retrograde phases of former bridgmanite inclusions in superdeep diamonds abstract mg fe sio3 bridgmanite is the dominant phase in the lower mantle however no naturally occurring samples had ever been found in terrestrial samples as it undergoes retrograde transformation to a pyroxene type structure to identify retrograde phases of former bridgmanite single phase and composite inclusions of mg fe sio3 in a series of superdeep diamonds have been examined with electron microscopy electron microprobe raman spectroscopy and x ray diffraction techniques our study revealed that mg fe sio3 inclusions are represented by orthopyroxene orthopyroxenes in single phase and composite inclusions inherit initial chemical composition of bridgmanites including a high al and low ni contents in composite inclusions they coexist with jeffbenite ex tapp and olivine the bulk compositions of these composite inclusions are rich in al ti and fe which are similar but not fully resembling al rich bridgmanite produced in experiments on the morb composition the retrograde origin of composite inclusions due to decomposition of al rich bridgmanite may be doubtful because each of observed minerals may represent coexisting hp phases i e bridgmanite or ringwoodite

inclusions of nanocrystalline hydrous aluminium silicate phase egg in superdeep diamonds from juina mato grosso state brazil abstract inclusions in alluvial diamond from juina mato grosso brazil have been investigated by tem methods electron diffraction hrtem aem haadf eels and raman spectroscopy the inclusion paragenesis of juina diamonds is dominated by ultrahigh pressure superdeep phases one of these diamonds sample 1 1 4 contains several micrometer sized approximately 200 m by 50 70 m inclusions which have been studied tem foils prepared applying focused ion beam fib technique revealed that these inclusions consist of a porous nanocrystalline groundmass which is composed of nanometre sized crystals of a hydrous aluminium silicate phase with al si approximately 1 1 and chemical composition of phase egg alsio 3 oh a minor volume fraction of nanocrystalline stishovite and pore space which was originally filled with a fluid or gas the nanocrystalline hydrous aluminium silicate phase is idiomorphic randomly oriented approximately 20 30 nm in size predominantly with tetragonal crystal structure a 0 0 743 nm c 0 0 706 nm the monoclinic structure of synthetic phase egg determined at ambient conditions m w schmidt l w finger r j ross r e dinnebier synthesis crystal structure and phase relations of alsio 3 oh a high pressure hydrous phase american mineralogist 83 1998 881 888 is only occasionally observed the fluid filling in the porosity has been released into the vacuum of the fib during tem specimen preparation quench products of the fluid containing minor concentrations of f p s cl k ca and ba were detected at the walls of the pores in addition phase egg is identified by raman spectroscopy within a second sample rs 43a from the same location the presence of phase egg in the inclusions in diamond may suggest that crustal material has been subducted to a depth of the lower transition zone although metastable growth of nanocrystalline high pressure phases or extension of their respective stability fields to lower pressure can not ruled out completely

geochemical and sr nd isotopic characteristics of cretaceous to paleocene granitoids and volcanic rocks se tibet petrogenesis and tectonic implications abstract northward subduction of the neo tethyan oceanic lithosphere beneath south asia gave rise to an andean type convergent margin with arc magmatism starting since at least the early jurassic and lasting until the eocene this study reports geochemical and sr nd isotope data of the early cretaceous 133 110 ma to paleocene 60 ma magmatic belt that formed in the eastern lhasa terrane se tibet including three major transhimalayan batholiths namely azhagong demulha and chayu and an early cretaceous volcanic succession from ranwu area all these rocks show relative enrichments in lile and lree and depletions in hfse corresponding to the geochemical characteristics of arc magmas from modern subduction zones while the azhagong batholith consists typically of metaluminous i type granitoids that occasionally contain mafic enclaves highly fractionated peraluminous s type and a type granites are observed from the chayu and demulha batholiths respectively these granitoids as a whole show heterogeneous sr and nd isotope ratios with e nd t varying from 1 5 to 13 and i sr from 0 703 to 0 745 the ranwu volcanic rocks which range from basaltic to dacitic compositions are calc alkaline in nature they have e nd t from 3 to 6 and i sr from 0 705 to 0 707 overlapping the isotopic range of the azhagong mafic enclaves the overall geochemical and sr nd isotope data suggest three magma source components involved in the petrogenesis which are the mantle wedge and the lower and upper parts of the lhasa continental crust accordingly we propose a two stage petrogenetic model involving 1 deep level differentiation of the mantle wedge derived mafic magmas associated with assimilation by the lower continental crust of the lhasa terrane and 2 additional differentiation and upper crustal contamination of the evolved magmas as they rise and install in shallow level magma chambers while the first stage can explain how the ranwu volcanics and azhagong enclaves formed the second accounts for the emplacement of the azhagong and chayu batholiths the shallow intrusions moreover may have caused low pressure melting of existing calc alkaline rocks of paleoproterozoic nd isotope model age to produce the early cretaceous 125 ma a type granites in the demulha batholith a specific rock type that occurs rarely in subduction zones but echoes with the notion for an extension setting in the region this setting may have taken place after the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes and interacted with the back arc evolution in the neo tethyan subduction system

linking soil element mass transfer to microscale mineral weathering across a semiarid environmental gradient abstract understanding controls on silicate weathering is critical to characterizing critical zone evolution the objective of this study was to investigate how climate vegetation and landscape position control feldspar transformations across a semiarid environmental gradient granitic surface soil and saprock samples were collected from desert scrub and mixed conifer sites within the santa catalina mountain critical zone observatory where mean annual temperature ranges from 24 c to 10 c and mean annual precipitation from 25 to 85 cm quantitative x ray diffraction x ray fluorescence and electron microprobe analyses were employed to quantify elemental changes in bulk soils and across plagioclase grains the chemical depletion of na in bulk soils ranged from 5 4 15 in the desert scrub sites relative to 16 33 in the mixed conifer sites plagioclase grain alteration was classified into unaltered edge and altered sections to compare microscale weathering and elemental variation the na al and si al ratios decreased from unaltered to edge to altered grain sections in the mixed conifer sites whereas the element ratios of the desert scrub system were similar between unaltered and edge grain sections and only exhibited significant decreases in na al and si al ratios between edge and altered materials the microscale depletion of na and si suggested increased silicate weathering in the cooler wetter and more biologically productive mixed conifer system compared to the hot dry desert scrub system the results also demonstrated a topographic control on mineral transformation where increased plagioclase weathering occurred in convergent footslope landscapes with little change in elemental depletion of soils in divergent summit sites

in situ sims u pb dating of phanerozoic apatite with low u and high common pb abstract apatite is a common accessory mineral in various igneous metamorphic and sedimentary rocks it has strong potential to provide important information for geochronology and petrogenesis however precise u th pb dating of apatite especially young samples is difficult due to low abundances of u and less radiogenic pb posing significant challenges for accurate common pb correction an additional issue is the lack of suitable apatite to serve as a standard for in situ analyses here we present both analytical and data reduction protocols for sims in situ u pb analyses on apatite with low u and high common lead with nw 1 apatite as the u pb age standard which was separated from 1160 ma carbonatite in the prairie lake complex in canada apatites from the kovdor carbonatite in the kola peninsula which contains low u mostly 2 5 ppm and high common pb 20 80 yielded weighted average 207pb corrected u pb ages of 375 13 ma kv 8 and kv 18 and 377 11 ma kv a respectively apatites from the quruqtagh ultramafic intrusion in nw china containing low u 2 3 ppm and high common pb 70 yield 207pb corrected u pb age of 805 21 ma the cenozoic durango apatite was dated at 31 2 ma all these new apatite u pb ages are indistinguishable from independently known age constraints to within 2 4 our results demonstrate that a u pb age can be accurately and precisely measured for apatite with low u 50 by sims with a suitable standard and a careful choice of common pb composition

two billion years of evolution enclosed in hydrothermal rutile recycling of the sao francisco craton crust and constraints on gold remobilisation processes abstract the quadrilatero ferrifero in the sao francisco craton brazil is known for its world class gold deposits hosted by the rio das velhas greenstone belt rdv as in other greenstone belts gold is also concentrated in late archean early paleoproterozoic supracrustal units in this case within the moeda formation this unit has been compared to the witwatersrand basin where there has been a long term debate over the nature of the gold and whether it is detrital placer hydrothermal or hybrid modified placer presently links between gold in the moeda formation and rdv are tenuous to enlighten this area of ambiguity a new approach using chemical isotopic and mineral inclusion data from detrital rutile found in the gold bearing horizons of the moeda formation is presented grain textures and mineral inclusions have contributed to establishing a primary hydrothermal origin for the rutile related to as fe cu sb pb w rich mineralising fluids fe nb and v indicate that the likely source of the gold related rutiles is the archean banded iron formations within the rdv where most of the lode gold occurs average nb ta values of these rutiles are lower than average continental crust ratios which suggests fractionation driven by fluid precipitation and or competing mineral phases u pb data yield primary crystallization ages older than deposition ages 2 58 ga supporting the detrital nature of these rutiles rutiles record either resetting or new growth at 2 1 ga and at ca 500 ma during which gold was remobilised hence this study supports a modified placer model for the gold bearing horizons of the moeda formation these fluid assisted gold remobilisation events can be found in other correlated paleoproterozoic gold bearing horizon units that represent intracratonic basins related to the rifting of the kenorland supercontinent this study reinforces the suitability of rutile and mineral inclusions as a powerful tool to elucidate processes and provenance

local variations of carbon isotope composition in diamonds from sao luis brazil evidence for heterogenous carbon reservoir in sublithospheric mantle abstract taking advantage of the common occurrence of superdeep mineral inclusion assemblages we examined core to rim primary zonation in 69 diamonds from the alluvial deposits of the sao luis river juina brazil syngenetic inclusions were represented by phases of superdeep paragenesis the dominant inclusions are majoritic garnets ferropericlases and casi and casiti perovskites rare inclusions of mgsi perovskites olivines clinopyroxenes tapp phases of sio2 kyanites alsi phases kfsp k hollandite cf nal grossular merwinite native iron fe sulphides magnesite and caco3 camgsi2o6 composite inclusions were also found the diamonds from sao luis display wide variations in carbon isotopic compositions 13c from 2 7 to 25 3 the diamonds with inclusions of ferropericlase have a very narrow range of 13c values from 2 1 to 7 7 which are close to the normal mantle values in many cases diamonds with inclusions of calcic majoritic garnet and casi and casiti perovskites display marked differences from this range low 13c values 10 to 25 were observed exclusively in a series of diamonds with majorite garnets ca silicates aluminous silicates and sio2 the 13c values from the cores to rims in certain individual crystals varied substantially indicating multiple stages of growth the highly negative 13c values in the cores 20 to 25 potentially represent organic matter in metasediments of altered oceanic crust and the lower 13c values may represent mixing trends towards normal mantle compositions in this study we also found a set of diamonds that display an opposite trend of change of the carbon source from primordial mantle to subducted crust either biotic or abiotic carbon

coevolution of nonlinear trends in vegetation soils and topography with elevation and slope aspect a case study in the sky islands of southern arizona 1 feedbacks among vegetation dynamics pedogenesis and topographic development affect the critical zone the living filter for earth s hydrologic biogeochemical and rock sediment cycles assessing the importance of such feedbacks which may be particularly pronounced in water limited systems remains a fundamental interdisciplinary challenge the sky islands of southern arizona offer an unusually well defined natural experiment involving such feedbacks because mean annual precipitation varies by a factor of five over distances of approximately 10 km in areas of similar rock type granite and tectonic history here we compile high resolution spatially distributed data for effective energy and mass transfer eemt the energy available to drive bedrock weathering above ground biomass soil thickness hillslope scale topographic relief and drainage density in two such mountain ranges santa catalina scm pinaleno pm strong correlations exist among vegetation soil topography variables which vary nonlinearly with elevation such that warm dry low elevation portions of these ranges are characterized by relatively low above ground biomass thin soils minimal soil organic matter steep slopes and high drainage densities conversely cooler wetter higher elevations have systematically higher biomass thicker organic rich soils gentler slopes and lower drainage densities to test if eco pedo geomorphic feedbacks drive this pattern we developed a landscape evolution model that couples pedogenesis and topographic development over geologic time scales with rates explicitly dependent on vegetation density the model self organizes into states similar to those observed in scm and pm our results highlight the potential importance of eco pedo geomorphic feedbacks mediated by soil thickness in water limited systems

mineral inclusions in diamonds associations and chemical distinctions around the 670 km discontinuity three new mineral associations have been discovered within diamonds from the juina district of brazil these include a previously unrecorded na al mg fe sio3 phase associated with ferropericlase and the tetragonal almandine pyrope phase tapp also reported are an association of corundum with aluminous pyroxene and an olivine composition phase associated with ferropericlase the minerals in each association often occurred within the same diamonds in addition to being recovered from individual diamonds in different combinations high pressure experimental data indicate that these associations formed at different depths within a region ca 60 km on either side of the upper mantle lower mantle boundary mineral compositions show that for the regions sampled the deep transition zone and lower mantle are chemically distinct and inhomogeneous importantly in the shallow lower mantle al is not solely accommodated within perovskite structured mg fe sio3 as some recent experimental studies have suggested

lithologic controls on regolith weathering and mass flux in forested ecosystems of the southwestern usa abstract parent material has a profound impact on chemical weathering mineral transformation and chemical denudation however there remains a relative paucity of lithosequence studies that directly examine parent material control on pedogenic processes we sampled a lithosequence of four parent materials rhyolite granite basalt dolostone volcanic cinders under pinus ponderosa in mesic and ustic soil moisture and temperature regimes of central and southern arizona usa to quantify the contribution of parent material to chemical weathering and elemental mass flux we quantified chemical weathering and mass flux using a combination of quantitative x ray diffraction and elemental mass balance mass flux calculations were confounded by the addition of volcanic cinders in the dolostone soils and addition of eolian materials in both the basalt and dolostone soils these variations in parent material were accounted for using a combination of refractory element indices and x ray diffraction results indicated significant differences in profile characteristics and chemical weathering among parent materials chemical mass loss from the basalt and dolostone soils were balanced or exceeded by addition of eolian materials leading to positive and highly variable mass fluxes of 14 48 kg m 2 and 10 22 kg m 2 respectively rhyolite and granite soils exhibited large differences in chemical mass flux despite nearly identical elemental and mineralogical compositions of the respective parent materials total chemical mass flux from the granite soils averaged 173 31 kg m 2 whereas mass flux from the rhyolite soils was much larger on the order of 930 71 kg m 2 these large differences result from the variation of parent material grain size and bulk density the data demonstrate strong control of parent material on chemical weathering and mass flux in cool semiarid forested ecosystems

magmatic pulses of the tatun volcano group northern taiwan revisited constraints from zircon u pb ages and hf isotopes abstract the initiation and duration of magmatism in the tatun volcano group tvg likely resulting from extensional collapse of the northern taiwan mountain belt remains an important issue of debates in the taiwan orogeny here we report a detailed study of u pb ages determined by sims and la icpms together with hf isotopic data of zircon separates from a total of 22 extrusive rocks from the tvg lava flow and additional two andesites from keelungyu kly a volcanic islet off ne taiwan magmatic zircons from the tvg are characterized by uniform and high hf isotopic ratios with ehf t mostly from 20 to 10 their overall 206pb 238u ages suggest that the tvg magmatism was initiated 3 ma but more active 0 8 ma with a flare up 0 35 ma magmatic zircons from the two kly samples reveal identical 206pb 238u ages 0 41 ma coupled with hf isotopes ehf t 25 to 9 comparable to those of the tvg thus kly is proposed as part of the tvg consequently we argue that the main body of the tvg formed 0 8 ma by post collisional volcanism but the mechanism resulting in the magmatic episodes 1 0 ma remains obscure due to the scarcity of rock exposures

corundum inclusions in diamonds discriminatory criteria and a corundum compositional dataset abstract mineral inclusions of corundum are reported from diamonds from alluvial deposits of tributaries of the rio aripuana juina brazil we present the first recorded occurrence of sapphire as an inclusion in diamond and expand on the database of ruby and white corundum inclusions ruby inclusions are found to occur both as isolated and touching grains with aluminous pyroxene and associated with ferropericlase mineral chemistry and phase relations place the origin of such ruby bearing diamonds within the lower mantle at 770 km mineral associations indaving other corundum inclusions were not observed hence their depth of origin is less certain compositions of corundum samples were characterised by electron and ion microprobe given the scarcity of literature data corundum samples from a variety of other geological settings were also analysed samples comprised corundums associated with granitic emplacement metasomatism amphibolite facies and granulite facies rocks gem and industrial synthetic origins and carmine coloured corundums recovered from kimberlite drill cores in addition to variable amounts of cr fe ti mg and si measurable quantities of other transition elements and high field strength elements were also detected corundums from similar geological settings show very similar compositions and are easily distinguishable from other settings irrespective of locality rubies from norwegian tanzanian and kenyan amphibolite facies rocks are compositionally indistinguishable additionally corundums from metasomatised zones associated with contact metamorphism from arizona and japan were very similar particularly characterised by unusually high abundance of mobile zr and nb tens of ppm all juina inclusions are particularly distinguishable from other corundums by high concentrations of ni 18 171 ppm weight typically at least an order of magnitude enriched over the same corundum varietal types from elsewhere furthermore the sapphire inclusion exhibited much larger ratios of ga and ge to hfse elements compared to otherwise similar samples and ruby inclusions are distinguished by high mg fe ratios 0 27 1 56 by weight compositional differences between inclusions in diamonds and corundums from other settings in addition to corundum s physical and chemical durability suggest that with the employment of rapid identification tools such as energy dispersive spectrometry eds and laser icpms corundum has promise as an indicator of diamond prospectivity

post collisional magmatism around northern taiwan and its relation with opening of the okinawa trough being part of an active mountain belt formed by oblique collision of the luzon arc with asia northern taiwan and the offshore islets are marked by a series of latest pliocene quaternary volcanoes whose eruptions have been conventionally ascribed to westward propagation of the ryukyu volcanic arc on the basis of new geochemical data along with supporting geologic and geophysical evidence we propose instead that this young volcanism resulted from post collisional lithospheric extension in the northern taiwan mountain belt and the mantle source regions involved in the melt generation have been significantly modified by the nearby ryukyu subduction related processes magmas thus produced through the northeast to the southwest in the northern taiwan volcanic zone ntvz vary from low k to calc alkaline and then shoshonitic compositions such a spatial geochemical variation characterized by southwestward increase in enrichments of potassium and incompatible trace elements runs subparallel to the southwestern part of the present day ryukyu trench the geochemical variation that can be explained by southwestward decrease in degrees of partial melting of the mantle sources is reconciled with a southwestward weakening extensional regime observed in the ntvz the post collisional extension in northern taiwan furthermore might have played a role in reactivation of the opening in the middle okinawa trough and gave way to its rapid southwestward propagation with associated development of the ryukyu subduction zone west of124oe this nascent subduction in turn resulted in abundant submarine volcanoes which delineate an embryo volcanic front along the southern margin of the trough therefore the southwestern okinawa trough is not a fore arc basin as had been previously alleged but represents an atypical back arc basin which developed broadly synchronously or prior to its arc trench system in this particular collision extension subduction tectonic environment 1999 elsevier science b v all rights reserved

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

strong climate and tectonic control on plagioclase weathering in granitic terrain abstract investigations to understand linkages among climate erosion and weathering are central to quantifying landscape evolution we approach these linkages through synthesis of regolith data for granitic terrain compiled with respect to climate geochemistry and denudation rates for low sloping upland profiles focusing on na as a proxy for plagioclase weathering we quantified regolith na depletion na mass loss and the relative partitioning of denudation to physical and chemical contributions the depth and magnitude of regolith na depletion increased continuously with increasing water availability except for locations with mean annual temperature

u pb zircon geochronology of silicic tuffs from the timber mountain oasis valley caldera complex nevada rapid generation of large volume magmas by shallow level remelting large volumes of silicic magma were produced on a very short timescale in the nested caldera complex of the sw nevada volcanic field swnvf voluminous ash flows erupted in two paired events topopah spring ts 1 200 km3 12 8 ma tiva canyon tc 1 000 km3 12 7 ma and rainier mesa rm 1 200 km3 11 6 ma ammonia tanks at 900 km3 11 45 ma all cited ages are previously published 40ar 39ar sanidine ages within each pair eruptions are separated by only 0 1 0 15 my and produced tuffs with contrasting isotopic values these events represent nearly complete evacuation of sheet like magma chambers formed in the extensional basin and range environment we present ion microprobe ages from zircons in the zoned ash flow sheets of ts tc rm and at in conjunction with 18o values of zircons and other phenocrysts which differ dramatically among subsequently erupted units bulk zircons in the low 18o at cycle were earlier determined to exhibit 1 5 core to rim oxygen isotope zoning and high spatial resolution zircon analyses by ion microprobe reveal the presence of older grains that are zoned by 0 5 2 5 the following u pb isochron ages were calculated after correcting for the initial u pb disequilibria at zircon rims 11 7 0 2 ma cores 12 0 0 1 ma pre at rhyolite lava 12 0 0 3 ma rm 12 4 0 3 tc 13 2 0 15 ma ts 13 5 0 2 average zircon crystallization ages calculated from weighted regression or cumulative averaging are older than the ar ar stratigraphy but preserve the comparably short time gaps within each of two major eruption cycles ts tc rm at notably every sample yields average zircon ages that are 0 70 0 35 ma older than the respective ar ar eruption ages the th u ratio of swnvf zircons are 0 4 4 7 higher than typically found in igneous zircons which correlates with elevated th u of the whole rocks 5 16 high th u could be explained if uranium was preferentially removed by hydrothermal solutions or is retained in the protolith during partial melting for low 18o at cycle magmas rim ages from unpolished zircons overlap within analytical uncertainties with the 40ar 39ar eruption age compared to core ages that are on average 0 2 0 3 my older than even the age of the preceding caldera forming eruption of rm tuff this age difference the core to rim oxygen isotope zoning in at zircons and disequilibrium quartz zircon and melt zircon isotopic fractionations suggest that at magma recycled older zircons derived from the rm and older eruptive cycles these results suggest that the low 18o at magmas were generated by melting a hydrothermally altered protolith from the same nested complex that erupted high 18o magmas of the rm cycle only 0 15 my prior to the eruption of the at the largest volume low 18o magma presently known

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet the first in situ hf and u pb isotope analyses of zircon separates from mesozoic granites in southern tibet identify a significant previously unknown stage of magmatism igneous zircons n 34 from a granite within the gangdese batholith show a weighted mean 206 pb 238 u age of 188 1 1 4 ma and e hf t the parts in 10 4 deviation of initial hf isotope ratios between the zircon sample and the chondritic reservoir values between 10 4 and 16 8 suggesting predominantly early jurassic intrusive activity with a juvenile mantle contribution of 40 inherited zircons from two cretaceous s type granites in the northern magmatic belt 23 delineate a slightly older 206 pb 238 u age cluster between 188 and 210 ma these zircons have e hf t values from 3 9 to 13 7 yielding crustal hf model ages from ca 1 4 to 2 1 ga suggesting a major episode of crustal growth in proterozoic time and remelting of this crust in early jurassic time combining these with literature data we interpret the jurassic gangdese magmatism as an early product of the neo tethyan subduction that played a long lasting role in the tectonic evolution of southern tibet prior to the india asia collision

lahars in and around the taipei basin implications for the activity of the shanchiao fault abstract in the last decade more than 21 deep geological cores have been drilled in the taipei basin to obtain a firmer grasp of its basic geology and engineering properties prior to the construction of new infrastructure thirteen of those cores contain lahar deposits with the number of layers varying from one to three and the thickness of each layer varying from several to over 100 m based on their occurrence petrology and geochemistry it has been determined that the deposits originated from the southern slope of the tatun volcano group tvg k ar age dating has shown that the lower layer of lahars was deposited less than 0 4 ma and this is clearly correlated to outcrops in the kauntu chengtzeliao and shihtzutao areas these findings may well suggest that the taipei basin has been formed in last 0 4 ma and that the shanchiao normal fault commenced its activity within this period the surface trace and the activity of the shanchiao normal fault have also been inferred and subsequently defined from stratigraphic data derived from these cores

elastic moduli of jadeite enstatite majorite 1 the adiabatic bulk ks and shear g moduli of a polycrystalline majorite garnet solid solution with composition na0 92mg2 08 mg0 02al1 06si0 92 si3o12 were measured at ambient conditions by brillouin spectroscopy ks and g were found to be 171 6 3 5 gpa and 103 5 2 0 gpa respectively assuming a linear dependence of the elastic moduli on composition for the mg2si2o6 enstatite majorite en mj naalsi2o6 jadeite majorite jd mj join the calculated ks and g of the fictive jd mj end member are 178 and 125 gpa respectively at ambient conditions the shear velocity change associated with the pyroxene to majorite transition increases dramatically with increasing na content in the system in contrast there is virtually no shear velocity increase associated with the pyroxene to majorite transition in mgsio3 if this relationship holds at high pressures and temperatures it suggests that for mineral assemblages containing an abundance of large radius cations such as ca and na the pyroxene garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone

reconstructing a high paleolatitude mesozoic paleoenvironment from a truncated and deeply buried regolith norwegian north sea abstract the paleoregolith in this study was unconformably overlain by lower cretaceous valanginian marine deposits of the asgard formation and buried below two kilometers of sediments on the utsira high norwegian north sea the upwards intensification of chemical alteration manifested in the replacement of feldspars by clays leaching of base cations and reduced mechanical rock strength in addition to the presence of terrestrial biotitic features suggested weathering during subaerial exposure of the utsira high during the mesozoic the paleoregolith can be divided into three weathering facies altered coherent rock saprock and saprolite whereas the absence of true soil horizons suggested erosional truncation of the regolith before burial possible remnants of the eroded soil were identified as pedogenic mud aggregates in the overlying asgard formation bearing similar compositional characteristics as the saprolite clay mineralogy bulk geochemical composition micromorphology and depth of biotic features were used to reconstruct the paleoenvironmental conditions that prevailed during the formation of the regolith in the mesozoic north sea our results point to a regolith formation under periodically water restricted conditions promoting the co existence of interstratified illite smectite beidellite and kaolinite deep presence of endomycorrhizae the fungal extension of the root structure and precipitation of iron oxide nodules application of recently developed geochemical climofunctions indicated that the regolith formed in a mesic 10 12 c and subhumid 1157 1406 mm yr environment and under strongly acidic soil conditions ph 5 2 5 6

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

shock induced minerals in meteorite provide prospecting tools for mineral physics over the last 40 years a combination of seismic data from earth s interior and experimentation at high pressures on materials of composition similar to that in earth s mantle has led to an increasingly accurate picture of what succession of phases must be present at increasing depths during the same time period it has been discovered that many of these phases are present in minute amounts in meteorites that before their arrival on earth were shocked to high pressures and temperatures during collisions between the asteroids from which the meteorites were derived in a recent issue of pnas chen et al 1 reported a previously uncharacterized mineral from such a shocked meteorite and by using diamond anvil experiments and synchrotron x ray analysis derived the stability conditions of that mineral and another closely related one discovered earlier this year from the same meteorite both of these phases are high pressure polymorphs of the mineral chromite fecr2o4 which is a common although minor mineral in peridotites rocks of the upper mantle that are abundantly exposed at the surface and also found as inclusions xenoliths in volcanic rocks some of this volcanism e g kimberlite also carries diamonds and hence must be derived from a minimum depth of 120 km the authors suggest that the newly discovered polymorphs of chromite if found in natural rocks on earth could serve as anchor points for estimation of the depths of origin of rocks transported from great depth the two polymorphs place minimum pressures of 12 13 gpa cafe2o4 structure and 20 gpa cati2o4 structure these pressures are equivalent in earth to depths of 400 km and 680 km respectively however is there any reason to believe that any rocks presently at the surface have ever seen such pressures

the effects of climate and landscape position on chemical denudation and mineral transformation in the santa catalina mountain critical zone observatory abstract understanding the interactions of climate physical erosion chemical weathering and pedogenic processes is essential when considering the evolution of critical zone systems interactions among these components are particularly important to predicting how semiarid landscapes will respond to forecasted changes in precipitation and temperature under future climate change the primary goal of this study was to understand how climate and landscape structure interact to control chemical denudation and mineral transformation across a range of semiarid ecosystems in southern arizona the research was conducted along the steep environmental gradient encompassed by the santa catalina mountains critical zone observatory scm czo the gradient is dominated by granitic parent materials and spans significant range in both mean annual temperature 10 c and precipitation 50 cm a 1 with concomitant shift in vegetation communities from desert scrub to mixed conifer forest regolith profiles were sampled from divergent and convergent landscape positions in five different ecosystems to quantify how climate landscape position interactions control regolith development regolith development was quantified as depth to paralithic contact and degree of chemical weathering and mineral transformation using a combination of quantitative and semi quantitative x ray diffraction xrd analyses of bulk soils and specific particle size classes depth to paralithic contact was found to increase systematically with elevation for divergent positions at approximately 28 cm per 1000 m elevation but varied inconsistently for convergent positions the relative differences in depth between convergent and divergent landscape positions was greatest at the low and high elevation sites and is hypothesized to be a product of changes in physical erosion rates across the gradient quartz plagioclase q p ratios were used as a general proxy for bulk regolith chemical denudation q p was generally higher in divergent landscape positions compared to the adjacent convergent hollows convergent landscape positions appear to be collecting solute rich soil waters from divergent positions thereby inhibiting chemical denudation clay mineral assemblage of the low elevation sites was dominated by smectite and partially dehydrated halloysite whereas vermiculite and kaolinite were predominant in the high elevation sites the increased depth to paralithic contact chemical denudation and mineral transformation are likely functions of greater water availability and increased primary productivity landscape position within a given ecosystem exerts strong control on chemical denudation as a result of the redistribution of water and solutes across the landscape surface the combined data from this research demonstrates a strong interactive control of climate landscape position and erosion on the development of soil and regolith

nanocrystalline diamond from the earth s mantle underneath hawaii abstract melt inclusions in a mantle derived garnet pyroxenite xenolith from salt lake crater hawaiian island of oahu have been analysed by means of transmission electron microscopy including energy dispersive x ray analysis electron energy loss spectroscopy and electron diffraction the melt inclusions represent trapped low degree melt that metasomatised the hawaiian mantle lithosphere before the eruption of the host magma the inclusions consist of a c cl s rich glass of basaltic composition an exsolved gas fluid phase mainly co2 with minor amounts of co h2o and some unidentified c h and h s species and or carbonate diamond is the major phase in the glass ranging in size between a few and several hundred nanometres two varieties of nanocrystalline diamonds are identified polycrystalline aggregates of nanometre size diamonds are tentatively explained as pseudomorphs after carbonate while single crystals are suggested to have crystallised from the melt other nanocrystalline phases include native fe and cu fes fes2 zns ags and several ti nb zr ir in pd rich phases of unknown composition overall the observed mineral assemblage suggests that the melt was highly reduced and strongly enriched in volatiles and trace elements of contrasting geochemical affinity our findings are the first evidence for a metasomatic impregnation of the hawaiian mantle by low degree melts here we report the first occurrence of diamond in the modern oceanic mantle

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

zircon u pb and hf isotopic constraints from eastern transhimalayan batholiths on the precollisional magmatic and tectonic evolution in southern tibet abstract before the indian collision with asia northward subduction of the neo tethyan oceanic lithosphere produced an andean type convergent margin in south asia characterized by arc magmatism starting from the early jurassic and lasting until the eocene the magmatic arc is now represented by widespread intrusive bodies or the so called transhimalayan batholiths in the lhasa terrane of southern tibet that have been divided into two main magmatic suites i e the northern plutonic belt and the southern gangdese batholith their temporal distribution concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern himalayan syntaxis however remains poorly constrained here we report the first combined zircon u pb and hf isotopic study of the transhimalayan batholiths from the eastern part of the lhasa terrane 95 97 5 e and 28 5 30 n se tibet zircon u pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the early cretaceous 133 110 ma and subordinately in the paleocene 66 57 ma long after an older granite intrusion in the earliest jurassic 198 ma the zircon ehf t values range from 5 to 20 yielding hf crustal model ages tdmc between 0 8 and 2 4 ga that peak at 1 7 ga suggesting a major episode of crustal growth in the proterozoic and a predominantly or even exclusively crustal source for the granitoid petrogenesis these zircon u pb and hf isotopic constraints together with whole rock geochemical characteristics allow us to correlate them to s type granitoids in the northern plutonic belt rather than to the i type gangdese batholith from the central part of the southern lhasa terrane in contrast to the gangdese magmatism that formed with a significant juvenile mantle input related to the neo tethyan subduction these s type granitoids show geochemical similarities to the north american cordilleran interior batholiths that did not form directly from a subduction setting thus we attribute the petrogenesis of the widespread early cretaceous granitoids in the northern belt and eastern himalayan batholiths to a postcollisional regime due to the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes under this framework the s type magmatism was generated in response to collision induced crustal thickening which may have capabilities of causing crustal anatexis by itself in the region however continued interplay with the neo tethyan subduction zone processes such as back arc extension could also have played a crucial and long lasting role in the magma generation

in situ observation of the decomposition of kyanite at high pressures and high temperatures in situ observations of the decomposition of kyanite al 2 sio 5 were carried out in a multi anvil high pressure apparatus using synchrotron radiation where the phase change from kyanite to stishovite corundum was observed at high pressures and high temperatures the phase boundary of this decomposition at t 1200 1900 k and p 5 15 gpa was determined to be p gpa 10 2 0 0016 t k previous studies using the quench method showed a discrepancy in the transition pressure of the decomposition our results using in situ observations resolve this dispute