a new martian meteorite from oman mineralogy petrology and shock metamorphism of olivine phyric basaltic shergottite sayh al uhaymir 150 the sayh al uhaymir sau 150 meteorite was found on a gravel plateau 43 3 km south of ghaba oman on october 8 2002 oxygen isotope 17o 2 78 18o 4 74 cre age 1 3 ma and noble gas studies confirm its martian origin sau 150 is classified as an olivine phyric basalt having a porphyritic texture with olivine macrocrysts set in a finer grained matrix of pigeonite and interstitial maskelynite with minor augite spinel ilmenite merrillite pyrrhotite pentlandite and secondary terrestrial calcite and iron oxides the bulk rock composition in particular mg 68 molar mg mg fe 100 fe mn 37 9 and na al 0 22 are characteristic of martian meteorites based on mineral compositions cooling rates determined from crystal morphology and crystal size distribution it is deduced that the parent magma formed in a steady state growth regime magma chamber that cooled at 70 365 c sau 150 is essentially identical to sau 005 094 all representing samples of the same fall that are similar to but distinct from the dag shergottites

fates of satellite ejecta in the saturn system abstract we assess the fates of ejecta from the large craters aeneas on dione and ali baba on enceladus 161 and 39 km in diameter respectively as well as that from herschel 130 km in diameter on mimas the ejecta are treated either as spalls launched from hard surfaces or as rubble launched from a weak rubble pile regolith once in orbit we consider the ejecta as massless test particles subject to the gravity of saturn and its classical satellites the great majority of escaped ejecta get swept up by the source moons the best fit to the ejecta population decay is a stretched exponential with exponent near 1 2 dobrovolskis et al icarus 188 481 505 2007 we bracket the characteristic ejecta sizes corresponding to grady kipp fragments and spalls based on this and computed impact velocities and incidence angles the resulting sesquinary craters if they exist should have diameters on the order of a few meters to a few km the observed longitude distribution of small craters on mimas along with the findings of bierhaus et al that small moons should not have a secondary crater population icarus 218 602 621 2012 suggest that the most likely place to find sesquinary craters in the saturn system is the antapex of mimas

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

mechanisms of ringwoodite formation in shocked meteorites evidence from l5 chondrite dhofar 1970 the formation of the high pressure compositional equivalents of olivine and pyroxene has been well documented within and surrounding shock induced veins in chondritic meteorites formed by crystallization from a liquid or solid state phase transformation typically polycrystalline ringwoodite grains have a narrow range of compositions that overlap with those of their olivine precursors whereas the formation of iron enriched ringwoodite has been documented from only a handful of meteorites here we report backscattered electron images quantitative wavelength dispersive spectrometry wds analyses qualitative wds elemental x ray maps and micro raman spectra that reveal the presence of fe rich ringwoodite fa44 63 as fine grained 500 nm polycrystalline rims on olivine fa24 25 wall rock and as clasts engulfed by shock melt in a previously unstudied l5 chondrite dhofar 1970 crystallization of majorite magnesiowustite in the vein interior and metastable mineral assemblages within 35 m of the vein margin attest to rapid crystallization of a superheated shock melt 2300 k from 20 25 gpa to ambient pressure and temperature the texture and composition of bright polycrystalline ringwoodite rims fa44 63 mno 0 01 0 08 wt surrounding dark polycrystalline olivine fa8 14 mno 0 56 0 65 wt implies a solid state transformation mechanism in which fe was preferentially partitioned to ringwoodite the spatial association between ringwoodite and shock melt suggests that the rapidly fluctuating thermal regimes experienced by chondritic minerals in contact with shock melt are necessary to both drive phase transformation but also to prevent back transformation

the martian surface the past four years have been particularly fruitful for martian research as the enormous volumes of data collected during the viking mission became readily available to the general science community and as reformatting of the remote sensing data into cartographic products made the data more useable the 1 5 000 000 scale map series is complete and 1 2 000 000 scale controlled mosaics of the entire planet are nearing completion in addition 1 500 000 scale mosaics have been prepared of about thirty local areas a uniform scale digital imaging data base is in preparation batson 1986 and the infrared data have been reformatted to make it more accessible to the general user martin and kieffer 1985

effects of postdepositional processing on nitrogen isotopes of nitrate in the greenland ice sheet project 2 ice core records of ice core nitrate and its isotopes hold the potential to assess past atmospheric conditions regarding nox and oxidant levels however relating such records to past atmospheric conditions requires a site specific understanding of the postdepositional processing of snow nitrate we report 15n no3 records from the greenland ice sheet project 2 gisp2 ice core over major climate transitions model calculations and comparison with records of parameters influencing uv driven postdepositional processing of snow nitrate suggest that the observed variability in gisp2 15n no3 over major climate transitions is primarily driven by changes in the degree of postdepositional loss of snow nitrate estimates of the fractional loss of snow nitrate is 16 23 in the holocene and 45 53 in the glacial period suggesting a 41 32 lower nitrate depositional flux to greenland during the glacial period relative to the holocene

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

major features of glaciochemistry over the last 110 000 years in the greenland ice sheet project 2 ice core major chemical species cl no3 so42 na nh4 k mg2 ca2 and 18o covering the last 110 000 years from the greenland ice sheet project 2 gisp2 ice core were utilized in this study in order to reconstruct the soluble chemistry of the atmosphere over greenland and interpret major climate events that have affected the region during the holocene the major chemical species and 18o do not display any significant relationship however a strong inverse correlation was found between concentrations of the major chemical species and 18o a proxy for temperature during the last glacial period suggesting that in general during periods of decreased temperature there is an increase in atmospheric chemical loading examination of changes in major chemical composition over the last 110 000 years of the gisp2 ice core reveals that during the holocene the atmosphere was acidic during inters t adials the atmosphere was neutral or alkalescent and during stadials the atmosphere was alkaline in addition the relative abundance of major chemical species varied during the holocene stadials and interstadials during the holocene nh4 and no3 are the dominant cations and anions while ca2 and so42 are the dominant cations and anions during the stadials and inters t adials this suggests that source regions or types differed between the holocene and the last glacial period in addition changes in chemical composition and changes in chemical ratios also indicate that source regions differed during the holocene stadials and interstadials twenty four previously identified dansgaard oeschger stadial interstadial events dansgaard et al 1993 were in the gisp2 chemical series the duration of the stadials is inversely correlated with variations in sea level over the last glacial period i e the more extensive the northern hemisphere ice sheet the longer the duration of the stadial there is also a close correspondence between the duration of interstadials and the timing of heinrich events massive icebergs discharged into the ocean in the gisp2 ice core long up to 2000 years warm periods follow each heinrich event suggesting perhaps that enhanced deep water circulation is re initiated following heinrich events

shock induced growth and metastability of stishovite and coesite in lithic clasts from suevite of the ries impact crater germany the microtextures of stishovite and coesite in shocked non porous lithic clasts from suevite of the ries impact structure were studied in transmitted light and under the scanning electron microscope both high pressure silica phases were identified in situ by laser raman spectroscopy they formed from silica melt as well as by solid state transformation in weakly shocked rocks stage i fine grained stishovite 1 8 m occurs in thin pseudotachylite veins of quartz rich rocks where it obviously nucleated from high pressure frictional melts generally no stishovite was found in planar deformation features pdfs within grains of rock forming quartz the single exception is a highly shocked quartz grain trapped between a pseudotachylite vein and a large ilmenite grain in which stishovite occurs within two sets of lamellae it is assumed that in this case the small stishovite grains formed by the interplay of conductive heating and shock reverberation in strongly shocked rocks stages ib iii above 30 gpa grains of former quartz typically contain abundant and variably sized stishovite 6 m embedded within a dense amorphous silica phase in the interstices between pdfs the formation of transparent diaplectic glass in adjacent domains results from the breakdown of stishovite and the transformation of the dense amorphous phase and pdfs to diaplectic glass in the solid state coesite formed during unloading occurs in two textural varieties granular micrometre sized coesite occurs embedded in silica melt glass along former fractures and grain boundaries these former high pressure melt pockets are surrounded by diaplectic glass or by domains consisting of microcrystalline coesite and earlier formed stishovite the latter is mostly replaced by amorphous silica

structures uplift and magmatism of the western myanmar arc constraints to mid cretaceous paleogene tectonic evolution of the western myanmar continental margin abstract knowledge of trans himalayan tectono magmatic evolution is critical to understanding the complex pre collisional history of southern eurasia active continental margin it has been proposed that magmatic rocks of the trans himalayan batholith extending from southern tibet to southeast asia are now exposed as the western myanmar arc and central granite belt in myanmar yet origin emplacement and relationships of the two juxtaposed belts remain poorly constrained in this study 2d seismic and drilling data for the western myanmar arc zircon u pb age and hf isotope and whole rock geochemical data for magmatic rocks from the arc have been applied our seismic profiles borehole stratigraphic sequences and zircon u pb data show that a typical arc basin system was well developed along the western myanmar continental margin the magmatic arc has experienced at least three igneous events in the mid cretaceous 110 90 ma latest cretaceous early paleocene 69 64 5 ma and eocene 53 38 ma as well as three associated uplift processes in the late cretaceous eocene and late oligocene whole rock geochemical characteristics and zircons showing variable but predominately positive e hf t values suggest a significant juvenile mantle source involving a proportion of ancient subducted sediments and juvenile crustal materials for these typical arc related magmatic rocks the identification of mid cretaceous to paleogene magmatic rocks having positive e hf t values from the western myanmar arc 1 indicates that the magmatism can be correlated with the gangdese arc within the lhasa terrane of the southern tibetan plateau 2 provides evidence for the proximal derived model that paleogene sediments in the central myanmar basin were from the western myanmar arc but were not delivered by the paleo yarlung tsangpo irrawaddy river system from the gangdese arc and 3 enables a model of eastward subduction of the neo tethyan indian oceanic crust to reflect onset of the magmatism at the mid cretaceous and a long existed back arc extension in western myanmar

mercury cratering record viewed from messenger s first flyby morphologies and size frequency distributions of impact craters on mercury imaged during messenger s first flyby elucidate the planet s geological history plains interior to the caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages smooth plains exterior to caloris exhibit a crater density 40 less than on interior plains and are thus volcanic and not caloris impact ejecta the size distribution of smooth plains craters matches that of lunar craters postdating the late heavy bombardment implying that the plains formed no earlier than 3 8 billion years ago ga at diameters less than or equal to 8 to 10 kilometers secondary impact craters on mercury are more abundant than primaries this transition diameter is much larger than that on the moon or mars a low density of craters on the peak ring basin raditladi implies that it may be younger than 1 ga

jurassic to miocene magmatism and metamorphism in the mogok metamorphic belt and the india eurasia collision in myanmar situated south of the eastern himalayan syntaxis at the western margin of the shan thai terrane the highgrade mogok metamorphic belt mmb in myanmar occupies a key position in the tectonic evolution of southeast asia the first sensitive high resolution ion microprobe u pb in zircon geochronology for the mmb shows that strongly deformed granitic orthogneisses near mandalay contain jurassic 170 ma zircons that have partly recrystallized during 43 ma high grade metamorphism a hornblende syenite from mandalay hill also contains jurassic zircons with evidence of eocene metamorphic recrystallization rimmed by thin zones of 30 9 plus or minus 0 7 ma magmatic zircon the relative abundance of jurassic zircons in these rocks is consistent with suggestions that southern eurasia had an andean type margin at that time mid cretaceous to earliest eocene 120 to 50 ma i type granitoids in the mmb myeik archipelago and western myanmar confirm that prior to the collision of india an up to 200 km wide magmatic belt extended along the eurasian margin from pakistan to sumatra metamorphic overgrowths to zircons in the orthogneiss near mandalay date a period of eocene 43 ma high grade metamorphism possibly during crustal thickening related to the initial collision between india and eurasia at 65 to 55 ma this was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 ma similar syntectonic syenites and leucogranites intruded the ailao shan red river shear belt in southern china and vietnam during the eocene oligocene to miocene and the wang chao and three pagodas faults in northern thailand that most likely link with the mmb were also active at this time the complex history of eocene to early miocene metamorphism deformation and magmatism in the mmb provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of india and resulting extrusion or rotation of indochina

rock relationships in the mogok metamorphic belt tatkon to mandalay central myanmar abstract the mogok metamorphic belt mmb over 1450 km long and up to 40 km wide consists of regionally metamorphosed rocks including kyanite and sillimanite schists and granites lying along the western margin of the shan plateau in central myanmar and continuing northwards to the eastern himalayan syntaxis exposures in quarries allow correlation of palaeozoic meta sedimentary early mesozoic meta igneous and late mesozoic intrusive rocks within a 230 km long northerly trending segment of the mmb from tatkon to kyanigan north of mandalay and with the mogok gemstone district 100 km to the northeast relationships among the metamorphic and intrusive rocks with sparse published radiometric age controls indicate at least two metamorphic events one before and one after the intrusion of late jurassic to early cretaceous calc alkaline rocks these relationships can be explained by either of two possible tectonic histories one constrained by correlation of mid permian limestones across myanmar requires early permian and early jurassic regional metamorphic events prior to an early tertiary metamorphism in the western part of but within a shan thai western myanmar block the second not compatible with a single laterally continuous permian limestone requires pre upper jurassic regional metamorphism and orogenic gold mineralization in the mergui group and western myanmar early cretaceous collision of an east facing mergui western myanmar island arc with the shan plateau and early tertiary metamorphism in the mmb related to reversal in tectonic polarity following the arc plateau collision

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust

searching for the source regions of martian meteorites using mgs tes integrating martian meteorites into the global distribution of igneous materials on mars the objective of this study was to identify and map possible source regions for all 5 known martian meteorite lithologies basalt lherzolite clinopyroxenite orthopyroxenite and dunite using data from the mars global surveyor thermal emission spectrometer mgs tes we deconvolved the tes data set using laboratory spectra of 6 martian meteorites los angeles zagami alh a77005 nakhla alh 84001 and chassigny as end members along with atmospheric and surface spectra previously derived from tes data global maps 16 pixels degree of the distribution of each meteorite end member show that meteorite like compositions are not present at or above tes detectability limits over most of the planet s dust free regions however we have confidently identified local scale 100s1000s km2 concentrations of olivine and orthopyroxene bearing materials similar to alh a77005 chassigny and alh 84001 in nili fossae in and near ganges chasma in the argyre and hellas basin rims and in eos chasma nakhla like materials are identified near the detection limit throughout the eastern valles marineris region and portions of syrtis major basaltic shergottites were not detected in any spatially coherent areas at the scale of this study martian meteorite like lithologies represent only a minor portion of the dust free surface and thus are not representative of the bulk composition of the ancient crust meteorite like spectral signatures identified above tes detectability limits in more spatially restricted areas tens of km are targets of ongoing analysis

mineralogy microtexture and composition of shock induced melt pockets in the los angeles basaltic shergottite analytical electron microscopy of shock features in the basaltic shergottite los angeles stone 1 reveals 1 shock recorded in the bulk sample and 2 localized pressure and temperature excursions that have generated melt pockets up to 4 mm in diameter bulk shock effects include microfaulting offsets 1 200 mm mosaicism deformed exsolution lamellae and planar fracturing in pyroxene undulose extinction in whitlockite mechanical twinning in titanomagnetite and ilmenite and the transformation of plagioclase to maskelynite 4 remnant reduced birefringence the pressure estimates for bulk shock are 35 40 gpa localized shock excursions have generated three types of discrete melt zones 0 07 1 3 mm to 3 0 3 5 mm apparent diameter possessing glassy to microcrystalline groundmasses these melt pockets are differentiated on the basis of size clast volume and degree of crystallization and vesiculation melt veins and melt dikelets emanate from the melt pockets up to 3 mm into the host rock but do not necessarily connect with other melt pockets the melt pockets were generated by pressure temperature excursions of 60 80 gpa and 1600 2000 c resulting in discrete melting of adjacent host rock minerals at grain boundary margins concentric zoning in the margins of clinopyroxenes coincides with a progressive reduction in birefringence as melt pockets are approached this suggests that the shock excursions were focused as point sources in the wake of the shock front that induced bulk damage

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

formation of melt droplets melt fragments and accretionary impact lapilli during a hypervelocity impact abstract we present a model that describes the formation of melt droplets melt fragments and accretionary impact lapilli during a hypervelocity impact using the isale hydrocode coupled to the aneos equation of state for silica we create high resolution two dimensional impact models to track the motion of impact ejecta we then estimate the size of the ejecta products using simple analytical expressions and information derived from our hydrocode models ultimately our model makes predictions of how the size of the ejecta products depends on impactor size impact velocity and ejection velocity in general we find that larger impactor sizes result in larger ejecta products and higher ejection velocities result in smaller ejecta product sizes we find that a 10 km diameter impactor striking at a velocity of 20 km s creates millimeter scale melt droplets comparable to the melt droplets found in the chicxulub ejecta curtain layer our model also predicts that melt droplets melt fragments and accretionary impact lapilli should be found together in well preserved ejecta curtain layers and that all three ejecta products can form even on airless bodies that lack significant volatile content this prediction agrees with observations of ejecta from the sudbury and chicxulub impacts as well as the presence of accretionary impact lapilli in lunar breccia

crustal lithospheric structure and continental extrusion of tibet crustal shortening and thickening to c 70 85 km in the tibetan plateau occurred both before and mainly after the c 50 ma india asia collision potassic ultrapotassic shoshonitic and adakitic lavas erupted across the qiangtang c 50 29 ma and lhasa blocks c 30 10 ma indicate a hot mantle thick crust and eclogitic root during that period the progressive northward underthrusting of cold indian mantle lithosphere since collision shut off the source in the lhasa block at c 10 ma late miocene pleistocene shoshonitic volcanic rocks in northern tibet require hot mantle we review the major tectonic processes proposed for tibet including rigid block continuum and crustal flow as well as the geological history of the major strike slip faults we examine controversies concerning the cumulative geological offsets and the discrepancies between geological quaternary and geodetic slip rates low present day slip rates measured from global positioning system and insar along the karakoram and altyn tagh faults in addition to slow long term geological rates can only account for limited eastward extrusion of tibet since mid miocene time we conclude that despite being prominent geomorphological features sometimes with wide mylonite zones the faults cut earlier formed metamorphic and igneous rocks and show limited offsets concentrated strain at the surface is dissipated deeper into wide ductile shear zones

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

timing of syenite charnockite magmatism and ruby and sapphire metamorphism in the mogok valley region myanmar we thank the oxford burma aung san suu kyi trust for funding research and fieldwork visits to myanmarfor ms ng and lr geochronology was funded by ucsb and nsf grants ear 1348003and ear 1551054

formation of a martian pyroxenite a comparative study of the nakhlite meteorites and theo s flow the unusual composition of the nakhlites a group of pyroxenitic martian meteorites with young ages presents an opportunity to learn about nonbasaltic magmatic activity on another planet however the limited number of these meteorites makes unraveling their history difficult a promising terrestrial analog for the formation of the nakhlites is theo s flow in ontario canada this atypical 120 m thick flow differentiated in place forming distinct layered lithologies of peridotite pyroxenite and gabbro theo s pyroxenite and the nakhlites share strikingly similar petrographies with concentrated euhedral to subhedral augite grains set in a plagioclase rich matrix these two suites of rocks also share specific petrologic features mineral and whole rock compositional features and size and spatial distributions of cumulus grains the numerous similarities suggest that the nakhlites formed by a similar mechanism in a surface lava flow or shallow intrusion their formation could have involved settling of crystals in a phenocryst laden flow or in situ nucleation and growth of pyroxenes in an ultramafic lava flow the latter case is more likely and requires steady state nucleation and growth of clusters of pyroxene grains and olivine in the nakhlites circulating in a strongly convecting melt pool followed by settling and continued growth in a thickening cumulate pile trapped pockets of intercumulus liquid in the pile gradually evolved finally growing fe enriched rims on cumulus grains with sufficient evolution the melt reached plagioclase supersaturation causing rapid growth of plagioclase sprays and late stage mesostasis growth

neo tethyan magmatism and metallogeny in myanmar an andean analogue abstract plate margin tectonism magmatic and hydrothermal processes and the genesis of mineral deposits are intricately linked in myanmar two near parallel magmatic belts that together contain a significant proportion of that country s mineral wealth have contrasting metallogenic endowments the mogok mandalay mergui belt hosts crustal melt s type granites with significant tin tungsten mineralization while the wuntho popa arc comprises i type granites and granodiorites with copper gold mineralization the spatial juxtaposition of the two belts and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the south american cordillera recent u pb age dating has shown the potential for the two belts to be near contemporary from the late cretaceous to eocene here we investigate whether an andean type setting during subduction of neo tethys could explain the observed magmatism and mineralization within these two belts

modeled variations of precipitation over the greenland ice sheet abstract a parameterization of the synoptic activity at 500 hpa and a simple orographic scheme are used to model the spatial and temporal variations of precipitation over the greenland ice sheet for 1963 88 from analyzed geopotential height fields produced by the national meteorological center nmc model coefficients are fitted to observed accumulation data primarily from the summit area of the ice sheet all major spatial characteristics of the observed accumulation distribution are reproduced apart from the orographic accumulation maximum over the northwestern coastal slopes the modeled time averaged total precipitation amount over greenland is within the range of values determined by other investigators from surface based observations a realistic degree of interannual variability in precipitation is also simulated a downward trend in simulated ice sheet precipitation over the 26 years is found this is supported by a number of lines of evidence it matches the accumulation trends during this peri

paleomineralogy of the hadean eon a preliminary species list the hadean eon encompassing earth9s first 550 million years was a time of significant planetary evolution nevertheless prebiotic earth9s near surface environment may have held no more than approximately 420 different rock forming or accessory mineral species that were widely distributed and or volumetrically significant this relative hadean mineralogical parsimony is a consequence of the limited modes of mineral paragenesis prior to 4 ga compared to the last 3 0 billion years dominant hadean eon mineralizing processes include the evolution of a diverse suite of intrusive and extrusive igneous lithologies hydrothermal alteration over a wide temperature range notably serpentinization authigenesis in marine sediments diagenesis and low grade metamorphism in near surface environments and impact related processes including shock mineralization creation of marginal hydrothermal zones and excavation of deep metamorphosed terrains on the other hand the hadean eon may have been notably lacking in mineralization generated by plate tectonic processes such as subduction zone volcanism and associated fluid rock interactions which result in massive sulfide deposition convergent boundary orogenesis and consequent extensive granitoid rooted continental landmasses and the selection and concentration of incompatible elements in complex pegmatites with hundreds of accompanying minerals the dramatic mineralogical consequences of life are reflected in the absence of hadean biomineralization for example the lack of extensive carbonate deposits and the associated restricted development of skarn and cave minerals prior to 4 ga most importantly it was not until after the establishment via photosynthesis of significant near surface redox gradients that supergene alteration redox controlled ore deposition and subaerial weathering in an oxidizing environment could diversify earth9s near surface mineralogy these post hadean processes may be responsible for over 4000 of the more than 4800 approved mineral species any scenario for life9s origins that invokes minerals as agents of molecular synthesis selection protection or organization must take into account the limited mineralogical repertoire of the time

a preliminary stable isotope study on mogok ruby myanmar the primary occurrence of ruby in the mogok area northern myanmar is exclusively found in marble along with spinel forsterite bearing marble and phlogopite graphite marble these marble units are enclosed within banded biotite garnet sillimanite oligoclase gneisses samples of these marbles collected for c o stable isotope analysis show two trends of 13c 18o variation resulting most likely from fluid rock interactions ruby bearing marble and phlogopite graphite marble followa trend with coupled c o depletion whereas spinel forsterite bearing marble follows a 18o depletion trend with relatively constant 13c values ruby formation might have resulted from co2 rich fluid rock interaction while spinel forsterite bearing marble was genetically related to co2 poor fluid rock interaction both fluids may have arisen from external sources based on graphite raman spectral thermometry the estimated temperature for phlogopite graphite marble and probably ruby bearing marble was lower than 607 c and for spinel forsterite bearing marble lower than 710 c contrasting c o diffusion between graphite ruby spinel forsterite and calcite local variations of isotopic compositions of newly formed minerals as a result of non pervasive fluid infiltration and open system isotopic disturbance during cooling may have affected c o isotopic fractionations between minerals the estimated high formation temperatures for ruby and spinel forsterite imply that the parental fluidsmay have been related to nearby igneous intrusions and or metamorphic processes whether these two types of fluid were genetically related is unclear based on the present data

shock metamorphism of elephant moraine a79001 implications for olivine ringwoodite transformation and the complex thermal history of heavily shocked martian meteorites abstract lithology a of martian meteorite elephant moraine eet a79001 contains fragments entrained within a 100 m thick shear induced shock vein these fragments the shock vein matrix and walls of olivine along the vein as well as shock deformation and transformation in rock forming minerals in the bulk rock were investigated using scanning electron microscopy the electron microprobe and raman spectroscopy the presence of ringwoodite the spinel structured high pressure mg fe 2 sio 4 polymorph has been confirmed in eeta79001 for the first time ringwoodite occurs within and around the shock vein exhibiting granular and lamellar textures in both textures ringwoodite consists of 500 nm size distinct grains ringwoodite lamellae are 115 nm to 1 3 m wide planar fractures in olivine provided sites for heterogeneous nucleation of ringwoodite analyses performed on the largest grains 1 m show that ringwoodite is consistently higher in iron fa 27 4 32 4 relative to surrounding olivine fa 25 1 267 7 implying that there was fe mg exchange during their transformation and therefore their growth was diffusion controlled in the shock environment diffusion takes place dynamically i e with concurrent deformation and grain size reduction this results in enhanced diffusion rates 10 8 m 2 s over nm m distances shock deformation in host rock minerals including strong mosaicism pervasive fracturing polysynthetic twinning pyroxene only extensive shock melting local transformation of olivine to ringwoodite and complete transformation of plagioclase to maskelynite in the bulk rock indicate that eeta79001 was strongly shocked the short shock duration 0 01 s combined with a complex thermal history resulted in crystallization of the 100 m thick shock vein in eeta79001 during the pressure release and partial back transformation of ringwoodite to olivine based on the pressure stabilities of clinopyroxene ringwoodite crystallization at the shock vein margin began at 18 gpa olivine and clinopyroxene crystallized at

the self secondary crater population of the hokusai crater on mercury whether or not self secondaries dominate small crater populations on continuous ejecta deposits and floors of fresh impact craters has long been a controversy this issue potentially affects the age determination technique using crater statistics here the self secondary crater population on the continuous ejecta deposits of the hokusai crater on mercury is unambiguously recognized superposition relationships show that this population was emplaced after both the ballistic sedimentation of excavation flows and the subsequent veneering of impact melt but it predated the settlement and solidification of melt pools on the crater floor fragments that formed self secondaries were launched via impact spallation with large angles complex craters on the moon mercury and mars probably all have formed self secondaries populations dating young craters using crater statistics on their continuous ejecta deposits can be misleading impact melt pools are less affected by self secondaries overprint by subsequent crater populations with time reduces the predominance of self secondaries

rummaging through earth s attic for remains of ancient life abstract we explore the likelihood that early remains of earth mars and venus have been preserved on the moon in high enough concentrations to motivate a search mission during the late heavy bombardment the inner planets experienced frequent large impacts material ejected by these impacts near the escape velocity would have had the potential to land and be preserved on the surface of the moon such ejecta could yield information on the geochemical and biological state of early earth mars and venus to determine whether the moon has preserved enough ejecta to justify a search mission we calculate the amount of terran material incident on the moon over its history by considering the distribution of ejecta launched from the earth by large impacts in addition we make analogous estimates for mars and venus we find for a well mixed regolith that the median surface abundance of terran material is roughly 7 ppm corresponding to a mass of approximately 20 000 kg of terran material over a 10 10 square km area over the same area the amount of material transferred from venus is 1 30 kg and material from mars as much as 180 kg given that the amount of terran material is substantial we estimate the fraction of this material surviving impact with intact geochemical and biological tracers

nitrate in greenland and antarctic ice cores a detailed description of post depositional processes a compilation of nitrate no 3 data from greenland has shown that recent no 3 concentrations reveal a temperature dependence similar to that seen in antarctica except for sites with very low accumulation rates lower temperatures tend to lead to higher no 3 concentrations preserved in the ice accumulation rate which is closely linked to temperature might influence the concentrations preserved in snow as well but its effect cannot be separated from the temperature imprint processes involved in no 3 deposition are discussed and shown to be temperature and or accumulation rate dependent apart from scavenging of nitric acid hno 3 during formation of precipitation uptake of hno 3 onto the ice crystal s surface during and after precipitation seems to contribute further to the no 3 concentrations found in surface snow post depositional loss of no 3 from the top snow layers is caused by release of hno 3 and by photolysis of no 3 it is suggested that photolysis accounts for considerable losses at sites with very low accumulation rates depending on the site characteristic and given that the temperature and accumulation rate dependence is quantified it should be possible to infer changes in atmospheric hno 3 concentrations

recent aqueous environments in martian impact craters an astrobiological perspective the discovery of gullies and debris aprons raises the question of the existence of aqueous environments on mars in recent geological times and its astrobiological implications three cases of such environments are surveyed at moc high resolution in the e gorgonum chaos and newton and hale craters the regional setting of these craters suggests that the mechanisms of aquifer destabilization flow discharge and gully formation in these three cases result from local geological triggers that can include impact cratering and tectonic processes rather than climate or insolation factor we take as a working hypothesis that microbial life appeared on mars in ancient geological times probably in a geothermal environment but potentially evolving via infrared detection systems to give photosynthetic communities under the selective pressure of energetic solar radiation we hypothesize that some microbial communities could have survived underground in either dormant or active state or that their biomolecules could be preserved either frozen or desiccated in the subsurface beneath the upper oxidized zone we assess the known environmental constraints for life and what type of potential habitats are provided in these three craters by aquifer discharges using comparison with terrestrial analogues and their associated microbial communities these environments include 1 the release of water on a dry crater floor in e gorgonum and the possibility for microorganisms and preserved biomolecules to be flushed out and mixed in with the sediment exposed at the surface 2 the evidence of a recent lacustrine episode in the newton crater with analogy to antarctic dry valley lakes 3 the exposure on the floor of hale crater of material from a regional subsurface that is likely to have retained traces of one of the oldest martian bodies of water recognized to date parker et al 2000 in the argyre basin we show how the water in argyre 3 8 billion years ago gya was likely to have been alterated by hydrothermal processes and how the subsequent formation of the 150 km hale crater on the northern ring of argyre generated hydrothermal pumping this accounts for the anomalously high location of the springs on the crater crests today with respect to the rest of the regional subsurface distribution finally we envision current impact cratering as a factor for destabilizing aquifers on mars today thus creating new environments we analyze the implications of impacts for two geological types of rock units that could harbor traces of life as a result we compare the potential of astrobiological exploration of crater floors rims and ejecta on future missions to mars

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

ejecta blocks on 243 ida and on other asteroids abstract seventeen positive relief features 45 150 m across are identified as probable blocks in galileo high resolution images of ida their presence provides direct evidence for regolith retention on asteroids the spatial distribution maximum size and integrated volume of the blocks are consistent with those of blocks associated with craters on the earth the moon phobos and deimos the concordance suggests that the features are impact ejecta fragments and that cratering mechanics on ida an object of average diameter 32 km are similar to those applying on previously studied rocky bodies the blocks that lie within or near the rims of craters lascaux and mammoth were likely mobilized in the low velocity tail portion of the excavation flow that formed those craters a few blocks located near smaller craters may have migrated some distance away from their source possibly by impact induced spallation hopping rolling and or sliding some blocks on ida could be surviving fragments from the koronis parent body accreted after its breakup the lifetime of 102 m sized boulders against collisional disruption is estimated to be in the 108 109year range consistent with ages considered for the largest and oldest craters on ida extrapolation of successful ejecta scaling laws to other asteroids suggests that blocks 15 and 70 m across could be present on dactyl and gaspra respectively in both cases too small to be identified in available galileo images blocks 100 m in size could be present on 433 eros and km sized megablocks on 4 vesta

origin of the charnockites of the louis lake batholith wind river range wyoming the 2 63 ga louis lake batholith a calc alkalic pluton exposed opxand fayalite fay bearing felsic igneous rocks inin wind river range of western wyoming consists of minor diorite clude opdalite opx granodiorite enderbite opx tonalquartz diorite granodiorite and granite at shallow structural levels ite and mangerite opx monzonite le maitre et al the batholith is pyroxene free but at deeper levels all units of the 1989 many of these rock names are not commonly batholith contain pyroxenes on its northern margin the batholith used the term charnockite sensu lato is typically applied was emplaced at p 5 6 kbar t 775 800 c fo2 at to any opx bearing granitoid regardless of its bulk fmq fayalite magnetite quartz 1 5 to fmq 1 8 and composition for example the charnockite suite of south ah2o 0 1 along the southern margin of the batholith the india includes enderbites opdalites and charnockites emplacement pressure was 3 kbar the batholith includes two howie 1955 the nigerian suite includes charnockite compositional series the peraluminous high ree series is rich in and opdalite olarewaju 1987 and that of lofoten is k2o and displays larger feo feo mgo the metaluminous associated with mangerites malm ormaasen 1978 low ree series has less k2o and smaller feo feo mgo because the terms enderbite and opdalite are so rarely in the boulder canyon area most of the rocks belong to the lowused in this paper we use the term charnockite for all ree series the nd pb and sr initial isotopic compositions of opx bearing granitic rocks where it is important to both series vary and do not correlate with sio2 abundance relatively describe a specific rock type we use opx as a varietal constant fe mg ratios over a wide range of sio2 and the large modifer to the rock name e g opx granodiorite instead variation in initial isotopic compositions indicate that the sources of opdalite for the louis lake batholith include older wyoming province crustin the 1980s workers in southern india recognized and mantle derived mafic melts the calc alkalic nature of the areas where biotite bearing granitic gneiss had been boulder canyon charnockites indicates that there is no special cconverted to pyroxene bearing gneiss along fluid pathtype magma instead charnockites will form in any rock type if ways janardhan et al 1982 friend 1985 this led to the water activity is low enough the term charnockitization srikantappa et al 1985 and the concept that charnockite is a metamorphic rather than an igneous rock as a result charnockite has been used incorrectly by some workers as a synonym for

the closure of palaeo tethys in eastern myanmar and northern thailand new insights from zircon u pb and hf isotope data abstract two of the major granite belts of southeast asia are the main range and eastern province together these are interpreted to represent the magmatic expression of the closure of palaeo tethys during late palaeozoic to early mesozoic times recent geochronological and geochemical work has better delineated these belts within peninsular malaysia thereby providing important constraints on the timing of palaeo tethys suturing however the northern extension of this palaeo tethyan suture is less well understood here we present new ion microprobe u pb zircon age data from northern thailand and eastern myanmar measured ages of 219 and 220 ma from the kyaing tong granite imply northern extension of the main range province into eastern myanmar the tachileik granite in far eastern myanmar yields an age of 266 ma consistent with published eastern province ages and this therefore constrains the northern extension of the palaeo tethys suture in eastern myanmar we further discuss how this suture may extend northwards into yunnan a late cretaceous age 70 ma measured in thailand represents later magmatic activity and is similar to published magmatic ages from central myanmar this younger magmatism is interpreted to be related to the subduction of neo tethys prior to india asia collision further we present new laser ablation zircon hf isotope data from eastern myanmar which suggest that palaeoproterozoic crust underlies both the main range and eastern province granites our ehf model age of ca 1750 ma from sibumasu the basement underlying eastern myanmar lies within the range of other model ages reported thus far for the baoshan block north in yunnan interpreted by some to be the northern extension of sibumasu

charnockites and the genesis of gem minerals abstract charnockitic rocks that occur in many proterozoic high grade metamorphic terrains correspond to regions of crustal thickening and are often associated with continental collision processes the charnockites of the highland group of sri lanka represent this type and show genetic relationships to the central high land group geochemical investigations indicate that charnockites play a key role in the formation of the gem minerals it seems probable that the contact metamorphic effects of charnockitic plutonic activity in the highly aluminous metasediments such as those found in sri lanka result in the formation of an assemblage of gem minerals such as sapphirine cordierite spinel ruby and corundum the pegmatites with which gem minerals like beryl chrysoberyl and tourmaline are associated can also be considered as being derived from a charnockitic parent

ejection of rock fragments from planetary bodies the recent discovery of alha81005 a small meteorite that undoubtedly came from the moon has raised questions about how an intact rock fragment could survive acceleration to planetary escape velocities this acceleration could only have been produced by a large impact on the lunar surface a small amount of material 0 005 to 0 02 projectile volume may be ejected from an impact crater at speeds exceeding lunar escape velocity without suffering petrographically detectable shock damage the ejected material is protected by stress wave interference close to the free surface the existence and size of this zone depend upon parameters such as the rise time of the stress pulse produced by an impact the fragment size is a function of ejection velocity the lunar meteorite was ejected during an impact event that produced a crater at least 3 6 km in diameter other meteorites may have originated in a similar way

mac88105 a regolith breccia from the lunar highlands mineralogical petrological and geochemical studies abstract the new large lunar meteorite mac88105 is a dense breccia with lithic and mineral clasts and fragments set into a welded matrix it is a regolith breccia which shows some recrystallization and evidence for a late shock event during which anorthositic glass veins were formed shock effects most probably due to the impact ejection from the moon are present throughout the sample and require a shock pressure of about 25 30 gpa in agreement with observations made on other lunar meteorites some components of mac88105 have been subjected to a shock pressure of about 40 45 gpa as evident from melt pockets in a clast the population of lithic clasts in mac88105 is similar to other lunar highland breccias vitric breccias are more abundant than granulitic breccias and plutonic rock fragments the presence of devitrified glass spheres and shards supports a regolith origin most common are metameltbreccias consisting of abundant anorthitic plagioclase clasts and a dense fine grained matrix some fine grained hornfelsic to granulitic metabreccias are also present lithic clast compositions are predominantly anorthositic noritic or noritic anorthositic and anorthositic troctolitic spinel bearing rocks are present but do not belong to the spinel troctolite group a spinel bearing clast in mac88105 consists of anorthite pigeonite spinel and indicates a different heritage possibly similar to spinel cataclasites described from apollo 17 the pyroxenes in mac88105 have somewhat unusual compositions orthopyroxenes and augites appear to be rare most lithologies breccias and igneous rocks contain solely pigeonite we have found one igneous mafic rock a gabbro which has a low mg number and is possibly of mare origin a metal grain of a composition similar to metal in h chondrites supports the interpretation of mac88105 as a regolith breccia the bulk composition of mac88105 is similar to the other lunar highland meteorites the ree contents are slightly higher than for the other anorthositic meteorites with a smaller positive eu anomaly this is in agreement with a possible kreep contribution possibly introduced from glasses macs 8105 is a mixture of rocks with a predominant contribution from the anorthosite suite and small admixtures from other rock types mare basalt mg suite which becomes obvious in plots of molar mg or sm content vs the ti sm ratio the siderophile element abundances in mac88105 are similar to other highland meteorites and show the characteristic co excess and a au ir ratio similar to the other anorthositic meteorites and lower than the hyperchondritic ratio in apollo 16 rocks thus support the notion that the lunar meteorites are a more representative sample of the lunar highlands than the apollo samples the chemistry and mineralogy of mac88105 is different from that of the other lunar meteorites and suggests a different source which is supported by cosmic ray and noble gas data at this time it seems likely that about four individual impact events have been responsible for delivering the seven highland meteorites mac88105 and other lunar meteorites are important as they are probably random samples from the lunar surface and may thus be more representative than the apollo and luna rocks which come from only a small area of the moon

a laser probe 40ar 39ar investigation of poikilitic shergottite nwa 4797 implications for the timing of shock metamorphism spatially resolved argon isotope measurements have been performed on neutron irradiated samples of nw africa nwa 4797 shock heating of nwa 4797 completely melted and vesiculated precursor igneous plagioclase which cooled to an assemblage of plagioclase crystals with interstitial glasses of variable composition ca k ratios using a focused ultraviolet laser beam is has been possible to distinguish between argon isotopic signatures from groundmass minerals igneous olivine pyroxene plagioclase and a shock vein this study focuses on the potential for this meteorite to shed light on shock ages of shergottites apparent 40 ar 39 ar ages of groundmass minerals show that there are large amounts of excess argon in this phase yielding a wide range of calculated ages from 690 30 ma to several apparent ages older than 4 5 ga a traverse of laser probe extractions across the 1 mm diameter shock vein in nwa 4797 yielded apparent 40 ar 39 ar ages younger than the groundmass a signature of the martian atmosphere identified by 40 ar 36 ar ratios of 1600 1900 was not found in the nwa 4797 shock vein this is distinct from other shergottites where the products of shock melting contain a nearly pure sample of martian atmosphere we attribute this to a distinct formation mechanism and hence gas trapping mechanism of the nwa 4797 shock vein we undertook 44 analyses of plagioclase areas identified by sem analysis ages ranged from 45 27 to 3771 109 ma and yield an average age of 375 77 ma considerably younger than ages obtained in this study from either the groundmass or the shock vein a plot of age v 37 ar 39 ar for plagioclase showed a continuum of ages from the oldest to youngest ages measured older ages are correlated with higher ca k ratios of plagioclase indicating contamination from groundmass minerals rich in excess argon the youngest ages correlate to plagioclase extractions with the lowest ca k ratios interpreted to have crystallized from a nearly pure plagioclase melt with contributions from a k rich mesostasis we see no evidence for multiple shock events in nwa 4797 rather we favour the interpretation that the cosmic ray exposure cre age of 3 0 0 5 ma obtained on nwa 4797 in this study using cosmogenic 38 ar approximates the timing of shock melting in this meteorite

shock conditions recorded in nwa 8159 martian augite basalt with implications for the impact cratering history on mars nwa 8159 is an augite rich martian basalt formed by cooling of a relatively evolved ca rich ti poor and lree depleted lava under relatively oxidizing conditions during the early amazonian in addition to its distinct igneous petrogenesis and high fo 2 nwa 8159 is also set apart from most martian shergottites with respect to the low degree of shock metamorphism required to preserve crystalline igneous plagioclase an 50 65 in this study mineral transformations within and adjacent to shock veins in nwa 8159 were investigated using scanning electron microscopy raman spectroscopy and transmission electron microscopy to better constrain the unusal shock history of this meteorite the transformation of olivine to ahrensite fe ringwoodite along shock vein margins and tissintite and coesiteformed from igneous mineral labradorite and silica grains entrained as clasts within shock veins has been documented in this study we report on a previously unidentified mineral assemblage of ca na majoritic garnet sodic clinopyroxene and stishovite crystallized from shock melt this mineral assemblage indicates a crystallization pressure of approximately 16 gpa which is within the range of previous shock pressure estimates for this meteorite 15 23 gpa the presence of a majoritic garnet bearing assemblage throughout veins up to 0 6 mm wide indicates that the sample remained at high pressure throughout the melt vein quench based on thermal models the sample must have remained at high pressure for 100 ms this shock duration is an order of magnitude longer than those experienced by more highly shocked shergottites such as tissint or zagami 30 gpa 10 20 ms and would seem to imply a relatively large impact event recent numerical models demonstrate that a range of shock pressures and durations are realized by rocks within the ejected spall zone of a hypervelocity impact the shock conditions experienced by nwa 8159 therefore do not require an impact event distinct from other shergottites rather our findings suggest that this meteorite originated from near the martian surface at the edge of the impact site the shock history of nwa 8159 provides a picture of mars consistent with that derived from remote observation that of a random cratering process that samples a geologically long lived and complex planet

dynamic tensile strength of lunar rock types the dynamic tensile strengths of four rocks have been determined a flat plate impact experiment is used to generate 1 s duration tensile stress pulses in rock samples by superposing rarefaction waves to induce fracture a gabbroic anorthosite and a basalt were selected because they are the same rock types as occur on the lunar highlands and mare respectively although these have dynamic tensile strengths which lie within the ranges 153 174 mpa and 157 179 mpa whereas arkansas novaculite and westerly granite exhibit dynamic tensile strengths of 67 88 mpa and 95 116 mpa respectively the effect of chemical weathering and other factors which may affect application of the present results to the moon have not been explicitly studied the reported tensile strengths are based on a series of experiments on each rock where determination of incipient spallation is made by terminal microscopic examination these data are generally consistent with previous determinations at least one of which was for a significantly chemically altered hydroxylated but physically coherent rock the tensile failure data do not bear a simple relation to compressive results and imply that any modeling involving rock fracture consider the tensile strength of igneous rocks under impulse loads distinct from the values for static tensile strength generally the dynamic tensile strengths of nonporous igneous rocks range from 100 to 180 mpa with the more basic and even amphibole bearing samples yielding the higher values

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

isotopic view on nitrate loss in antarctic surface snow 1 massive post depositional processes alter the nitrate concentration in polar firn where the annual snow accumulation is low this hinders a direct atmospheric interpretation of the ice core nitrate record fractionation of nitrate isotopes during post depositional nitrate loss may allow estimating the amount of nitrate loss in the past we measured 15 n of nitrate in two antarctic surface cores from the dome c area in concert with the known concentration decrease with depth we observe an increase in the isotopic signature assuming a rayleigh type process we find an isotope effect of e 54 o we measured the fractionation factor for photolysis in the laboratory and obtained e 11 7 1 4 o as the observed fractionation factor in the fim is much lower this rules out that photolysis in the surface snow is the main process leading to the dramatic nitrate loss in the top centimeters of the firn citation blunier t g l floch h w jacobi and e quansah 2005 isotopic view on nitrate loss in antarctic surface snow

localized shock melting in lherzolitic shergottite northwest africa 1950 comparison with allan hills 77005 the lherzolitic martian meteorite northwest africa nwa 1950 consists of two distinct zones 1 low ca pyroxene poikilically enclosing cumulate olivine fo70 75 and chromite and 2 areas interstitial to the oikocrysts comprised of maskelynite low and high ca pyroxene cumulate olivine fo68 71 and chromite shock metamorphic effects most likely associated with ejection from the martian subsurface by large scale impact include mechanical deformation of host rock olivine and pyroxene transformation of plagioclase to maskelynite and localized melting pockets and veins these shock effects indicate that nwa 1950 experienced an equilibration shock pressure of 35 45 gpa large millimeter size melt pockets have crystallized magnesian olivine fo78 87 and chromite embedded in an fe rich al poor basaltic to picro basaltic glass within the melt pockets strong thermal gradients minimum 1 c m existed at the onset of crystallization giving rise to a heterogeneous distribution of nucleation sites resulting in gradational textures of olivine and chromite dendritic and skeletal olivine crystallized in the melt pocket center has a nucleation density 1 0 x 10 3 crystals mm 2 that is two orders of magnitude lower than olivine euhedra near the melt margin 1 6 x 10 5 crystals mm 2 based on petrography and minor element abundances melt pocket formation occurred by in situ melting of host rock constituents by shock as opposed to melt injected into the lherzolitic target despite a common origin nwa 1950 is shocked to a lesser extent compared to allan hills alh 77005 45 55 gpa assuming ejection in a single shock event by spallation this places nwa 1950 near to alh 77005 but at a shallower depth within the martian subsurface extensive shock melt networks the interconnectivity between melt pockets and the ubiquitous presence of highly vesiculated plagioclase glass in alh 77005 suggests that this meteorite may be transitional between discreet shock melting and bulk rock melting

isotopic and petrographic evidence for young martian basalts radiometric age data for shergottites yield ages of 4 0 ga and 180 575 ma the interpretation of these ages has been and remains a subject of debate here we present new 39 ar 40 ar laser probe data on lherzolitic shergottites allan hills alh 77005 and northwest africa nwa 1950 these two meteorites are genetically related but display very different degrees of shock damage on a plot of 40 ar 36 ar versus 39 ar 36 ar the more strongly shocked alh 77005 45 55 gpa does not yield an array of values indicating an isochron but the data are highly scattered with the shock melts yielding 40 ar 36 ar ratios of 1600 2026 apparent ages calculated from these extractions range from 374 8183 ma with 50 of the data particularly from the shock melts yielding impossibly old ages 4 567 ga on the same plot extractions from igneous minerals in the less shocked nwa 1950 30 44 gpa yield a fitted age of 382 36 ma argon extractions from the shock melts are well distinguished from minerals with the melts exhibiting the highest 40 ar 36 ar ratios 1260 1488 and the oldest apparent ages laser step heating was also performed on maskelynite separates from nwa 1950 yielding ages of 1000 ma at the lowest release temperatures and ages of 360 and 362 ma at higher temperature steps stepped heating data from previous studies have yielded ages of 500 and 700 ma to 1 7 ga for alh 77005 maskelynite separates if the ages obtained from igneous minerals represent undegassed argon from an ancient 4 0 ga rock then the ages are expected to anticorrelate with the degree of shock heating the data do not support this inference our data support young crystallization ages for minerals and martian atmosphere as the origin of excess 40 ar in the shock melts the shock features of shergottites are also reviewed in the context of what is known of the geologic history of the martian surface through remote observation the oldest most heavily cratered surfaces of mars are thought to be 4 0 ga we contend that ancient rocks from mars noachian 3 5 ga are likely to record multiple impact events reflecting megaregolith formation and the cumulative effects of erosion and aqueous alteration occurring during or since that era young rocks late amazonian 0 6 ga should record a relatively simple history of emplacement and ejection from the near surface we show that although shergottites are strongly shocked they are relatively pristine crystalline igneous rocks and not pervasively altered breccias the petrography of shergottites is at odds with an ancient age interpretation a model in which young coherent rocks are preferentially sampled by hypervelocity impact because of material strength is considered highly plausible

biomass burning recorded in the gisp2 ice core a record from eastern canada combustion byproducts from biomass burning are preserved in annually stratified layers in the greenland ice sheet electrical conductivity ecm and ammonium records from the gisp2 ice core in central greenland have been used to develop a 6000 year record of biomass burning although there is some uncer tainty regarding the source area for the combustion byproducts it is likely that the majority of the material originates in eastern canada time periods of high biomass burning activity occurred in 0 150 bp 350 750 bp and 5000 to 6000 bp the period 1150 3250 bp is characterized by moderately elevated levels of biomass burning activity these periods are associated with drier conditions the 5000 to 6000 bp period of high biomass burning activity may also be related to forest successional sequences following the removal of the laurentide ice sheet this paper explains how ice cores can be used to develop records of biomass burning and offers suggestions for future studies

understanding the textures and origin of shock melt pockets in martian meteorites from petrographic studies comparisons with terrestrial mantle xenoliths and experimental studies we present a textural comparison of localized shock melt pockets in martian meteorites and glass pockets in terrestrial mantle derived peridotites specific textures such as the development of sieve texture on spinel and pyroxene and melt migration and reaction with the host rock are identical between these two apparently disparate sample sets based on petrographic and compositional observations it is concluded that void collapse variable shock impedance is able to account for the occurrence of pre terrestrial sulfate bearing secondary minerals in the melts high gas emplacement efficiencies and s al ca and na enrichments and fe and mg depletion of shock melt compositions compared to the host rock previously used as arguments against such a formation mechanism recent experimental studies of xenoliths are also reviewed to show how these data further our understanding of texture development and can be used to shed light on the petrogenesis of shock melts in martian meteorites

meteorite and asteroid reflectance spectroscopy clues to early solar system processes although earth has a magnetic shield that protects it from energetic ions and a cushioning atmosphere that catches the tons of small particles i mm that bombard it daily solid material from extraterrestrial sources nevertheless reaches the surface of earth many times a year dodd 1 98 1 when the largest of these bodies impact the surface with great velocity they release immense energy usually form a crater and often disrupt the terrestrial biosphere fortunately such events occur relatively infrequently although individual impacts are currently unpredictable beyond a statistical accounting shoemaker et al 1979 grieve 1 982 cosmic material between the size of small dust particles and the larger crater forming bodies is slowed by the terrestrial atmosphere upon entry the outermost portion of these objects is melted and ablated during passage forming a fusion crust which protects the interior and they land

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

relationship of e type apollo asteroid 3103 1982 bb to the enstatite achondrite meteorites and the hungaria asteroids visible and near infrared observations confirm that apollo asteroid 3103 1982 bb has a reflectance spectrum consistent with its previous assignment to taxonomic type e it has been generally believed that the e type asteroids are analogous and perhaps even genetically related to the enstatite achondrite meteorites aubrites correlated variations of previously published visible and thermal infrared lightcurves and the lack of rotational color variations in the present data indicate that this is an elongated object with no substantial surface albedo variations apollo asteroid 3103 1982 bb is presently in an orbital resonance 3 5 with earth and appears to be a relatively long lived member of the earthapproaching population its orbit is consistent with both the fall dates and long cosmic ray exposure ages of the aubrites combined with the rarity of e type asteroids in the near earth asteroid population this indicates that 3103 1982 bb is probably either a major or the primary immediate source body of the aubrites the aphelion location and the mineralogy of 3103 1982 bb indicate that it was most probably derived from the hungaria region at the innermost edge 1 9 au of the asteroid belt although the exact dynamical mechanism for producing its present orbit is not clear these results represent the first plausible direct link of a set of meteorites aubrites or enstatite achondrites back to a particular source region in the asteroid belt this link allows the composition of the solar nebula to be constrained at that heliocentric distance during the time interval when the parent assemblage of the aubrites was isolated from contact with the nebular gas by accretion into its parent planetesimal 1992 academic press inc

secondary and sesquinary craters on europa abstract we address impact cratering on io and europa with the emphasis on the origin of small craters on europa as secondary to the primary impacts of comets on io europa and ganymede in passing we also address the origin of secondary craters generated by zunil a well studied impact crater on mars that is a plausible analog to impact craters on io at nominal impact rates and taking volcanic resurfacing into account we find that there should be 1 3 impact craters on io equally likely to be of any diameter between 100 m and 20 km the corresponding model age of europa s surface is between 60 and 100 ma this range of ages does not include a factor three uncertainty stemming from the uncertain sizes and numbers of comets the mass of basaltic impact ejecta from io to reach europa is found to meet or exceed the micrometeoroid flux as a source of rock forming elements to europa s ice crust to describe impact ejecta in more detail we adapt models for impact generated spalls and grady kipp fragments originally developed by melosh our model successfully reproduces the observed size number distributions of small craters on both mars and europa however the model predicts that a significant fraction of the 200 500 m diameter craters on europa are not traditional secondary craters but are instead sesquinary craters caused by impact ejecta from io that had gone into orbit about jupiter this prediction is not supported by observation which implies that high speed spalls usually break up into smaller fragments that make smaller sesquinary craters iogenic basalts are also interesting because they provide stratigraphic horizons on europa that in principle could be used to track historic motions of the ice and they provide materials suitable to radiometric dating of europa s surface

the tectonic and metallogenic framework of myanmar a tethyan mineral system myanmar is perhaps one of the world s most prospective but least explored minerals jurisdictions containing important known deposits of tin tungsten copper gold zinc lead nickel silver jade and gemstones a scarcity of recent geological mapping available in published form coupled with an unfavourable political climate has resulted in the fact that although characterized by several world class deposits the nation s mineral resource sector is underdeveloped as well as representing a potential new search space for a range of commodities many of myanmar s known existing mineral deposits remain highly prospective myanmar lies at a crucial geologic juncture immediately south of the eastern himalayan syntaxis however it remains geologically enigmatic its mesozoic recent geological history is dominated by several orogenic events representing the closing of the tethys ocean we present new zircon u pb age data related to several styles of mineralization within myanmar we outline a tectonic model for myanmar from the late cretaceous onwards and document nine major mineralization styles representing a range of commodities found within the country we propose a metallogenetic model that places the genesis of many of these metallotects within the framework of the subduction and suturing of neo tethys and the subsequent himalayan orogeny temporal overlap of favourable conditions for the formation of particular deposit types during orogenic progression permits the genesis of differing metallotects during the same orogenic event we suggest the evolution of these favourable conditions and resulting genesis of much of myanmar s mineral deposits represents a single evolving mineral system the subduction and suturing of neo tethys

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

observations of high velocity weakly shocked ejecta from experimental impacts a small proportion of meteorites found on earth are thought to come from planet sized bodies1 2 the lunar meteorites are now well established as having come from the moon3 6 on the basis of direct comparison with lunar samples the snc meteorites shergottites nakhlites and chassignites seven achondrite meteorites distinguished by extremely young formation ages 1 3 gyr high volatile contents distinctive oxygen isotopic ratios and rare earth compositions are igneous rocks believed2 to have formed on a planet probably mars but it is hard to reconcile the weakly shocked nature of many lunar and snc meteorites with the strong shock metamorphism known to accompany impacts of the size required to eject material from a planet sized body computer modelling7 10 of impacts has yet to resolve this issue although it has been proposed9 10 that surface rarefaction near an impact can produce high velocity weakly shocked ejecta here we present the results of a cratering experiment which separates and captures the ejecta from diffe rent regions around the impact site we recover high velocity weakly shocked material as predicted9 10 lending additional support both to our understanding of cratering mechanics and to a planetary or lunar origin for the snc and lunar meteorites

antarctic aerosol and snowfall chemistry implications for deep antarctic ice core chemistry in this paper we first summarise major findings of recent atmospheric studies of nitrogen and sulphur species present in the boundary layer of coastal antarctic regions we then discuss the implications of such atmospheric data for the interpretation of nitrate ammonium methanesulphonate and sulphate records in deep ice cores extracted from central antarctica in terms of past atmospheric chemistry changes

glacial interglacial changes in the isotopes of nitrate from the greenland ice sheet project 2 gisp2 ice core received 3 march 2005 revised 23 september 2005 accepted 26 october 2005 published 24 december 2005 1 the 15 n 14 n and 18 o 16 o ratios of nitrate in the greenland ice sheet project 2 gisp2 summit greenland ice core are much higher in ice from the last glacial period than in the pre industrial holocene despite the lack of a significant glacial interglacial change in nitrate concentration while both the 15 n 14 n and 18 o 16 o records are anticorrelated with snow accumulation rate neither is satisfactorily explained by accumulation changes or post depositional processes the similarity in the glacial interglacial change in 15 n 14 n from several different greenland ice cores and the large amplitude of this change relative to observed seasonal variation raise the possibility that the isotopes of nitrate in ice cores indicate a large scale glacial interglacial change in the isotopic composition of atmospheric nox the glacial interglacial change in 18 o 16 oi s best explained by a greater contribution of hno3 production from hydrolysis of n2o5 which has implications for reconstruction of past atmospheric oxidant levels although isotope effects associated with nox photochemistry and nitrate scavenging have not been fully characterized the 15 n 14 n data may indicate glacial interglacial changes in the relative contributions from different natural sources of nox on a hemispheric or global scale

heterogeneous mineral assemblages in martian meteorite tissint as a result of a recent small impact event on mars the microtexture and mineralogy of shock melts in the tissint martian meteorite were investigated using scanning electron microscopy raman spectroscopy transmission electron microscopy and synchrotron micro x ray diffraction to understand shock conditions and duration distinct mineral assemblages occur within and adjacent to the shock melts as a function of the thickness and hence cooling history the matrix of thin veins and pockets of shock melt consists of clinopyroxene ringwoo dite stishovite embedded in glass with minor fe sulfide the margins of host rock olivine in contact with the melt as well as entrained olivine fragments are now amorphosed silicate perovskite magnesiowustite or clinopyroxene magnesiowustite the pressure stabilities of these mineral assemblages are 15 gpa and 19 gpa respectively the 200 lm wide margin of a thicker mm size up to 1 4 mm shock melt vein contains clinopyroxene olivine with central regions comprising glass vesicles fe sulfide spheres fragments of host rock within the melt are polycrystalline olivine after olivine and tis sintite glass after plagioclase from these mineral assemblages the crystallization pressure at the vein edge was as high as 14 gpa the interior crystallized at ambient pressure the shock melts in tissint quench crystallized during and after release from the peak shock pressure crystallization pressures and those determined from olivine dissociation therefore represent the minimum shock loading shock deformation in host rock minerals and complete transformation of plagioclase to maskelynite suggest the peak shock pressure experienced by tissint p 29 30 gpa these pressure estimates support our assessment that the peak shock pressure in tissint was significantly higher than the minimum 19 gpa required to transform olivine to silicate perovskite plus magnesiowustite small volumes of shock melt 100 lm quench rapidly 0 01 s whereas thermal equilibration will occur within 1 2 s in larger volumes of melt 1 mm 2 the apparent variation in shock pressure recorded by variable mineral assemblages within and around shock melts in tissint is consistent with a shock pulse on the order of 10 20 ms combined with a longer duration of post shock cooling and complex thermal history this implies that the impact on mars that shocked and ejected tissint at 1 ma was not exceptionally large

the ice age methane budget 1 accounting for the natural 40 reduction in methane during the last glacial maximum lgm represents one of the most challenging problems posed by polar ice core studies inverse modelling constrained by observations suggest it is driven by a decline in wetland sources but this is not supported by forward modelling using a comprehensive earth system model we show that closure of the methane budget requires reduced emissions and an amplified sink caused by reduction in emissions of volatile organic compounds vocs from lgm forests our study emphasizes a key role for the terrestrial biosphere in the methane budget during the quaternary

magmatic history of central myanmar and implications for the evolution of the burma terrane the burma terrane is a microplate at the eastern edge of the himalayan tibetan orogen the origin of which remains poorly understood its basement comprises metamorphic and igneous rocks forming the wuntho popa arc wpa and has been correlated with tibetan gondwana or transtethyan rocks yet little is known about the magmatic history of the wpa we report elemental and sr nd isotopic compositions of magmatic rocks crystallization zircon and apatite u pb and exhumation apatite fission track ages from rocks and river sands and structural measurements from the wuntho ranges central myanmar where the wpa is best exposed we show that the wpa in the wuntho ranges is characterized by two magmatic events at 108 90 ma and 46 32 ma magmatism is subduction related for both events characterized by depleted nd and sr isotopic compositions with more enriched values with time apatite fission track data suggest arc exhumation during the 39 22 ma time interval partly overlapping with the last magmatic event structural data indicate nw se striking tilting folding and thrusting that we associate with at least two phases of deformation in the cretaceous and the late paleogene correlating the wpa with tibetan gondwana or transtethyan rocks based on its magmatic history remains ambiguous however models arguing for a transtethyan origin for the wpa are most compatible with our results combined with available burmese geological data

petrography and geochemistry of five new apollo 16 mare basalts and evidence for post basin deposition of basaltic material at the site we present the petrography and geochemistry of five 2 4 mm basalt fragments from the apollo 16 regolith these fragments are 1 a high ti vitrophyric basalt compositionally similar to apollo 17 high ti mare basalts 2 a very high ti vitrophyric basalt compositionally similar to apollos 12 and 14 red black pyroclastic glass 3 a coarsely crystalline high al basalt compositionally similar to group 5 apollo 14 high al mare basalts 4 a very low ti vlt crystalline basalt compositionally similar to luna 24 vlt basalts and 5 a vlt basaltic glass fragment compositionally similar to apollo 17 vlt basalts high ti basalt has been reported previously at the apollo 16 site the other basalt types have not been reported previously as there are no known cryptomaria or pyroclastic deposits in the highlands near the apollo 16 site ruling out a local origin and scant evidence for basaltic material in the apollo 16 ancient regolith breccias or apollo 16 soils collected near north ray crater ruling out a basin ejecta origin we infer that the basaltic material in the apollo 16 regolith originated in maria near the apollo 16 site and was transported laterally to the site by small to medium sized post basin impacts on the basis of tio2 concentrations derived from the clementine uvvis data mare tranquillitatis 300 km north is the most likely source for the high ti basaltic material at the apollo 16 site craters ross arago dionysius maskelyne moltke sosigenes schmidt mare nectaris sinus asperitatis 220 km east is the most likely source for the low ti and vlt basaltic material craters theophilus madler torricelli and a large regional pyroclastic deposit near mare vaporum 600 km northwest is the most likely source region for pyroclastic material although no source craters are apparent in the region

two parallel magmatic belts with contrasting isotopic characteristics from southern tibet to myanmar zircon u pb and hf isotopic constraints before the india asia collision neotethyan subduction gave rise to an andean type convergent margin on the southern margin of asia to investigate the spatial and temporal distribution of the subduction related magmatism we undertook a combined determination of zircon u pb ages and hf isotopes of mesozoic to paleogene intrusive and volcanic rocks from southern tibet to myanmar to characterize the two parallel magmatic belts that have previously been considered separately one belt extends from the gangdese batholith in the southern lhasa sub terrane to the lohit batholith the sodon pluton and the popa loimye arc in the west burma block and the other from the central lhasa plutonic belt to the bomi chayu batholith the dianxi batholith and the shan scarps batholith in central myanmar the gangdese belt as the main arc component consists typically of i type granitoids that contain magmatic zircons showing positive ehf t values in contrast the central lhasa plutonic belt belt is dominated by s type granites in which most zircons show negative ehf t values suggesting the involvement of older continental crust in their petrogenesis the distinct geochemical characteristics indicate not only distinct tectonic settings of their genesis but also the diverse nature of the crust forming the exotic continental ribbons amalgamated to asia supplementary material details of sample locations and analytical results are available at https doi org 10 6084 m9 figshare c 4311485

variation in ejecta size with ejection velocity a knowledge of the size velocity distribution of ejecta from impact craters is important for a number of processes that occur or may have occurred in the solar system such as planetary accretion collisional evolution of asteroids the ejection of meteorites from parent bodies larger than asteroids such as the lunar meteorites and the snc meteorites which may be from mars and massive biological extinctions on the earth in order to estimate the size velocity distribution of impact crater ejecta the sizes and ranges from the primary crater were measured for the secondary craters of twelve large craters on mercury the moon and mars the ballistic equation for spherical bodies was used to convert the ranges to velocities and the velocities and crater sizes were used in the appropriate schmidt holsapple scaling relation to estimate ejecta sizes assuming that d v lines were fitted to the log maximum size vs log ejection velocity using the least squares method to determine the velocity exponent certain problems with data collection such as partial burial of some craters and interference from other craters and topographic features made it impossible to determine a simple unique relation between size and velocity the velocity exponents are generally between 1 and 3 with an average value of approximately 1 9 the complicating effect of secondaries produced by clusters of impactors implies that the calculated lines are probably steeper than the slopes of the true fragment size velocity distributions

sudden death at the end of the mesozoic abstract a paleoecological analysis of the fossil record before and after the cretaceous tertiary boundary indicates that the widespread extinctions and biological stresses around the boundary are best explained in terms of a sudden significant but short temperature rise l alvarez and co authors having found an enrichment in iridium at the same boundary postulated that it was associated with the impact of an extraterrestrial body if this body struck the ocean the water injected into the atmosphere may have led to a transient increase in the global surface temperature this temperature pulse may have been primarily responsible for the effects observed in the biosphere the pattern of extinction of higher plant species suggests that splash down occurred in the northern pacific bering sea area

regional variability of ice core dust composition and provenance in greenland 1 mineralogical and isotopic composition sr and nd of six dust samples obtained from six widely spread ice coring sites in greenland were analyzed in order to investigate the regional geographic variability of dust provenance we show that long range transport from eastern asian deserts provides mineral dust with essentially the same composition to all elevated interior sites dye 3 site a grip and northgrip while most material deposited at sites located closer to the edge and at lower altitude hans tausen and renland derives from proximal source regions no contribution from other sources is apparent at any of the interior sites from the mineralogical and isotopic composition of the dust samples each of which represents several decades of dust deposition during the 17th 18th century these results provide additional evidence that african and north american deserts do not play a significant role in the dust deposited over greenland which has implications for ice core record interpretation and atmospheric dust transport model validation

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

snc meteorites clues to martian petrologic evolution the shergottites nakhlites and chassigny snc meteorites are apparently cumulate mafic and ultramafic rocks that crystallized at shallow levels in the crust of their parent body the mineralogy and chemistry of these meteorites are remarkably like equivalent terrestrial rocks although their ratios of fe fe mg and certain incompatible elements and their oxygen isotopic compositions are distinctive all have crystallization ages of 1 3 b y or younger and formed from magmas produced by partial melting of previously fractionated source regions isotope systematics suggest that the snc parent body had a complex and protracted thermal history spanning most of geologic time some meteorites have been severely shock metamorphosed and all were ejected from their parent body at relatively recent times possibly in several impact events late crystallization ages complex petrogenesis and possible evidence for a large gravitational field suggest that these meteorites are derived from a large planet trapped gases in shergottite shock melts have compositions similar to the composition measured in the martian atmosphere ejection of martian meteorites may have been accomplished by acceleration of near surface spalls or other mechanisms not fully understood if snc meteorites are of martian origin they provide important information on planetary composition and evolution the bulk composition and redox state of the martian mantle as constrained by shergottite phase equilibria must be more earthlike than most current models planetary thermal models should benefit from data on the abundances of radioactive heat sources the melting behavior of the mantle and the timing of planetary differentiation calculated depletion of chalcophile elements in source regions indicates a core dominated by sulfides and paleomagnetic measurements suggest the presence of a weak magnetic field within the last several hundred thousand years concentrations of volatile elements indicate that the snc parent body was not volatile depleted and trapped atmospheric components measured in shock melts may be useful in understanding planetary degassing by providing comparisons for spectral reflectance data and viking soil analyses these meteorites may also constrain surface mineralogy and weathering mechanisms

zircon u pb ages in myanmar magmatic metamorphic events and the closure of a neo tethys ocean abstract previous isotopic age studies have concluded that the main metamorphism in the mogok metamorphic belt mmb in myanmar was tertiary and caused by collision with or underthrusting by india we present here results of zircon u pb age determinations on 18 samples from myanmar largely on intrusive rocks from the north trending 550 km long shan scarps segment of the sickle shaped mmb the oldest determination is 491 ma on orthogneiss north of mandalay interpreted as a protolith age and similar to the stratigraphic age of the bawdwin volcanics augen gneiss at kyaukse has a 114 ma protolith age our zircon u pb ages on undeformed intrusive rocks in the mmb range from cretaceous to miocene the oldest 128 ma on a diorite near yebokson implies an earliest cretaceous minimum age for regional metamorphism here younger ages on undeformed intrusions include 91 ma on diorite at mokpalin 72 ma on the weakly foliated garnet bearing nattaung granite 44 and 48 ma respectively on the mec and sedo granites and 17 20 ma on granite dykes for the 128 ma diorite sr and nd isotopes indicative of a continental crust component and mapped continuity of metamorphic host rocks suggest correlation with mid early cretaceous plutons in the eastern transhimalayas zircon u pb ages for the mec sedo and other granites within the mmb and slate belt help to define a late cretaceous to early eocene age range for mostly ilmenite series peraluminous granites within the western granite belt and more restricted western tin belt of myanmar and southern thailand in the wuntho popa arc west of the dextral sagaing fault our new u pb zircon age of 105 ma on diorite at salingyi supports previous k ar ages 106 93 ma for pre tertiary intrusions in the cretaceous this arc may have occupied the andaman sea and continued northwards through the mokpalin diorites and west of the mmb to the 103 80 ma i type plutons in the gandise batholith of southern tibet we interpret the mmb and slate belt as part of a western myanmar block separated in the jurassic from the shan plateau to the east by the southwestward continuation of the bangong nujiang luxi neo tethys i ocean we relate most intrusive and metamorphic events in and near the mmb to westward subduction of this ocean and end jurassic collision of the plateau with the overriding western myanmar slate belt block to orogenic polarity reversal and early cretaceous westward translation of the plateau sequence over the suture zone and to eastward subduction of the ancestral indian ocean or neo tethys ii beneath myanmar with generation of the wuntho popa arc beginning before the late cretaceous the mmb includes meta plateau rocks near mandalay but meta slate belt rocks to the north and south within the mmb previous monazite xenotime thorite ages of eocene oligocene and oligocene early miocene cooling ages on micas with no deformation in eocene granites suggest a high temperature thermal event related to intrusion of these and other granites during a previously proposed regional extension our data imply that the main fabric forming metamorphic event in the mmb pre dated the india asia collision

continental biogenic species in the greenland ice core project ice core tracing back the biomass history of the north american continent ammonium nitrate and organic acid records from the greenland ice core project deep ice core are discussed all species have a continental biogenic source that is situated predominantly on the north american continent for species deposited in summit central greenland the record therefore can be used to trace back the biomass history of the north american continent difficulty in the interpretation of these records arises from their unknown transfer behavior in a more alkaline atmosphere which characterizes glacial time periods compared to interglacial stadials this may have implications not only for weak acids such as formate and acetate but also possibly for the transport and incorporation of hno3 into aerosols whereas ammonium is probably not affected by the alkalinity change of the atmosphere our approach is to compare samples with similar h concentrations throughout the record from the records we infer several significant fluctuations in the extent of the laurentide ice sheet during the last glaciation we find evidence against the occurrence of an extensive younger dryas event in north america

effect of an impact generated gas cloud on the acceleration of solid ejecta a large amount of petrologic geochemical isotopic and rare gas evidence strongly indicates that the shergottite nakhlite and chassigny snc meteorites originated on a parent body large enough to have sustained recent geological activity probably mars the most straightforward interpretation of the cosmic ray exposure evidence requires that the protoshergottites were at least 5 and more likely 15 m in diameter this large size combined with the 5 km s escape velocity for mars presents a formidable dynamic problem this study investigates the possibility that the entrainment of large blocks of solid ejecta within the rapidly expanding vapor cloud produced by an impact provides sufficient additional acceleration to overcome this problem a large number of impact parameters such as impactor and target material impact velocity times of ejection and crater size were varied to determine their relative effects ejection time was found to be the single most important variable rocks entrained at very early times are invariably crushed by high dynamic pressures and rocks ejected at late times after the gas density has become very low are little affected by the gas only rocks ejected within a fairly narrow window of intermediate times have their velocities significantly changed rocks initially ejected at very high velocities such as those predicted by the melosh spallation model are strongly decelerated by the gas rocks injected into the gas stream with velocities much different from the average gas velocity at times early enough that the gas density is still significant are often subjected to dynamic pressures great enough to crush them thus the net effect of a large rapidly expanding impact generated gas cloud on solid ejecta is to homogenize the velocity distribution and to reduce the average size for 30 km diameter craters the only rocks with final velocities greater than 5 km s were those whose initial velocities were greater than or approximately equal to 5 km s since the average final velocity increases with crater size it may be necessary to invoke a crater much larger than 30 km to explain the martian origin of snc meteorites if the proto sncs had diameters of greater than 1 m on the other hand if the proto sncs were only a few tens of centimeters or less gas acceleration of ejecta from a 30 km diameter crater is consistent with the martian origin of these unusual meteorites