fingerprinting the water site in mantle olivine nominally anhydrous minerals such as olivine contain trace amounts of water and may accommodate the entire water budget of the upper mantle here we report for the first time synthetic olivines crystallized experimentally under upper mantle conditions that reproduce the most common and intense infrared hydroxyl stretching bands at 3572 and 3525 cm 1 observed in spinel peridotite mantle olivines these bands arise from water accommodated at point defects associated with the trace element ti and we suggest that this is the most important defect site in the shallow upper mantle additional hydrated defects may occur at higher pressures we also identify bands related to water associated with fe3 these are unlikely to reflect equilibrium with the mantle and indicate water incorporation during exhumation or retrogression water must be present at the defect site appropriate for the mantle at the conditions of interest for partitioning seismic wave speed and deformation experiments on hydrous olivine to be relevant

rapid magma ascent recorded by water diffusion profiles in mantle olivine mechanisms and rates of magma ascent play a critical role in eruption dynamics but remain poorly constrained phenomena water dissolved in mantle minerals as hydrogen and partitioned into the magma during ascent may provide clues to quantifying magma ascent rates prior to eruption we determined the dehydration profiles in olivine crystals from peridotite mantle xenoliths within the pali aike alkali basalt from patagonia chile the results demonstrate that the amount of water stored in the uppermost mantle has likely been underestimated due to water loss during transport using experimental diffusion data for hydrogen we estimate that the xenoliths reached the surface from 60 70 km depth in several hours a surprisingly rapid rise comparable to ascent rates for kimberlite magmas

the behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite schwertmannite is a ubiquitous mineral formed from acid rock drainage ard and plays a major role in controlling the water chemistry of many acid streams the formation of schwertmannite was investigated in the acid discharge of the monte romero abandoned mine iberian pyrite belt sw spain schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of fe ii to fe iii and transformed with time into goethite and jarosite in a few hours schwertmannite precipitation removed more than half of the arsenic load from solution whereas the concentration of divalent trace metals zn cu pb cd ni and co remained almost unchanged in the laboratory natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid liquid mass ratio of 1 5 for 353 days during this time the ph of the solution dropped from 3 07 to 1 74 and the concentrations of sulfate and fe increased during the first 164 days schwertmannite transformed into goethite plus h3o jarosite but subsequently goethite was the only mineral to form some of the trace elements such as al cu pb and as were depleted in solution during the first stage as schwertmannite transformed into goethite plus h3o jarosite on the contrary the transformation of schwertmannite to goethite with no jarosite during the second stage released al cu and as to the solution despite the variation in their concentrations in solution approximately 80 of the total al and cu inventories and more than 99 as and pb remained in the solid phase throughout the entire aging process

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

chemistry and mineralogy of outcrops at meridiani planum analyses of outcrops created by the impact craters endurance fram and eagle reveal the broad lateral continuity of chemical sediments at the meridiani planum exploration site on mars approximately ten mineralogical components are implied in these salt rich silicic sediments from measurements by instruments on the opportunity rover compositional trends in an apparently intact vertical stratigraphic sequence at the karatepe west ingress point at endurance crater are consistent with non uniform deposition or with subsequent migration of mobile salt components dominated by sulfates of magnesium striking variations in cl and enrichments of br combined with diversity in sulfate species provide further evidence of episodes during which temperatures ph and water to rock ratios underwent significant change to first order the sedimentary sequence examined to date is consistent with a uniform reference composition modified by movement of major sulfates upward and of minor chlorides downward this reference composition has similarities to martian soils supplemented by sulfate anion and the alteration products of mafic igneous minerals lesser cementation in lower stratigraphic units is reflected in decreased energies for grinding with the rock abrasion tool survival of soluble salts in exposed outcrop is most easily explained by absence of episodes of liquid h2o in this region since the time of crater formation

transformation of jarosite to hematite in simulated martian brines the presence of jarosite a hydrous iron sulfate at meridiani planum supports the past existence of water on mars surface thermodynamic calculations suggest that jarosite should transform to ferric oxyhydroxides in aqueous media here we show that jarosite can transform directly to hematite the iron oxide identified at meridiani planum in simulated martian brines our results are consistent with a short aqueous history but also indicate that jarosite can persist in highly saline martian brines the formation of goethite a common iron oxyhydroxide on earth is prevented by the low water activity and or high phosphate concentration of martian brines

structural control and tectonic setting of mesozoic volcanism in hong kong middle jurassic to lower cretaceous silicic volcanic rocks and granitoid plutons in hong kong form part of the broad ne trending yanshanian tectonomagmatic belt that extends through se china pyroclastic deposits in hong kong are typically proximal and infill linear flared vents and ellipsoidal calderas these pass down through elongate rift like conduits into extensive multiple fault and shear zone hosted 9sheeted9 dyke complexes and granitoid plutons dykes also emphasize the limits of calderas the spatial distribution and geometry of the vents calderas dykes and plutons are structurally controlled during each of four temporally well constrained periods of petrogenetically related volcanism and plutonism e and ene trending axes of extension and transtension were dominant nw trending faults increased in importance with time and their intersections with ene trending faults influenced the loci of volcanic centres nesting of the calderas confirms persistent reactivation of some faults the loci of magmatism migrated over 25 ma from nw to se zones of silicic crust created during these magmatic episodes have a broadly tripartite crustal 9stratigraphy9 pluton dyke volcanic reminiscent in very general terms of ophiolites the zones were created during periods of unusually rapid extension as the continental margin of se china changed from an active margin dominated by subduction to a back arc regime and dextral strike slip along ene trending faults gave way to sinistral strike slip

experimental study of acid sulfate alteration of basalt and implications for sulfate deposits on mars 1 acid sulfate alteration of basalt by so2 bearing volcanic vapors has been proposed as one possible origin for sulfate rich deposits on mars to better define mineralogical signatures of acid sulfate alteration laboratory experiments were performed to investigate alteration pathways and geochemical processes during reaction of basalt with sulfuric acid pyroclastic cinders composed of phenocrysts including plagioclase olivine and augite embedded in glass were reacted with sulfuric acid at 145 c for up to 137 days at a range of fluid rock ratios during the experiments the phenocrysts reacted rapidly to form secondary products while the glass was unreactive major products included amorphous silica anhydrite and fe rich natroalunite along with minor iron oxides oxyhydroxides probably hematite and trace levels of other sulfates at the lowest fluid rock ratio hexahydrite and an unidentified fe silicate phase also occurred as major products reaction path models indicated that formation of the products required both slow dissolution of glass and kinetic inhibitions to precipitation of a number of minerals including phyllosilicates and other aluminosilicates as well as al and fe oxides oxyhydroxides similar models performed for martian basalt compositions predict that the initial stages of acid sulfate alteration of pyroclastic deposits on mars should result in formation of amorphous silica anhydrite fe bearing natroalunite and kieserite along with relict basaltic glass in addition analysis of the experimental products indicates that fe bearing natroalunite produces a mossbauer spectrum closely resembling that of jarosite suggesting that it should be considered an alternative to the component in sulfate rich bedrocks at meridiani planum that has previously been identified as jarosite

behavior of ni zn and cr during low temperature aqueous fe oxidation processes on mars abstract the behavior of ni ii zn ii and cr iii during the melanterite feso4 7h2o to hematite fe2o3 oxidative transformations involving evolution pathways via jarosite h3o k fe3 oh 6 so4 2 schwertmannite fe8o8 oh 6 so4 and goethite feooh were investigated in an acidic saturated mgso4 matrix results provide important clues about how elevated levels of trace elements are incorporated into the secondary fe mineralogy assemblages found on mars and the mechanism for formation of hematitic concretions at meridiani planum on mars our results demonstrate that starting at the same concentrations in the initial solution final amounts of ni zn and cr in hematite via different pathways are very different in path 1 melanterite jarosite hematite partitioning of ni zn and cr into jarosite and hematite formed through dissolution of jarosite is most likely in the order cr zn ni in path 2 melanterite schwertmannite goethite hematite schwertmannite and goethite exhibited strong affinities for divalent ni and zn during such a pathway ni should accumulate more than zn by at least a factor of two and partitioning of ni zn and cr to the hematite is most likely in the order cr ni zn therefore our results suggest that the high ni and moderate zn distribution pattern observed in meridiani hematitic spherule bearing samples can be explained best by the schwertmannite goethite to hematite pathway path 2 without need for an additional high ni source in this region although the lack of goethite at meridiani renders it uncertain if goethite ever served as a precursor to facilitate hematite formation dehydration of nano crystalline goethite is thermodynamically favored and cannot be ruled out on the other hand if hematitic concretions were formed by dissolution of jarosite path 1 then much higher initial ni zn ratios than 1 in initial diagenetic fluids may be necessary to explain the elevated levels of ni in the spherules cr iii when starting in equal amounts as ni and zn in the solution accumulated at least two orders of magnitude more than ni and zn in all fe iii phases given that cr concentrations are of the same order of magnitude as ni and zn in most rocks and soils measured by the rover opportunity cr concentrations should be much lower than ni and zn in the initial diagenetic fluids mobility of cr was greatly limited by precipitation of fe iii phases due to substitution for fe iii and sequestration in the solids

unravelling an allochthonous subaqueously deposited volcanic epiclastic to subaerial andesitic lava assemblage in hong kong age stratigraphy and provenance studies of the middle jurassic tuen mun formation the middle jurassic tuen mun formation hong kong is a fault bounded block of rare andesitic and related rocks that preserve a snapshot of the developing se china continental arc system during the late mesozoic the forearc depositional setting is considered to have been dominated by an emergent andesitic volcanic massif which shows a transition to a fluvial dominated volcanic plain and then to an offshore marine environment the youngest laser ablation inductively coupled plasma mass spectrometry u pb detrital zircon ages obtained from the three packages define a coherent group n 396 mswd 1 8 suggesting a maximum depositional age of 169 5 0 3 ma the dominance of large euhedral and concentrically zoned zircons reflects a common volcanic provenance hf isotope data e hf t 0 to 11 on the youngest representative zircon grains imply derivation of magmas from dominantly recycled crustal sources the detrital zircon age signatures and hf isotope data show no indication of magmatic interaction with adjacent late palaeozoic and early to middle jurassic sedimentary rocks or middle jurassic to early cretaceous magmatic rocks of hong kong on the basis of the structural zircon age and isotope data the tuen mun formation is interpreted to be an allochthonous block emplaced in the hong kong region during the late middle jurassic supplementary material a full dataset of u pb dating and hf isotope analysis of detrital zircons stratigraphic drillhole logs and a description of the terminology used in this paper are available at https doi org 10 6084 m9 figshare c 3736972

mg si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the mg2sio4 sio2 h2o system direct observation of aqueous fluids coexisting with mgsio 3 enstatite and or mg2sio4 forsterite was performed at 0 5 5 8 gpa and 800 1000 c with an externally heated diamond anvil cell and synchrotron x rays at 1000 c in the mgsio3 h2o system forsterite crystallizes below 3 gpa but not above that pressure at 1000 c in the mg2sio4 h2o system forsterite congruently dissolves into the aqueous fluids up to 5 gpa these observations suggest that the aqueous fluids coexisting with enstatite and forsterite have mg si 1 below 3 gpa and 1 mg si 2 above that pressure comparison with the previous studies reporting mg si ratios of the aqueous fluid coexisting with enstatite and forsterite indicates that the mg si ratios change rapidly from sio2 rich to mgo rich at around 3 gpa and 1000 c this change can be related to possible structural changes of liquid water under these conditions the aqueous fluids coexisting with enstatite and forsterite do have mg si ratios similar to those found in the partial melts of h2o saturated peridotite somewhere within the upper mantle these two fluids unite to form a single regime and cannot be distinguished from each other

the effect of small amounts of h2o on olivine to ringwoodite transformation growth rates and implications for subduction of metastable olivine abstract it has been suggested that in relatively cold subduction zones the interior of down going lithospheric plates may be cool enough to inhibit the transformation of olivine to its high pressure polymorphs wadsleyite and ringwoodite resulting in the persistence of metastable olivine in the mantle transition zone the rapid transformation of this metastable olivine has been identified as a possible cause of deep focus earthquakes however it is known that olivine can incorporate hydrogen at high pressure and this hydrogen may enhance transformation rates we conducted a series of high pressure experiments to hydrate and then partially transform olivine to ringwoodite we measured transformed rim thickness as a function of run duration and fit a linear function to our results to determine transformation growth rates the addition of h2o to olivine appears to promote olivine to ringwoodite transformation by increasing the growth rate decreasing the activation enthalpy for growth and weakening the ringwoodite and or olivine to allow for dissipation of elastic strain sufficient to maintain constant or near constant growth rates throughout transformation the addition of approximately 300 ppmw 2h2o to olivine increases the growth rate of olivine to ringwoodite transformation at 1100 c and 18 gpa by almost a factor of 40 from 4 0 0 8 10 9 ms 1 to 1 5 0 3 10 7 ms 1 there is a corresponding decrease in the activation enthalpy of growth from 392 kj mol to 237 kj mol assuming activation volume of 0 cm3 mole analyses of hydrogen distributions in partially transformed samples suggest that the hydrogen concentration in the bulk of the olivine crystal may be less important than hydrogen at the olivine and ringwoodite interface

origin of iron oxide spherules in the banded iron formation of the bababudan group dharwar craton southern india the banded iron formation of the bababudan group western dharwar craton india is composed of millimetric to centimetric alternating quartz and grey to red fe oxide bands major phases are quartz and martite hematized magnetite with minor fe sulfides and ca mg fe carbonates micrometric fe oxide spherules fill cavities in discontinuous micrometric layers of fe oxides that occur in the massive quartz layers and at the interface of massive fe oxide and quartz layers the spherules are composed of micrometric radial plates of hematite intergrown with nanometric magnetite these spherules contain carbonaceous matter cm with nanometric fe particles and have low n contents 900 ppm cm1 the spherule formation is attributed to a low temperature hydrothermal process 150 200 c at around 2 52 ga possibly favored by the presence of cm these hydrothermal fluids dissolved diagenetic interstitial sulfides or carbonates creating cavities which provided space for the spherule precipitation carbonaceous matter of semi anthracite maturity is encapsulated in quartz grains adjacent to the fe oxide spherules cm2 and it is thus concluded that cm1 and cm2 are most likely contemporaneous and of the same origin either incorporated at the time of bif formation or during the hydrothermal event at 2 52 ga from the underlying phyllitised black shales carbonaceous matter cm3 was also found around the fe oxide spherules and the martite grains cm3 has much higher n contents 5000 ppm is of a lower maturity than cm1 and cm2 and is related to weathering which is also indicated by the presence of goethite and kaolinite the 13c of all cms varies from 19 4 to 24 7 similar to values measured in the underlying phyllitised black shales and likely reflect denitrifying microbial activity

a low velocity zone atop the transition zone in northwestern canada 1 seismic studies over the past decade have identified an s wave low velocity zone lvz above the transition zone at various locations around the globe this layer is hypothesized to be a lens of dense hydrous silicate melt ponding atop the 410 km discontinuity beneath the silicate melt density crossover predicted to exist within the upper mantle we have assembled a p and s receiver function data set to quantify the physical properties and geographical extent of the layer in northwestern canada geographic profiles formed from 1 d migration of receiver functions computed for the canadian northwest experiment canoe and portable observatories for lithospheric analysis and research investigating seismicity polaris slave arrays reveal an lvz beneath many stations at a nominal depth of 340 km to constrain layer thickness and poisson s ratio we performed a grid search over a suite of 1 d velocity profiles to model the relative delay times of direct conversions and reverberations from the top of the lvz and 410 km discontinuity as recorded at the yellowknife array in addition we performed linearized inversion of transmission coefficient amplitudes to estimate s velocity contrasts at the bounding interfaces the lvz is characterized by a thickness of 36 km with an s velocity contrast of 7 8 and poisson s ratio of 0 42 taken at face value the two latter results require an increase in p velocity into the lvz the poisson s ratio lies well above the iasp91 average of 0 29 0 3 for this depth range and favors the presence of high melt or fluid fractions

formation of the hematite bearing unit in meridiani planum evidence for deposition in standing water 1 the most plausible models for the origin and evolution of a unique geologic unit in meridiani planum mars are low temperature precipitation of fe oxides oxyhydroxides from standing water precipitation from circulating fluids of hydrothermal origin or the thermal oxidation of magnetite rich ash analysis of odyssey thermal emission imaging system themis infrared and visible images together with mgs tes mola and moc data has provided additional insight into the meridiani region the hematite at meridiani was most likely derived from a fe oxyhydroxide precursor such as goethite is mixed with basalt as the major component occurs as a thin layer meters to 200 m thick and is thermophysically distinct from units immediately above and below remnants of a hematite poor unit lie directly above the hematite layer indicating that hematite formation was sharply confined vertically the hematite unit appears to embay preexisting channels and occurs only as outliers within closed crater basins suggesting that it was deposited in a gravity driven fluid rather than as a dispersed air fall the hematite unit lieswithinatopographictroughover 3 4ofitscircumference withtheremainingperimeter 150mlowerinelevation oxidationofashduringemplacementisunlikelygivenagoethite precursor and basalt as the major component hydrothermal alteration does not account for the confined vertical extent of the hematite layer over large distances and across disconnected outliers the preferred model is the deposition of hematite or precursor fe oxyhydroxides in water filled basins followed by dehydroxylation to hematite in lowtemperature diagenesis this model accounts for 1 the uniform deposition of a thin hematite bearing unit over an area 150 000 km 2 in size 2 the transition from hematiterichtohematite poorunitsoverlessthan 10mverticaldistance 3 thedistinctdifferences from the underlying layers 4 goethite as the precursor to hematite 5 the embayment relationships 6 the occurrence of remnants of the hematite bearing unit in isolated craters surrounding the main deposit 7 the lack of other hydrothermal minerals and 8 the presence of coarse grained low albedo basalt rather than ash as the major component the occurrence of unweathered olivine pyroxene and feldspar throughout the equatorial region provides strongevidencethat extensive aqueousweathering hasnotoccurred onmars thus the presence of a small number of bodies of standing water appears to represent brief localized phenomena set against the backdrop of a cold frozen planet index terms 5410 planetology solid surface planets composition 6225 planetology solar system objects mars 5464 planetology solid surface planets remote sensing 3672 mineralogy and petrology planetary mineralogy and petrology 5410 keywords hematite meridiani standing water

pressure and temperature dependence of water solubility in fe free wadsleyite the effects of temperature and pressure on water solubility in wadsleyite in the system mgo sio 2 h 2 o were investigated experiments were carried out using a 1000 ton multi anvil press one series of experiments was performed at a fixed pressure of 15 gpa and at various temperatures and in a second series the temperature was fixed at 1200 c and pressure was varied from 13 to 18 gpa the starting material was a mixture of oxides and hydroxides equivalent to the composition mg 2 sio 4 5 wt h 2 o run products consisted of wadsleyite quenched hydrous melt and minor amounts of clinoenstatite the water content of wadsleyite was quantified by ion probe results show that at 15 gpa the water solubility in wadsleyite decreases significantly with increasing temperature from 2 2 wt h 2 o at 900 c down to 0 9 wt h 2 o at 1400 c the corresponding mg si ratios increase from 1 80 to 1 91 over this temperature range this effect appears to be largely due to changes in the water activity in the coexisting melt the partition coefficient of water between wadsleyite and coexisting melt is nearly independent of temperature with d w a t e r w a d s l e y i t e m e l t 0 08 no significant effect of pressure on water solubility was observed at 1200 c our data suggest that the water storage capacity of wadsleyite in the transition zone is much lower than previously suggested together with previous results on ringwoodite our data imply a strong decrease of the water partition coefficient between wadsleyite and ringwoodite with temperature this decrease could have two important consequences 1 the width of the 520 km discontinuity may vary strongly as a function of temperature 2 during cooling of the earth s mantle since the hadean water may have increasingly partitioned from the lower into the upper part of the transition zone

formation of jarosite bearing deposits through aqueous oxidation of pyrite at meridiani planum mars 1 the discovery of sulfate rich layered deposits with hematite spherules at the landing site of the opportunity rover is consistent with mineral deposition in an aqueous environment we evaluate conditions responsible for the formation of a jarosite goethite gypsum assemblage with speciation calculations the results show that the assemblage could have precipitated from acidic solutions formed through near surface aqueous oxidation of pyrite our hypothesis is that regional heating in the meridiani planum caused a release of sulfide rich hydrothermal waters leading to formation of pyrite rich regional deposits in a depression aqueous oxidation of these deposits by atmospheric o2 created an acidic environment that allowed formation of sulfates and goethite partial neutralization of the solution caused further goethite precipitation and conversion of jarosite to goethite leading to formation of goethite concretions subsequent dehydration of goethite to coarse grained hematite would also have been facilitated by regional heating

fe oxidation processes at meridiani planum and implications for secondary fe mineralogy on mars fe oxidation processes may have occurred during groundwater mediated diagenesis in meridiani planum sediments to address this question melanterite oxidation experiments were conducted at epsomite saturation as a function of ph results show that schwertmannite is initially formed from acidic fe oxidation and that its formation and aging to mixtures of jarosite and nanocrystalline goethite is strongly controlled by ph over the range b 2 0 4 0 the ph is controlled in turn by fe oxidation and fe3 hydrolysis in one 77 d oxidation experiment nanocrystalline hematite was tentatively identified by mc6ssbauer spectroscopy accordingly aging experiments with synthetic nanocrystalline goethite were conducted 1 to further resolve the formation mechanisms of fe phases identified from oxidation experiments and 2 to test whether low water activity aw controls the thermodynamically favored goethite to hematite transition at low temperature mc6ssbauer spectroscopy and total x ray scattering show no observable changes after 4 months of aging and instead these results point to a jarosite precursor for the tentatively identified hematite on the basis of these results we suggest that the oxidation and maturation of initially formed fe2 bearing saline minerals may account in large part for the distribution of secondary fe minerals at the martian surface contributing to the association of fe oxides and mg ca sulfates observed from orbital surface analyses we hypothesize that oxidation of fe2 sulfates at low temperature could account for sustained diagenetic acidity in addition to much of the observed fe mineralogy in meridiani planum outcrop rocks the origin of the gray crystalline hematite at meridiani however is deserving of further experimental work to test this mechanism copyright 2008 by the american geophysical union

tectonic transition from subduction to retreat of the palaeo pacific plate new geochemical constraints from the late mesozoic volcanic sequence in eastern fujian province se china

geochemistry of coeval mesozoic plutonic and volcanic suites in hong kong middle jurassic to lower cretaceous intermediate to silicic plutonic and volcanic rocks of hong kong record a transition from calc alkaline through high k calc alkaline to transitional shoshonitic compositions with time close spatial and temporal associations among comagmatic volcanic plutonic pairs indicate that magmatism occurred in discrete episodes mostly of less than one million years duration synchronous high k calc alkaline and transitional shoshonitic magmatic activity during at least one pulse suggests a relatively rapid transition from a subduction related to an extension related tectonic setting geochemical signatures indicate that the magmatic suites have a mantle origin with a decreasing crustal contribution from two distinct sources the earliest mantle derived magmas interacted strongly with a dominantly archaean crustal protolith younger magmas show evidence for interaction with a dominantly proterozoic crustal protolith the strongest mantle influence is shown by magmas which were intruded along the boundary between the two dominant crustal sources this interface marks a deep crustal discontinuity which promoted the passage of magmas to the surface

effect of water on olivine wadsleyite phase boundary in the mg fe 2sio4 system 1 the phase boundary between san carlos olivine and its high pressure phase wadsleyite have been studied comparatively in dry and water saturated condition by comparing saturated and dry samples from the same experimental run we determine that both boundaries of the two phase coexisting loop shift towards lower pressure or lower iron content and the pressure width of the loop decreases to 0 3 gpa under saturated conditions at 1473 k thus the presence of water in the earth s mantle will sharpen the 410 kilometer seismic discontinuity shallow the depth of the discontinuity and reduce the velocity jump across the discontinuity

synthesis of akaganeite in the presence of sulfate implications for akaganeite formation in yellowknife bay gale crater mars abstract akaganeite a cl bearing fe iii hydr oxide has been recently discovered in yellowknife bay in gale crater on mars by the mars science laboratory msl curiosity rover akaganeite was associated with sulfate and sulfide minerals at yellowknife bay indicating that sulfate ions could be present in solution during akaganeite formation the mechanism and conditions of akaganeite formation in the yellowknife bay mudstone are unknown we investigated formation of akaganeite through hydrolysis of ferric chloride solution in the presence of 0 0 01 0 05 0 1 and 0 2 m sulfate and at initial ph of 1 5 2 and 4 at 90 c mineralogy of the precipitated fe iii phases was characterized by x ray diffraction and infrared spectroscopy the precipitates were also acid digested to determine total sulfate and chloride contents akaganeite and natrojarosite formed at initial solution ph of 1 5 akaganeite goethite and natrojarosite precipitated in initial ph 2 solutions and goethite hematite and 2 line ferrihydrite precipitated at initial solution ph of 4 sulfate addition did not inhibit akaganeite formation increasing initial solution sulfate concentrations resulted in increasing sulfate to chloride ratio in the precipitated akaganeite infrared spectroscopy revealed akaganeite bands at 2 m h 2 o combination band and at 2 46 m oh combination band the h 2 o combination band position linearly correlated with total chloride content in akaganeite overall laboratory studies demonstrated formation of akaganeite at initial sulfate concentration 0 2 m sulfate to chloride molar ratio 0 3 and ph 2 implying that those conditions might prevail perhaps as micro environments during akaganeite formation in yellowknife bay mudstone the occurrence of fe ii sulfides pyrite and pyrrhotite in yellowknife bay mudstone is a potential acidity source dissolution of sulfide minerals might occur under localized oxidizing water limiting cl rich conditions creating favorable environments for akaganeite formation

sensitivity of glacial isostatic adjustment to a partially molten layer at 410 km depth we present a sensitivity analysis aimed at testing whether observables related to glacial isostatic adjustment can support or refute the occurrence of a low viscosity melt rich layer mrl above the mantle transition zone as required by the transition zone water filter model bercovici karato 2003 in total 1600 model runs were performed sampling a range of mrl thicknesses 1 10 and 20 km and viscosities 10 15 10 19 pa s plausible viscosity values in the upper and lower mantle regions and four distinct ice histories to determine decay time constraints we consider relative sea level rsl data from two sites angerman river ar sweden and richmond gulf rg canada and use a new method of observational sea level data correction comparing model output of postglacial decay times and j 2 to observational constraints we find numerous possible solutions largely as a result of parameter trade off the investigated observables are sensitive to the existence of an mrl and reasonable variations in its thickness and viscosity the magnitude and nature of this sensitivity varies between the two data types as well as the adopted background viscosity structure decay time results from either considered location do not strictly support or exclude mrl existence however both locations offer mrl viscosity requirements for given thicknesses with ar being more restrictive rg constraints allow mrl viscosities as low as 10 16 pa s 10 km and 10 17 pa s 20 km ar results narrow these permitted viscosity ranges to 10 18 pa s or greater for both 10 and 20 km mrl thicknesses in the case of a 1 km thick mrl ar constraints permit the viscosity to be as low as 10 17 pa s whereas those of rg permit any mrl viscosity the decay time observations are satisfied by only a small subset of background mantle viscosities regardless of the mrl properties none of which support a spherically symmetric solution of earth viscosity finally comparing model output to the observed j 2 value did not provide any constraints on mrl properties however our results show that this observable has a strong preference for viscosity values in the lower mantle that are equal to or greater than 10 22 pa s

hematite spherules in basaltic tephra altered under aqueous acid sulfate conditions on mauna kea volcano hawaii possible clues for the occurrence of hematite rich spherules in the burns formation at meridiani planum mars abstract iron rich spherules 90 fe2o3 from electron microprobe analyses 10 100 m in diameter are found within sulfate rich rocks formed by aqueous acid sulfate alteration of basaltic tephra on mauna kea volcano hawaii although some spherules are nearly pure fe most have two concentric compositional zones with the core having a higher fe al ratio than the rim oxide totals less than 100 93 99 suggest structural h2o and or oh 1 the transmission mossbauer spectrum of a spherule rich separate is dominated by a hematite fe2o3 sextet whose peaks are skewed toward zero velocity skewing is consistent with al3 for fe3 substitution and structural h2o and or oh 1 the grey color of the spherules implies specular hematite whole rock powder x ray diffraction spectra are dominated by peaks from smectite and the hydroxy sulfate mineral natroalunite as alteration products and plagioclase feldspar that was present in the precursor basaltic tephra whether spherule formation proceeded directly from basaltic material in one event dissolution of basaltic material and precipitation of hematite spherules or whether spherule formation required more than one event formation of fe bearing sulfate rock and subsequent hydrolysis to hematite is not currently constrained by analogy a formation pathway for the hematite spherules in sulfate rich outcrops at meridiani planum on mars the burns formation is aqueous alteration of basaltic precursor material under acid sulfate conditions although hydrothermal conditions are present on mauna kea such conditions may not be required for spherule formation on mars if the time interval for hydrolysis at lower temperatures is sufficiently long

first non destructive internal imaging of rangea an icon of complex ediacaran life the origins of multicellular life have remained enigmatic due to the paucity of high quality three dimensionally preserved fossils rangea was a centimetre to decimetre scale frond characterised by a repetitive pattern of self similar branches and a sessile benthic lifestyle fossils are typically preserved as moulds and casts exposing only a leafy petalodium and the rarity and incompleteness of specimens has made it difficult to reconstruct the three dimensional 3d morphology of the entire organism this in turn has led to many differing interpretations of its morphology and phylogenetic affinities here we use high resolution x ray micro computed tomography microct to investigate the 3d internal morphology of rare exceptionally preserved ironstone fossils of rangea from the nama group in southern namibia our investigation reveals a series of structures that represent boundaries between individual fronds or structural elements that divide into smaller secondary and tertiary elements leading to a repetitive pattern of branches these elements surround an internal core of a distinctly different texture and internal appearance there is no distortion of the walls of the primary elements thus we conclude that rangea likely had a rigid or semi rigid skeleton like structure that prevented buckling or compression and maintained integrity during life we compare these findings with previous interpretations of rangea morphology and present new insights on the architecture of internal structures such as the central core and the overall appearance of this complex ediacaran life form our insights based on microct scans of these rare uniquely preserved specimens provide a more accurate interpretation of the 3d morphology essential for determining the true affinities and modes of life of the ediacaran biota during this early stage in the evolution of complex macroscopic life

rifting and reactivation of a cretaceous structural belt at the northern margin of the south china sea abstract the tiu tang lung fault hong kong special administrative region china is located on the northern stretched continental margin of the south china sea along this fault middle jurassic volcanic rocks of the tai mo shan formation are tectonically juxtaposed on lower cretaceous sedimentary rocks of the pat sin leng formation both extensional detachments and compressional features are observed and various genetic strain configurations are proposed for the tiu tang lung fault with implications for understanding the dynamics of the pre south china sea rifting during the cretaceous we have identified tilted bedding planes in the continental deposits of the pat sin leng formation which can be related to early cretaceous syn extensional deposition a mid cretaceous penetrative top to the south to top to the west shear fabric is also observed and serves as an indicator of the strain pattern this deformation is expressed by cleavages schistosity s c fabrics kink folds phacoids and stretched pebbles at both a macroscopic and microscopic scale cleavages and bedding are generally sub parallel to the local shear orientation the whole sedimentary pile is crosscut by cenozoic n70 and n150 normal faults these constraints together with previous fission track seismic and structural data allow us to reinterpret the kinematics of this domain during syn orogenic to syn extensional periods the observed top to the south thrusting event is coeval with ne sw strike slip sinistral fault movement subsequent n s extension can be correlated with south china sea rifting from eocene to oligocene these observations reveal a polyphase history associated with continental margin inversion which witnessed localized extension on previous compressional structures

seismic signature of a hydrous mantle transition zone abstract although water has a major influence on tectonic and other geodynamic processes little is known about its quantity and distribution within the deep earth in the last few decades laboratory experiments on nominally anhydrous minerals nams of the transition zone have shown that these minerals can contain significant amounts of water up to 3 3 wt in this study we investigate if it is possible to use seismic observations to distinguish between a hydrous and anhydrous transition zone we perform an extensive literature search of mineral experimental data to generate a compilation of the water storage capacities elastic parameters and phase boundary data for potentially hydrous minerals in the transition zone and use thermodynamic modelling to compute synthetic seismic profiles of density v p and v s at transition zone temperatures and pressures we find that large uncertainties on the mineral phase equilibria ca 2 gpa and elastic properties produce a wide range of seismic profiles in particular there is a lack of data at temperatures corresponding to those along a 1300 c adiabat or hotter which may be expected at transition zone pressures comparing our hydrous transition zone models with equivalent profiles at anhydrous conditions we see that the depths of the 410 and 660 discontinuities cannot at present be used to map the water content of the transition zone due to these uncertainties further while average velocities and densities inside the transition zone clearly decrease with increasing water content there is a near perfect trade off with increases in temperature it is therefore difficult to distinguish thermal from water effects and the conventional view of a slow and thick transition zone for water and slow and thin transition zone for high temperature should be regarded with caution a better diagnostic for water may be given by the average velocity gradients of the transition zone which increase with increasing water content but decrease for increasing temperature however the significance of this effect depends on the degree of water saturation and partitioning between the nams since seismology is better able to constrain the thickness of the transition zone than velocity gradients our study indicates that the most useful input from future mineral physics experiments would be to better constrain the phase relations between hydrous olivine and its high pressure polymorphs especially at high temperatures additionally the uncertainties on the mineral seismic properties could be reduced significantly if the experimentally observable correlations between bulk and shear moduli and their corresponding pressure derivatives would be published

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

a geophysical perspective on mantle water content and melting inverting electromagnetic sounding data using laboratory based electrical conductivity profiles abstract this paper applies electromagnetic sounding methods for earth s mantle to constrain its thermal state chemical composition and water content we consider long period inductive response functions in the form of c responses from four stations distributed across the earth europe north america asia and australia covering a period range from 3 9 to 95 2 days and sensitivity to 1200 km depth we invert c responses directly for thermo chemical state using a self consistent thermodynamic method that computes phase equilibria as functions of pressure temperature and composition in the na 2 o cao feo mgo al 2 o 3 sio 2 model system computed mineral modes are combined with recent laboratory based electrical conductivity models from independent experimental research groups yoshino 2010 and karato 2011 to compute bulk conductivity structure beneath each of the four stations from which c responses are estimated to reliably allocate water between the various mineral phases we include laboratory measured water partition coefficients for major upper mantle and transition zone minerals this scheme is interfaced with a sampling based algorithm to solve the resulting non linear inverse problem this approach has two advantages 1 it anchors temperatures composition electrical conductivities and discontinuities that are in laboratory based forward models and 2 at the same time it permits the use of geophysical inverse methods to optimize conductivity profiles to match geophysical data the results show lateral variations in upper mantle temperatures beneath the four stations that appear to persist throughout the upper mantle and parts of the transition zone calculated mantle temperatures at 410 and 660 km depth lie in the range 1250 1650 c and 1500 1750 c respectively and generally agree with the experimentally determined temperatures at which the measured phase reactions olivine spinel and spinel ferropericlase perovskite occur the retrieved conductivity structures beneath the various stations tend to follow trends observed for temperature with the strongest lateral variations in the uppermost mantle for depths 300 km conductivities appear to depend less on the particular conductivity database conductivities at 410 km and at 660 km depth are found to agree overall with purely geophysically derived global and semi global one dimensional conductivity models both electrical conductivity databases point to 2 o in the upper mantle for transition zone minerals results from the laboratory database of yoshino 2010 suggest that a much higher water content up to 2 wt h 2 o is required than in the other database karato 2011 which favors a relatively dry transition zone 2 o incorporating laboratory measurements of hydrous silicate melting relations and available conductivity data allows us to consider the possibility of hydration melting and a high conductivity melt layer above the 410 km discontinuity the latter appears to be 1 regionally localized and 2 principally a feature from the yoshino 2010 database further there is evidence of lateral heterogeneity the mantle beneath southwestern north america and central china appears wetter than that beneath central europe or australia

acid sulfate weathering of synthetic martian basalt the acid fog model revisited the acid fog model has received considerable attention as a model of soil formation on mars previous evaluations of this model have focused on experimental weathering of terrestrial basalt samples however these samples differ significantly from what now is thought to be typical of martian basalt the acid fog model is tested here using synthetic basaltic analogs derived from mars pathfinder soil and rock compositions reaction of synthetic basalt with various acidic solutions and subsequent evaporation has led to the formation of several putative secondary mineral phases many of these phases were not produced in prior experimental studies aimed at aqueous interactions on mars of these alteration phases mg fe ca and al sulfates were identified in addition secondary ferric oxide phases formed via rapid fe oxidation under relatively high ph levels buffered by basalt dissolution amorphous silica is a ubiquitous product in these experiments and has formed by precipitation from solution and by the dissolution of minerals and glasses leaving behind leached surface layers composed of residual silica the secondary products formed in these experiments demonstrate the importance of primary mineralogy when testing models of aqueous interactions on mars new constraints are placed on both the reactivity of primary basalt and the secondary mineralogy present at the martian surface copyright 2004 by the american geophysical union

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

geochemical and mineralogical aspects of sulfide mine tailings abstract tailings generated during processing of sulfide ores represent a substantial risk to water resources the oxidation of sulfide minerals within tailings deposits can generate low quality water containing elevated concentrations of so 4 fe and associated metal loid s acid generated during the oxidation of pyrite fes 2 pyrrhotite fe 1 x s and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate oxy hydroxide and silicate minerals the extent of acid neutralization and therefore pore water ph is a principal control on the mobility of sulfide oxidation products within tailings deposits metals including fe iii cu zn and ni often occur at high concentrations and exhibit greater mobility at low ph characteristic of acid mine drainage amd in contrast hydr oxyanion forming elements including as sb se and mo commonly exhibit greater mobility at circumneutral ph associated with neutral mine drainage nmd these differences in mobility largely result from the ph dependence of mineral precipitation dissolution and sorption desorption reactions cemented layers of secondary oxy hydroxide and hydroxy sulfate minerals referred to as hardpans may promote attenuation of sulfide mineral oxidation products within and below the oxidation zone hardpans may also limit oxygen ingress and pore water migration within sulfide tailings deposits reduction oxidation redox processes are another important control on metal loid mobility within sulfide tailings deposits reductive dissolution or transformation of secondary oxy hydroxide phases can enhance fe mn and as mobility within sulfide tailings production of h 2 s via microbial sulfate reduction may promote attenuation of sulfide oxidation products including fe zn ni and tl via metal sulfide precipitation understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings

nickeliferous pyrite tracks pervasive hydrothermal alteration in martian regolith breccia a study in nwa 7533 martian regolith breccia nwa 7533 and the seven paired samples is unique among martian meteorites in showing accessory pyrite up to 1 by weight pyrite is a late mineral crystallized after the final assembly of the breccia it is present in all of the lithologies i e the fine grained matrix icm clast laden impact melt rocks climr melt spherules microbasalts lithic clasts and mineral clasts all lacking magmatic sulfides due to degassing pyrite crystals show combinations of cubes truncated cubes and octahedra polycrystalline clusters can reach 200 lm in maximum dimensions regardless of their shape pyrite crystals display evidence of very weak shock metamorphism such as planar features fracture networks and disruption into subgrains the late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration the distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just saturated near neutral 6 fmq 2 log units it is inferred from the maximum ni contents 4 5 wt that pyrite started crystallizing at 400 500 c during or shortly after a short duration relatively low temperature thermal event that lithified and sintered the regolith breccias 1 4 ga ago as deduced from disturbance in several isotope systematics

new u pb age and geochemical constraints on the stratigraphy and distribution of the lantau volcanic group hong kong abstract seven new high precision u pb single crystal zircon ages are reported from jurassic and early cretaceous volcanic rocks in the hong kong special administrative region sar these ages are used in combination with zr vs tio2 ratios to refine the stratigraphy of the lantau volcanic group on lantau island and in adjoining districts in hong kong as a result three major unconformities are proposed and the rift controlled paleogeography of the region which influenced the development of the lantau caldera and lacustrine basins during the latest jurassic to earliest cretaceous is clarified the data also suggest the possibility that the base of the cretaceous system may be preserved within the sequence

comparative planetary mineralogy implications of martian and terrestrial jarosite a crystal chemical perspective abstract the importance of the discovery of jarosite at the meridiani planum region of mars is discussed terrestrial studies demonstrate that jarosite requires a unique environment for its formation crystallizing from highly acidic ph 2 that reacted with aqueous solutions in shallow aquifers or on the martian surface this interaction forms both h 2 so 4 and h 2 s a martian oxidant must be identified to both oxidize h 2 s to produce the required acidity of the fluid and to oxidize fe 2 to fe 3 we suggest that reactions involving both sulfur and the reduction of co 2 to co may provide part of the answer the jarosite crystal structure is truly remarkable in terms of its tolerance for the substitution of a large number of different cations with different ionic radii and charges the structure accommodates hydrogen oxygen and sulfur the stable isotope systematics of which are strong recorders of low temperature fluid rock atmosphere interactions jarosite has been proven to be a robust chronometer for ar ar and k ar dating techniques and there is every reason to believe that u pb rb sr and nd sm techniques for older jarosite from mars will also be robust although the discovery of jarosite on mars alone with no other analytical measurements on the phase has given us insights to martian surficial processes the true power of jarosite can not be exploited until jarosite is sampled and returned from mars mars sample return is a long way off but until then we should be vigilant about examining martian meteorites for alteration assemblages that contain jarosite a suite of jarosite samples representing a significant time span on mars may hold the key to reading the record of martian atmospheric evolution

hydrothermal synthesis of hematite spherules and jarosite implications for diagenesis and hematite spherule formation in sulfate outcrops at meridiani planum mars we synthesized hematite spherules whose mineralogic chemical and crystallographic properties are strikingly similar to those for the hematite rich spherules in lag deposits on the surface and embedded in outcrops at meridiani planum mars the spherules were synthesized in the laboratory along with hydronium jarosite and minor hydronium alunite from fe al mg s cl acid sulfate solutions under hydrothermal conditions the reaction sequence was 1 precipitation of hydronium jarosite 2 jarosite dissolution and precipitation of hematite spherules and 3 precipitation of hydronium alunite upon depletion of hydronium jarosite the spherules exhibit a radial growth texture with the crystallographic c axis aligned along the radial direction so that thermal emission spectra have no hematite emissivity minimum at 390 cm 1 our experiments show that hydrothermal acid sulfate solutions are a pathway for formation of jarosite and the hematite spherules at meridiani planum mars

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

olivine hydration in the deep upper mantle effects of temperature and silica activity 1 although water controls the biology and geology of the surface hydrogen is perhaps the most poorly constrained compositional variable in the bulk earth its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases olivine pyroxene garnet wadsleyite and ringwoodite here we describe a series of experiments showing that the solubility of h2o in olivine at 12 gpa increases with temperature to 8900 ppm by weight at 1250 c and decreases at higher temperature with the onset of melting sample characterization by infrared spectroscopy indicates that the primary hydration mechanism is the substitution of 2h for mg2 similar results obtained from samples coexisting with clinohumite low silica and with clinoenstatite high silica indicate that silica activity has minimal effect on hydration under these conditions single crystal x ray diffraction measurements constrain the volume of hydration and indicate significant m site vacancies hydrogen thus appears to become a geochemically compatible element as depths approach 400 km

highly fractionated jurassic i type granites and related tungsten mineralization in the shirenzhang deposit northern guangdong south china evidence from cassiterite and zircon u pb ages geochemistry and sr nd pb hf isotopes abstract the shirenzhang tungsten deposit is a classic wolframite quartz vein type deposit located in northern guangdong province eastern segment of the nanling w sn polymetallic belt the ore veins controlled by the nw striking fault system are mainly hosted in the ordovician metasedimentary rocks and can also be found with less amount in the cupola of the concealed granitic stock displaying a typical five floor vertical zonation proposed by the chinese geologists the concealed granitic stock mainly comprises two intrusive facies the porphyritic biotite granite g1 in the outer zone and the medium to fine grained monzogranite g2 in the inner zone in this paper we report new cassiterite u pb ages and pb isotopes of sulfides for the shirenzhang tungsten deposit combined with new zircon u pb ages and hf isotopes elemental geochemistry and sr nd pb isotopes of the concealed granitic rocks with aims to elucidate the origin of the ore related granites and the link between the tungsten mineralization and granitic magmatism la icp ms zircon u pb dating gives the weighted mean ages of 164 2 ma for g1 and 162 4 ma for g2 respectively cassiterite from the wolframite bearing quartz vein and the drusy quartz vein yield the weighted mean ages of 164 2 ma and 160 2 ma respectively these ages suggest that both the granitic intrusion and related w sn mineralization in the shirenzhang deposit were initiated during the late jurassic ca 160 ma the shirenzhang granitic rocks are weakly peraluminous highly fractionated i type granites detailed elemental and isotopic data demonstrate that the granitic rocks were derived from partial melting of the paleoproterozoic basement rocks at a relatively shallow depth of 30 km triggered by underplating of basaltic magma and underwent extensive fractional crystallization of hornblende biotite feldspar and monazite and or allanite a continental arc setting induced by northwesterly subduction of the paleo pacific plate is suggested for the genesis of the shirenzhang i type granites the comparable pb isotopic compositions of feldspar and sulfides imply that the lead in the ore veins was of magmatic origin integrating the spatial temporal relationship between the ore veins and the concealed granitic rocks with the pb isotopes from the sulfides and granites we suggest that the tungsten mineralization is genetically linked with the concealed granitic rocks in the shirenzhang deposit fractional crystallization and melt fluid interaction may play an important role on the formation of the granite related tungsten mineralization

temperature dependence and mechanism of hydrogen incorporation in olivine at 12 5 14 0 gpa 1 the concentration and incorporation mechanisms of hydrogen into mg fe 2sio4 olivine have been studied under water saturated conditions at 12 5 14 0 gpa and 1100 2000 c the hydrogen content of olivine fo90 fo95 coexisting with enstatite and hydrous melt increases from about 4600 ppmw at 1100 c to a maximum of 6250 ppmw at 1200 c above 1400 c the hydrogen content of olivine decreases non linearly reaching 160 240 ppmw in the 1800 2000 c range where there is a high melt fraction and no enstatite polarized infrared spectra of the recovered olivines exhibit oh absorption bands in both the 3450 3650 cm 1 range group i and 3160 3450 cm 1 range group ii results indicate that hydration of olivine is associated with both mg and si site vacancies microprobe analyses of the samples show a clear deficit of si in olivine the water storage capacity of olivine is probably no more than 1 5 2 0 times less than wadsleyite at 1400 c and transition zone pressures

volcanic plutonic connections in a tilted nested caldera complex in hong kong 1 exceptional exposures of four precisely dated middle jurassic to early cretaceous silicic volcanic centers and their plutonic equivalents in hong kong have provided an excellent opportunity to examine close connections in time and space between magma chambers and their overlying calderas here we describe a 14 km crustal section through a collapsed caldera in southeastern hong kong where the intracaldera fill suggests that the magmatic discharge was of supereruption scale the main subvolcanic components that link a magma chamber with surface are revealed by well established field relationships supplemented by high precision geochronology whole rock geochemistry and geophysical data exposures and outcrop patterns reveal kilometer scale caldera subsidence and evidence of the simultaneous evacuation of hundreds of cubic kilometers of high silica rhyolite magma through dike like conduits from a shallow subcrustal reservoir the resultant volcanotectonic depression within which is preserved a single cooling unit of massively columnar jointed densely welded tuff high island tuff is interpreted to form part of a larger tilted early cretaceous nested caldera complex the high island eruption signaled the end of a 24 myr period of voluminous pulsed middle jurassic to early cretaceous silicic magmatism in the hong kong region characterized by four discrete ignimbrite flare ups

enhancement of radiative transfer in the upper mantle by oh in minerals abstract diffusion of heat by radiation in the mantle has previously been associated with absorption of light by fe 2 the near ir absorptions of structurally incorporated oh provide another mechanism to convert the energy of photons into lattice vibrations the effective diffusive radiative thermal conductivity due to protonation k rdf wet may be important within the mantle because low absorption strengths as expected for trace to minor oh contents allow light to travel long distances in the medium available calibrations of band strength with oh content are used to develop a formula for k rdf wet as a function of temperature grain size and hydroxyl concentration that is generally applicable to mantle phases these results are compared to new data on the phonon contribution for olivine and to calculations of fe 2 radiative transfer as t increases k rdf wet increases as oh content increases k rdf wet initially increases reaches a maximum near 100 1000 ppm hydroxyl content as h 2 o and then decreases at higher concentrations a similar dependence on grain size exists with the maximum k rdf wet near d 1 cm grain sizes and oh contents of hydrous upper mantle samples foster radiative transport via protonation for example at 1500 k sub cm grain sizes with 10 100 ppm h 2 o provide k rdf wet that is 1 4 of k rdf arising from the combined effect of overtones and fe 2 transitions and 1 8 of the lattice contribution to k of olivine given that oh concentrations vary among mantle minerals the above results suggest that mantle heat flow is heterogeneous and anisotropic the dependence of both k rdf and viscosity on grain size and hydration suggests that the dynamical behavior in or near subducting slabs will be complex

the effect of silica activity on the incorporation mechanisms of water in synthetic forsterite a polarised infrared spectroscopic study pure forsterite crystals were grown from hydrous melts using controlled cooling experiments at 2 0 gpa and varying the bulk mg si ratio from 2 0 to 1 5 oriented single crystals were then studied by polarised infrared spectroscopy the spectra of the samples with the lowest silica activity asio2 contain the main oh bands in the range 3 620 3 450 cm 1 only in contrast the spectra of the samples synthesised with the highest asio2 contain additional pleochroic bands at 3 160 3 220 and 3 600 cm 1 the variations are interpreted in terms of protonated silicon vacancies being dominant at low asio2 and mg vacancies dominant at high asio2 xenolithic mantle olivines generally do not have the spectrum expected for orthopyroxene buffered conditions suggesting that they re equilibrated with their host melts during ascent but mantle olivine from the zabargad peridotite massif probably is in equilibrium with the coexisting orthopyroxene

high precision u pb zircon ages for mesozoic igneous rocks from hong kong abstract sixteen new high precision u pb zircon ages are reported from jurassic and early cretaceous silicic volcanic and plutonic rocks of hong kong when combined with the existing age dataset the new ages constrain more tightly the timing of major periods of volcanism and plutonism at 162 6 4 5 ma 146 7 1 1 ma 143 0 1 0 ma and 140 8 0 6 ma however two ages of 151 9 0 2 ma and 148 1 0 2 ma from eastern new territories and southern hong kong indicate additional and therefore more continuous albeit pulsed magmatic activity than previously thought

effect of oxygen fugacity on the h2o storage capacity of forsterite in the carbon saturated systems abstract high pressure experiments have been performed in the systems mg 2 sio 4 c o h and mg 2 sio 4 k 2 co 3 c at 6 3 gpa and 1200 to 1600 c using a split sphere multi anvil apparatus in the mg 2 sio 4 c o h system the composition of fluid was modeled by adding different amounts of water and stearic acid the f o 2 was controlled by the mo moo 2 or fe feo oxygen buffers several experiments in the mg 2 sio 4 c o h system and all experiments in the mg 2 sio 4 k 2 co 3 c system have been conducted without buffering the f o 2 forsterite in the system mg 2 sio 4 k 2 co 3 c does not reveal oh absorption bands in the ir spectra while forsterite coexisting with carbon bearing fluid and silicate melt at log f o 2 from fmq 2 to fmq 5 from 2 to 5 log units below fayalite magnetite quartz oxygen buffer contains 800 1850 wt ppm h 2 o the maximum concentrations were detected at 1400 c and fmq 3 5 we observed an increase in the solidus temperature in the system mg 2 sio 4 c o h from 1200 to above 1600 c with log f o 2 decreasing from fmq 2 to fmq 5 the increase of the solidus temperature and the broadening of the stability field of the h 2 o h 2 ch 4 subsolidus fluid phase at 1400 1600 c explain the high h 2 o storage capacity of forsterite relative to that crystallized from carbon free oxidized hydrous silicic melt at temperatures above 1400 c liquidus forsterite precipitated along with diamond from oxidized fmq 1 carbonate silicate melt and from silicate melt dissolving the moderately reduced c o h fluid from fmq 2 to fmq 3 5 formation of diamond was not detected under ultra reduced conditions fmq 5 at 1200 1600 c olivine co precipitating with diamond from dry carbonate silicate or hydrous silicic fluid melt can provide information on the h 2 o contents and speciation of the diamond forming media in the mantle the conditions for minimum post crystallization alteration of olivine and its hydrogen content are discussed

deep seismic structure of the northeastern south china sea origin of a high velocity layer in the lower crust we present a 2 d seismic tomographic image of the crustal structure along the obs2012 profile which delineates the moho morphology and magmatic features of the northeastern south china sea margin the image was created by forward modeling rayinvr and traveltime tomographic inversion tomo2d overall the continental crust thins seaward from 27 km to 21 km within the continental shelf across the zhu i depression and dongsha rise with slight local thickening beneath the dongsha rise accompanying the increase in the moho depth the dongsha rise is also characterized by 4 7 km thick high velocity layer hvl 7 0 7 6 km s in the lower crust and exhibits a relatively high velocity 5 5 6 4 km s in the upper crust with a velocity gradient lower than those of the zhu i depression and tainan basin across the continental slope and continent ocean transition cot which contain the tainan basin the crust sharply thins from 20 km to 10 km seaward and a 2 3 km thick hvl is imaged in the lower crust we observed that volcanoes are located only within the cot but none exist in the continental shelf the dongsha rise exhibits a high magnetic anomaly zone and different geochemical characteristics from the cot based on those observations we conclude that the hvl underlying the cot is probably extension related resulting from the decompression melting in the cenozoic whereas the hvl beneath the dongsha rise is probably arc related and associated with the subduction of the paleo pacific plate these findings are inconsistent with those of some previous studies

sulfur bearing phases detected by evolved gas analysis of the rocknest aeolian deposit gale crater mars the sample analysis at mars sam instrument suite detected so2 h2s ocs and cs2 from 450 to 800 c during evolved gas analysis ega of materials from the rocknest aeolian deposit in gale crater mars this was the first detection of evolved sulfur species from a martian surface sample during in situ ega so2 3 22 mol is consistent with the thermal decomposition of fe sulfates or ca sulfites or evolution desorption from sulfur bearing amorphous phases reactions between reduced sulfur phases such as sulfides and evolved o2 or h2o in the sam oven are another candidate so2 source h2s 41 109 nmol is consistent with interactions of h2o h2 and or hcl with reduced sulfur phases and or so2 in the sam oven ocs 1 5 nmol and cs2 0 2 1 nmol are likely derived from reactions between carbon bearing compounds and reduced sulfur sulfates and sulfites indicate some aqueous interactions although not necessarily at the rocknest site fe sulfates imply interaction with acid solutions whereas ca sulfites can form from acidic to near neutral solutions sulfides in the rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source the presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering the possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage understanding the sulfur mineralogy in rocknest materials which exhibit chemical similarities to basaltic fines analyzed elsewhere on mars can provide insight in to the origin and alteration history of martian surface materials

u pb dating of mesozoic igneous rocks from hong kong twenty two new zircon and monazite u pb ages have been obtained for mesozoic plutonic and volcanic rocks of hong kong these have revealed the existence of four distinct periods of mid jurassic to lower cretaceous volcano plutonism 164 6 0 2 to 159 3 0 3 ma 146 6 0 2 to 146 2 0 2 ma 143 7 0 3 to 142 5 0 3 ma and 140 9 0 2 to 140 4 0 2 ma a concordant monazite age of 236 3 0 8 ma has also been obtained from one intrusive body representing the first known occurrence of a mid triassic granitoid in the territory among these rocks discordant u pb data projected to the concordia curve have given a broad range of inheritance ages from early phanerozoic to late archaean a xenocrystic zircon from one sample has yielded a concordant age of 1872 3 ma the new u pb ages have refined the results of recent rb sr whole rock age dating of the granitoid rocks and have considerably improved correlation between intrusive and extrusive units the occurrence of inherited components in many of the analysed rocks indicates that they were derived from or erupted through older crust containing a wide variety of age components either as primary igneous or detrital material

petrogenesis of jurassic fractionated i type granites in southeast china constraints from whole rock geochemical and zircon u pb and hf o isotopes abstract whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for twelve granitic intrusions from inland to coastal areas of the cathaysia block southeast se china in order to constrain their magma sources and petrogenesis they are mainly composed of biotite granites with minor granodiorites zircon u pb dating by la icpms and sims methods gave emplacement ages of 165 154 ma for these rocks which are metaluminous to weakly peraluminous a cnk 0 95 1 10 with variable sio 2 contents and high k 2 o contents they are all depleted in high field strength elements hfses and enriched in light rare earth elements lrees and large ion lithophile elements liles and show negative sr ba and eu anomalies in the spidergrams petrographic and geochemical features suggest the granodiorites that contain hornblende to be typical of i type while the biotite granites without hornblende are fractionated i type granites their variable major and trace element concentrations are due to fractional crystallization of feldspar biotite hornblende and accessory minerals including apatite allanite and monazite moreover our data indicate significant variations in isotopic compositions of these granitoids from inland to coastal areas the inland granites from the lapu fogang xinfengjiang and baishigang plutons have relatively high initial 87 sr 86 sr ratios 0 7105 0 7155 and low e nd t 11 2 to 7 3 and e hf t 10 9 to 6 3 values for whole rocks and variable 18 o values of 7 69 9 25 and e hf t values of 13 5 to 6 7 for zircons in contrast the coastal granites from the longwo wushikeng lianhuashan shigushan chiliao hulutian mantoushan and fenghuang plutons show relatively low initial 87 sr 86 sr ratios 0 7056 0 7110 and high e nd t 7 6 to 6 2 and e hf t 6 5 to 2 8 values for whole rocks together with e hf t values of 7 2 to 3 9 and 18 o values of 6 69 8 38 for zircons the spatial isotopic variations suggest that these jurassic granitoids were generated by different percentage mixing of mantle and ancient paleoproterozoic crust derived magmas with subsequently minor crustal assimilation our results highlight that jurassic fractionated i type granites occur widely from inland to coastal areas of se china arguing against the previous view that jurassic granites occur only in inland while coastal granites are mainly cretaceous the widespread occurrence of jurassic granitoids in se china is attributed to ascending of mantle derived magmas which provide heat for partial melting of lower crustal materials in an extensional setting

iron sulfur mineralogy of mars magmatic evolution and chemical weathering products models for the evolution of sulfide minerals on mars and reaction pathways to their oxidative weathering products in martian regolith have been proposed based on petrogenetic associations between komatiitic rock types viking geochemical data snc meteorites and terrestrial fe ni sulfide deposits to test the weathering model komatiitic pyrrhotites and olivines were exposed to sulfuric acid solutions with and without dissolved ferric iron added to simulate deep weathering processes and the reaction products were identified by mossbauer spectroscopy secondary fes sub 2 pyrite or marcasite feooh goethite and possibly jarosite were formed from pyrrhotite while olivine was oxidized to nanophase goethite these results suggest that on mars acidic groundwater induced pyrrhotite yields fes sub 2 yields feooh jarosite oxidative weathering reactions particularly in the presence of dissolved fe sup 3 such gossaniferous materials occurring in martian regolith were derived mainly from fe ni sulfides associated with komatiitic basalts and not from sulfides occurring in calc alkaline porphyry copper deposits granitic hydrothermal veins sediment hosted pbs zns ores etc which presumably did not evolve on mars due to the virtual lack of plate tectonic activity there

phase relations and melt compositions in cmas pyrolite h2o system up to 25 gpa abstract phase relations and melt compositions in the cao mgo al 2 o 3 sio 2 pyrolite under hydrous 2 of h 2 o and anhydrous conditions have been determined at 10 25 gpa and temperatures from 1400 to 2400 c at the pressure of 16 and 25 gpa the apparent solidus temperatures for the hydrous system are about 200 and 100 c lower than the solidus temperatures for the dry system respectively the apparent solidus temperature changes drastically from 1600 c at 13 5 gpa to about 1850 c at 16 gpa majorite is a liquidus phase in the hydrous pyrolite from 10 to 25 gpa the liquidus phases in the dry pyrolite are olivine at 10 14 gpa majorite at 14 20 gpa and periclase at pressures above 20 gpa we observed expansion of the stability field of anhydrous phase b and its complex relations with the other phases in the cmas pyrolite system we suppose it is formed not only by incongruent melting of wadsleyite but also by the subsolidus reaction of wadsleyite and majorite in the dry condition compositions of partial melts formed by low degree of melting 10 20 have al 2 o 3 depleted and cao rich compositions up to 22 gpa and enriched in al 2 o 3 5 7 wt and cao at 25 gpa at 10 gpa dry and hydrous melts formed by low degree of melting have high sio 2 48 51 wt and relatively high al 2 o 3 3 5 5 2 wt their compositions are generally consistent with those of aluminum depleted komatiite at 13 22 gpa dry and hydrous melts have low sio 2 44 49 wt and al 2 o 3 1 7 3 0 wt and high cao contents 9 15 wt an essential depression of the apparent solidus temperature in the hydrous deep upper mantle compared to that in the transition zone provides the dehydration melting of the hydrous plume the present results support a model of komatiite genesis by dehydration melting of rising wet plumes at the base of the upper mantle

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

jarosites and their application in hydrometallurgy the alunite supergroup consists of more than 40 minerals with the general formula dg 3 t o4 2 oh h2o 6 wherein d represents cations with a coordination number greater or equal to 9 and g and t represent sites with octahedral and tetrahedral coordination respectively smith et al 1998 the supergroup is commonly subdivided into various groups but the simplest primary subdivision is on the basis of the g cations for all of the minerals in the supergroup the dominant g cation is trivalent most of the minerals have g represented by fe3 or al3 but exceptions are the rare minerals gallobeudantite in which g is ga3 and springcreekite in which g is v3 table 1 thus the primary grouping adopted here is on whether formula fe3 exceeds or is subordinate to al3 the hierarchical sequence in mineralogy seems to be variable but here the decreasing sequence is given as supergroup family group and subgroup minerals with fe3 al3 are referred to as belonging to the jarosite family and those with a13 fe3 are allocated to the alunite family view this table table 1 minerals of the alunite supergroup subdivision of the alunite and jarosite families has also been variable scott 1987 for example used seven groups novak et al 1994 used six gaines et al 1997 used four and mandarino 1999 used three the arbitrary decision here is to use three groups which differ from those of mandarino 1999 but which in general indicate whether sulfate phosphate or arsenate predominates in the t o4 tetrahedra the three groups are the alunite group in which t o4 is dominated by so4 the crandallite group in which po4 is

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

receiver function imaging of upper mantle complexity beneath the pacific northwest united states abstract small scale topographic variations on the upper mantle seismic discontinuities provide important constraints on the thermal influences of upwellings and downwellings in geodynamically complex regions subduction of the juan de fuca plate and other tectonic processes dominating the pacific northwest united states in the cenozoic involve massive thermal flux that likely result in an upper mantle that has strong 3 d temperature variations we address the interaction of such processes in the region using receiver functions to image the upper mantle seismic discontinuities at 410 and 660 km we utilized over 15 000 high quality receiver functions gathered from 294 teleseismic earthquakes recorded at 277 regional broadband seismic stations primarily those of the earthscope usarray transportable array we find the average depths of the discontinuities to be 412 km and 658 km respectively with no obvious 520 km discontinuity detected the peak to peak range is greater on the 410 than the 660 suggesting the possibility of more significant regional dynamic processes at upper mantle depths our results are not consistent with a mantle plume below central oregon in the high lava plains region our observation of a thinner transition zone beneath the western snake river plain region however is consistent with a regional increase in mantle temperatures perhaps due to either asthenospheric flow from beneath and around the southern edge of the juan de fuca plate or to vertical flow in the form of regional mantle upwelling related to the snake river plain yellowstone hotspot track further our results are not consistent with a simple subducting juan de fuca slab morphology but rather suggest similar levels of significant complexity in slab structure found by recent regional tomographic studies we find evidence for a thickened and therefore cooler mantle transition zone beneath the wallowa idaho batholith region consistent with tomographic models which suggest broad scale increased seismic velocities to transition zone depths we speculate that this region may be the location of mantle downwelling at larger scales than previously proposed