high al gabbros in the laramie anorthosite complex wyoming implications for the composition of melts parental to proterozoic anorthosite high al gabbro represents one of the latest phases of magmatism in the 1 43 ga laramie anorthosite complex lac in southeastern wyoming this lithology which is mineralogically and geochemically the most primitive in the lac forms dikes and small intrusions that cross cut monzonitic and anorthositic rocks high al gabbro is characterized by high al2o3 15 19 wt ree patterns with positive europium anomalies eu eu 1 2 3 8 and the lowest initial 87sr 86sr as low as 0 7033 and highest initial nd up to 2 in the lac their sr and nd isotopic characteristics indicate a mantle origin followed by crustal assimilation during ascent intermediate plagioclase an50 60 and mafic silicate fo54 63 compositions suggest that they are not primary mantle melts and that they differentiated prior to final emplacement high al gabbros of the lac are similar compositionally to gabbros from several other proterozoic anorthosite complexes including rocks from the harp lake complex and the hettasch intrusion in labrador and the adirondack mountains of new york these gabbros are considered to be parental to their associated anorthositic rocks a theory that is supported by recent experimental work we interpret lac high al gabbros to represent mantle derived melts produced by the differentiation of a basaltic magma in an upper mantle chamber continued evolution of this magma eventually resulted in the formation of plagioclase rich diapirs which ascended to mid crustal levels and formed the anorthositic rocks of the lac because these gabbros intrude the anorthositic rocks they do not represent directly the magma from which anorthosite crystallized and instead are younger samples of magma formed by identical processes

40ar 39ar geochronological constraints on the age and evolution of the permo triassic emeishan volcanic province southwest china abstract the biostratigraphically constrained permo triassic emeishan volcanic province evp extending over wide areas in southwest china has been recently considered as a large igneous province contemporaneous with the siberian traps and the siliceous tuffs at the p t boundary in south china we report the first 40ar 39ar ages on this igneous province minimum ages have been obtained on phenocrystic plagioclase of the emeishan basalt which has undergone a pervasive metamorphism most likely during subsequent tectonization as a consequence of terrane amalgamation comparison between the ar release spectra obtained on clear vs cloudy plagioclase indicates a 40 30 ma sericite resetting time a minimum apparent age of 246 4 ma for plagioclase from a plagiogranite a late differentiate of the panzhihua layered complex and an age of 254 5 ma for phlogopite from a pyroxenite near lake erhai provide the first absolute age constraint on this igneous province additional ar ar age measurements on post emeishan alkaline and mafic magmatism yielded 104 2 and 100 2 ma for an alkaline complex near panzhihua and 42 1 ma for a gabbro sill emplaced near the ertan dam further study is still needed to determine the age of the emeishan volcanic emission accurately and to test the validity of the assumed short duration of the eruption

permian rifting related fayalite syenite in the panxi region sw china abstract within the panxi rift of the permian emeishan large igneous province elip sw china a 20 km 2 quartz bearing fayalite syenitic pluton intrudes the 260 ma baima igneous complex bic the fayalite syenite is dated using shrimp zircon u pb techniques at 252 2 5 ma the panxi fayalite syenite is mainly composed of alkali feldspar ferroan augite fayalite quartz and fe ti oxides and contains 61 8 63 7 wt sio 2 5 0 7 3 wt fe 2 o 3 t and 9 9 12 1 wt total alkalis belonging to an a type variety of ferroan alkalic metaluminous granitoids the fayalite syenite displays positive eu anomalies eu eu 0 9 8 9 and is enriched in lree la yb n 6 6 11 5 the nd values and 87 sr 86 sr initial ratios of the fayalite syenite range from 1 3 to 1 9 and from 0 7035 to 0 7068 respectively the fayalite syenite and the bic had the same mantle source however the 8 myr age gap between them suggests the fayalite syenite formed by remelting of underplated mafic magmas injected into the crust during elip magmatism the ages of the fayalite syenite and bic are coincident with two permian mass extinction events and suggest that elip may have influenced both

growth characteristics and genetic types of pores and fractures in a high rank coal reservoir of the southern qinshui basin abstract in this paper field investigations such as underground coal wall observations and core log analyses have been conducted and combined with laboratory experiments such as the mercury intrusion method the low temperature liquid nitrogen adsorption method photomicrography and scanning electron microscopy sem to study the growth characteristics and genetic types of pores micro fractures and macro fractures in coal bed 3 of the southern qinshui basin and to analyze the connections between pores and fractures the results show that this coal bed prioritizes micropores and transition pores i e intermolecular pores and residual gas pores followed by macropores i e plant tissue pores and intergranular pores mesopores metamorphic gas pores do not develop moreover coal bed 3 contains a considerable number of closed and semi closed pores it develops two groups of exogenous fractures and cleats i e endogenous fractures and the formation is controlled by a paleotectonic stress field the cleats have a relatively small density and are usually filled by calcite and other minerals which are harmful to the permeability of the coal bed shrinkage micro fissures static pressure micro fissures structure micro fissures and ultramicroscopic fissures are all widely developed and are not filled by minerals micro fissures are important channels for the connections between pores and cleats ultramicroscopic fissures cut through some gas pores these two types of fractures improve the permeability and connectivity of the coal bed and are important links between different sizes of pores and fractures there are three levels of connections between pores and fractures namely connections between ultramicrostructures and microstructures connections between microstructures and cleats and connections between cleats and exogenous fractures

a physical and numerical model based research on the subsidence features of overlying strata caused by coal mining in henan china the major environmental consequence of coal mining is anthropogenic land subsidence in particular mine subsidence can cause damage to public and private infrastructure such as railroads roads pipelines and buildings what is more it is an engineering problem which troubles engineering construction and safety ground surface deformation is related to the measure of mining and the deformation mechanism of overlying strata above the gob in this paper a physical and numerical model on the subsidence of longwall mining within a geotechnical setting is presented the physical model is developed within the framework of physical similar law and geological model in henan province china the numerical solution is developed within continuum poromechanics and finite element setting the law of overlying strata deformation is obtained according to physical model experiment and numerical simulation

stress relief coalbed methane drainage by surface vertical wells in china abstract this paper summarizes the status of engineering practice technology and research related to stress relief coalbed methane cbm drainage using surface wells in china during the past 10 years comments are provided on the theory and technical progress of this method in high gas mining areas such as the huainan huaibei and tiefa mining areas characterized by heavily sheared coals with relatively low permeability stress relief cbm surface well drainage has been successfully implemented and has broad acceptance as a cbm exploitation technology the fundamental theories underpinning stress relief cbm surface well drainage were established in china and include elements relating to 1 rock layer deformation theory vertical zoning and horizontal partitioning and the change in the stress condition in mining stopes 2 a theory regarding an abscission circle in the development of mining horizontal abscission fracture and vertical broken fracture in overlaying rocks and 3 the theory of stress relief inducing permeability increase in protected coal seams during mining and the gas migration accumulation theory of stress relief cbm surface well drainage three kinds of technical drainage modes are described protected seam surface well drainage in areas influenced by mining represented mainly in the huainan mining area gob surface well drainage most prominently in the tiefa mining areas and the multipurpose surface well drainage used in the huaibei mining areas serial well allocation in which wells are used for different purposes as extraction and mining proceeds and well bore configurations and designs suitable for this purpose are described the development and utilization of cbm is significant to energy saving emission reduction and to ensure safety in coal production

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

zircon u pb geochronology and elemental and sr nd isotope geochemistry of permian mafic rocks in the funing area sw china mafic layered intrusions and sills and spatially associated andesitic basalts are well preserved in the funing area sw china the 258 3 ma layered intrusions are composed of fine grained gabbro gabbro and diorite the 260 3 ma sills consist of undifferentiated diabases both the layered intrusions and volcanic rocks belong to a low ti group whereas the diabases belong to a high ti group rocks of the high ti group have feo tio2 and p2o5 higher but mgo and th nb ratios lower than those of the low ti group they have initial 87sr 86sr ratios 0 706 0 707 lower and nd 1 5 to 0 6 higher than the low ti equivalents 0 710 0 715 and 9 6 to 4 0 respectively the high ti group was formed from relatively primitive high ti magmas generated by low degrees 7 3 9 5 of partial melting of an enriched oib type asthenospheric mantle source the low ti group may have formed from melts derived from an em2 like lithospheric mantle source the mafic rocks at funing are part of the emeishan large igneous province formed by a mantle plume at 260 ma

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

a shared borehole approach for coal bed methane drainage and ground stabilization with grouting abstract in underground longwall coal mines the risks of surface subsidence and coal bed methane cbm emission are generally controlled separately e g subsidence mitigation by overburden stabilization using grout injection and pressure relief cbm drainage using surface boreholes however some longwall panels require both gas drainage and ground stabilization for this purpose we propose a shared borehole approach for ground stabilization grouting and adjacent seam pressure relief cbm drainage by using mining induced fractures and voids in this method overlying seam pressure relief cbm is drained through a surface borehole during extraction of a longwall panel whereas grout injection is applied to stabilize the ground using the same borehole following drainage a combined drainage injection model that determines the allowable lag distance for grout injection is proposed the effectiveness of the shared borehole approach was tested at a longwall panel in a chinese coal mine no obvious interactions between the injection and drainage processes were detected during the case study verifying the effectiveness of the shared borehole approach

numerical modeling of gas flow in deformed well casing for the prediction of local resistance coefficients pertinent to longwall mining and its engineering evaluation during gob gas venthole ggv drainage the borehole casing is to withstand various forces induced by the movement of overlying strata of the longwall panel so as to become deformed tensile deformation compressive deformation and shear deformation are the most typical deformation modes of the casing once deformation of the casing occurs the flow resistance of gas in casing increases sharply which causes the volumetric flow of gob gas recovery to decrease through an analysis of the cross sectional shapes of three typical casing deformations the characteristic parameters of each kind of deformation were determined in addition a numerical simulation of the gas flow field was carried out using the four casing models i e one without deformation and three with typical deformations the changing characteristics of the local resistance coefficient of the deformed casing with varying characteristic parameters of corresponding deformation were analyzed in addition this study compared the local resistance coefficient of casings for the three deformation models and deduced that the local resistance coefficient resulting from shear deformation is the largest furthermore by considering the flow field characteristics of gas in the three models this study determined that the vortex induced by the separation of the boundary layer in the areas of deformation was a major cause of local resistance finally a method for predicting the characteristic parameter values of casing deformation was proposed and a case study was performed the research results provide a theoretical basis for predicting the influence of casing deformation on ggv drainage

estimation of methane emission from shallow gas bearing sandstones abstract this paper presents exponential model created by the author to estimate gas flow time relationships for shallow methane bearing donetsk sandstones in donetsk ukraine such estimation is indispensable in case of passing subway tunnels through these sandstones the proposed model involves not only time but also a ratio between average widths of shallow fractures in sandstones and average horizontal distances between these fractures it is revealed that an increase in this ratio leads to an increase in gas volumetric flow rate acceleration of gas emission and an increase in the volume of methane emitted from borehole it is shown that gas flow vs time curves obtained for 17 boreholes drilled from the ground surface through sandstones are similar to those estimated by the proposed model observations show that the volume of methane extracted from each borehole is between 161 m3 and 673 m3 and maximum value of volumetric flow rate is ranged from 0 00265 m3 min to 0 0455 m3 min

analysis of gob gas venthole production performances for strata gas control in longwall mining longwall mining of coal seams affects a large area of overburden by deforming it and creating stress relief fractures as well as bedding plane separations as the mining face progresses stress relief fractures and bedding plane separations are recognized as major pathways for gas migration from gas bearing strata into sealed and active areas of the mines in order for strata gas not to enter and inundate the ventilation system of a mine gob gas ventholes ggvs can be used as a methane control measure the aim of this paper is to analyze production performances of ggvs drilled over a longwall panel these boreholes were drilled to control methane emissions from the pratt group of coals due to stress relief fracturing and bedding plane separations into a longwall mine operating in the mary lee blue creek coal seam of the upper pottsville formation in the black warrior basin alabama during the course of the study pratt coal s reservoir properties were integrated with production data of the ggvs these data were analyzed by using material balance techniques to estimate radius of influence of ggvs gas in place and coal pressures as well as their variations during mining the results show that the ggvs drilled to extract gas from the stress relief zone of the pratt coal interval is highly effective in removing gas from the upper pottsville formation the radii of influence of the ggvs were in the order of 330 380 m exceeding the widths of the panels due to bedding plane separations and stress relieved by fracturing material balance analyses indicated that the initial pressure of the pratt coals which was around 648 kpa when longwall mining started decreased to approximately 150 kpa as the result of strata fracturing and production of released gas approximately 70 of the initial gas in place within the area of influence of the ggvs was captured during a period of one year

magma sources for mesozoic anorogenic granites of the white mountain magma series new england usa the magma sources for granitic intrusions related to the mesozoic white mountain magma series in northern new england usa are addressed relying principally upon nd isotopes many of these anorogenic complexes lack significant volumes of exposed mafic lithologies and have been suspected of representing crustal melts sm nd and rb sr isotope systematics are used to evaluate magma sources for 18 felsic plutons with ages ranging from about 120 to 230 ma the possibility of crustal sources is further examined with analyses of representative older crust including paleozoic granitoids which serve as probes of the lower crust in the region multiple samples from two representative intrusions are used to address intrapluton initial isotopic heterogeneities and document significant yet restricted variations 1 in end overall mesozoic granite plutons range in end t from 4 2 to 2 3 with most 2 to 0 and in initial 87sr 86sr from 0 7031 to 0 709 the isotopic variations are roughly inversely correlated but are not obviously related to geologic geographic or age differences older igneous and metamorphic crust of the region has much lower nd isotope ratios with the most radiogenic paleozoic granitoid at end 180 ma of 2 8 these data suggest mid proterozoic separation of the crust in central northern new england moreover the bulk of the mesozoic granites cannot be explained as crustal melts but must have large mantle components the ranges of nd and sr isotopes are attributed to incorporation of crust by magmas derived from midly depleted mantle sources crustal input may reflect either magma mixing of crustal and mantle melts or crustal assimilation which is the favored interpretation the results indicate production of anorogenic granites from mantle derived mafic magmas

petrogenesis of the red mountain pluton laramie anorthosite complex wyoming implications for the origin of a type granite abstract the red mountain pluton the youngest intrusion in the laramie anorthosite complex is one of five monzonitic to granitic a type plutons intruded at 1 43 ga in the laramie mountains of southeastern wyoming the red mountain pluton ranges in composition from fayalite monzonite clinopyroxene quartz monzonite and biotite hornblende quartz syenite to granite the red mountain pluton is petrologically and geochemically distinct from the northern and southern sherman batholith the sybille intrusion and the maloin ranch pluton it has higher feo t feo t mgo and higher k 2 o is more strongly enriched in rees and at any given silica content it has lower abundances of tio 2 feo mgo cao and p 2 o 5 the fayalite monzonite in the red mountain pluton crystallized at temperatures around 1000 c and oxygen fugacities 1 2 log units below that of the fmq buffer similar to the crystallization conditions of the sybille and maloin ranch plutons the biotite hornblende quartz syenite crystallized at oxygen fugacities near or slightly below those of fmq most of the units in the pluton carry mantle like nd sr and pb isotopic compositions similar to the least contaminated anorthositic and ferrodioritic rocks of the lac indicating that the pluton evolved mainly via differentiation substantial crustal assimilation occurred only in the late dikes and the granite we suggest that all of the 1 43 ga a type intrusions in southeastern wyoming are ultimately derived from tholeiites extreme differentiation or partial melting produced monzonitic magmas that have assimilated varying amounts of siliceous crust the differences between the red mountain pluton and other a type granitoids in southeastern wyoming are related to the extent of differentiation prior to crustal assimilation the compositional ranges of a type granitoids in southeastern wyoming suggest that the geochemical spectrum of a type granites worldwide similarly are produced from evolved mantle derived melt that has assimilated varying proportions of crustal material

yardea dacite large volume high temperature felsic volcanism from the middle proterozoic of south australia the yardea dacite is a large volume felsic volcanic unit from the middle proterozoic gawler range volcanics of south australia it has been previously described as an ignimbrite however some samples contain no petrographic evidence for a pyroclastic origin but have characteristics compatible with final crystallization from a nonfragmented magma these samples may have erupted as lavas but others are likely to be extremely densely welded ignimbrites suggesting a compound nature for the unit geothermometry and phase equilibria indicate that the yardea dacite originated from a high temperature 1000 c felsic magma with a low water content 2 the yardea dacite is not associated with a known caldera of the valles type and shares many characteristics of recently described cenozoic felsic volcanic rocks from the western united states interpreted as rheoignimbrites or as unusually extensive lavas

permeability evolution during progressive deformation of intact coal and implications for instability in underground coal seams abstract we report measurements of deformation strength and permeability evolution during triaxial compression of initially intact coals permeability is continuously measured by the constant pressure differential method together with axial and volumetric strains for both water h2o and strongly adsorbing carbon dioxide co2 gas strength and young s modulus increase with increasing confining stress and permeability is hysteretic in the initial reversible deformation regime as deviatoric stress and strain increase permeability first decreases as pre existing cleats close and then increases as new vertical dilatant microcracks are generated post peak strength the permeability suddenly increases by 3 4 orders of magnitude during loading the inflection point where permeability begins to increase occurs earlier than the turning point of volumetric strain which may be explained by the competing processes of axial crack opening and closure of oblique and transverse cracks the generation of these vertical microcracks does not enhance gas migration in the horizontal direction but will accelerate the rate of gas desorption and weaken the coal based on this mechanistic observation we propose a process based model for bursting in underground coal seams horizontal and vertical stresses redistribute ahead of the mining face immediately after the excavation and influence pore pressure permeability and desorption rate due to this redistribution the zone closest to the mining face may experience tensile failure interior to this zone a region may develop with gas overpressures induced by desorption and this may contribute to the occurrence of coal and gas outbursts beyond this an overstressed zone may initiate shear failure driven by gas pressures if the desorption rate outstrips the rate of drainage we discuss the implications of this on the instability of coal seams to co2 injection and the potential for induced fault slip

sedimentary evidence for a rapid kilometer scale crustal doming prior to the eruption of the emeishan flood basalts biostratigraphic and sedimentologic investigations in 67 sections have been carried out for the middle permian maokou formation that immediately underlies the emeishan flood basalts in southwest china the results suggest a domal crustal thinning before the emplacement of the emeishan large igneous province variably thinned carbonates in the maokou formation are capped by a subaerial unconformity which is generally manifested by karst paleotopography paleoweathering zone or locally by relict gravels and basal conglomerates provenance analysis indicates that these gravels and conglomerates were mainly derived from the uppermost maokou formation therefore the stratigraphic thinning likely resulted from differential erosion due to regional uplift iso thickness contours of the maokou formation delineate a subcircular uplifted area in accordance with the crustal doming caused by a starting mantle plume as predicted by experimental and numerical modeling the duration of this uplift is estimated to be less than 3 myr and the magnitude of uplift is greater than 1000 m the sedimentary records therefore provide independent supporting evidence for the mantle plume initiation model for the generation of the emeishan flood basalts

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

an experimental and numerical investigation on the deformation of overlying coal seams above double seam extraction for controlling coal mine methane emissions abstract this study investigates the deformation and the resultant pressure relief of highly gassy coal seams where a double seam mining operation takes place at lower depths at the wulan coal mine china in order to predict the depressurization effect in the overlying coal seams we simulate the extraction process by constructing a scaled model in the laboratory using similar rock materials analyses of experimental results concluded that due to the mining induced stress redistribution the pressure within target coal seams which were 109 m above the mined seams could be fully relieved to attain the statutory approval for gas drainage in addition to scaled model studies computational modeling studies were conducted using udec universal distinct element code which showed that the features of deformation resulting from the double seam extraction were different from that of in the case of single seam extraction the results of the numerical studies revealed that in addition to the panel margin on the air return side areas near the intake entry could also be considered as borehole drilling positions besides it was found that the gob of the extracted seams below the gassy one provided a buffering effect for the would mined protective coal seam and that the depressurization effect was largely weakened the laboratorial findings are instructive to the field practice of methane drainage during the mining operation a displacement comparison method was adopted to measure the dilated amount of protected coal seams and as expected the maximum dilation percentage was much more than 0 2 the critical value upon which the target coal seam is appropriately depressurized to allow gas drainage to be safely and effectively implemented

activity composition relations in fetio3 mntio3 ilmenite solid solutions from emf measurements at 1050 1300 k the activity of fetio3 in the binary ilmenitepyrophanite fetio3 mntio3 solid solution has been determined for the temperature range 1050 1300 k by displacement of the reaction 2 fetio3 2 fe 2 tio2 o2 in t o2 space using an electrochemical technique with calcia and yttria stabilized zirconia solid electrolytes the activities show small positive deviations from ideality which although the data are unusually precise may be perfectly described by the simple regular solution model with an interaction parameter w fe mn ilm of 2 2 0 3 kj g atom 1 which is independent of temperature this value together with the experimental data on the partitioning of fe and mn between ilmenite and garnet pownceby et al 1987 gives w fe mn gt 1 2 0 5 kj g atom 1 for the almandine spessartine fe3al2si3o12 mn3al2si3o12 solid solution

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

a numerical study on optimization of multilateral horizontal wellbore patterns for coalbed methane production in southern shanxi province china abstract china s southern shanxi province contains thick gassy coals of anthracite rank these high methane content higher than 500 ft 3 ton coals necessitate pre mining methane drainage to enhance the health and safety of underground coal workers both traditional vertical wells and multilateral horizontal wells which were shown to perform better have been drilled in the area in order to effectively reduce the gas content of coals however optimization of well drilling patterns is crucial to improve the gas drainage by boosting well performance and resulting in significant additional recovered gas in a cost effective manner in this study exploration borehole data from an undeveloped coalbed methane field in china s qinshui basin was obtained where permeability is expected to range from 0 1 to 10 md reservoir modeling conducted in this study concludes that in the presence of low permeability coals less than 1 0 md well patterns can be optimized to maintain high methane production rates in this work relationships to determine combinations of horizontal lateral spacing and permeability that yield similar production curves were developed in order to maximize production pinnate wells with laterals spaced at 600 ft intervals in reservoirs with 2 0 md permeability performed similar to those with 200 ft lateral intervals in 0 5 md reservoirs additional similar relationships were drawn for reservoirs ranging from 0 1 to 8 0 md furthermore because of the qinshui basin s potential high stress regime pitchfork and pinnate horizontal well patterns were analyzed based on their potential for catastrophic wellbore failure at well junctions and producing well branches analyses concluded that pitchfork wells had a significantly lower risk for significant wellbore loss due to borehole collapse while providing the opportunity for higher gas recovery in reservoirs exhibiting directional permeability

zircon ages and nd isotopic and chemical compositions of orthogneisses from the black forest germany evidence for a cambrian magmatic arc single zircon u pb dating combined with 207pb 206pb ages obtained by the evaporation method constrains the emplacement of tonalitic trondhjemitic and granodioritic orthogneisses of the moldanubian zone in the black forest between 500 and 510 ma two detrital zircon populations of 1 9 and 1 6 ga indicate early middle proterozoic material in the former setting of the basement the initial end values range from 0 1 to 3 4 and mean crustal residence ages of 1 0 1 4 ga are consistent with involvement of early middle proterozoic crust and a subordinate juvenile component probably originating from subduction related melting of the mantle the orthogneisses have fractionated ree patterns and slightly higher k2o na2o ratios than typical low k tonalite trondhjemite granite suites the chemical data are interpreted as evidence for melting of amphibolite and contributions from evolved crust the emplacement of the orthogneisses was superceded by a high temperature metamorphic event at 480 ma which we interpret as a result of lithospheric thinning in a marginal basin behind a cambrian magmatic arc

the effective stress law for stress sensitive transversely isotropic rocks abstract this paper first presents a review of the development of the concept of effective stress followed by major experimental and theoretical studies carried out to estimate the biot s coefficient it then uses the constitutive equations for vertically transverse isotropic vti reservoirs like coal derived using the principles of thermodynamics for estimation of the biot s coefficients in the vertical and horizontal directions laboratory data for tests conducted on two coal types retrieved from different geologic settings and geographical locations was used to carry out the modeling and validation exercise evidence is presented that values of biot s coefficient can be greater than one proposed by biot to be the limiting value for sorptive rocks to address this the term biot s coefficient is replaced with effective stress coefficient finally this paper discusses the pressure and stress dependent behavior of the biot s coefficient the results clearly show that the estimated values of biot s coefficients in both vertical and horizontal directions are different varying with pressure for methane depletion but remaining constant for helium depletion at the same time the nature of biot s coefficient re termed as effective stress coefficient was found to be greater than unity for methane depletion as a last step a conceptual physical model is proposed to explain the pressure dependent variation of effective stress biot s coefficients in terms of the contact area between grains based on the findings that the effective stress coefficient decreases with pressure it is concluded that the effective vertical stress would increase significantly with depletion which in turn would result in shear failure and increased permeability

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

reservoir simulation based modeling for characterizing longwall methane emissions and gob gas venthole production abstract longwall mining alters the fluid flow related reservoir properties of the rocks overlying and underlying an extracted panel due to fracturing and relaxation of the strata these mining related disturbances create new pressure depletion zones and new flow paths for gas migration and may cause unexpected or uncontrolled migration of gas into the underground workplace one common technique to control methane emissions in longwall mines is to drill vertical gob gas ventholes into each longwall panel to capture the methane within the overlying fractured strata before it enters the work environment thus it is important to optimize the well parameters e g the borehole diameter and the length and position of the slotted casing interval relative to the fractured gas bearing zones this paper presents the development and results of a comprehensive dynamic three dimensional reservoir model of a typical multi panel pittsburgh coalbed longwall mine the alteration of permeability fields in and above the panels as a result of the mining induced disturbances has been estimated from mechanical modeling of the overlying rock mass model calibration was performed through history matching the gas production from gob gas ventholes in the study area results presented in this paper include a simulation of gas flow patterns from the gas bearing zones in the overlying strata to the mine environment as well as the influence of completion practices on optimizing gas production from gob gas ventholes

emeishan basalt ar ar overprint ages define several tectonic events that affected the western yangtze platform in the mesozoic and cenozoic abstract ar ar whole rock dating was carried out as part of a detailed stratigraphical investigation of the emeishan basalt large igneous province lip in the stratotype area sichuan china thirteen from twenty one specimens from three sections yielded reliable reversed isochron and plateau ages maximum 1 errors of 2 1 and 1 6 m y respectively and form two clusters centered on the late jurassic early cretaceous and early late cretaceous with a tail spanning 82 40 ma however all are appreciably younger than the magnetobiostratigraphically constrained late middle permian 255 260 ma age of the basalts reflecting varying degrees of thermal resetting during the mesozoic and cenozoic recently middle jurassic early cretaceous ages reported from elsewhere in the lip have been used to infer a single 40 m y long tectonic episode that affected the western yangtze platform developing this idea the new information have been combined with data we hold for other parts of the terrain and results from three emeishan lip ar ar dating studies published during 2002 to give 32 reliable age dates three 10 12 m y events appear to be recorded in different parts of the province middle jurassic late jurassic early cretaceous and early late cretaceous with a fourth shorter middle eocene episode the 40 m y mesozoic episode appears to be a sampling artifact following a review of the regional deformation tectonic features it is argued that activity related to various phases of deformation in the longmen shan thrust belt is the most likely cause of resetting the final suturing of the north and south china blocks may have also been responsible for the middle jurassic event however the oligocene present indentation of india into asia appears not to have had an impact possibly due to the large scale related strike slip faults that have effectively shielded the lip sichuan basin

geologic geochemical and geophysical consequences of plume involvement in the emeishan flood basalt province prevolcanic kilometer scale lithospheric doming in the emeishan large igneous province southwest china allows us to evaluate the spatial and temporal consequences of uplift on the paleogeography geology geochemistry and geophysics of the region systematic spatial variations are observed across the domal structure in the distribution and thickness of clastic and carbonate sediments the extent of erosion thickness and chemistry of volcanic rocks and the crust mantle structure these features which are best explained by a mantle plume may be used to track older plume sites in the geologic record

chondritic meteorite fragments associated with the permian triassic boundary in antarctica multiple chondritic meteorite fragments have been found in two sedimentary rock samples from an end permian bed at graphite peak in antarctica the ni fe co ni and p fe ratios in metal grains the fe mg and mn fe ratios in olivine and pyroxene and the chemistry of fe ni p and s bearing oxide in the meteorite fragments are typical of cm type chondritic meteorites in one sample the meteoritic fragments are accompanied by more abundant discrete metal grains which are also found in an end permian bed at meishan southern china we discuss the implications of this finding for a suggested global impact event at the permian triassic boundary

regional ai fe mafic magmas associated with anorthosite bearing terranes proterozoic anorthosite massifs are nearly monomineralic accumulations of plagioclase feldspar which must result from unusual conditions of crystallization and emplacement1 2 their chemistry is compatible with derivation from a high alumina basalt parent of mantle origin1 and mafic magmas rich in aluminium and iron have long been suspected of having an important connection to anorthosites and their parent magmas1 4 regional examples of mafic magmas clearly compatible with an anorthosite lineage have not been generally recognized3 in part because of the paucity of candidates within the anorthosite massifs themselves samples of such magmas should also be sought in the country rocks surrounding the massifs here we report the widespread occurrence of al fe mafic magmas in the anorthosite bearing adirondack highlands of new york state they are chemically distinct from typical high ai basalt fe basalt and most common magma types identification of similar al fe basaltic magmas in other areas suggests that such magmas are characteristic of anorthosite bearing terranes

characteristics of natural fractures in the upper paleozoic coal bearing strata in the southern qinshui basin china implications for coalbed methane cbm development abstract natural fractures as the effective storage space and fluid flow pathway of hydrocarbons play a critical role in the exploration and development of unconventional gas resources in the coal bearing strata in the present study to reveal the effects of natural fractures on coalbed methane cbm preservation and development the types origins and development characteristics of natural fractures in the upper paleozoic permian shanxi formation in the southern qinshui basin were systematically described and analyzed based on outcrops cores borehole image logs thin sections and sem four types of natural fractures have been identified in the shanxi formation according to their geologic origins including the endogenic fractures cleats and exogenous fractures in the no 3 coal seam and tectonic fractures and diagenetic fractures in its roof and floor tectonic fractures can be further divided into small faults intraformational shear fractures intraformational open fractures and slip fractures while diagenetic fractures are mainly bed parallel fractures the statistical results show that the development and distribution characteristics of those types of fractures are significantly different which are mainly influenced by lithology layer thickness and geological structure further natural fractures with different types and distributions show different influences on cbm preservation and well productivity exogenous fractures can effectively improve the seepage capability of coal reservoirs and are conducive to cbm wells productivity whereas endogenic fractures have less contributions to coal permeability due to their poor effectiveness the intraformational open fractures in the fold axis zones and intraformational shear fractures and small faults in the fault zones are generally excessive developed those fractures may result in gas dissipation and external water supplement which have negative effects on cbm preservation and production however moderate developed intraformational shear fractures in the sandstone roof can favorably affect the pressure reduction of coal reservoir and improve the recovery potential of unconventional gas resources these investigations may serve as a geological basis for unconventional gas exploration and development of the upper paleozoic coal bearing strata in the southern qinshui basin

in situ study of intensity of weathering induced fractures and methane emission to the atmosphere through these fractures abstract the width and length of weathering induced fractures horizontal distances between through channels formed due to weathering number of through channels in a very weak sandy shale surface layer and methane emission through these fractures to the atmosphere are studied sampling from the studied weathered sandy shale exhibiting very low rock quality rqd in situ directly in the walls of five surface vertical boreholes 1 5 m deep using an original measurement device the radial expansion of measurement devise due to air pressure is used to press wet gypsum into the fractures in borehole surface in order to make gypsum casts of the fractures semi empirical relations between methane volumetric flow rate into the atmosphere through weathering induced fractures and dimensions area and number of weathering induced fractures and gas pressure difference are obtained the comparison between the values of gas seepage through the fractures and rock matrix is performed

coal permeability improving mechanism of multilevel slotting by water jet and application in coal mine gas extraction multilevel slotting by water jet is one of the effective methods used to improve the coal seam permeability as the example of the 1603 working face of guhanshan coalmine first using acoustic emission technology we analyzed the mechanical properties and crack propagation characteristics of the multilevel slotting coal under the condition of uniaxial loading then using the particle flow software pfc2d we numerically simulated the fracture stress and porosity evolutions of the multilevel slotting coal and analyzed the coal permeability improving mechanism of the slot crack network meanwhile the borehole gas extraction slotted by water jet underground was field tested the study found that the coal s body strength could be weakened significantly when the number of slots was increased and the multilevel distribution of the slots induced a great amount of crack growth and extension which formed the slot crack network reduced the stress concentration and increased the coal porosity field tests demonstrated that the gas extraction effect underground was significantly improved the ability of gas extraction of multilevel slotting borehole was enhanced by 5 10 times compared with the conventional borehole and the coal permeability coefficient was increased by about six times

volcanism impact and mass extinctions incredible or credible coincidences massive continental volcanism and or bolide impacts are considered by many authors to have caused three major mass extinction events during the last 300 million years the end permian end cretaceous and end triassic extinctions however reevaluation of the frequency of bolide impacts and plume related flood basalt provinces indicates that both types of event occur much more frequently than mass extinctions and so in isolation may not be responsible for the largest extinctions furthermore the kill mechanisms associated with either flood basalts or impacts do not appear to be sufficiently powerful to cause worldwide collapse of ecosystems leading to the largest mass extinctions contemporaneous flood basalts and bolide impact may be prerequisites for the largest mass extinctions we present a statistical analysis of the probability of coincidence between volcanism and impact and show that three random coincidences of these events in the last 300 m y are likely no causal relationship between impact and volcanism is necessary the lesser mass extinctions on the other hand may not require juxtaposition of two such catastrophic events such coincidences occurring on more than three occasions during the last 300 m y become increasingly unlikely d 2004 elsevier b v all rights reserved

coalbed methane from hazard to resource abstract coalbed gas which mainly consists of methane has remained a major hazard affecting safety and productivity in underground coal mines for more than 100 years coalbed gas emissions have resulted in outbursts and explosions where ignited by open lights smoking or improper use of black blasting powder and machinery operations investigations of coal gas outbursts and explosions during the past century were aimed at predicting and preventing this mine hazard during this time gas emissions were diluted with ventilation by airways e g tunnels vertical and horizontal drillholes shafts and by drainage boreholes the 1970 s energy crisis led to studies of the feasibility of producing the gas for commercial use subsequent research on the origin accumulation distribution availability and recoverability has been pursued vigorously during the past two decades since the 1970 s research investigations on the causes and effects of coal mine outbursts and gas emissions have led to major advances towards the recovery and development of coalbed methane for commercial use thus coalbed methane as a mining hazard was harnessed as a conventional gas resource

residual liquid origin for a monzonitic intrusion in a mid proterozoic anorthosite complex the sybille intrusion laramie anorthosite complex wyoming the sybille intrusion 100 km 2 is one of three large monzonitic intrusions in the 1 43 ga laramie anorthosite complex of southeastern wyoming the petrographic geochemical isotopic and geophysical characteristics of sybille monzonitic rocks are consistent with an origin by extensive crystallization of liquids residual to nearby anorthositic cumulates ferrodiorites and contamination by archean wall rocks the exposed part of the intrusion is composed mainly of coarse grained monzosyenites with abundant alkali feldspar phenocrysts the monzosyenites preserve mineralogical evidence for high crystallization temperatures 1000 c mid crustal emplacement pressures 3 kbar relatively reduced crystallization conditions 2 log units below the fayalite magnetite quartz fmq oxygen buffer and they crystallized in the presence of a co2 rich fluid phase fuhrman et al 1988 frost and touret 1989 the eastern monzosyenites those adjacent to contemporaneous anorthosite are distinguished by an anhydrous mineral assemblage fo16 fo8 olivine high ca pyroxene lacking modal quartz silica contents of 60 wt and smaller eu anomalies eu eu 1 2 to 1 3 abundant xenoliths of archean wall rocks and anorthosite from the adjacent intrusions in all monzosyenites attest to a stoping emplacement mechanism near the roof of the chamber we propose that the monzosyenites represent a relatively thin 0 5 1 0 km thick roof to a magma chamber dominated by dense ferrodioritic cumulates at depth extensive open system fractionation of a ferrodioritic parent magma residual after crystallization of anorthosite produced fe enriched monzodioritic and or monzonitic magma in the upper part of the chamber and complementary fe and ti rich cumulates in the lower levels we have corroborated the production of monzonitic liquids from crystallization of ferrodiorite through a series of reconnaissance equilibrium crystallization experiments the presence of dense ferrodioritic cumulates at depth is consistent with the prominent positive gravity anomaly associated with the sybille intrusion hodge et al 1973 in the upper parts of the chamber the fractionated monzodioritic and or monzonitic magmas eventually became saturated in alkali feldspar owing to density contrasts the alkali feldspar phenocrysts floated to the roof of the chamber thus producing the exposed porphyritic monzosyenites in addition the roof of the chamber was the site of significant melting of archean gneiss and locally metapelite the sr and nd isotopic compositions of the monzosyenites with sr isotopic ratios becoming increasingly radiogenic from east i sr 0 7059 and initial nd 2 5 to west i sr 0 7092 and initial nd 2 6 are consistent with a 5 to 15 addition of archean orthogneiss to a ferrodioritic parent magma that had isotopic characteristics similar to adjacent anorthositic rocks the stratigraphic and compositional similarity of the sybille monzosyenites to mangerites in the bjerkreim sokndal intrusion of the rogaland anorthosite complex southern norway indicates that similar open system magmatic processes are capable of having produced high temperature k rich monzonitic rocks in other proterozoic anorthosite complexes

formation of fractured zones in overburden due to longwall mining the fractured zones caused by mining were studied in the overburden of the torezko snezhnyanskaya area ukraine through the change in natural gas emission from these zones during longwall coal excavation zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings the maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19 41 and 53 92 times the thickness of the coal seam respectively it was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof it is shown that the growth of the zone of interconnected fractures occurred during 17 39 days at an average rate of 0 94 1 97 m day 1 and it was accompanied by increasing methane emission from overburden observation shows that the formation of separate horizontal fractures began only 11 49 5 days after the height of the zone of interconnected fractures reached its maximum value formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone sandy shale layer interfaces in the direction of the ground surface

geochronology of the karadere basement nw turkey and implications for the geological evolution of the istanbul zone earlier geological work in the istanbul zone western pontide tectonic belt has revealed the presence of extensive basement outcrops exposed underneath palaeozoic and mesozoic to tertiary cover sequences the basement of suspected neoproterozoic age plays an important role in understanding the crustal accretion process in nw turkey we report the first results of a detailed pb pb and u pb zircon study complemented by nd sr whole rock and mineral data from basement rocks exposed in the karadere valley safranbolu area five samples were selected for this study comprising three metagranitoids and two metasediments zircon geochronology indicates that the metagranitoids were formed during late proterozoic pan african magmatic events between 590 and 560 ma the rocks are of tonalitic and granitic composition and have low nb y ratios and ti contents consistent with those of arc rocks a continental arc setting is supported by their sr and nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis the metasediments can clearly be distinguished from the metagranitoids by their higher 87sr 86sr ratios and lower end values at 580 ma which supports the suggestion that the arc was underlain by mature continental crust zircons from the metasediments yield a range of pb pb ages between 1 860 and 710 ma thirty per cent of them fall between 890 and 710 ma possibly suggesting a derivation from gondwana afro arabian regions a sm nd garnet whole rock analysis obtained on a metagranite gives an age of 559 8 ma which either reflects pre metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high temperature metamorphic event uplift and cooling of the basement is further constrained by rb sr biotite ages of 548 545 ma these lower cambrian mineral ages demonstrate that the istanbul zone was not thermally reactivated during the hercynian cimmerian or alpine orogeny in contrast to its neighbouring tectonic zones confirming its role as a suspect terrane in the modern western pontide tectonic belt

reduced rapakivi type granites the tholeiite connection reduced rapakivi type granites are the most iron enriched and reduced i e least oxidized of the anorogenic granite association the low oxygen fugacity and chemical composition of these granites severely limit their sources in this paper we argue that reduced rapakivi type granites and their eruptive equivalents high potassium fayalite rhyolites are derived from mafic sources because tholeiitic magmas and their derivatives have the required low oxygen fugacity reduced rapakivi type granites are produced either by extreme differentiation of basaltic melts or by partial melting of underplated basalts and their differentiated equivalents they form in extensional environments where the asthenosphere is present at shallow depths we envision three stages in the origin of these rocks 1 tholeiitic melts are emplaced at the base of the crust 2 continued introduction of heat partially remelts these tholeiitic rocks and 3 the hot dry melts so produced migrate into the middle crust to produce rapakivi batholiths or erupt as rhyolites partial melting of felsic continental crust may accompany the intrusion of rapakivi type magmas thereby producing the other metaluminous and peraluminous granite compositions of the anorogenic suite

major perturbation of ocean chemistry and a strangelove ocean after the end permian mass extinction the severe mass extinction of marine and terrestrial organisms at the end of the permian period c 251 ma was accompanied by a rapid 1 ma decrease in sedimentary burial of organic carbon in the early triassic

mineralogy and fluvial history of the watersheds of gale knobel and sharp craters a regional context for the mars science laboratory curiosity s exploration a 500 km long network of valleys extends from herschel crater to gale knobel and sharp craters the mineralogy and timing of fluvial activity in these watersheds provide a regional framework for deciphering the origin of sediments of gale crater s mount sharp an exploration target for the curiosity rover olivine bearing bedrock is exposed throughout the region and its erosion contributed to widespread olivine bearing sand dunes fe mg phyllosilicates are found in both bedrock and sediments implying that materials deposited in gale crater may have inherited clay minerals transported from the watershed while some topographic lows of the sharp knobel watershed host chloride salts the only salts detected in the gale watershed are sulfates within mount sharp implying regional or temporal differences in water chemistry crater counts indicate progressively more spatially localized aqueous activity large scale valley network activity ceased by the early hesperian though later hesperian amazonian fluvial activity continued near gale and sharp craters