geochemistry and nd isotope systematics of archaean granites of the eastern goldfields yilgarn craton australia implications for crustal growth processes abstract the archaean granites and granitic gneisses of the eastern goldfields in the yilgarn craton western australia can be divided into two major groups high ca and low ca and three minor groups high hfse high field strength elements mafic and syenitic the high ca group 68 77 sio 2 with high al 2 o 3 na 2 o and sr and low y shares many features with typical archaean tonalite trondhjemite suites but has higher k 2 o rb and th contents the low ca group 70 76 sio 2 differs from the high ca group in having lower al 2 o 3 cao and na 2 o but higher k 2 o rb th zr y la and ce contents granites of the high hfse mafic and syenitic groups form a minor component 10 20 of the eastern goldfields granites the siliceous 74 77 sio 2 high hfse granites are restricted to a narrow nnw trending zone and are characterised by high tio 2 total feo mgo y zr and ce but only moderate rb th and pb contents the a type syenites 50 68 sio 2 are distinguished by their high total alkalies and mainly occur along tectonic lineaments the mafic group 55 70 sio 2 is lithologically diverse and exhibits a wide range of k 2 o rb th la and ce contents granite emplacement occurred between 2 69 and 2 60 ga contemporaneous with or post dating greenstone formation nd values for the high ca mafic and syenitic groups are similar mostly 0 0 to 2 5 whereas those for the low ca group show a pronounced polarity from 4 5 in the west to 2 0 in the east nd depleted mantle model ages for the low ca granites range from 3 2 ga in the west to 2 75 ga in the east model ages for the high ca group 2 75 2 9 ga overlap with ages for inherited zircons from these granites the high ca granites appear to have been derived at high pressures by partial melting of a mafic to intermediate source subducted oceanic crust crustal underplate or thickened crust or remelting of an older tonalitic source derived by such a process if the high ca granites were largely crust derived then their extensive source rocks must have formed less than 250 ma prior to granite formation the low ca granites appear to be the products of crustal reworking probably from a tonalitic to granodioritic protolith that was progressively younger towards the east perhaps in the order of several hundred million years younger or involved an additional younger component the localisation of the crustally derived high hfse granites suggests either geochemical zonation of the crust or specific tectonic processes such as rifting the mafic granites and possibly the syenites imply a significant mantle contribution and new crustal growth although the extent is equivocal the crust of the eastern goldfields appears to have been generated by both lateral and vertical accretion over a significant period from or before 3 0 ga until the time of granite emplacement

reconstructing the pre quaternary landscape in agnew lawlers area western australia with emphasis on the permo carboniferous glaciation and post glacial weathering the pre quaternary stratigraphic section in agnew lawlers area consists of permo carboniferous glacial sediments unconformably overlain by tertiary clastics of palaeochannel sequence and quaternary alluvial and colluvial sediments the unique permo carboniferous glacial sedimentary succession in the yilgarn craton has not been studied in detail in terms of vertical chemostratigraphic variations basin and landscape evolution diagenesis and post permian weathering overprints in agnew lawlers district continental facies of glacial diamictites glaciofluvial sandstones and glaciolacustrine rhythmites vary in thickness from 28 m to 181 m and is preserved beneath cenozoic sediments as relict landforms in highly irregular asymmetrical and poorly drained basins the permo carboniferous sediments were mechanically weathered and eroded by glaciers from the surrounding archaean basement palaeohighs under a cold arid climate textural relationships of diamictites indicate that they were derived from proximal and distal source rocks the denuded palaeotopography of the basement palaeohighs source rocks and permo carboniferous sediments were subjected simultaneously to an intensive post permian chemical weathering the exposed basement rocks were deeply weathered into residual saprolite whereas the permo carboniferous sediments were differentiated into three chemostratigraphic units the diamictite and rhythmite of the lower unit are unweathered and preserves the signature of the glacial interglacial weathering mineralogical and geochemical changes dominated in this unit are related mainly to diagenesis at shallow depth eogenesis with no significant compaction the formation of a paragenetic diagenetic sequence of chlorite ferroan dolomite and pyrite indicates diagenesis has occurred under reducing and alkaline conditions below the permafrost and modern water table mineralogical and geochemical changes dominated in the middle unit are linked mainly to eogenetic redox reactions the formation of smectite and ferruginous cements in this unit is attributed to weathering of ferromagnesian and opaque heavy minerals under oxic and slightly alkaline conditions mineralogical and geochemical changes dominated in the upper unit is related mainly to post permian chemical weathering where almost all rock forming minerals are altered to kaolinite and alkali and alkaline earth elements are leached forming bleached white saprolitic diamictites a change in clay minerals from kaolinite in the weathered permo carboniferous succession to smectite in the overlying cenozoic succession demarcates the unconformity and probably reflects a change to an arid climatic condition chemically the cenozoic succession shows a sharp increase in ti al and la ce ratios and a decrease in ce anomaly that remain constant in the permo carboniferous section these mineralogical and chemical variations through the phanerozoic stratigraphic section can be used to follow the landscape and climatic evolution since the late palaeozoic glaciation

ancient impactor components preserved and reworked in martian regolith breccia northwest africa 7034 abstract northwest africa nwa 7034 and paired stones represent unique samples of martian polymict regolith breccia multiple breccia subsamples characterized in this work confirm highly siderophile element hse re os ir ru pt pd contents that are consistently elevated e g os 9 3 18 4 ppb above indigenous martian igneous rocks mostly 187 os 188 os ratios of 0 119 0 136 record a wider variation than observed for all major chondrite types combined with the measured 187 re 188 os ratios of 0 154 0 994 the range in os isotope ratios indicates redistribution of re and os from originally chondritic components early in the history of the regolith commencing at 4 4 ga superimposed recent re mobility reflects exposure and weathering at or near the martian and terrestrial surfaces elevated os concentrations 38 0 and 92 6 ppb os superchondritic os hse ratios and 187 os 188 os of 0 1171 and 0 1197 measured for two subsamples of the breccia suggest the redistribution of impactor material at 1 5 1 9 ga possibly overlapping with a partial resetting event at 1 4 ga recorded by u pb isotope systematics in the breccia martian alteration of the originally chondritic hse host phases to form os ir rich nuggets and ni rich pyrite implies the influence of potentially impact driven hydrothermal systems multiple generations of impactor component admixture redistribution and alteration mark the formation and evolution of the martian regolith clasts and matrix of nwa 7034 and paired meteorites from the pre noachian until impact ejection to earth

triggering of liquefaction flow slides in coastal soil deposits abstract liquefaction flow slides have been observed in coastal soil deposits throughout the world the causes of many of these slides have never been well understood the materials involved in and circumstances surrounding eight reported liquefaction flow slides are reviewed and compared many of these slides have occurred in very similar materials shortly following small to moderate drawdowns of the adjacent water level liquefaction susceptibility of sands may be evaluated by steady state methods recent research indicates that liquefaction of loose sands similar to those typically involved in these slides may be triggered by very small changes in stress conditions if the sand is initially in equilibrium under high shear stresses the triggering of liquefaction may lead to flow sliding if the unbalanced driving stresses exceed the steady state strength of the liquefied soil elasticity methods are used to estimate the initial stress conditions in a gentle infinite slope and the effect of unloading due to drawdown it is shown that liquefaction flow slides in coastal soil deposits may be initiated by small to moderate drawdowns consistent with those observed in actual slides

the noble gas concentrations of the martian meteorites grv 99027 and paired nwa 7906 nwa 7907 here we present the isotopic concentrations of he ne ar kr and xe for the three martian meteorites namely grove mountains 99027 grv 99027 northwest africa 7906 nwa 7906 and northwest africa 7907 nwa 7907 the cosmic ray exposure cre age for grv 99027 of 5 7 0 4 ma 1 is consistent with cre ages for other poikilitic basaltic shergottites and suggests that all were ejected in a single event 5 6 ma ago after correcting for an estimated variable sodium concentration the cre ages for nwa 7906 and nwa 7907 of 5 4 0 4 and 4 9 0 4 ma 1 respectively are in good agreement with the cre age of 5 ma favored by cartwright et al 2014 for nwa 7034 the data therefore support the conclusion that all three basaltic regolith breccias are paired the 40ar gas retention age for nwa 7907 of 1 3 ga is in accord with cartwright et al 2014 for nwa 7906 we were unable to determine a 40ar gas retention age the 4he gas retention ages for nwa 7906 and 7907 are in the range of 200 ma and are much shorter than the 40ar gas retention age of nwa 7907 indicating that about 86 88 of the radiogenic 4he has been lost the kr and xe isotopic concentrations in grv 99027 are composed almost exclusively of martian interior mi gases while for nwa 7906 and nwa 7907 they indicate gases from the mi elementally fractionated air and possibly martian atmosphere

the nature age and petrogenesis of the cartier batholith northern flank of the sudbury structure ontario canada abstract the cartier batholith exposed about 50 km northwest of sudbury ontario canada is a late archean k rich granitic batholith along with the levack gneiss complex it forms the footwall of the north range of the sudbury igneous complex the cartier batholith dominantly monzogranitic to granodioritic is relatively homogeneous unfoliated and contains k feldspar megacrysts it shows several distinctive chemical features including high concentrations of zr th u and lree and low concentrations of nb ti and hree several discriminants suggest a post orogenic tectonic environment for the batholith this inference is consistent with a u pb age of 2642 1 ma obtained on zircon only slightly younger than the inferred timing of high grade metamorphism of the levack gneiss complex the cartier batholith could have formed as a result of approximately 33 partial melting of the levack gneiss complex

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

structural setting and geochemistry of archaean i type granites in the bardoc coolgardie area of the norseman wiluna belt western australia abstract regional structures in the bardoc coolgardie area of the archaean norseman wiluna greenstone belt in western australia developed during early large scale thrusting followed by a transpressional regime characterized by enewsw shortening and large scale sinistral strike slip faults structural relationships between granites and greenstone successions indicate emplacement of granitic rocks throughout this deformation history emplacement mechanisms include solid or liquid state diapirism forceful dilation of country rocks and passive stoping i type granites are common and include early and late tectonic intrusions the widespread occurrence of i type granodiorite and monzogranite probably derived by partial melting of lower continental crust or subducted oceanic crust suggests a continental margin setting for the belt alkalic quartz diorite occurs as rounded enclaves in granodiorite and is enriched in ba rb sr ce la p and f which suggests a mantle derived volatile component these quartz diorite melts may have formed by partial melting of metasomatized mantle or alternatively mantle degassing may have lowered solidus temperatures in the source region and thus induced melting emplacement of hot volatilerich quartz diorite melts into the lower crust may have lowered solidus temperatures in the source rocks for granodiorite and monzogranite recent models for archaean gold mineralization suggest that auriferous fluids contained co 2 derived from lower crustal or mantle sources in the bardoc coolgardie area co 2 may have been flushed out during partial melting of the lower continental crust however the origin of the gold in the mineralizing fluids requires some other explanation because gold mineralization is generally a late stage event and took place over a considerably shorter time interval than the formation and emplacement of i type granites

decline of giant impacts on mars by 4 48 billion years ago and an early opportunity for habitability the timing of the wane in heavy meteorite bombardment of the inner planets is debated its timing determines the onset of crustal conditions consistently below the thermal and shock pressure limits for microbiota survival and so bounds the occurrence of conditions that allow planets to be habitable here we determine this timing for mars by examining the metamorphic histories of the oldest known martian minerals 4 476 4 429 gyr old zircon and baddeleyite grains in meteorites derived from the southern highlands we use electron microscopy and atom probe tomography to show that none of these grains were exposed to the life limiting shock pressure of 78 gpa 97 of the grains exhibit weak to no shock metamorphic features and no thermal overprints from shock induced melting by contrast about 80 of the studied grains from bombarded crust on earth and the moon show such features the giant impact proposed to have created mars hemispheric dichotomy must therefore have taken place more than 4 48 gyr ago with no later cataclysmic bombardments considering thermal habitability models we conclude that portions of mars crust reached habitable pressures and temperatures by 4 2 gyr ago the onset of the martian wet period about 0 5 gyr earlier than the earliest known record of life on earth early abiogenesis by 4 2 gyr ago is now tenable for both planets the oldest known minerals from mars have no strong shock features indicating early cessation of giant impacts there according to microanalysis of zircon and baddeleyite grains in meteorites

crustal evolution of archaean granitoids in the murchison province western australia abstract four suites of granitoids intruded the supracrustal greenstone sequence in the murchison province of the archaean yilgarn craton during a 300 million year period the earliest granitoid suite intruded the base of the developing greenstone sequence as a series of thin subhorizontal tabular plutons of monzogranite and granodiorite at 2 9ga this suite has been deformed and metamorphosed and is now a pegmatite banded gneiss at about 2 7 ga thick subhorizontal tabular plutons of monzogranite intruded the base of the greenstone sequence this suite which now forms much of the regions between greenstone belts was folded and recrystallized during regional deformation and metamorphism two distinct but contemporaneous suites of post folding granitoids intruded the greenstone belts at 2 6 ga largely post dating regional metamorphism one suite of post folding granitoids comprises tonalite trondhjemite granodiorite and monzogranite plutons confined mainly to the north of the province the other suite comprises quartz rich monzogranite and syenogranite plutons confined mainly to the south of the province pegmatite banded gneiss recrystallized monzogranite and the northern suite of post folding granitoids were all derived by partial melting of mafic crustal rocks most post folding granitoids from the southern suite were derived by partial melting of siliceous crustal material at least as old as basal greenstones the modes and sites of intrusion of all granitoid plutons were controlled by active tectonic processes or by structural features of the crust widespread 2 6 ga rb sr ages of pegmatite banded gneiss and recrystallized monzogranite reflect post metamorphic cooling which was contemporaneous with intrusion of post folding granitoids

mechanics of dual mode dilative failure in subaqueous sediment deposits abstract we introduce dual mode dilative failure with flume experiments dual mode dilative failure combines slow and steady release of sediments by breaching with periodic sliding which rapidly releases an internally coherent wedge of sediments it occurs in dilative sandy deposits this periodic slope failure results from cyclic evolution of the excess pore pressure in the deposit sliding generates large transient negative excess pore pressure that strengthens the deposit and allows breaching to occur during breaching negative excess pore pressure dissipates the deposit weakens and ultimately sliding occurs once again we show that the sliding frequency is proportional to the coefficient of consolidation we find that thicker deposits are more susceptible to dual mode dilative failure discovery of dual mode dilative failure provides a new mechanism to consider when interpreting the sedimentary deposits linked to submarine slope failures

neutron capture 36cl 41ca 36ar and 150sm in large chondrites evidence for high fluences of thermalized neutrons we have measured significant concentrations of 36cl 41ca 36ar from decay of 36cl and 150sm produced from the capture of thermalized neutrons in the large chico l6 chondrite activities of 36cl and 41ca corrected for a high energy spallogenic component and a terrestrial age of 50 ka give average neutron capture production rates of 208 atoms min g cl and 1525 atoms min kg ca which correspond to thermal neutron n fluxes of 6 2 n cm2 s and 4 3 n cm2 s respectively if sustained for the 65 ma single stage cosmic ray exposure age of chico these values correspond to thermal neutron fluences of 1 3 1016 and 0 8 1016 n cm2 for 36cl and 41ca respectively stepwise temperature extraction of ar in chico impact melt shows 36ar 38ar ratios as large as 9 the correlation of high 36ar 38ar with high cl ca phases in neutron irradiated chico indicates that the excess 36ar above that expected from spallation is due to decay of neutron produced 36cl excess 36ar in chico requires a thermal neutron fluence of 0 9 1 7 1016 n cm2 decreases in 149sm 152sm due to neutron capture by 149sm correlate with increases in 150sm 152sm for three samples of chico and one of the torino h chondrite the 0 08 decrease in 149sm 152sm shown by chico corresponds to a neutron fluence of 1 23 1016 n cm2 this fluence derived from sm considers capture of epithermal neutrons and effects of chemical composition on the neutron energy distribution excess 36ar identified in the arapahoe bruderheim and torino chondrites and the shallowater aubrite suggest exposure to neutron fluences of 0 2 0 6 1016 n cm2 depletion of 149sm in torino and the lew86010 angrite suggest neutron fluences of 0 8 1016 n cm2 and 0 25 1016 n cm2 respectively neutron fluences of 1016 n cm2 in chico are almost as large as those previously observed for some lunar soils consideration of exposure ages suggests that the neutron flux in chico may have been greater than that in many lunar soils neutron capture effects although seldom reported may be common for large meteorites and could affect calculation of exposure ages based on cosmogenic ar combining measurements of radioactive and stable species produced from neutron capture has the potential for identifying large meteorites with complex exposure histories

mineralogical constraints on the thermal history of martian regolith breccia northwest africa 8114 abstract martian meteorite northwest africa nwa 8114 a paired stone to nwa 7034 provides an opportunity to examine the thermal history of a martian regolith and study near surface processes and ancient environmental conditions near an impact crater on mars our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains some of the pyroxene clasts show exsolution lamellae indicating a high temperature magmatic origin and slow cooling however transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re crystallised to form magnetite and a k bearing feldspathic glassy material together with relict pyroxene this breakdown event was associated with oxidation with up to 25 fe3 fe in the relict pyroxene measured using fe k xanes by comparison with previous studies this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating being held at a temperature above 700 c for at least 7 days in an oxidising regolith environment we report an approximate 40ar 39ar maximum age of 1 13 1 25 ga for an individual separated augite clast the disturbed nature of the spectra precludes precise age determination in section this clast is porous and contains iron oxide grains this shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts and has up to 25 fe3 fe we infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes after consolidation of the impact ejecta blanket high temperatures above 700 c may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut and in some cases surround the oxidised pyroxene however the veins could alternatively be the result of a hydrothermal event in the impact regolith a simple fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days low temperature hydrous alteration took place forming goethite identified via xrd xanes and ftir comparing with previous studies the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite

rb sr and sm nd isotopic and ree studies of igneous components in the bulk matrix domain of martian breccia northwest africa 7034 the bulk matrix domain of the martian breccia nwa 7034 was examined petrographically and isotopically to better understand the provenance and age of the source material that make up the breccia both 147sm 143nd and 146sm 142nd age results for mineral separates from the bulk matrix portion of breccia nwa 7034 suggest that various lithological components in the breccia probably formed contemporaneously 4 44 ga ago this old age is in excellent agreement with the upper intersection ages 4 35 4 45 ga for u pb discordia and also concordia defined by zircon and baddeleyite grains in matrix and igneous textured clasts consequently we confirm an ancient age for the igneous components that make up the nwa 7034 breccia substantial disturbance in the rb sr system was detected and no age significance could be gleaned from our rb sr data the disturbance to the rb sr system may be due to a thermal event recorded by bulk rock k ar ages of 1 56 ga and u pb ages of phosphates at about 1 35 1 5 ga which suggest partial resetting from an unknown thermal event s possibly accompanying breccia formation the nwa 7034 bulk rock is lree enriched and similar to kreep rich lunar rocks which indicates that the earliest martian crust was geochemically enriched this enrichment supports the idea that the crust is one of the enriched geochemical reservoirs on mars that have been detected in studies of other martian meteorites

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

hyperconcentrated sand water mixture flows over erodible bed field surveys and experiments in a tilting flume on hyperconcentrated sand water mixture swm flows were conducted at slopes slightly smaller than the equilibrium slope a rapid development of sand bars propagating upstream was observed these bars consist of an almost horizontal terrace with subcritical flow a steep lee side slope with supercritical flow and a hydraulic jump between subsequent bars the erosion processes on the bar are limited by the high sand concentrations and flow velocities on the steep slopes as a result the erosion rate is more moderate than predicted by the pickup functions used in classical sediment transport theory a simple one dimensional model is presented to study the behavior of triangular schematized bars from an analysis of the equations it is concluded that an increase in erosion rate requires an increase in bed slope to maintain equilibrium flow conditions finally simulations with the model are compared with observations in the field and in the tilting flume t

constraints on the depth and thermal vigor of melting in the martian mantle studies of rocks in gale crater and clasts within the martian meteorite breccia northwest africa nwa 7034 and paired stones have expanded our knowledge of the diversity of igneous rocks that make up the martian crust beyond those compositions exhibited in the meteorite collection or analyzed at any other landing site therefore the magmas that gave rise to these rocks may have been generated at significantly different conditions in the martian mantle than those derived from previously studied rocks here we build upon our previous models of basalt formation based on rocks analyzed in gusev crater and meridiani planum to the new models of basalt formation for compositions from gale crater and a clast in meteorite nwa 7034 estimates for the mantle potential temperature tp based on noachian age rock analyses in gale crater gusev crater and bounce rock in meridiani planum and a vitrophyre clast in nwa 7034 are within error which suggests that the calculated average tp of 1450 70 c may represent an average global mantle temperature during the noachian the tp estimates for the hesperian and amazonian based on orbital analyses of the chemistry of the crust are lower in temperature than our estimates for the noachian which is consistent with simple convective cooling of the interior of mars however the tp estimates from the young meteorites are significantly higher than the estimates based on surface chemistry and are consistent with localized hot spot melting and not heating up of the interior

the northwest africa 8159 martian meteorite expanding the martian sample suite to the early amazonian abstract northwest africa nwa 8159 is an augite rich shergottite with a mineralogy dominated by ca fe rich pyroxene plagioclase olivine and magnetite nwa 8159 crystallized from an evolved melt of basaltic composition under relatively rapid conditions of cooling likely in a surface lava flow or shallow sill redox conditions experienced by the melt shifted from relatively oxidizing with respect to known martian lithologies qfm on the liquidus to higher oxygen fugacity qfm 2 during crystallization of the groundmass and under subsolidus conditions this shift resulted in the production of orthopyroxene and magnetite replacing olivine phenocryst rims nwa 8159 contains both crystalline and shock amorphized plagioclase an50 62 often observed within a single grain based on known calibrations we bracket the peak shock pressure experienced by nwa 8159 to between 15 and 23 gpa the bulk composition of nwa 8159 is depleted in lree as observed for tissint and other depleted shergottites however nwa 8159 is distinct from all other martian lithologies in its bulk composition and oxygen fugacity we obtain a sm nd formation age of 2 37 0 25 ga for nwa 8159 which represents an interval in mars geologic time which until recently was not represented in the other martian meteorite types the bulk rock 147sm 144nd value of 0 37 0 02 is consistent with it being derived directly from its source and the high initial e143nd value indicates this source was geochemically highly depleted cr nd and w isotopic compositions further support a unique mantle source while the rock shares similarities with the 2 4 ga nwa 7635 meteorite there are notable distinctions between the two meteorites that suggest differences in mantle source compositions and conditions of crystallization nevertheless the two samples may be launch paired nwa 8159 expands the known basalt types ages and mantle sources within the mars sample suite to include a second igneous unit from the early amazonian

the geochemistry and crustal origin of the archaean acid intrusive rocks of the agnew dome lawlers western australia abstract acid intrusive rocks of the agnew dome intrude a supracrustal sequence part of the lawlers mt white greenstone belt the acid intrusives form a complex batholith with multiple intrusions three distinct groups of granitoids have been recognised both in terms of style of intrusion and on petrological grounds the oldest intrusion was that of the lawlers tonalite granitoid group i which includes a variety of rock types from quartz diorite through tonalite to granodiorite these are characterised by high na k high concentrations of lree ba and sr very high la yb low hree and low y intrusion of the lawlers tonalite pre dates the first deformation of the intruded greenstones a second granitoid suite group ii occupies the dominant area of the batholith and comprises a diverse group ranging from granodiorite through adamellite to trondhjemite these have lower na k and la yb ratios and a higher sio2 content than the tonalites their intrusion pre dates the main folding of the greenstones d2 the third granitoid group group iii comprises highly leucocratitic true granites of near minimum melt composition k and rb rich but with very low concentrations of p zr ti sr and ba they have flat ree patterns with eu anomalies these are clearly the latest intrusive phase and form a network of intersecting dykes sheets and small plugs on geochemical grounds the three granitoid suites of lawlers are not related the tonalites are likely to have been derived from the fusion of mafic source rocks while some features of the leucogranites suggest source material must include a k rich granite component these features suggest that at least in this part of the yilgarn block the crust which pre dates both the 2 65 ga lawlers tonalite and the mt white lawlers greenstone belt must have been of mixed character with mafic and sialic rocks very like the presently exposed yilgarn archaean suite

an overview of the nature distribution and inferred tectonic setting of granitoids in the late archaean norseman wiluna belt abstract the highly mineralized late archaean norseman wiluna belt yilgarn block western australia has lithostratigraphic associations and a structural style and history that has recently been interpreted in terms of a subduction related tectonic setting it is important to investigate whether the geochemistry and petrology of the granitoids in the belt are compatible with such a model the granitoid suite within the belt can be subdivided into association 1 large composite batholiths of calc alkaline affinity spatially and temporally associated with calc alkaline volcanic centres association 2 plutons ranging from quartz diorite and tonalite to monzogranite and syenogranite spatially related to dike swarms of felsic to intermediate porphyries and calc alkaline lamprophyres and association 3 peralkaline to alkaline batholiths and stocks which are spatially and temporally associated with rhyolitic volcanic centres and major lineaments the calc alkaline associations 1 and 2 have characteristics comparable with suites of variable fractionated i type granitoids in phanerozoic continental margin are settings including 1 a wide range in sio 2 2 meta to peraluminous compositions 3 a progression from granodiorite to granite with plutons becoming more k 2 o rich and hornblende poor with time 4 lile enrichment and relative depletion of ta nb and ti in contrast to most phanerozoic granitoids the norseman wiluna belt granitoids have highly fractionated ree patterns and low contents of yb and y with respect to average post archaean equivalents ree data and trace element characteristics suggest derivation from a mafic source leaving hornblende and or garnet as residual phases peralkaline granitoids of association 3 exhibit enrichments on sio 2 na 2 o k 2 o zr y nb and ta with respect to the calc alkaline granitoids they post date associations 1 and 2 and are consistent with the concept that they represent a continuation of magmatism in a post orogenic environment thus the nature and distribution of the granitoids of the norseman wiluna belt are consistent with interpretations that the belt formed in a subduction related convergent margin setting

sediment pick up functions experimental research has been performed to determine the sediment pick up by a uniform flow without initial sediment load a sediment lift was designed by which the sediment particles were moved upwards at a constant rate through a circular opening in the flume bottom five types of bed material sand have been used with d d5 d0 values in the range 130 1500 m the mean flow velocities were in the range 9 5 1 0 m s the experimental results have been used to derive an empirical pick up function the results have also been used to evaluate several existing pick up functions finally the proposed empirical pick up function has been applied to predict the bed load and suspended load transport in the latter application the proposed function has been used as a bed boundary condition in a mathematical model for suspended sediment transport

contrasting types of late archean plutonic rocks in northwestern ontario implications for crustal evolution in the superior province abstract the late archean aulneau and lount lake batholiths have contrasting geochemical characteristics that are interpreted to be a consequence of derivation from different sources the aulneau batholith which was intruded into low grade metavolcanic rocks of the wabigoon subprovince is characterized by high na2o and low k2o rb and y together with enriched light rare earth elements lree near chondritic heavy rare earth elements hree negligible eu anomalies and mantle type initial sr and nd isotopic compositions these geochemical characteristics are consistent with derivation from the partial melting of metamorphosed tholeiitic basalt in contrast the lount lake batholith which was intruded into older 2 83 3 17 ga tonalitic plutonic rocks of the winnipeg river subprovince has relatively high k2o rb y and ree low na2o and prominent eu anomalies the initial sr and nd isotopic compositions of the lount lake batholith are consistent with a crustal source at least 200 400 ma older than the crystallization age of the batholith these geochemical characteristics indicate that the lount lake batholith originated from the partial melting of deeper level equivalents of the tonalitic metaplutonic rocks 2 83 3 17 ga which they intrude these results suggest that reworked 3 0 ga crust may be extensive in the winnipeg river subprovince and that the geochemical and isotopic signature of late archean plutonic rocks may be a useful reconnaissance tool in the identification of areas of extensive older crust the results can be interpreted within a uniformitarian model diachronous ensimatic magmatic arcs represented by the winnipeg river and western wabigoon subprovinces developed independently collision of these arcs at 2707 8 ma marks the cessation of subduction and related magmatic activity and the initiation of high grade metamorphism and melting in tectonically thickened portions of the crust

the importance of breaching as a mechanism of subaqueous slope failure in fine sand large bank failures comprising up to 10 6 m 3 of sediment are common features along steep channel banks in estuaries and large rivers that consist of clean fine sands and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall steeper than the angle of repose instead of the voluminous surging plastic sediment water flow or hyperconcentrated density flow sensu mulder alexander 2001 generated by liquefaction this type of failure known as breaching by dredging companies and hydraulic engineers produces a sustained quasi steady turbidity current to date sedimentologists have not recognized the process of breaching as such in this paper it is suggested that breaching may be the origin of many thick massive sand layers known from ancient deposits from various environments notably in some turbidite successions possible differences in the sedimentary structure of the deposits produced by breach failures vs liquefaction slope failures liquefaction flow slides can be deduced from a knowledge of the sediment transport processes initiated by the failure a field study is presented on some poorly structured beds in the eocene vlierzele sands in belgium which are supposed to have originated from liquefaction failures but are reinterpreted to be the products of breaching it is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure liquefaction flow slide failure or local erosion by river or tidal channel flow at the initial stage of the failure event

large scale experiments on breaching flow slides and the associated turbidity current breaching flow slides are accompanied by the generation of turbidity currents measurements of these currents are critical for understanding the interaction between the turbidity current and the slope surface as well as for the validation of numerical models however there are insufficient data available detailing the velocity distribution or sediment concentration in these currents this paper presents experimental results of unique large scale physical model experiments on breaching flow slides conducted at the water lab of delft university of technology the netherlands the model tests were carried out in a tank with a subaqueous sandy slope steeper than the internal friction angle for that sand we performed a series of novel experiments in which various non vertical initial slope angles were tested providing the first quantitative data for such initial conditions measurements of flow thickness velocities and sediment concentrations are obtained providing the spatial and temporal evolution of the turbidity currents and the resulting underwater slope morphology the experimental results reveal that the breaching generated turbidity currents are self accelerating and that they dominate the problem of breaching flow slides we evaluated the theoretical expression for the erosion velocity in the case of pure beaching where the turbidity current has no influence on the erosion and it overestimated the observed erosion the analysis of the failure evolution showed that the sand erosion rate increases due to the acceleration of the turbidity currents downslope until a certain threshold leading to the steepening of the breach face and thus the occurrence of surficial slides

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

the ksar ghilane 002 shergottite the 100th registered martian meteorite fragment we report on the discovery of a new shergottite from tunisia ksar ghilane kg 002 this single stone weighing 538 g is a coarse grained basaltic shergottite mainly composed of maskelynitized plagioclase approximately 52 vol and pyroxene approximately 37 vol it also contains fe rich olivine approximately 4 5 vol large ca phosphates including both merrillites and cl apatites approximately 3 4 vol minor amounts of silica or sio 2 normative k rich glass pyrrhotite ti magnetite ilmenite and accessory baddeleyite the largest crystals of pyroxene and plagioclase reach sizes of approximately 4 to 5 mm pyroxenes fs 26 96 en 5 50 wo 2 41 they typically range from cores of about fs 29 en 41 wo 30 to rims of about fs 68 en 14 wo 17 maskelynite is ab 41 49 an 39 58 or 1 7 in composition but some can be as anorthitic as an 93 olivine fa 91 96 occurs mainly within symplectitic intergrowths in paragenesis with ilmenite or at neighboring areas of symplectites kg 002 is heavily shocked s5 as indicated by mosaic extinction of pyroxenes maskelynitized plagioclase the occurrence of localized shock melt glass pockets and low radiogenic he concentration oxygen isotopes confirm that it is a normal member of the snc suite kg 002 is slightly depleted in lree and shows a positive eu anomaly providing evidence for complex magma genesis and mantle processes on mars noble gases with a composition thought to be characteristic for martian interior is a dominant component measurements of 10 be 26 al and 53 mn and comparison with monte carlo calculations of production rates indicate that kg 002 has been exposed to cosmic rays most likely as a single meteoroid body of 35 65 cm radius kg 002 strongly resembles los angeles and nwa 2800 basaltic shergottites in element composition petrography and mineral chemistry suggesting a possible launch pairing the similar cre ages of kg 002 and los angeles may suggest an ejection event at approximately 3 0 ma

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

meteorite constraints on martian atmospheric loss and paleoclimate abstract the evolution of mars atmosphere to its currently thin state incapable of supporting liquid water remains poorly understood and has important implications for martian climate history martian meteorites contain trapped atmospheric gases that can be used to constrain both the timing and effectiveness of atmospheric escape processes in this paper measurements of xenon isotopes in two ancient martian meteorites alh 84001 and nwa 7034 are reported the data indicate an early episode of atmospheric escape that mass fractionated xenon isotopes culminated within a few hundred million years of planetary formation and little change to the atmospheric xenon isotopic composition has occurred since this time in contrast on earth atmospheric xenon fractionation continued for at least two billion years pujol et al 2011 such differences in atmospheric xe fractionation between the two planets suggest that climate conditions on mars may have differed significantly from those on archean earth for example the hydrogen escape flux may not have exceeded the threshold required for xenon escape on mars after 4 2 4 3 ga which indicates that mars may have been significantly drier than earth after this time

early archaean gneisses from the yilgarn block western australia the yilgarn block is an ancient crustal block which extends over 650 000km2 in the south west of western australia and consists of high grade gneiss and granite greenstone terrains1 being one of the largest segments of archaean crust in the world it is important to studies of early crustal evolution we report here a geochronological study of banded gneisses near mount narryer in the north west of the yilgarn block which has given a rb sr whole rock isochron age of 3 348 43 myr with an initial 87sr 86sr ratio of 0 7037 0 0005 the data indicate that the rocks had a prior crustal residence time of 200 myr the validity of this early archaean age is supported by model sm nd ages of 3 510 myr and 3 630 myr for two of the samples taken together these ages represent the oldest evolutionary sequence so far identified in the yilgarn block and are comparable with old ages from other archaean cratons elsewhere in the world

dynamics of dilative slope failure breaching is a style of retrogressive subaqueous slope failure controlled by dilation and consequent pore pressure drop it has the potential to generate turbidity currents that build thick successions of turbidites we present pore pressure measurements made during breaching failure as well as a physical model that shows how the pore pressure field within the failing deposit is connected to the erosion rate associated with the failure surface we show that breaching can occur in any dilative granular material conditions for breaching could be common on the continental shelf making it an important mechanism in transferring sediment into the deep ocean a dynamic equilibrium exists between the slope failure and the pore pressure dissipation during breaching this equilibrium leads to a way to estimate the rate of sediment release from breaching using a simple material property the coefficient of consolidation contrary to previous work we find that the erosion rate is independent of the dilation of the deposit due to the coupling between erosion and pore pressure dissipation the equilibrium between the erosion and pore pressure dissipation decouples the steady state pore pressure field from the permeability of the deposit this is the first time this behavior has been recognized in sediment failures

shock implantation of martian atmospheric argon in four basaltic shergottites a laser probe 40ar 39ar investigation spatially resolved argon isotope measurements have been performed on neutron irradiated samples of two martian basalts los angeles and zagami and two martian olivine phyric basalts dar al gani dag 476 and north west africa nwa 1068 with a similar to 50 mu m diameter focused infrared laser beam it has been possible to distinguish between argon isotopic signatures from host rock matrix minerals and localized shock melt products pockets and veins the concentrations of argon in analyzed phases from all four meteorites have been quantified using the measured j values ar 40 ar 39 ratios and k2o wt in each phase melt pockets contain on average 10 times more gas 7 24 ppb ar 40 than shock veins and matrix minerals 0 3 3 ppb ar 40 the ar 40 ar 36 ratio of the martian atmosphere estimated from melt pocket argon extractions corrected for cosmogenie ar 36 is los angeles similar to 1852 zagami similar to 1744 and nwa 1068 similar to 1403 in addition los angeles shows evidence for variable mixing of two distinct trapped noble gas reservoirs 1 martian atmosphere in melt pockets and 2 a trapped component possibly martian interior ar 40 ar 16 480 490 in matrix minerals average apparent ar 40 ar 39 ages determined for matrix minerals in the four analyzed meteorites are 1290 ma los angeles 692 ma zagami 515 ma nwa 1068 and 1427 ma dag 476 these ar 40 ar 39 apparent ages are substantially older than the similar to 170 0474 ma radiometric ages given by other isotope dating techniques and reveal the presence of trapped 40ar cosmic ray exposure cre ages were measured using spallogenic ar 16 and ar 38 production los angeles 3 1 0 2 ma zagami 2 9 0 4 ma and nwa 1068 2 0 0 5 ma yielded ages within the range of previous determinations dag 476 however yielded a young cre age 0 7 0 25 ma attributed to terrestrial alteration the high spatial variation of argon indicates that the incorporation of martian atmospheric argon into near surface rocks is controlled by localized glass bearing melts produced by shock processes in particular the larger mm size melt pockets contain near end member martian atmospheric argon based on petrography composition and argon isotopic data we conclude that the investigated melt pockets formed by localized in situ shock melting associated with ejection three processes may have led to atmosphere incorporation 1 argon implantation due to atmospheric shock front collision with the martian surface 2 transformation of an atmosphere filled cavity into a localized melt zone and 3 shock implantation of atmosphere trapped in cracks pores and fissures

modern atmospheric signatures in 4 4 ga martian meteorite nwa 7034 the nwa 7034 martian basaltic breccia dated at 4 4 ga 4 4 ga represents an entirely new type of martian meteorite however due to the unique make up of nwa 7034 compared to other martian meteorite types including its anomalous oxygen isotope ratios noble gas analyses a key tool for martian meteorite identification are important to confirm its martian origin here we report the first noble gas results for nwa 7034 which show the presence of a trapped component that resembles the current martian atmosphere this trapped component is also similar in composition to trapped gases found in the much younger shergottites 150 600 ma 150 600 ma our formation ages for the sample suggest events at 1 6 ga k ar and 170 ma u th he which are considerably younger than those observed by rb sr 2 1 ga and sm nd 4 4 ga zircons 4 4 ga however our k ar age is similar to a disturbance in the u pb zircon data at 1 7 ga which could hint that both chronometers have been subjected to disturbance by a common process or event the u th he age of 170 ma could relate to complete loss of radiogenic 4he at this time and is a similar age to the crystallisation age of most shergottites while this may be coincidental it could indicate that a single event is responsible for both shergottite formation and nwa 7034 thermal metamorphism as for cosmic ray exposure ages our favoured age is 5 ma which is outside the ranges for other martian meteorite groups and may suggest a distinct ejection event nwa 7034 shows evidence for neutron capture on br which has caused elevations in kr isotopes 80 kr and 82 kr these elevated abundances indicate significant shielding and could relate to either a large meteoroid size and or shielding in relation to a regolithic origin we have also applied similar neutron capture corrections to ar and xe data which further refine the likelihood of a modern atmospheric component though such corrections remain speculative cosmogenic production rates and noble gas data are consistent with a meteoroid radius of 50 cm fission contributions are clear in the xe data with evidence to suggest that nwa 7034 contains both 238 u and 244 pu derived fission xe components if the gas in nwa 7034 was trapped at its ancient igneous formation this would suggest little evolution of the martian atmosphere between 4 4 ga and present day however as nwa 7034 is a regolith breccia with multiple lithologies and a strong compositional similarity to gusev soils the timing and incorporation of trapped atmospheric gases is unclear with hints of resetting events at 1 5 2 1 ga 1 5 2 1 ga the atmospheric component may have been incorporated during breccia formation possibly in the amazonian though it could also have been incorporated on ejection from the surface

comment on john s stone a possible fragment of the 1908 tunguska meteorite anfinogenov et al 2014 icarus 243 139 147 anfinogenov et al anfinogenov et al 2014 icarus 243 139 147 argue that a highly silicified gravelite sandstone referred to as john s stone could be a fragment of the long sought after impactor from the 1908 tunguska event we have analyzed the oxygen isotopic composition of two distinct samples of john s stone both kindly provided by dr yana anfingenova both samples had very similar isotopic compositions such that the average of the two was as follows 17o 6 67 0 15 18o 12 78 0 28 17o 0 01 0 01 errors 1sd this value is well within the range for samples of terrestrial quartz bearing sedimentary and metamorphic rocks john s stone has an oxygen isotope composition and mineralogy that is unlike any known group of meteorites if john s stone is extraterrestrial this would imply that it represents a previously unknown type of meteorite as suggested by anfinogenov et al however since sandstones can only form on a parent body with liquid water and by inference also an atmosphere we argue that there are only two possible parent bodies in the solar system the earth and mars mars can be ruled out for several reasons including the oxygen isotopic and noble gas composition of john s stone which is clearly distinct from martian meteorites consistent with the o study the noble gases do not provide any evidence for an extraterrestrial origin of the samples the lack of any cosmogenic noble gases particularly striking in 3he 21ne 38ar is consistent with a terrestrial origin or an extraterrestrial origin under large shielding based on the combined evidence obtained in this study we infer that john s stone is a terrestrial rock unrelated to the tunguska impactor

breaching in fine sands and the generation of sustained turbidity currents in submarine canyons natural moderately loosely packed sands can only erode from the surface of the bed after an increase in pore volume because of this shear dilatancy negative pore pressures are generated in the bed in cases of low permeability these negative pressures are released relatively slowly which retards the maximum rate of erosion this effect is incorporated in a new analytically derived pick up function that can explain the observation of gradual retrogressive failure of very steep subaqueous slopes sometimes more than 5 m high in fine non cohesive sands this process termed breaching in the field of sediment dredging may produce large failures in sand bars or river banks the analytical function that describes the breaching process in fine sand is incorporated in a one dimensional steady state numerical model of turbidity currents describing the spatial development of flow this model is applied to simulate a large flushing event in scripps submarine canyon pacific coast of california breach retrogradation and the successive evolution in time of the resulting turbidity current in the canyon are predicted in a sequence of discrete steps predicted velocities are compared with values measured during a flushing event implications for the interpretation of deep water massive sands are discussed

isotopic composition of trapped and cosmogenic noble gases in several martian meteorites isotopic abundances of the noble gases were measured in the following martian meteorites two shock glass inclusions from elephant moraine eet 79001 shock vein glass from shergotty and yamato y 793605 and whole rock samples of allan hills alh 84001 and queen alexandra range que 94201 these glass samples when combined with literature data on a separate single glass inclusion from eet 79001 and a glass vein from zagami permit examination in greater detail of the isotopic composition of ne ar kr and xe trapped from the martian atmosphere the isotopic composition of martian ne if actually present in these glasses remains poorly defined the 40ar 36ar ratio of trapped martian atmospheric ar is probably considerably lower than the nominal ratio of 3000 measured by viking and data on impact glasses suggest a value of 1900 the atmospheric 36ar 38ar ratio is 4 0 martian atmospheric kr may be enriched in lighter isotopes by 0 5 amu compared to both solar wind kr and to the martian composition previously reported the isotopic composition of xe in these glasses agrees with that previously reported in the literature the martian atmospheric 36ar 132xe and 84kr 132xe elemental ratios are higher than those reported by viking by factors of 2 5 1 6 depending on the 40ar 36ar ratio adopted and 1 8 respectively and are discussed in a separate paper cosmogenic gases indicate space exposure ages of 2 7 0 6 ma for que 94201 and shergotty and 14 1 ma for alh 84001 small amounts of 21ne produced by energetic solar protons may be present in que 94201 but are not present in alh 84001 or y 793605 the space exposure age for y 793605 is 4 9 0 6 ma and appears to be distinctly older than the ages for basaltic shergottites however uncertainties in cosmogenic production rates still makes somewhat uncertain the number of martian impact events required to produce the exposure ages of martian meteorites

terrestrial and martian weathering signatures of xenon components in shergottite mineral separates abstract xenon isotopic ratios step heating release patterns and gas concentrations of mineral separates from martian shergottites roberts massif rbt 04262 dar al gani dag 489 shergotty and elephant moraine eet 79001 lithology b are reported concentrations of martian atmospheric xenon are similar in mineral separates from all meteorites but more weathered samples contain more terrestrial atmospheric xenon the distributions of xenon from the martian and terrestrial atmospheres among minerals in any one sample are similar suggesting similarities in the processes by which they were acquired however in opaque and maskelynite fractions martian atmospheric xenon is released at higher temperatures than terrestrial atmospheric xenon it is suggested that both martian and terrestrial atmospheric xenon were initially introduced by weathering low temperature alteration processes however the martian component was redistributed by shock accounting for its current residence in more retentive sites the presence or absence of detectable 129xe from the martian atmosphere in mafic minerals may correspond to the extent of crustal contamination of the rock s parent melt variable contents of excess 129xe contrast with previously reported consistent concentrations of excess 40ar suggesting distinct sources contributed these gases to the parent magma

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

helium loss from martian meteorites mainly induced by shock metamorphism evidence from new data and a literature compilation noble gas data from martian meteorites have provided key constraints about their origin and evolution and their parent body these meteorites have witnessed varying shock metamorphic overprinting at least 5 to 14 gpa for the nakhlites and up to 45 55 gpa e g the lherzolitic shergottite allan hills alh a77005 solar heating cosmic ray exposure and weathering both on mars and earth influences on the helium budgets of martian meteorites were evaluated by using a new data set and literature data concentrations of 3he 4he u and th are measured and shock pressures for same sample aliquots of 13 martian meteorites were determined to asses a possible relationship between shock pressure and helium concentration partitioning of 4he into cosmogenic and radiogenic components was performed using the lowest 4he 3he ratio we measured on mineral separates 4he 3he 4 1 pyroxene of alha77005 our study revealed significant losses of radiogenic 4he systematics of cosmogenic 3he and neon led to the conclusion that solar radiation heating during transfer from mars to earth and terrestrial weathering can be ruled out as major causes of the observed losses of radiogenic helium in bulk meteorites for bulk rock we observed a correlation of shock pressure and radiogenic 4he loss ranging between 20 for chassigny and other moderately shocked martian meteorites up to total loss for meteorites shocked above 40 gpa a steep increase of loss occurs around 30 gpa the pressure at which plagioclase transforms to maskelynite this correlation suggests significant 4he loss induced by shock metamorphism noble gas loss in rocks is seen as diffusion due to 1 the temperature increase during shock loading shock temperature and 2 the remaining waste heat after adiabatic unloading post shock temperature modeling of 4he diffusion in the main u th carrier phase apatite showed that post shock temperatures of 300 c are necessary to explain observed losses this temperature corresponds to the post shock temperature calculated for bulk rocks shocked at about 40 gpa from our investigation data survey and modeling we conclude that the shock event during launch of the meteorites is the principal cause for 4he loss

noble gases in mineral separates from three shergottites shergotty zagami and eeta79001 this study provides a complete data set of all five noble gases for bulk samples and mineral separates from three martian shergottites shergotty bulk pyroxene maskelynite zagami bulk pyroxene maskelynite and elephant moraine eet a79001 lithology a bulk pyroxene we also give a compilation of all noble gas and nitrogen studies performed on these meteorites our mean values for cosmic ray exposure ages from 3he 21ne and 38ar are 2 48 myr for shergotty 2 73 myr for zagami and 0 65 myr for eeta79001 lith a serious loss of radiogenic 4he due to shock is observed cosmogenic neon results for bulk samples from 13 martian meteorites new data and literature data are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic ray effects while a contribution of this low energy irradiation is strongly indicated for all of the shergottites spallation ne in chassigny allan hills alh 84001 and the nakhlites is fully explained by galactic cosmic ray spallation implanted martian atmospheric gases are present in all mineral separates and the thermal release indicates a near surface siting we derive an estimate for the 40ar 36ar ratio of the martian interior component by subtracting from measured ar in the k poor pyroxenes the small radiogenic component as well as the implanted atmospheric component as indicated from 129xe excesses unless compromised by the presence of additional components a high ratio of 2000 is indicated for martian interior argon similar to that in the martian atmosphere since much lower ratios have been inferred for chassigny and alh 84001 the result may indicate spatial and or temporal variations of 40ar 36ar in the martian mantle

isotopic dating and structural relationships of granitoids and greenstones in the east pilbara western australia a structural rb sr isotopic study has been made on two small areas in the eastern pilbara block western australia the sites were chosen because they showed good interrelationships of granitoid and greenstone units at warrery gap on the western side of the corunna granitic dome the acid volcanics of the duffer formation at the top of the lower talga talga subgroup of the warrawoona group show some updating but a good 3506 62 ma isochron with initial ratio ir of 0 7006 0 0011 was recognized consistent with the 3452 16 ma zircon measurement of pidgeon 1978b both a penetrative d1 deformation and the doming of d2 preceded intrusion of late tectonic granitoids dated at 3270 22 ma ir 0 7015 0 0003 into both the duffer formation and the overlying pillow lavas of the salgash subgroup thus the salgash subgroup is much older than suggested by glikson 1979 and the stratigraphic succession cannot contain a hiatus between the apparently conformable talga talga and salgash subgroups of the magnitude he proposed the granitic domes clearly owe their form to the d2 deformation rather than to batholitic intrusion but near horizontal structural lineations suggest that they were not formed by diapiric movements a granodiorite and pink feldspar granite from just within the corunna granitic dome are slightly deformed pooled isochrons indicate an age of 3232 27 ma but different irs of 0 7032 and 0 7009 respectively at tambourah in the eastern shaw granitic dome local d2 also deforms an intrusive microadamellite of age 3087 34 ma and ir 0 7103 0 0057 there is therefore a real spread in ages of d2 granitoids and d2 deformation between about 3300 and 3100 ma layered megacrystic gneiss at tambourah also intruded by the microadamellite contains a nebulous foliation argued to be local s1 layered and homogeneous megacrystic gneiss produce updated rb sr total rock isochrons of 2995 95 and 2779 38 ma respectively the primary age of these d1 gneisses is clearly greater than that of the d2 granitoids and is probably indicated by pidgeon s 1978c zircon age of 3417 40 ma from the shaw granitic dome if so hickman s 1975 migmatite suite contains both d1 gneisses and d2 granitoids separated in age at tambourah by ca 300 ma although neither appears to be older than the lower part of the preserved layered sequence the protocrust on which that sequence was deposited has yet to be directly identified

noble gases and nitrogen in martian meteorites dar al gani 476 sayh al uhaymir 005 and lewis cliff 88516 efa and extra neon meteorite finds from the terrestrial hot deserts have become a major contributor to the inventory of martian meteorites in order to understand their nitrogen and noble gas components we have carried out stepped heating experiments on samples from two martian meteorites collected from hot deserts we measured interior and surface bulk samples glassy and non glassy portions of dar al gani 476 and sayh al uhaymir 005 we have also analyzed noble gases released from the antarctic shergottite lewis cliff 88516 by crushing and stepped heating for the hot desert meteorites significant terrestrial ar kr xe contamination is observed with an elementally fractionated air efa component dominating the low temperature releases the extremely low ar kr xe ratios of efa may be the result of multiple episodes of trapping loss during terrestrial alteration involving aqueous fluids we suggest fractionation processes similar to those in hot deserts to have acted on mars with acidic weathering on the latter possibly even more effective in producing elementally fractionated components addition from fission xenon is apparent in dag 476 and sau 005 the ar kr xe patterns for lew 88516 show trends as typically observed in shergottites including evidence for a crush released component similar to that observed in eeta 79001 a trapped ne component most prominent in the surface sample of dag 476 may represent air contamination it is accompanied by little trapped ar 20ne 36ar 50 and literature data suggest its presence also in some antarctic finds data for lew 88516 and literature data on the other hand suggest the presence of two trapped ne components of martian origin characterized by different 20ne 22ne possibly related to the atmosphere and the interior caution is recommended in interpreting nitrogen and noble gas isotopic signatures of martian meteorites from hot deserts in terms of extraterrestrial sources and processes nevertheless our results provide hope that vice versa via noble gases and nitrogen in meteorites and other relevant samples from terrestrial deserts martian secondary processes can be studied

erosion velocity of large grains subjected to a high uniform flow velocity abstractthere is limited knowledge on the erosion rates of large grains the available erosion models of granular material at large flow velocities are only validated up to a median particle diamet

geochemical and mineralogical indicators for aqueous processes in the columbia hills of gusev crater mars 1 water played a major role in the formation and alteration of rocks and soils in the columbia hills the extent of alteration ranges from moderate to extensive five distinct rock compositional classes were identified the order for degree of alteration is watchtower clovis wishstone peace backstay the rover s wheels uncovered one unusual soil paso robles that is the most s rich material encountered clovis class rocks have compositions similar to gusev plains soil but with higher mg cl and br and lower ca and zn watchtower and wishstone classes have high al ti and p and low cr and ni peace has high mg and s and low al na and k backstay basalts have high na and k compared to plains adirondack basalts and paso robles soil has high s and p some rocks are corundum normative indicating that their primary compositions were changed by loss and or gain of rock forming elements clovis materials consist of magnetite nanophase ferric oxides npox hematite goethite ca phosphates ca and mg sulfates pyroxene and secondary aluminosilicates wishstone and watchtower rocks consist of fe oxides oxyhydroxides ilmenite ca phosphate pyroxene feldspar mg sulfates and secondary aluminosilicates peace consists of magnetite npox mg and ca sulfates pyroxene olivine feldspar apatite halides and secondary aluminosilicates paso robles consists of fe3 mg ca and other sulfates ca phosphates hematite halite allophane and amorphous silica columbia hills outcrops and rocks may have formed by the aqueous alteration of basaltic rocks volcaniclastic materials and or impact ejecta by solutions that were rich in acid volatile elements

the case for old basaltic shergottites abstract the crystallization age of shergottites is currently not agreed upon although mineral 87 rb 87 sr 147 sm 143 nd 176 lu 176 hf and u pb isochrons all give very young ages typically in the range of 160 180 ma 207 pb 206 pb data support a much older crystallization age at 4 1 ga which is consistent with published whole rock 87 rb 87 sr data on basaltic shergottites different isotopic systems present different complexities but crater counting chronology which shows that a substantial fraction of the martian surface was resurfaced during the late heavy bombardment is in favor of an old martian lithosphere with ages in accordance with pb pb and rb sr isotopic data a 4 1 ga pb pb age of shergottites also agrees with the 142 nd and 182 w anomalies found in these rocks and concur with the presence of an actively convecting mantle during the first 500 myr of the planet s history we here present new sm nd lu hf and pb pb mineral isochrons for the basaltic shergottites shergotty and los angeles complementing our previous results on zagami bouvier a blichert toft j vervoort j d and albarede f 2005 the age of snc meteorites and the antiquity of the martian surface earth planet sci lett 240 221 233 the internal 147 sm 143 nd and 176 lu 176 hf isochrons give young ages of respectively 172 40 mswd 2 0 and 188 91 mswd 3 1 for shergotty and 181 13 mswd 0 14 and 159 42 mswd 0 01 for los angeles in contrast the pb isotope compositions of the leached whole rock fragments and maskelynite separates of shergotty and los angeles fall on the whole rock isochron previously established for zagami and other shergottite samples and collectively yield a pb pb age of 4050 70 ma for the crystallization of the basaltic shergottite suite the contrast between the 170 ma ages of internal isochrons and the 4 1 ga age supported by pb pb and 87 rb 87 sr on whole rocks simply reflects that the younger age dates the perturbation of a suite of rocks of noachian age the internal rb sr sm nd lu hf and u pb errorchrons are heavily biased by the presence of disseminated phosphate minerals and inclusions for which d h ratios d 4600 indicate strong interaction with martian subsurface waters in contrast baddeleyite occasionally present in sncs and also having extremely young u pb ages reflect resetting under the shock conditions that prevailed either during shergottite extraction from the planet or from impacts associated with a major break up event of planetesimals in the main asteroid belt we finally also re examine 39 ar 40 ar data on snc meteorites and suggest that they as well support old crystallization ages

relationships between calc alkaline acidic and basic mantle derived magmas in late archaean composite dykes kambalda goldfield western australia abstract composite dykes from the north dome area kambalda comprise basic spessartite hornblende plagioclase lamprophyre 56 sio 2 with mg numbers cr and ni contents typical of primitive mantle derived rocks and more acidic plagioclase phyric quartz andesite 66 sio 2 together with felsic net veins and hornblendic patches suggesting local differentiation the spessartites can be regarded chemically as volatile lile and incompatible element enriched versions of siliceous high magnesian basalts from the local greenstone sequence a pb pb isochron on one dyke yields an age of 2636 27 ma making this the oldest composite dyke so far dated field and geochemical evidence including identical pb initial ratios for the constituent rock types virtually indistinguishable ree spectra and tight linear trends on plots such as y versus ti and ce cr versus ti cr suggests that the two magmas lamprophyric and acidic were genetically related and were emplaced contemporaneously into the same fracture quantitative least squares modelling of whole rock and mineral compositions suggests that the acidic components resulted mainly from fractionation of hornblende from parental spessartite magmas together with a possible contribution from mixing of the same spessartite magma with crustally derived acidic e g trondjhemitic magma the latter is represented by separate dykes and stocks in the kambalda area close similarities between the kambalda composite dykes and archaean tertiary composite dykes in other parts of the world imply a persistent role for mantle derived magmas such as lamprophyres in the genesis of the dominant intermediate acidic e g granitoid magmas in many calc alkaline provinces

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

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

prediction of ignitive turbidity currents in scripps submarine canyon swift highly erosive continuous turbidity currents are known to be triggered in scripps submarine canyon during storms a relatively modest agitation due to edge waves can generate currents at least as swift as 1 9 m s 1 pantin 1979 and parker 1982 have described a mechanism by which a turbidity current can self accelerate by entraining sediment from the bed parker termed the mechanism ignition herein two models of steady spatially developing turbidity currents are developed and applied to scripps submarine canyon fairly specific predictions are obtained for the onset of ignitive acceleration and for the downstream development of the turbidity currents the results are in general agreement with available measurements in the same canyon it is speculated that ignitive turbidity currents constitute a major mechanism by which sand submarine canyons are eroded and by which sand is delivered to the abyssal plain

constraints on interpretations of lower crustal structure tectonic setting and metallogeny of the eastern goldfields and southern cross provinces provided by granite geochemistry new trace element geochemical data on granites fromthe eastern southern cross province and the western eastern goldfields province of the yilgarn block provide additional constraints on tectonic and metallogenic syntheses the new data also enables estimates of the nature and composition of the lower crust to be made all granites were derived by partial melting of the lower crust and all appear to have had a significant crustal prehistory using multi element primordial mantle normalised trace element abundance patterns the granites can be divided into four broad groups three of which are predominantly sr undepleted and y depleted whilst the fourth group is always sr depleted and y undepleted the first three groups are believed to have had garnet but not plagioclase stable at some stage of their prehistory whilst the fourth group had plagioclase but not garnet seismic data does not show any evidence of a significant garnet bearing layer within the crust as the present day trace element signatures of the granites were probably derived from earlier melting events interpretations of tectonic setting existing at the time of their emplacement based solely on their geochemistry are questionable the ultimate source of granites of groups 1 2 and 3 may have been derived by partial melting associated with subduction group 4 granites which have never had garnet as a significant component in their source regions closely resemble the rift related proterozoic anorogenic suites the geochemistry of the granites also predicts the sharp crustmantle boundary shown by seismic data some plutons are enriched in rb u and y and also have decreasing krb ratios with increasing sio2 similar trends are found in granites which have associated sn w and au mineralisation in other australian provinces alteration is common in some parts of plutons and regional mapping of these altered granites could define regional fluid circulation systems which may be related to mineralisation

geochemistry of martian basalts with constraints on magma genesis abstract over the past decade our knowledge of the geochemical and mineralogical diversity of martian rocks has greatly increased rocks on the surface of mars are older than most martian meteorites and have a wider range in bulk chemistry higher sio 2 higher total alkalis and lower mgo contents recent martian meteorite discoveries nwa 7034 nwa 7635 and nwa 8159 are also significantly older than the shergottites and nwa 7034 contains clasts which have a similar range in chemistry of the surface basalts in this invited review i summarize what is known about the bulk chemistry major elements of martian igneous rocks and use the chemistry to constrain the formation conditions in the interior and how these conditions have changed through time the basalts at gale crater are consistent with forming from a metasomatized mantle source which affected not only the chemistry of the basalts but also the formation conditions basalts at gusev crater bounce rock at meridiani planum and those basalts not affected by metasomatism like those at gale crater have a mantle potential temperature of 1450 c for the noachian conversely martian shergottites have a much higher mantle potential temperature 1745 c which has always been problematic to explain for such young rocks new formation conditions calculations are consistent with previous models of formation by a hot mantle plume but solve the pressure of formation paradox from the previous model combining the calculations for mantle potential temperature with previous estimates for grs measurements of surface volcanics from the hesperian and amazonian i calculate a baseline cooling curve and mantle melting conditions for the martian interior through time

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

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

a nitrogen and argon stable isotope study of allan hills 84001 implications for the evolution of the martian atmosphere the abundances and isotopic compositions of n and ar have been measured by stepped combustion of the allan hills 84001 alh 84001 martian orthopyroxenite material described as shocked is n poor n approximately 0 34 ppm delta 15n approximately 23 although during stepped combustion 15n enriched n delta 15n approximately 143 is released in a narrow temperature interval between 700 degrees c and 800 degrees c along with 13c enriched c delta 13c approximately 19 and 40ar cosmogenic species are found to be negligible at this temperature thus the isotopically heavy component is identified in part as martian atmospheric gas trapped relatively recently in the history of alh84001 the n and ar data show that alh84001 contains species from the martian lithosphere a component interpreted as ancient trapped atmosphere in addition to the modern atmospheric species and excess 40ar from k decay deconvolution of radiogenic 40ar from other ar components on the basis of end member 36ar 14n and 40ar 36ar ratios has enabled calculation of a k ar age for alh 84001 as 3 5 4 6 ga depending on assumed k abundance if the component believed to be martian palaeoatmosphere was introduced to alh 84001 at the time the k ar age was set then the composition of the atmosphere at this time is constrained to delta 15n or 200 40ar 36ar or 17 x 10 5 in terms of the petrogenetic history of the meteorite alh 84001 crystallised soon after differentiation of the planet may have been shocked and thermally metamorphosed in an early period of bombardment and then subjected to a second event this later process did not reset the k ar system but perhaps was responsible for introducing recent atmospheric gases into alh 84001 and it might mark the time at which alh 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages

petrography and composition of martian regolith breccia meteorite northwest africa 7475 the northwest africa nwa 7475 meteorite is one of the several stones of paired regolith breccias from mars based on petrography oxygen isotope mineral compositions and bulk rock compositions its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten other clast types include crystallized impact melt rocks evolved plutonic rocks possible basalts contact metamorphosed rocks and siltstones impact spherules and vitrophyre shards record airborne transport and accreted dust rims were sintered on most clasts presumably during residence in an ejecta plume the clast assemblage records at least three impact events one that formed an impact melt sheet on mars 4 4 ga ago a second that assembled nwa 7475 from impactites associated with the impact melt sheet at 1 7 1 4 ga and a third that launched nwa 7475 from mars 5 ma ago mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to 5 and 15 gpa the mild postshock heating that resulted from these shock pressures would have been insufficient to sterilize this water bearing lithology during launch magnetite maghemite and pyrite are likely products of secondary alteration on mars textural relationships suggest that calcium carbonate and goethite are probably of terrestrial origin yet trace element chemistry indicates relatively low terrestrial alteration comparison of mars odyssey gamma ray spectrometer data with the fe and th abundances of nwa 7475 points to a provenance in the ancient southern highlands of mars gratteri crater with an age of 5 ma and an apparent diameter of 6 9 km marks one possible launch site of nwa 7475

exsolution and shock microstructures of igneous pyroxene clasts in the northwest africa 7533 martian meteorite northwest africa nwa 7533 is a martian regolith breccia this meteorite and its pairings offers a good opportunity to study near surface processes that occurred on early mars here we have conducted a transmission electron microscope study of medium and coarse grained a few tens to hundreds of micrometers ca rich pyroxene clasts in order to define their thermal and shock histories the pyroxene grains have a high temperature magmatic origin as revealed by the well developed pigeonite augite exsolution microstructure exsolution lamella characteristics composition thickness and spacing indicate a moderately slow cooling some of the pyroxene clasts display evidence for local decomposition into magnetite and silica at the submicron scale this phase decomposition may have occurred at high temperature and occurred at high oxygen fugacity at least 2 3 log units above the qfm buffer after the formation of the exsolution lamellae this corresponds to oxidizing conditions well above typical martian magmatic conditions these oxidizing conditions seem to have prevailed early and throughout most of the history of nwa 7533 the shock microstructure consists of 100 mechanical twins which have accommodated plastic deformation other pyroxene shock indicators are absent compared with snc meteorites that all suffered significant shock metamorphism nwa 7533 appears only mildly shocked the twin microstructure is similar from one clast to another suggesting that the impact which generated the 100 twins involved the compacted breccia and that the pyroxene clasts were unshocked when they were incorporated into the nwa 7533 breccia

heterogeneous distribution of h2o in the martian interior implications for the abundance of h2o in depleted and enriched mantle sources we conducted a petrologic study of apatite within 12 martian meteorites including 11 shergottites and one basaltic regolith breccia these data were combined with previously published data to gain a better understanding of the abundance and distribution of volatiles in the martian interior apatites in individual martian meteorites span a wide range of compositions indicating they did not form by equilibrium crystallization in fact the intrasample variation in apatite is best described by either fractional crystallization or crustal contamination with a cl rich crustal component we determined that most martian meteorites investigated here have been affected by crustal contamination and hence cannot be used to estimate volatile abundances of the martian mantle using the subset of samples that did not exhibit crustal contamination we determined that the enriched shergottite source has 36 73 ppm h2o and the depleted source has 14 23 ppm h2o this result is consistent with other observed geochemical differences between enriched and depleted shergottites and supports the idea that there are at least two geochemically distinct reservoirs in the martian mantle we also estimated the h2o cl and f content of the martian crust using known crust mantle distributions for incompatible lithophile elements we determined that the bulk martian crust has 1410 ppm h2o 450 ppm cl and 106 ppm f and cl and h2o are preferentially distributed toward the martian surface the estimate of crustal h2o results in a global equivalent surface layer gel of 229 m which can account for at least some of the surface features on mars attributed to flowing water and may be sufficient to support the past presence of a shallow sea on mars surface

flow slides in the netherlands experience and engineering practice this paper deals with flow slide experience in the netherlands it gives an extensive survey of empirical field data concerning the geological characteristics of the region the profiles just before the flow slides and the damage that flow slides can cause the traditional dutch procedure for analyzing the flow slide potential of underwater sand slopes is described this is an engineering approach that is mainly based on the empirical field data together with geological surveys and soil investigations performed at the relevant site key words sand collapse flow slides liquefaction slope stability

a unique piece of mars following the pioneering mars exploration rovers nasa s curiosity rover is actively exploring the crustal rocks of mars despite the exciting results returned by the rovers there is no substitute for a hand sample of crustal rock because such samples will not be returned to earth anytime soon geochemists who want a piece of mars in their labs must satisfy themselves with martian meteorites 1 these comprise a group of igneous rocks with telltale signs of martian alteration products 2 and have provided ground truth for the information returned by the rovers oddly however the hundred or so known martian meteorites are chemically unrepresentative of the martian crust determined by missions 3 on page 780 of this issue agee et al 4 put an end to this conundrum with the finding of a new martian meteorite northwest africa nwa 7034 a basaltic breccia unique among known martian meteorites with respect to age oxygen isotopes and petrology

conditions for the ignition of catastrophically erosive turbidity currents abstract the basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment this problem is addressed herein a detailed analysis indicates that the bagnold criterion is necessary but insufficient for self sustaining turbidity currents the analysis reveals two possible equilibrium states a relatively low velocity ignitive state and a high velocity dense catastrophic state a stability analysis indicates that the ignitive state is unstable flows below it invariably die out and flows above it ignite i e accelerate and entrain sediment to the catastrophic state which is stable the ignitive state thus defines the criterion for a self sustaining turbidity current estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons

the northwest africa nwa 5790 meteorite a mesostasis rich nakhlite with little or no martian aqueous alteration northwest africa nwa 5790 is the most recently discovered member of the nakhlite group its mineralogy differs from the other nakhlites with a high abundance mesostasis 38 1 3 6 vol and scarcity of olivine 4 0 2 2 vol furthermore zoning of augite phenocrysts and other petrographic and chemical characteristics suggest that nwa 5790 samples the chilled margin of its parent lava flow sill nwa 5790 contains calcite and rare clay minerals that are evidence for its exposure to liquid water the calcite forms a cement to coatings of dust on the outer surface of the find and extends into the interior of the meteorite within veins the presence of microbial remains within the coating confirms that the dust and its carbonate cement are terrestrial in origin consistent with the carbon and oxygen isotope composition of the calcite the clay minerals are finely crystalline and comprise 0 003 vol of the meteorite d values of the clay minerals range from 212 109 to 96 132 and cannot be used to distinguish between a terrestrial or martian origin as petrographic results are also not definitive we conclude that secondary minerals produced by martian groundwaters are at best very rare within nwa 5790 the meteorite has therefore sampled a region of the lava flow sill with little or no exposure to the aqueous solutions that altered other nakhlites this isolation could relate to the scarcity of olivine in nwa 5790 because dissolution of olivine in other nakhlites by martian groundwaters enhanced their porosity and permeability and provided solutes for secondary minerals

ancient geologic events on mars revealed by zircons and apatites from the martian regolith breccia nwa 7034

mineral exploration and basement mapping in areas of deep transported cover using indicator heavy minerals and paleoredox fronts yilgarn craton western australia abstract glacial sediments have been thoroughly integrated into mineral exploration protocols in the northern hemisphere e g canada and fennoscandia but have received less attention in australia in western australia wa permo carboniferous diamictites buried by younger cenozoic sediments cover scattered areas that have potential to host gold and nickel mineralization in the ne of the yilgarn craton a systematic stratigraphic mineralogical and geochemical study was undertaken to determine whether diamictites in the agnew lawlers gold province have properties that may help target concealed mineralization at the agnew lawlers district rocks intersected in 31 drill holes ne of the waroonga gold mine were interpreted in terms of lithological textural and paleolandscape mineralogical and geochemical variations to select the best sampling media for mineral exploration and provenance assessment the paleotopographic variation asymmetry of the depositional basin polymictic composition matrix supported mixed angular and rounded and poorly sorted texture of the diamictite clasts indicate mechanical dispersal from proximal and distal heterogeneous source rocks ferromagnesian minerals chromite cr magnetite magnetite and ni cu fe sulfides are abundant in the diamictite close to mafic ultramafic source rocks monazite apatite zircon and clasts derived from pyrite bearing quartz veins increase in abundance in the diamictite close to the waroonga shear zone that separates granitoid gneiss terrain from the scotty creek metasediments ilmenite is extensively distributed in diamictites throughout the study area and its mn content can be used to differentiate between felsic and mafic source rocks alteration of ilmenite to titanite monazite to apatite and thorite and replacement and fracture filling of pentlandite to monazite suggest felsic intrusive related hydrothermal alteration of the source rocks prior to mechanical weathering late paleozoic tropical weathering associated with oscillation of water table and icehouse to greenhouse climatic shift has created paleoredox fronts in the permo carboniferous sequence below the redox fronts diamictites are unweathered rich in detrital sulfide and opaque oxide minerals and can be used in provenance studies and tracing mineralization these characteristics of unweathered diamictite are the optimal sampling medium target for provenance studies and mineral exploration these are cemented mainly by calcareous cement where they overlie mafic ultramafic rocks and by pyrite cement where they overlie the scotty creek metasediments above the redox fronts diamictites are variably weathered to ferruginous and bleached kaolinitic saprolites which are stable under oxidizing circum neutral conditions ferruginous diamictites are rich in recycled redox sensitive elements derived from oxidation of ferromagnesian sulfide and opaque oxide heavy minerals these weathering features can be used to identify weathered diamictite for sampling for hydromorphic metal dispersion studies

ejection times of martian meteorites noble gas isotopic analyses were made for four meteorites whose origin is mars basaltic shergottites queen alexandra range 94201 zagami the iherzolite lew88516 and orthopyroxenite allan hills 84001 the latter one was separated into orthopyroxene chromite and maskelynite fractions ejection times were calculated for all martian meteorites using cosmic ray exposure ages based on 3he 21ne and 38ar concentrations and literature data on the terrestrial ages we discuss the arguments for a scenario in which they were ejected from mars by asteroidal or cometary impact as small meteoroids and were delivered to earth within and up to 15 million years the basaltic shergottites que94201 shergotty and zagami show an ejection age cluster at 2 76 ma the fourth basaltic shergottite eet79001 being younger 0 82 ma lherzolites lew88516 and alh77005 were ejected by a later event 3 84 ma ago all nakhlites nakhla governador valadares and lafayette originate from an event 11 0 ma ago although chassigny is chemically distinct from the nakhlites its ejection age is 11 6 ma whether this is a separate event cannot be decided from the available data finally orthopyroxenite alh84001 was launched from mars 14 4 ma ago the distribution of the delivery times for martian meteorites to earth reflect individual impact events onto five or six different source terrains this result is significant in the context of a comprehensive knowledge of the martian crust composition finally we derived the k 40ar gas retention age of alh84001 mineral fractions adopting two different models assuming a component of martian atmospheric ar with 40ar36ar 1790 trapped by this meteorite we obtained an age of 3390 ma on the other hand assuming no contribution of martian atmospheric ar the resulting k 40ar age is about 4100 ma that is roughly 500 ma younger than the reported sm nd crystallization age

volatiles nitrogen noble gases in recently discovered snc meteorites extinct radioactivities and evolution abstract we report noble gas and nitrogen analyses of newly discovered snc meteorites one nakhlite nwa817 and four shergottites nwa480 nwa856 nwa1068 and sau 005 the k ar age 1 3 ga as well as the cosmic ray exposure cre age 10 0 1 3 ma of nakhlite nwa817 agree with data of nakhla the cre ages of nwa480 nwa856 and nwa1068 2 35 0 20 2 60 0 21 and 2 01 0 65 ma respectively are consistent within uncertainties with other basaltic shergottites but the cre age of sau 005 1 25 0 07 ma is distinct and indicates a different ejection event bulk k ar ages of all shergottites exceed the reported radiometric ages and reveal the presence of inherited radiogenic 40 ar in basaltic lavas the isotopic composition of nitrogen trapped in these snc meteorites is not homogeneous since 15 n values of either 15 to 20 or 45 indicate different nitrogen reservoirs all shergottites contain fission xenon from 238 u and fission xe of extinct t 1 2 82 ma 244 pu previously identified in alh84001 in chassigny and in nakhla is also present in at least one shergottite nwa856 the shergottites contain less fissiogenic xe than other snc suggesting that either their source was more degassed or that the magma source region closed at a later time in nakhlites fission xenon from 244 pu correlates with uranium a geochemical proxy of plutonium thus it is possible that fissiogenic xe was not inherited during magma differentiation but rather was produced in situ and retained in refractory mineral assemblages in this interpretation the magma evolution that settled the mineralogy and geochemistry of nakhlites took place at a time when 244 pu was alive and pre dated the late events recorded in their radiometric ages alternatively fissiogenic xenon was trapped from a mantle source during closed system evolution of the parent magmas in which case such evolution might have taken place at considerable depth pressure in order to inhibit magma degassing during the course of differentiation

noble gases in e chondrites noble gas data are reported for 12 e chondrites combined with literature data they show that k ar ages are 4 ae for 14 out of 18 meteorites yet u th he ages are often shorter perhaps due to late mild reheating cosmic ray exposure ages differ systematically between types 4 and 6 with e4 s mostly below 16 myr and e6 s above 30 myr this may mean that the e chondrite parent body contains predominantly a single petrologic type on the 1 km scale of individual impacts in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites the heavy noble gases consist of at least two primordial components the usual planetary component 36ar132xe 80 and a less fractionated subsolar component 2700 36ar132xe 3800 the latter is found in highest concentration in the e4 chondrite south oman 36ar 760 10 8cc g 36ar132xe 2700 the isotopic compositions of both components are similar to typical planetary values indicating that some factor other than mass controlled the noble gas elemental ratios the heavy xe isotopes occasionally show some of the lowest 134xe132xe and 136xe132xe ratios measured in bulk chondrites suggestive of nearly fission free xe e g 136xe132xe 0 3095 0 0020 amounts of planetary gas in e4 e6 chondrites fall in the range for ordinary chondrites of types 4 6 but in contrast to the ordinary chondrites fail to correlate with petrologic type or volatile trace element contents another unusual feature of e chondrites is that primordial ne is present even in most 4 s and 5 s 20nep 1 to 7 10 8cc g with an isotopic composition consistent with planetary ne analyses of mineral separates show that the planetary gases are concentrated in an hf and hcl insoluble mineral similar to phase q the poorly characterized hno3 soluble carrier of primordial gases in carbonaceous and ordinary chondrites the subsolar gases on the other hand are located in an hcl and hno3 resistant phase possibly enstatite or a minor phase included in enstatite much of the 129xer 50 for e4 s 70 for e6 s is in hcl resistant but hf soluble sites suggestive of a silicate a similar subsolar component may be responsible for the high 36ar132xe ratios of some c3 s unequilibrated ordinary chondrites and the unique aubrite shallowater the planet venus also has a high arkr ratio well above the planetary range and hence may have acquired its noble gases from an e chondrite like material similar to south oman

acoustic velocity profiler for laboratory and field studies a monostatic acoustic doppler velocity profiler advp for use in hydraulic research is presented including signal treatment algorithms the 1 mhz advp used in the present study has an accuracy better than 2 mms s 1 with a range of up to 100 cm for velocities up to 290 cms s 1 and a resolution of 256 points in the profile results of advp measurements in uniform flow in two laboratory open channels with smooth and gravel beds compare favorably with established distribution laws for mean velocity variance and reynold s stress indicating that the turbulence scales are sufficiently resolved by the instrument measurements with the same instrument in a river and a lake illustrate that it is capable of producing excellent results in the field as well it was demonstrated that unaffected by water quality the instrument is a good research tool for nonintrusive and accurate instantaneous profile measurements under turbulent flow conditions

laboratory shock emplacement of noble gases nitrogen and carbon dioxide into basalt and implications for trapped gases in shergottite eeta 79001 abstract basalt samples have been analyzed mass spectrometrically for shock implanted noble gases n2 and co2 after exposure to 20 60 gpa 200 600 kbar shock in the presence of 0045 3 0 atm of ambient gas isotopically labelled gases were used in some samples to distinguish implanted atmospheric gases from contaminant or indigenous gases abundances of emplaced gases varied linearly with ambient gas pressure for constant shock pressure and gas emplacement was most efficient in the range of 35 50 gpa shock pressure uncrushed samples shocked in this range gave emplacement efficiencies number densities of gases in shocked samples number densities in ambient gas of 2 0 6 7 for heavy noble gases and nitrogen while powdered samples with higher effective porosity yielded 40 50 efficiencies indicating that 50 of noble gases and nitrogen available in porespaces was emplaced no elemental or isotopic fractionation was detected with ar kr xe or n2 helium and in some samples ne were lost by diffusion subsequent to shock emplacement efficiencies for co2 averaged a factor of 1 8 0 2 greater than those of n2 and noble gases in 4 samples with 20 50 gpa shock and yielded 3 2 times greater efficiency in a sample shocked to 60 gpa enhanced co2 emplacement is thought to be due to reaction with silicate materials data from shergottite eeta 79001 glass may be consistent with co2 efficiencies a factor of 2 3 greater than noble gas efficiencies trapped gases in eeta 79001 glass were probably emplaced by shock however apparent emplacement efficiencies are somewhat higher than even shocked powder samples possible explanations for the difference include atmospheric overpressure at the time of shock trapping of gas already in vugs by intruding melt material or collapse of gas filled vugs to form gas laden glass inclusions not enough is yet known about the behavior of vugs under shock to discount the latter possibility

regolith breccia northwest africa 7533 mineralogy and petrology with implications for early mars northwest africa 7533 a polymict martian breccia consists of fine grained clast laden melt particles and microcrystalline matrix while both melt and matrix contain medium grained noritic monzonitic material and crystal clasts the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars microbasaltic clasts vitrophyric and microcrystalline spherules and shards the clast laden melt rocks contain clump like aggregates of orthopyroxene surrounded by aureoles of plagioclase some shards of vesicular melt rocks resemble the pyroxene plagioclase clump aureole structures submicron size matrix grains show some triple junctions but most are irregular with high intergranular porosity the noritic monzonitic rocks contain exsolved pyroxenes and perthitic intergrowths and cooled more slowly than rocks with zoned pyroxene or fine grain size noritic material contains orthopyroxene or inverted pigeonite augite calcic to intermediate plagioclase and chromite to cr bearing magnetite monzonitic clasts contain augite sodic plagioclase k feldspar ti bearing magnetite ilmenite chlorapatite and zircon these feldspathic rocks show similarities to some rocks at gale crater like black trout mara and jake m the most magnesian orthopyroxene clasts are close to alh 84001 orthopyroxene in composition all these materials are enriched in siderophile elements indicating impact melting and incorporation of a projectile component except for ni poor pyroxene clasts which are from pristine rocks clast laden melt rocks spherules shards and siderophile element contents indicate formation of nwa 7533 as a regolith breccia the zircons mainly derived from monzonitic melt rocks crystallized at 4 43 0 03 ga humayun et al 2013 and a 147sm 143nd isochron for nwa 7034 yielding 4 42 0 07 ga nyquist et al 2016 defines the crystallization age of all its igneous portions the zircon from the monzonitic rocks has a higher 17o than other martian meteorites explained in part by assimilation of regolith materials enriched during surface alteration nemchin et al 2014 this record of protolith interaction with atmosphere hydrosphere during regolith formation before melting demonstrates a thin atmosphere a wet early surface environment on mars and an evolved crust likely to have contaminated younger extrusive rocks the latest events recorded when the breccia was on mars are resetting of apatite much feldspar and some zircons at 1 35 1 4 ga bellucci et al 2015 and formation of ni bearing pyrite veins during or shortly after this disturbance lorand et al 2015

geology mineralogy and geochemistry of magnetite associated au mineralization of the ultramafic basalt greenstone hosted crusader complex agnew gold camp eastern yilgarn craton western australia a late archean intrusion related au deposit abstract the crusader complex part of the agnew gold camp of the lawlers anticline of the yilgarn craton western australia is located close to or along the contact between the lawlers basalt and agnew ultramafics units au mineralization within the four orebodies that form the crusader complex is dominated by very pure au containing less than 1 wt ag with au variably associated with scheelite bi tellurides and minor chalcopyrite within a magnetite and titanite gangue assemblage hydrothermal alteration associated with this style of mineralization is characterized by increasing concentrations of mo be li sn and fe and depletions in na cu ba pb mn zn si and k relative to protolith concentrations these enrichments are more typical in orebodies associated with felsic intrusive related mineralizing systems rather than the more well known orogenic au deposits found elsewhere within the lawlers anticline e g at waroonga and within the greater yilgarn craton we propose that flexures of the contact between the lawlers basalt and agnew ultramafic units acted as conduits for au bearing felsic intrusive derived fluids and generated structural traps that enhanced fluid flow the mineralizing fluids that formed the crusader deposits were derived from the lawlers granitoid pluton that intruded into the study area enhanced fluid flow promoted interaction between hydrothermal fluids and the reactive mafic ultramafic rock sequence augmenting the amount of au that was precipitated during formation of the orebodies at crusader the magnetite dominated quartz and sulfide poor intrusion related mineralization at crusader contrasts sharply with other late archean intrusion related deposits of the yilgarn craton that are usually sulfide and or quartz rich this may in turn suggest that the crusader deposit represents a new class of under explored intrusion derived deposits possibly opening new mineral exploration opportunities for the agnew region and potentially the wider eastern goldfields superterrane enrichments in mo and sn and significant depletions in cu suggest that other parts of the lawlers batholith may also be prospective for base metal mineralization integration of stratigraphic interpretation with the identification of key structural fluid pathways and the presence of felsic intrusive bodies as presented in this study enables the delineation of the key elements that underlie mineralization at the crusader complex we propose that these key elements provide vital information for future gold exploration models that can be used within other archean terranes and within the eastern yilgarn craton in particular