on the origin of a wedge crack within the icy crust of europa 1 we suggest that a crack that developed into a wedge shaped band within the icy crust of europa at 28 s 170 w see schenk and mckinnon 1989 figure 4 prockter et al 1999 figure 1 originated under an applied compressive stress through the operation of a frictional sliding mechanism we analyze this suggestion using a scale independent sliding crack model and obtain an estimate of the maximum compressive stress to initiate the crack that compares reasonably well with earlier estimates helfenstein and parmentier 1985 mcewen 1986 greenberg et al 1998 of europan crustal stresses that are based upon elastic deformation of a shell we then show through an application of both power law dislocation creep and diffusion creep that colder near surface europan ice appears to be capable of supporting the deduced stresses with little relaxation over a period from 104 to 105 years

brittle failure of ice ice exhibits either ductile or brittle behavior depending upon the conditions under which it is loaded glaciers for instance are loaded by gravity under deviatoric stresses of 0 1 mpa or lower at temperatures of interest they flow through dislocation creep at strain rates of the order of 10 9 s 1 or lower patterson 1994 sheets of sea ice another terrestrially important ice feature are loaded predominantly by wind under global compressive stresses similar in magnitude to the shear stresses within glaciers richter menge and elder 1998 these bodies deform through a combination of creep and fracture the latter process manifested by oriented leads or open cracks and by compressive shear faults which often form as conjugate sets that traverse a large fraction of the arctic basin kwok 1999 schulson 2002 the cold icy crust of europa an extraterrestrial feature which may shield an ocean beneath within which a form of life may exist or may once have existed reynolds et al 1987 hoppa et al 1999 pappalardo et al 1999 greenberg et al 2000 kargel et al 2000 is loaded by the motion of diurnal tides and by non synchronous rotation greenberg and weidenschilling 1984 the crust deforms in a brittle manner as evident from the networks of cracks that lace through it greeley et al 2000 of the two kinds of ice deformation creep is probably the better known by readers of the geological and geophysical literature and is certainly the more fully explored and better understood the interested reader may wish to consult a number of excellent reviews of the subject e g see duval et al 1983 weertman 1983 durham and stern 2001 fracture in comparison has only recently been systematically examined the motivation with respect to terrestrial mechanics schulson 2001 comes largely

testing 87sr 86sr as a paleosalinity indicator on mixed marine brackish water and terrestrial vertebrate skeletal apatite in late paleocene early eocene near coastal sediments mississippi abstract mixed marine brackish water and terrestrial vertebrate skeletal apatite is found in the late paleocene early eocene tuscahoma and bashi formations of mississippi the co occurrence in these near coastal marine deposits of skeletal apatite with different provenances offers a unique opportunity for unraveling the effects of diagenesis on apatite 87sr 86sr composition with bearings on the use of this isotope pair as paleosalinity indicator the results show that the sr isotopes of all originally poorly ordered phases of skeletal apatite have extensively re equilibrated with pore water with significantly lower 87sr 86sr ratios than late paleocene early eocene seawater for example marine shark and ray teeth from the bashi formation all have clearly nonmarine 87sr 86sr ratios 0 7073 0 7075 compared with a coeval seawater ratio in the range 0 7077 0 7078 however separated shark tooth enamel with a high original crystallinity appears to have retained all or most of its in vivo sr isotopic signature until the present here we also show that 87sr 86sr results on recent vertebrate skeletal material from different environments are in good agreement with expected values for respective habitat earlier analyses of calcite material from the bashi formation indicated the existence of a shift in seawater 87sr 86sr to a lower value at the paleocene eocene boundary the strong influence of pore water with low nonmarine 87sr 86sr on the apatite in the bashi formation suggests that the proposed isotopic shift may be an artifact related to diagenetic processes

an experimental study of water in nominally anhydrous minerals in the upper mantle near the water saturated solidus the incorporation of water in olivine and pyroxenes interlayered within fertile lherzolite compositions was explored experimentally near the wet solidus of lherzolite at 2 5 and 4 gpa the concentrations and activities of water were varied to establish the partitioning of water between nominally anhydrous minerals nams and the hydrous minerals pargasite and phlogopite the water content in nams was determined by fourier transform infrared ftir spectroscopy the main absorption bands in nams from these experiments are very similar to those generally found in natural upper mantle peridotites olivine orthopyroxene and clinopyroxene contain 32 190 290 320 and 910 980 ppm of water under the studied conditions the partition coefficients between coexisting clinopyroxene and orthopyroxene d cpx opx are 2 7 1 1 and 3 5 1 5 at 2 5 and 4 gpa respectively whereas values for coexisting orthopyroxene and olivine d opx ol are 6 7 2 and 4 7 1 1 at 2 5 and 4 gpa respectively the storage capacity in nams in a model mantle composition close to the vapour saturated solidus water rich vapour is 190 ppm at both 2 5 and 4 gpa pargasite is the most important phase accommodating significant amounts of water in the uppermost mantle its breakdown with increasing pressure at 3 gpa at the vapour saturated solidus which is at 1025 c at 2 5 gpa results in a sharp drop in the water storage capacity of peridotite from 1000 ppm to 190 ppm h 2o at pressures 3 gpa melting in fertile lherzolite begins at the vapour saturated solidus if the bulk h 2o concentration exceeds 190 ppm the author 2012 published by oxford university press all rights reserved

apatite for destruction isotopic and geochemical analyses of bioapatites and sediments from the upper devonian escuminac formation miguasha quebec abstract the paleoenvironmental context and diagenetic history of the middle frasnian escuminac formation were investigated through geochemical rare earth elements and isotopic rb sr nd sm analyses of fossil fish material and sediments samples of sediments and bioapatite were collected from the base to the top of the escuminac formation strontium isotope ratios 87 sr 86 sr for bioapatites vary from 0 70804 to 0 70845 and overlap with frasnian seawater sr isotope compositions though most of the biogenic apatites analyzed show a variable drift from marine values toward a more radiogenic continental signature this trend is possibly the result of post mortem sr exchange between fossils and a fluid isotopically distinct from the waters in which they developed all bioapatites are heavily enriched in rare earth elements ree and display a shale normalized pattern that shows heavy ree hree depletion and a slight middle ree mree enrichment the e nd t values of the sediments range from 4 8 to 6 4 and are consistent with a sedimentary provenance derived from an appalachian source for the escuminac formation in contrast more radiogenic e nd t values ranging from 2 6 to 4 6 were obtained for the bioapatites the discrepancy between sediments and fossil material e nd t implies the presence of a second diagenetic nd reservoir for the escuminac bioapatites we propose that this reservoir reflects in part seawater the similarity between the nd isotope compositions of the escuminac fossils and late devonian conodonts from poland argues for a close connection between waters of the devonian rheic ocean and the escuminac formation collector basin

elastic properties of hydrogrossular garnet and implications for water in the upper mantle the single crystal elastic properties of a hydrous silicate garnet hibschite ca 3al 2 sio 4 1 72 h 4o 4 1 28 were measured using brillouin spectroscopic techniques the adiabatic bulk modulus of hibschite k s 99 8 1 0 gpa and the shear modulus 64 3 0 5 gpa are 40 lower than the bulk and shear moduli for anhydrous grossular garnet ca 3al 2 sio 4 3 this increased compressibility of hydrogarnet is attributed to increased hydrogen bonding with pressure in the h 4o 4 tetrahedron density considerations indicate that hydrogarnet is likely to be stable relative to an assemblage with h 2o as a separate phase throughout the upper mantle and probably the transition zone assuming garnet to be the sole repository for mantle water the seismic wave velocities of a wet eclogitic layer are 6 8 lower than those of dry eclogite a hydrated eclogitic layer several times thicker than the oceanic crust would probably be required for a water rich region of the mantle to be seismologically detectable lesser quantities of mantle water than those implied by the above scenario may be invisible to seismic techniques

high resolution strontium isotope stratigraphy across the cambrian ordovician transition we have analyzed 214 fossil apatite samples from nine stratigraphic sections worldwide that cover the lower cambrian to lower ordovician for their strontium isotope ratios of these samples 180 from six sections that cover the cambrian ordovician transition 5 ma reveal how the extent of isotopic alteration can differ greatly according to lithology and sample type from three limestone sections 126 euconodont samples yield the most consistent 87sr 86sr ratios and are used in this article to constrain seawater 87sr 86sr across the cambrian ordovician boundary by contrast protoconodonts paraconodonts and inarticulate brachiopods are far less likely to retain a primary 87sr 86sr signature and appear to be of only limited value for chemostratigraphy seawater 87sr 86sr fell from maximum values for the phanerozoic of more than 0 7092 during the early late cambrian to 0 7090 by the earliest ordovician high resolution sampling has permitted the recognition of sinusoidal variations with a wavelength on the order of 1 ma that are superimposed on the overall fall in 87sr 86sr these variations may be caused by high order cycles in seawater 87sr 86sr or diagenetic alteration

water content in natural eclogite and implication for water transport into the deep upper mantle abstract infrared spectroscopy and ion micro probe measurements showed that the major constituent minerals of eclogites from the kokchetav massif which have been subducted to 180 km depths contain significant amounts of water up to 870 ppm h 2 o by weight in omphacite 130 ppm h 2 o in garnet and 740 ppm h 2 o in rutile omphacite shows three hydroxyl absorption bands at 3440 3460 3500 3530 and 3600 3625 cm 1 garnet has a single band at 3580 3630 cm 1 and rutile has a single sharp band at 3280 cm 1 the hydroxyl absorbance at these wavenumbers changes with the crystal orientation in polarized infrared radiation indicating that the water is structurally incorporated in these minerals the water contents in omphacite and garnet increase systematically with the metamorphic pressure of the host eclogites the partitioning coefficient of the water content between coexisting garnet and omphacite is similar in different eclogites d grt omp 0 1 0 2 but decreases slightly at high pressure based on the mineral proportions of the eclogites we estimate bulk rock water content in the eclogites ranging from 3070 to 300 ppm h 2 o by weight although hydrous minerals are absent in the diamond grade eclogite 60 kbar and 1000 c trace amounts of water are incorporated in the nominally anhydrous minerals such as omphacite and garnet the presence of significant water in these minerals implies that the subducting oceanic crust can transport considerable amounts of water into the deep upper mantle beyond the stability of hydrous minerals such water may be stored in the deep upper mantle and have an important influence on dynamics in the earth s interior

effect of water on rheological properties of garnet at high temperatures and pressures abstract the effect of water on the rheological properties of garnet was investigated with triaxial compressive creep experiments at high temperatures 1223 t 1423 k and high pressures 1 6 p 5 6 gpa using a deformation dia d dia apparatus samples fabricated from a natural polycrystalline garnet pyr 23 alm 20 gro 57 together with samples prepared from san carlos olivine were deformed under water saturated conditions with water supplied by the dehydration of talc during the experiments experiments were carried out on a synchrotron x ray beamline in each experiment differential stress and sample displacement were determined using synchrotron x ray diffraction and time resolved radiography techniques respectively water fugacity was calculated based on equation of state for water at experimental p t conditions a fit of our experimental results on the creep of garnet samples to a power law demonstrates strong dependencies of strain rate on water fugacity with a water fugacity exponent of r 1 and on pressure with an activation volume of v 28 10 6 m 3 mol importantly under water saturated conditions the water content of deformed garnet samples measured by infrared spectroscopy increases with increasing pressure i e increasing water fugacity up to an average value of 21 000 h 10 6 si at 3 0 gpa and then decreases with increasing pressure down to 3000 h 10 6 si at 5 6 gpa the flow law for garnet quantified in this study provides an important constraint on the strength of the subducted oceanic crust for a water enriched environment the viscosity of a garnet rich layer will be low above the shallow upper mantle because the water content in garnet increases with increasing pressure at relatively low pressures however at greater depth the viscosity will be high because the direct effect of pressure on the creep through thermally activated processes outweighs the indirect effect on the creep through water solubility

across column cracks and axial splits in s2 saline ice under compression experiments on plate like specimens have established that across column cracks form within s2 columnar salt water ice when compressed uniaxially along a direction inclined to the long axis of the grains wing cracks initiate from the across column cracks and lengthen into axial splits when the ice is rapidly deformed correspondingly the macroscopic behavior changes from ductile to brittle the across column cracking is attributed to grain boundary sliding and the splitting to the suppression of crack tip creep

oriented quartz calcic amphibole inclusions in omphacite from the saualpe and pohorje mountain eclogites eastern alps an assessment of possible formation mechanisms based on ir and mineral chemical data and water storage in eastern alpine eclogites abstract the composition of mineral phases and their modal proportions have been determined for three representative eoalpine eclogites from the saualpe type locality eastern austria sample skp31 and the pohorje massif slovenia cm31 03 and cm15 01 using electron microprobe laser icp ms ir spectroscopy and modal analysis to evaluate possible mechanisms for the formation of composite oriented calcic amphibole quartz inclusions cois in omphacite and to assess the relative importance of hydrous and nominally anhydrous phases as h 2 o carriers in these eclogites for omphacites in cm31 03 with a zonal distribution of cois a comparison of water and trace element concentrations of areas containing cois and those free of cois and a comparison with the trace element concentration of calcic amphibole indicate that cois have formed through an open system alteration of clinopyroxene and not through a closed system exsolution process in sample skp31 both textural and mineral chemical evidence suggests that cois did not form by exsolution involving a ca eskola component in clinopyroxene but formed by progressive growth under eclogite facies p t conditions and prior to the onset of retrogressive symplectite formation analogous to the formation of poikiloblastic quartz calcic amphibole grains in the matrix bulk h 2 o contents of the eclogites are between ca 750 and 2150 ppm with 6 25 of the total water contributed by nominally anhydrous minerals nams because of high modal amounts of 37 65 omphacite is the major nominally anhydrous water carrier containing 145 580 ppm h 2 o with significant concentration variations on a thin section scale due to their very low h 2 o concentrations of 2 o content calcic amphibole forming part of cois may be a major carrier of h 2 o as evidenced by cm31 03 containing both cois and texturally primary calcic amphibole in this sample calcic amphibole of the cois contributes 63 whereas primary calcic amphibole only accounts for 13 of the bulk water the relative order of h 2 o concentrations in nams is h 2 o rutile h 2 o omphacite h 2 o garnet for cm31 03 and cm15 01 and h 2 o rutile h 2 o omphacite h 2 o garnet in skp31

an experimental investigation of hydroxyl solubility in jadeite and na rich clinopyroxenes the solubility and incorporation mechanisms of water in synthetic water saturated jadeite and na rich clinopyroxenes have been experimentally investigated infrared spectra for water saturated jadeite synthesised from 2 0 to 10 gpa show two prominent sharp peaks at 3 373 and 3 613 cm 1 together with several weaker features in the oh stretching region indicating that there are at least 5 distinct modes of hydrogen incorporation in the structure water solubility in pure jadeite reaches a maximum of about 450 ppm by weight at 2 gpa and slowly decreases with increasing pressure to about 100 ppm at 10 gpa solubility can be described by the function coh a fh2o0 5 exp p vsolid rt where coh is water solubility in ppm h2o by weight a is 7 144 ppm bar0 5 fh2o is water fugacity and vsolid 8 019 cm3 mol is the volume change of the clinopyroxene upon incorporation of oh jadeite provides a good model for understanding hydrogen incorporation mechanisms in more complex omphacite compositions assignment of absorption bands in ir spectra verifies the importance of cation vacancies on the m2 site in providing mechanisms for hydrogen incorporation however results also suggest that substitution of lower valency cations onto the m1 site may also be important solid solution of jadeite with diopside and in particular with ca eskola component leads to a drastic increase of water solubility and the bulk composition has a more important effect on the capacity of omphacite to store water than pressure and temperature omphacite is expected to be the major carrier of water in a subducted eclogite after the breakdown of hydrous minerals

oriented inclusions of pyroxene amphibole and rutile in garnet from the luliangshan garnet peridotite massif north qaidam uhpm belt nw china an electron backscatter diffraction study

the retention of primary oxygen isotope compositions of fossil elephant skeletal phosphate fossil elephant remains from sediments of plio pleistocene age in the vicinity of lake turkana kenya provide insights into the ability of the phosphate oxygen system to preserve original 18o values 18op in the depositional environment individual fossil specimens exhibit systematic variations in the 18op values of their various tooth and bone components differences in 18op values between these skeletal components can be as high as 3 6 despite the fact that equivalent phases for individual modern elephants have 18op values which vary by less than 0 6 xrd traces of the different skeletal phases of modern and fossil samples also infer differential preservation of primary apatite crystallinities among the various fossil phases fossil samples of dentine cementum and bone have x ray spectra with sharper and more intense peaks compared to their modern counterparts but little change in crystallinity is observed for fossil enamel samples a model based on the premise that the enamel phase preserves primary isotope signatures and that the accompanying skeletal phases are partially re equilibrated with the fluids associated with the microbial decomposition of the elephant s carcass is consistent with the features of the 18op dataset this isotopic evidence in conjunction with the physical and chemical attributes of enamel has led us to postulate that enamel could be preserving primary isotope signatures while other skeletal components are affected to varying degrees by alteration processes in the burial environment

isotopic composition of recent shark teeth as a proxy for environmental conditions abstract the o c and sr isotope compositions of teeth from ten species belonging to five families and three orders of sharks were measured to determine the influence of habitat diet and possible species specific fractionation effects on the isotopic composition of biogenic phosphate from fish the sharks were recently caught in subtropical waters off the kwazulu natal kzn coast of south africa as well as from cold waters in prince william sound pws alaska and victor bay vb nunavut canada 18 o values of tooth phosphate 18 o p range from 20 9 to 23 5 for the kzn sharks for most species the range in measured 18 o p values is about 0 6 but it may be as high as 1 1 for different teeth from a single shark dentine and enameloid within individual teeth have no apparent differences in 18 o p values the 18 o p values of the kzn shark teeth reflect the typical habitat of the studied species primarily the thermal structure of the water column off kzn at depths between 20 and 280 m the 18 o p values of teeth from different greenland sharks from vb and pacific sleeper sharks from pws are very homogeneous averaging 25 8 and 24 7 respectively these values appear to be in equilibrium with deep 500 m ocean waters in each case at temperatures of about 0 3 c or less there is little discernable evidence for species specific fractionation effects for the oxygen isotope composition of phosphate in the studied marine fish the oxygen isotope composition of carbonate in apatite averages about 9 1 higher than corresponding 18 o p values in agreement with equilibrium fractionation between carbonate and phosphate but with a large variance 1 1 5 18 o c values also vary by up to 1 between enameloid and dentine within single teeth but in a non systematic way differences in 13 c values between carbonate in enameloid and dentine is also large up to 8 but the 13 c values vary systematically enameloid is always enriched in 13 c compared to dentine and the 13 c content increases with developmental stage of the teeth 13 c values measured for enameloid 1 6 to 4 8 appear to approach equilibrium with dissolved inorganic carbon in seawater in contrast 13 c values for dentine range from 6 4 to 2 3 for kzn sharks and 9 0 to 10 8 for the cold water sleeper sharks and are compatible with a predominantly dietary carbon source the 87 sr 86 sr ratios of teeth from kzn sharks as well as those from pws and vb are uniform averaging 0 709167 sr content varies from 1270 to 2100 ppm a range that is similar to that in well preserved fossilized teeth seawater sr is thus clearly incorporated in vivo concentrations of sm and nd are in the ppb range and contrast the ppm range in fossilized teeth indicating a postmortem incorporation of rare earth elements in apatite of the teeth

fluid regime in continental subduction zones petrological insights from ultrahigh pressure metamorphic rocks abstract intensive studies of ultrahigh pressure uhp metamorphic rocks in continental collision zones have provided petrological insights into the fluid regime during subduction and exhumation recent studies in the dabie sulu orogen of china have made important contributions to understanding fluid action in such systems hence these rocks are the main focus of this review sources of metamorphic fluid can be deduced from study of hydrous minerals structural hydroxyl and molecular water in nominally anhydrous minerals fluid and solid inclusions of uhp metamorphic minerals are also a record of fluid action in deep subduction zones the presence or absence of metamorphic fluid during subduction and exhumation dictates zircon growth and recrystallization making available materials for u pb dating isotopic dating demonstrates that after peak uhp metamorphism retrograde fluid with deuteric origin became active the decomposition of hydrous minerals and the exsolution of molecular water and structural hydroxyl during exhumation can provide sufficient amounts of aqueous fluid for quartz veining and amphibolite facies retrogression within uhp slabs aqueous fluid released by the exsolution of molecular water and structural hydroxyl from uhp nominally anhydrous minerals is characterized by low salinity and light hydrogen and oxygen isotope compositions therefore one part of the uhp slab is a source of aqueous fluid whereas another part is a sink in both cases the fluid action during subduction and exhumation is episodic rather than continuous supplementary material a description of the dabie sulu uhp metamorphic rocks analytical methods la icpms zircon u pb isotope data and rare earth element compositions are available at http www geolsoc org uk sup18355

geochemistry and trace element behaviors of eclogite during its exhumation in the xitieshan terrane north qaidam uhp belt nw china abstract the xitieshan terrane located in the central part of the north qaidam ultrahigh pressure uhp metamorphic belt china is mainly composed of orthogneiss and paragneiss and a few intercalated eclogite layers and boudins based on their bulk rock tio 2 contents the eclogites can be subdivided into a high ti group tio 2 2 and a low ti group tio 2 e nd t and restricted i sr values and therefore provide further evidence for the formation of the protoliths of the eclogites in an oceanic environment on the other hand the sr nd isotopes of high ti eclogites show mainly positive but also some negative e nd t values and relatively broadly distributed i sr values indicating minor crustal contamination of the ocean floor basalts considering available 750 877 ma protolith ages preserved in zircon cores it is inferred that some of the eclogites derived from neoproterozoic protoliths were emplaced onto the crust far ahead of the paleozoic deep subduction while the other eclogites originate from a different oceanic crust e g the paleo qilian ocean indicating multiple orogenies in the geological history of the xitieshan terrane china whole rock and in situ la icp ms mineral trace element analyses of eclogites revealed two stages of fluid behavior during retrogression that correspond to the two exhumation stages uncovered by phase equilibrium calculations the mineral scale trace element distributions and trace element inheritance of newly formed amphibole from its precursors indicate that at the peak metamorphic stage m1 and at the earlier eclogite facies overprint m2 the fluid was internally controlled by the rock itself within a mafic lens the amount of water soluble elements e g rb sr ba u pb and lree observed in the whole rock compositions as well as in amphiboles increases from the core phengite bearing eclogite to the rim amphibolite and implies an external fluid source for the amphibolite facies retrogression m3 which should be helpful for the final exhumation of uhp eclogite

experimental investigation of eclogite rheology and its fabrics at high temperature and pressure eclogite plays an important role in mantle convection and geodynamics in subduction zones an improved understanding of processes in the deeper levels of subduction zones and collision belts requires information on eclogite rheology however the deformation processes and associated fabrics in eclogite are not well understood incompatible views of deformation mechanism have been proposed for both garnet and omphacite we present here deformation behaviour of eclogite at temperatures of 1027 1427 c confining pressures of 2 5 3 5 gpa and strain rates of 1 10 5 s 1 to 5 10 4 s 1 we obtained a power law creep for the high temperature and pressure deformation of a dry eclogite 50 vol garnet 40 omphacite and 10 quartz with a 103 3 1 0 n 3 5 0 4 e 403 30 kj mol 1 and v 27 2 cm3 mol 1 the two principal minerals of eclogite have greatly different strengths progressive increase of garnet results in a smooth increase in strength analysis by electron back scattered diffraction shows that 1 garnet displays pole figures with near random distributions of misorientation angle under both dry and wet conditions 2 omphacite shows pronounced lattice preferred orientations lpos suggesting a dominant dislocation creep mechanism further investigation into the water effects on eclogite show 3 water content does not influence the style of omphacite fabric but increases slightly the fabric strength 4 grain boundary processes dominate the deformation of garnet under high water fugacity or high shear strain conditions yielding a random lpo similar to that of non deforming garnet despite the strong shape preferred orientation spo observed 110 001 slip may dominate the deformation of rutile quartz displays complicated and inconsistent lpos in eclogite these results are remarkably similar to observations from deformed eclogites in nature

crystal structure refinement of na bearing clinopyroxenes from mantle derived eclogite xenoliths nine omphacitic clinopyroxenes with a jadeitic content between 25 and 57 from the udachnaya and zagadochnaya diamond bearing kimberlites were investigated using single crystal x ray diffraction electron microprobe analysis and mossbauer and infrared spectroscopy crystal structure refinements incorporating constraints from chemical analyses and mossbauer data show a significant concentration of vacancies at the m2 site in three of the samples the cell volumes of the non stoichiometric samples plot below the linear trend defined by stoichiometric diopside jadeite compositions where the deviation from the linear trend is positively correlated with the concentration of vacancies charge balance appears to be achieved primarily through substitution of al3 for mg2 on the m1 site which causes a contraction of the m1 site volume compared to stoichiometric clinopyroxenes with the same composition vacancies are not associated with oh incorporation as the sample with the highest concentration of vacancies contains only 89 ppm wt h2o significant hydrogen loss through iron oxidation during ascent is ruled out based on the low fe3 concentrations h content in omphacite samples from kimberlites could provide a sensitive tool for determining f h2o during diamond formation

preservation of successive diagenetic stages in middle triassic bonebeds evidence from in situ trace element and strontium isotope analysis of vertebrate fossils abstract bonebeds comprise reworked and time averaged constituents of different phosphatic vertebrate remains and hence provide an ideal substrate for the study of long and short term diagenetic processes to test whether trace elements u sr ree and 87 sr 86 sr ratios can be used for distinguishing between successive diagenetic signals we performed geochemical analyses on vertebrate remains bones teeth scales and coprolites from two triassic bonebeds located near palzem germany trace element analysis was done on 170 vertebrate remains by la icp ms while 87 sr 86 sr ratios were determined for 39 bioclasts using la mc icp ms although a low inter and intra bioclast ree variability indicates long term open system behaviour the observed ree patterns suggest the preservation of different diagenetic stages a distinct difference in the geochemical composition exists between dark luminescent sem cl domains and greyish ones dark domains represent dense diagenetically more resistant material of low porosities such as enamel and ganoine these domains display distinctly lower ree contents and a higher inter clast variability than those of various grey tones together with lower hence more seawater like 87 sr 86 sr ratios this argues for a preservation of an earlier diagenetic signal notably most dark domains are characterised by negative eu anomalies while all grey ones display positive eu anomalies with the exception of eu both domains display almost identical ree patterns with different concentrations indicating that late diagenetic ree uptake is not necessarily accompanied by fractionation processes in vertebrate bioclasts negative eu anomalies are most likely inherited from eu depleted surface waters possibly as a result of eu depleted aeolian input conversely positive eu anomalies were presumably affected by eu enriched late diagenetic fluids with a possible high temperature origin causing a fractionation of europium our study therefore demonstrates the potential of high resolution geochemical analysis in bonebed strata to disentangle different stages of diagenesis and to detect least altered areas in vertebrate fossils for recovering pristine palaeoenvironmental signals

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

quantitative analysis of trace oh in garnet and pyroxenes to calibrate infrared ir spectroscopy for quantitative analysis of trace structural oh in specific minerals we have determined concentrations of h in pure separates of mantle derived pyrope garnet 56 6 ppm h 2o by weight augite 268 8 ppm h 2o and enstatite 217 11 ppm h 2o by manometry after heating the samples and extracting h 2 gas under vacuum ir spectroscopy confirmed the presence of intrinsic oh in these samples prior to extraction and indicated between 86 and 100 removal of h during the extraction procedure the integral specific absorption coefficients of 1 39 0 14 l 7 09 0 32 and 15 6 0 94 ppm h 2o cm 2 for pyrope augite and enstatite respectively allow precise spectroscopic determination of the oh content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million uncertainties in accuracy depend on mineral composition and characteristics of the oh absorption spectrum and are estimated to range between 10 and 50

sodic amphibole exsolutions in garnet from garnet peridotite north qaidam uhpm belt nw china implications for ultradeep origin and hydroxyl defects in mantle garnets two types of amphibole exsolution lamellae were discovered in garnet from a few garnet peridotites from the north qaidam ultrahigh pressure metamorphic belt northern tibet nw china the amphibole lamellae are strictly oriented in four directions corresponding to the isometric form 111 i e octahedron planes of garnet observations by transmission electron microscopy tem show that amphibole lamellae are topotaxtially concordant with the host garnet and possess 9 8 to 10 a lattice c spacing electron microprobe analysis reveals that these exsolved amphibole lamellae are high in na and ti the tem observations and recalculated compositions indicate that the oriented amphibole lamellae exsolved from original supersilicic majorites with high concentrations of na2o 0 3 wt and hydroxyl up to 1000 ppm by weight these results imply that the host garnet peridotites were formed at depths greater than 200 km and that garnet can be an important reservoir of water at such depths in the mantle

hydroxyl defects in garnets from mantle xenoliths in kimberlites of the siberian platform a suite of more than 200 garnet single crystals extracted from 150 xenoliths covering the whole range of types of garnet parageneses in mantle xenoliths so far known from kimberlites of the siberian platform and collected from nearly all the kimberlite pipes known in that tectonic unit as well as some garnets found as inclusions in diamonds and olivine megacrysts from such kimberlites were studied by means of electron microprobe analysis and single crystal ir absorption spectroscopy in the voh vibrational range in search of the occurrence energy and intensity of the voh bands of hydroxyl defects in such garnets and its potential use in an elucidation of the nature of the fluid phase in the mantle beneath the siberian platform the voh single crystal spectra show either one or a combination of two or more of the following major voh bands i 3645 3662 cm 1 ii 3561 3583 cm 1 iii 3515 3527 cm 1 and minor bands ia 3623 3631 cm 1 iia 3593 3607 cm 1 the type of combination of such bands in the spectrum of a specific garnet depends on the type of the rock series of the host xenolith mg mg ca ca mg fe or alkremite on the xenolith type as well as on the chemical composition of the respective garnet nearly all garnets contain band systems i and ii band system iii occurs in ti rich garnets with wt tio2 ca 0 4 from xenoliths of the mg ca and mg fe series only the voh spectra do not correspond to those of oh defects in synthetic pyropes or natural ultra high pressure garnets from diamondiferous metamorphics there were no indications of voh from inclusions of other minerals within the selected 60 60 m measuring areas in the garnets the voh spectra of pyrope knorringite and pyrope knorringite uvarovite rich garnets included in diamonds do not show band systems i to iii instead they exhibit one weak broad band voh 200 460 cm 1 near 3570 cm 1 a result that was also obtained on pyrope knorringite rich garnets extracted from two olivine megacrysts the quantitative evaluation on the basis of relevant existing calibrational data bell et al 1995 of the sum of integral intensities of all voh bonds of the garnets studied yielded a wide range of water concentrations within the set of the different garnets between values below the detection limit of our single crystal ir method near 2 10 4 wt up to 163 10 4 wt the water contents vary in a complex manner in garnets from different xenolith types obviously depending on a large number of constraints inherent in the crystal chemistry as well as the formation conditions of the garnets during the crystallization of their mantle host rocks secondary alteration effects during uplift of the kimberlite play if any only a minor role despite the very complex pattern of the water contents of the garnets preventing an evaluation of a straightforward correlation between water contents of the garnets and the composition of the mantle s fluid phase during garnet formation at least two general conclusions could be drawn 1 the wide variation of water contents in garnets is not indicative of regional or local differences in the composition of the mantle s fluid phase 2 garnets formed in the high pressure high temperature diamond pyrope facies invariably contain significantly lower amounts of water than garnets formed under the conditions of the graphite pyrope facies this latter result 2 may point to significantly lower fh2o and fo2 in the former as compared to the latter facies

paleoceanography of the late cretaceous maastrichtian western interior seaway of north america evidence from sr and o isotopes abstract well preserved fossils of the late cretaceous western interior seaway wis of north america have been analyzed for sr concentration and sr and o isotopes in order to decipher paleosalinities and paleotemperatures the samples are from four biofacies within the seaway late maastrichtian offshore interior pierre shale nearshore interior fox hills formation brackish reduced salinity fox hills formation and freshwater hell creek formation samples were also obtained from the severn formation of maryland considered to be representative of the open ocean all biofacies except the freshwater are demonstrably within the jeletzkytes nebrascensis ammonite zone 87 sr 86 sr ratios show significant and systematic decreases from marine mean 1 s d 0 707839 0 000024 to brackish facies mean 1 s d 0 707677 0 000036 consistent with dilution by freshwater with a lower 87 sr 86 sr ratio than seawater such variation disallows using the 87 sr 86 sr ratios of fossil shell material to assign ages to fossils from the late cretaceous wis without knowledge of the salinity in which the organism grew the sr isotope ratios for scaphitid ammonites within a single biofacies are similar to each other and different from those for scaphites in other biofacies implying that these organisms are restricted in their distribution during life the 87 sr 86 sr values of freshwater unionid mussels range widely and are not compatible with the freshwater endmember 87 sr 86 sr ratio required by the trend in 87 sr 86 sr vs biofacies established from the other samples paleosalinities for the biofacies are estimated to range from 35 in the open marine to a minimum of 20 in the brackish based on the presence of cephalopods in all four facies and the known salinity tolerance of modern cephalopods producing reasonable 87 sr 86 sr values for the freshwater endmember of a 87 sr 86 sr vs 1 sr plot requires a sr concentration 0 2 0 5 that of seawater for the dominant freshwater input to the wis such high sr concentrations relative to seawater are not observed in modern rivers and we suggest that the brackish environment in the wis arose through the mixing of freshwater and seawater in a nearshore aquifer system reactions of the solution with aquifer solids in this subterranean estuary moore mar chem 65 1999 111 125 produced brackish water with the sr concentration and isotopic composition recorded in the brackish biofacies 18 o values of the fossils show decreases from the marine to brackish biofacies consistent with increasing temperatures from 13 to 23 c or if temperatures were relatively constant to a decrease in the 18 o of the water in which the shell formed the latter interpretation is consistent with less than fully marine salinities in the nearshore biofacies but both changes in temperature and the isotopic composition of the water may have occurred in this environment

testing a potential mantle geohygrometer the effect of dissolved water on the intracrystalline partitioning of al in orthopyroxene the presence of water in the earth s mantle has wide ranging implications and a detailed picture of the spatial and temporal distribution of water in the mantle is needed to be able to understand fundamental global scale processes however the interpretation of measured water concentrations in nominally anhydrous minerals nams from xenoliths or magmatic phenocrysts is complicated by fast diffusion of h and hence the probability of hydration or dehydration during ascent rauch and keppler 1 m rauch h keppler water solubility in orthopyroxene contrib mineral petrol 143 2002 525 536 have proposed that the partitioning of al between octahedral and tetrahedral sites in orthopyroxene has the potential to be used as a more reliable mantle geohygrometer than direct measurements of water concentrations in xenolith minerals in the present study we have tested the theoretical basis for this geohygrometer by experimentally producing aluminous orthopyroxene samples and measuring the intracrystalline partitioning of al using very high field 27al magic angle spinning nuclear magnetic resonance in both dry and hydrous orthopyroxene aluminium is shown to be incorporated by a tschermak s substitution one tetrahedral and one octahedral al thus the incorporation mechanism of al in orthopyroxene is not a valid basis for a geohygrometer however the effect of oh on the local environment of al has been observed and quantification of all the different types of al in the hydrous samples suggests that oh is incorporated by protonation of o21 and o22 sites the results suggest that nmr studies on nuclei other than 1h offer new possibilities for studying the interaction of water with mantle minerals 2005 elsevier b v all rights reserved

definition and global correlation of the santonian campanian boundary review of biostratigraphical evidence from different regions shows that criteria used by workers on various marine fossil groups to define the santonian campanian boundary differ considerably in relative age and position probably the most widely recognizable of these criteria is the extinction of the distinctive crinoid marsupites testudinarius north america europe asia north africa australia which coincides exactly with two separate definitions of the boundary appearances of the ammonite placenticeras bidorsatum and the belemnite gonioteuthis granulataquadrata and may also coincide with a third entry of the planktic foraminiferan globotruncana elevata a comparison of evidence from upper santonian and lower campanian successions in widely separated regions allows us to place a series of important biostratigraphical markers in correct order defining the boundary at the extinction of m testudinarius corresponds to a 87sr 86sr of 0 707479 and a small positive excursion in 13c the base of magnetochron 33r generally considered to coincide with or fall just above the base of the campanian is shown to lie within the upper santonian uintacrinus socialis zone

strontium isotope stratigraphy potential resolution and event correlation abstract a new generation 87sr 86sr isotope curve for the phanerozoic seawater based on a compilation of 3635 stratigraphically well defined and well preserved skeletal components results in a substantially narrower band with some discrepancies if compared to the curve of burke et al 1982 which is based mostly on whole rock samples the results obtained from low mg calcite shells foraminifers belemnites brachiopods and oysters are mostly superior to those from phosphatic skeletal components such as conodonts even if the latter are exceptionally well preserved cai 1 5 at this stage the phanerozoic data set based on fossils is patchy for the cambrian upper ordovician lower devonian and upper carboniferous triassic intervals the major practical constraint that precludes delineation of an unequivocal sr isotope curve for the phanerozoic seawater is the uncertainty in the assignment of absolute ages to the samples as a result the curve is in reality a band this is a reflection of the limitations of biostratigraphy and geochronology that are inherited by any derivative correlation and dating technique including isotope stratigraphy it is therefore unlikely that in the near future the sr isotope stratigraphy will surpass the resolution capability of biostratigraphy as a global correlation tool on the other hand if complemented by lithostratigraphy it is potentially a valuable tool for correlation of sequences on intrabasinal and regional scales taking into account the above limitations careful consideration must be given to assignment of higher order isotope peaks to specific events within a biozone and to the use of such events as a global correlation tool

water contents of roberts victor xenolithic eclogites primary and metasomatic controls a suite of eclogites from the roberts victor kimberlite has been extensively characterized in terms of petrology and geochemical compositions greau et al in geochim cosmochim acta 75 22 6927 6954 2011 huang et al in lithos 142 143 161 181 2012a in the present study the water contents of eclogitic garnet and omphacite were analyzed by fourier transform infrared spectrometry garnet does not contain measureable oh in any sample the water content of omphacite in the studied eclogites ranges from 211 to 1 496 ppm mantle metasomatism has modified the water content of some of the eclogites while others retain water contents characteristic of their original environment the oh contents of the metasomatized eclogites may be mainly controlled by the h2o fugacity and mineral compositions the oh contents of the non metasomatized samples are interpreted to be more sensitive to their mantle equilibration temperature pressure and the local fugacities of h2o and o2 the calculated water content of the metasomatic medium is similar to that of carbonatitic kimberlitic melts fluids eclogites contain more water than peridotites recorded in the literature 341 161 vs 122 54 ppm and represent an important water reservoir in the lithospheric mantle wherever they occur this is an important parameter to be considered in the interpretation of mantle processes and geophysical data such as seismic wave speeds and electrical conductivity and in geodynamic modeling

oligocene and pliocene interglacial events in the antarctic peninsula dated using strontium isotope stratigraphy strontium isotope stratigraphy is used to date two interglacial marine deposits in the antarctic peninsula region on king george island interglacial pectinid rich sediments in the low head member of the polonez cove formation give a strontium isotope stratigraphy age of 29 0 0 7 0 6 to 29 8 0 8 0 7 ma mid oligocene which in conjunction with previous k ar dating of volcanic rocks indicates a glacial episode in the antarctic peninsula between middle eocene 42 0 1 0 ma and mid oligocene time in addition an inter glacial deposit pecten conglomerate from tectonically elevated exposures on cockburn island is dated as pliocene 3 5 5 3 ma published data suggest these latter sediments were deposited under shallow marine conditions which were warmer than those of present day antarctica

h2o contents and d h ratios of nominally anhydrous minerals from ultrahigh pressure eclogites of the dabie orogen eastern china abstract garnet and omphacite from ultrahigh pressure eclogites from the dabie orogen eastern china were investigated by micro ftir the results show that all garnet and omphacite grains contain structural water occurring as hydroxyl oh with h2o contents varying from 14 to 1915 ppm h2o wt and from 105 to 695 ppm respectively within the same sample the water contents are either homogeneous at the grain scale or vary systematically from higher in the core to lower in the rim low water contents at crystal rims possibly result from hydroxyl exsolution after pressure decrease upon rock exhumation the d values of omphacites are between 108 4 and 114 2 and independent of water contents heterogeneous water contents of garnet occur at the centimeter scale and fluid mobility during uhp metamorphism was very limited the estimated whole rock water content based on mineral h2o contents is between 260 and 750 ppm thereby implying that eclogitic rocks formed during continental subduction have the potential to recycle at least several hundreds ppm water to mantle depths the preserved chemical differences likely indicate that the eclogitic rocks resided at mantle conditions for a limited time span and imply that they were exhumed shortly after subduction the water released during decompression might represent the early stage retrograde fluid

micro and nano size hydrogrossular like clusters in pyrope crystals from ultra high pressure rocks of the dora maira massif western alps the supracrustal metamorphic rocks of the dora maira massif western alps have been intensively studied certain ultra high pressure lithologies contain coesite and nearly end member composition pyrope mg3al2si3o12 making this locality petrologically and mineralogically unique structural oh loosely termed water in pyrope crystals of different composition has been investigated numerous times using different experimental techniques by various researchers however it is not clear where the minor oh is located in them ir single crystal spectra of two pyropes of composition mg2 79 fe2 0 15 ca0 04 2 98 al 2 02 si 2 99o12 and mg2 90 fe2 0 04 ca0 02 2 96 al 2 03 si 3o12 were recorded at room temperature rt and 80 k the spectra show five distinct oh bands located above 3600 cm 1 at rt and seven narrow bands at 80 k and additional fine structure the spectra were curve fit and the oh stretching modes analyzed and assigned it is argued that oh is located in microscopic and nano size ca3al2h12o12 like clusters the basic substitution mechanism is the hydrogarnet one where h4o4 4 sio4 4 and various local configurations containing different numbers of h4o4 4 groups define the cluster type the amounts of h2o range between 5 and 100 ppm by weight depending on the ir calibration adopted and are variable among crystals hydrogrossular like clusters are also present in a synthetic pyrope with a minor ca content grown hydrothermally at 900 c and 20 kbar as based on its ir spectra at rt and 80 k experiment and nature are in agreement and oh groups are partitioned into various barely nano size hydrogrossular like clusters this proposal is new and significant mineralogical petrological and geochemical implications result ca and proton ordering occur hypothetical defect and or coupled substitution mechanisms to account for structural oh are not needed to interpret experimental results oh incorporation in pyrope of different generations at dora maira is discussed and oh could potentially be used as an indicator of changing p text h text 2 text o text a text h text 2 text o text t conditions in a metamorphic cycle published experimental hydration dehydroxylation and hydrogen diffusion results on dora maira pyropes can now be interpreted atomistically

transportation of h2o beneath the japan arcs and its implications for global water circulation abstract in order to understand the transportation and circulation of h2o in subduction zones geological and seismological observations and the corresponding quantitative modeling are reviewed and consolidated with a special emphasis on the japan arcs the japan arcs are ideal for such a study in that 1 they are very active magmatically and seismically with abundant high quality observations and 2 subduction parameters change significantly along the japan arcs allowing one to investigate how the variations of input parameters affect the resultant structures and processes first numerical models for the transportation of h2o and melting are introduced the generation and migration of aqueous fluid its interaction with the convecting solid and melting are considered based on the realistic phase relationships of the peridotitic and basaltic systems application of the models to the japan arcs and comparison between the model results and the observations distribution of volcanoes and seismic structures along the japan arcs are then discussed the three cases from the ne central and sw japan arcs clarify the following points first an aqueous fluid released from the subducting oceanic crust forms a serpentinite layer in the mantle wedge just above the subducting slab maintaining a condition close to equilibrium in terms of hydration dehydration reactions during aqueous fluid migration second most of the h2o is subducted to a depth where serpentine and chlorite in the serpentinite layer break down this depth depends on the thermal structure of the slab and is greater for the older plate beneath the japan arcs as a consequence aqueous fluid and melt are in general not supplied straight upward to the volcanic front this result is rather different from the conventional view finally based on the understanding obtained from the japan arcs the global budget and circulation of h2o are discussed even after the completion of dehydration of major hydrous mineral phases in the subducting materials especially at the base of the mantle wedge just above the subducting slab nominally anhydrous phases of the upper mantle assemblage i e olivine pyroxenes garnet can carry a significant amount of h2o 1 1 1011 to 7 8 1011 kg yr 1 into the deep mantle the minimum estimate is comparable to the outflow of h2o from the mantle at mid ocean ridges and hotspots while the maximum estimate greatly exceeds it the large estimated range is mainly due to the uncertainty of the maximum h2o contents in the nominally anhydrous minerals of the upper mantle which controls the net influx of h2o into the deep mantle through subduction zones water subduction magmatism global circulation

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

migration of sharks into freshwater systems during the miocene and implications for alpine paleoelevation trace element and isotopic compositions of fossilized shark teeth sampled from miocene marine sediments of the north alpine molasse basin the vienna basin and the pannonian basin generally show evidence of formation in a marine environment under conditions geochemically equivalent to the open ocean in contrast two of eight shark teeth from the swiss upper marine molasse locality of la moliere have extremely low 18o values 10 3 and 11 3 and low 87sr 86sr ratios 0 707840 and 0 707812 compared to other teeth from this locality 21 1 22 4 and 0 708421 0 708630 the rare earth element ree abundances and patterns from la moliere not only differ between dentine and enameloid of the same tooth but also between different teeth supporting variable conditions of diagenesis at this site however the ree patterns of enameloid from the exotic teeth analyzed for o and sr isotopic compositions are similar to those of teeth that have o and sr isotopic compositions typical of a marine setting at this site collectively this suggests that the two exotic teeth were formed while the sharks frequented a freshwater environment with very low 18o content and sr isotopic composition controlled by mesozoic calcareous rocks this is consistent with a paleogeography of high elevation 2300 m miocene alps adjacent to a marginal sea

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments

calculation of the energetics of water incorporation in majorite garnet interpretation of lateral variations in upper mantle seismic wave speeds requires constraints on the relationship between elasticity and water concentration at high pressure for all major mantle minerals including the garnet component we have calculated the structure and energetics of charge balanced hydrogen substitution into tetragonal mgsio3 majorite up to p 25 gpa using both classical atomistic simulations and complementary first principles calculations at the pressure conditions of earth s tran sition zone hydroxyl groups are predicted to be bound to si vacancies o as the hydrogarnet defect osi 4oho x at the si2 tetrahedral site or as the omg 2oho x defect at the octahedral mg3 site the hydrogarnet defect is more favorable than the omg 2oho x defect by 0 8 1 4 ev h at 20 gpa the presence of 0 4 wt al2o3 substituted into the octahedral sites further increases the likelihood of the hydrogarnet defect by 2 2 2 4 ev h relative to the omg 2oho x defect at the mg3 site oh defects affect the seismic ratio r dlnvs dlnvp in mgsio3 majorite r 0 9 1 2 at 20 gpa for 1400 ppm wt h2o differently than ringwoodite at high pressure yet may be indistinguishable from the thermal dlnvs dlnvp for ringwoodite the incorporation of 3 2 wt al2o3 also decreases r h2o by 0 2 0 4 therefore to accurately estimate transition zone compositional and thermal anomalies hydrous majorite needs to be considered when interpreting seismic body wave anomalies in the transition zone

hydrogarnet substitution in pyrope a possible location for water in the mantle abstract single crystal spectra of pyropes synthesized on the 3 1 3 composition of the system mgo al2o3 sio2 atph2o ptotal 25kbar and 1000 c show a broad band centered at around 3400 cm 1 due to h2o of h2o n aggregates in fluid inclusions and a sharp intense band near 3600 cm 1 due to oh of ho 44 clusters introduced by the hydrogarnet substitutionsi4 4h the water contents in the synthetic pyrope due to ho 44 clusters are estimated near 0 05 wt h2o from spectroscopic data si deficits in microprobe analyses of the pyropes studied support the hydrogarnet substitution these results show that the hydrogarnet substitution in pyrope may contribute to water contents in the mantle

strontium isotope stratigraphy of the middle devonian brachiopods and conodonts a set of 145 strontium isotope ratios based on skeletal components of emsian to frasnian age reveals a detailed structure of the seawater 87sr 86sr curve that can ultimately serve as a tool for high resolution isotope stratigraphy in the devonian brachiopod and conodont samples were collected in the eifel region of germany the area around the global stratotype for the middle devonian with an apparent average temporal resolution in the 105 y range preservation of the brachiopod shell material has been assessed by optical microscopy sem and cathodoluminescence and only the better preserved internal secondary layer of the shell has been utilized for strontium isotope measurements the 87sr 86sr curve shows a short decline from 0 7081 to 0 7078 through the late emsian followed by short term fluctuations with an amplitude of up to 10 4 around a mean of 0 7078 during the eifelian and givetian and a rise from late givetian into the late devonian the above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records due to erosional and nondepositional events but a direct confirmation for such a scenario can be claimed only for the latest eifelian otomari event insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes conodont skeletal elements even if well preserved at cai 2 5 yielded results that are mostly enriched in radiogenic 87sr if compared to coeval brachiopods although this enrichment is usually within the 10 5 range conodonts despite their superior stratigraphic resolution should be utilized only as a material of second choice in cases where brachiopods are rare or absent

heterogeneity of water in garnets from uhp eclogites eastern dabieshan china abstract garnets in uhp eclogites from bixiling in dabieshan were investigated by fourier transform infrared spectroscopy ftir the results indicate that all garnets contain structural water that occurs as hydroxyl oh and non structural molecular water h 2 o possibly in the form of sub microscopic fluid inclusions the structural hydroxyl contents range from 92 to 1735 ppm h 2 o wt and most are between 200 and 1000 ppm therefore garnet in eclogite can recycle surface water into the mantle various water contents were observed among different samples of the same outcrop 150 m and in different domains of the same sample 1 cm this variability in structural h 2 o contents suggests that the mobility of fluids during uhp metamorphism was very limited and that both subduction and exhumation processes of uhp rocks occurred in a short time interval

oxygen strontium and neodymium isotope composition of fossil shark teeth as a proxy for the palaeoceanography and palaeoclimatology of the miocene northern alpine paratethys the upper marine molasse sediments of southern germany were deposited during the early to middle miocene a period of significant change for the global miocene palaeoceanography palaeoclimate and the regional palaeogeography because of the ongoing alpine himalayan orogeny to address the influence of the alpine uplift on climate and oceanography of the northern alpine molasse basin a combined o sr and nd isotope study was undertaken on fossil teeth from sharks synodontaspis sp galeocerdo cf aduncus chaenogaleus sp and button like teeth from the bony fish of the upper marine molasse chrysophrys molassica average 18o values for hydroxyapatite of teeth from two sites are 20 3 1 0 6 and 21 2 1 0 5 while their average 87sr 86sr and 143nd 144nd ratios are 0 70850 0 00001 2 and 0 70882 0 00003 2 and 0 51220 and 0 51223 both at 0 00001 2 respectively by comparison to the sr evolution curve for the global ocean the sr isotope compositions suggest ages of about 22 and 17 ma for the teeth these ages are in good agreement with the depositional ages which suggests open marine conditions open marine conditions are also compatible with 1 lower average 18o values and 87sr 86sr ratios for the one site compared to higher 18o values and higher 87sr 86sr ratios for the other site 2 estimates for seawater temperatures which are similar to other estimates from deposits of similar latitude and age 3 a comparison of seawater temperatures with average ambient air temperature estimates deduced from continental palaeoclimate indicators nd isotope compositions are compatible with an influence of the north atlantic on the paratethys assuming constant salinity and seawater oxygen isotope composition a 4 c cooling can be inferred from average 18o values of the teeth between 22 and 17 ma this is similar to trends observed for foraminiferal records from the mediterranean tethys but different from foraminiferal and molluscan records of the north atlantic and the north sea during this period and allows for the possibility that the alpine orogeny had an influence on the regional circum alpine climate

strontium isotopes in biogenic phosphates from a neogene marine formation implications for palaeoseawater studies abstract neogene marine deposits of nw france faluns are rich in a variable array of well preserved phosphatic vertebrate fragments many of these are of the same age as the host sediments and consist of the remains of fish mammals and reptiles whilst others are clearly mesozoic turonian in age we have determined the sr isotopic composition of 24 phosphatic samples in order to study the efficacy of using the method to date the neogene materials and to investigate the effects of diagenesis and seawater alteration on the terrestrial material the sr isotope results obtained on the ichthyoliths and the other neogene marine vertebrates suggest an age of 11 ma for the base of the host sediments tortonian which corresponds precisely with the palaeontological data in contrast the initial isotopic composition of the contemporaneous terrestrial mammals and reptiles which should record higher continental sr ratios are close to the value of their marine counterparts the same trend is observed for a sample of shark s tooth of mesozoic age where the sr isotopic composition approaches a neogene value the results demonstrate that alteration by seawater or interstitial waters is able to introduce significant quantities of sr into the phosphate leaching experiments carried out on the materials does not remove this secondary strontium and we were unable to establish the original values of the terrestrial material our conclusion is that the use of sr isotopes to characterise phosphatic materials must be viewed with caution particularly if the materials are reworked

strontium isotopic signatures in the enameloid and dentine of upper cretaceous shark teeth from western alabama paleoecologic and geochronologic implications abstract the 87sr 86sr isotopic composition of the enameloid tips of teeth of scapanorhynchus texanus a common and widespread upper cretaceous shark differs from that found in the dentine inner portions of the same teeth using a marine 87sr 86sr isotopic evolution curve we converted the 87sr 86sr isotopic composition of different sections of the teeth to numerical ages portions of fossil teeth dominated by enameloid but that include some dentine yield numerical ages 74 2 0 8 ma 2 standard error s e that fall within the upper cretaceous and are consistent with the known geologic age range of these fossils as the proportion of dentine present in samples of the teeth increases the 87sr 86sr derived numerical ages trend from biostratigraphically reasonable upper cretaceous ages to those that are far younger and biostratigraphically impossible about 32 ma i e oligocene this deviation in isotopic composition and numerical age is likely the result of post burial diagenetic alteration of dentine which is generally more susceptible to such alteration than enameloid to avoid the contaminating effects of dentine we sampled only the enameloid portion of twelve s texanus teeth by scratching their surfaces the enameloid scratch samples yield numerical ages 78 8 0 4 ma 2 s e older than those obtained for any of the sectioned samples this suggests that sampling only the surface enameloid of shark teeth is useful in reducing spurious isotopic results arising from post burial alteration of teeth the numerical age for the enameloid scratch samples is consistent with the known early campanian early maastrichtian occurrence of s texanus in north america and with the radiometric age of the deposit from which these samples were recovered

differential diagenesis of strontium in archaeological human dental tissues the investigation of prehistoric human migration from the measurement of sr isotope ratios within preserved tissue is critically dependent on the preservation of biogenic sr a number of recent studies have involved isotope ratio measurements on samples of archaeological tooth and bone but doubt remains as to the extent of diagenesis in various skeletal tissues and the effectiveness of procedures designed to decontaminate them the authors have compared sr abundance and isotope ratios in enamel and dentine from archaeological teeth in order to assess the integrity of the biogenic sr signal preserved within the respective tissues it is concluded that enamel appears in most cases to be a reliable reservoir of biogenic sr but that dentine and by implication bone is not the diagenesis of dentine is highly variable even between burials within a single site for the majority of teeth dentine diagenesis was not simply by addition of soil derived sr but involved substantial sometimes complete turnover of the original biogenic material it is suggested that for most of the samples investigated current decontamination techniques may not have been effective in isolating biogenic sr from dentine similar considerations are likely to apply to archaeological and fossil bone but the possibility arises to use dentine and enamel measurements to assess the effectiveness of decontamination procedures which may then be used for bone

uppermost campanian maestrichtian strontium isotopic biostratigraphic and sequence stratigraphic framework of the new jersey coastal plain firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units sequences we correlate the well developed uppermost campanian and maestrichtian sequences of the new jersey coastal plain to the geomagnetic polarity time scale gpts by integrating sr isotopic stratigraphy and biostratigraphy to do this we developed a maestrichtian ca 73 65 ma sr isotopic reference section at deep sea drilling project hole 525a in the southeastern atlantic ocean maestrichtian strata can then be dated by measuring their 87 sr 86 sr composition calibrating to the gpts of s c cande and d v kent 1993 personal commun and using the equation age ma 37 326 894 52 639 89 87 sr 86 sr sr stratigraphic resolution for the maestrichtian is estimated as 1 2 to 2 m y at least two unconformity bounded units comprise the uppermost campanian to maestrichtian strata in new jersey the lower one the marshalltown sequence is assigned to calcareous nannofossil zones cc20 21 nc19 and cc22b nc20 it ranges in age from 74 1 to 69 9 ma based on sr isotope age estimates the overlying navesink sequence is assigned to calcareous nannoplankton zones cc25 26 nc21 23 it ranges in age from 69 3 to 65 ma based on sr isotope age estimates the upper part of this sequence the tinton formation has no calcareous planktonic control sr isotopes provide an age estimate of 66 1 2 ma latest maestrichtian sequence boundaries at the base and the top of the marshalltown sequence match boundaries elsewhere in the atlantic coastal plain owens and gohn 1985 and the inferred global sea level record of haq et al 1987 they support eustatic changes as the mechanism controlling depositional history of this sequence however the latest maestrichtian record in new jersey does not agree with haq et al 1987 we attribute this to correlation and time scale differences near the cretaceous paleogene boundary high sedimentation rates in the latest maestrichtian of new jersey shrewsbury member of the red bank formation and the tinton formation suggest tectonic uplift and or rapid progradation during deposition of the highstand systems tract

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

statistical characteristics for the type and length of deformation induced cracks in columnar grain ice observations are reported on craks formed during compressive unidirectional constant strain rate deformation of columnar grain ice the axis of hexagonal crystallographic symmetry of each grain te nded to be in the plane perpendicular to the long direction of the grains and to have a random orientation in that plane for stress applied perpendicular to the long direction of the grains the deformation was practically two dimensional it was found that the relative proportion of grain boundary cracks increased iwth increasing strain rate decreasing temperature and for strain rate greater that 7 x 10 5 s 1 with defreasing grain size almost all the grain boundary cracks has at least one edge at a triple point for each test the grain boundary and trascrystalline crack lengths tended to have a log normal distribution the logarithmic mean crack len gth lmcl decreased with increasing strain rate decreasing grain size and decreasing temperature and tended to a constant value of 0 75 mm at 10 c for grain size of 3 mm or greater the lmcl had a mximum at a strain rate of 10 5 to 10 6 s 1 at 10 c the lmcls and the relative proportion of grain boundary cracks tended to be normally distributed for given load conditions

cluster of water molecules in garnet from ultrahigh pressure eclogite through the use of transmission electron microscopy and infrared spectroscopy hydrous components have been identified as hydroxyl and free water h 2 o in elongate garnet of ultrahigh pressure eclogite from the dabie mountains eastern china the h 2 o occurs as clusters of water molecules and as hydroxyl in garnet the clusters of water molecules are interpreted to have promoted elongation of garnet through hydrolytic weakening the presence of hydrous species in ultrahigh pressure garnet from continental crust protoliths indicates that such protoliths are able to carry water into the mantle during the subduction of continental lithosphere

distribution of hydrous components in jadeite of the dabie mountains two kinds of jadeite occur in the jadeite quartzite from the dabie mountains eastern china associated either with weak or strong deformation the former shows a uniform composition while the latter shows both uniform and zoning composition these jadeites were examined with infrared ir spectroscopy all jadeite displays hydroxyl oh stretching bands implying that hydrous components commonly exist in jadeite the concentration of the hydrous components in the jadeite with weak deformation is homogenous whereas the concentration of the hydrous components in strongly deformed samples is variable the correlation between the intensity of oh band absorbance and compositional zoning of jadeite with strong deformation indicates that na rich jadeite can accommodate more oh than na poor jadeite its interpretation is that there is more na associated with greater oh availability in the initial crystallization environment our data of the comparatively high oh concentrations recorded in the core of the jadeite which contains relative high vacancies in m2 site imply that both oh content and the vacancies in m2 site could decrease during exhumation of the jadeite quartzite the decrease of oh solubility in jadeite would result in the formation of h2o fluid during the early exhumation of uhp metamorphic rocks the h2o fluid transformed from oh during exhumation could trigger and enhance the early retrograde metamorphism of the host rocks and facilitate plastic deformation of jadeite grain by dislocation creep and diffusion creep

definition of late cretaceous stage boundaries in antarctica using strontium isotope stratigraphy abstract new 87sr 86sr analyses of macrofossils from 13 key marker horizons on james ross and vega islands antarctica allow the integration of the antarctic late cretaceous succession into the standard biostratigraphic zonation schemes of the northern hemisphere the 87sr 86sr data enable late cretaceous stage boundaries to be physically located with accuracy for the first time in a composite southern hemisphere reference section and so make the area one of global importance for documenting late cretaceous biotic evolution particularly radiation and extinction events the 87sr 86sr values allow the stage boundaries of the turonian coniacian coniacian santonian santonian campanian and campanian maastrichtian as well as other levels to be correlated with both the united kingdom and united states these correlations show that current stratigraphic ages in antarctica are too young by as much as a stage immediate implications of our new ages include the fact that inoceramus madagascariensis a useful

water partitioning between nominally anhydrous minerals in the mgo sio2 h2o system up to 24 gpa implications for the distribution of water in the earth s mantle multi anvil experiments have been conducted in the mgo sio2 h2o system at pressures of 15 24 gpa and temperatures of 1200 1600 c to investigate the partitioning of water between mantle phases the water contents were obtained from fourier transform infrared spectroscopy on doubly polished and clear crystals most of the mineral phases coexisted with a hydrous melt the results show that among all magnesium silicate phases 1 mgsio3 perovskite is the only phase which does not dissolve a detectable amount of water and 2 the high pressure polymorphs of mg2sio4 wadsleyite and ringwoodite dissolve about one order of magnitude more water than the polymorphs of mgsio3 clinoenstatite majorite and akimotoite the following partition coefficients of water were measured dwadsleyite clinoenstatite 3 8 at 15 gpa and 1300 c dringwoodite akimotoite 21 at 19 gpa and 1300 c dakimotoite perovskite 1 at 24 gpa and 1600 c and dpericlase perovskite 1 at 24 gpa and 1500 c these results suggest that most of the water in the earth s mantle is partitioned in the transition zone

origin of retrograde fluid in ultrahigh pressure metamorphic rocks constraints from mineral hydrogen isotope and water content changes in eclogite gneiss transitions in the sulu orogen abstract by taking advantage of having depth profiles between contrasting lithologies from core samples of the chinese continental scientific drilling ccsd project a combined study was carried out to examine changes in mineral h isotope total water and hydroxyl contents in garnet and omphacite across the contacts between ultrahigh pressure uhp eclogite and gneiss in the sulu orogen east central china the samples of interest were from two continuous core segments from the ccsd main hole at depths of 734 21 737 16 and 929 67 932 86 m respectively the results show d values of 116 to 64 for garnet and 104 to 82 for omphacite consistent with incorporation of meteoric water into protoliths of uhp metamorphic rocks by high t alteration both equilibrium and disequilibrium h isotope fractionations were observed between garnet and omphacite suggesting fluid assisted h isotope exchange at local scales during amphibolite facies retrogression while bulk water analysis gave total h2o concentrations of 522 1584 ppm for garnet and 1170 20745 ppm for omphacite structural hydroxyl analysis yielded h2o contents of 80 413 ppm for garnet and 228 412 ppm for omphacite it appears that significant amounts of molecular h2o are present in the minerals pointing to enhanced capacity of water storage in the uhp eclogite minerals hydrogen isotope variations in the transition between eclogite and gneiss show correlations with variations in their water contents petrographically the degree of retrograde metamorphism generally increases with decreasing distance from the eclogite gneiss boundary thus retrograde metamorphism results in mineral reactions and h isotope variation because hydroxyl solubility in nominally anhydrous minerals decreases with dropping pressure significant amounts of water are expected to be released from the minerals during decompression exhumation decompression exsolution of structural hydroxyl from 1 m3 volume of eclogite composed of only garnet and omphacite results in release of a quantitative estimate of 3 07 3 44 kg water that can form 140 156 kg amphibole during exhumation therefore it is concluded that fluid for retrogression of the eclogites away from the eclogite gneiss boundary was derived from the decompression exsolution of structural hydroxyl and molecular h2o in nominally anhydrous minerals for the eclogites adjacent to gneiss in contrast the retrograde metamorphism was principally caused by aqueous fluid from the gneiss which is relatively rich in water consequently both the origin and availability of metamorphic fluid during exhumation of deeply subducted continental crust are deciphered by this combined study focusing on the transitions and the retrograde processes between the felsic and mafic uhp rocks

the distribution of hydroxyl in garnets from the subcontinental mantle of southern africa 166 garnets of dominantly mantle origin were analyzed for oh content by infrared ir spectroscopy ir spectra in the 3400 3700 cm 1 region display consistent absorption patterns attributable to oh structurally bound within the garnet crystal occasionally contaminated by low intensity oh absorptions from microscopic inclusions the principal structural oh absorption occurs near 3570 cm 1 with the appearance of additional absorptions near 3512 cm 1 and 3650 cm 1 dependent on garnet composition or paragenesis samples derive from a wide variety of rock types occurring as xenoliths in kimberlites of southern africa oh abundances using the best currently available calibration range from less than 1 up to 135 ppm h 2o and increase in the general order as follows on craton eclogites group 1 basaltic kimberlite alnoite alkali basalt the oh contents of common lithospheric granets from coarse peridotites including several phlogopite bearing samples are typically less than 20 ppm h 2o for tectonic settings of kimberlites both on and off the archaean kaapvaal craton ti rich garnets from deformed peridotites are richer in oh supporting previous suggestions of association of these xenoliths with putative megacryst magmas subcalcic cr rich xenocrysts diamond inclusion garnets and garnets from diamondiferous eclogites have very low oh contents similar to eclogites and depleted peridotites without macroscopic diamonds the oh content of southern african peridotite and eclogite garnets are significantly lower on average than those previously examined from the colorado plateau diatremes while details of emplacement related h mobility in garnets remain to be established our results suggest that garnets record useful information on the role of water or other hydrous volatile species in petrological processes at their source regions in the mantle although garnets do not appear to constitute a large reservoir of mantle hydrogen the large stability range of oh bearing garnet in the crust and mantle implies wide applicability as a qualitative hydrobarometer

paleoenvironmental conditions and strontium isotope stratigraphy in the paleogene gafsa basin tunisia deduced from geochemical analyses of phosphatic fossils fossil shark teeth and coprolites from three major phosphorite occurrences in the gafsa basin southwestern tunisia were investigated for their geochemical compositions to improve local stratigraphy and to better assess paleoenvironmental conditions 87sr 86sr isotope ratios of shark teeth from the early maastrichtian el haria formation and from the early eocene metlaoui s s formation yielded sr isotope ages of 68 1 and 47 9 1 3 ma respectively which accord with the expected stratigraphic positions of these sediments conversely shark teeth from the paleocene eocene chouabine formation have large variation in sr isotope ratios even within individual layers after statistical treatment and then elimination of certain outlier samples three age models are proposed and discussed the most reasonable solution includes three subsequent sr ages of 61 8 2 2 ma 57 2 1 8 and 54 6 1 6 for layer ix layers viii v and layers iv 0 respectively three scenarios are discussed for explanation of the presence of the outliers 1 diagenesis 2 re working and 3 locally controlled seawater sr isotope ratio the most plausible account for the higher 87sr 86sr ratios relative to the global ocean in some fossils is enhanced intrabasinal re working due to low sea level conversely the sample with lower 87sr 86sr than the global seawater may link to diagenesis or to seawater influenced by weathering of late cretaceous marine carbonates which latter is supported by model calculation as well the end values of these fossils are very similar to those reported for paleogene and late cretaceous tethyan seawater and are compatible with the above interpretations the relatively low oxygen isotope values in shark teeth from the topmost phosphate bed of the chouabine formation together with the sr isotope results point toward recovering better connections with the open sea these 18o data reflect elevated ambient temperature which may link to the early eocene climatic optimum

thermodynamics of water solubility and partitioning when it was realized that nominally anhydrous minerals could be a major storage site of water in the mantle smyth 1987 bell and rossman 1992 it also became rather obvious that many mantle samples probably have lost most of their water during ascent e g ingrin and skogby 2000 while analyses of natural samples therefore in many circumstances only provide a lower limit of the actual water content in the mantle measurements of water solubility give an upper limit of the amount of water that might be stored in a mineral experimental measurements of water solubility have therefore naturally evolved in the last decades as a major tool for understanding the water storage capacity of the mantle closely related to studies of water solubility are studies of water partitioning among minerals if the water solubility in two minerals is known under given conditions the partition coefficient is just the ratio of the water solubilities under the same conditions provided that the composition of the fluid coexisting with the two minerals is the same since the pioneering work of bai and kohlstedt 1992 and of kohlstedt et al 1996 the water solubility in all major upper mantle minerals has been studied as well as the partitioning of water between the minerals of the lower mantle and the transition zone solubility studies by themselves do not directly give the water content in the mantle they constrain the storage capacity of the mantle i e the maximum amount of water that may be stored if the mantle were water saturated however as most of the mantle is very likely water undersaturated the actual water content is probably far below the storage capacity estimates of the actual abundance and distribution of water in the mantle may be obtained by combining solubility and partitioning data with direct

the oh content of pyrope at high pressure the oh contents of pyrope garnets synthesised at 1000 c and pressures between 2 and 13 gpa have been measured by infrared spectroscopy we find that under the same conditions of pressure temperature ah2o and asio2 the oh content of pyrope is similar to that of grossular this shows that observed differences in nature between water contents of pyrope and grossular are related to paragenesis rather than reflecting higher intrinsic solubility in grossular in the presence of excess sio2 the h2o content increases with pressure to 5 gpa 1000 ppm then decreases to below the detection limit at pressures above 7 gpa thus garnet becomes more hydrous with pressure to some critical value beyond which dehydration occurs even under h2o saturated conditions this observation is consistent with the measured partial molar volume of water in hydrogarnet which becomes greater than that in fluid water within the pressure range of this study when corrected to upper mantle conditions we find that pyrope should dehydrate with increasing depth below about 250 km pyrope is unlikely therefore to be a major site of water storage in the transition zone and upper mantle