the early to middle cretaceous the crustal thickening of the kohistan arc was caused by accretion of basaltic magma at mid crustal depths

key role of continental margin sediments in the oceanic mass balance of zn and zn isotopes zinc is an essential micronutrient and its concentration and isotopic composition in marine sediments represent promising tracers of the ocean carbon cycle however gaps remain in our understanding of the modern marine cycle of zn including an explanation of the heavy zn isotopic composition of seawater relative to the known inputs and the identity of a required missing sink for light zn isotopes here we present zn isotope data for organic rich and trace metal rich continental margin sediments from the east pacific margins that together provide the first observational evidence for the previously hypothesized burial of light zn in such settings in turn this light zn output flux provides a means to enrich the seawater dissolved pool in heavy isotopes the size and isotopic composition of the margin sink are controlled by the uptake of zn into organic matter in the photic zone and the fixation of this pool probably in the form of zn sulfides in sediments an estimate of its significance to the overall zn oceanic mass balance both in terms of flux and isotopic composition indicates that such settings can fulfill the requirements of the missing zn sink taken together these observations have important implications for the interpretation of zn isotope data for marine sediments in the geologic record

zinc and cadmium stable isotopes in the geological record a case study from the post snowball earth nuccaleena cap dolostone abstract zinc and cadmium are important biologically cycled nutrients in the modern ocean recent analytical advances and sampling efforts such as geotraces have led to measurements of the global distribution of zn and cd and their stable isotope ratios 66zn and 114cd providing an understanding of how biological processes cycle these elements and their isotopes in the modern ocean this opens the door to better application of 66zn and 114cd as tracers of biogeochemical processes archived in the geological record here we present new measurements of cd and 114cd on samples from the nuccaleena cap dolostone in south australia which was deposited during deglaciation of the ca 635 ma old marinoan snowball earth our new data are combined with previously measured 66zn data from the same samples the combined record of 114cd and 66zn is used to explore various hypotheses about the sources and sinks of cd and zn in the post marinoan ocean key features of this record are that zn and cd remain relatively similar throughout that 66zn and 114cd change at the same stratigraphic level and in the same direction and that 66zn changes are about four times larger than 114cd changes even though both quantities reflect a similar fractional mass difference we suggest that both zn and cd concentration and isotopic data are consistent with a change in the sink by which zn and cd are removed from the oceans we propose that no isotope fractionation is expressed during removal of zn and cd as sulfides while zn and cd removed with biological material are about 0 6 and 0 2 lighter than deep ocean 66zn and 114cd respectively many previous studies attribute the burial of isotopically light biological zn to preferential assimilation of isotopically lighter zn by phytoplankton in contrast we propose that lighter biological 66zn occurs mostly because isotopically heavy zn was scavenged by organic matter which causes dissolved 66zn in the surface ocean to be lighter than deep ocean 66zn the organic matter originated from primary producers that thrived in the surface ocean during deglaciation for cd whose isotope cycling in the modern ocean is dominated by preferential assimilation of isotopically lighter cd by phytoplankton much less biological fractionation is expressed the combined analyses of 66zn and 114cd provide insight into the biogeochemical processes which occurred after the marinoan snowball earth glaciation and may be a useful new tool to explore the history of life on earth in other geological records as well

significance of zr in rutile thermometry for deducing the decompression p t path of a garnet clinopyroxene granulite in the moldanubian zone of the bohemian massif

volcanology vulcan rule beneath the sea over 70 of the volcanism on earth occurs beneath an ocean veil now robotic and fibre optic based technologies are beginning to reveal this deep environment and identify subaqueous volcanoes as rich sources of sulfur carbon dioxide and life

the influence of weathering and soil organic matter on zn isotopes in soils zinc is an essential micronutrient that is ultimately released during mineral weathering in soils organic matter plays a key role in influencing zn partitioning and therefore on zn biogeochemical cycling soil organic matter is partitioned between carbon that is more readily available for decomposition by microorganisms and more stable carbon transiently preserved from decomposition the role of the stable pool of soil organic matter on zn biogeochemical cycling remains poorly understood the pool of stable carbon is controlled by combination with mineral constituents or is material that is intrinsically resistant to decomposition the zn stable isotopes are fractionated by interactions between zn and soil mineral and organic constituents this study reports the zn isotope composition of five icelandic soil profiles derived from the same parent basalt and characterized by contrasting degrees of weathering and organic matter content 66zn 0 10 0 05 to 0 35 0 02 the distribution of reactive mineral constituents available to form associations with soil organic matter and the amount of stable organic carbon throughout these soils the 66zn isotope variations are little influenced by mineral constituents but rather by soil organic matter content these data suggest that a combination of organic matter accumulation and zn loss by leaching is required to explain the observed decrease in zn concentration in soils and lighter soil 66zn with increasing organic carbon content these results suggest that the presence of stable organic carbon in soils provides a pool of light zn attributed to the zn isotope signature of organic matter partially preserved from decomposition crucially this stable organic carbon pool may also contribute to the formation of the light zn isotope sink reported in organic rich marine sediments a key output required to explain the oceanic mass balance of zn isotopes

zinc and cadmium isotope evidence for redox driven perturbations to global micronutrient cycles during oceanic anoxic event 2 late cretaceous abstract this study uses organic rich sediments from the tarfaya basin morocco to assess the cd and zn isotope response to dramatic global palaeoenvironmental change during the cenomanian turonian interval late cretaceous these organic rich continental margin deposits include an expression of oceanic anoxic event 2 oae 2 94 ma an interval associated with the spread of low oxygen marine environments and widespread burial of organic rich sediments due to placement of the tarfaya basin in a region of upwelling and relatively constant local environmental conditions the stratigraphic variations in 114 cd and 66 zn values largely reflect changes in the seawater isotopic composition of the sub surface proto north atlantic ocean positive shifts of 0 2 0 3 away from background values in 114 cd and 66 zn are observed during the main phase of the positive carbon isotope excursion associated with oae 2 these isotopic shifts are coeval with decreases in cd toc and zn toc ratios and thus imply that drawdown of isotopically light cd and zn from seawater inventories was a result of extensive burial of these metals in organic rich marine sediments globally low 66 zn values during the plenus cold event a cooler episode during oae 2 are similar in timing and magnitude to variations found in the english chalk eastbourne uk and support the inference of a global control on these isotopic excursions the 66 zn values during the plenus cold event are taken to record global oxygenation possibly including the remobilization of isotopically light zn from continental margin sediments a considerably smaller change in 114 cd values for this interval implies that the cd and zn isotope systems can provide information about slightly different environmental processes with global seawater composition with respect to zn also being influenced by the magnitude of oxic removal sinks and isotopically light zn input fluxes from sediments and hydrothermal fluids

the biogeochemical cycling of zinc and zinc isotopes in the north atlantic ocean zinc zn is a marine micronutrient with an overall oceanic distribution mirroring the major macronutrients especially silicate seawater zn isotope ratios 66zn are a relatively new oceanographic parameter which may offer insights into the biogeochemical cycling of zn to date the handful of published studies of seawater 66zn show the global deep ocean to be both remarkably homogeneous approximately 0 5 and isotopically heavier than the marine sources of zn 0 1 to 0 3 here we present the first high resolution oceanic section of 66zn from the u s geotraces ga03 north atlantic transect from lisbon to woods hole throughout the surface ocean biological uptake and release of isotopically light zn together with scavenging of heavier zn leads to large variability in 66zn in the ocean below 1000 m 66zn is generally homogeneous 0 50 0 14 2 sd though deviations from 0 5 allow us to identify specific sources of zn the mediterranean outflow is characterized by 66zn of 0 1 to 0 3 while margin sediments are a source of isotopically light zn 0 5 to 0 8 which we attribute to release of nonregenerated biogenic zn mid atlantic ridge hydrothermal vents are also a source of light zn close to 0 5 though zn is not transported far from the vents understanding the biogeochemical cycling of zn in the modern ocean begins to address the imbalance between the light 66zn signature of marine sources and the globally homogeneous deep oceans 66zn of 0 5 on long timescales with overall patterns pointing to sediments as an important sink for isotopically light zn throughout the oceans

ductile shear zones as counterflow boundaries in pseudoplastic fluids discussion and theory abstract a model presented by talbot 1999 attempts to use the shapes of s or j shaped structures in ductile shear zones experiencing simple shear to infer information about rock rheology specifically the value of the stress exponent n in a power law rheology the model is incorrect so cannot yield any insight into the deformation or rheology of shear zones the shape of s or j shaped structures is more likely a function of variation across the shear zone of water fugacity grain size or other weakening mechanisms

arc crustal differentiation mechanisms abstract the detailed vertical compositional and thermal structure of the entire kohistan arc section is constructed using 63 p t constraints and 209 plutonic whole rock analyses the aim is to better understand the nature of the chemical differentiation in the plutonic arc crust at different crustal levels results indicate that a distinct difference in character exists between the upper and lower plutonic arc crust plutonic rocks in the lower crust 25 30 km have whole rock chemical characteristics that indicate mineral accumulation and residual melt loss in these cumulate rocks there is a systematic chemical stratification of decreasing incompatible trace elements with depth e g rb k2o in contrast the plutonic rocks of the upper crust represent mainly frozen liquids and show no systematic relationship between chemical composition and intrusion depth these results clearly indicate that magmatic differentiation in the kohistan arc dominantly occurred in the deeper arc crust 30 km consistent with the lower crustal hot zone model to understand the role of density barriers for melt stagnation in the crust and thereby for the observed chemical stratification the detailed density structure of the plutonic arc crust is compared to melt densities calculated for plutonic rocks with near liquid compositions results indicate that melts are consistently less dense than rocks and there is no evidence for a neutral buoyancy line controlling melt emplacement it is speculated that melt stagnation in the lower arc crust and subsequent chemical differentiation of a felsic upper and mafic lower continental crust is dominantly controlled by temperature and to a lesser extent to density or rheological barriers

the oceanic mass balance of copper and zinc isotopes investigated by analysis of their inputs and outputs to ferromanganese oxide sediments abstract the oceanic biogeochemical cycles of the transition metals have been eliciting considerable attention for some time many of them have isotope systems that are fractionated by key biological and chemical processes so that significant information about such processes may be gleaned from them however for many of these nascent isotopic systems we currently know too little of their modern oceanic mass balance making the application of such systems to the past speculative at best here we investigate the biogeochemical cycling of copper cu and zinc zn isotopes in the ocean we present estimates for the isotopic composition of cu and zn inputs to the oceans based on new data presented here and published data the bulk isotopic composition of dissolved cu and zn in the oceans 65cu 0 9 66zn 0 5 is in both cases heavier than their respective inputs at around 65cu 0 6 and 66zn 0 3 respectively implying a marine process that fractionates them and a resulting isotopically light sedimentary output for the better known molybdenum isotope system this is achieved by sorption to fe mn oxides and this light isotopic composition is recorded in fe mn crusts hence we present isotopic data for cu and zn in three fe mn crusts from the major ocean basins which yield 65cu 0 44 0 23 mean and 2sd and 66zn 1 04 0 21 thus for cu isotopes output to particulate fe mn oxides can explain the heavy isotopic composition of the oceans while for zn it cannot the heavy zn in fe mn crusts and in all other authigenic marine sediments measured so far implies that a missing light sink is still to be located these observations are some of the first to place constraints on the modern oceanic mass balance of cu and zn isotopes

zn isotope evidence for immediate resumption of primary productivity after snowball earth the ediacaran period began with the deglaciation of the ca 635 ma marinoan snowball earth and the deposition of cap dolostones on continental shelves worldwide during post glacial sea level rise these carbonates sharply overlie glacial sediments deposited at low paleolatitudes and preserve negative carbon isotope excursions the snowball earth hypothesis invokes an almost complete cessation of primary productivity in the surface ocean because assimilatory uptake of zn appears to fractionate its isotopes zn isotope ratios measured in carbonate precipitated in the surface ocean should track fluctuations in primary productivity here we report the first zn isotopic data together with carbon and oxygen isotopic profiles from a neoproterozoic cap dolostone the nuccaleena formation in the flinders ranges south australia we interpret the zn isotopic data in terms of a two stage evolution of the deglacial ocean slightly 66 zn enriched values at the base of the cap dolostone indicate immediate resumption of the biological pump upon melting of the surface ocean but this signal was diluted by intense surface runoff that drove 66 zn 66 zn 64 zn versus the jmc lyon reference values down to the composition of continentally derived zn a subsequent rise in 66 zn records a vigorous increase in primary production and export from a nutrient laden surface ocean

zn isotope fractionation during uptake into marine phytoplankton implications for oceanic zinc isotopes abstract the extreme scarcity of zinc zn in the euphotic zone coupled to deep enrichments is consistent with biological uptake at the surface and regeneration at depth in the context of a nutrient type depth profile so clearly shaped by uptake into phytoplankton the growing dataset for zn isotopes presents a challenge these data either show very minor isotope effects associated with extreme depletion or enrichment of the light isotopes in the upper ocean in contrast culturing of eukaryotes in the laboratory suggests that light zn isotopes are preferentially taken up into diatoms and coccoliths implying that zn depletion at the surface should be associated with extremely heavy residual dissolved signals here we present the first zn isotope measurements for cultured marine cyanobacteria and compare these data to those for eukaryotic diatoms grown under identical conditions of the four cyanobacteria cultured belonging to the genera synechococcus and prochlorococcus three preferentially take up light zn into the cell with a variability that is not fundamentally different between pro and eukaryotic phytoplankton we also observe only very subtle differences between zn p and fe p uptake ratios for these three cyanobacteria groups relative to diatoms grown under the same conditions a fourth strain exhibits preferential uptake of heavy zn isotopes and very high zn p ratios overall we speculate that the observed variability among cyanobacteria may be related to the molecular structure of their photosynthetic light harvesting apparatus adapted to significantly different light niches these new and published culture data support the hypothesis that cellular 66zn in culture might largely be controlled by the organic ligands that bind zn in the medium given that the zn binding ligands in the ocean have thermodynamic stability constants that are orders of magnitude smaller than the edta used in culture media the surprisingly subtle zn isotope variability in some parts of the surface ocean may be reconciled with culture data by the lesser near zero preference of these weaker complexes for heavy zn isotopes this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

k ar and ar ar geochronology of the himalayan collision in nw pakistan constraints on the timing of suturing deformation metamorphism and uplift mica and hornblende k ar and ar ar data are presented from each of the three crustal components of the himalayan collision zone in north pakistan the asian plate the kohistan island arc and the indian plate together with u pb and rb sr data published elsewhere these new data 1 date the age of suturing along the northern suture which separates kohistan from asia at 102 85 ma 2 establish that the basic magmatism in kohistan which postdates collision along the northern suture predates 60 ma and that the later granite magmatism spanned a range of 60 25 ma 3 show that uplift amounts within kohistan are greater toward the nanga parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 ma to a current figure of about 5 5 mm a year 4 show that much of southern kohistan had cooled to below 500 c by 80 ma and that the major deformation which imbricated kohistan probably predated 80 ma and certainly predated 60 ma and was related to the kohistan asia collision rather than the kohistan india one 5 imply that uplift along the hunza shear in the asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 ma and was associated with breakback thrusting in the hanging wall of the main mantle thrust 6 suggest that the indian plate has a lengthy pre himalayan history with an early metamorphism at about 1900 ma major magmatism at 500 550 ma and early jurassic lithospheric extension or inversion and 7 show that the indian plate rocks were metamorphosed shortly after the collision within kohistan which occurred at circa 50 ma and subsequently cooled back through 500 c at circa 38 ma and 300 c at 30 35 ma with ages of cooling through 200 and 100 c as determined by fission track data locally controlled by nanga parbat related uplift tectonics

metagabbros of the gangdese arc root south tibet implications for the growth of continental crust abstract the gangdese batholith of the southern tibet is regarded as a principal component of the pre himalayan collision andean type continental margin however the gangdese arc root remains poorly understood because most of previous studies concentrated on granitoids from the middle and upper crust of the arc in this paper we report new petrochemical and geochronological characteristics of metagabbros occurred as a part of the late cretaceous lilong batholith in the eastern gangdese arc the gabbros with protolith ages of 82 95 ma underwent slightly late 68 77 ma granulite facies metamorphism and nearly coeval anatexis typical of lower arc crusts the metagabbros and diorites of the lilong batholith show geochemical features of juvenile crust in continental magmatic arcs and an original magmatic differentiation trend with gabbros formed as the cumulates whereas diorites as the crystalline products of evolved magmas the lilong batholith forms an arc crustal section with a possible thickness of 20 30 km and may have an overall andesitic composition providing a support for the andesite model of continental crust growth

shear strain localization from the upper mantle to the middle crust of the kohistan arc pakistan shear structures from mantle to middle crust levels of the kohistan palaeo island arc in pakistan are described pre himalayan ductile shear zones show a wide variety in size and shape and developed from gabbro subsolidus to amphibolite facies conditions their lithological context and geological history give insights into mechanisms that initiate shear strain localization factors that control stabilization of deformation in shear zones and flow properties at the mantle crust transition shear strain localization began within compositional gradients gabbros were more prone to localization into anastomosing patterns than diorites and granites which show more homogeneous strain shear strain localization during cooling led to less numerous but longer and thicker shear zones viscous heating within shear zones resulted in melt production and segregation in deformation structures and seems to have taken part in the plutonic history of the arc using kohistan as an example we suggest that the plutonic lower crust of arcs is strongly affected by subhorizontal synmagmatic shear zones probably consistent with the bulk flow direction of the subduction zone these features can obviously be preserved in collision orogens and may be mistaken for structures documenting the continental collision

copper isotope signatures in modern marine sediments abstract the development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling to date no cu isotope data has been published for modern sediments deposited under low oxygen conditions we present data encompassing a broad spectrum of hydrographic and redox regimes including continental margin and euxinic sulphide containing settings taken together with previously published data from oxic settings these data indicate that the modern oceanic sink for cu has a surprisingly homogeneous isotopic composition of about 0 3 65cu relative to nist srm976 we suggest that this signature reflects one of two specific water column processes 1 an equilibrium isotope fractionation between soluble isotopically heavy cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver cu to the sediment or 2 an equilibrium isotope fractionation between the same isotopically heavy ligand bound pool and the particle reactive free cu2 species with the latter being scavenged by particulates and thereby delivered to the sediment an output flux of about 0 3 into sediments is isotopically light relative to the known inputs to the ocean at around 0 6 and the seawater value of 0 6 to 0 9 suggesting the presence of an as yet unidentified isotopically light source of cu to the oceans we hypothesize that this source may be hydrothermal or may result from the partial dissolution of continentally derived particles

zinc isotopic composition of the lower continental crust estimated from lower crustal xenoliths and granulite terrains abstract this study presents high precision zn stable isotope analyses for lower crustal rocks 9 granulites from archean terrains and 30 lower crustal xenoliths from the north margin of the north china craton ncc to understand the behavior of zn isotopes during deep crustal processes and the zn isotopic composition of the lower continental crust lcc the lower crustal xenoliths range in composition from mafic to felsic with mgo contents of between 0 4 to 20 2 wt the 66zn the permil deviation of the 66zn 64zn ratio from the jmc lyon standard values of lower crustal xenoliths range from 0 17 to 0 38 the lack of clear correlation of 66zn with geochemical indicators e g al2o3 cr ba la 87sr 86sr and 143nd 144nd indicates that assimilation of precambrian lower crust fluid metasomatism and accumulation of pyroxene and plagioclase had a limited effect on zn isotopic compositions of these lower crustal xenoliths the 66zn values 0 18 to 0 34 of garnet bearing mafic granulites decrease with increasing feo t and v contents which are likely results of the accumulation of fe ti oxides the average 66zn of the lower continental crust is estimated to be 0 29 0 02 95 se using lower crustal xenoliths from the neogene hannuoba basalts this 66zn value is similar to the estimated value 0 28 0 04 95 se obtained from the granulites from archean terrains suggesting that there is no significant difference in the zn isotopic composition between the archean and present day lower continental crust combining the 66zn data of the lower crustal xenoliths and granulite terrains and different weighting methods the zn isotopic composition of the lower continental crust is estimated to be 0 28 0 04 95 se

evaporative loss of moderately volatile metals from the superheated 1849 ma sudbury impact melt sheet inferred from stable zn isotopes the retention of moderately volatile elements on the growing earth remains a major uncertainty in models of terrestrial accretion large impactors were the main carriers of accreted material but their mutual energetic collisions and impacts onto the earth also caused chemical fractionation for which limited experimental data exist the objective of this work was to study several moderately volatile elements in the third largest impact basin preserved on earth at sudbury ontario we conducted a new chemostratigraphic transect n 41 of zn isotope ratios and concentrations by analysing melt sheet and basin fill samples the data were compared to common pb cs cd and sb concentration systematics within the crystallised melt sheet there are strong trends in the extent of moderately volatile element deficits zn isotope composition 66 64znjmc l from 0 18 to 0 47 and initial pb isotope composition the combined evidence suggests that these trends reflect footwall contamination of a melt sheet that had experienced evaporative zn loss of up to 75 80 accounting for plausible isotopic signatures of target rocks the maximum mass dependent zn isotope fractionation e was 0 29 0 04 1 s d which translates to modest fractionation factors 0 99986 to 0 99975 this is comparable to melt fallout glass and fused sands from nuclear detonation sites we attribute the observed zn loss and isotope fractionation to the formation of the impact melt the rapid formation of a solid lid of breccias upon seawater ingress may have prevented stronger evaporative loss and isotope fractionation within the crater fill there is an up stratigraphy increase in zn isotope variability 66 64znjmc l from 0 29 to 1 05 combined with evidence for biogenic reduced c this suggests sedimentation of authigenic particulates within an enclosed crater sea in the melt sheet the zn pb and rb cs pairs experienced different extents of maximum evaporative loss pb up to 98 4 vs zn 78 and cs 90 vs rb 30 the relative loss pattern could reflect evaporation from superheated silicate melt at 1 450 c and 1 atm loss from super liquidus melts formed by bolide impacts could have been a significant process shaping the earth s volatile and moderately volatile inventory

zinc and nickel isotopes in seawater from the indian sector of the southern ocean the impact of natural iron fertilization versus southern ocean hydrography and biogeochemistry abstract the southern ocean is the site of 20 of global ocean carbon export and the origin of water masses that significantly impact the chemistry of the global ocean much of the southern ocean is a high nutrient low chlorophyll hnlc region iron is the primary limiting nutrient for phytoplankton growth and may also be an important control on the biogeochemistry of the water masses emanating from the southern ocean here we investigate the response of zn and ni and their isotopes to natural fe fertilization from southern ocean islands using samples collected during the keops 2 oct nov 2011 program in the early austral spring near the kerguelen plateau indian sector of the southern ocean zinc and ni concentrations show depth distributions and relationships to major nutrients that are very similar to published data from the atlantic sector of the southern ocean away from island fertilization as in the atlantic sector and other regions outside the southern ocean there is a slight minimum in 66zn at about 100 150 m depth and a slightly heavier value at the surface at the keops 2 sites the light sub surface zn isotopes occur at the depth level where measured chl a has declined to near zero the heaviest zn isotope values in either the atlantic or indian sectors occur in bottom waters are associated with samples that show high dissolved si relative to zn these latter represent possible evidence for a heavy input directly to deep water or from sediment and the zn si 66zn systematics are consistent with a source in diatom opal nickel concentrations show much less variation than those of zn with the most depleted surface value only 15 20 lower than those in upwelled deep water in the southern ocean these small variations in ni concentration are associated with no significant variability in ni isotopes as also previously observed in the atlantic sector overall the key feature of the dataset is the apparent absence of any significant impact of natural fe fertilization on the distribution of zn and ni with the dominant control being the station location relative to the polar front in both the atlantic and indian sectors zinc and ni isotopes are invariant in surface waters whether inside or outside the fertilized zone and whether south or north of the polar front this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

effect of cadmium sulphide precipitation on the partitioning of cd isotopes implications for the oceanic cd cycle abstract the biogeochemical cycling of cadmium cd and its isotopes in the surface ocean is dominated by biological uptake into phytoplankton while regeneration of the sinking particulate cd governs the shapes of cd profiles in the deeper ocean additionally the water mass circulation plays an important role in the redistribution of cd and its isotopes superimposed on this general cycle it has recently been argued that cadmium sulphide cds precipitation can occur in oceanic oxygen deficient zones odz this has been proposed to account for the decrease in cd po4 ratios and the positive cd isotope excursion in seawater compared to sinking particles to assess whether cds precipitation results in a fractionation of cd isotopes we performed cadmium sulphide precipitation experiments under controlled low oxygen conditions in low pure water and high ionic strength synthetic seawater water with variable reaction times and cadmium sulphide ratios enrichment in light cd isotopes is systematically observed in the precipitated cds phase in agreement with recent ab initio simulations of isotope effects associated with cd speciation in aqueous solution our experimental results follow a closed system rayleigh fractionation model with the fractionation factor cdsol cds for 112cd 110cd decreasing with increasing salinity from 1 00026 for pure water to 1 00014 for a salinity twice that of modern seawater indicating a salinity control on the magnitude of cd isotope fractionation we propose that this fractionation varying with salinity is controlled by isotope equilibrium between the various cd aqueous species present in solution with preferential involvement of free cd2 ion in cds formation the magnitude of cd isotope fractionation in seawater cdsol cds 1 00016 determined in our study is in accord with the cd isotope shift observed in modern oceanic odz and attributed to removal by cds our experiments show that cds precipitation could have significant local impact on the cycling of cd and further demonstrates the utility of cd isotopes as tracers of the sequestration of cadmium into sulphides in restricted euxinic basins such as the black sea

pre collisional anastomosing shear zones in the kohistan arc nw pakistan ductile strain localisation commonly forms a pattern of shear zones anastomosing around lenses of less deformed rock initiation and development history of anastomosing shear zones which are little documented are studied through the description of the structures and the deformation history of plutonic rocks that form the lower crust of the kohistan complex structures and textures developed in these rocks result from primary magmatic to solid state regional strain overprinted by anastomosing shear zones the primary strain was mainly acquired during magmatic emplacement at 100 90 ma strain localisation took place continuously from magmatic emplacement to solid state deformation during cooling of the plutons and formed 3 successive sets of shear zones set 1 is composed of associated discrete riedel and thrust shear zones developed above solidus conditions during sw ward thrusting continuous deformation from solidus to amphibolite facies conditions between 100 and 83 ma formed the second set of shear zones the lower amphibolite facies set 3 shear zones are differentiated by larger strain recorded in the thicker mylonitic zones and enlargement of the spacing between shear zones during cooling the anastomosing pattern of shear zones described here probably represents arc related deformation during subduction of the tethys oceanic lithosphere below the kohistan arc complex

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

biogeochemical cycling of zinc and its isotopes in the southern ocean abstract we report zn concentration and isotope data for seawater samples from the atlantic sector of the southern ocean collected during the ipy geotraces ant xxiv iii cruise along the greenwich zero meridian data are reported for the full depth range of the water column at three stations as well as a transect of surface samples using a new analytical approach that is presented in detail here zn concentrations increase with depth though due to proximity to upwelling sites surface concentrations are not as low as in some parts of the ocean such as further northward into the sub antarctic zone for two depth profiles south of the polar front zone the physical stratification of the upper water column is reflected in sudden near surface changes in zn concentration with depth in contrast beneath 100 300 m zn concentrations barely change with depth zn isotopic data beneath 1000 m for the southern ocean data presented here as well as published data from the north atlantic and north pacific are strikingly homogeneous with an average 66zn 0 53 0 14 2sd 2se 0 03 n 21 the surface southern ocean is more variable with 66zn ranging from 0 07 to 0 80 between the two is a thin horizon at 40 80 m which in the southern ocean as well as the north atlantic and north pacific is characterised by distinctly light isotopic signatures with 66zn about 0 3 lower than surface waters strong correlations between si and zn concentrations seen here and elsewhere coupled to the lack of any systematic relationship between si and zn isotopes in the southern ocean suggest that the removal of zn associated with diatom opal involves little or no isotopic fractionation regeneration of this zn also explains the homogeneous zn isotopic composition of the global deep ocean so far sampled however the low zn content of opal requires that deep ocean zn does not directly come from the opal phase itself but rather from associated organic material external to the diatom frustule during growth experimental data are consistent with little or no fractionation during incorporation of zn into this material on the other hand the light zinc at 40 80 m is most consistent with the regeneration of an intra cellular pool that both culturing experiments and field data suggest will be isotopically light the data thus imply two processes by which zn is taken up in the surface ocean that these pools have very different regeneration lengthscales and that physical mixing of the oceans cannot eradicate their isotopic signatures finally the deep 66zn ocean value is significantly higher than the current best estimate of the input to the oceans the most obvious candidate for the required light sink is the survival of some of the cellular zn to be buried in sediment

establishing a new era of submarine volcanic observatories cabling axial seamount and the endeavour segment of the juan de fuca ridge abstract at least 70 of the volcanism on earth occurs along the 65 000 km network of mid ocean ridge mor spreading centers within these dynamic environments the highest fluxes of heat chemicals and biological material from the lithosphere to the hydrosphere occur during volcanic eruptions however because underwater volcanoes are difficult and expensive to access researchers are rarely if ever in the right place at the right time to characterize these events therefore our knowledge is limited about the linkages among hydrothermal chemical and biological processes during seafloor formation and crustal evolution to make significant advancements in understanding the evolution of mor environments the united states and canada have invested in the first plate scale submarine cabled observatory linked through the global internet spanning the juan de fuca tectonic plate these two networks include 1700 km of cable and 14 subsea terminals that provide 8 10 kw power and 10 gbs communications to hundreds of instruments on the seafloor and throughout the overlying water column resulting in a 24 7 365 presence in the oceans data and imagery are available in real to near real time the initial experimental sites for monitoring volcanic processes include the mor volcanoes called axial seamount and the endeavour segment that are located on the juan de fuca ridge axial a hot spot influenced seamount is the most robust volcano along the ridge rising nearly 1400 m above the surrounding seafloor and it has erupted twice in the last 15 years in contrast the endeavour segment is characterized by more subdued topography with a well defined axial rift and it hosts one of the most intensely venting hydrothermal systems known a non eruptive spreading event lasting 6 years was documented at endeavour between 1999 and 2005 hydrothermal venting intensity chemistry and temperature as well as associated biological communities at both sites were significantly perturbed by the magmatic and intrusive events this paper presents the similarities and differences between the axial and endeavour volcanic systems and identifies reasons why they are ideal candidates for comparative studies the u s has made a 25 year commitment for sustained observations using the cabled infrastructure the highly expandable nature of submarine optical networking will allow for the future addition of novel experiments that utilize ever evolving advancements in computer sciences robotics genomics and sensor miniaturization comprehensive modeling of the myriad processes involved will continue to assimilate and integrate growing databases yielding a new understanding of integrated processes that create the seafloor in the global ocean basins

multiple mantle sources during island arc magmatism u pb and hf isotopic evidence from the kohistan arc complex pakistan this paper presents high precision u pb ages and initial hf isotopic compositions of zircon from mafic to felsic rocks of the kohistan arc complex pakistan three magmatic pulses tapping geochemically different reservoirs are distinguished partial melting of mantle with morb type isotopic characteristics generated 99 92 ma old magmas plutonism around 85 ma tapped a more fertile mantle source most likely consisting of a 600 ma old metasomatically enriched mantle or of mantle contaminated by an old sedimentary component 82 ma old felsic peraluminous dykes have morb type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc the isotopic results demonstrate several and rather rapid changes in melt source region during arc development they also show that there was subordinate continental influence and negligible importance of slab components for the hf budget during the generation of the kohistan arc complex

high pressure high temperature seismic velocity structure of the midcrustal and lower crustal rocks of the ivrea verbano zone and serie dei laghi nw italy the ivrea verbano zone and the adjacent serie dei laghi in the inner arc of the western alps nw italy display an upended cross section through much of the thickness of the continental crust as it existed in that region in triassic jurassic time we collected a suite of oriented rock samples that represent most of the volume of the rocks of the region p and s wave velocity measurements were made in three orthogonal directions related to the mesoscopic fabric of the rocks at room temperature and up to 550 mpa confining pressure combined high temperature and high pressure measurements were made up to 700 c on a subset of the samples the lithologic units were divided into 23 different principal rock types and we present velocity data averaged in terms of these groups vertical and horizontal velocity and anisotropy sections are computed from the measured velocity data based on a restored geologic section these show that vp and vs both increase and anisotropy decreases systematically with depth of burial reflecting variations in rock type and metamorphic grade with depth vp and vs anisotropy arises mainly because of crystallographic preferred orientation or mineralogical banding with the slowest direction tending to be normal to the foliation or banding the vp velocity sections were used to compute synthetic seismic reflection profiles for the region when it lay at the bottom of the continental crust these correspond well with contemporary deep reflection profiles for regions of comparable tectonic evolution

detection of the 2012 havre submarine eruption plume using argo floats and its implications for ocean dynamics abstract more than 85 of the earth s volcanism and geothermal heat release occurs underwater at mid ocean ridges intra plate hotspots and oceanic island arcs however we lack a clear understanding of how a submarine eruption interacts with the overlying water column the structure of the submarine eruptive plume and the transport of volcanic products in the ocean by these plumes we describe here the detection of eruption derived temperature increase and salinity decrease from the 2012 havre submarine caldera eruption by an existing array of temperature salinity profiling floats known as argo the argo floats observed the signal significant at 3 sigma level with respect to the background ocean variability noise at ocean depths of 1750 2000 m deeper than the eruptive vent itself in order to understand this signal we develop a new conceptual submarine plume model which suggests that the sub vent level temperature and salinity anomalies are caused by large scale ocean mixing induced by the eruptive plume rather than heating directly from the eruption using results from scaling analysis and a modified numerical plume gravity current model we show that submarine eruptions can efficiently advect water masses from the deep ocean closer to the surface and form multiple subsurface intrusions during the process consequently the submarine eruptive plumes can initiate significant ocean mixing a process with significant implications for both long and short term influence of submarine volcanism on ocean chemistry dynamics and ecology finally our model confirms that a detectable anomaly would persist out to 100s of km from the eruption location comparable to argo s spatial sampling given the global ocean coverage and a decadal baseline the argo floats and other similar datasets in concert with hydrophone and seismic arrays can provide significant new constraints on subaqueous volcanism eruption dynamics and the impact on earth systems through enhanced ocean mixing and nutrient supply e g during submarine large igneous provinces

zinc and lead isotope signatures of the zhaxikang pbzn deposit south tibet implications for the source of the ore forming metals abstract stable zn isotopes may be applied to trace the source of ore forming metals in various types of pb zn deposits to test this application zn and pb isotope systematics for sulfides and associated basement rocks as well as fe mn carbonates gangue from the zhaxikang pb zn deposit in south tibet have been analyzed the basement in this region includes metamorphosed mafic to felsic rocks dolerite quartz diorite rhyolite porphyry pyroclastics and porphyritic monzogranite these rocks have similar 66 zn values of 0 33 to 0 37 with an average value of 0 36 0 03 2 except for the more evolved porphyritic monzogranite that has a heavier value of 0 49 fe mn carbonates are present as hydrothermal veins and were probably precipitated from magmatic fluids they have an average 66 zn value of 0 27 0 05 which is slightly lighter than the basement rocks possibly representing 66 zn isotopic compositions of the hydrothermal fluids sphalerite and galena have similar zn isotopic compositions with 66 zn ranging from 0 03 to 0 26 and 0 21 to 0 28 respectively considering the zn isotope fractionation factor between sphalerite and fluids of 0 2 at 300 c as reported in literature hydrothermal fluids from which these sulfides precipitated will have 66 zn values of ca 0 39 0 10 which are consistent with the values of basement rocks and the fe mn carbonates this similarity supports a magmatic hydrothermal origin of the zhaxikang pb zn deposit both pb and s isotopes in these sphalerite and galena show large variations and are consistent with being derived from a mixture of basement and sedimentary rocks in various proportions zn isotopic compositions of the sulfides significantly extend the range of regional basement rocks suggesting that sedimentary rocks e g shales are also a significant source of zn however the zn isotopic compositions of sphalerite and galena differ from those of marine carbonates and those of typical sedex type deposits e g kelley et al 2009 confirming a magmatic hydrothermal model combined with regional geological observations and the age constraints of 20 ma zheng et al 2012 2014 the results of our investigation indicate that the zhaxikang pb zn deposit is most likely a magmatic hydrothermal deposit

dynamics of a powerful deep submarine eruption recorded in h2o contents and speciation in rhyolitic glass the 2012 havre eruption constraining the syn eruptive volatile contents of magmatic melt is critical to understanding the intensities and styles of deep submarine volcanic eruptions for which direct observations are scarce quantifying residual magmatic water contents in volcanic glass is complicated by rehydration i e late stage addition of molecular water the 2012 deep submarine silicic eruption of havre volcano provides an unusual opportunity to quantify glass water contents from a recent well sampled stratigraphic sequence fourier transform infrared and microraman spectroscopy measurements of water concentration and water speciation across the havre 2012 eruptive sequence reveal an unanticipated range of excess molecular water within pumice this excess water requires rapid timescales of diffusion that are inconsistent with our current understanding of low temperature secondary rehydration in both subaerial and subaqueous eruptive products diffusion models applied to enrichment profiles at vesicle edges confirm that low temperature rehydration is an unlikely cause we instead support higher temperature syn eruptive pumice rehydration by condensed magmatic water and seawater in a submarine plume hydroxyl concentrations suggest shallow quenching depths of havre pumice hundreds of meters above the 900 meter deep main vent our data also support the presence of a vapor rich plume and consequent modification of ocean pressure above the vent we combine this novel volatile data with textural information and cooling rate calculations to explore the conditions that would cause slower shallow cooling of clasts from a deep submarine eruption by exploring the physical conditions for the interaction between pumice and submarine plumes we emphasize fundamental differences between subaerial and submarine clast producing eruptions

quantitative estimation of exponents of power law flow with confidence intervals in ductile shear zones abstract talbot journal of structural geology 21 1535 1551 1999b introduced a new model for ductile shear zones as counterflow boundaries in pseudoplastic power law fluids and demonstrated that natural shear zones empirically fit theoretical curves generated by his model thus estimates of the power law exponent relating stress and strain are deduced it is shown here how application of standard non linear statistical techniques to shear zone displacement data allows quantitative estimation of the power law exponent together with confidence intervals of the calculated value application to natural shear zones verifies the method and also validates the applicability of the model it is hoped that this will encourage field geologists to apply the model of talbot to natural examples thereby a database of power law exponents for a wide variety of lithologies and metamorphic grades may be assembled

metamorphism of an obducted island arc example of the kohistan sequence pakistan in the himalayan collided range in northern pakistan the extraordinary 40 km thick kohistan sequence of metamorphosed mafic ultramafic and calc alkaline layered plutonic and volcanic mainly andesitic to rhyodacitic rocks has been recently reinterpreted as the only complete vertical section of an intra oceanic island arc presently exposed anywhere in the world plate scale models have been suggested to explain the origin and the tectonic evolution of this arc in the himalayan collision range despite some noticeable differences in the models there is general agreement that the kohistan sequence represents the crust of an arc obducted onto the northern edge of the indian plate before the oligocene collision of india against asia new data on the tectonometamorphic evolution of the kohistan sequence have led to the conclusion that a first major d 1 event developed with increasing metamorphic grades oriented downward the kohistan pile but also toward ensandwiched basic ultrabasic granulitic rocks rare geochronological data and petrological evidence indicate that the latter granulites pyriclasites and various plagiopyrigarnites pyrigarnites metatroctolites metawebsterites metadunites etc were parts of enormous lower to middle cretaceous layered calc alkaline plutons emplaced during the arc building stages as the d 1 metamorphic event is correlated with the upper cretaceous obduction process of the kohistan onto india it is proposed that the d 1 thermal structure was strongly controlled by remnant magmatic heat source s within the obducted arc this interpretation fits nicely with recent theoretical thermal models since the obduction of the arc was probably shortly after 10 20 ma the emplacement of the former plutonic arc rocks a blueschist tectonic melange underlying the obducted arc was possibly synchronous to the obduction and not clearly linked to the older subductive process the oligocene collision of india against asia was associated with a barrovian overprinting metamorphism in the kohistan arc during this second event the dynamo thermal structure was much more classical and not controlled by the occurrence of the cretaceous metaplutonic rocks a tentative model of the thermal structures during the major events which affected the kohistan arc is proposed

effect of mechanical interactions on the development of shape preferred orientations a two dimensional experimental approach abstract modifications in the development of preferred orientations of rigid particles due to mechanical interactions between particles are studied experimentally in two dimensions experiments in both pure shear and simple shear were performed and the results analysed using an easy and fast new automatic method for increased concentration of rigid particles the rotation of individual particles may be slowed down or even stopped due to collisions or disturbance of the flow in the matrix caused by neighbours in coaxial flow the fabric intensity is consequently reduced in simple shear flow the fabric evolution is no longer cyclic the intensity is on average weaker and the fabric axis rotates asymptotically toward the shear plane in the case of preferred orientations of particles having a low aspect ratio 2 5 the fabric rotates through the shear plane then undergoes a reverse rotation and rotates toward the shear plane again in the light of these experimental results we emphasize that quantification of finite strain based on such fabrics may lead to significant underestimates and calculated values should be taken as minimum estimates the kinematic significance of concentrated rigid particle preferred orientations in rocks is modified by interactions between particles techniques for qualitative or quantitative kinematic analysis may become unreliable for simple shear flows the concentrated population fabrics show an angular behaviour close to that of passive markers they tend to align parallel to the shear plane in simple shear flow