cyanobacteria are confined to dewless habitats within a dew desert implications for past and future climate change for lithic microorganisms although covering almost all rock outcrops around the world little is known regarding the factors that govern the spatial distribution of lithic cyanobacteria and lichens this is also the case in the negev desert where cyanobacteria predominate on the rock outcrops of the south facing slopes and lichens on the rock outcrops of the north facing slopes hypothesizing that abiotic conditions determine their distribution radiation temperature rain dew and fog were monitored over a two year period 2008 2010 at cyanobacteria and lichen dwelling habitats within a first order drainage basin in the negev highlands while non significant differences characterized the rain amounts substantial differences in substrate temperatures were recorded which resulted in turn in fundamental differences in the non rainfall water regime while dew condensed at the rock outcrops of the lichen habitat no condensation took place at the cyanobacteria habitat contrary to the common belief cyanobacteria were found to inhabit dewless habitats as a result cyanobacteria solely rely on rain precipitation for growth and can therefore serve as bioindicators for dewless habitats within the dewy negev desert the findings may have important implications regarding earth colonization soil forming processes and geochemical processes following climate warming they may explain lichen expansion and subsequent o2 increase during the mid neoproterozoic providing indirect support for substantial photosynthetic activity and high weathering rates during this era

geology the smile of the cheshire cat little is known about geological processes on earth during the hadean over 4000 million years ago in his perspective kramers discusses evidence for crust formation during this early period the new calibration of the lutetium 176 decay constant reported by scherer et al necessitates a new interpretation of existing data it appears that continental crust existed as long as 4400 million years ago but that it was rare

trace and rare earth element geochemistry in tourmaline and cassiterite from the yunlong tin deposit yunnan china implication for migmatitic hydrothermal fluid evolution and ore genesis abstract yunlong tin deposit is a medial sized hydrothermal deposit in western yunnan province of china this deposit is unusual because the tin mineralization occurs exclusively within the migmatite bodies the genesis of the ore deposit has been hotly debated and various models have been proposed including granite related magmatic hydrothermal and migmatitic hydrothermal origins this paper reports a systematic trace and rare earth elements ree geochemical study in tourmaline and cassiterite from the orebodies and associated migmatites from the yunlong tin deposit tourmaline and cassiterite from this deposit show light ree lree enriched patterns with variable eu and ce anomalies consistent with hydrothermal fluids being derived from local high grade metamorphism and migmatization the data suggest that tourmaline and cassiterite were likely precipitated from migmatitic hydrothermal fluids and indicate that the yunlong tin deposit was probably formed during migmatitic hydrothermal process the high concentrations of transition metals e g sc ti v cr mn and zn in tourmalines are also consistent with this model the high concentrations of sn sr and especially sc v and cr in tourmalines can be used to discriminate tourmaline from barren deposits relative to those associated with economic tin mineralization

erosional valleys in the thaumasia region of mars hydrothermal and seismic origins analysis of erosional valleys geologic materials and features and topography through time in the thaumasia region of mars using co registered digital spatial data sets reveals significant associations that relate to valley origin valleys tend to originate 1 on noachian to early hesperian stages 1 and 2 large volcanoes 2 within 50 100 km of stages 1 and 2 rift systems and 3 within 100 km of noachian stage 1 impact craters 50 km in diameter these geologic preferences explain observations of higher valley source densities vsds in areas of higher elevations and regional slopes 1 because the volcanoes rifts and craters form high steep topography or occur in terrain of high relief other stage 1 and stage 2 high steep terrains however do not show high vsds the tendency for valleys to concentrate near geologic features and the overall low drainage densities in thaumasia compared to terrestrial surfaces rule out widespread precipitation as a major factor in valley formation as is proposed in wann wet climate scenarios except perhaps during the early noachian for which much of the geologic record has been obliterated instead volcanoes and rifts may indicate the presence of shallow crustal intrusions that could lead to local hydrothermal circulation melting of ground ice and snow and groundwater sapping however impact crater melt would provide a heat source at the surface that might drive away water fonning valleys in the process post stage 1 craters mostly have low nearby vsds which for valleys incised in older rocks suggests burial by ejecta and for younger valleys may indicate desiccation of near surface water and deepening of the cryosphere later hesperian and amazonian stages 3 and 4 valleys originate within 100 200 km of three young large impact craters and near rifts systems at warrego valles and the southern part of coprates rise these valleys likely developed when the cryosphere was a couple kilometers or more thick inhibiting valley development by hydrothermal circulation however eruption of groundwater may have occurred from impact induced fracturing and lateral and perhaps minor upward transport of water due to seismic pumping the two smaller craters formed along the plateau margin where the highest potential hydraulic head would occur in aquifers beneath the plateau in the case of the larger crater lowell 200 km in diameter potential aquifers would likely be at depths of kilometers below the cryosphere seismic energy generated by the lowell impactor would have been much greater pumping both groundwater and perhaps fluidized slurry to the surface from beneath the cryosphere to form the young valleys and flow deposit along the margin of thaumasia tectonic pressurization of groundwater also may have contributed to valley formation dissection of rim materials of the argyre impact may relate to tectonic activity and the unconsolidated state of basin ejecta

postglacial rebound observed by lageos and the effective viscosity of the lower mantle sixty four observations of the orbital node made by the lageos satellite over a five year time interval reveal an acceleration of 8 1 or 1 8 x 10 to the 8 power arcseconds day 2 due to a source which is not presently modeled in the geodyn orbit determination computer program this acceleration cannot be explained by the ocean tide with 18 6 year period assuming it to be an equilibrium tide instead it seems to be due to postglacial rebound which changes the j 2 coefficient in the spherical harmonic expansion of the earth s gravitational field at the rate of 8 2 or 18 x 10 to the 19th power s this in turn accelerates the node this rate does not agree with the 32 x 10 to the 19th power s predicted by wu and peltier s 1982 l2 model which has upper and lower mantle effective viscosities of 10 to the 21st and 22nd powers pa s respectively it does agree well with their l1 model which gives about 10 x 10 to the 19th power s since the effective viscosity is 10 to the 21st power pa s throughout the entire mantle in the l1 model the results support the contentions that the efective viscosity is near 10 to the 21st power pa s everyhere in the mantle and this relatively low value for the effective viscosity may have permitted several degrees of polar wander due to glaciation during the quaternary ice age previously announced in star as n84 13705

age and origin of the lowlands of mars one of the many significant findings of the mars global surveyor mission is the presence of hundreds of quasi circular depressions qcds observed from high resolution mola topography data their presence has recently been interpreted to reflect a northern lowlands that archive some of the earliest recorded rocks on mars mostly below a veneer of hesperian and amazonian materials here we analyze these data coupled with a recent synthesis of geologic geophysical geomorphic topographic and magnetic information such analysis allows us to suggest a potential plate tectonic phase during the recorded early into middle noachian martian history that transitioned into a monoplate world with episodic magmatic driven activity persisting to present this working hypothesis is based on 1 the observation that the basement of the northern plains is younger than the basement of the southern highlands but older than the material exposures of the cratered highlands suggesting different formational ages for each one of the three geologic time units 2 the observation that parts of the very ancient highland s crust are highly magnetized thus suggesting that most if not all of the formation of the lowlands basement postdates the shut off of the martian dynamo some 4 gyr ago and so allowing hundreds of millions of years for the shaping of the buried lowlands consequently the role of endogenic processes in the earliest geological evolution of mars early perhaps into middle noachian requires reconsideration since mola topographic and mgs magnetic data afford a temporal window sufficient for very early non primordial shaping of the northern lowlands basement

recent earth oblateness variations unraveling climate and postglacial rebound effects earth9s dynamic oblateness j2 has been decreasing due to postglacial rebound pgr however j2 began to increase in 1997 indicating a pronounced global scale mass redistribution within earth9s system we have determined that the observed increases in j2 are caused primarily by a recent surge in subpolar glacial melting and by mass shifts in the southern pacific and indian oceans when these effects are removed the residual trend in j2 2 9 x 10 11 year 1 becomes consistent with previous estimates of pgr from satellite and eclipse data the climatic significance of these rapid shifts in glacial and oceanic mass however remains to be investigated

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

mineralogy geochemistry and petrogenesis of green nephrite from dahua guangxi southern china abstract a new nephrite deposit with potential for economic exploitation was recently discovered in dahua county hechi city guangxi autonomous region china previous studies have focused primarily on white black and black cyan nephrite from dahua whereas few studies have been carried out on green nephrite in this study the mineralogical petrological and geochemical characteristics of nephrite from this new deposit were systematically studied using polarized light microscopy scanning electron microscopy electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry and the deposit genesis was discussed the results show that dahua green nephrite consists of interwoven microfibers and the main mineral component is tremolite the mg2 mg2 fe2 ratio ranges from 0 951 to 1 00 andthe subordinate minerals include diopside chlorite calcite quartz apatite albite titanite and andradite the contents of trace elements cr ni and co are much lower than in metasomatized serpentinite type nephrite the rare earth element content is generally high 62 011 223 116 ppm with a positive eu anomaly 1 009 2 343 positive and negative ce anomalies 0 913 1 078 enrichment in light rare earth elements and flatness in heavy rare earth elements the distribution curves of the rare earth elements differ between the nephrite and the surrounding rock samples indicating multiple sources and a multiperiod superposition of the ore forming fluids the fe2 mg2 fe2 ratio in dahua green nephrite is lower than 0 06 indicating that the nephrite deposit is surrounded by carbonates by taking c ca2 c mg2 and c fe2 fe3 as endmembers for projection amphibole can be concluded to have originated from contact metasomatism considering the findings of the geological survey the dahua green nephrite likely belongs to the magmatic hydrothermal metasomatic type and its ore deposit is related to basic intrusive rocks such as diabase and hydrothermal fluid carried by magma contact metasomatism and hydrothermal metamorphism occurred with dolomitic limestone and other carbonate rocks under certain temperature and pressure conditions during the variscan indosinian period this systematic study of the newly discovered dahua green nephrite deposit provides a theoretical basis for the prospecting of nephrite deposits in the study area

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

simultaneous inversion for the earth s mantle viscosity and ice mass imbalance in antarctica and greenland redistribution of mass in the earth due to pleistocene deglaciation and to present day glacial melting induces secular changes in the earth s gravitational field the earth is affected today by the former mechanism because of the viscous memory of the mantle and by the latter because of ongoing surface mass redistribution and related elastic response a self consistent procedure allows us to invert simultaneously for the lower and upper mantle viscosity and for the present day mass imbalance in antarctica and greenland using the observed time variations of the long wavelength gravity field from satellite laser ranging slr analyses the procedure is based on our normal mode relaxation theory for the forward modeling and a newly developed inversion scheme based on the levenberg marquardt method we obtain a large viscosity increase across the 670 km depth transition zone separating the upper and the lower mantle with the lower mantle viscosity varying over the range 5 1021 to 1022 pa s and the less resolved upper mantle viscosity of the order of 1020 pa s when antarctica is the only present day source its rate of melting is 240 gt yr 1 corresponding to a sea level rise of 0 7 mm yr 1 when greenland is added as a source of ice loss the rates of melting are 280 gt yr 1 for antarctica and 60 gt yr 1 for greenland corresponding to sea level rises of 0 8 and 0 2 mm yr 1 slr data indicate that ice melting in the polar regions of the earth is ongoing

fluid and metal sources of the wenquan porphyry molybdenum deposit western qinling nw china the wenquan porphyry moybdenium deposit western qinling nw china with a resource of 247 million tonnes at 0 048 mo formed during triassic collision between south china and north china blocks ore fluids at wenquan vary widely in composition from single phase low salinity aqueous to low salinity vapor and hypersaline inclusions fluid inclusion assemblages in a quartz molybdenite vein contain 60 vol vapor are equant to negative crystal shaped and form clusters or distinct inclusion trails they yield homogenization temperatures of 285 295 c with an estimated trapping temperature of 425 c suggesting a paleodepth of about 5 km calculated at a pressure correction of 100 150 mpa hydrothermal k feldspar from early stockwork veins related to potassic alteration have calculated 18ofluid values of 1 9 to 1 9 hydrothermal sericite from an overprinting phyllic alteration associated with late quartz pyrite veins has calculated dfluid values between 68 and 60 and 18ofluid values from 3 7 to 1 4 these isotopic data suggest that both early and late stage fluids are dominated by magmatic fluids with influx of meteoric water during the late stage exsolution of volatiles from magma in a late stage open system results in more variable d values than an earlier closed system molybdenite and pyrite have 34s values ranging from 1 1 to 6 6 indicating that sulfur at wenquan had a magmatic source a linear relationship between 34s values of sulfides separated from early potassic alteration and late phyllic alteration could reflect incorporation of isotopically heavy evaporate sulfate into source magmas from underlying devonian sedimentary rocks during late alteration the 56fe whole rock values of altered porphyries range from 0 08 to 0 26 similar to 56fe values of 0 15 0 32 for pyrite from quartz veins related to both the potassic and phyllic alteration assemblages the 56fe values of pyrite are positively correlated to but in general slightly lighter than those of altered porphyries indicating similar metal sources moreover both altered porphyries and the pyrite are progressively enriched in heavy fe isotopes from biotite through potassic to late phyllic alteration consistent with isotopic evolution from an early lithostatic load to a late hydrostatic load the triassic intrusive rocks and fluids responsible for mineralization were derived from a deeply sourced hybrid mantle crustal magma crystallizing at a paleodepth of 5 km under lithostatic load external late triassic meteoric or devonian formational fluids became a part of the hydrothermal system during the post fracturing final stage of ore formation under a hydrostatic regime the formation of the wenquan magmatic hydrothermal systems spans the ductile brittle transition based on a normal thermal gradient as constrained by the temperature range of 550 300 c the early high temperature potassic alteration developed under a ductile regime whereas the later low temperature phyllic alteration correlates to a brittle environment where hydraulic rock fracturing enhances permeability and fluid circulation most sulfur and metals were precipitated from vapor rich fluids resulting from cooling and expansion of a single phase fluid exsolved from a hybrid magma

outflow channel sources reactivation and chaos formation xanthe terra mars abstract the undulating warped and densely fractured surfaces of highland regions east of valles marineris located north of the eastern aureum chaos east of the hydraotes chaos and south of the hydaspis chaos resulted from extensional surface warping related to ground subsidence caused when pressurized water confined in subterranean caverns was released to the surface water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of ares tiu and simud valles of the eastern part of the circum chryse outflow channel system progressive surface subsidence and associated reduction of the subsurface cavernous volume and or episodes of magmatic driven activity led to increases of the hydrostatic pressure resulting in reactivation of both catastrophic and non catastrophic outflow activity ancient cratered highland and basin materials that underwent large scale subsidence grade into densely fractured terrains collapse of rock materials in these regions resulted in the formation of chaotic terrains which occur in and near the headwaters of the eastern circum chryse outflow channels the deepest chaotic terrain in the hydaspis chaos region resulted from the collapse of pre existing outflow channel floors the release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow basal warming related to dike intrusions thermokarst activity involving wet sediments and or dissected ice enriched country rock permafrost exposed to the atmosphere by extensional tectonism and channel incision and or the injection of water into porous floor material may have enhanced outflow channel floor instability and subsequent collapse in addition to the possible genetic linkage to outflow channel development dating back to at least the late noachian clear disruption of impact craters with pristine ejecta blankets and rims as well as preservation of fine tectonic fabrics suggest that plateau subsidence and chaos formation may have continued well into the amazonian period the geologic and paleohydrologic histories presented here have important implications as new mechanisms for outflow channel formation and other fluvial activity are described and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation and thus chaotic terrains mark prime locations for future geologic hydrologic and possible astrobiologic exploration

latent outflow activity for western tharsis mars significant flood record exposed observations permitted by the newly acquired mars observer laser altimeter data have revealed a system of gigantic valleys northwest of the huge martian shield volcano arsia mons in the western hemisphere of mars northwestern slope valleys nsvs these features which generally correspond spatially to gravity lows are obscured by veneers of materials including volcanic lava flows air fall deposits and eolian materials geologic investigations of the tharsis region suggest that the system of gigantic valleys predates the construction of arsia mons and its extensive associated lava flows of mainly late hesperian and amazonian age and coincides stratigraphically with the early development of the outflow channels that debouch into chryse planitia similar to the previously identified outflow channels which issued tremendous volumes of water into topographic lows such as chryse planitia the nsvs potentially represent flooding of immense magnitude and as such a source of water for a northern plains ocean

pancam multispectral imaging results from the opportunity rover at meridiani planum panoramic camera pancam images from meridiani planum reveal a low albedo generally flat and relatively rock free surface within and around impact craters and fractures laminated outcrop rocks with higher albedo are observed fine grained materials include dark sand bright ferric iron rich dust angular rock clasts and millimeter size spheroidal granules that are eroding out of the laminated rocks spectra of sand clasts and one dark plains rock are consistent with mafic silicates such as pyroxene and olivine spectra of both the spherules and the laminated outcrop materials indicate the presence of crystalline ferric oxides or oxyhydroxides atmospheric observations show a steady decline in dust opacity during the mission astronomical observations captured solar transits by phobos and deimos and time lapse observations of sunsets

the slr secular gravity variations and their impact on the inference of mantle rheology and lithospheric thickness a long history of slr satellite laser ranging observations of the geodetic satellites lageos i lageos ii starlette and stella have been analyzed in order to estimate the time series of the low degree zonal coefficients in the earth gravity field up to degree six and derive their secular drifts the paper will point out the critical aspects of the analysis process and will compare the estimated zonal rates with other published results comparison of these zonal rates with the results of global viscoelastic earth models forced by pleistocenic deglaciation shows that the slr retrieved zonals and the lumped odd zonals can be used to infer the upper mantle viscosity and lithospheric thickness discrepancies in the viscosity profiles required to reproduce the different zonals seem to indicate ongoing mass redistribution over the earth

mantle viscosity inferences from joint inversions of pleistocene deglaciatio induced changes in geopotential with a new slr analysis and polar wander joint inversions of post glacial rebound induced secular changes in low degree harmonics of the geopotential and true polar wander tpw systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 10 21 pas the lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent unmodeled glacial forcings and or insufficient precision in the evaluation of the mass loss from pleistocene ice sheets the influence of systematic errors in slr data reduction due to thermal drag on the lageos satellites for the uneven zonals of the geopotential is avoided by making use of the starlette and stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms

martian surface paleotemperatures from thermochronology of meteorites the temporal evolution of past martian surface temperatures is poorly known we used thermochronology and published noble gas and petrographic data to constrain the temperature histories of the nakhlites and martian meteorite alh84001 we found that the nakhlites have not been heated to more than 350 c since they formed our calculations also suggest that for most of the past 4 billion years ambient near surface temperatures on mars are unlikely to have been much higher than the present cold 0 c state

mineralogy geochemistry and petrogenesis of nephrite from tieli china abstract concurrent with the increase in nephrite mining in recent years many new nephrite deposits have been discovered worldwide however studies of these new deposits remain limited to address this knowledge gap the objective of this study was to systematically investigate the nephrite deposit in tieli heilongjiang province china electron probe micro analysis and laser ablation inductively coupled plasma mass spectrometry were used to measure the mineralogical petrological and geochemical characteristics of samples from this deposit the nephrite exhibits a fine and smooth texture with felted blastic and fibroblastic structures indicating high quality compared with nephrites from other deposits the main mineral composition is tremolite with a mg fe2 mg ratio of 0 982 0 992 which is purer than nephrite samples from most other deposits furthermore all tremolite examined in the tieli nephrite has low amounts of cr2o3 0 000 0 060 wt and nio 0 000 0 061 wt relative to dolomite related nephrites the nephrite samples all have very low total rare earth element ree contents ranging from 2 8633 to 10 8375 ppm and are characterized by positive and negative eu anomalies 0 3286 1 4570 light ree enrichment and flat heavy ree the varied ree patterns of the samples highlight the multiple sources of ore forming fluids multistage superimposed mineralization and oxidized mineralization environment the mineral composition of the wall rocks indicates that during formation two typical processes results in nephrite genesis contact and hydrothermal metasomatism generally this nephrite is of a dolomite related origin the discovery of the tieli deposit and this first time systematic study provide a theoretical basis for prospecting nephrite deposits in the study area where intermediate to felsic igneous rocks or si enriched hydrothermal fluids intruded limestone or dolomite marble formed during the variscan indosinian epoch

petrogenesis of granitoids in the dewulu skarn copper deposit implications for the evolution of the paleotethys ocean and mineralization in western qinling china abstract the tethyan tectonic domain hosts numerous world class mineral deposits among these the dewulu skarn copper deposit in western qinling china belongs to the paleotethys ore belt the skarn and orebodies here occur as stratoids or lenses at the contact between the triassic dewulu intrusive complex and permian marine clastic and carbonates alteration minerals include prograde skarns garnet diopside wollastonite plagioclase hornblende actinolite tremolite epidote chlorite calcite quartz and sericite the main ore types include early disseminated skarn type replacement orebodies and late stage quartz sulfide veins chalcopyrite is the major ore mineral along with pyrite bornite and sphalerite the dewulu intrusive complex comprises quartz diorite quartz diorite porphyry and dioritic mafic microgranular enclaves mme the mmes are spheroidal in shape and have igneous mineral assemblages acicular apatites complex oscillatory zoned plagioclase and quartz megacrysts surrounded by mafic minerals the mmes are metaluminous and calc alkaline to high k calc alkaline and possess relatively high ni cr and mgo contents and mg values they display sub parallel patterns in trace element spider diagrams and rare earth element ree plots they are also characterized by the enrichment of rb u and th depletion of ba sr nb and ta and negative eu anomaly zircon la icp ms u pb dating of the dioritic mme yields an age of 247 0 2 2 ma coeval with the host quartz diorite quartz diorite porphyry and ore related sericite 40ar 39ar plateau ages within analytical uncertainties oxygen fugacity estimated from trace element compositions of zircons from the dioritic mme shows fmq 3 3 the zircons have negative ehf t values in a range of 8 0 to 3 3 corresponding to two stage model ages ranging from 1 48 to 1 78 ga the integrated data from petrology geochronology and bulk geochemistry suggest that the early triassic granitoids associated with cu skarn mineralization at dewulu were products of arc magmatism and involved magma mixing in an active continental margin setting the magma was sourced through partial melting of enriched sub continental lithospheric mantle that had been previously modified by slab derived melt during the continuous northward subduction of the paleotethys oceanic slab

ion microprobe zircon u pb age and geochemistry of the myanmar jadeitite combined geochemistry and geochronology of the myanmar jadeitite were determined bulk rock trace element compositions display u shaped ree patterns with pronounced positive eu anomalies the total ree abundances are very low less than half chondritic and the high field strength elements and some large ion lithophile elements are moderately enriched these features indicate a metasomatic origin there are three groups of zircons with different interior characteristics cathodoluminescence mineral inclusions chemical compositions and sensitive high resolution ion microprobe u pb ages group i zircons with a mean age of 163 2 3 3 ma mostly have distinct oscillatory zoning highest u and th contents and na free mg rich mineral inclusions and thus indicate an igneous formation of oceanic crust or hydrothermal serpentinization and or rodingitization event in the middle jurassic group ii zircons with a mean age of 146 5 3 4 ma have bright luminescence without oscillatory zoning and include jadeite and jadeitic pyroxene inclusions suggesting that formation of the myanmar jadeitites as well as subduction of the eastern indian oceanic plate occurred in the late jurassic group iii zircons have an age of 122 2 4 8 ma which represents a later unknown thermal event discovery of the middle jurassic zircons provides geochronological constraint on the tectonic evolution of the eastern indo burman range

hydrogeologic processes of large scale tectonomagmatic complexes in mongolia southern siberia and on mars large scale tectonomagmatic complexes are common on earth and mars many of these complexes are created or at least influenced by mantle processes including a wide array of plume types ranging from superplumes to mantle plumes among the most prominent complexes the mongolian plateau on earth and the tharsis bulge on mars share remarkable similarities in terms of large domal uplifted areas great rift canyon systems and widespread volcanism on their surfaces water has also played an important role in the development of the two complexes in general atmospheric and surface water play a bigger role in the development of the present day mongolian plateau than for the tharsis bulge as evidenced by highly developed drainages and thick accumulation of sediments in the basins of the baikal rift system on the tharsis bulge however water appears to have remained as ground ice except during periods of elevated magmatic activity glacial and periglacial processes are well documented for the mongolian plateau and are also reported for parts of the tharsis bulge ice magma interactions which are represented by the formation of subice volcanoes in parts of the mongolian plateau region have been reported for the valles marineris region of mars the complexes are also characterized by cataclysmic floods but their triggering mechanism may differ mainly ice dam failures for the mongolian plateau and outburst of groundwater for the tharsis bulge probably by magma ice interactions although ice dam failures within the valles marineris region cannot be ruled out as a possible contributor comparative studies of the mongolian plateau and tharsis bulge provide excellent opportunities for understanding surface manifestations of plume driven processes on terrestrial planets and how they interact with hydro cryospheres

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

ice sheet collapse and sea level change at the end of the last ice age the melting of large ice sheets led to substantial sea level rises but the sea level changes were not even in time or space in his perspective sabadini 1 explains how clark et al 2 use the geographic patterns of sea level change to deduce the pattern of ice sheet melting and hence of climatic change during deglaciation 1 http www sciencemag org cgi content full 295 5564 2376 2 http www sciencemag org cgi content short 295 5564 2438

new evidence for 250 ma age of halotolerant bacterium from a permian salt crystal the purported oldest living organism the spore forming bacterium virgibacillus sp perm ian strain 2 9 3 was recently cultured from a brine inclusion in halite of the 250 ma permian salado formation however the antiquity of virgibacillus sp 2 9 3 has been chal lenged it has been argued that the halite crystal and the fluid inclusion from which the bacterial spores were extracted may be younger than the permian salado salts here we report that brine inclusions from the same layer of salt that housed virgibacillus sp 2 9 3 are composed of evaporated late permian seawater that was trapped in halite cement crys tals precipitated syndepositionally from shallow groundwater brines at temperatures of 17 37 8c these results support the 250 ma age of the fluid inclusions and by inference the long term survivability of microorganisms such as virgibacillus sp 2 9 3

new lu hf and pb pb age constraints on the earliest animal fossils abstract the neoproterozoic doushantuo formation south china preserves a unique assemblage of early multicellular fossils and overlies rocks which are thought to have formed during an ice age of global extent the age of this formation is thus critical for understanding the important biological and climatic events that occurred towards the end of the proterozoic eon until now direct dating of sedimentary formations such as the doushantuo has been difficult and associated with large uncertainties here we show that dating of doushantuo phosphorites by a novel lu hf dating method and conventional pb pb geochronometry independently yield ages of 584 26 ma and 599 3 4 2 ma respectively these ages are in agreement with bio and chemostratigraphical observations and show that the doushantuo animal remains predate diverse ediacaran fossil assemblages making them the oldest unambiguous remains of metazoans currently known furthermore the pb pb age for the post glacial doushantuo rocks suggests that the neoproterozoic glaciation in china might predate glacial rocks in eastern north america commonly associated with the younger marinoan of two major neoproterozoic glaciations the combination of lu hf and pb pb dating shows considerable potential for dating other phosphorite successions and future application of these methods could therefore provide further constraints on proterozoic biological and environmental history

new perspectives on ancient mars mars was most active during its first billion years the core mantle and crust formed within 50 million years of solar system formation a magnetic dynamo in a convecting fluid core magnetized the crust and the global field shielded a more massive early atmosphere against solar wind stripping the tharsis province became a focus for volcanism deformation and outgassing of water and carbon dioxide in quantities possibly sufficient to induce episodes of climate warming surficial and near surface water contributed to regionally extensive erosion sediment transport and chemical alteration deep hydrothermal circulation accelerated crustal cooling preserved variations in crustal thickness and modified patterns of crustal magnetization

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

asphalt volcanism and chemosynthetic life in the campeche knolls gulf of mexico in the campeche knolls in the southern gulf of mexico lava like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt which chilled and contracted after discharge the site also includes oil seeps gas hydrate deposits locally anoxic sediments and slabs of authigenic carbonate asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the gulf of mexico

episodic flood inundations of the northern plains of mars throughout the recorded history of mars liquid water has distinctly shaped its landscape including the prominent circum chryse and the northwestern slope valleys outflow channel systems and the extremely flat northern plains topography at the distal reaches of these outflow channel systems paleotopographic reconstructions of the tharsis magmatic complex reveal the existence of an europe sized noachian drainage basin and subsequent aquifer system in eastern tharsis this basin is proposed to have sourced outburst floodwaters that sculpted the outflow channels and ponded to form various hypothesized oceans seas and lakes episodically through time these floodwaters decreased in volume with time due to inadequate groundwater recharge of the tharsis aquifer system martian topography as observed from the mars orbiter laser altimeter corresponds well to these ancient flood inundations including the approximated shorelines that have been proposed for the northern plains stratigraphy geomorphology and topography record at least one great noachian early hesperian northern plains ocean a late hesperian sea inset within the margin of the high water marks of the previous ocean and a number of widely distributed minor lakes that may represent a reduced late hesperian sea or ponded waters in the deepest reaches of the northern plains related to minor tharsis and elysium induced amazonian flooding

secular variations in zonal harmonics of earth s geopotential and their implications for mantle viscosity and antarctic melting history due to the last deglaciation

geochemistry and petrogenesis of placer nephrite from hetian xinjiang northwest china article the yurungkash and karakash rivers also known respectively as the white jade and black jade rivers located in hetian xinjiang province northwest china are the two main sources in china of white green and black placer nephrite with a long history 5000 years of exploration and mining the twenty nine placer nephrite samples collected from both rivers and analyzed in the present study possess fine grained and compact microstructures the mineral assemblages in the samples provide clues to the metamorphic metasomatic processes that formed the nephrite which was the result of one of the following reactions dolomitic marble tremolite or dolomitic marble diopside tremolite white nephrite from the yurungkash river and green nephrite from the karakash river are predominantly tremolite based on electron probe microanalytical data backscattered electron images and raman spectra two kinds of black nephrite from the karakash river are identified one dominated by actinolite aggregates and another consisting of tremolite aggregates with graphite crystals up to 2 mm in length compared with black nephrite white and green nephrites contain fewer mineral inclusions and have lower feo and mno contents all the amphiboles in the nephrites have very low contents of cr2o3 0 00 0 07 wt and nio 0 00 0 05 wt relative to serpentinite related nephrite 0 07 0 43 wt cr2o3 0 08 0 36 wt nio most of the nephrite samples have low total rare earth element ree contents ranging from 12 22 to 49 40 ppm in two nephrite samples relatively high ree concentrations 161 and 190 ppm are related to the presence of ree bearing minerals whole rock ree chondrite normalized patterns of all samples are characterized by strong negative eu anomalies 0 16 0 48 moderate light ree enrichment la ndn 1 8 5 0 and nearly flat heavy ree distributions gd ybn 0 3 1 7 nephrite samples from both river locations have 18

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

martian plate tectonics the northern lowlands of mars may have been produced by plate tectonics preexisting old thick highland crust was subducted while seafloor spreading produced thin lowland crust during late noachian and early hesperian time in the preferred reconstruction a breakup margin extended north of cimmeria terra between daedalia planum and isidis planitia where the highland lowland transition is relatively simple south dipping subduction occurred beneath arabia terra and east dipping subduction beneath thatsis montes and tempe terra lineations associated with gordii dotsum are attributed to ridge parallel structures while phelegra montes and scandia colles are interpreted as transform parallel structures or ridge fault fault triple junction tracks other than for these few features there is little topographic roughness in the lowlands seafloor spreading if it occurred must have been relatively rapid quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower c 0 4 g gravity of mars the absence of vertical scarps from age differences across fracture zones and the smooth axial topography to the first order the height of vertical scarps across fracture zones does not involve gravity crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity thus the velocity of the rough smooth transition for axial topography also scales inversely with gravity plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age possible plate reorganizations for example the end of spreading through alba patera occur when the ridge axis is far from the trench that is rapid plate motions are inferred to have placed young oceanic crust far from the ridge axis the preferred full spreading rate 900 from the plate pole is 80 mm yr 1 plate tectonics if it occurred dominated the thermal and stress history of the planet a geochemical implication is that the lower gravity of mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the earth age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about mars plate tectonics

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

control of impact crater fracture systems on subsurface hydrology ground subsidence and collapse mars 1 noachian layered materials are pervasively exposed throughout the highlands of mars the layered deposits in places many kilometers thick exhibit impact craters of diverse morphologic characteristics ranging from highly degraded to pristine most of which formed during the period of heavy bombardment in addition exhumed impact craters ancient channels and fluvial and alluvial fans are visible in the layered deposits through moc imagery these features are more abundant in noachian terrains which indicates relatively high erosion rates during ancient mars that competed with heavy meteoritic bombardment the noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation here we propose that impact craters buried and exposed and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic driven hydrothermal activity in and surrounding the tharsis region for example the formation of chaotic terrains the source regions of the circum chryse outflow channel system and a large diversity of collapse structures including impact crater moats and pit chains appear to be the result of enhanced hydrothermal activity

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

scenarios for the evolution of life on mars received 10 march 2005 revised 2 august 2005 accepted 7 september 2005 published 22 november 2005 1 as the environmental histories of earth and mars have diverged drastically after the first few hundred million years so would the history of any life on them while earth has had liquid water on its surface for billions of years mars most likely had long dry and cold environments interspersed with warmer and wetter periods life thrived on earth but may have been severely restricted on mars there it could be present today in liquid water in or beneath ice sheets or glaciers in subterranean aqueous reservoirs especially in regions of elevated heat flow or in protected habitats such as lava tubes caves or cracks and fissures the potential for life is enhanced in regions where elevated heat flow may occur such as in parts of the tharsis and elysium volcanic provinces possible organisms would be chemoautotrophic psychrophiles adapted to a nutrient poor environment or photoautotrophic life in selected near surface habitats alternatively life may have evolved alternating cycles between active and dormant forms in which case microbes could be present in dormant forms close to the surface and in active forms in protected environments periodic liquid water on mars could have provided opportunities for biologic activity as well as evolutionary progress at the surface during the short lived climatic perturbations ancient organisms from any of these environments may also have left a detectable fossil record

the biological potential of mars the early earth and europa the potential biomass that could have existed on mars is constrained by the total amount of energy available to construct it from an inventory of the available geochemical sources of energy we estimate that from the time of the onset of the visible geologic record 4 b y ago to the present as much as 20 g cm 2 of biota could have been created this is the same amount that could have been constructed on the early earth in only 100 million years this indicates that there likely was sufficient energy available to support an origin of life on mars but not sufficient energy to create a ubiquitous and lush biosphere similar calculations for europa suggest that even less geochemical energy would have been available there

present day secular variations in the zonal harmonics of earth s geopotential we develop a new formalism for the prediction of secular variations in the gravitational potential field of a spherically symmetric self gravitating maxwell viscoelastic planetary model subjected to an arbitrary surface load which may include a gravitationally self consistent ocean loading component the theory is applied to generate the most accurate predictions to date of the present day secular variations in the zonal harmonics of the geopotential the so called for degree arising as a consequence of the late pleistocene glacial cycles in this respect we use the very recent ice 3g reconstruction of the last late pleistocene deglaciation event tushingham and peltier 1991 a comparison of these predictions with those generated using simplified disk models of the ice sheets which have been used in all previous studies of the harmonics 2 indicates that the disk model approximation introduces unacceptably large errors at all spherical harmonic degrees except perhaps 2 predictions have also been made using a eustatic loading approximation also used in previous studies in place of a gravitationally self consistent ocean loading component and we have found that the resulting discrepancy is largest at degrees 2 8 and 10 in the case of the magnitude of the error incurred using the eustatic approximation can be as large as order 10 15 of the predicted value we have attributed this discrepancy to the present day net flux of water away from the equatorial regions arising from the remnant present day adjustment associated with the late pleistocene glacial cycles the effect represents a heretofore unrecognized contribution to the harmonics or alternatively the nontidal acceleration of earth s axial rate of rotation in terms of the latter the maximum anomaly in the length of day is approximately 1 7 s yr we also consider the sensitivity of the data to variations in the radial mantle viscosity profile by using a suite of forward calculations and an examination of frechet kernels the theory required for the computation of those kernels is described herein we find that the radial variation in sensitivity can be a strong function of the viscosity model used in the calculations for models with a uniform upper mantle viscosity um of 1021 pa s forward predictions of the harmonics exhibit a pronounced peak when a wide enough range of lower mantle viscosities lm are considered we denote the lm value at this peak as at the lowest degrees 4 frechet kernels computed for a series of increasing lm values 1021 pa s lm 1023 pa s indicate a migration of the dominant sensitivity of the data to variations in viscosity from regions below approximately 1200 km depth for to regions above this depth in the lower mantle for the sensitivity of the data to variations in the viscosity profile in the shallowest parts of the lower mantle for the case is also reflected in a set of forward calculations described herein as an example predictions made using earth models in which the viscosity above 1200 km depth is constrained to be 1021 pa s do not exhibit the multiple solutions characteristic of the um 1021 pa s calculations the same is true of earth models in which the upper mantle viscosity is weakened an order of magnitude to 1020 pa s the theory described herein is also applied to compute the signal 10 arising from the retreat of small ice sheets and glaciers described by meier 1984 and also from any potential variations in the mass of the antarctic and greenland ice sheets the present day signal due to the late pleistocene glacial cycles dominates the signal from meier s sources at all degrees except 3 in contrast the signal arising from mass variations in the antarctic and greenland ice sheets is potentially comparable to the former a comparison of observational constraints on the data with predictions of the postglacial rebound signal described in this paper in order to infer mantle rheology cannot proceed until constraints are placed on the present day mass flux of these large polar ice sheets we show that the constraints required are weakest at degrees 2 and 4 finally we outline a potentially important procedure for incorporating predictions of the signal due to the late pleistocene glacial cycles and meier s sources with an observational constraint on the datum to yield bounds on the present day net mass flux from the antarctic and greenland ice sheets a rigorous application of this procedure must wait until observational constraints on are reestablished in the literature

mineralogy geochemistry and petrogenesis of nephrite from panshi jilin northeast china abstract nephrite is an important variety of jade that is of great significance in prospecting management little research has been carried out on the newly discovered nephrite deposit in panshi jilin province northeast china this paper presents the first systematic study of this new deposit the mineralogical petrological and geochemical characteristics along with the petrogenesis of samples from this deposit were evaluated by microscopic observation scanning electron microscopy electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry the main mineral component of the panshi nephrite was determined to be tremolite and diopside chlorite apatite calcite and dolomite were observed as secondary minerals the tremolite presented two microstructures feltlike and fibroblastic all the examined tremolite samples contained low amounts of feo 0 006 0 249 wt cr2o3 0 000 0 047 wt and nio 0 000 0 053 wt along with high values 0 99 of mg2 mg2 fe2 relative to dolomite related nephrites the nephrite samples all exhibited very low total rare earth element contents ranging from 1 831 to 5 121 ppm and were characterized by positive and negative eu anomalies 0 267 4 446 negative ce anomalies 0 283 0 650 positive u anomalies and negative ba nb ti and ce anomalies these characteristics indicate a multistage superimposed mineralization formation mechanism for the panshi nephrite the test results and regional geological survey results indicate that the panshi nephrite deposit was likely formed by intermediate felsic magmas that intruded into dolomitic marble in many stages during the variscan indosinian epoch generally the genesis of the panshi nephrite can be ascribed to two typical processes contact metasomatism and late metamorphism and the panshi nephrite is of dolomite related origin the results of this study provide theoretical guidance for the search for nephrite deposits of dolomite related origin

primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of mars five main stages of radial and concentric structures formed around tharsis from the noachian through the amazonian as determined by geologic mapping of 24 452 structures within the stratigraphic framework of mars and by testing their radial and concentric orientations tectonic activity peaked in the noachian stage 1 around the largest center claritas an elongate center extending more than 20 in latitude and defined by about half of the total grabens which are concentrated in the syria planum thaumasia and tempe terra regions during the late noachian and early hesperian stage 2 extensional structures formed along the length of present day valles marineris and in thaumasia with a secondary concentration near warrego vallis radial to a region just to the south of the central margin of valles marineris early hesperian stage 3 radial grabens in pavonis syria ulysses and tempe terra and somewhat concentric wrinkle ridges in lunae and solis plana and in thaumasia sirenum memnonia and amazonis are centered northwest of syria with secondary centers at thaumasia tempe terra ulysses fossae and western valles marineris late hesperian early amazonian stage 4 structures around alba patera the northeast trending alignment of tharsis montes and olympus mons appears centered on alba patera stage 5 structures middle late amazonian represent the last pulse of tharsis related activity and are found around the large shield volcanoes and are centered near pavonis mons tectonic activity around tharsis began in the noachian and generally decreased through geologic time to the amazonian statistically significant radial distributions of structures formed during each stage centered at different locations within the higher elevations of tharsis secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout tharsis

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

rare earth element geochemistry of the woxi w sb au deposit hunan province south china the woxi w sb au deposit in hunan south china is hosted by proterozoic metasedimentary rocks a turbiditic sequence of slightly metamorphosed greenschist facies gray green and purplish red graywacke siltstone sandy slate and slate the mineralization occurs predominantly 70 as stratabound stratiform ore layers and subordinately as stringer stockworks the former consists of rhythmically interbedded banded to finely laminated stibnite scheelite quartz pyrite and silty clays whereas the latter occurs immediately beneath the stratabound ore layers and is characterized by numerous quartz pyrite gold scheelite stringer veins or veinlets that are typically either subparallel or subvertical to the overlying stratabound ore layers the deposit has been the subject of continued debate in regard to its genesis rare earth element geochemistry is used here to support a sedimentary exhalative sedex origin for the woxi deposit the ree signatures of the metasedimentary rocks and associated ores from the woxi w sb au deposit remained unchanged during post depositional processes and were mainly controlled by their provenance the original ore forming hydrothermal fluids as demonstrated by fluid inclusions in quartz from the banded ores are characterized by variable total ree concentrations 3 5 to 136 ppm marked lree enrichment lan ybn 28 248 lree hree 16 to 34 and no significant eu anomalies eu eu 0 83 to 1 18 they were most probably derived from evolved seawater that circulated in the clastic sediment pile and subsequently erupted on the seafloor the bulk banded ores are enriched in hree lan ybn 4 6 11 4 lree hree 3 to 14 and slightly depleted in eu eu eu 0 63 to 1 14 relative to their parent fluids this is interpreted as indicating the influence of seawater rather than a crystallographic control on ree content of the ores within a single ore layer the degree of hree enrichment tends to increase upward while the total ree concentrations decrease reflecting greater influence and dilution of seawater there is a broad similarity in chondrite normalized ree patterns and the amount of ree fractionation of the bandedoresinthisstudyandexhalitesfromothersedex typepolymetallicoredeposits suggestingasimilargenesisforthesedeposits

geochemistry and petrology of nephrite from alamas xinjiang nw china abstract the hetian nephrite deposit is one of the largest nephrite deposits worldwide located within the hetian deposit xinjiang northwest china the alamas ore body occurs as veins on the contact between the late variscan granodiorite and precambrian dolomitic marble petrographic studies and electronic microprobe analyses reveal two possible nephrite formation processes 1 dolomitic marble tremolite and 2 dolomitic marble diopside tremolite nephrite veins show continuous coloration zones ranging from white and white green zones to a green zone towards the granodiorite with increasing concentrations of cr feo and tfe2o3 all these nephrite samples have quite low cr and ni contents 8 95 178 7 ppm and 0 05 3 95 ppm respectively relative to serpentinite related nephrite cr2o3 0 07 0 43 wt nio 0 08 0 36 wt their bulk rock ree patterns exhibit strong negative eu anomalies 0 03 0 21 with declined lree flat hree and low ree concentration 2 84 84 81 ppm similar to those of host dolomitic marble samples with negative eu anomalies 0 15 0 23 declined lree flat hree and lower ree concentration 8 48 11 1 ppm indicating a close genetic relationship between them homogenization temperatures analyses on the fluid inclusions in tremolite yield a minimum temperature 293 c for the nephrite formation nephrites have oxygen and hydrogen isotope compositions in the range from 3 2 to 6 2 per mil and 83 0 to 94 7 per mil respectively the corresponding equilibrated fluids have isotope compositions of 18o 3 1 to 6 1 293 c combined with field observation there are at least three possible fluid sources meteoric water magmatic water and co2 derived from decarbonation of dolomite and a metasomatic and dolomite related origin is suggested for the alamas ore body in the hetian nephrite deposit xinjiang nw china

low degree gravity changes from grace earth rotation geophysical models and satellite laser ranging 1 several independent time series of variations c 21 s 21 and c 20 in earth s gravity field are compared for the period april 2002 to may 2007 we examine estimates from the gravity recovery and climate experiment grace earth rotation variations climate models and satellite laser ranging slr recently released grace solutions show significant improvement relative to earlier results especially for c 21 and s 21 at the annual period all estimates agree remarkably well and good correlation is found among time series at intraseasonal periods in general earth rotation values for c 21 and s 21 and slr values for c 20 agree best with grace estimates grace c 20 time series are contaminated by aliased ocean tide model errors slr c 21 and s 21 time series have been reported without an ocean pole tide opt correction and with an older solid earth pole tide sept model after correcting for opt and sept deficiencies slr c 21 and s 21 time series show improved agreement with other estimates

water on early mars possible subaqueous sedimentary deposits covering ancient cratered terrain in western arabia and sinus meridiani western arabia and northern sinus meridiani 30 n 10 s 40 w 40 e are almost entirely covered by wind eroded horizontally bedded sedimentary layers that lap against local topographic features this portion of mars ancient cratered terrain is relatively low 1 km elevation and flat sloping westward 0 7 m km over 3 000 km the region lacks valley network channels we propose that at some time in early martian history this region was under water the water hypothesis is strengthened by the presence of 1 a shore like contact between smooth surfaced deposits and ancient cratered terrain in central sinus meridiani 2 polygonal structures in northern sinus meridiani and 3 sand which cannot be from airfall possibly reworked by wind from the underlying sedimentary units the september 1997 arrival of mars global surveyor s thermal emission spectrometer offers an opportunity to begin to test this hypothesis by searching for carbonate and evaporite minerals among the sediment covering the region

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

determination of long term changes in the earth s gravity field from satellite laser ranging observations temporal changes in the earth s gravity field have been determined by analyzing satellite laser ranging slr observations of eight geodetic satellites using data spanning an interval of over 20 years the satellites used in the analysis include starlette lageos 1 and 2 ajisai etalon 1 and 2 stella and be c geophysical parameters related to both secular and long period variations in the earth s gravity field including the geopotential zonal rates and and the 18 6 year tide parameter were estimated the estimated values for these parameters are centimeters and s18 6 20 0 1 0 2 centimeters the amplitude and phase for the 18 6 year tide are in general agreement with the effects predicted by the earth s mantle anelasticity the solution accuracy was evaluated by considering the effects of errors in various non estimated dynamical model parameters and by varying the data span and data sets used in the solution estimates for from individual lageos 1 and starlette slr data sets are in good agreement the lumped sum values for and are very different for lageos 1 and starlette the zonal rate determination is limited to degree 6 with the current slr data sets analysis of the sensitivity of the solution for the zonal rates to the satellite tracking data span suggests that the temporal extension of the current slr data sets will enhance the solution of zonal rates beyond degree 6

gia induced secular variations in the earth s long wavelength gravity field influence of 3 d viscosity variations abstract predictions of present day secular variations in the earth s long wavelength geopotential driven by glacial isostatic adjustment gia have previously been analyzed to infer the radial profile of mantle viscosity and to constrain ongoing cryospheric mass balance these predictions have been based on spherically symmetric earth models we explore the impact of lateral variations in mantle viscosity using a new finite volume formulation for computing the response of 3 d maxwell viscoelastic earth models the geometry of the viscosity field is constrained from seismic to mographic images of mantle structure while the amplitude of the lateral viscosity variations is tuned by a free parameter in the modeling we focus on the zonal j l harmonics for degrees l 2 8 and demonstrate that large scale lateral viscosity variations of two to three orders of magnitude have a modest 5 10 impact on predictions of j 2 in contrast predictions of higher degree harmonics show a much greater sensitivity to lateral variation in viscosity structure we conclude that future analyses of secular trends for degree l 2 estimated from ongoing grace champ satellite missions must incorporate gia predictions based on 3 d viscoelastic earth models

postglacial rebound and sea level contributions to changes in the geoid and the earth s rotation axis summary the rate of change of the spherical harmonic degree 2 component of the earth s gravitational potential coa 20 and polar wander velocity are two signals which are sensitive to late pleistocene deglaciation current changes in sea level and deep mantle viscosity diierent load and earth models have been used in earlier papers to predict the component of these geophysical signals caused by the collapse of the last great ice sheets and recent melting of polar ice caps in this paper we present a systematic analysis of the dependence of the predictions on parameters of the ice and earth model we show that the key parameters of the ice model which govern the predictions are the mass the location of the centre of mass and the midpoint of the deglaciation phase of secondary importance is the length of the deglaciation phase and the mean ice load prior to the last glacial maximum these conclusions enable us to make a more robust inference of mantle viscosity than has been made before allowing for the uncertainties in the model of late pleistocene and present deglaciation as previous authors have shown the lower mantle viscosity is the most important rheological parameter and therefore thecoa 20 observation complements sea level observations which are primarily sensitive to lithospheric thickness and the viscosity of the upper part of the mantle using realistic constraints on the sizes locations and timing of deglaciation of the late pleistocene ice sheets and current changes in polar ice caps the observation of coa 20 is used to infer lower mantle viscosity as a function of the present rate of sea level change if the present rate of non steric sea level change is 1 mm yr 1 and that change has been occurring for less than 1000 years then the lower mantle viscosity satis es log10 glm 21 82 0 15 which is consistent with inferences drawn from recent sea level analyses and con rms other analyses of thecoa 20 observation if the polar wander signal is produced entirely by postglacial rebound and current sea level change no more than 20 per cent of the present contribution to global sea level change comes from greenland the above conclusions also hold if the density discontinuities at 420 and 670 km are modelled as phase boundaries rather than material chemical boundaries

themis observes possible cave skylights on mars 1 seven possible skylight entrances into martian caves were observed on and around the flanks of arsia mons by the mars odyssey thermal emission imaging system themis distinct from impact craters collapse pits or any other surface feature on mars these candidates appear to be deep dark holes at visible wavelengths while infrared observations show their thermal behaviors to be consistent with subsurface materials diameters range from 100 m to 225 m and derived minimum depths range between 68 m and 130 m most candidates seem directly related to pit craters and may have formed in a similar manner with overhanging ceilings that remain intact

comparative fe and sr isotope study of nephrite deposits hosted in dolomitic marbles and serpentinites from the sudetes sw poland implications for fe as au bearing skarn formation and post obduction evolution of the oceanic lithosphere abstract nephrites belonging to both the dolomite related and serpentinite related genetic types from the zloty stok deposit and jordanow l ski and naslawice prospects in the leza ophiolite respectively were analyzed for fe and sr isotope compositions these deposits in the central sudetes sw poland are unusually situated relatively close to each other this study is a first attempt to perform combined fe and sr isotope study of nephrites our results show that fe in the fe as au bearing skarn samples from zloty stok 2 77 7 00 wt fe 56fe 0 07 to 0 14 and 57fe 0 12 to 0 21 to which the dolomite related nephrite belongs is not inherited from the host dolomitic marbles ca 0 4 wt fe 56fe 0 08 to 0 07 and 57fe 0 12 to 0 09 but derived from the nearby ca 340 ma granite intrusion 2 64 5 64 wt fe in contrast iron in the serpentinite related nephrites 2 06 3 88 wt fe 56fe 0 41 to 0 45 and 57fe 0 59 to 0 66 was likely inherited from host serpentinites 5 27 4 81 wt fe rather than metasomatically derived from adjacent granite intrusions 0 13 0 45 wt fe moreover both the marble transformation into a dolomite related nephrite and fe as au bearing skarn and the abyssal serpentinite through ophiolite towards serpentinite related nephrite transformation are accompanied by a progressive increase of 56fe and 57fe this increase is regardless of changes in the bulk fe content increasing during the dolomite related nephrite formation and decreasing during serpentinite related nephrite formation this phenomena may be caused by one of the below listed factors or combinations a preferential incorporation of heavy iron by tremolite and diopside b preferential incorporation of the heavy iron in the fe3 bearing phases crystallizing during nephrite formation c preferential incorporation of the heavy fe from migrating granite derived fluids positive fractionation between aqueous fe bearing fluid and tremolite diopside d positive isotope fractionation between dolomite antigorite precursor and newly formed amphibole clinopyroxene e change of the fe oxidation state furthermore fe in the rock forming tremolite from the serpentinite related nephrites is isotopically heavier than fe in tremolite from the dolomite related ones in contrast to the iron the isotopic composition of strontium combined with its content and structural evidence suggest multiple sources for this element in the case of the dolomite related nephrite ca 3 4 ppm sr initial 87sr 86sr 0 7085 sr inheritance from the host dolomitic marble ca 90 ppm sr initial 87sr 86sr 0 7081 as well as its derivation from intrusions of both the syn to late tectonic ca 340 ma granites ca 400 440 ppm sr and post tectonic 305 ma granites 86 4 ppm sr is suggested in the case of the serpentinite related nephrite 6 3 61 7 ppm sr initial 87sr 86sr 0 7037 to 0 7081 the situation is similar i e sr in the most primitive samples tends to be sourced from ophiolitic rocks up to 2 4 ppm sr in serpentinite whereas in the more evolved types it was likely delivered from the adjacent ca 340 ma 8 8 102 6 ppm sr partially rodingitized granites as well as 305 ma granites ca 80 ppm sr moreover these granites caused the fluid flow responsible for sr bearing clinozoisite vein formation these veins are likely related with nephrite formation and with a metallic mineralization

present day secular variations in the low degree harmonics of the geopotential sensitivity analysis on spherically symmetric earth models 1 we predict present day rates of change of the long wavelength components of the earth s geopotential due to the late pleistocene glacial cycles hereinafter referred to as glacial isostatic adjustment or gia these predictions are generated using spherically symmetric self gravitating maxwell viscoelastic earth models previous studies have generally considered only zonal i e azimuthally independent harmonics or the so called coefficients we extend these efforts to focus on the nonzonal harmonics and explore the sensitivity of our predictions to changes in a variety of model inputs as an example we examine the influence on the gia predictions of ignoring rotational perturbations and assuming an elastically incompressible model and find that these assumptions can have a significant impact on the degree 2 order 1 coefficients while the other harmonics are generally affected by 10 though the gia predictions are generally insensitive to variations in lithospheric thickness and upper mantle viscosity reasonable variations in either lower mantle viscosity or the late pleistocene ice history will have a more significant effect mindful of upcoming dedicated gravity missions we show that predictions of the gia induced changes of the geoid can vary by at least 0 5 mm yr 1 over a plausible range of earth and ice models

the state potential distribution and biological implications of methane in the martian crust the search for life on mars has recently focused on its potential survival in deep 2 km subpermafrost aquifers where anaerobic bacteria similar to those found in deep subsurface ecosystems on earth may have survived in an environment that has remained stable for billions of years an anticipated by product of this biological activity is methane the detection of large deposits of methane gas and hydrate in the martian cryosphere or as emissions from deep fracture zones would provide persuasive evidence of indigenous life and confirm the presence of a valuable in situ resource for use by future human explorers

do ice caves exist on mars we have developed a numerical model for assessing the lifetime of ice deposits in martian caves that are open to the atmosphere our model results and sensitivity tests indicate that cave ice would be stable over significant portions of the surface of mars ice caves on earth commonly occur in lava tubes and mars has been significantly resurfaced by volcanic activity during its history including the two main volcanic provinces the tharsis and elysium rises these areas known or suspected of having subsurface caves and related voids are among the most favorable regions for the occurrence of ice stability the martian ice cave model predicts regions which if caves occur would potentially be areas of astrobiological importance as well as possible water sources for future human missions to mars