cenozoic deformation of the tarim plate and the implications for mountain building in the tibetan plateau and the tian shan 1 the tarim basin in nw china developed as a complex foreland basin in the cenozoic in association with mountain building in the tibetan plateau to the south and the tian shan orogen to the north we reconstructed the cenozoic deformation history of the tarim basement by backstripping the sedimentary rocks two dimensional and three dimensional finite element models are then used to simulate the flexural deformation of the tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts the results suggest that uplift of both the western kunlun shan and the tian shan orogens started during or before oligocene since the miocene mountain building accelerated in the western kunlun shan but showed segmented development in the tian shan the results also indicate reduced tectonic load along the altyn tagh fault since late miocene consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the cenozoic evolution

did the growth of tibetan topography control the locus and evolution of tien shan mountain building the tien shan in central asia are the pre eminent example of intraplate mountain building and are typically considered an indirect result of the india eurasia collision via the northward indentation of the relatively strong precambrian lithosphere of the tarim plate into the relatively weak paleozoic lithosphere of the tien shan region this hypothesis fails to fully explain the concentration of tien shan mountain building along a tibet parallel axis located 500 700 km from tibet and also fails to explain the close synchronization of tien shan mountain building events with mountain building in tibet i suggest that bending stresses from lithospheric flexure in central asia exerted a critical influence on the locus and evolution of the tien shan models of paleogene to middle miocene flexure indicate that the growth of northeast tibet may have superimposed a strong bending stress field on the regional stress field the resultant stress field is characterized by strong topography normal tensile stress in the tarim basin and an 15 increase in compressive stress in the vicinity of the tien shan this stress field severely reduces the likelihood of mountain building south of the tien shan and increases the likelihood of mountain building within the tien shan this result suggests that the generation of bending stresses from lithospheric flexure is a viable and important mechanism for the propagation of stress and hence deformation into continental interiors

theoretical estimates of equilibrium chromium isotope fractionations equilibrium chlorine isotope 37 cl 35 cl fractionations have been determined by using published vibrational spectra and force field modeling to calculate reduced partition function ratios for cl isotope exchange ab initio force fields calculated at the hf 6 31g d level are used to estimate unknown vibrational frequencies of 37 cl bearing molecules whereas crystalline phases are modeled by published lattice dynamics models calculated fractionations are principally controlled by the oxidation state of cl and its bond partners molecular mass or the absence of c h bonds also appears to play a role in determining relative fractionations among simple cl bearing organic species molecules and complexes with oxidized cl i e cl 0 cl etc will concentrate 37 cl relative to chlorides substances with cl at 298 k clo 2 containing cl 4 and clo 4 containing cl 7 will concentrate 37 cl relative to chlorides by as much as 27 and 73 respectively in rough agreement with earlier calculations among chlorides 37 cl will be concentrated in substances where cl is bonded to 2 cations i e fecl 2 mncl 2 micas and amphiboles relative to substances where cl is bonded to 1 cations such as nacl by 2 to 3 at 298 k organic molecules with c cl bonds will be even richer in 37 cl 5 to 9 at 298 k precipitation experiments in combination with our results provide an estimate for cl isotope partitioning in brines and suggest that silicates to the extent that their cl atoms are associated with nearest neighbor 2 cations analogous with fecl 2 and mncl 2 will have higher 37 cl 35 cl ratios than coexisting brine by 2 to 3 at room temperature calculated fractionations between hcl and cl 2 and between brines and such alteration minerals are in qualitative agreement with both experimental results and systematics observed in natural samples our results suggest that cl bearing organic molecules will have markedly higher 37 cl 35 cl ratios by 5 8 to 8 5 at 295 k than coexisting aqueous solutions at equilibrium predicted fractionations are consistent with the presence of an isotopically heavy reservoir of hcl that is in exchange equilibrium with cl aq in large marine aerosols

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

first principles calculations of equilibrium ca isotope fractionation implications for oldhamite formation and evolution of lunar magma ocean abstract calcium is a major element of the earth the moon terrestrial planets and rocky meteorites here we present equilibrium ca isotope fractionation factors of ca bearing minerals using the first principles calculations based on density functional theory dft the sequence of minerals from the isotopically heaviest to the lightest in ca is forsterite orthopyroxene opx grossular pigeonite diopside anorthite oldhamite overall the equilibrium fractionation of ca isotopes is mainly controlled by the average bond lengths although oldhamite is enriched in light ca isotopes relative to silicate minerals in equilibrium natural oldhamite of enstatite chondrites are isotopically heavier than coexisting silicate materials this implies that enstatite chondrites oldhamites should have been formed during solar nebular gas condensation instead than during parent body processing following previous models for crystallization of the lunar magma ocean lmo we simulated ca isotopic fractionation of the lmo based on our calculated equilibrium ca isotope fractionation factors it shows that the 44 40 ca of the lunar anorthositic crust should be lower than the average of the bulk moon by 0 09 0 11 considering that the lunar mantle might have overturned and mixed after solidification of the lmo we further predict that the lunar mantle should be isotopically heavier than the bulk moon by 0 17 0 26 if the mantle was fully overturned or only by 0 06 0 08 for the case of fully mixing therefore we predict that the potential offset of ca isotopic composition between the anorthositic crust and the lunar mantle can be used to test lmo evolution models

calcium isotope δ44 40ca variations of neogene planktonic foraminifera measurements of the calcium isotopic composition 44 40ca of planktonic foraminifera from the western equatorial pacific and the indian sector of the southern ocean show variations of about 0 6 over the past 24 myr the stacked 44 40ca record of globigerinoides trilobus and globigerina bulloides indicates a minimum in 44 40casw seawater calcium at 15 to 16 ma and a subsequent general increase toward the present interrupted by a second minimum at 3 to 5 ma applying a coupled calcium carbon cycle model we find two scenarios that can explain a large portion of the observed 44 40casw variations in both cases variations in the ca input flux to the ocean without proportional changes in the carbonate flux are invoked the first scenario increases the riverine calcium input to the ocean without a proportional increase of the carbonate flux the second scenario generates an additional calcium flux from the exchange of ca by mg during dolomitization in both cases the calcium flux variations lead to drastic changes in the seawater ca concentrations on million year timescales our 44 40casw record therefore indicates that the global calcium cycle may be much more dynamic than previously assumed

interpreting the ca isotope record of marine biogenic carbonates an 18 million year record of the ca isotopic composition 44 42ca of planktonic foraminiferans from odp site 925 in the atlantic on the ceara rise provides the opportunity for critical analysis of ca isotope based reconstructions of the ca cycle 44 42ca in this record averages 0 37 0 05 1 sd and ranges from 0 21 to 0 52 the record is a good match to previously published neogene ca isotope records based on foraminiferans but is not similar to the record based on bulk carbonates which has values that are as much as 0 25 lower bulk carbonate and planktonic foraminiferans from core tops differ slightly in their 44 42ca i e by 0 06 0 06 n 5 while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger leaving open the question of the cause of the difference modeling the global ca cycle from downcore variations in 44 42ca by assuming fixed values for the isotopic composition of weathering inputs 44 42caw and for isotope fractionation associated with the production of carbonate sediments sed results in unrealistically large variations in the total mass of ca2 in the oceans over the neogene alternatively variations of 0 05 in the ca isotope composition of weathering inputs or in the extent of fractionation of ca isotopes during calcareous sediment formation could entirely account for variations in the ca isotopic composition of marine carbonates ca isotope fractionation during continental weathering such as has been recently observed could easily result in variations in 44 42caw of a few tenths of permil likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean until better constraints on variations in 44 42caw and sed have been established modeling the ca2 content of seawater from ca isotope curves should be approached cautiously

cenozoic tectonic and geodynamic evolution of the kyrgyz tien shan mountains a review of geological thermochronological and geophysical data abstract the complex crustal structure of the tien shan has a strong impact on the distribution of strain induced by the india eurasia collision with intracontinental deformation in eurasia s interior as a distant effect the northward propagation of the india eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins the tien shan basement is formed by the rigid heterogeneous precambrian blocks microcontinents of tarim issyk kul or central tien shan and aktyuz boordin surrounded by a soft matrix of paleozoic accretion collision belts the kyrgyz tien shan mountains are situated between the active structures of the tarim plate and the pamir indenter south and the stable kazakhstan shield north underplating by the tarim plate and thrusting by the pamirs are responsible for the building of the cenozoic tien shan the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area large earthquakes m 6 delineate the northern and southern margins of the issyk kul microcontinent indicating that crustal heterogeneity influenced the location of active structures in the northern kyrgyz tien shan

the calcium riverine and hydrothermal isotopic fluxes and the oceanic calcium mass balance calcium isotope ratios relative to seawater were studied in natural waters in order to constrain the ca isotopic flux to the oceans and to discuss the oceanic ca budget this study includes the analysis of 1 ca isotopes in continental waters at the regional scale of the upper rhine valley and 2 the determination of the 44ca values of some major rivers and hydrothermal vents the data indicate that the global 44ca variability of the studied waters with a maximal range of 1 is limited and must be linked to mass fractionation processes at the scale of a small watershed aubure vosges france the 44ca river flux changes due to the variation of the proportion of waters resulting from chemical alteration of rocks and biologically fractionated soil solutions ca isotopes could therefore be an important tool to quantify the impact of the plants and the biosphere on the river water chemistry at the regional scale of the rhine valley as well as at the global scale of world rivers the 44ca variability of river samples ranges from 0 5 to 1 without any relationship with the lithology of the watershed or the climate similarly the 44ca value of hydrothermal vents is also uniform and close to the mean value of river waters consequently the 44ca flux to the ocean should remain rather constant through time with a mean of 1 1 0 2 this value confirms that the ca budget of the present day seawater is in steady state this was not necessarily the case in the past non steady state periods should have been due to intensity variations of incoming and outcoming ca fluxes rather than to the variations in their isotopic signatures

first principles investigations of equilibrium calcium isotope fractionation between clinopyroxene and ca doped orthopyroxene equilibrium fractionation factors of ca isotopes among mantle minerals are essential for using ca isotopes as an important tracer in mantle geochemistry using the vibrational frequencies obtained by the first principles calculations based on density functional theory dft we calculated equilibrium fractionation factors of ca isotopes between two major ca bearing minerals clinopyroxene cpx and orthopyroxene opx our results show that opx has much higher 44 ca 40 ca than its co existing cpx even at high temperatures e g 1273 k agreeing with the observations on mantle peridotites in addition to the wellknown temperature effect our calculations for the first time reveal that the inter mineral ca isotope fractionation factor between opx and cpx also has a strong dependence on the chemical composition of opx i e ca content specifically it increases substantially with decreasing ca mg atomic ratio of opx when ca mgopx is lower than 1 15 such compositional effect on inter mineral ca isotope fractionation provides a convincing interpretation to the different isotope fractionations between coexisting opx and cpx observed in kilbourne hole and san carlos peridotites 2014 elsevier ltd all rights reserved

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

comparison of element and isotope diffusion of k and ca in multicomponent silicate melts recent experimental work has shown that the homogenization of elemental concentrations can be much slower than that of isotopic ratios when there are strong concentration gradients in sio 2 and al 2o 3 the ramifications of this result for magma homogenization and other petrological problems related to diffusion are significant we report here a comparison of experimental profiles of elemental concentrations and isotopic fractions of k and ca in rhyolite andesite large concentration gradients and rhyolite rhyolite small concentration gradients melt couples when the concentration profile and the isotopic profile of the same element in a single couple are compared the former is much shorter than the latter in the rhyolite andesite couple consistent with other recent studies however the lengths of both concentration and isotopic profiles are similar in the rhyolite rhyolite couple therefore diffusion of an element or oxide may be decoupled from or coupled with isotopic diffusion depending on whether large concentration gradients of major components are present when the two couples are compared the intrinsic effective binary diffusivities obtained from isotopic profiles are similar for each element in the two couples whereas the effective binary diffusivity of k obtained from the concentration profile in the rhyolite rhyolite couple is 37 times that in the rhyolite andesite couple therefore isotopic homogenization is roughly independent of elemental homogenization and the presence of sio 2 al 2o 3 and other concentration gradients whereas elemental homogenization is strongly affected by concentration gradients our experimental data isotopic and concentration profiles including uphill diffusion profiles can be modeled quantitatively to a good approximation using a modified effective binary diffusion model in which the flux of a component is assumed to be proportional to its activity gradient instead of its concentration gradient therefore the multicomponent diffusion effect in the silicate systems of our experiments seems to be largely due to contributions of non ideal mixing to the cross terms of the diffusivity matrix

tomographic evidence for localized lithospheric shear along the altyn tagh fault seismic tomography across the altyn tagh fault at the north edge of the tibetan plateau reveals a low p wave velocity anomaly below the fault down to 140 kilometers this anomaly probably reflects strike slip shear in the lithosphere slip partitioning may also induce a wedge of crust from the tarim basin to plunge into the mantle

calcium isotopic ratios and rare earth element abundances in refractory inclusions from the allende cv3 chondrite abstract refractory inclusions in primitive meteorites are the oldest objects formed in the solar system they exhibit large mass dependent isotopic effects in many elements including si mg and ca indicative of their complex origin we report data for both mass dependent and mass independent e ca isotopic effects and rare earth element ree abundances in six refractory inclusions from the allende cv3 meteorite our data reveal large mass dependent ca isotopic effects in these refractory inclusions with 44 40 ca ranging from 5 60 to 0 35 relative to nist srm 915a which are significantly lower than that of the bulk silicate earth 44 40 ca 1 05 0 04 importantly 44 40 ca is correlated with ree patterns refractory inclusions with group ii ree patterns have lighter ca isotope compositions compared to those with group i ree patterns specifically the studied refractory inclusions form negative 44 ca 40 ca tm er and 44 ca 40 ca nd er trends implying segregation of up to 3 of an ultrarefractory evaporation residue from a chondritic reservoir prior to the formation of refractory inclusions this residue would have to be characterized by high 44 ca 40 ca and low tm er and nd er at 2 levels of 0 5 and 1 5 for e 40 44 ca and e 43 44 ca respectively the six refractory inclusions studied show no detectable 40 ca or 43 ca anomalies relative to the terrestrial standards however five out of the six refractory inclusions do show a 48 ca excess of several e units clearly resolvable from the terrestrial standards

calcium isotopes in the marine environment and the oceanic calcium cycle abstract a systematic investigation of 44 ca 40 ca ratios in the oceanic ca cycle indicates that the average ca isotopic composition of input and output are quite different suggesting that the present ocean is not in a steady state our data show that sea water has uniform 44 ca 40 ca as expected from the long residence time of ca in the oceans it also exhibits the heaviest isotopic composition among all samples measured consistent with recent results by skulan et al 1997 and must be maintained at this value by strong biogenic isotope fractionation during the precipitation of caco 3 our measurements show that the riverine input is variable the most radiogenic river waters we have measured lowest 44 ca 40 ca are from ganges tributaries which also have high 87 sr 86 sr although there does not appear to be a systematic correlation between ca and sr isotopic compositions based on available data there is also significant isotopic variability among samples of caco 3 precipitated from the present ocean with coccolith oozes showing the most highly fractionated isotopic values relative to seawater among foraminifera ca isotopes exhibit species dependent fractionation effects but also appear to display systematic temperature dependent fractionation within inidividual species

44ca 42ca and 143nd 144nd isotope variations in cretaceous eocene tethyan francolites and their bearing on phosphogenesis in the southern tethys measurements of 4 4 ca 4 2 ca and 1 4 3 nd 1 4 4 nd isotope ratios in carbonate fluorapatite cfa through the aptian eocene section of the negev israel together with quantified rates of p and ca accumulation and bulk sedimentation permit an examination of the relationships of these five factors to tethyan phosphogenesis the data provide an aptian eocene ca 70 ma record of the ca isotope composition of 35 cfa samples 24 of which were also analyzed for nd isotopes representing 11 time stratigraphic phosphate horizons within the sequence the 4 4 ca values are significantly lower in the aptian albian samples 4 4 ca 0 11 to 0 06 than in the campanian eocene samples 4 4 ca 0 22 to 0 42 whereas the e n d values increase from continental crust like in the aptian albian e n d t 10 9 to more radiogenic pacific like e n d t 6 6 to 6 1 in the campanian both peaks of 4 4 ca and e n d t in the campanian coincide with the peak of tethyan phosphogenesis in the negev which is marked by a sharp increase of p accumulation rates from 200 mol cm 2 k y 1 in pre campanian time to 1700 mol cm 2 k y 1 in the campanian and a decrease in rates of ca accumulation and bulk sedimentation the coincident increases of 4 4 ca and e n d t values and p accumulation rates in the negev area during the campanian suggest that they are related in this time interval and were induced by the global late cretaceous sea level rise and increasing circumequatorial tethyan flow

characterization of calcium isotopes in natural and synthetic barite abstract the mineral barite baso4 accommodates calcium in its crystal lattice providing an archive of ca isotopes in the highly stable sulfate mineral holocene marine pelagic barite samples from the major ocean basins are isotopically indistinguishable from each other 44 40ca 2 01 0 15 but are different from hydrothermal and cold seep barite samples 44 40ca 4 13 to 2 72 laboratory precipitated synthetic barite samples are more depleted in the heavy ca isotopes than pelagic marine barite and span a range of ca isotope compositions 44 40ca 3 42 to 2 40 temperature saturation state a ba 2 a so 4 2 and aca2 aba2 each influence the fractionation of ca isotopes in synthetic barite however the fractionation in marine barite samples is not strongly related to any measured environmental parameter first principles lattice dynamical modeling predicts that at equilibrium ca substituted barite will have much lower 44ca 40ca than calcite by 9 at 0 c and 8 at 25 c based on this model none of the measured barite samples appear to be in isotopic equilibrium with their parent solutions although as predicted they do record lower 44 40ca values than seawater and calcite kinetic fractionation processes therefore most likely control the extent of isotopic fractionation exhibited in barite potential fractionation mechanisms include factors influencing ca2 substitution for ba2 in barite e g ionic strength and trace element concentration of the solution competing complexation reactions precipitation or growth rate temperature pressure and saturation state as well as nucleation and crystal growth rates these factors should be considered when investigating controls on isotopic fractionation of ca2 and other elements in inorganic and biogenic minerals

variations in the marine ca cycle over the past 20 million years a 20 million year marine ca isotope record is constructed based on measurements of 36 nannofossil ooze samples from dsdp site 590 the ca isotopic composition d 44 ca relative to our bbulk earthq average of carbonate ooze samples varies between 0 2 and 0 9 and the inferred d 44 ca of seawater calcium varies between 1 1 and 0 4 modern seawater value is 0 95 on our scale fluctuations in the seawater ca isotope ratio occur in 2 to 4 million year intervals and indicate that the supply and removal of ca from the oceans are seldom in balance the ca isotope record is used to reconstruct past weathering fluxes and marine calcium concentrations the inferred marine concentration of ca fluctuates by about f20 on 2 4 million year time scales and by about f50 over the 20 million year record these variations are presumably superimposed on the previously inferred 100 million year variations the seawater ca concentration was about 0 5 times present at 20 ma and generally increased until 6 ma 1 7 times present local maxima in seawater calcium concentrations occur at 6 4 and 4 ma preceding periods of enhanced marine productivity and high mass accumulation rates at site 590 while the calculated calcium concentrations are sensitive to the assumed d 44 ca value for the weathering flux the 2 4 million year features of the derived

tracking physicochemical conditions of evaporite deposition by stable magnesium isotopes a case study of late permian langbeinites magnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition we report mg isotopic values delta mg 26 dsm3 measured from an evaporite deposit of langbeinite k2mg2 so4 3 found in the permian salado formation we used these data to model mg isotope fractionation between langbeinite and its parent brine in addition both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment the salado langbeinite delta mg 26 values are relatively low and fall within a relatively narrow range 4 12 0 03 parts per thousand to 3 81 0 07 parts per thousand equilibrium fractionation factors between langbeinite and aqueous mg2 solutions were calculated using quantum chemical density functional theory all computations were performed at the b3lyp 6 31 g d p level solvation effects were addressed using a solvent model water droplet approach and mineral structures were investigated using volume variable cluster models vvcm the equilibrium mg isotopic fractionation factors a between langbeinite and model brine solution we obtained are 1 0005 1 0004 and 1 0003 delta mg 26 langb water approximate to 10 3 ln alpha 0 473 parts per thousand 0 390 parts per thousand and 0 322 parts per thousand at 10 degrees c 25 degrees c and 40 degrees c respectively these relatively large equilibrium fractionation factors indicate significant mg isotope fractionation between langbeinite and its parent brine during precipitation as langbeinite preferentially incorporates the heavier mg 26 and mg 25 isotopes rayleigh distillation modeling of the salado langbeinite s relatively light mg isotopic composition requires delta mg 26 dsm3 values of 4 parts per thousand for the parent brine models favor a precipitation temperature as high as 40 degrees c under equilibrium conditions potential disequilibrium precipitation conditions suggested by mg isotopic data also imply rapid deposition in a hot arid sedimentary environment prevailing in the southwestern u s during the late permian

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

behavior of calcium isotopes during continental subduction recorded in meta basaltic rocks abstract in order to investigate the behavior of ca isotopes during subduction we report high precision ca isotopic data of a suit of well characterized meta basaltic rocks from the dabie sulu orogen including six greenschists six amphibolites and seven eclogites except two samples that may have been affected by carbonation alteration greenschists amphibolites and eclogites yield comparable 44 42ca values ranging from 0 36 to 0 41 0 32 to 0 39 and 0 32 to 0 42 respectively overall dabie sulu meta basaltic rocks have an average 44 42ca of 0 37 0 06 2sd n 17 19 comparable to terrestrial basalts previously reported 0 36 0 05 2sd n 34 combined with no correlation of 44 42ca with h2o and rb tio2 this study suggests that prograde metamorphism dehydration cannot significantly fractionate ca isotopic compositions of meta basaltic rocks given the comparable cao contents in meta basaltic rocks with increasing metamorphism grade isotope fractionation may be limited by insignificant ca loss during dehydration two heavy greenschists with 44 42ca of 0 46 and 0 49 also have high co2 concentrations indicating carbonation alteration that is evidenced by 0 04m hcl leaching experiments the limited 44 42ca variation observed in the other metamorphic samples is most likely inherited from their igneous protoliths considering that terrestrial basalts have 44 42ca systematically lower than the upper mantle subduction of mafic lithologies e g oceanic slabs thus could reflux light ca isotopes back into the mantle and may create mantle heterogeneity

calcium isotope fractionation in selected modern and ancient marine carbonates the calcium isotope composition 44 42ca was analyzed in modern cretaceous and carboniferous marine skeletal carbonates as well as in bioclasts non skeletal components and diagenetic cements of cretaceous and carboniferous limestones in order to gain insight in ca2 aq caco3 isotope fractionation mechanisms in marine carbonates splits of samples were analyzed for sr mg fe and mn concentrations and for their oxygen and carbon isotopic composition biological carbonates generally have lower 44 42ca values than inorganic marine cements and there appears to be no fractionation between seawater and marine inorganic calcite a kinetic isotope effect related to precipitation rate is considered to control the overall discrimination against 44ca in biological carbonates when compared to inorganic precipitates this is supported by a well defined correlation of the 44 42ca values with sr concentrations in cretaceous limestones that contain biological carbonates at various stages of marine diagenetic alteration no significant temperature dependence of ca isotope fractionation was found in shells of cretaceous rudist bivalves that have recorded large seasonal temperature variations as derived from 18o values and mg concentrations the reconstruction of secular variations in the 44 42ca value of seawater from well preserved skeletal calcite is compromised by a broad range of variation found in both modern and cretaceous biological carbonates independent of chemical composition or mineralogy despite these variations that may be due to still unidentified biological fractionation mechanisms the 44 42ca values of cretaceous skeletal calcite suggest that the 44 42ca value of cretaceous seawater was 0 3 0 4 lower than that of the modern ocean

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

theoretical prediction for several important equilibrium ge isotope fractionation factors and geological implications article i nfo this study estimates equilibrium fractionation factors in the ge isotope system including the dominant aqueous ge oh 4 and geo oh 3 species in seawater ge bearing organic complexes e g ge catechol ge oxalic acid and ge citric acid and ge in quartz or opal albite k feldspar olivine and sphalerite like structures estimations are based on urey model or bigeleisen mayer equation and high level quantum

calcium isotope fractionation in calcite and aragonite abstract calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite precipitation temperatures ranged from 0 to 28 c calcium isotope fractionation shows a temperature dependence in accordance with previous observations 1000 ln cc 1 4 0 021 t c for calcite and 1000 ln ar 1 9 0 017 t c for aragonite within uncertainty the temperature slopes are identical for the two polymorphs however at all temperatures calcium isotopes are more fractionated in aragonite than in calcite the offset in 44 40 ca is about 0 6 the underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals or to different ca reaction behavior at the solid liquid interface recently the observed temperature dependence of the ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting lemarchand et al 2004 we show that this mechanism can in principle also be applied to caco 3 precipitation in natural environments in normal marine settings following this model ca isotope fractionation in marine ca carbonates is primarily controlled by precipitation rates on the other hand the larger ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates the rate control model of ca isotope fractionation predicts a strong dependence of the ca isotopic composition of carbonates on ambient co 3 2 concentration while this model is in general accordance with our observations in marine carbonates cultured specimens of the planktic foraminifer orbulina universa show no dependence of ca isotope fractionation on the ambient co 3 2 concentration the latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water

boron and calcium isotope composition in neoproterozoic carbonate rocks from namibia evidence for extreme environmental change the level and evolution of atmospheric carbon dioxide throughout earth s history are key issues for palaeoclimate reconstructions especially during times of extreme climate change such as those that marked the neoproterozoic the carbon isotope ratios of marine carbonates are crucial in the correlation and identification of neoproterozoic glacial deposits and they are also used as a record for biogeochemical cycling and potential proxy for atmospheric pco2 likewise the boron and calcium isotope compositions of marine carbonates are potential proxies for palaeo seawater ph and the ratio of calcium fluxes into and out of seawater respectively and together they may be used to estimate atmospheric carbon dioxide here we use b and ca isotopes to estimate palaeoenvironmental conditions in the aftermath of a major neoproterozoic glaciation in namibia the validity of the b and ca isotope variation in the ancient marine carbonates is evaluated using the oxygen isotope composition of the carbonates and its correlation to the carbon isotope variation a negative 2 7 to 6 2 11b excursion occurs in the postglacial carbonates and is interpreted to reflect a temporary decrease in seawater ph associated variations in 44ca values ranging between 0 35 and 1 14 are linearly coupled with the carbon isotope ratios and imply enhanced postglacial weathering rates the reconstructed seawater ph and weathering profiles indicates that high atmospheric co2 concentrations were likely during the melt back of neoproterozoic glaciations and precipitation of cap carbonates however the b isotope trend suggests that these concentrations rapidly ameliorated and they do not co vary with 13c thus models attempting to link long lived negative 13c excursions to elevated pco2 need to be reconsidered

origin of rodingite forming fluids constrained by calcium and strontium isotope ratios in the leka ophiolite complex abstract alteration of oceanic lithosphere plays an important role in the global element cycling due to its dominant abundance on the earth s surface the formation of rodingites a ca rich lithology that occurs intimately associated with ca depleted serpentinite complexes is a widespread process during strong alteration of ocean floor lithologies and may represent a key process that influences the global ca cycle stable ca and radiogenic sr isotope compositions of rodingites and associated lithologies from the leka ophiolite complex norway preserve mantle signatures and thus provide evidence that the ca and sr sources for rodingitisation are dominantly mantle derived with no detectable seawater input the difference of 0 7 in 44 40ca of different phases found in the rocks is overall consistent with inter mineral fractionation at high temperatures related to the cao bonding environment but there are also indications for isotopic disequilibria between non cogenetic mineral phases while the water required for rodingite formation may originate from seawater the dissolved ca and sr involved in the mineral reactions during rodingitisation plg ca gros clz al can be balanced at a local scale being derived from the serpentinisation of mantle peridotites cpx1 h2o al srp chlorite ca cpx2 consequently rodingites do not act as a sink for oceanic ca instead they are a sink for ca released during serpentinisation of the oceanic lithospheric mantle

ca isotopes record rapid crystal growth in volcanic and subvolcanic systems kinetic calcium isotope effects can be used as growth rate proxies for volcanic and subvolcanic minerals here we analyze ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects 2 can occur during magmatic plagioclase crystallization experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase ca diffusivity r d plagioclase phenocrysts from the 1915 mount lassen rhyodacite eruption the 650 y old deadman creek dome eruption and several mafic subvolcanic orbicules and plagioclase comb layers from northern california have disequilibrium ca isotopic compositions that suggest rapid crystal growth rates 1 cm y to 15 cm y the ca isotope results combined with complementary crystal size distribution analyses suggest that magmatic rejuvenation and eruption events as reflected in crystal growth times can be as short as 10 3 y although mafic systems are predicted to have shorter magmatic rejuvenation periods we find similarly short timescales in both mafic and silicic systems these results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption by focusing on a common mineral such as plagioclase this approach can be applied across all major magmatic compositions suggesting that ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions

thermodynamic properties and phase relations in mantle minerals investigated by first principles quasiharmonic theory this research has been motivated by geophysics and materials physics the objective of this research has been to advance materials theory and computations for high pressure and high temperature applications to the point that it can make a difference in our understanding of the earth understanding of the mineralogy composition and thermal structure of the earth evolves by close interaction of three fields seismology geodynamics and mineral physics earth s structure is imaged by seismology which obtains body wave velocities and density throughout the earth s interior fig 1 interpretation of this data relies on knowledge of aggregate properties of earth forming materials either measured in laboratory or calculated in many cases by both however the conditions of the earth s interior especially at the core may be challenging for important experiments and materials computations have emerged to contribute decisively to this field earth s evolution is simulated by geodynamics but these simulations need as input information about rheological and thermodynamic properties of minerals including phase transformation properties such as clapeyron slopes our research has concentrated on the phases of the earth s mantle particularly the deep mantle whose conditions are more challenging for experiments the mantle accounts for 83 of the earth s volume in this article we will review the essential first principles approach used to investigate solids at high temperatures and pressures summarize their performance for mantle minerals fig 2 and point to critical results that have stirred us in the current research path the success is remarkable but some limitations point the way to future developments in this field figure 1 a velocities and density profiles kennett et al 1995 b earth s cross section and c composition and mineralogy of earth s layers figure 2 phases proportions versus depth and or pressure ol mg fe 2sio4 olivine also known as phase mg fe

latitudinal dependence of diapycnal diffusivity in the thermocline estimated using a finescale parameterization 1 the spatial distribution of diapycnal diffusivity in the thermocline over a large area in the interior of the north pacific is obtained by incorporating the finescale vertical shear of horizontal velocity measured by expendable current profilers into the empirical formula proposed by gregg 1989 it is clearly shown that diapycnal diffusivity in the north pacific strongly depends on the latitude for example the estimated diapycnal diffusivities near the hawaiian ridge and the izu ogasawara ridge exceed 10 4 m2 s 1 whereas those near the aleutian ridge and the emperor seamounts are of the order of 0 1 10 4 m2 s 1 even though the available semidiurnal internal tidal energy is similar among all of these prominent topographic features the observed results are consistent with the numerical prediction that the cascade of internal tidal energy down to dissipation scales is dominated by parametric subharmonic instability which is expected to occur only below 30 n