chalcophile element geochemistry and petrogenesis of high ti and low ti magmas in the permian emeishan large igneous province sw china sulfide poor mafic layered intrusions sills dykes and lava flows in the funing region sw china are part of the 260 ma emeishan large igneous province they belong to either a high ti group tio2 1 6 4 4 wt with elevated ti y ratios 351 1 018 or a low ti group tio2 1 low y pd pm ratios 0 2 7 1 and nearly constant cu pd pm ratios 1 5 3 8 the even and parallel chalcophile element patterns of the high pge low ti subgroup rocks are likely a result of olivine dominated fractionation under s undersaturated condition the low pge low ti group rocks have low mgo 4 5 8 9 wt and very poor pge pt pd 0 5 1 6 ppb ir 0 004 0 02 ppb with low cu zr ratios 0 1 0 5 high y pd pm 26 70 and variable cu pd pm ratios 2 8 14 the trough like chalcophile element patterns of the low pge low ti subgroup rocks indicate that the magmas were sulfide saturation and sulfide melts were extracted from the magmas the extracted sulfide melts might be potential ni cu sulfide ores at depth in the funing region

low ti iron oxide deposits in the emeishan large igneous province related to low ti basalts and gabbroic intrusions abstract the yanyuan region in the emeishan large igneous province elip contains some low ti iron oxide deposits that are spatially associated with low ti basalts and related gabbroic intrusions the pingchuan deposit is the largest of this type and the adjacent lanzhichang deposit is the first stratiform deposit hosted in the emeishan basalts discovered in 2005 the pingchuan deposit occurs in veins and is hosted in caldera near the dabanshan low ti gabbroic complex which is composed of gabbro and gabbronorite that intruded the gabbro the adjacent lanzhichang deposit is hosted in the lower section of the low ti emeishan basalts and geological characteristics obviously indicate a volcanic sedimentary genesis the magnetite of these two deposits contains minor tio2 0 002 and v2o3 0 027 and there is no ilmenite in the mineral assemblages apatite u pb and fission track ft dating of the pingchuan deposit indicates a u pb age of 245 26 ma and ft age of 51 8 4 9 ma zircon u pb dating of the dabanshan complex indicates two similar ages of 259 9 1 1 ma and 260 3 1 3 ma within the error range for the gabbro and gabbronorite respectively three u pb ages together with geological evidence indicate that the pingchuan deposit is formed after both the basalts and dabanshan gabbroic complex reported bulk rock major element data indicate that the basalts and the dabanshan gabbroic intrusions belong to the low ti basalts and associated intrusions the gabbro has similar chemical composition to the basalt but the gabbronorite is distinctly different from gabbro and basalt using zircon u pb ages we found that the fe2o3 decreased by 4 51 from the gabbro to the gabbronorite within a very short time interval this sudden drop of fe2o3 was probably caused by immiscibility of the low ti basaltic magma and the isolated low ti fe rich melts can account for the mineralization of the lanzhichang and pingchuan deposits from two ascents contribution of phosphorus from the country rocks may have triggered this liquid immiscibility the sr nd isotope compositions of the basalts and gabbroic intrusions indicate a transition between the igneous rocks related to the fe ti v oxide deposits and the cu ni pge sulfide deposits in the elip all of these factors indicate the pingchuan and lanzhichang deposits in the yanyuan region belong to a specific type of low ti iron oxide deposits that are related to the low ti basalts and gabbroic intrusions in the elip

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

frost and soils implications for paleosols paleoclimates and stratigraphy abstract frost is a pedogenetic agent this paper describes the use of frost features in soil for paleoclimatic and stratigraphic interpretation it is possible to differentiate periods of frost activity from those of temperate pedogenesis by macroscopic and microscopic criteria and to distinguish between soils with pre syn and epigenetic frost effects an experimental approach is necessary to determine initial frost effects because they are usually difficult to observe at natural active sites work with ecologists also clarifies the evolution of frost affected soils under climatic and vegetational constraints vegetation has important effects on the thermal and hydraulic regimes of soils and on erosion susceptibility the recognition of fossil cryosoils often allows the reconstruction of sequences of paleoclimatic events in periods or environments with little or no micropaleontological evidence the interrelations between frost and other pedogenetic processes allow a better understanding of climatic evolution and deterioration throughout the neogene and especially during the quaternary and the holocene most of the inherited frost features in european soils are younger than 480 ka bp the differentiation between frost and tectonic perturbations is very important for calculation of soil erosional budgets

the western ailaoshan volcanic belts and their se asia connection a new tectonic model for the eastern indochina block the western ailaoshan wal volcanic belts mark the western boundary of the south china indochina suture zone along the ailaoshan fold belt geochronological and geochemical evidence suggests that the wal volcanic belts vary in ages and origins and includes 1 l carboniferous earliest m permian ca 300 270 ma incipient backarc basin magmatism 2 m permian ca 265 ma island arc mature backarc basin magmatism 3 early l permian ca 260 255 ma wal indochina arc continent collision and the associated syn collisional granitic magmatism as well as subsequent 4 e triassic ca 250 245 ma post collisional magmatism regional geological comparison indicates that the post l carboniferous wal tectonic evolution was closely related to the eastern indochina block we present a new g plate geodynamic evolution model for the ailaoshan fold belt and its surrounding south china indochina region based on new and published u pb zircon ages together with whole rock and pb isotope geochemical data

two magma series and associated ore deposit types in the permian emeishan large igneous province sw china the late middle permian 260 ma emeishan large igneous province in sw china contains two magmatic series one comprising high ti basalts and fe rich gabbroic and syenitic intrusions the other low ti basalts and mafic ultramafic intrusions the fe rich gabbros are spatially and temporally associated with syenites each series is associated with a distinctive type of mineralization the first with giant fe ti v oxide ore deposits such as panzhihua and baima the second with ni cu pge sulfide deposits such as jinbaoshan limahe and zhubu new shrimp zircon u pb isotopic data yielded 263 3 ma for the limahe intrusion 261 2 ma for the zhubu intrusion and 262 2 ma for a syenitic intrusion these new age dates together with previously reported shrimp zircon u pb ages suggest that all these intrusions are contemporaneous with the emeishan flood basalts and formed during a major igneous event at ca 260 ma the oxide bearing intrusions have higher al2o3 feo as total iron and total alkalis na2o k2o but lower mgo than the sulfide bearing intrusions all intrusions are variably enriched in lree relative to hree the oxide bearing intrusions display positive nb and ti anomalies and in certain cases negative zr hf anomalies whereas the sulfide bearing intrusions have obvious negative nb and ti anomalies a feature of crustal contamination individual intrusions have relatively small ranges of nd t values all the intrusions however have nd t values ranging from 3 9 to 4 6 and initial 87sr 86sr ratios from 0 7039 to 0 7105 the syenites have very low mgo 2 wt but highly variable fe2o3 2 5 to 13 wt with initial 87sr 86sr ratios ranging from 0 7039 to 0 7089 magmas from both series could have derived by melting of a heterogeneous mantle plume the high ti series from a fe rich more fertile source and the low ti series from a fe poor more refractory source in addition the low ti series underwent significant crustal contamination the two magma series evolved along different paths that led to distinct mineralization styles

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

geochemistry and geochronology of native copper mineralization related to the emeishan flood basalts yunnan province china abstract native copper mineralization in northeastern yunnan is related to the emeishan flood basalts which have high cu background concentrations the deposits are located in the ludian maoling and yiche synclines between the flood basalts and the overlying xuanwei formation evidence from ree and hsfe concentrations oxygen isotope compositions bitumen reflectance and mineral paragenesis indicates that the high grade copper orebodies were deposited from moderate to low temperature hydrothermal solutions 420 to 100 c in a reducing environment 40 ar 39 ar spectra for the laumontites that coexist with native copper in the high grade ores yield consistent plateau and isochron ages 226 to 228 ma these are interpreted to represent the age of the first stage of hydrothermal mineralization which took place at temperatures of 200 to350 c concordant with that of zn pb ag ge mineralization also occurring in the area the heulandites yield a stable 40 ar 39 ar plateau age of 134 0 1 7 ma consistent with isochron ages indicated by u th pb isotopic systematics indicating a second stage of native copper mineralization at lower temperatures 100 to 200 c that took place during the early cretaceous

results of pilot re os dating of sulfides from the sukhoi log and olympiada orogenic gold deposits russia abstract the pilot study with re os dating of sulfides from sukhoi log and olympiada gold deposits revealed early paleozoic ages of the auriferous sulfides from the two largest orogenic gold systems in the neoproterozoic orogens of the baikalides framing the siberian craton the age dating results indicate that gold mineralization is therefore epigenetic the formation of the dated orogenic gold deposits is synchronous with some regional metamorphic events in the baikalides at least in case of the sukhoi log deposit the metamorphic events occurred in the rear parts of the early paleozoic magmatic arcs where coeval subduction related magmatism produced porphyry copper molybdenum mineralization

late permian basalts in the yanghe area eastern sichuan province sw china implications for the geodynamics of the emeishan flood basalt province and permian global mass extinction abstract we report the finding of a 20 m thick sequence of massive pyroxene plagioclase phyric basalt lava flows in the yanghe area of the northeastern sichuan basin within the yangtze craton of sw china which were previously considered to be located outside the emeishan flood basalt province this basaltic sequence above the middle permian maokou formation fm is overlain by the late permian longtan fm thus the yanghe basalts should be stratigraphically correlated with the emeishan flood basalts the yanghe basalts show typical oceanic island basalt oib affinity and geochemically resemble emeishan basalts especially in the case of high ti ht basalts from the eastern domain of the emeishan flood basalt province the rocks have low age corrected 87sr 86sr t t 260 ma ratios 0 704158 0 704929 and pb isotopic ratios 206pb 204pb t 18 264 18 524 207pb 204pb t 15 543 15 58 and 208pb 204pb t 38 147 38 519 and positive end t values 3 15 to 3 61 suggesting that the lavas have not undergone any significant crustal contamination the crystallization temperature of clinopyroxene is estimated to be 1368 1420 c suggesting anomalously thermal inputs from a mantle source and a possible plume head origin the fractionation of middle rare earth elements mree to heavy ree hree suggests that these rocks were produced by small degrees of partial melting of mantle peridotite within the garnet spinel transition region the stratigraphic relationships and similar geochemical signatures with the emeishan flood basalts suggest that the yanghe basalts are part of the emeishan flood basalt province and can be considered as the northeastern limit of the emeishan flood basalt province our finding extends the diameter of the emeishan flood basalt province to 1200 1400 km covering an area of up to 7 105 km2 two times more than previously estimated the larger areal extent and giant eruption volume incorporating the sichuan basin lend support to the correlation between the end guadalupian mass extinction and the emeishan flood basalt province

a synthesis of magmatic ni cu pge sulfide deposits in the 260 ma emeishan large igneous province sw china and northern vietnam abstract magmatic ni cu pge sulfide deposits in the ca 260 ma emeishan large igneous province lip are all hosted in relatively small mafic ultramafic intrusions with surface areas usually less than 1 km 2 these deposits are mainly distributed in the danba panzhihua xichang panxi huili yuanmou midu funing and jinping regions in sw china and the ta khoa region in northern vietnam they include ni cu pge sulfide dominated ni cu sulfide dominated and pge dominated types sulfide ores of the ni cu pge and ni cu sulfide dominated deposits contain more than 10 vol sulfides and have low pge concentrations relative to the ores that contain 34 s values ranging from 6 7 to 3 4 whereas sulfides from sulfide ores of the baimazhai no 3 yingpanjie jinbaoshan and nantianwan intrusions in sw china have highly variable 34 s ranging from 0 2 to 21 4 indicating the addition of crustal sulfur into the mantle derived mafic magmas platinum group minerals pgm are abundant in the ni cu pge sulfide bearing intrusions and they span a wide range of composition more than 130 pgm grains have been identified in the pt pd rich jinbaoshan intrusion whereas only one small froodite pdbi 2 grain was observed in the ni cu sulfide dominated baimazhai no 3 intrusion overall the three types of ni cu pge sulfide deposits in the emeishan lip can be taken as a spectrum of ni cu pge sulfide mineralization the formation of which involved similar magmatic processes in open systems of magma conduits the magma conduits developed along the cross linking structures created by numerous strike slip faults and each intrusion appears to be part of a connecting trellis of conduits that formed complex pathways from the mantle to the surface the ni cu sulfide dominated deposits are attributed to a single sulfide segregation event in staging magma chambers whereas the pge dominated deposits were likely formed by a multistage dissolution upgrading process in the staging chambers the ni cu pge sulfide dominated deposits may have experienced interaction between successive pulses of s undersaturated mafic magma and early segregated sulfide melts in the staging chambers this study is intended to provide a better understanding of the magmatic processes related to the formation of conduit type ni cu pge sulfide deposits associated with continental flood basalt magmatism

longevity of the permian emeishan mantle plume sw china 1 ma 8 ma or 18 ma after the formation of the 260 ma emeishan large igneous province there were two volumetrically minor magmatic pulses at 252 ma and 242 ma respectively alkaline mafic dykes intruding both 260 ma and 252 ma felsic plutons in the panxi region southwestern china have compositions similar to the emeishan flood basalts one dyke is dated using the shrimp zircon u pb technique at 242 2 ma 18 ma younger than the start of emeishan magmatism the dykes have enriched light rare earth element patterns la ybn 4 4 18 8 and trace element patterns similar to the emeishan flood basalts and average ocean island basalts some trace element ratios of the dykes zr nb 3 8 8 2 la nb 0 4 1 7 ba la 7 5 25 6 are somewhat similar to em1 source material however there are differences their end values end 2 6 and 2 7 and i sr i sr 0 704542 and 0 704554 ratios are indicative of a mantle source thus emeishan magmatism may have lasted for almost 20 ma after the initial eruption however geological evidence precludes the possibility that the post 260 ma magmatic events were directly related to emeishan magmatism which began at and ended shortly after 260 ma the 252 ma plutons and 242 ma dykes represent volumetrically minor melting of the fossil emeishan plume head beneath the yangtze crust the 252 ma magmatic event was likely caused by post flood basalt extension of the yangtze crust whereas the 242 ma event was caused by decompressional melting associated with the collision between the south china and north china blocks during the middle triassic

precise zircon u pb and molybdenite re os dating of the shuikoushan granodiorite related pb zn mineralization southern hunan south china abstract the shuikoushan ore district located in southern hunan province south china contains pb zn au mineralization hosted in the devonian to triassic strata and mesozoic granodiorite intrusions ore minerals are mainly pyrite sphalerite galena and minor molybdenite molybdenite usually intergrown with pyrite formed during pb zn hydrothermal mineralization in order to determine the precise age of pb zn mineralization and further understand the relationship between magma emplacement and hydrothermal mineralization in the ore district molybdenite re os dating and zircon sims u pb dating were undertaken the zircon u pb dating reveals that the granodiorite intrusion was emplaced at 158 8 1 8 ma mswd 0 40 re os isotopic age of seven molybdenite samples yields model ages ranging from 157 5 2 5 ma to 161 0 2 4 ma and gives a well defined 187re 187os isochron age of 157 8 1 4 ma 2 mswd 1 3 indicating the timing of pb zn mineralization in the shuikoushan ore district at about 158 ma this date coincides well with the zircon sims u pb age of the granodiorite revealing a genetic association between the pb zn mineralization and the granitic magmatism combined with geochronological data published for other pb zn cu deposits in southern hunan it can be concluded that the granodiorite related pb zn mineralization throughout southern hunan mainly occurred at 160 156 ma rather than 180 170 ma or 170 160 ma as considered previously the pb zn mineralization and major w sn mineralization in southern hunan are coeval and may be related to the same geological event

an 18 million year record of vegetation and climate change in northwestern canada and alaska tectonic and global climatic correlates abstract we reconstruct long term vegetation paleoclimatic trends spanning the last 18 million years in alaska yukon and far western northwest territories twenty one average percentage spectra for pollen and spores are assembled from eight surface subsurface sections the sections are dated independently or by correlation pollen and spore ratios indicate the direction of change in vegetation and climatic parameters growing season temperature test tree canopy density cest and paludification at study sites pest a global warm peak ca 15 ma is shown by the abundance of thermophilous taxa including fagus and quercus a temperature decline immediately following 15 ma parallels climatic reconstructions based on marine oxygen isotopes subsequent declines correlate to the messinian event and the onset of late pliocene pleistocene glaciation after 7 ma herbs and shrubs become more important elements of the palynological assemblages suggesting a more continental colder drier climate however a late pliocene warm interval is evident vegetation climatic changes during the early to late miocene show synchrony with and are most economically attributable to global events after 7 ma vegetation climate change is attributed primarily to latest miocene to pleistocene uplift of the alaska range and st elias mts the continuing influence of global climatic patterns is shown in the late pliocene warm interval despite uplift to the south the opening of the bering strait ca 3 ma may have moderated the climate in the study area

geometrical aspects of sorted patterned ground in recurrently frozen soil a model for sorted patterned ground shows that some types arise from density driven rayleigh free convection that occurs during thawing of water saturated recurrently frozen soils the regularly spaced convection cells result in an uneven melting of the underlying ice front frost action causes stones to be upthrusted and to form in a pattern on the ground surface that mirrors the corrugation in the underlying ice front the implications of the water circulation direction in the cells on the sorting process are considered

martian seasonal co2 ice in polygonal troughs in southern polar region role of the distribution of subsurface h2o ice the mars orbiter camera onboard the mars global surveyor has obtained several images of polygonal features in the southern polar region in images taken during the end of the southern spring when the surrounding surface is free of the seasonal frost co2 ice still appears to be present within the polygonal troughs in earth s polar regions polygons such as these are indicative of water ice in the ground below we analyzed the seasonal evolution of the thermal state and the co2 content of these features our 2 d model includes condensation and sublimation of the co2 ice a self consistent treatment of the variations of the thermal properties of the regolith and the seasonal variations of the local atmospheric pressure which we take from the results of a general circulation model we find that the residence time of seasonal co2 ice in troughs depends not only on atmospheric opacity and albedo of the co2 ice but also and most significantly on the distribution of water ice in the regolith optical properties of the atmosphere and surface co2 ice can be independently obtained from observations to date this is not true about the distribution of water ice below the surface our analysis quantifies the dependence of the seasonal cycle of the co2 ice within the troughs on the assumed distribution of the water ice below the surface we show that presence of water ice in the ground at a depth smaller than the depth of the troughs reduces winter condensation rate of co2 ice this is due to higher heat flux conducted from the water ice rich regolith toward the facets of the troughs

sand veins and wedges in cold aeolian environments sedimentary structures formed by the progressive primary infilling of thermal contraction cracks with sand are termed primary sand veins and sand wedges in addition to simple vein or wedge shapes irregularities can be caused by sand veins branching from their sides and toes primary sand wedges form widely in sandy polar deserts locally in sandy areas of tundra and probably in seasonally frozen ground there are no unique criteria for distinguishing primary sand veins and wedges from sand veins and wedges of other origins identification of the former depends on the occurrence of distinctive features not always present and on evaluation of their lithofacies and palaeoenvironmental contexts care and caution are advocated in the use of ancient relict primary sand veins and wedges as quantitative palaeoenvironmental indicators because modern active wedge distribution is poorly known and hence inferred thermal climatic threshold values are questionable it is suggested that ancient relict primary sand wedges exceeding 2 m in depth and with well developed vertical lamination probably indicate the former occurrence of continuous permafrost whereas sand veins and narrow sand wedges frost cracks are potentially ambiguous as they may form not only in the active layer above and within continuous permafrost but also in seasonally frozen ground in non permafrost areas

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

re os dating of chalcopyrite from selected mineral deposits in the kalatag district in the eastern tianshan orogen china the kalatag cu zn au district contains a number of economically important cu deposits in eastern tianshan in xinjiang nw china due to the lack of precise mineralization ages the metallogenesis of this area has long been a matter of debate in this study chalcopyrite re os isotope methods are used to date the south meiling cu zn and hongshi cu deposits in the eastern part of kalatag area the south meiling cu zn deposit is hosted in volcanic sedimentary rocks of the late ordovician to early silurian daliugou formation the deposit consists of two parts a concordant massive sulfide ores and discordant vein type ores located in the footwall strata the principal ore minerals are pyrite chalcopyrite sphalerite minor tetrahedrite galena and pyrrhotite gangue minerals include quartz sericite and barite and minor chlorite plagioclase and carbonate minerals the hongshi cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of daliugou formation the orebodies are associated with quartz veins and controlled by subsidiary faults of the kalatag fault the ore forming process can be divided into the early middle and late stages and is characterized by quartz pyrite quartz chalcopyrite pyrite and quartz carbonate gypsum veins respectively re os analyses of chalcopyrite from the south meiling cu zn deposit yield an isochron age of 434 2 3 9 ma and initial 187os 188os ratio of 0 647 0 098 mswd 0 59 re os analyses of chalcopyrite from the hongshi cu deposit yield an isochron age of 431 8 2 7 ma and initial 187os 188os ratio of 0 165 0 075 mswd 0 77 since chalcopyrite is the primary copper mineral we interpret these isochron ages as the timing of cu mineralization based on field geology and petrographic evidence these results suggest that the re os ages presented here provide for the first time a direct constraint on an early paleozoic cu mineralization event of the eastern tianshan orogen the high initial 187os 188os ratios 0 647 0 098 ratio of 434 ma chalcopyrite from the south meiling deposit suggest that the metal was sourced from a two end member mixing of crust and mantle materials moreover we propose that the vms mineral system and hydrothermal vein system of the kalatag district were related to the south dipping subduction of the kalamaili oceanic plate during the late ordovician silurian

precise age determination of mafic and felsic intrusive rocks from the permian emeishan large igneous province sw china abstract radiogenic isotopic dating using different mainly micro beam analyses techniques of rocks from the emeishan large igneous province elip has yielded a range of ages from the capitanian to the early triassic in contrast estimates based on paleontological and paleomagnetic data suggest the elip was emplaced rapidly 2 ma and that volcanism ended by 257 ma new zircon ca tims u pb ages that have superior precision compared to ages from micro beam analyses were obtained from strategic intrusive rocks of the panxi region inner zone of the elip the huangcao 258 9 0 7 ma daheishan 259 1 0 5 ma woshui 259 6 0 5 ma and cida 258 4 0 6 ma syenitic and granitic plutons and three mafic dykes 259 2 0 4 ma 259 5 0 8 ma 257 6 0 5 ma yielded a narrow range of ages between 257 ma and 260 ma the new results are consistent with the estimates from magneto biostratigraphic data and a rapid emplacement model the new wuchiapinqian ages of the huangcao and daheishan plutons suggests that magmatism may have lasted significantly less than 10 ma as previously suggested and the precise ages of the mafic dykes refute the hypothesis that emeishan high ti basalts represent the waning stages of the elip magmatism the short duration of magmatism also implies that degassing of the host sediments mostly carbonates and thus releasing of greenhouse gasses occurred within a substantially shorter interval than previously thought which significantly changes the loading of atmosphere per time unit the latter corollary potentially has severe environmental effects that may have contributed to causing the end guadalupian mass extinction

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

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

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

population based analysis and graphic interpretation of fossil palynomorph records from palynodata taxonomic and biostratigraphic implications abstract palynodata is a comprehensive database of the occurrences of pre quaternary palynomorphs encompassing over 20 000 publications taxa are assumed to have distributions in time and space which are localized to a region around a central point and in the idealized case can be visualized as a bell shaped curve a palynological study can be imagined as drawing a sample from each taxon s time space distribution the probability of recording any taxon is partly a function of its abundance at the sampled point in the distribution a comprehensive database such as palynodata should allow approximation of the underlying population distribution of the taxon retrievals show that useful information is recovered from palynodata although there are errors and inadequacies in the database of which the chief is the generalized study locality record a computer program palynoplot produces graphic plots of retrievals from palynodata allowing improved recognition of the patterns and problems in the database images of the database may have future applications for palynological taxonomy paleoclimatology paleoecology modelling of palynomorph distributions and possibly plate tectonic reconstruction

a reappraisal of the high ti and low ti classification of basalts and petrogenetic linkage between basalts and mafic ultramafic intrusions in the emeishan large igneous province sw china abstract based on published data we reappraise the classification of high ti and low ti basalt from the emeishan large igneous province elip and the correlations between basalts and mafic ultramafic intrusions because of the lack of clear spatial and temporal variations of different types of basalts we suggest that the basalts in the elip cannot be classified into high ti and low ti groups by tio 2 contents and or ti y ratios the distinctive characteristics of these high ti and low ti lavas probably result largely from the different fractionating assemblages whether or not fractional crystallization of the fe ti oxides occurred probably is the key factor that controls the ti abundances and ti y ratios in the residual melts e g lavas although the nature of the mantle sources variable degrees of partial melting of mantle and crustal contamination also influence the geochemical signatures of the lavas therefore neither ti abundance nor ti y ratios in basalts can reflect the nature of their mantle source moreover the different types of mafic ultramafic intrusions in the elip cannot simply be attributed to be genetically related special types of basalts either high ti or low ti basalts it is likely that they are merely the cumulus phases i e chamber or conduit of the basaltic lavas hence caution should be exercised in the use of high ti or low ti basalts as prospecting vectors for ore deposits in the region potential implications are proposed that both the fe v ti oxide and cu ni pge sulfide mineralization in the elip intrusions is largely due to the variable differentiation and crustal contamination during magmatic processes

geological features and origin of the huize carbonate hosted zn pb ag district yunnan south china abstract the huize zn pb ag district in the sichuan yunnan guizhou zn pb ag metallogenic region contains significant high grade zn pb ag deposits the total metal reserve of zn and pb exceeds 5 mt the district has the following geological characteristics 1 high ore grade zn pb 25 wt 2 enrichment in ag and a range of other trace elements ge in ga cd and tl with galena sphalerite and pyrite being the major carriers of ag ge cd and tl 3 ore distribution controlled by both structural and lithological features 4 simple and limited wall rock alteration 5 mineral zonation within the orebodies and 6 the presence of evaporite layers in the ore hosting wall rocks of the early carboniferous baizuo formation and the underlying basement fluid inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165 220 c and salinities of 6 6 12 wt nacl equiv and that the ore forming fluids and metals were predominantly derived from the kunyang group basement rocks and the evaporite bearing rocks of the cover strata ores were deposited along favourable specific ore controlling structures the new laboratory and field studies indicate that the huize zn pb ag district is not a carbonate replacement deposit containing massive sulphides but rather the deposits can be designated as deformed carbonate hosted mvt type deposits detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the huize zn pb ag district and of the potential for similar carbonate hosted sulphide deposits elsewhere in ne yunnan province as well as the sichuan yunnan guizhou zn pb ag metallogenic region

zircon u pb and hf isotope constraints on crustal melting associated with the emeishan mantle plume abstract shrimp zircon u pb dates combined with in situ hf isotopic data provide new constraints on the petrogenesis and protolith of peralkaline metaluminous and peraluminous intrusions and rhyolitic tuffs in the emeishan large igneous province with significant bearing on crustal melting associated with mantle plumes syenite and a type granitic intrusions from huili miyi and taihe in the center of this large igneous province yield u pb dates at 260 ma consistent with the ages obtained for mafic layered intrusions in the same province zircon from these rocks exhibits a wide range of initial hf isotope ratios ehf t 1 4 to 13 4 with corresponding tdm1 of 400 900 ma the highest ehf t value is only marginally lower than that of depleted mantle reservoir at 260 ma suggesting that their source is primarily juvenile crust added during emeishan volcanism with incorporation of variable amounts of neoproterozoic crust the trigger of crustal melting is most likely related to advective heating associated with magmatic underplating in contrast the 255 251 ma peraluminous granites from ailanghe and 238 ma rhyolitic tuff from binchuan have negative initial ehf values of 1 3 to 4 4 and of 7 7 to 14 respectively hf isotopic model ages and presence of inherited zircons indicate their derivation from mesoproterozoic and paleoproterozoic crust respectively given the time lag relative to the plume impact 260 ma and insignificant mantle contribution to 255 238 ma magmatism conductive heating is suggested as the trigger of crustal melting that resulted in formation of delayed felsic magmas the involvement of older crust in younger felsic magmas is consistent with upward heat transfer to the lithosphere during plume impregnation if the age of crust is inversely stratified i e changes from paleoproterozoic to mesoproterozoic to neoproterozoic to permian with increasing depth such crust may have resulted from episodic downward crustal growth during the evolution of the western yangtze craton

rb sr geochronology and geochemistry of the xiaotongchang basalt hosted copper deposit in the jinping area sw china abstract the xiaotongchang basalt hosted copper deposit in jinping southern yunnan province sw china is located in the southern part of the emeishan large igneous province here we use rb sr re os and s pb c o isotope data to constrain the age and genesis of the deposit petrological investigations reveal two main stages of mineralization the early stage is characterized by disseminated or massive sulfides in an assemblage of pyrite chalcopyrite quartz albite calcite rb sr isotopic dating of early stage chalcopyrite yields an age of 256 9 4 ma mswd 5 4 which is slightly younger than the eruption age of the jinping basalts the 34 s cdt values of the sulfides range from 5 8 to 7 7 suggesting that the metals of the early stage copper mineralization originated from the emeishan basalts and that the ore forming fluids were contaminated by crustal rocks these units may indicate that the early stage orebodies represents syngenetic hydrothermal mineralization related to the eruption of emeishan flood basalts the late stage mineralization is characterized by a pyrite chalcopyrite bornite chalcocite quartz calcite assemblage that is developed in veins or breccia the re os isotopic dating of late stage chalcopyrite samples reveals that they formed at 240 231 ma the pb isotopic compositions 206 pb 204 pb t 17 521 19 227 207 pb 204 pb t 15 480 15 760 and 208 pb 204 pb t 37 778 38 731 t 235 ma show that the late stage copper orebodies have a heterogeneous source and originated mainly from the crust the late stage sulfides have higher 34 s cdt values 7 9 to 10 7 than the early stage sulfides the narrow range of sulfur isotopic compositions of the sulfides associated with both stages and the pb isotopic compositions of late stage chalcopyrite indicate that some of the metals associated with late stage mineralization originated from the jinping basalts the c o isotopic compositions of calcite samples show that the magmatic hydrothermal fluids in the late stage flowed through and were contaminated by the maokou limestone therefore we suggest that the late stage orebodies represent magmatic hydrothermal mineralization associated with the late triassic rhyolite porphyry and that the tectono magmatic hydrothermal fluid remobilized copper from the basalts the copper deposits formed at favourable interfaces within the basalt stratigraphy or in favorable structural locations

effects of frictional viscous oscillations and fluid flow events on the structural evolution and re os pyrite chalcopyrite systematics of cu rich carbonate veins in northern norway abstract mesothermal chalcopyrite pyrite magnetite bearing calcite dominated vein deposits in the repparfjord tectonic window northern norway have been studied to constrain the mechanics of their emplacement and the timing of initial vein formation and reactivation the veins cut across paleoproterozoic tholeiitic metabasalts and present textural contrast between their hydrofractured coarse grained margins and the fine grained mylonitic cores they formed under overall viscous conditions although cyclically increased fluid pressures caused transient embrittlement as mineral precipitation sealed the fractures deformation was accommodated again viscously leading to mylonitization of the vein s core local brecciation of the calc mylonite demonstrates the cyclicity of this process re os chalcopyrite pyrite and k ar fault gouge dates define an almost continuous age range from 2540 ma to 460 ma regression of three re os analyses yields a 2069 14 ma age 187os 188os 0 18 0 04 interpreted as the age of vein emplacement sulfide precipitation and initial frictional viscous deformation k ar ages are mixed ages that constrain a maximum age of faulting in association with the veins at approximately 460 ma hence indicating structural reactivation connected with silurian caledonian orogenic compression the spread in re os model ages reflects this reactivation wherein renewed strain accommodation and circulating oxidizing fluids caused fracturing dynamic recrystallization and isotopic disturbance of the sulfides the study provides evidence for fluid flow during viscous deformation and demonstrates that strain and flow of oxidizing fluids can have a significant yet localized control on the integrity of the re os systematic in pyrite and chalcopyrite

gold mineralization associated with emeishan basaltic rocks mineralogical geochemical and isotopic evidences from the lianhuashan ore field southwestern guizhou province china abstract a number of gold deposits are newly discovered in the lianhuashan ore field southwestern guizhou province china the gold orebodies are restricted to the emeishan basaltic rocks and the interlayer fractures between the emeishan basaltic rocks and the limestone of the maokou formation three generations of pyrite py0 py1 and py2 have been recognized in these deposits based on morphology and paragenetic relationships electron microprobe emp laser ablation inductively coupled plasma mass spectrometry la icp ms and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses were carried out to characterize their chemical and sulfur isotopic compositions the framboidal py0 is enriched in as but depleted in most of the other trace elements it has negative 34s values of 14 5 1 9 which are typical of diagenetic pyrites resulted from bacterial reduction of marine sulfate py1 and arsenopyrite exhibit high concentrations of au and as making them the most dominant auriferous minerals they yield comparable 34s values of 2 8 2 1 consistent with the derivation of sulfur from the emeishan basaltic rocks py2 is characterized by well developed oscillatory zoned textures that are interpreted in terms of internal self organization processes it contains low concentrations of au and highly variable concentrations of as sb co and ni the py2 grains show slightly positive 34s values of 0 4 7 0 indicating that the sulfur was mainly sourced from the emeishan basaltic rocks with variable amounts of contamination from reduced marine sulfate the emeishan basaltic rocks may have provided not only ore hosting space but also au s and other associated elements for gold mineralization in the lianhuashan ore field similar gold deposits are expected to be discovered in the areas of emeishan basaltic rocks with high au backgrounds and small thicknesses

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

early jurassic decratonic gold metallogenesis in the eastern north china craton constraints from s pb c d o isotopic systematics and pyrite rb sr geochronology of the guilaizhuang te au deposit abstract the north china craton ncc is a window to decratonization and associated gold metallogenesis during the mesozoic although early cretaceous gold mineralization associated with craton destruction has been reported information on decratonic gold metallogenesis during the other periods remain scarce here we investigate the guilaizhuang crypto explosive breccia type te au deposit from eastern ncc and present rb sr geochronological data on pyrite which provide new constraints on the timing of mineralization as 180 8 2 3 ma corresponding to jurassic gold metallogenesis the s pb c o isotopic systematics and the 87sr 86sr i value of the pyrite as ca 0 712429 0 000076 suggest that the ore forming nutrients were derived from crustal and mantle sources the guilaizhuang te au deposit formed during the tectonic transformation from compression to extension associated with the extensional collapse of the dabie sulu uhp orogen and the delamination of the ncc lithosphere triggering mantle upwelling and extensive crustal melting

nonlinear dynamics of ice wedge networks and resulting sensitivity to severe cooling events patterns of subsurface wedges of ice that form along cooling induced tension fractures expressed at the ground surface by ridges or troughs spaced 10 30 m apart are ubiquitous in polar lowlands1 fossilized ice wedges which are widespread at lower latitudes have been used to infer the duration2 3 4 and mean temperature5 6 of cold periods within proterozoic2 and quaternary climates3 4 5 6 7 8 9 10 11 12 13 and recent climate trends have been inferred from fracture frequency in active ice wedges14 here we present simulations from a numerical model for the evolution of ice wedge networks over a range of climate scenarios based on the interactions between thermal tensile stress fracture and ice wedges we find that short lived periods of severe cooling permanently alter the spacing between ice wedges as well as their fracture frequency this affects the rate at which the widths of ice wedges increase as well as the network s response to subsequent climate change we conclude that wedge spacing and width in ice wedge networks mainly reflect infrequent episodes of rapidly falling ground temperatures rather than mean conditions

a model for water transport and ice lensing in freezing soils a one dimensional model for water transport and ice lensing in incompressible saturated and solute free soil specimens is proposed for the simulation of small scale frost heave tests in the laboratory the model considers 1 open system freezing in which the variables t and pw are independent 2 an ice lens that continues to grow as long as enough energy is available in the frozen fringe to produce the work required for mass transfer to the ice lens and 3 a new ice lens that forms when the vertical strain in the frozen soil reaches the instantaneous tensile failure strain the proposed frost heave model is amenable to computer simulation procedures which provide predictions of rate of frost heave and rate of pore freezing front penetration as functions of applied load thermal and water flow regimes and soil properties position time of initiation and ultimate thickness of individual ice lenses emerge also as a part of the solution a quantitative comparison of observed and simulated responses for various boundary conditions is shown for a reference soil known as devon silt the model was found to exhibit many of the characteristics observed in frost heave tests on devon silt and predicted the effects of overburden pressure on frost heave rate

perennial water ice identified in the south polar cap of mars the inventory of water and carbon dioxide reservoirs on mars are important clues for understanding the geological climatic and potentially exobiological evolution of the planet1 from the early mapping observation of the permanent ice caps on the martian poles2 3 the northern cap was believed to be mainly composed of water ice whereas the southern cap was thought to be constituted of carbon dioxide ice however recent missions nasa missions mars global surveyor and odyssey have revealed surface structures4 altimetry profiles5 underlying buried hydrogen6 and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide7 here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes at a resolution of 2 km during the local summer when the extent of the polar ice is at its minimum we observe that this south polar cap contains perennial water ice in extended areas as a small admixture to carbon dioxide in the bright regions associated with dust without carbon dioxide at the edges of this bright cap and unexpectedly in large areas tens of kilometres away from the bright cap

re os dating of sulphides from the yushui cu polymetallic deposit in eastern guangdong province south china abstract the yushui cu polymetallic deposit which is associated with ag pb and zn is located in the middle part of the yongan meixian late paleozoic hercynian depression it was discovered in eastern guangdong province in the late 1980s and is one of the richest copper deposits in china with high grade copper averaging 3 25 and locally reaching 50 60 the main ore body is located along the unconformity between the upper carboniferous hutian group limestone and the lower carboniferous zhongxin formation quartz sandstone with a bedded and lenticular morphology the ores exhibit massive textures dominated by chalcopyrite bornite chalcocite pyrite sphalerite galena and a trace amount of argentite although researchers began studying the yushui deposit in the early 1990s the ore genesis remains controversial because of the lack of precise mineralisation age constraints in this study direct re os dating of cu sulphides aided in facilitating a better understanding of the timing of formation of the yushui deposit this study is the first attempt to use the re os isotopic system for directly dating chalcopyrite and bornite ores for the yushui deposit the contents of re common os 187re and 187os in nine sulphides are 1 68 219 35 ppb 0 003 0 427 ppb 1 05 137 31 ppb and 0 045 0 734 ppb respectively the isotope data yielded an isochron age of 308 15 ma mean square weighted deviates 2 4 using the 87re 188os 187os 188os plot which is interpreted to represent the age of formation for these sulphides suggesting that the mineralisation age of the yushui deposit is close to the age of the host rocks the 187os 188os initial value obtained from the re os isochron is 1 81 0 34 which corresponds to the os value of 1349 this value indicates that the ore forming materials were derived from the crust without mixing with materials from the mantle and that the yushui massive sulphide deposit may be of sedimentary exhalative origin

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

characteristics and origin of polygonal terrain in southern utopia planitia mars results from mars orbiter laser altimeter and mars orbiter camera data giant polygons on mars with several kilometers in diameter were first observed in mariner 9 and viking orbiter images and their origin formation and evolution have remained enigmatic since that time new data obtained by the mars orbiter laser altimeter mola and the mars orbiter camera moc on board the mars global surveyor spacecraft now permit analysis of topography and morphology of the polygonal terrain in unprecedented detail mola data show that 1 giant polygonal terrain in utopia is located at the lower slopes of a basin structure that is the utopia basin 2 the onset of polygonal terrain in utopia is close to the same elevation in several profiles and lies at about the same elevation as a terrace which was interpreted as a shore line of an ancient body of standing water within the utopia basin proper 3 polygonal terrain occurs over a wide range of elevations on regional slopes of 0 1 4 the depths of the troughs range from 5 m to 115 m averaging about 30 m and tend to be greater toward the center of the utopia basin 5 the mean width of polygonal troughs is of the order of 2 km ranging from 0 5 to 7 5 km data from the mars orbiter camera moc indicate that 1 the troughs are generally broad graben like features with varying morphologies i e terraces and lobateness and dimensions widths and depths 2 trough morphology has been modified by aeolian processes 3 polygonal troughs are weakly interconnected at moc resolutions and there are no smaller polygons observed within the giant polygons 4 circular depressions which are probably related to subsurface collapse sometimes occur at the bottoms of polygonal troughs 5 small scale polygonal terrain on the ejecta blankets of young craters with fluidized ejecta in the investigated area exhibits different characteristics i e smaller size presence of rims greater degree of interconnections than giant polygons in the viking images we see that 1 old impact craters are increasingly buried with younger materials toward the basin center and that 2 a large number of superposed impact craters on polygonal terrain exhibit distinctive ejecta morphologies such as rampart ejecta blankets and single and double lobate ejecta blankets mola and moc observations are consistent with the formation of polygonal terrain in the area of a former standing body of water but polygon size seems too large to be readily accounted for by desiccation or freezing processes alone on the basis of the observed characteristics we propose that the giant polygons are primarily of tectonic origin being caused by uplift of the floor of the utopia basin there are several candidates for the cause of uplift 1 the removal of the load representing former standing bodies of water water thickness estimated for the utopia basin is about 1 km in this scenario removal of this load comparable to loads placed on terrestrial continental lithosphere by the laurentide and scandinavian ice sheets by loss of the water or ice could cause uplift of the floor and polygon formation 2 the freezing and expansion of residual water buried by sediments or in the near subsurface or 3 a combination of these from the discussion of alternative models in the light of the mola and moc data we conclude that formation of giant polygons by tectonic uplift of the basin floor is most likely and deserves further investigation

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

silurian to carboniferous re os molybdenite ages of the kalinovskoe mikheevskoe and talitsa cu and mo porphyry deposits in the urals implications for geodynamic setting abstract the urals can be regarded as a significant cu mo porphyry province hosting over 30 porphyry deposits although their geological structure and ore forming processes have been studied in great detail uncertainty remains about their age and related geotectonic setting in this contribution we report for the first time the re os dating of molybdenites from three cu mo porphyry deposits namely kalinovskoe mikheevskoe and talitsa three molybdenite samples from the kalinovskoe deposit yield silurian re os ages ranging from 427 1 ma to 431 7 ma mean 429 8 4 8 ma 2 standard deviation and a re os isochron age of 430 7 1 3 ma mswd 0 63 which coincides with previous u pb zircon dating of ore hosting diorites from the same ore field 427 6 ma the molybdenite from the mikheevskoe deposit gives re os ages of 357 8 1 8 ma and 356 1 1 4 ma mean 357 0 2 4 ma carboniferous tournaisian which corresponds to previous u pb dating of zircons from the diorite hosting porphyry deposit 356 6 ma the molybdenite from talitsa mo porphyry deposit yields the youngest re os ages of 298 3 1 3 and 299 9 2 9 ma mean 299 1 2 3 ma at carboniferous permian boundary thus the studied cu and mo porphyry deposits are not synchronous and belong to distinct tectonic events of the urals

new paleomagnetic investigations of the emeishan basalts in ne yunnan southwestern china constraints on eruption history abstract paleomagnetic and magnetostratigraphic investigations have been conducted on two consecutive sections of the emeishan trap at shuimo sm and dadi dd in northeastern yunnan province southwestern china rock magnetic analysis indicates that the magnetic carrier of the basalts is dominantly low ti magnetite stepwise thermal demagnetization isolates a stable characteristic remanent magnetization chrm at high temperatures 400 585 c the chrms 301 323 at sm section are northeasterly upward of normal polarity with a mean direction of ds is 11 0 5 2 n 12 k 53 7 95 6 0 at dd section the chrms are southwesterly downward of reversed polarity with a mean direction of 205 9 10 0 n 5 k 78 4 95 8 7 the chrms from the basaltic gravels from the overlying conglomerate layer in late permian xuanwei formation at dd section pass the conglomerate test suggesting the primary nature of magnetization together with other magnetostratigraphic studies e g n r pattern of the emeishan basalts and the known radiometric ages ca 260 ma it suggests that the eruption period of the emeishan large igneous province is less than 3 myr

dynamics of periglacial sorted circles in western spitsbergen a working hypothesis for the development and maintenance of sorted circles which are finegrained soil domains delineated by borders of coarser material involves clast motion relative to soil and intermittent circulatory motion of soil in the active layer the hypothesis is compatible with the observed size regularity sorting microtopography surface soil motion vegetation cover and subsurface organic carbon content of soil patterns studied in spitsbergen theoretical considerations of buoyancy driven convection suggest that intermittent convection of thawed soils is plausible and that the requisite bulk density decrease with depth arises naturally from moisture gradients that develop during the thaw consolidation of ice rich soils these considerations also help in understanding the dependence of sorted circles on soil characteristics and on moisture moreover they point to the possible use of sorted patterns as paleoclimatic indicators based on the expected relation between pattern size and active layer depth

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

re os systematics of sulfides chalcopyrite bornite pyrite and pyrrhotite from the jiama cu mo deposit of tibet china abstract the jiama cu mo deposit one of the largest skarn porphyry deposits in china currently being mined is located in the eastern part of the gangdese porphyry cu belt tibet china chalcopryite and bornite concentrate in the skarn ore zone at jiama with molybdenite concentration whereas molybdenite occurs in the porphyry ore zone and hornfels ore zone relatively by itself cu and mo have different distributions in the porphyry ore zone with cu concentrating above the porphyry and with mo inside of porphyry intrusion the direct re os dating on cu sulfides will be helpful for us to understand the cu and mo mineralization at jiama this study is the first attempt to use the re os isotope system to directly date chalcopyrite bornite pyrite and pyrrhotite at jiama the contents of re common os and 187 os in these four sulfides are 0 145 32 9 ppb 0 0022 0 0669 ppb and 0 0003 0 0118 ppb respectively they have very low ratios of 187 os to common os 0 09 0 55 therefore they are different from low level highly radiogenic llhr sulfides the plot of 187 re 188 os and 187 os 188 os did not yield an isochron age based on the scatter points even if age of 15 ma based on molybdenite re os age is used to calculate the initial 187 os 188 os the ratios show a wide range and low ratios of 187 re 188 os 187 os 188 os the geology suggests the cu and mo mineralizations at jiama are both related to porphyry intrusions and the cu mineralization should also have occurred in miocene based on the molybdenite re os age and porphyry zircon u pb ages

numerical simulation of selforganized stone stripes geometrically regular stripes of stones are found on many unvegetated alpine and polar hillslopes known as sorted stripes because of the characteristic textural sorting between surface stones and fine grained soil they contrast markedly with the lack of order typical of natural landscapes the spacing of the stripes can range from centimetres to metres about 10 20 times the average stone diameter1 2 with individual stripes extending down slope for many tens of metres fig 1 a variety of formative mechanisms have been proposed3 but it is still unclear how such orderly stripes can arise spontaneously and what dictates the spacing here we present two dimensional computer simulations in which the displacement of surface stones is governed by the preferential growth of needle ice in stone free regions of soil during each freezing cycle regular patterns of stones and soil that closely resemble natural stripes are found to emerge spontaneously from the model as a result of identifiable feedbacks between soil texture ice growth and local slope

observational evidence for an active surface reservoir of solid carbon dioxide on mars high resolution images of the south polar residual cap of mars acquired in 1999 and 2001 show changes in the configuration of pits intervening ridges and isolated mounds escarpments have retreated 1 to 3 meters in 1 martian year changes that are an order of magnitude larger than can be explained by the sublimation of water ice but close to what is expected for sublimation of carbon dioxide ice these observations support a 35 year old conjecture that mars has a large surface reservoir of solid carbon dioxide the erosion implies that this reservoir is not in equilibrium with the present environment and that global climate change is occurring on mars

origin of fe ti oxide ores in mafic intrusions evidence from the panzhihua intrusion sw china economicconcentrationsof fe ti oxidesoccuras massive conform able lenses or layers in the lower part of the panzhihua intrusion emeishan large igneous province sw china mineral chemistry textures and quilfequilibria indicate that oxides in rocks of theintrusion were subjected to extensive subsolidus re equilibration andexsolution the primary oxide reconstructed from compositions oftitanomagnetite in the oresand associated intergrowths isan alumi nous titanomagnetite usp

ice wedges on hillslopes and landform evolution in the late quaternary western arctic coast canada in rolling to hilly areas of the western arctic coast of canada anti syngenetic wedges which by definition are those that grow on denudational slopes are the most abundant type of ice wedge through prolonged slope denudation hilltop epigenetic wedges can evolve into hillslope anti syngenetic wedges and some bottom slope anti syngenetic wedges by means of deposition from upslope can evolve into bottom slope syngenetic wedges the axis of a hillslope wedge is oriented perpendicular to the slope so the wedge foliation varies according to the trend of the wedge with respect to the slope because the tops of hillslope wedges are truncated by slope recession the mean chronological age of anti syngenetic wedge ice decreases with time so the growth record for an old wedge is incomplete summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the t

global distribution and migration of subsurface ice on mars a thermal diffusive model of h2o kinetics and equilibrium was developed to investigate the long term evolution and depth distribution of subsurface ice on mars the model quantitatively takes into account 1 obliquity variations 2 eccentricity variations 3 long term changes in the solar luminosity 4 variations in the argument of subsolar meridian in planetocentric equatorial coordinates 5 albedo changes at higher latitudes due to seasonal phase changes of co2 and the varying extent of co2 ice cover 6 planetary internal heat flow 7 temperature variations in the regolith as a function of depth time and latitude due to the above factors 8 atmospheric pressure variations over a 104 year time scale 9 the effects of factors 1 through 5 on seasonal polar cap temperatures and 10 knudsen and molecular diffusion of h2o through the regolith the migration of h2o into or out of the regolith is determined by two boundary conditions the h2o vapor pressure at the subsurface ice boundary and the annual average h2o concentration at the base of the atmosphere these are controlled respectively by the annual average regolith temperature at the given depth and seasonal temperatures at the polar cap starting from an arbitrary initial uniform depth distribution of subsurface ice h2o fluxes into or out of the regolith are calculated for 100 selected obliquity cycles each representing a different epoch in mars history the h2o fluxes are translated into ice thicknesses and extrapolated over time to give the subsurface ice depth as a function of latitude and time the results show that obliquity variations influence annual average regolith temperatures in varying degrees depending on latitude with the greatest effect at the poles and almost no effect at 40 lat insolation changes at the pole due to obliquity argument of subsolar meridian and eccentricity variations can produce enormous atmospheric h2o concentration variations of 6 orders of magnitude over an obliquity cycle superimposed on these cyclic variations is a slow monotonic change due to the increasing solar luminosity albedo changes at the polar cap due to seasonal phase changes of co2 and the varying thickness of the co2 ice cover are critically important in determining annual average atmospheric h2o concentrations despite the strongly oscillating character of the boundary conditions only small amounts of h2o are exchanged between the regolith and the atmosphere per obliquity cycle 10 g cm2 the net result of h2o migration is that the regolith below 30 40 lat is depleted of subsurface ice while the regolith above 30 40 lat contains permanent ice due to the depth of penetration of the annual thermal wave this result is supported by recent morphological studies the rate of migration of h2o is strongly dependent on average pore capillary radius for which we have assumed values of 1 and 10 m we estimate that the h2o ice removed from the regolith would produce a permanent ice cap with a volume between 2 106 and 6 106 km3 this generally agrees with estimates deduced from deflationary features at lower latitudes depositional features at higher latitudes and the mass of the polar caps

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

late cretaceous metallogeny in the zhongdian area constraints from re os dating of molybdenite and pyrrhotite from the hongshan cu deposit yunnan china abstract the zhongdian area in yunnan southwestern china located at the southern end of the yidun volcano magmatic arc that was formed during the triassic westward subduction of the gaze litang ocean hosts numerous triassic large porphyry and skarn deposits the arc suffered jurassic to cretaceous arc continental orogenic collision and cenozoic intracontinental strike slip shearing the hongshan cu mo pb zn deposit is potentially a large deposit and contains two ore types 1 predominant layered skarn cu pb zn ores along marble hornfels contacts and 2 minor crosscutting vein type cu mo mineralization previous research forwards a two stage genetic model without sufficient dating evidence supposing the skarn mineralization is related to the triassic calc alkalic intrusions and the vein type mineralization related to cretaceous quartz monzonite porphyries re os dating of molybdenite from vein type ores and quartz monzonite porphyries and that of pyrrhotite from skarn ores are presented here to constrain the mineralization age and rebuild the genetic model analyses of eight molybdenite samples yield an isochron age of 79 7 3 1 ma mswd 9 2 for the vein type mineralization and a model age of 81 9 1 1 ma for the quartz monzonite porphyries isotope data on seven pyrrhotite samples from the skarn ores yield an isochron age of 79 16 ma z mswd 8 4 the re os ages for the two ore types are concordant within analytical errors indicating that the hongshan deposit was formed in the late cretaceous elevated re contents in molybdenite 13 65 to 63 91 g g and extremely radiogenic initial 187 os 188 os ratios in pyrrhotite 0 7673 to 0 8184 weighted average 0 796 0 038 together with elevated os values in pyrrhotite 507 to 547 average 528 imply a significant crustal component in the ore forming materials that was likely derived from a lower crustal reservoir combined with the tectonic evolution of the zhongdian area and geochemical characteristics of corresponding intrusions the ages of mineralization obtained in this study indicate that the hongshan deposit was formed in a post collision setting with a genetic relationship to the emplacement of the quartz monzonite porphyry these results provide significant new information for the study and exploration of the late cretaceous metallogeny in the zhongdian area

a model for sorted patterned ground regularity sorted patterned ground refers to polygons nets or stripes defined by rocky borders which are the result of sorting in soil subjected to frost action this paper presents a model in which convection cells driven by unstable density stratification in the aqueous phase result in uneven melting of the underlying ice front during thawing the resulting undulatory ice front with regularly spaced peaks and troughs provides the pattern which results in the regularity observed for certain types of patterned ground in addition the model predicts the width to depth of sorting ratio for both polygons and stripes and explains the characteristic hexagonal shape of sorted polygons the transition from sorted polygons to sorted stripes on sloped terrain and the formation of sorted polygons under water the predicted ratio of width to depth of sorting of 3 81 for sorted polygons is compared with the ratio of width to depth of sorting of 3 57 found from a linear regression analysis of 18 field study data

dating the giant zhuxi w cu deposit taqian fuchun ore belt in south china using molybdenite re os and muscovite ar ar system abstract the recently discovered zhuxi w cu ore deposit is located within the taqian fuchun ore belt in the southeastern edge of the yangtze block south china its inferred tungsten resources based on new exploration data are more than 280 mt by 2016 at least three paragenetic stages of skarn formation and ore deposition have been recognized prograde skarn stage retrograde stage and hydrothermal sulfide stage secondly greisenization marmorization and hornfels formation are also observed scheelite and chalcopyrite are the dominant metal minerals in the zhuxi deposit and their formation was associated with the emplacement of granite stocks and porphyry dykes intruded into the surrounding carboniferous carbonate sediments huanglong and chuanshan formations and the neoproterozoic slate and phyllites the scheelite was mostly precipitated during the retrograde stage whereas the chalcopyrite was widely precipitated during the hydrothermal sulfide stage a muscovite 40ar 39ar plateau age of about 150 ma is interpreted as the time of tungsten mineralization and molybdenite re os model ages ranging from 145 9 2 0 ma to 148 7 2 2 ma for the subsequent hydrothermal sulfide stage of activity as the time of the copper mineralization our new molybdenite re os and muscovite 40ar 39ar dating results along with previous zircon u pb age data indicate that the hydrothermal activity from the retrograde stage to the last hydrothermal sulfide stage lasted up to 5 myr from 150 6 1 5 to 145 9 1 ma and is approximately coeval or slightly later than the emplacement of the associated granite porphyry and biotite granite the new ages reported here confirm that the zhuxi tungsten deposit represents one of the mesozoic magmatic hydrothermal mineralization events that took place in south china in a setting of lithospheric extension during the late jurassic 160 150 ma it is suggested that mantle material played a role in producing the zhuxi w cu mineralization and associated magmatism

sulfur isotope evidence for thermochemical reduction of dissolved sulfate in mississippi valley type zinc lead mineralization bongara area northern peru the bongara area northern peru contains mississippi valley type mvt zn pb mineralization hosted in late triassic jurassic carbonate rocks of the pucara group mineralization is interpreted to have formed during the late cretaceous peruvian orogenic event florida canyon and florcita located within 30 km of each other in the bongara area were studied to determine the origin and possible sources of sulfur in the mineralization one hundred and two in situ sulfur isotope analyses were determined on sphalerite galena and pyrite the narrow and symmetric distributions of the sphalerite 1 34s values are consistent with sulfate reduction in an open system with regard to sulfate the 34s values of sphalerite 1 from florida canyon 13 7 to 14 2 v cdt median 1 9 v cdt are lower and more variable than those for florcita 6 2 to 19 3 v cdt median 15 9 v cdt sphalerite 2 34s 0 3 to 17 6 v cdt median 2 4 v cdt postdating sphalerite 1 probably formed in a closed system with regard to sulfate the geologic setting fluid inclusion microthermometry and 34s values indicate that thermochemical reduction of dissolved sulfate tsr was the principal h2s production mechanism for metal precipitation possible sources of sulfate include late cretaceous seawater 34s 18 to 21 and evaporitic sulfate minerals in the middle late triassic chambara condorsinga formations 34s 12 to 15 and or in the late jurassic sarayaquillo formation 13 to 18 reduced sulfur from thermal cracking of organosulfur compounds and probably also remnants of h2s formed by bacterial sulfate reduction bsr might have been present during metal precipitation in florida canyon sample scale 34s variations observed in some samples from both areas reflect variable proportions of sulfate from different sources temperature effects on isotopic fractionation from sulfate to sulfide and the addition of reduced sulfur from organic compounds sample scale 34s variations can be interpreted as evidence for in situ sulfate reduction during mineralization this study places constraints on the mineralization mechanism the nature of sulfate reduction and the source of sulfur in mvt mineralization in northern peru the observed sample scale 34s variations lend support to the conclusion that in situ thermochemical sulfate reduction can occur during mineralization in these environments

diverse and multistage mo au ag pb zn and cu deposits in the xiong er terrane east qinling from triassic cu mineralization abstract the xiong er terrane is one of the representative regions in east qinling orogenic belt various polymetallic deposits have been discovered in the xiong er terrane such as porphyry mo carbonatite hosted type mo quartz vein type mo breccia pipes type au and orogenic type au ag pb zn deposits indicating that diverse significant mineralization occurred in the xiong er terrane recently numerous cu deposits have been observed in the xiong er terrane xianglugou is a quartz vein type copper mineralization which was discovered in xiayu district southern of the xiong er terrane four chalcopyrite samples from xianglugou yield re os isochron age of 230 31 ma 2 mswd 0 8 this is the first evidence for triassic cu mineralization in the xiong er terrane this not only shows the xiong er terrane contains considerable mo au and ag pb zn reserve but also indicates that there is a great potential of cu mineralization the discoverable cu mineralization can further emphasize the significance of the widespread triassic mineralization and widened exploration ideas and goals in the future in the xiong er terrane the xiong er terrane experienced three polymetallic mineralization events including paleoproterozoic triassic and late jurassic to early cretaceous deposits during the qinling orogen evolution these metallogenic events may be related to multiple tectonic events the paleoproterozoic mineralization was associated with the continental outgrowth occurred along the southern margin of the north china craton before 1760 ma the triassic cu mineralization may be associated with the northward subduction of the north qinling orogen beneath the huaxiong block during the collision between north china craton and yangtze craton late jurassic to early cretaceous mineralization perhaps caused by decompressional extension of the qinling orogenic belts and the north china craton intense destruction and lithospheric thinning which is now generally related to the westward subduction of paleo pacific plate

re os pseudo isochron of disseminated ore from the kalatongke cu ni sulfide deposit xinjiang northwest china implications for re os dating of magmatic cu ni sulfide deposits abstract re os dating of disseminated ore from the kalatongke cu ni sulfide mineral deposit xinjiang northwest nw china yields an apparent isochron age of 433 31 ma with an apparent initial 187os 188os 433 ma ratio of 0 197 0 027 this apparent age is older than not only the zircon u pb age of the host intrusion 287 5 ma han et al 2004 but also the stratigraphic age of the intruded country rock thus the regression line is a pseudo isochron however previous re os dating of massive ores of the same deposit yielded an age that is consistent within analytical uncertainty with the zircon u pb age zhang et al 2008 this relationship is similar to that observed in the jinchuan deposit nw china therefore we suggested that the same mechanism post segregation diffusion of os yang et al 2008 is applicable to the kalatongke deposit re os isotopic studies of kalatongke jinchuan and representative magmatic cu ni sulfide deposits suggest that the massive ores of mafic ultramafic rock associated cu ni sulfide deposits would yield geologically meaningful re os age whereas a pseudo isochron would be obtained for the disseminated ores therefore to obtain a geologically meaningful re os age the type of the deposit the type of the ore and the ore forming process should be taken into account

pathological martian craters evidence for a transient obliteration event we have detected three unusual low relief circular features 1 2 to 2 1 km in diameter in the northwest noachis highlands which may be craters that have undergone isostatic deformation they may shed light on the existence nature and timing of suspected widespread martian erosion obliteration events and offer clues to a type of martian terrain softening in the surrounding area we find an anomalous deficiency of craters in the 3 11 km diameter range and evidence that larger older craters have undergone relief softening and infill we discuss three different hypotheses to explain these features two of which involve martian ice this region may have undergone a transient event in which a near surface permafrost layer several hundred meters deep underwent partial melting or softening this would allow relaxation of kilometer scale craters and softening of larger craters crater data presented here suggest that this event happened some time in mid martian history whether the event was regional or related to global scale events is uncertain though it may represent a class of events that also happened in other martian areas

south polar layered deposits of mars the cratering record data from the mars orbiter laser altimeter mola and mars orbiter camera moc instruments aboard the mars global surveyor mgs were used in a detailed search of a selected part of the south polar layered deposits spld for impact craters impact craters with diameters from 0 8 to 5 km were identified from a mola derived shaded relief map and were primarily validated using individual mola tracks and in select cases moc narrow angle images the resultant crater population determined in this study is at least four times the density of the crater population previously recognized from these new statistics we estimate the mean apparent surface age of the spld to be 30 100 ma depending on the established production model isochrons used all of these craters are considerably shallower than other martian craters in the same diameter range we attribute this shallowness to be the cause of the lower detection rates of previous studies there is a correlation between crater depth and rim height which suggests that both erosion and infilling have affected the crater forms a similar study of the north polar layered deposits uncovered no craters in this diameter range a limited population of craters smaller than 800 m was uncovered in higher resolution moc narrow angle images these do not appear to have been degraded to the same degree this separate population implies a surface exposure age of only 100 000 years and perhaps indicates an event that erased all small craters and degraded and infilled the larger ones

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

controls on the metal compositions of magmatic sulfide deposits in the emeishan large igneous province sw china abstract magmatic sulfide deposits in the emeishan large igneous province sw china have variable chalcophile and siderophile metal contents and can be divided into pge ni cu pge and ni cu deposits pge sulfide deposits include the jinbaoshan and zhubu deposits and have ores with very low sulfide contents 1 to 2 vol and very high pt and pd 0 3 to 10 ppm and ir 0 02 to 0 5 ppm typical ni cu pge sulfide deposits include the yangliuping and qingkuangshan deposits which contain sulfide ores with more than 10 vol sulfides 0 1 6 2 wt ni 0 03 11 wt cu and have moderate pge contents 0 1 5 ppm pt 0 01 1 8 ppm pd on the 100 sulfide basis pt and pd correlate positively with ir in the ores from the pge deposits whereas they correlate negatively in the ni cu pge and ni cu deposits pge geochemistry and model calculations indicate that the pge rich sulfides were separated from primary basaltic magmas whereas the ni cu pge sulfides were produced from magmas that had experienced minor sulfide removal about 0 01 and the ni cu sulfides were separated from magmas that experienced about 0 025 sulfide segregation fractionation of monosulfide solid solution resulted in differentiation between ipge and ppge in the ni cu pge and ni cu deposits

single grain pyrite rb sr dating of the linglong gold deposit eastern china abstract this study employs the single grain pyrite rb sr technique to date mineralization using the example of the linglong lode gold deposit jiaodong peninsula eastern china the gold deposits in this area are interpreted to have a consistent spatial temporal relationship with widespread late jurassic early cretaceous magmatism in eastern china likely related to lithospheric thinning around 120 ma pyrite of the linglong gold mine contains different types of mineral inclusions such as sericite and feldspar that cause distinguishable variations in rb and sr contents and rb sr ratios four pyrite samples from veins of different mineralization stages give an average isochron age of 120 6 0 9 ma analyses of one quartz and two sericite samples yield isochron ages between 122 ma and 120 ma dating of mineralization is often hampered by disequilibrium of isotopic systems and or the lack of suitable minerals for dating purposes hence the successful attempt of the single grain rb sr technique of pyrite which occurs as a common mineral phase in orebodies and is genetically related to the mineralization has great potential for precise geochronology of hydrothermal mineral deposits

paleogene magmatism and gold metallogeny of the jinping terrane in the ailaoshan ore belt sanjiang tethyan orogen sw china geology deposit type and tectonic setting abstract the jinping terrane is situated in the southern segment of the ailaoshan ore belt sanjiang tethyan orogen sw china the paleogene intrusions in jinping consist of syenite porphyry fine grained syenite and biotite granite stocks dikes and contain relatively low tio 2 0 21 0 38 wt p 2 o 5 0 01 0 35 wt and high na 2 o 2 00 4 62 wt and k 2 o 4 48 7 06 wt belonging to high k alkaline series paleogene gold mineralization in jinping comprises four genetic types i e orogenic alkali rich intrusion related porphyry and supergene laterite the nw nnw trending faults and their subsidiaries are the major ore controlling structures the orogenic au mineralization dominated by polymetallic sulfide quartz veins occurs in the diorite and minor in silurian devonian sedimentary rocks it contains a co 2 rich mesothermal fluid system generated from the mixing of mantle derived fluids with crustal derived metamorphic fluids and the ore forming materials were upper crustal or orogenic derived the alkali rich intrusion related au mineralization is hosted in the ordovician silurian sedimentary rocks and minor in the paleogene alkaline intrusions and the au orebodies occur predominantly in the alteration halos it contains a co 2 bearing largely metamorphic sourced mesothermal fluid system and the ore forming materials were derived from the ore hosting rocks and minor from the alkali rich intrusions the porphyry cu mo au mineralization occurs in the granite syenite porphyries and or along their contact skarn with the mineralizing fluids being magmatic hydrothermal in origin the former two hypogene au mineralization types in jinping were mainly formed in the late eocene ca 34 33 ma and slightly after the porphyry cu mo au mineralization ca 35 34 ma which is coeval with the regional himalayan orogenic event subsequent weathering produced the laterite au mineralization above or near the hypogene au orebodies

triassic collision in the paleo tethys ocean constrained by volcanic activity in sw china abstract a suite of collision related triassic volcanic rocks cropping out within the jinshajiang ailaoshan orogenic belt in sw china offers insights into closure of the paleo tethys and associated terrane continent collision combined geochemical and sr nd isotopic data for samples from the jinshajiang segment demonstrate that the lower part of the volcanic suite is dominated by high si rhyolites the pantiange formation derived through crustal anatexis whereas the upper units the cuiyibi formation are characterized by basalts alternating with intermediate felsic lavas that share similar sr nd isotopic signatures and may have originated from partial melting of subduction enriched lithospheric mantle shrimp u pb analyses on zircons yield ages of 247 246 ma for the rhyolites of the pantiange formation and ages ranging from ca 245 ma to 237 ma for the basaltic and intermediate felsic samples from the overlying cuiyibi formation these data integrated with other geologic evidence e g stratigraphic record suggest an early middle triassic timing of terrane continent collision along the jinshajiang and ailaoshan sutures with the 247 246 ma pantiange high si rhyolites representing the early magmatic products generated by this event the development of the 245 237 ma bimodal volcanism was associated with subsidence and deep marine sedimentation we interpret this as reflective of an extensional setting within an evolving collisional orogen probably related to oblique convergence along the collisional zone triassic volcanic rocks with similar geochemical signatures and ages have been identified along the 1000 km length of the jinshajiang ailaoshan suture zone the indochina block to the south of the suture records 250 240 ma tectonothermal activity taken together these relationships suggest that initial collision and amalgamation of the qamdo simao terrane indochina with the yangtze block south china along the jinshajiang ailaoshan and song ma sutures probably took place in the early triassic following consumption of the paleo tethys ocean

element migration of pyrites during ductile deformation of the yuleken porphyry cu deposit nw china abstract the strongly deformed yuleken porphyry cu deposit ypcd occurs in the kalaxiangar porphyry cu belt kpcb which occupies the central area of the central asian orogenic belt caob between the sawu er island arc and the altay terrane in northern xinjiang the ypcd is one of several typical subduction related deposits in the kpcb which has undergone syn collisional and post collisional metallogenic overprinting the ypcd is characterized by three pyrite forming stages namely a hydrothermal stage a py i a syn ductile deformation stage b py ii characterized by cu au enrichment and a fracture filling stage c py iii in this study we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite which formed during different stages in order to constrain the physicochemical conditions of the ore formation euhedral fragmented py i has low pb and high te and se concentration and ni contents are low with co ni ratios mostly between 1 and 10 average 9 00 py i is further characterized by enrichments of bi as ni cu te and se in the core relative to the rim domains anhedral round py ii has moderate co and ni contents with high co ni ratios 10 average 95 2 and average contents of 46 5 ppm pb and 5 80 ppm te py ii is further characterized by decreasing bi cu pb zn ag te mo sb and au contents from the rim to the core domains annealed py iii has the lowest co content of all pyrite types with co ni ratios mostly

north south geological differences between the residual polar caps on mars polar processes can be sensitive indicators of global climate and the geological features associated with polar ice caps can therefore indicate evolution of climate with time the polar regions on mars have distinctive morphologic and climatologic features thick layered deposits seasonal co 2 frost caps extending to mid latitudes and near polar residual frost deposits that survive the summer the relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained mainly by the limited spatial resolution of the available data in particular it has not been known if the residual caps represent simple thin frost cover or substantial geologic features here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography this is very different from the residual cap on the north pole which grades into the underlying layered materials these findings indicate that the differences between the caps are substantial rather than reflecting short lived differences in frost cover and so support the idea of long term asymmetry in the polar climates of mars

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

rb sr geochronology of chalcopyrite from the chehugou porphyry mo cu deposit northeast china and geochemical constraints on the origin of hosting granites the chehugou porphyry mo cu deposit is located ca 300 km north of beijing in the boundary zone between the archean north china craton and the neoproterozoic mesozoic central asian orogenic belt using hydrothermal chalcopyrite from this deposit we are able to show for the first time that the rb sr isotope system in massive nonfractured chalcopyrite grains can provide reliable age constraints for mo cu deposits we analyzed two chalcopyrite samples from slightly different petrogenetic environments showing contrasting texture and deformation history five 2 to 5 mg fragments of a single nonfractured chalcopyrite grain containing spatially isolated inclusions of k mica k feldspar and quartz yielded an rb sr isochron age of 256 7 ma 2 including uncertainty for this sample the dense chalcopyrite matrix apparently inhibited diffusion of rb and sr after chalcopyrite crystallization and the age should therefore reflect the time of crystallization of chalcopyrite from the mo cu mineralizing fluids the evidence for mo cu mineralization during the late permian requires a revision of the previous notion that the chehugou deposit was formed during the yanshanian orogeny lasting from 200 to 60 ma fragments of a second chalcopyrite sample that in contrast to the first had experienced deformation as indicated by intragranular fractures and alignment of k mica and k feldspar inclusions along these fractures this sample yielded a clearly younger rb sr isochron age of 207 15 ma 2 this age obviously reflects an isotopically open system due to fluid movement and or prolonged diffusion of rb and sr along the fractures single biotite crystals from an associated monzogranite yielded an rb sr isochron age of 250 ma which is interpreted as a lower age limit for the mo cu mineralization and the time when the granite cooled below 400 to 300 c considering the field evidence for a broadly contemporaneous origin of the mo cu mineralization and the hosting granitoids we suggest that the granitoids are not much older than ca 260 ma the mo cu hosting granitoids range in composition from monzogranite to highly evolved syenogranite with high la yb and sr y ratios initial end values of ca 21 to 23 nd crustal residence times of the sources 1 9 to 2 7 ga indicate melting of the predominantly archean north china craton and a subordinate juvenile mantlederived component much older u depleted lower crustal sources for the granitoids are supported by high initial 208pb 204pb ratios lithospheric delamination and underplating of hot mantle derived material may have facilitated crustal melting in a late orogenic to postcollision

re os isochron ages for arsenopyrite from carlin like gold deposits in the yunnan guizhou guangxi golden triangle southwestern china abstract the yunnan guizhou guangxi golden triangle is considered to be one of the regions hosting carlin like gold deposits in china gold deposits in this region can be grouped into lode type that are controlled by faults and layer like type controlled by stratigraphy arsenopyrite is one of the major gold bearing minerals in these deposits rhenium os isotopic dating of arsenopyrite from the lode type lannigou and jinya and the layer like type shuiyindong gold deposits yields isochron ages of 204 19 ma 206 22 ma and 235 33 ma respectively the data suggest that the carlin like gold deposits formed in late triassic to early jurassic which is clearly earlier than the ca 100 80 ma acid to ultra basic magmatism in this part of southwestern china the ages are consistent with ore formation during a period of post collisional lateral transpression which is similar to that of the carlin like gold deposits in western qinling of china but quite different from carlin type gold deposits in nevada u s a

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

physical modelling of gelifluction and frost creep some results of a large scale laboratory experiment an experimental slope was constructed in a 5 m 5 m square refrigerated tank the slope was formed of four sections each consisting of regolith soil collected from a distinct bedrock lithology the four lithologies utilized were granite limestone mudstone and slate the slope was subjected to freezing and thawing from the surface downwards water was supplied at the base of the soil during freezing frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle the experimental soils were non cohesive those derived from granite and limestone were respectively sandy and gravelly in texture while those derived from mudstone and slate were silt rich mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice in the mudstone and slate soils gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice mean per cycle rates of downslope soil transport for the granite limestone mudstone and slate soils were 5 8 cm3 cm 1 6 9 cm3 cm 1 21 2 cm3 cm 1 and 31 2 cm3 cm 1 respectively units referring to the volume of soil passing a unit width of slope per cycle mass movement rates were shown to be strongly related to the silt content of the soils