the upper limit of maturity of natural gas generation and its implication for the yacheng formation in the qiongdongnan basin china abstract vitrinite reflectance vr ro measurements from residual kerogen of pyrolysis experiments were performed on immature maoming oil shale substituted the samples for the gas prone source rocks of yacheng formation of the qiongdongnan basin in the south china sea the work was focused on determination an upper limit of maturity for gas generation ulmgg or the deadline of natural gas generation ro values at given temperatures increase with increasing temperature and prolonged heating time but ro value given a definition of the difference of all values for vr related to higher temperature and adjacent lower temperature in open system non isothermal experiment at the heating rate of 20 c min is better than vr and representative examples are presented in this paper it indicates that the range of natural gas generation for ro in the main gas generation period is from 0 96 to 2 74 in which ro is in concordance with the stage for the onset and end of the main gas generation period corresponding to 0 02 up to 0 30 and from 0 30 up to 0 80 respectively after the main gas generation period of 0 96 2 74 the evolution of vr approach to the ulmgg of the whole rock for type ii kerogen it is equal to 4 38 of vr where the gas generation rates change little with the increase of maturation ro is the maximum of 0 83 corresponding to vr of 4 38 ro and the source rock does not nearly occur in the end process of hydrocarbon gas generation while ro is over 4 38 it shows that it is the same the ulmgg from the whole rock for type ii kerogen as the method with both comparison and kinetics by comparing to both the conclusions of pyrolysis experiments and the data of vr from the source rock of yacheng formation on a series of selected eight wells in the shallow water continental shelf area it indicate that the most hydrocarbon source rock is still far from reaching ulmgg from the whole rock for type ii kerogen the source rock of yacheng formation in the local areas of the deepwater continental slope basin have still preferable natural gas generative potential especially in the local along the central depression belt namely the ledong lingshui songnan and baodao sags from southwest to northeast from the depocenter to both the margin and its adjacent areas it help to evaluate the resource potential for oil and gas of the hydrocarbon source rock in the deepwater continental slope of the qiongdongnan basin or other basins with lower exploration in the northern of the south china sea and to reduce the risk in exploration

maskelynite hosted apatite in the chassigny meteorite insights into late stage magmatic volatile evolution in martian magmas apatite hosting maskelynite and alkali maskelynite within regions interstitial to cumulus olivine differ compositionally from that found within melt inclusions in the chassigny martian meteorite feldspar glass compositions within the interstitial regions evolve along a high temperature crystallization path within the melt inclusions feldspar glass shows evolution to low temperatures extending into the subsolidus regime coupled with these differences in maskelynite compositions are differences in volatile abundance in apatite included within the maskelynite apatite found within the large olivine hosted polyphase melt inclusions is uniformly fluorapatite whereas that interstitial to cumulus olivine is chlor fluorapatite we propose that the differences in maskelynite and apatite compositions within the melt inclusion and interstitial regions arose primarily from different crystallization conditions melt inclusion maskelynite and apatite are consistent with nearly closed system buildup of magmatic volatiles during crystallization within the melt inclusions exsolution of a cl bearing fluid phase and retention of this fluid phase within the melt inclusions into the hydrothermal regime for the interstitial regions however the higher solidus temperatures of the interstitial melts the early crystallization of feldspar with significant ternary component and the cl rich nature of the apatite all suggest open system fluid migration through the cumulus pile ingress of cl rich h2o poor brine from a hotter less evolved portion of the magma plumbing system and interaction of this cl rich fluid with melt prior to the crystallization of feldspar such processes of fluid migration through a cumulus pile have been suggested on earth in layered intrusions and apatite is the primary recorder of this process

the chlorine isotopic composition of martian meteorites 1 chlorine isotope composition of martian mantle and crustal reservoirs and their interactions the martian meteorites record a wide diversity of environments processes and ages much work has been done to decipher potential mantle sources for martian magmas and their interactions with crustal and surface environments chlorine isotopes provide a unique opportunity to assess interactions between martian mantle derived magmas and the crust we have measured the cl isotopic composition of 17 samples that span the range of known ages martian environments and mantle reservoirs the 37cl of the martian mantle as represented by the olivine phyric shergottites nwa 2737 chassignite and shergotty basaltic shergottite has a low value of approximately 3 8 this value is lower than that of all other planetary bodies measured thus far the martian crust as represented by regolith breccia nwa 7034 is variably enriched in the heavy isotope of cl this enrichment is reflective of preferential loss of 35cl to space most basaltic shergottites less shergotty nakhlites chassigny and allan hills 84001 lie on a continuum between the martian mantle and crust this intermediate range is explained by mechanical mixing through impact fluid interaction and assimilation fractional crystallization

volatiles in the martian crust and mantle clues from the nwa 6162 shergottite abstract martian meteorites of various petrogeneses retain a record of volatiles on mars from the hydrosphere crustal water to the mantle sputtering of the martian atmosphere by solar wind after the loss of mars magnetic field enriched it in deuterium which exchanged with martian crustal water recent studies show that the hydrogen isotopic composition of the martian crustal water reservoir varies from 3000 to 7000 but requires better constraints melt inclusion glasses maskelynite and fusion crust from the depleted olivine phyric shergotite nwa 6162 were analyzed using nanosims providing a unique insight into the hydrogen isotopic and volatile elemental content of both the martian crustal water reservoir and the mantle source the h2o s and cl contents of the melt inclusion glasses are 0 3137 14 239 and 16 967 ppm respectively d values vary from 560 to 6137 the water content positively correlates with the d values in both the melt inclusion glasses and maskelynite in a two end member mixing trend one end member is the magmatic water with a d value of 0 and the other end member is the martian crustal water with d ranging from 5000 to 6000 nwa 6162 a depleted olivine phyric shergottite originated from a different mantle source to the enriched lherzolitic shergottites however both types of shergottites exchanged with martian crustal water with the same d values indicating a homogeneous martian crustal water hydrogen isotopic composition 5000 6000 most melt inclusion glasses from nwa 6162 have low water content 0 234 ppm except for two enriched locations as micron sized bands and dendrites the low water content in most melt inclusion glasses the dendritic shaped water enriched areas in melt inclusions and the martian crustal water diffusion profile recorded in maskelynite collectively suggest short lived water rock interactions in the nwa 6162 parent rock that was probably induced by impact furthermore a great contribution up to 98 of surface cl accompanying d enriched water was recorded in the melt inclusions supported by the positive correlation between cl and h2o the presence of sulfide and s rich hot spots and low d end member of the magmatic water indicate that the degassing during post entrapment crystallization and ascent of the melt inclusion is negligible h2o s and cl contents of the martian mantle reservoir are estimated to be 0 1 3 0 5 15 and 0 5 4 ppm respectively after the correction of fractional crystallization of the melt inclusions and contribution from the martian surface reservoir the martian mantle reservoir estimated from nwa 6162 was water s and cl poorer than the earth s interior

chassigny petrogenesis melt compositions intensive parameters and water contents of martian magmas abstract the snc meteorites are a class of eight basaltic achondrites that have extremely young crystallization ages 1 3 ga chassigny a unique snc meteorite is a dunite containing fo68 olivines and rare poikilitic ca pyroxenes it is one of the most primitive snc meteorites and thus is most likely to reveal information about the snc basalt source region this study presents a detailed examination of partially crystallized melt inclusions in cumulus olivine grains in chassigny these trapped melts are argued to be representative samples of the melt that existed when chassigny crystallized this melt has been modified however by interaction with the host olivine and by closed system crystallization the phases inside the melt inclusions include hydrous ti rich amphibole kaersutite biotite two pyroxenes and rhyolitic and alkali feldspar glasses all phases have been extensively analyzed with an electron microprobe the new mineralogical information is combined with a complementary experimental study of kaersutite melt equilibria this combined data set can be used to formulate a system of linear equations which can then be solved to determine the composition of the originally trapped melt this calculation reveals that the trapped melt was an feo rich and al2o3 poor basalt the melt composition is shown to be consistent with the crystallization sequence both inside the melt inclusions and in the rock matrix the major element chemistry of this liquid closely resembles terrestrial boninite lavas the new data also allow the intensive conditions temperature total pressure and water fugacity of chassigny crystallization to be estimated two pyroxene geothermometry indicates that equilibration temperatures were 1000 50 c although amphibole does not coexist with melt until t 960 c the trapped liquid initially contained 1 5 wt dissolved water crystallization of anhydrous phases caused water to buildup in the trapped melt prior to kaersutite crystallization the melt must have contained at least 4 wt dissolved water suggesting that a minimum of 1 5 kbar total pressure is required a maximum total pressure cannot be inferred but all available data are consistent with low pressure 5 kbar crystallization finally x h2o in the fluid in the melt inclusion is estimated to have been at least 0 8 in order to stabilize amphibole without plagioclase implying that the water fugacity was 1480 bars the existence of hydrous melts and conditions appropriate for amphibole crystallization suggest that evolved sio2 rich lavas exist on the chassigny parent body mars

the temporal and spatial distribution of volcanism in the south china sea region cenozoic magmatism in the south china sea the associated continental margins coastal south china and indochina is reviewed volcanism contemporaneous with rifting and sea floor spreading in the south china sea was very weak in the margins and adjacent areas there was only very limited magmatic activity most probably after the cessation of sea floor spreading the south china sea has non volcanic margins large basement relief caused by extension formed major basins and a continental oceanic transitional zone in the northern margin reflects high crustal rigidity during rifting and drifting the paucity of a magma supply and presence of rigid fault blocks are unfavorable to the mantle flow model previously proposed to account for the opening of the south china sea which was supposedly linked to the escape of indochina induced by indo eurasia collision c 2005 published by elsevier ltd

source rock deposition controlled by tectonic subsidence and climate in the western pearl river mouth basin china evidence from organic and inorganic geochemistry abstract interest in factors controlling lacustrine source rock deposition has increased over the last few decades because this type of deposits contain significant petroleum resources generally tectonic subsidence and climate are the two root causes as they control the accommodation potential water column properties and sources of organic matter in this study coupling organic geochemical and elemental geochemical data two potential source rocks i e the eocene wenchang formation e 2 w and oligocene enping formation e 3 e were investigated two models were finally raised to explain deposition of the two set of source rocks according to their paleoclimatic and tectonic properties the source rock potential shows a strong heterogeneity the second member of the eocene wenchang formation e 2 w 2 is characterized by high organic matter content and oil prone kerogen type in contrast the first member of the eocene wenchang formation e 2 w 1 and the oligocene enping formation e 3 e are characterized by low organic matter content and gas prone kerogen type the primary productivity and depositional environment exhibit notable differences between the two potential source rocks horizons and show an obvious variation from the depocenter to the slope and can be best explained by the coevolution of tectonic subsidence and climate during the e 2 w depositional stage low sediment supply led to mudstone deposited in deep lacustrine environment and resulted in underfilled lake basin the low water inflow provided little terrigenous organic matter low bicadinane perylene and floranthene contents and oxygen besides the low area depth ratio impeded the water circulation thus resulted in shallow thermocline and anoxic suboxic bottom environment abundant dibenzothiophene and high c 35 c 31 22s hopane ratios therefore abundant algae which contributed to the high amorphous organic matter aom content can be preserved the warm and wet climate high mn mg ratios gave birth to autochthonous organism such as dinoflagellates and pavlova gyrans abundant 4 methyl sterane during the e 3 e depositional stage the sufficient sedimentary supply resulted in expanding shallow lacustrine and swamp environment the higher area depth ratio and high sediment supply made environment unstable and can be strongly influenced by external environment broader range of mn mg ratios enough terrigenous organic matter tom was transported to the slope but little to the depocenter the slightly hot and dry climate low mn mg ratios led to decreasing autochthonous organism and evaporation environment the shallow water depth and relative dry climate resulted in saline suboxic dysoxic acid bottom environment the co variation of organic and inorganic indexes indicates the combination is a valid method in reconstructing source rock depositional models

infiltration metasomatism in layered intrusions an example from the stillwater complex montana abstract the contact between anorthosite zone ii an ii and the overlying troctolite of olivine bearing zone v ob v of the stillwater complex is characterized by a 5 m thick adcumulate anorthosite this adcumulate anorthosite separates rocks of an ii characterized by the apparent crystallization sequence plagioclase followed by orthopyroxene clinopyroxene quartz fe ti oxide assemblages from those of ob v where the apparent crystallization sequence is olivine plagioclase followed by orthopyroxene the grain size and compositional zoning of plagioclase in this transition zone is similar to that in the overlying troctolite and distinct from the coarser complexly zoned plagioclase that makes up the underlying anorthosite in contrast the minor interstitial pyroxene in the transition zone compositionally overlaps that in the underlying anorthosite and both have a lower molar mg mg fe ratio than the pyroxene of the troctolite these relationships suggest that the intercumulus liquids of an ii and ob v were compositionally distinct model phase diagram considerations suggest that infiltration of any plagioclase saturated liquids into a troctolite assemblage will result in the assimilation of olivine and depending on the actual composition of the anorthositic liquid will also either assimilate or crystallize plagioclase as well hence the monomineralic anorthosite zone at the top of an ii can be attributed to infiltration of interstitial liquids from an ii that were displaced upward into the troctolite during compaction of an ii this reaction can be either exothermic or endothermic depending on the actual composition of the infiltrating liquid and the bulk solids composition numerical models of the thermal effects of infiltration suggest that heat of reaction can significantly affect the liquid solid ratio away from the infiltration boundary

fluids on differentiated asteroids evidence from phosphates in differentiated meteorites gra 06128 and gra 06129 abstract paired meteorites graves nunatak 06128 and 06129 gra represent an ancient cumulate lithology 4565 9 ma 0 3 containing high abundances of sodic plagioclase textures and stable isotope compositions of gra indicate that superimposed on the igneous lithology is a complex history of subsolidus reequilibration and low temperature alteration that may have extended over a period of 150 myr in gra apatite is halogen rich with cl between 4 5 and 5 5 wt and f between 0 3 and 0 9 wt the cl cl f oh ratio of the apatite is between 0 65 and 0 82 the cl and f are negatively correlated and are heterogeneously distributed in the apatite merrillite is low in halogens with substantial na in the 6 fold coordinated na site 2 5 and mg in the smaller octahedral site the merrillite has a negative eu anomaly whereas the apatite has a positive eu anomaly the chlorine isotope composition of the bulk gra leachate is 1 2 relative to standard mean ocean chloride smoc ion microprobe chlorine isotope analyses of the apatite range between 0 5 and 1 2 textural relationships between the merrillite and apatite and the high cl content of the apatite suggest that the merrillite is magmatic in origin whereas the apatite is a product of the interaction between merrillite and a cl rich fluid if the replacement of merrillite by apatite occurred at approximately 800 c the fluid composition is f hcl f h2o 0 0383 and a hcl molality of 2 13 and f hcl f hf 50 100 it is anticipated that the calculated f hcl f h2o and a hcl molality are minimum values due to assumptions made on the oh component in apatite and basing the calculations on the apatite with the lowest xcl the bulk 37cl of gra is a 2 outlier from chondritic meteorites and suggests that parent body processes resulted in fractionation of the cl isotopes

uniform geothermal gradient and heat flow in the qiongdongnan and pearl river mouth basins of the south china sea abstract the pearl river mouth basin prmb and qiongdongnan basin qdnb are oil and gas bearing basins in the northern margin of the south china sea scs geothermal survey is an important tool in petroleum exploration a large data set comprised of 199 thermal conductivities 40 radioactive heat productions 543 measured geothermal gradient values and 224 heat flow values has been obtained from the two basins however the measured geothermal gradient data originated from diverse depth range make spatial comparison a challenging task taking into account the variation of conductivity and heat production of rocks we use a uniform geothermal gradient to characterize the geothermal gradient distribution of the prmb and qdnb results show that in the depth interval of 0 5 km the uniform geothermal gradient in the prmb varies from 17 8 c km to 50 2 c km with an average of 32 1 6 0 c km in comparison the qdnb has an average uniform geothermal gradient of 31 9 5 6 c km and a range between 19 7 c km and 39 5 c km heat flows in the prmb and qdnb are 71 3 13 5 mw m 2 and 72 9 14 2 mw m 2 respectively the heat flow and geothermal gradient of the prmb and qdnb tend to increase from the continental shelf to continental slope owing to the lithosphereic crustal thinning in the cenozoic

petrography and geochemistry of the chassignite northwest africa 2737 nwa 2737 we report on the petrology and geochemistry of the northwest africa 2737 nwa 2737 meteorite that was recovered from the morrocan sahara in 2000 it is the second member of the chassignite subclass of the snc shergotitte nakhlite chassignite group of meteorites that are thought to have originated on mars it consists of black olivine and spinel cumulate crystals 89 7 and 4 6 wt respectively with intercumulus pyroxenes augite 3 1 wt and pigeonite orthopyroxene 1 0 wt analbite glass 1 6 wt and apatite 0 2 wt unlike chassigny plagioclase has not been observed in nwa 2737 olivine crystals are rich in mg and highly equilibrated fo 78 7 0 5 mol the black color of olivine grains may be related to the strong shock experienced by the meteorite as revealed by the deformation features observed on the macroscopic to the atomic scale chromite is zoned from core to rim from cr83 4uv3 6sp13 0 to cr72 0uv6 9sp21 1 pyroxene compositional trends are similar to those described for chassigny except that they are richer in mg compositions range from en78 5wo2 7fs18 8 to en76 6wo3 2fs20 2 for the orthopyroxene from en73 5wo8 0fs18 5 to en64 0wo22 1fs13 9for pigeonite and from en54 6wo32 8fs12 6 to en46 7wo44 1fs9 2 for augite bulk rock oxygen isotope compositions confirm that nwa 2737 is a new member of the martian meteorite clan 17o 0 305 0 02 n 2 ree abundances measured in nwa 2737 mineral phases are similar to those in chassigny and suggest a genetic relationship between these two rocks however the parent melt of nwa 2737 was less evolved and had a lower al abundance

early degassing of lunar urkreep by crust breaching impact s current models for the moon s formation have yet to fully account for the thermal evolution of the moon in the presence of h2o and other volatiles of particular importance is chlorine since most lunar samples are characterised by unique heavy 37cl values significantly deviating from those of other planetary materials including earth for which 37cl values cluster around 0 in order to unravel the cause s of the moon s unique chlorine isotope signature we performed a comprehensive study of high precision in situ cl isotope measurements of apatite from a suite of apollo samples with a range of geochemical characteristics and petrologic types the cl isotopic compositions measured in lunar apatite in the studied samples display a wide range of 37cl values reaching a maximum value of 36 which are positively correlated with the amount of potassium k rare earth element ree and phosphorous p kreep component in each sample using these new data integrated with existing h isotope data obtained for the same samples we are able to place these findings in the context of the canonical lunar magma ocean lmo model the results are consistent with the urkreep reservoir being characterised by a 37cl 30 such a heavy cl isotope signature requires metal chloride degassing from a cl enriched urkreep lmo residue a process likely to have been triggered by at least one large crust breaching impact event that facilitated the transport and exposure of urkreep liquid to the lunar surface

the sources of water in martian meteorites clues from hydrogen isotopes abstract h isotope measurements of carbonate phosphate feldspathic and mafic glasses and post stishovite silica phase in the shergottites zagami shergotty sau 005 dag 476 alha 77005 and eeta 79001 as well as in chassigny and alh 84001 show that all these phases contain deuterium enriched water of extraterrestrial origin the minerals and glasses analyzed may contain an initial primary hydrogen component but their isotopic composition was modified to varying degrees by three different processes interaction with a fractionated exchangeable water reservoir on mars hydrogen devolatilization by impact melting and terrestrial contamination positive correlations between d and water abundance in feldspathic glass and post stishovite silica in zagami shergotty and sau 005 is indicative of mixing of a high d component 3000 4000 and a less abundant low d component 0 the high d component is primarily derived from the martian exchangable reservoir but may also have been influenced by isotopic fractionation associated with shock induced hydrogen loss the low d component is either a terrestrial contaminant or a primary magmatic component the negative correlation between d and water abundances in mafic and feldspathic glasses in alh 84001 alha 77005 and eeta 79001 is consistent with the addition of a low d terrestrial contaminant to a less abundant high deuterium martian component the low d of magmatic glass in melt inclusions suggests that the d of martian parent magma was low and that the initial h isotope signature of mars may be similar to that of earth

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

the age of the martian meteorite northwest africa 1195 and the differentiation history of the shergottites samarium neodymium isotopic analyses of unleached and acid leached mineral fractions from the recently identified olivine bearing shergottite northwest africa 1195 yield a crystallization age of 347 13 ma and an end143 value of 40 1 0 9 maskelynite fractions do not lie on the sm nd isochron and appear to contain a martian surface component with low 147sm 144nd and 143nd 144nd ratios that was added during shock the rb sr system is disturbed and does not yield an isochron terrestrial sr appears to have affected all of the mineral fractions although a maximum initial 87sr 86sr ratio of 0 7016 is estimated by passing a 347 ma reference line through the maskelynite fraction that is least affected by contamination the high initial end143 value and the low initial 87sr 86sr ratio combined with the geologically young crystallization age indicate that northwest africa 1195 is derived from a source region characterized by a long term incompatible element depletion the age and initial sr and nd isotopic compositions of northwest africa 1195 are very similar to those of queen alexandra range 94201 indicating these samples were derived from source regions with similar sr nd isotopic systematics these similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano the meteorites yamato 980459 dar al gani 476 sayh al uhaymir 005 008 and dhofar 019 also have relatively old ages between 474 and 575 ma and trace element and or isotopic systematics that are indicative of derivation from incompatible element depleted sources this suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible element depleted sources closed system fractional crystallization of this suite of meteorites is modeled with the melts algorithm using the bulk composition of yamato 980459 as a parent these models reproduce many of the major element and mineralogical variations observed in the suite in addition the rare earth element systematics of these meteorites are reproduced by fractional crystallization using the proportions of phases and extents of crystallization that are calculated by melts other shergottites that demonstrate enrichments in incompatible elements and have evolved sr and nd isotopic systematics have some geochemical systematics that are similar to those observed in the depleted group most notably although they exhibit a very limited range of incompatible trace element and isotopic compositions they have highly variable major element compositions this is also consistent with evolution from a common mantle source region by variable amounts of fractional crystallization if this scenario is correct it suggests that the combined effects of source composition and fractional crystallization are likely to account for the major element trace element and isotopic diversity of all shergottites

petrogenetic linkages among martian basalts implications based on trace element chemistry of olivine the shergottites exhibit a range of major and trace element compositions crystallization ages and initial sr nd hf and pb isotopic compositions to constrain the physical mechanisms by which shergottites obtain their compositional characteristics we examined the major and trace element record preserved in olivine in the more primitive shergottites based on such characteristics as the mg v zoning calculated dni co the olivine in y 980459 are most likely phenocrysts many of these same characteristics indicate that the olivines in other shergottites are not in equilibrium with the adjacent melt however in most cases they are not xenocrystic but additions of olivine from the same basaltic system elephant moraine eet a79001 may be an exception with the olivine data suggesting that it is xenocrystic in this case the olivine crystallized from a reduced and lreedepleted melt and was incorporated into an oxidized and enriched basalt vanadium and cao in olivine appear to record the appearance of spinel and pyroxene on the liquidus of most of the shergottites most of the olivine shergottites represent basalts produced by melting of reduced iw to iw 1 depleted mantle sources olivine data indicate that many of the primary melts derived from this source had similar ni co and mn shergottites such as northwest africa nwa 1110 1068 and perhaps roberts massif rbt 04261 that appear to be derived from more enriched sources have distinctly different olivine in the case of nwa 1110 1068 the olivine data suggests that the enriched component was added to system prior to olivine crystallization

heat flow and thermal history of the south china sea abstract a total of 589 heat flow values are available from the south china sea the values are widely scattered ranging from 9 to 181 mw m 2 with a mean of 77 mw m 2 in the northern margin the values are less scattered and the average is about 75 mw m 2 heat flow increases gradually from the northern margin to the central basin in which two high heat flow centers appear one in the east subbasin and the other in the southwest subbasin the southern margin has an average heat flow of 80 mw m 2 similar to the northern margin the western margin where the manila trench is located has an average heat flow as low as 49 mw m 2 in order to understand the high heat flow in the basin in the context of its tectonic history we carried out thermal modeling using a 2d finite element method along a profile across the northern margin a theoretical thermal history has been inferred on the basis of a multistage pure shear extension model the result shows that before miocene the basement heat flow showed relatively low values ranging from 48 to 57 mw m 2 since late miocene the basement heat flow has increased as a result of greater extension the present day high heat flow is primarily the result of pliocene extension

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

chlorine distribution and its isotopic composition in rusty rock 66095 implications for volatile element enrichments of rusty rock and lunar soils origin of rusty alteration and volatile element behavior on the moon abstract an interesting characteristic of the pyroclastic glass bead deposits select impact produced lithologies such as the rusty rock 66095 and unique lunar soils from the apollo 16 landing site is their unusual enrichments in 204 pb cd bi br i ge sb tl zn and cl which indicates that portions of these sample contain a substantial volatile component sample 66095 a fine grained subophitic to ophitic polymict melt breccia also hosts a pervasive low temperature volatile rich oxyhydrated mineral assemblage the volatile element enrichments in these assorted lunar lithologies have been attributed to a variety of extra lunar and lunar processes whereas the oxyhydration in 66095 has long been thought to represent either terrestrial alteration of lunar chlorides and fe ni metal to feo oh cl or indigenous lunar processes in 66095 cl is accommodated in feo oh cl phosphates and chlorides and is heterogeneously distributed the low temperature alteration occurs as rims around fe ni metal and sulfide grains and as dispersed grains in the adjacent matrix micro raman and transmission electron microscope tem imaging indicate that akaganeite feo oh cl is the dominant feo oh polymorph and is intergrown with goethite feo oh and hematite fe 2 o 3 tem observations indicate a well defined nanometer scale stratigraphy to the alteration for example kamacite body centered cubic face centered cubic fcc fe ni alloy lawrencite fecl 2 akaganeite the lunar lawrencite fe ni cl 2 in 66095 does not react directly to akaganeite on earth rather lawrencite exposed to terrestrial conditions reacts to form an amorphous fe and cl bearing phase nano crystalline goethite and hematite the morphology of these terrestrial alteration products is significantly different than that of the akaganeite occurring in 66095 the chlorine isotopic compositions of these volatile rich samples are enriched in heavy cl for 66095 the 37 cl ranges from 14 0 to 15 6 whereas the 37 cl for the volatile rich a16 soils ranges from 5 6 to 15 7 based on these data it appears likely that the volatile element enrichments and the cl isotopic fractionation observed in 66095 and the apollo 16 soils did not result from extra lunar additions but are most likely indigenous to the moon lawrencite was deposited on mineral surfaces at approximately 650 c to 570 c from a metal chloride bearing h poor gas phase this gas phase was also responsible for the transport of other metals e g zn cu pb fe the fractionation of cl isotopes in the rusty rock can be attributed to fumarole processes in a low h system the origin and formation of the akaganeite is more enigmatic the cl isotopes are consistent with it replacing lawrencite however numerous nanometer scale observations are not consistent with a terrestrial origin and indicate multiple episodes of oxyhydration

deuterium and 37 chlorine rich fluids on the surface of mars evidence from the enriched basaltic shergottite northwest africa 8657 abstract apatite a major hydrous mineral in martian meteorites has the potential to reveal history of volatiles on mars here we report the h and cl isotopic systematics of apatite from the enriched basaltic shergottite nwa 8657 to better understand the processes influencing volatiles at or near the martian sub surface the apatite in nwa 8657 has the highest reported d value up to 6509 of any phosphates in martian meteorites the positive correlation between the h2o contents 72 2251 ppm and d values 3965 6509 as well as between the cl contents 1 28 6 17 wt and 37cl values 1 7 4 0 in nwa 8657 apatite are consistent with mixing between volatiles derived from the martian mantle and meteoric water fluid the d and 37cl enrichment of apatite in nwa 8657 implies isotopic exchange with sub surficial fluids during post crystallization hydrothermal event s plain language summary mars was probably a wet and warm world during its earliest geological history supported by many lines of evidence present day mars is cold and arid although recent remote sensing data support the existence of subsurface glaciers and seasonal fluid activities at some locations in this study our aim was to use ground truth about the potential water rock interaction on or near surface environments on recent mars via measuring the h and cl isotopic compositions of apatite from a geologically young meteorite from mars the enriched basaltic shergottite nwa 8657 the petrography and mineral chemistry of apatite and other associated phases e g merrillite maskelynite mesostasis and pyroxene were documented prior to in situ h and cl isotopes analysis the water contents of apatite merrillite maskelynite mesostasis and pyroxene are positively correlated with the d values all of the datasets can be reconciled in terms of mixing between two endmembers a d poor 0 mantle reservoir and a d rich 5920 500 near surface underground water reservoir moreover apatite in nwa 8657 displays 37cl enriched 1 1 in average characteristics these signatures are consistent with d and 37cl rich fluid assisted isotopic exchange in recent near surface environment on mars

martian low temperature alteration materials in shock melt pockets in tissint constraints on their preservation in shergottite meteorites we apply an array of in situ analytical techniques including electron and raman microscopy electron and ion probe microanalysis and laser ablation mass spectrometry to the tissint martian meteorite in order to find and elucidate a geochemical signature characteristic of low temperature alteration at or near the martian surface tissint contains abundant shock produced quench crystallized melt pockets containing water in concentrations ranging from 73 to 1730 ppm water content is positively correlated with cl content the isotopic composition of hydrogen in the shock produced glass ranges from d 2559 to 4422 water is derived from two distinct hydrogen reservoirs the martian near surface 500 and the martian mantle 100 in one shock melt pocket comprising texturally homogeneous vesiculated glass the concentration of h in the shock melt decreases while simultaneously becoming enriched in d attributable to the preferential loss of h over d to the vesicle while the pocket was still molten while igneous sulfides are pyrrhotite in composition fe 0 88 0 90 s the iron to sulfur ratios of spherules in shock melt pockets are elevated up to fe 1 70 s which we attribute to shock oxidation of igneous pyrrhotite and the formation of hematite at high temperature the d and cl enrichment and higher oxidation of the pockets as indicated by hematite support a scenario in which alteration products formed within fractures or void spaces within the rock the signature of these alteration products is preserved within shock melt now glass which formed upon collapse of these fractures and voids during impact shock thermal modeling of tissint shock melt pockets using the heat program demonstrates that the shock melt pockets with the greatest potential to preserve a signature of aqueous alteration are small isolated from other regions of shock melt vesicle free and glassy

thermal and rheological structures of the xisha trough south china sea the xisha trough located in the northwest of the south china sea scs mainly rifted 30 ma ago has been a failed rift since the cessation of the seafloor spreading of the nw subbasin based on the velocity depth model along profile obh 4 across the xisha trough a seven layer density depth model is used to estimate density structure for the profile the relationship between seismic velocity and radiogenic heat production is used to estimate the vertical distribution of heat sources in the lower crust the 2 d temperature field is calculated by applying a 2 d numerical solution of the heat conduction equation and the thermal lithosphere thickness is obtained from the basalt dry solidus bds the rheology of the profile is estimated on the basis of frictional failure in the brittle regime and power law steady state creep in the ductile regime rheological model is constructed for a three layer model involving a granitic upper crust a quartz diorite lower crust and an olivine upper mantle gravity modeling supports basically the velocity depth model the moho along profile obh 4 is of relatively high heat flow ranging from 46 to 60 mw m 2 and the moho beat flow is higher in the trough than on the flanks the depth of the thermal lithospheric lower boundary is about 54 km in the center deepens toward two sides and is about 75 km at the northern slope area and about 70 kin at the southern xisha zhongsha block rheological calculation indicates that the two thinnest ductile layers in the crust and the thickest brittle layer in the uppermost mantle lie in the central region showing that the xisha trough has been rheologically strengthened which are mainly due to later thermal relaxation in addition the strengthening in rheology during rifting was not the main factor in hampering the breakup of the xisha trough c 2002 elsevier science b v all rights reserved

characteristics of surface heat flow in the south china sea a total of 592 heat flow measurements ranging from 8 to 192 mw m 2 78 percent of which are between 50 and 100 mw m 2 have been collected in the south china sea scs to overcome shortcomings such as the uneven distribution of the measurements and the occurrence of abnormal heat flow values the tectonic evolution of different areas and their crustal thickness have been combined in analyzing geothermal characters the results show that the oceanic basins where they are floored by oceanic crust the western part of the southern margin and the western fault system have high heat flow values heat flow along the northern margin of the scs increases from 61 mw m 2 on the shelf to 73 80 mw m 2 in the slope area and in the xisha zhongsha area increases from about 70 mw m 2 to about 85 mw m 2 from the nw to the se heat flow in the nansha spratley islands is about 60 mw m 2 or even higher and decreases from the nw to se the average heat flow of the mekong basin is about 60 mw m 2 which is similar to that of the beibuwan basin on the northern margin heat flow on the eastern margin and on the eastern part of the southern margin is lower especially in the luzon trough where the average heat flow is lower than 40 mw m 2 observed heat flow values in the sw subbasin are generally lower than predicted theoretically from the age of the ocean floor unlike values in the eastern subbasin a high heat flow zone in the lower slope area of the northern margin is recognized for the first time c 2003 elsevier ltd all rights reserved

silicate mineralogy of martian meteorites abstract basalts and basaltic cumulates from mars delivered to earth as meteorites carry a record of the history of that planet from accretion to initial differentiation and subsequent volcanism up to recent times we provide new microprobe data for plagioclase olivine and pyroxene from 19 of the martian meteorites that are representative of the six types of martian rocks we also provide a comprehensive wds map dataset for each sample studied collected at a common magnification for easy comparison of composition and texture the silicate data shows that plagioclase from each of the rock types shares similar trends in ca na k and that k2o na2o wt of plagioclase multiplied by the al content of the bulk rock can be used to determine whether a rock is enriched or depleted in nature olivine data show that meteorite y 980459 is a primitive melt from the martian mantle as its olivine crystals are in equilibrium with its bulk rock composition all other olivine bearing shergottites have been affected by fractional crystallization pyroxene quadrilateral compositions can be used to isolate the type of melt from which the grains crystallized and minor element concentrations in pyroxene can lend insight into parent melt compositions in a comparative planetary mineralogy context plagioclase from mars is richer in na than terrestrial and lunar plagioclase the two most important factors contributing to this are the low activity of al in martian melts and the resulting delayed nucleation of plagioclase in the crystallizing rock olivine from martian rocks shows distinct trends in ni co and cr systematics compared with olivine from earth and moon the trends are due to several factors including oxygen fugacity melt compositions and melt structures properties which show variability among the planets finally fe mn ratios in both olivine and pyroxene can be used as a fingerprint of planetary parentage where minerals show distinct planetary trends that may have been set at the time of planetary accretion although the silicate mineralogical data alone cannot support one specific model of martian magmatism over another the data does support the basic igneous reservoirs proposed for mars and may also be used to constrain some aspects of specific petrogenetic models examples include enriched and depleted reservoirs that can be identified by plagioclase k na and al composition multivalent element partitioning in olivine and pyroxene v cr elucidates oxygen fugacity conditions of the reservoirs and minor element concentrations i e cr in pyx show that proposed fractional crystallization models linking y 980459 to que 94201 will not work

the northwest africa 8159 nwa 8159 martian meteorite part 2 spinel orthopyroxene intergrowths a record of fo2 and crust basalt interactions abstract in part 1 of our examination of martian meteorite northwest africa 8159 nwa 8159 we illustrated many interesting mineralogical and textural attributes that make this martian basalt unique unlike the shergottites that illustrate a clear relationship between the extent of trace element and isotopic characteristics and oxygen fugacity reduced depleted magmas oxidized enriched magmas nwa 8159 illustrates a decoupling of this relationship as it has oxidized and depleted signatures in part 2 using a series of new observations and measurements cl isotopes xanes tem empirical modeling we use nwa 8159 to explore the interaction between mantle derived magmas and the martian crust the magnetite orthopyroxene intergrowths associated with olivine are a product of a martian subsolidus oxidation event near the qfm buffer and not a magmatic reaction in an oxidizing magma qfm 3 this subsolidus event is further supported by cr valence in the olivine alteration of p rich olivine and end member magnetite in the matrix of the meteorite although this subsolidus alteration makes it extremely difficult to determine the original fo2 of the parental magma for nwa 8159 there is evidence that during the initial stages of crystallization the fo2 was modestly reducing iw 1 potential manifestations of more reducing magmatic conditions include p rich cores in the olivine and low fe3 in silicates plagioclase pyroxene further if analogous to all other depleted shergottites nwa 8159 initially crystallized under reducing conditions this decoupling between oxygen fugacity and isotopic trace element characteristics suggests that basalts derived from the martian mantle interacted with the crust in ways that significantly influenced redox history and volatile element isotopic composition cl s without dramatically modifying many of its radiogenic isotope and trace element mantle fingerprints

geologic history of martian regolith breccia northwest africa 7034 evidence for hydrothermal activity and lithologic diversity in the martian crust the timing and mode of deposition for martian regolith breccia northwest africa nwa 7034 were determined by combining petrography shape analysis and thermochronology nwa 7034 is composed of igneous impact and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact volcanic glass the brecciated clasts are likely lithified portions of martian regolith with some evidence of past hydrothermal activity represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4 4 ga one ancient zircon was hosted by an alkali rich basalt clast confirming that alkalic volcanism occurred on mars very early nwa 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water the clast size distribution is similar to terrestrial pyroclastic deposits we infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption s and or impact event s although the ancient ages of igneous components favor mobilization by impact s despite ancient components the breccia has undergone a single pervasive thermal event at 500 800 c evident by groundmass texture and concordance of 1 5 ga dates for bulk rock k ar u pb in apatite and u pb in metamict zircons the 1 5 ga age is likely a thermal event that coincides with rainout breccia lithification we infer that the episodic process of regolith lithification dominated sedimentary processes during the amazonian epoch the absence of pre amazonian high temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification

tree ring analysis of ancient baldcypress trees and subfossil wood abstract ancient baldcypress trees found in wetland and riverine environments have been used to develop a network of exactly dated annual ring width chronologies extending from the southeastern united states across mexico and into western guatemala these chronologies are sensitive to growing season precipitation in spite of frequently flooded site conditions and have been used to reconstruct moisture levels the southeastern united states and mexico for over 1000 years the el nino southern oscillation enso is a major influence on the climate reconstructions derived from these baldcypress chronologies especially in mexico where some of the most extreme reconstructed droughts occurred during el nino events in the southeast the enso influence on climate and tree growth changes sign from spring to summer and this change in dynamical forcing is recorded by sub seasonal chronologies of earlywood and latewood width most existing baldcypress chronologies have been extended with tree ring data from subfossil wood recovered from surface and submerged deposits well preserved subfossil logs have also been recovered in quantity from buried deposits of great age and may permit development of long continuously dated holocene chronologies and discontinuous floating pleistocene chronologies the extensive subfossil baldcypress swamp discovered 6 m below the streets of washington d c was overrun by a transgression of the potomac estuary possibly during the previous super interglacial marine ois 5e and provides direct evidence for one potential impact of unmitigated anthropogenic warming and sea level rise

martian mantle mineralogy investigated by the 176lu 176hf and 147sm 143nd systematics of shergottites abstract chemical heterogeneities in the martian mantle are believed to result from the crystallization of a magma ocean in the first 100 million years of its history shergottite meteorites from mars are thought to retain a compositional record of such early differentiation and the resulting mineralogy at different depths the coupled 176 lu 176 hf and 147 sm 143 nd isotope systematics in 9 shergottites are used here to investigate these issues three compositional groups in the shergottites display distinct isotope systematics one group commonly termed as depleted is characterized by positive 176 hf i from 46 2 to 50 4 and 143 nd i from 36 2 to 39 1 another termed as enriched has negative 176 hf i 16 5 to 13 2 and 143 nd i 7 0 to 6 5 the third group is intermediate between the depleted and enriched groups with positive 176 hf i 30 0 to 33 4 and 143 nd i 16 9 together they describe mixing curves between 176 hf 177 hf 143 nd 144 nd lu hf and sm nd implying that they sample two distinct sources in the martian mantle all shergottites are characterized by sm nd source sample but lu hf source lu hf sample this decoupling can be explained by two successive partial melting episodes in the depleted shergottite source and localized in the martian upper mantle the genesis of shergottites can be modeled using non modal equilibrium partial melting in a source initially composed of 60 olivine 21 clinopyroxene 9 orthopyroxene and 10 garnet with degrees of partial melting of 8 8 and 3 9 respectively for the two successive events the enriched end member of the shergottite mixing curve is best modeled by late stage quenched residual melt resulting from the crystallization of a magma ocean the depleted shergottite source may be modeled as a mixture of cumulates and residual melt as convection in the martian magma ocean is expected to reduce the incompatible trace element heterogeneity in the final solidified layers consequently equilibrium crystallization is preferred to model the crystallization of the martian magma ocean the models that best explain the shergottite data are those where the magma ocean is at a depth of at least 1350 km in mars

the age of dar al gani 476 and the differentiation history of the martian meteorites inferred from their radiogenic isotopic systematics samarium neodymium isotopic analysis of the martian meteorite dar al gani 476 yields a crystallization age of 474 11 ma and an initial end143 value of 36 6 0 8 although the rb sr isotopic system has been disturbed by terrestrial weathering and therefore yields no age information an initial 87sr 86sr ratio of 0 701249 33 has been estimated using the rb sr isotopic composition of the maskelynite mineral fraction and the sm nd age the sr and nd isotopic systematics of dar al gani 476 like those of the basaltic shergottite que94201 are consistent with derivation from a source region that was strongly depleted in incompatible elements early in the history of the solar system nevertheless dar al gani 476 is derived from a source region that has a slightly greater incompatible enrichment than the que94201 source region this is not consistent with the fact that the parental magma of dar al gani 476 is significantly more mafic than the parental magma of que94201 and underscores a decoupling between the major element and trace element isotopic systematics observed in the martian meteorite suite combining the end142 end143 isotopic systematics of the martian meteorites yields a model age for planetary differentiation of 4 513 0 033 0 027 ga using this age the parent daughter ratios of martian mantle sources are calculated assuming a two stage evolutionary history the calculated sources have very large ranges of parent daughter ratios 87rb 86sr 0 037 0 374 147sm 144nd 0 182 0 285 176lu 177hf 0 028 0 048 these ranges exceed the ranges estimated for terrestrial basalt source regions but are very similar to those estimated for the sources of lunar mare basalts in fact the range of parent daughter ratios calculated for the martian meteorite sources can be produced by mixing between end members with compositions similar to lunar mare basalt sources two of the sources have compositions that are similar to olivine and pyroxene rich mafic cumulates with variable proportions of a rb enriched phase such as amphibole whereas the third source has the composition of liquid trapped in the cumulate pile i e similar to kreep after 99 crystallization correlation between the proportion of trapped liquid in the meteorite source regions and estimates of fo2 suggest that the kreep like component may be hydrous the success of these models in reproducing the martian meteorite source compositions suggests that the variations in trace element and isotopic compositions observed in the martian meteorites primarily reflect melting of the crystallization products of an ancient magma ocean and that assimilation of evolved crust by mantle derived magmas is not required furthermore the decoupling of major element and trace element isotopic systematics in the martian meteorite suite may reflect the fact that trace element and isotopic systematics are inherited from the magma source regions whereas the major element abundances are limited by eutectic melting processes at the time of magma formation differences in major element abundances of parental magma therefore result primarily from fractional crystallization after leaving their source regions

heat flow and thermal evolution of a passive continental margin from shelf to slope a case study on the pearl river mouth basin northern south china sea abstract the pearl river mouth basin prmb the largest basin in the northern continental margin of the south china sea scs has been one of the key areas to characterize geothermal field and thermal evolution of a passive continental margin the thermal history of the pearl river mouth basin is related to the seafloor spreading of the scs in the late early oligocene heat flow measurements show that the prmb is characterized by a high background heat flow with average heat flow of 71 8 13 6 mw m2 the present day heat flow of the northern scs increases from the northern shelf with the thick crust to the southern slope with the thinned crust this study employs forward and inverse modeling to simulate the rift and post rift processes exampled by four wells at different structural settings two thermal evolution models of the prmb are established for continental shelf and continental slope in the continental shelf heat flow increased rapidly twice during the syn rift stage and then followed by continuous thermal subsidence with heat flow value decreased during the post rift stage while the heat flow in the slope continuously increased due to lithospheric thinning mantle upwelling and resulting multi episode seafloor spreading in scs during the neogene post rift stage which is different from the previously proposed decreasing heat model for the slope during the post rift heat flow gradually reduced after the cessation of the sea floor spreading 10 ma the local multi staged magmatic activities mainly contribute to the high level of maturity in the liwan sag located in the lower slope

light and variable 37 cl 35 cl ratios in rocks from gale crater mars possible signature of perchlorate cl isotope ratios measured on hcl thermally evolved from as yet unknown phases in sedimentary rocks and sand in gale crater provide unexpected insights to the martian surficial cl cycle the seven samples yield 37 cl values ranging from 1 25 to 51 5 five analyses from two samples of the sheepbed mudstone yellowknife bay study area are analytically indistinguishable with a mean 37 cl of 11 7 1 in contrast four mudstones sandstones from the kimberley and pahrump study areas also yielded indistinguishable ratios but with a mean 37 cl of 43 6 the rocknest sand deposit gave a highly uncertain 37 cl value of 7 44 these light and highly variable 37 cl values are unique among known solar system materials two endmember models are offered to account for these observations and in both perchlorate with its extreme ability to fractionate cl isotopes is critical in the first model sam is detecting hcl from an oxychlorine compound e g perchlorate produced from volcanic gas emissions by atmospheric chemical reactions similar reactions in earth s atmosphere may be responsible for the isotopically lightest known cl outside of this study in perchlorate from the atacama desert some of the gale crater 37 cl values are more negative than those in atacama perchlorate but because reaction mechanisms and associated fractionation factors are unknown it is impossible to assess whether this difference is prohibitive if the negative 37 cl signal is produced in this fashion the isotopic variability among samples could arise either from variations in the relative size of the reactant chloride and product perchlorate reservoirs or from variations in the fraction of perchlorate reduced back to chloride after deposition such reduction strongly enriches 37 cl in the residual perchlorate perchlorate reduction alone offers an alternative endmember model that can explain the observed data if sam measured hcl derived from chloride in this model isotopically normal perchlorate produced by an unspecified mechanism is reduced to chloride depending on the relative size of the reduced reservoir the integrated product chloride can vary in isotopic composition from 70 in the first increment all the way to the starting composition if the perchlorate is fully reduced thus variable degrees of perchlorate reduction can produce chloride with the appropriate 37 cl range combination of the two endmember models in which the perchlorate subject to post deposition reduction is isotopically negative from atmospheric reactions is also possible determination of the phase hosting the cl measured by sam an oxychlorine compound or chloride is critical for selecting between these models and for developing implications of the results for the mars surficial cl cycle at present it is not possible to conclusively establish which phase is responsible possibly both but limited evidence favors the conclusion that the measured cl derives mostly from an oxychlorine compound

distinct chlorine isotopic reservoirs on mars implications for character extent and relative timing of crustal interactions with mantle derived magmas evolution of the martian atmosphere and the building blocks of an early mars the style magnitude timing and mixing components involved in the interaction between mantle derived martian magmas and martian crust have long been a point of debate understanding this process is fundamental to deciphering the composition of the martian crust and its interaction with the atmosphere the compositional diversity and oxygen fugacity variations in the martian mantle the bulk composition of mars and the materials from which it accreted and the noble gas composition of mars and the sun recent studies of the chlorine isotopic composition of martian meteorites imply that although the variation in delta sup 37 cl is limited total range of approximately14 per mille there appears to be distinct signatures for the martian crust and mantle however there are potential issues with this interpretation new cl isotope data from the sam sample analysis at mars instrument on the mars science lab indicate a very wide range of cl isotopic compositions on the martian surface recent measurements by 10 duplicated the results of 7 8 but placed them within the context of sam surface data in addition martian meteorite chassigny contains trapped noble gases with isotopic ratios similar to solar abundance and has long been considered a pristine mantle derived sample however previous studies of apatite in chassigny indicate that crustal fluids have interacted with regions interstitial to the cumulus olivine the initial cl isotope measurements of apatite in chassigny suggest an addition of crustal component to this lithology apparently contradicting the rare gas data here we examine the cl isotopic composition of multiple generations and textures of apatite in chassigny to extricate the crustal and mantle components in this meteorite and to reveal the style and timing of the addition of crustal components to mantle derived magmas these data reveal distinct martian cl sources whose signatures have their origins linked to both the early solar system and the evolving martian atmosphere

the composition and thickness of the crust of mars estimated from rare earth elements and neodymium isotopic compositions of martian meteorites isotopic and trace element compositions of martian meteorites show that early differentiation of mars produced complementary crustal and mantle reservoirs that were sampled by later magmatic events this paper describes a mass balance model that estimates the rare earth element ree content and thickness of the crust of mars from the compositions of shergottites the diverse ree and nd isotopic compositions of shergottites are most easily explained by variable addition of light rare earth element lree enriched crust to basaltic magmas derived from lree depleted mantle source regions antarctic shergottites eet 79001 alh 77005 lew 88516 and que 94201 all have strongly lree depleted patterns and positive initial 143nd isotopic compositions which is consistent with the generation of these magmas from depleted mantle sources and little or no interaction with enriched crust in contrast shergotty and zagami have negative initial 143nd isotopic compositions and less pronounced depletions of the lree which have been explained by incorporation of enriched crustal components into mantle derived magmas jones 1989 longhi 1991 borg et al 1997 the mass balance model presented here derives the ree composition of the crustal component in shergotty by assuming it represents a mixture between a mantle derived magma similar in composition to eet 79001a and a lree enriched crustal component the amount of crust in shergotty is constrained by mixing relations based on nd isotopic compositions which allows the ree pattern of the crustal component to be calculated by mass balance the effectiveness of this model is demonstrated by the successful recovery of important characteristics of the earth s continental crust from terrestrial columbia river basalts self consistent results for nd isotopic compositions and ree abundances are obtained if shergotty contains 10 30 of lree enriched crust with 10 ppm nd this crustal component would have moderately enriched lree sm nd 0 25 0 27 147sm 144nd 0 15 0 17 la yb 2 7 3 8 relatively unfractionated heavy rare earth elements hree and no eu anomaly crust with these characteristics can be produced from a primitive lherzolitic martian mantle by modest amounts 2 8 of partial melting and it would have a globally averaged thickness of 45 km which is consistent with geophysical estimates mars may serve as a laboratory to investigate planetary differentiation by extraction of a primary basaltic crust

martian magmas contained abundant chlorine but little water the martian water cycle a key for the habitability of mars largely relies on the abundance of water in martian magmas and their mantle sources yet martian snc shergottite nakhlite and chassigny classes meteorites contain minimal water however some experimental studies have suggested that martian parental magmas contained as much as 2 h2o here we integrate mineral chemical experimental and cosmochemical constraints to show that martian magmas contained little water but abundant chlorine apatite and amphibole in martian meteorites are chlorine rich and water poor this constrains the chlorine contents in their parental magmas to 0 3 wt and water contents to 0 3 wt our experimental work has shown that large amounts of water are not needed to explain the mineralogy of the martian meteorites because chlorine has effects similar to those of water on crystallization such chlorine rich water poor martian magmas are consistent with mars being chlorine rich 2 5 compared with the earth furthermore the bulk cl composition of martian meteorites shows that they have not preferentially lost cl by degassing of an h2o rich vapor together these results show that chlorine not water was the dominant volatile species in martian basalts and that these basalts contributed little h2o to mars surface environment

trace and minor elements in minerals of nakhlites and chassigny clues to their petrogenesis abstract ion microprobe measurements of ree rare earth element and other selected trace and minor element concentrations were made in clinopyroxene olivine feldspar and chlorapatite in chassigny and the three nakhlites nakhla governador valadares and lafayette in chassigny we have found pigeonite occurring in a poikilitic habit it is the first reported occurrence of this mineral in this meteorite the most significant implication of this finding is that estimates of the major element composition of the chassigny parent melt will have to accommodate pigeonite as a primary mineral crystallizing before plagioclase chlorapatite contains the highest ree abundances in all meteorites studied here the ree patterns of chlorapatite plagioclase and augite in nakhlites and chassigny are similar although the downward trends of ree patterns are somewhat steeper for these minerals in chassigny than in the nakhlites pyroxenes in nakhlites and chassigny are extensively zoned in rees and other trace and minor elements such as y zr ti and al which appear to be resistant to diffusive reequilibration thus primary igneous zoning of these elements has been preserved in the pyroxenes of these meteorites and can be used to infer their crystallization histories the calculated ree patterns of the parent melts of nakhlites and chassigny are lree enriched and parallel to their whole rock ree patterns indicating that once crystal accumulation occurred the intercumulus trapped melt fractionally crystallized in an essentially closed system and that infiltration i e metasomatism by lree enriched magmas need not be invoked to explain the lree enrichment in bulk samples of these meteorites fractional crystallization model calculations for nakhla also confirm these conclusions the distributions of trace and minor elements in augites in nakhlites and chassigny suggest that all three nakhlites could be samples from different horizons of the same lithologic unit but that chassigny was not comagmatic with the nakhlites

early martian mantle overturn inferred from isotopic composition of nakhlite meteorites following the crystallization of a magma ocean the martian mantle probably underwent an overturning event but its initiation timing and geochemical consequences are poorly constrained isotopic data for martian meteorites and numerical simulations provide strong evidence for early overturning in the martian mantle