physical volcanology and geological relationships of the jurassic ferrar large igneous province antarctica abstract the ferrar large igneous province forms a linear belt for 3500 km along the transantarctic mountains and as a geochemical province extends into southeastern australasia the principal components of the ferrar are intrusive ferrar dolerite sills and dikes and dufek intrusion pyroclastic the prebble mawson and exposure hill formations effusive the kirkpatrick basalt in terms of the three dimensional architecture of the ferrar a range of facies can be recognized in each of the principal components the ferrar province was initiated with a major episode of phreatomagmatism leading to formation of tephra cones and associated deposits and near surface vent structures activity switched to predominantly quiet effusion of alternating thick flood basalt flows and thin pahoehoe lobes and flows intrusive bodies were emplaced early given the occurrence of dolerite clasts in tuff breccias but most sills were probably intruded after accumulation of extrusive rocks pre existing rift structures played a major role in controlling the transport and distribution of the ferrar magmas and the apparent centers of extrusive activity the associated paleohydrology controlled the eruption styles

synchronous fluvial response to surface uplift in the eastern tibetan plateau implications for crustal dynamics synchronous response of river erosion to surface uplift is often assumed by studies using thermochronometer constrained erosion histories to estimate changes in landscape and tectonics we have tested this assumption by studying river incision histories at two sites heishui and lianghekou located in the westernmost inland part of the deeply incised eastern tibetan plateau apatite fission track age elevation plots for the two sites show clear late miocene inflection points marking the time when apparent erosion rates increased fourfold to eightfold to 300 800 m myr this timing is further refined as 10 12 ma by thermal history modeling and overlaps within analytical uncertainties with that recorded from the eastern tibetan plateau margin 150 200 km to the east demonstrating that river incision propagated rapidly from the margin to the interior in less than 2 ma such synchronous regional river incision is consistent with regional surface uplift generated by crustal extrusion along a detachment at depth

crust and upper mantle q from seismic refraction data peace river region crustal refraction data from the peace river region of alberta canada have been analyzed using the spectral ratio method to obtain q a total of 1205 first and later arrivals corresponding to turning and reflected p waves within the crust and upper mantle were studied source spectra were estimated from near offset traces assuming typical sedimentary q values the large scatter of measured spectral ratios restricted the resolution to a three layer model of the crust and upper mantle with q constant in each layer this model was obtained using a linear inverse method since the measured spectral ratios and known traveltimes in each layer are linearly related through the attentuation q 1 in each layer a weighted l1 norm was minimized using linear programming the weights being a measure of the certainty of each spectral ratio the inversion was performed using the 25 most certain spectral ratios regardless of magnitude or sign model bounds taking account of the scattered data were estimated the resu

regional variation and frequency dependence of qβ in the crust of the united states approximate lg attenuation coefficient values are determined for paths in eastern north america at periods between 2 and 4 sec where no data were previously available these new data together with reported values at a period of 1 sec are consistent with values predicted by a frequency dependentent q of the crust in which q varies as 0 2 the new data are inconsistent with values which would be predicted by models having prominent maxima or minima in q 1 within the period range 1 to 5 sec lg attenuation coefficients were computed for the frequency independent crustal q models of cheng and mitchell 1981 for the basin and range province and colorado plateau of the western united states the predicted values at 1 sec for the colorado plateau and basin and range province are about twice as large and three times as large respectively as those predicted for the eastern united states recently reported values of q for 1 sec lg in those regions are consistent with the attenuation coefficients and q values of lg predicted by the colorado plateau and basin and range province models a model with a small degree of frequency dependence of q would be consistent but is not required by the data

burial and exhumation of the eisenhower range transantarctic mountains based on thermochronological sedimentary rock maturity and petrographic constraints abstract the eisenhower range is a n s trending mountain range in the transantarctic mountains tam adjacent to the nw ross sea embayment new aft and apatite u th sm he ahe data from vertical basement profiles supplemented by paleotemperature and pressure estimates derived from beacon sandstones provide new quantitative results on regional burial evolution and first regional constraints on basin inversion and exhumation processes aft ages between 32 2 and 259 18 ma and ahe ages of 37 3 173 16 ma correlate positively with sample elevations thermal history modeling of these data and complementary thermal indications detect heating of the paleosurface on the eisenhower range to temperatures 80 c subsequent to ferrar magmatism and constrain late eocene rapid cooling regression of modeled paleotemperatures against sample elevations refers to a high jurassic 45 c km and a moderate cretaceous eocene 28 8 c km geothermal gradient the texture of beacon sandstones supports strong mechanical compaction that requires a higher overburden than preserved in the stratigraphic record modeled paleotemperatures and pressures suggest basement burial that increases from late jurassic 0 7 1 1 km to eocene 1 8 2 1 km the overburden comprises 0 7 1 1 km cumulative beacon ferrar rocks and 0 7 1 4 km of post ferrar sediments rapid cooling of the whole sample suite between 35 and 30 ma implies fast erosion of the post ferrar sediments and re exposure of underlying magmatic rocks subsequent differential sample cooling to present day surface temperature infers ongoing exhumation by glacial incision enhanced by isostatic response to basin inversion decreasing amounts of exhumation from the coast 3 km toward the interior 1 5 2 2 km point to backstepping incision along the fault controlled priestley glacier substantial exhumation of the eisenhower range since the late eocene is hence triggered by both tectonic and climatic factors superimposed by considerable lithological influence during the initial exhumation stage

seismic attenuation in northeastern sonora mexico we studied the attenuation of local and regional earthquake body waves recorded by the seismic network of northeastern sonora mexico red sismica del noreste de sonora resnes the source station paths of the selected data set cover the epicentral region of the may 1887 m w 7 5 sonora earthquake we used the best located earthquakes recorded by resnes between 2003 and 2004 to analyze the spectral amplitude decay of body waves with hypocentral distance the database consists of 44 earthquakes with magnitudes between 1 8 and 3 2 and hypocentral distances between 25 and 150 km we calculated fourier spectral amplitudes from more than 400 records and defined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes at 23 individual frequencies between 0 4 and 63 1 hz we determined regional attenuation curves based on events located more than 100 km northwest of the center of the network and local curves based on earthquakes located near the fault zone that ruptured in the 1887 earthquake the obtained attenuation curves indicate that the spectral amplitudes decay faster in the area of the 1887 rupture than in the surrounding region to analyze the possible sources of attenuation we parameterized the attenuation functions considering three terms one that accounts for geometrical spreading another one for anelastic attenuation and a third for near surface attenuation we found the s wave quality factor q to be similar in both the general region and near the 1887 rupture however in the region of the 1887 rupture the near surface attenuation exceeds the regional average finally in the region of the 1887 rupture the nonparametric attenuation functions and the estimates of q indicate that at between 0 6 and 63 1 hz p waves attenuate more than s waves q p 20 8 f 1 1 whereas q s 83 8 f 0 9

radiometric ages of basaltic achondrites and their relation to the early history of the solar system pbpb mineral isochrons were determined for three cumulate eucrites moama moore county and serra de mage and three noncumulate eucrites nuevo laredo bouvante and stannern two noncumulate eucrites bereba and cachari show disturbed pb isotope patterns the mineral isochron ages of cumulate eucrites range from 4 40 ga to 4 48 ga the latter is the age of moore county 4 484 0 019 ga which was also dated by the smnd method at 4 456 0 025 ga nuevo laredo and bouvante give the same pb pb age 4 514 0 015 ga and 4 510 0 004 ga respectively the pb isochron of stannern corresponds to 4 128 0 016 ga which is a reequilibration age both cachari and bereba show evidence of isotope resetting at about 4 ga a pb pb multicotrelation approach is introduced and applied to the data the younger ages of the cumulate eucrites preclude their formation by fractional crystallization from the melts that produced the noncumulate eucrites the 1 of the source of the cumulate eucrites is 14 whereas that of the source of the noncumulate eucrites is 150 this large difference in 1 values suggests that eucrites were derived from separate planetesimals or from a single heterogeneous layered parent body

generation of abnormal trace element abundances in antarctic eucrites by weathering processes abstract based on rees antarctic eucrites can be divided into two groups those showing normal trace element characteristics e g similar to juvinas and those showing abnormal trace element abundances many antarctic eucrite polymict eucrite and basaltic clast samples show the abnormal trace element abundances with ree patterns exhibiting positive ce anomalies sometimes negative ce anomalies positive eu anomalies and low abundances of the remainder of the rees with the lrees generally being at lower relative abundances than the hrees most samples of crystalline clasts from the polymict eucrites lew85300 lew85302 and lew85303 show the abnormal patterns while the glassy matrixes of these meteorites show normal patterns exterior samples generally show more abnormal patterns larger anomalies greater depletions than interior samples from the same meteorites comparison of all basaltic eucrite literature data combined with our data shows that positive and negative ce anomalies and positive eu anomalies are found in about 61 of antarctic eucrite analyses and are virtually unknown in non antarctic eucrite analyses further positive ce anomalies and positive eu anomalies are commonly associated with antarctic eucrites having low ree concentrations consideration of mineral melt partition coefficients shows that it is unlikely that ce anomalies are magmatic features from the hed parent body cerium anomalies on earth are generally restricted to the weathering zone where the relative ease of oxidizing ce to the 4 state allows for fractionation of ce from the 3 rees we believe the unusual ree patterns of abnormal antarctic eucrites arise from weathering effects generated in or on the antarctic ice our suggested scenario involves formation of melt water and its equilibration with the atmosphere which promotes dissolution of ree rich phosphates and oxidation of ce tetravalent ce can then be fractionated from the trivalent ree in solution the details of the weathering process are unclear and will require detailed chemical and sem investigations of eucrites for their elucidation we predict that rapidly chilled eucrites with glassy rather than crystalline mesostases will be more likely to survive the antarctic environment without alteration of their ree patterns occasional s se and k enrichments are likely due to weathering in the antarctic environment as well but these enrichments are not well correlated with ce anomalies

experimental study of trace element partitioning between lunar orthopyroxene and anhydrous silicate melt effects of lithium and iron abstract orthopyroxene opx was present during a significant portion of crystallisation of the lunar magma ocean but its influence on co existing melt trace element contents is not well quantified we performed high pressure p 1 1 to 3 2 gpa high temperature t 1400 to 1600 c experiments on synthetic fe rich compositions at reducing conditions relevant to the lunar mantle to constrain trace element partitioning between opx and anhydrous silicate melts opx melt partition coefficients d opx melt for a wide range of trace elements lile li ba ree la ce nd sm dy eu er tm y yb lu hfse zr nb hf ta th u and transition metals sc v mn co mo show only very minor variations across the considered p t range ree partition coefficients increase from d la opx melt 0 0014 0 0008 to d lu opx melt 0 051 0 007 d values for highly charged elements vary from d th opx melt 0 0013 0 0008 through d nb opx melt 0 0018 0 0006 and d u opx melt 0 0015 0 0006 to d ti opx melt 0 068 0 0010 d lu opx melt d hf opx melt values of 6 3 2 4 are at the high end of reported values for minerals that played a role during crystallisation of the lunar magma ocean and higher than previously reported for opx under identical oxygen fugacity conditions implying opx rich cumulates in the lunar mantle have highly superchondritic lu hf ratios lattice strain modelling of our ree partitioning data suggests that varying the concentration of divalent fe in opx very slightly decreases the ideal cation radius for m 3 elements entering the m2 site r 0 m2 whereas the partitioning of m 3 elements entering the m1 site is unaffected a subtle increase in the maximum partition coefficient for m 3 elements entering both the m1 and m2 sites with decreasing t is identified when experiments carried out at similar reducing oxygen fugacities are considered the presence of li at concentrations of up to 350 ppm does not have a measureable effect on the opx melt partitioning behaviour of ree or any other element showing that charge balancing of m 3 m 4 and m 5 elements in opx is likely dominated by a vacancy mechanism

rubidium isotopic composition of the earth meteorites and the moon evidence for the origin of volatile loss during planetary accretion abstract understanding the origin of volatile element variations in the inner solar system has long been a goal of cosmochemistry but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations an improved method for the chemical purification of rb for high precision isotope ratio measurements by multi collector inductively coupled plasma mass spectrometry this method has been used to measure the rb isotopic composition for a suite of planetary materials including carbonaceous ordinary and enstatite chondrites as well as achondrites eucrite angrite terrestrial igneous rocks basalt andesite granite and apollo lunar samples mare basalts alkali suite volatile depleted bodies e g hed parent body thermally metamorphosed meteorites are enriched in the heavy isotope of rb by up to several per mil compared to chondrites suggesting volatile loss by evaporation at the surface of planetesimals in addition the moon is isotopically distinct from the moon in rb the variations in rb isotope compositions in the volatile poor samples are attributed to volatile loss from planetesimals during accretion this suggests that either the rb and other volatile elements were lost during or following the giant impact or by evaporation earlier during the accretion history of theia

development and inversion of the mesozoic victoria basin in the terra nova bay transantarctic mountains derived from thermochronological data abstract the terra nova bay region of the transantarctic mountains hosts three n s to nnw sse extending mountain ranges deep freeze range eisenhower range and northern prince albert mountains all ranges consist of basement rocks locally overlain by permo triassic sediments and jurassic volcanic rocks recent thermochronological studies recognized that the eisenhower range was originally covered by a kilometre thick jurassic eocene sedimentary sequence here we present a comprehensive apatite fission track aft and u th sm he ahe data set of vertical sample profiles from the terra nova bay to reconstruct architecture extension and geometry of this depocentre and place its evolution in the context of supraregional geodynamic processes the study comprises new data and thermal history models from the deep freeze range and new thermal history models of published data from the northern prince albert mountains new aft and ahe ages of 25 275 ma from the deep freeze range correlate tightly with sample elevations thermal history modelling of these data and complementary proxies detects common heating of the jurassic surface and rapid late eocene cooling regression of vertical paleotemperature profiles reveals an increased jurassic and a moderate cretaceous eocene geothermal gradient of 45 and 25 c km respectively paleotemperatures and gradients used in tandem infer basement burial increasing from 2 km in deep freeze and eisenhower ranges to 3 4 km in the prince albert mountains such a varying overburden probably reflects regional differences in the jurassic basement topography subsequently sediment thickness uniformly increased in the order of 1 km until late eocene mid jurassic basin initiation and subsequent sediment accumulation is explained by extension of a mesozoic victoria basin during gondwana breakup between antarctica and australia late eocene early oligocene basin inversion is associated with the formation of the west antarctic rift system while differential final exhumation represents the change from downwearing to backstepping incision

accretion timescales and style of asteroidal differentiation in an 26al poor protoplanetary disk the decay of radioactive 26al to 26mg half life of 730 000 years is postulated to have been the main energy source promoting asteroidal melting and differentiation in the nascent solar system high resolution chronological information provided by the 26al 26mg decay system is therefore intrinsically linked to the thermal evolution of early formed planetesimals in this paper we explore the timing and style of asteroidal differentiation by combining high precision mg isotope measurements of meteorites with thermal evolution models for planetesimals in detail we report mg isotope data for a suite of olivine rich al mg 0 achondritic meteorites as well as a few chondrites main group pyroxene and the zinder pallasites as well as the lodranite all record deficits in the mass independent component of 26mg 26mg relative to chondrites and earth this isotope signal is expected for the retarded ingrowth of radiogenic 26mg in olivine rich residues produced through partial silicate melting during 26al decay and consistent with their marginally heavy mg isotope composition relative to ordinary chondrites which may reflect the early extraction of isotopically light partial melts from the source rock we propose that their parent planetesimals started forming within 250 000 years of solar system formation from a hot 500 k inner protoplanetary disk region characterized by a reduced initial 26al 27al 0 abundance 1 2 10 5 relative to the 26al 27al 0 value in cais of 5 25 10 5 this effectively reduced the total heat production and allowed for the preservation of solid residues produced through progressive silicate melting with depth within the planetesimals these non carbonaceous planetesimals acquired their mass throughout an extended period 3 myr of continuous accretion thereby generating onion shell structures of incompletely differentiated zones consisting of olivine rich residues overlaid by metachondrites and undifferentiated chondritic crusts in contrast individual olivine crystals from eagle station pallasites record variable 26mg excesses suggesting that these crystals captured the 26mg evolution of a magmatic reservoir controlled by fractional crystallization processes during the lifespan of 26al similar to previous suggestions based on isotopic evidence we suggest that eagle station pallasites formed from precursor material similar in composition to carbonaceous chondrites from a cool outer protoplanetary disk region characterized by 26al 27al 0 2 7 10 5 protracted planetesimal accretion timescales at large orbital distances with onset of accretion 0 3 1 myr post cais may have resulted in significant radiative heat loss and thus efficient early interior cooling of slowly accreting carbonaceous planetesimals

the late accretion and erosion of vesta s crust recorded by eucrites and diogenites as an astrochemical window into the formation of jupiter and the early evolution of the solar system abstract the circumsolar disc was the birthplace of both planetesimals and giant planets yet the details of their formation histories are as elusive as they are important to understand the origins of the solar system for decades the limited thickness of vesta s basaltic crust revealed by the link between the asteroid and the howardite eucrite diogenite family of meteorites and its survival to collisional erosion offered an important constraint for the study of these processes some results of the dawn mission however cast doubts on our understanding of vesta s interior composition and of the characteristics of its basaltic crust weakening this classical constraint in this work we investigate the late accretion and erosion experienced by vesta s crust after its differentiation and recorded in the composition of eucrites and diogenites and show that it offers an astrochemical window into the earliest evolution of the solar system in our proof of concept case study focusing on the late accretion and erosion of vesta s crust during the growth and migration of jupiter the water enrichment of eucrites appears to be a sensitive function of jupiter s migration while the enrichment in highly siderophile elements of diogenites appears to be particularly sensitive to the size frequency distribution of the planetesimals the picture depicted by the enrichments created by late accretion in eucrites and diogenites is not qualitatively affected by the uncertainty on the primordial mass of vesta crustal erosion instead is more significantly affected by said uncertainty and vesta s crust survival appears to be mainly useful to study violent collisional scenarios where highly energetic impacts can strip significant amounts of vestan material while limitedly contributing to vesta s late accretion while our proof of concept case study is based on a simplified physical model and explores only a limited set of scenarios our results suggest that the astrochemical record of the late accretion and erosion of vesta s crust provided by eucrites and diogenites can be used as a tool to investigate any process or scenario associated to the evolution of primordial vesta and of the early solar system

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

thermal history and exhumation of basement rocks from mesozoic to cenozoic subduction cycles central north island new zealand a new thermochronological study of the basement rocks of the central north island new zealand records thermal and exhumation histories related to two subduction cycles since the latest jurassic the basement comprises metasedimentary terranes accreted onto eastern gondwana during mesozoic subduction since the oligocene these terranes have been located on the hanging wall of the hikurangi subduction margin overriding the pacific plate results of zircon fission track 121 264 ma analysis yield detrital or slightly reset ages apatite fission track 19 8 122 ma and u th sm he 10 3 95 2 ma ages are fully reset results from inverse thermal history modeling of the data of individual and stacked samples imply the following 1 after their accretion the basement rocks were cooled and exhumed to shallow depths of the crust in the early cretaceous by 150 135 ma this was followed by an episode of reheating until 100 ma which we interpret to be the result of burial by sedimentation above the accretionary wedge during extensional deformation caused by continued underplating and thickening of the wedge from beneath 2 from 100 ma our data indicate thermotectonic quiescence until the oligocene 27 ma 3 during initiation of the hikurangi margin the fore arc proto axial ranges began to exhume during the late oligocene to early miocene 27 20 ma subduction triggered unroofing removed 1 2 2 8 km of overburden most of which was probably the less lithified passive margin sediments 4 along the western central north island the exhumational response to the hikurangi subduction was limited with a total magnitude of erosion 1 5 km in the cenozoic

the eisenhower range transantarctic mountains evaluation of qualitative interpretation concepts of thermochronological data abstract the transantarctic mountains tam were one of the first regions where apatite fission track aft thermochronology was applied routinely to study exhumation processes and long term landscape evolution pioneering publications from the region introduced or refined interpretation concepts of thermochronological data such as the break in slope in vertical age profiles as qualitative marker for the onset of accelerated rock cooling new aft data were compiled from vertical profiles in the eisenhower range northern tam and compared with published data samples originally examined by the population technique were re analyzed via the external detector technique aft ages increase from 32 2 ma at an elevation of 220 m to 175 14 ma at 2380 m geological evidence and thermal history modeling of the aft data require jurassic to late eocene reheating of the samples and an onset of cooling at 35 30 ma this requires the deposition of an 3 to 3 5 km thick sedimentary sequence on the granitic basement subsequent to jurassic ferrar magmatism at 180 ma the regression of paleotemperatures against sample altitudes infers a high jurassic geothermal gradient of 60 c km related to rifting processes and ferrar magmatism and a moderate cretaceous eocene geothermal gradient of 30 c km comparison of ages generated with population and external detector technique shows the importance of determining single grain ages for each sample even from granitic rocks of the same intrusion and thus strongly supports previous cases made for the determination of annealing kinetics and grain age evaluation age comparison additionally illustrates that samples above a break in slope record larger deviations between population and external detector ages than samples below a break in slope we demonstrate that the position and shape of a break in slope result from various factors such as the thermal history prior to final cooling maximum paleotemperatures cooling rate and geothermal gradient a break in slope does not straightly date the onset of final cooling and cannot substitute thermal history modeling therefore earlier studies from the tam and similar settings elsewhere need to be validated by combining thermal history modeling of thermochronological data and supplementary geological information

petrogenesis of d orbigny like angrite meteorites and the role of spinel in the angrite source this research was supported by an australian national university phd scholarship to smck who is currently a postdoctoral fellow of the research foundation flanders

mineralogy and petrology of the angrite northwest africa 1296 we report on a new angrite northwest africa nwa 1296 a fine grained rock with a magmatic texture of rapid cooling dendritic olivine fo50 crystallized first in association with anorthite microcrysts an98100 forming composite chains separated from one another by intergrown al fe diopside hedenbergite pyroxenes in addition some olivines with lower mg and increased cao up to 12 are found between the chains as equant microphenocrysts pyroxenes and olivines are both normally zoned from mg 0 52 to less than 0 01 in the rims ca rich olivines are surrounded by intergrown with or replaced by subcalcic kirschsteinite they appear after plagioclase crystallization stopped at the end of the crystallization sequence minor phases are pyrrhotite fapatite and titanomagnetite pyroxene is the last silicate phase to grow interstitial to idiomorphic olivine kirschsteinite numerous small vesicles and some channels are filled with microcristalline carbonate the mode vol is about 28 olivine 3 kirschsteinite 32 anorthite 34 pyroxene and 3 of the minor phases close to that reported previously for d orbigny and sahara sah 99555 the bulk chemical composition of nwa 1296 is similar to d orbigny and sah 99555 nwa 1296 differs by its texture and mineralogy which are interpreted as resulting from rapid crystallization an evidence of impact melting angrites cannot be produced by partial melting of a cv source because segregation of a planetary core is necessary to explain the low feo mgo ratio of magnesian olivines neither the odd ca al ratio nor the very low sio2 content can be explained by conventional partial melting scenarios we suggest that carbonate is the key to angrite genesis this is supported by the striking similarities with terrestrial melilitites low sio2 superchondritic ca al ratio presence of carbonate the lack of alkalies could be the result of either loss after impact melting or absence of alkalies in the source

impact histories of angrites eucrites and their parent bodies abstract eucrites which are probably from 4 vesta and angrites are the two largest groups of basaltic meteorites from the asteroid belt the parent body of the angrites is not known but it may have been comparable in size to vesta as it retained basalts and had a core dynamo both bodies were melted early by 26al and formed basalts a few myr after they accreted despite these similarities the impact histories of the angrites and eucrites are very different angrites are very largely unshocked and none are breccias whereas most eucrites are breccias and many are shocked we attribute the lack of shocked and unbrecciated angrites to an impact possibly at 4558 myr ago the radiometric age of the younger angrites that extracted the angrites from their original parent body into smaller bodies these bodies which may have had a diameter of approximately 10 km suffered much less impact damage than vesta during the late heavy bombardment because small bodies retain shocked rocks less efficiently than large ones and because large bodies suffer near catastrophic impacts that deposit vastly more impact energy per kg of target our proposed history for the angrites is comparable to that proposed by bogard and garrison 2003 for the unbrecciated eucrites with ar ar ages of 4 48 gyr and that for unbrecciated eucrites with anomalous oxygen isotopic compositions that did not come from vesta we infer that the original parent bodies of the angrites and the anomalous eucrites were lost from the belt when the giant planets migrated and the total mass of asteroids was severely depleted alternatively their parent bodies may have formed in the terrestrial planet region and fragments of these bodies were scattered out to the primordial main belt as a consequence of terrestrial planet formation

thurston island west antarctica between gondwana subduction and continental separation a multistage evolution revealed by apatite thermochronology

consequences of explosive eruptions on small solar system bodies the case of the missing basalts on the aubrite parent body aubrite meteorites are composed of constituents which are almost certainly of igneous origin if they were generated by the melting and fractionation of enstatite chondrite like parental material as seems very likely then plagioclase rich basaltic complements to the aubrites should have formed however such materials are not known as individual meteorites and the compositions of two plagioclase silica clasts and one albite silica diopside anorthite clast probably an impact melt in the norton county aubrite breccia suggest that they are not the putative enstatite plagioclase basalts we propose a new mechanism that explains the absence of these materials showing that the expansion of even very small amounts of volatiles present in a melt approaching the surface of a small low gravity body will be enough to disrupt the melt into a spray of droplets moving faster than the local escape velocity this explosive volcanic process of melt removal requires larger melt volatile contents on larger bodies and data on the solubility of volatiles in basaltic melts suggest that the process was limited to bodies smaller than about 100 km in radius

q estimates along the wasatch front in utah derived from sg and lg wave amplitudes abstract this study develops estimates for the attenuation of peak vertical ground motions using a conventional least squares regression model applied to unfiltered and bandpass filtered ground motion data the input data are from 88 earthquakes 1 0 m 3 3 epicentral distance range 10 to 450 km located along the utah idaho border and propagating sg and lg waves southward to seismograph stations along the wasatch front in north central utah the regression model includes parameters to account for geometric spreading anelastic attenuation with a power law frequency dependence source size and station site effects the maximum ground motion amplitudes are derived from waves arriving about 3 sec on the average after the s wave arrivals and are interpreted to be sg in close roughly 100 km or two crustal thicknesses and lg at greater distances accordingly geometric spreading coefficients of 1 0 and 0 9 for body waves sg and 0 83 5 6 for higher mode airy phase surface waves lg are chosen for testing similarly a range of initial values of the power dependence of the attenuation 0 5 to 0 9 are also tested the suite of estimates that result from regressing the amplitude data while employing the family of fixed parameter values leads to the following q model q f 97 f 0 80 for 3 hz f 10 hz these results are important to the estimation of the seismic hazard for the study area this pronounced level of attenuation comparable to that found in california has been reported in previous investigations of the study area using psrv spectra intensity attenuation and fall off of wood anderson seismogram amplitudes

spatial variations of seismic attenuation in the north west of iranian plateau from analysis of coda waves abstract in this study spatial variation of coda wave attenuation in the north western nw iranian plateau is explored using local earthquakes single backscattering method is used to map the spatial variations of coda q qc using 14 969 earthquakes which are recorded digitally by sixteen permanent stations observed spatial attenuation maps are well correlated with geological setting of study area north west of iranian plateau is dominated with high attenuation which is well correlated with quaternary deposits as well as the sahnad sabalan volcanic zone and tabriz fault these observation is in accordance with numerous 2d velocity tomograms which have shown very low velocity in the nw iran the region characterized by volcanic structures exhibits mainly higher seismic attenuation than the surrounding regions whereas paleo tethys basin in the eastern part of covered area are categorized by smaller attenuation than the other zone our observation shows good correlation with reported lower crustal low velocity region beneath the sahand and sabalan volcanos the sahand and sabalan volcanoes are very large structures and they dominate the pliocene quaternary magmatic landscape of nw iran in addition our observation has clearly shown existence of a probable fault zone trending in ne sw direction between tabriz city and urmia lake which is consistent with the trend of meizoseismal zone of the deh khareqan modern azarshahr earthquake m 6 8 in 1641

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

zinc isotopes in heds clues to the formation of 4 vesta and the unique composition of pecora escarpment 82502 the 66zn permil deviation of the 66zn 64zn ratio from a terrestrial standard values for a suite of 20 non antarctic hed howardite eucrite diogenite meteorites and one mesosiderite and for 8 antarctic eucrites and diogenites were measured in order to determine the role of volatization in the formation of their presumed parent body the asteroid 4 vesta the 20 non antarctic heds had 66zn values that ranged from 2 0 to 1 67 with a mean value of 0 01 0 39 2se this range likely represents a small scale heterogeneity due to brecciation induced by multiple impacts the non antarctic eucrites 66zn 0 00 0 58 2se n 12 were isotopically the same as the diogenites 66zn 0 31 0 80 2se n 4 and the howardites 66zn 0 26 0 37 2se n 4 on average non antarctic eucrite falls were isotopically heavier 0 50 than non antarctic finds 1 00 the antarctic finds studied were all unbrecciated samples and they were significantly heavier than the non antarctic samples with a 66zn range of 1 63 to 6 22 for 4 eucrites mean 4 32 and 0 94 to 1 60 for 3 diogenites mean 1 23 excluding one anomalous sample while their zn concentration is significantly lower than the brecciated samples these data suggest that the unbrecciated eucrites probably represent the eucritic crust shortly after differentiation and cooling of the parent asteroid at which time volatization of lighter zinc isotopes led to an isotopically heavy crust early impact events caused the ejection of these unbrecciated meteorites which were subsequently spared from brecciation caused by multiple additional impacts on the much larger vesta the range of 66zn values and zn concentration for the brecciated heds in this study supports a major contribution to the vestan surface by chondritic impactors 1 30 66zn 0 76 for ordinary and carbonaceous chondrites the anomalous eucrite pca 82502 66zn 7 75 is significantly isotopically lighter than the other heds and is the natural sample with the lightest zn isotopic composition reported in the solar system to date this meteorite most likely originated from a distinct parent body

core formation in earth s moon mars and vesta stimulated by new experimental results on metal silicate partitioning of elements at elevated temperatures and pressures we have revisited the question of core formation in earth s moon mars and vesta the probable source of the eucritic meteorites earlier studies suggested metal silicate equilibrium in mars but led to the paradox that mars accreted homogeneously while the earth accreted heterogeneously using new elevated pressure and temperature metal silicate partition coefficients we show that abundances of the moderately siderophile elements in the mantles of the moon mars and vesta are consistent with early magma oceans on these bodies the most successful model for explaining the lunar mantle siderophile element abundances requires a core of 5 of the mass of the moon 500 km radius siderophile element abundances in mars are consistent with intermediate pressure metal silicate equilibrium as has also been recently suggested for the earth the most successful model for explaining the martian siderophile element abundances requires a bulk planetary composition that has greater than ci chondritic abundances of the moderately siderophile elements and a core of 30 of the mass of mars siderophile element abundances in the mantle of vesta are consistent with low pressure liquid metal liquid silicate equilibrium as expected for an asteroid sized body and a core of 10 of the mass of vesta comparison of our best fit oxygen fugacities for vesta with thermodynamic calculations of oxygen fugacity for silicate bearing iron meteorites indicates that parts of the inner solar system were homogeneous with respect to redox state at 4 5 ga approximately 2 log fo2units below the fe feo buffer much higher than estimates for the solar nebula similar comparisons for mars and the earth indicate that these bodies have undergone oxidation since 4 5 ga because the oxygen fugacities associated with metal silicate equilibrium in both mars and the earth moon system are much lower than those recorded in martian and terrestrial basaltic and periodotitic samples the oxidation on mars is most likely due to atmospheric effects whereas earth s much wider range of oxygen fugacities must be due to both atmospheric and plate tectonic effects

uplift and denudation of the central alaska range a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters apatite fission track thermochronology aftt on granitic samples collected in the central alaska range in conjunction with geologic constraints from basins to the north nenana basin and south cook inlet of the range is used to constrain the timing amount rate and pattern of surface uplift rock uplift and denudation since the late miocene the conversion from a thermal frame of reference apatite fission track data to an absolute frame of reference with respect to mean sea level which requires constraining the paleoland surface elevation the paleomean annual temperature and the paleogeothermal gradient is evaluated and shown to be viable in the context of an exhumed apatite partial annealing zone paz apatite ages at denali mount mckinley range from 16 ma near the summit 6 km elevation to 4 ma at 2 km elevation a distinctive break in slope in the apatite age profile at an elevation of 4 5 km also marked by a change in confined track length distributions marks the base of an exhumed apatite paz rock uplift and denudation are greatest at denali decreasing southward away from the mckinley strand of the denali fault system as shown by progressively older apatite ages 7 35 ma from a suite of samples along the kahiltna glacier a correlative decrease in topography occurs southward from the fault the central alaska range lies within an arc defined by the denali fault with the highest peaks including denali concentrated at the arc apex patterns of rock uplift and denudation within the central alaska range mimic topography between early and late miocene and possibly earlier the central alaska range was most likely an area of relative tectonic and thermal stability rock uplift denudation and mean surface uplift of the denali region began by the late miocene 5 6 ma being 8 5 km 5 7 km and 2 8 km respectively at average rates of 1 5 km m y 1 km m y and 0 5 km m y the amount of rock uplift denudation and surface uplift decreases to 3 km 2 km and 1 km at little switzerland some 45 km south of the denali fault we conclude that the topographic and rock uplift patterns of the central alaska range the shape and proximity of the mckinley strand of the denali fault to these patterns the timing of the onset of rock uplift and denudation at 5 6 ma and a significant change in relative plate motion between north america and the pacific plates circa 5 6 ma are all inherently related

tectonic and denudational history of the rennick graben north victoria land implications for the evolution of rifting between east and west antarctica 1 the tectonic depression of the rennick graben northern victoria land antarctica is a key element for deciphering the cenozoic separation history between east and west antarctica and evolution of the west antarctic rift system the geometry kinematics and timing of the boundary faults of the rennick graben are presented on the basis of a detailed structural study of the major fault segments combined with apatite fission track data the structural architecture of the rennick graben is controlled by distributed and partitioned right lateral strike slip faulting fission track data indicate that the last significant denudation stage of the rennick graben shoulders started from eocene times with increasing cooling and denudation since 40 50 ma a direct structural connection is then established between cenozoic denudation and the activation of the dextral strike slip regime in north victoria land during the cenozoic in this framework the rennick graben is interpreted as a localized tectonic depression generated as a displacement accommodation area of the regionally sized dextral strike slip shearing the results of this study 1 invalidate the commonly assumed link between mesozoic ross sea rifting and opening of the rennick graben 2 argue against orthogonal rifting models for the cenozoic evolution of the ross sea region and 3 provide constraints to the modalities and timing of the separation between the east antarctic craton and the west antarctica extensional province

unroofing of fore arc ranges along the hikurangi margin new zealand constraints from low temperature thermochronology abstract the axial ranges of north island new zealand parallel the hikurangi subduction margin they consist of uplifted and exhumed mesozoic meta sedimentary basement rocks of the overriding australian plate beneath which the pacific plate has been subducting since at least the late oligocene we investigate the unroofing histories of these fore arc mountains during the evolution of the hikurangi margin based on new and previous zircon and apatite fission track and apatite u th sm he data which we interpret based on inverse modelling the results suggest that the exhumation of rocks in the axial ranges initiated in the west and migrated trench wards towards the east onsets of accelerated exhumation in different parts of the ranges indicate significant eastwards thrusting on the margin parallel ngamatea fault before 20 17 ma and on the wellington mohaka fault before 10 7 ma the exhumation rate has varied significantly along strike since the late miocene lower in the central part of the axial ranges and significantly higher to the south since the late miocene the increasing exhumation rate from the central to southern axial ranges is consistent with the clockwise vertical axis rotation of eastern north island relative to the australian plate in the hikurangi margin although underplating of subducted material at the basal upper plate may have contributed to localised rock uplift e g in the raukumara range we suggest that the shortening of the fore arc upper plate was the chief driver of unroofing of the proto axial ranges

q determined from local earthquakes in the south carolina coastal plain abstract coda q or qc is determined from the rate of coda decay in the coastal plain near charleston south carolina the mean of qc calculated from individual estmates is near 190 at 1 hz and increases to over 1650 at 10 hz a possible temporal change in qc is identified high values being associated with increased seismic activity during late 1977 temporal changes have been observed elsewhere and laboratory measurements of q under different stress states correlate high q with high stress a spatial variation in qc is identified increasing from west qc at 10 hz equal to 850 to east qc at 10 hz greater than 2100 across the coastal plain the demarcation of high to highest zones of qc is coincident with the western boundary of the innermost isoseismal of the charleston 1886 earthquake it is hypothesized that the 1886 earthquake was mislocated originally because of this spatial variation in energy attenuation that was unrecognized at that time

late accretion as a natural consequence of planetary growth the mantles of the terrestrial planets contain elemental abundances that suggest accretion continued at a late stage after core formation geochemical data of meteorites from differentiated asteroids are consistent with such a late accretion event suggesting that the phenomenon occurred throughout the solar system and was related to planet formation

lapse time and frequency dependent attenuation characteristics of kumaun himalaya abstract we have analyzed local earthquake data set consists of 84 well located events recorded by a digital seismic network in the kumaun himalaya region during 2004 2007 to study seismic attenuation characteristics of the region single back scattering assumption is used to estimate coda q q c values of the region at frequency range of 1 5 3 6 8 12 and 18 hz for different lapse time window length the values of q c show a ubiquitous observation of frequency dependence and follow a substantially similar trend as observed in other tectonically active parts of the himalaya the lapse time dependencies of coda waves are investigated which reveal that by increasing lapse time window from 20 to 50 s q 0 q c at 1 hz increases from 64 2 to 230 19 while frequency dependent parameter n decreases from 1 08 to 0 81 increase in q c with lapse time indicates decrease in heterogeneity with depth the observed values of q 0 and n infer that the medium beneath the study area is highly heterogeneous and tectonically very active the variation of q c with lapse time at 1 5 hz follow a similar pattern with the theoretically predicted values of gusev 1995 although the frequency parameter n does not match with the model it may suggest that the turbidity decays rapidly with depth for the kumaun himalaya our results are comparable with those obtained from tectonically active regions in the world

the heating history of vesta and the onset of differentiation in this work we study the link between the evolution of the internal structure of vesta and thermal heating due to 26 al and 60 fe and long lived radionuclides taking into account the chemical differentiation of the body and the affinity of 26 al with silicates we explored several thermal and structural scenarios differing in the available strength of energy due to the radiogenic heating and in the postsintering macroporosity by comparing them with the data supplied by the heds and the dawn nasa mission we use our results to constrain the accretion and differentiation time as well as the physical properties of the core differentiation takes place in all scenarios in which vesta completes its accretion in 1 4 ma after the injection of 26 al into the solar nebula in all those scenarios where vesta completes its formation in 1 ma from the injection of 26 al the degree of silicate melting reaches 100 vol throughout the whole asteroid if vesta completed its formation between 1 and 1 4 ma after 26 al injection the degree of silicate melting exceeds 50 vol over the whole asteroid but reaches 100 vol only in the hottest outermost part of the mantle in all scenarios where the porosity is lower than 5 vol if the formation of vesta occurred later than 1 5 ma after the injection of 26 al the degree of silicate melting is always lower than 50 vol and is limited only to a small region of the asteroid the radiation at the surface dominates the evolution of the crust which ranges in thickness from 8 to about 30 km after 5 ma a layer about 3 20 km thick is composed of primitive unmelted chondritic material while a layer of about 5 10 km is eucritic

attenuation of coda waves in northern greece the single scattering model has been applied for the estimation of codaq values for local earthquakes that occurred in northern greece during the period 1983 1989 and recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki codaq estimations were made for four frequency bands centered at 1 5 hz 3 0 hz 6 0 hz and 12 0 hz and for the lapse time windows 10 20 sec 15 30 sec 20 45 sec 30 60 sec and 50 100 sec the codaq values obtained show a clear frequency dependence of the formq c q 0 f n whileq 0 andn depend on the lapse time window q 0 was found equal to 33 andn equal to 1 01 for the time window of 10 to 20 sec while for the other windowsq 0 increased from 60 to 129 withn being stable close to 0 75 this lapse time dependence is interpreted as due to a depth dependent attenuation the high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity in agreement with studies in other seismic regions

abundance of highly siderophile elements in lunar basalts controlled by iron sulfide melt the moon accreted meteoritic material towards the end of solar system formation quantification of this late accretion requires an estimation of the abundance of highly siderophile or iron loving elements in the lunar mantle as lunar mantle samples are not available estimates are derived from lunar basalt compositions but the melting phase relations needed to derive the mantle composition are poorly constrained here we present sulfur solubility measurements from laboratory experiments combined with thermodynamic calculations which show that the lunar basalt source is likely to be saturated in a sulfur poor iron rich sulfide melt that concentrates some highly siderophile elements more than others we found that the observed range in the ratios of highly siderophile elements in primitive lunar basalts is much smaller than expected from residual sulfide control alone instead the elemental ratios are consistent with mixing between primary sulfide saturated melts and minute 1 amounts of lunar regolith that contain impact debris although the composition of some samples suggests a highly depleted lunar mantle the exact level of depletion is unclear because mixing trajectories overlap at the inferred level of regolith contamination we conclude that the composition of the lunar mantle is veiled by regolith contamination of the lunar basalts if so highly siderophile element abundances in lunar mantle derived materials cannot be used to determine the mass of material accreted late onto the moon the abundance of iron loving elements in moon rocks cannot indicate the amount of late accretion onto the moon according to experiments and thermodynamic calculations constraining the behaviour of these elements under lunar mantle conditions

formation of vesicles in asteroidal basaltic meteorites rare asteroidal vesicular basalts have previously been thought to form in surficial lava flows with co as the vesicle forming gas however vesicular lava flows are unlikely on small airless bodies such as asteroids to unravel the origin of these rocks we analyzed vesicle sizes and abundances for two angrites and two eucrites using high resolution x ray computed tomography and conducted numerical modeling of bubble formation in a dike of ascending magma modeling results indicate that thin 30 cm wide dikes are trapped at 5 km depth where 75 ppm of co and co2 contribute equally to vesicle formation vesicular eucrites were metamorphosed in this deep seated environment the gas was lost and they were excavated by impacts

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

the effect of melt composition on metal silicate partitioning of siderophile elements and constraints on core formation in the angrite parent body we present 275 new metal silicate partition coefficients for p s v cr mn co ni ge mo and w obtained at moderate p 1 5 gpa and high t 1683 1883 k we investigate the effect of silicate melt composition using four end member silicate melt compositions we identify possible silicate melt dependencies of the metal silicate partitioning of lower valence elements ni ge and v elements that are usually assumed to remain unaffected by changes in silicate melt composition results for the other elements are consistent with the dependence of their metal silicate partition coefficients on the individual major oxide components of the silicate melt composition suggested by recently reported parameterizations and theoretical considerations using multiple linear regression we parameterize compiled metal silicate partitioning results including our new data and report revised expressions that predict their metal silicate partitioning behavior as a function of p t x fo2 we apply these results to constrain the conditions that prevailed during core formation in the angrite parent body apb our results suggest the siderophile element depletions in angrite meteorites are consistent with a cv bulk composition and constrain apb core formation to have occurred at mildly reducing conditions of 1 4 0 5 log units below the iron wustite buffer iw corresponding to a apb core mass of 18 11 the core mass range is constrained to 21 8 mass if light elements s and or c are assumed to reside in the apb core incorporation of light elements in the apb core does not yield significantly different redox states for apb core mantle differentiation the inferred redox state is in excellent agreement with independent fo2 estimates recorded by pyroxene and olivine in angrites

depth dependance of q beneath the baltic shield inferred from modeling of short period seismograms we use rg waves fundamental rayleigh wave to measure shear wave velocity and attenuation in the crust in central finland we used seismograms from quarry blasts in ussr recorded during the lithoscope sveka 89 experiment we deduced from dispersion curves a shear wave velocity model for the upper crust from the attenuation of rg waves as a function of frequency we found the quality factor qs in the uppermost crust as a function of depth the quality factor appears to be low about 100 in the shallow crust and to increase rapidly at depth to about 1000 in order to test this result we calculated complete synthetic seismograms for this velocity attenuation model we were able to simulate accurately the arrival times and the relative amplitudes of all the major phases present in the actual seismograms including pg and lg waves this comparison supports the presence of a very attenuative surface layer with a thickness of about 1 km beneath the baltic shield while the deep crust presents a very weak attenuation this relatively thick attenuative superficial layer plays an important part in the overall attenuation observed in shield areas

constraints on core formation in vesta from metal silicate partitioning of siderophile elements abstract it is now widely accepted that the asteroid 4 vesta has an fe rich metallic core but the composition of the core and the conditions prevailing during core mantle differentiation are poorly constrained in light of new constraints on vesta s geophysical and geochemical properties obtained by the dawn mission we have re examined the conditions at which core mantle differentiation in vesta may have occurred by linking the estimated mantle depletions of siderophile elements p co ni cu ga ge mo and w in the vestan mantle to newly derived predictive equations for core mantle partitioning of these elements we extend the number of elements previously considered in geochemical modeling of vestan core formation and use published metal silicate partitioning data obtained at low pressures to characterize the dependence of metal silicate partition coefficients d on pressure temperature oxygen fugacity and composition of the silicate and metallic melt in our modeling we implement newly derived mantle depletions of p co ni and ga through analysis of published hed meteorite analyses and assess two contrasting bulk compositional models for vesta modeling results using monte carlo simulations constrain vestan core formation to have occurred at mildly reducing conditions of approximately 2 log units below the iron wustite iw buffer iw 2 05 0 20 if the two most likely bulk compositions binary mixtures of h cm or h cv chondritic meteorites are considered assuming a temperature range between 1725 and 1850 k and a sulfur free pure fe core if the core is assumed to be sulfur rich 15 wt s as predicted by the latter bulk compositional models observed depletions for all eight siderophile elements can be simultaneously satisfied at iw 2 35 0 10 and 1725 1850 k for the h cv bulk composition and iw 2 30 0 15 and 1725 1850 k for the h cm bulk composition more reducing conditions are not consistent with the observed siderophile element depletions in the vestan mantle independent of the sulfur content of the vestan core and of the bulk compositional model chosen our analysis shows that a previously proposed shallow magma ocean on vesta during core formation is not consistent with the observed mantle depletion of ga for the two considered bulk compositions irrespective of core composition instead our results are consistent with the existence of a deep magma ocean during core formation on vesta requiring 50 100 mantle melting

widespread magma oceans on asteroidal bodies in the early solar system our solar system formed about 4 6 billion years ago and within 4 million years small planetary bodies had formed some melting to form volcanic and related rocks two families of meteorites the heds and angrites are thought to have originated from asteroids that melted at this time new oxygen isotope measurements confirm that these meteorites are from two distinct asteroids that underwent large scale melting in the early solar system these new results show that early global scale melting was a feature of all the differentiated planets earth moon and mars and asteroids so far sampled immediately following the formation of the solar system small planetary bodies accreted1 some of which melted to produce igneous rocks2 3 over a longer timescale 15 33 myr the inner planets grew by incorporation of these smaller objects4 5 through collisions processes operating on such asteroids strongly influenced the final composition of these planets4 including earth5 currently there is little agreement about the nature of asteroidal igneous activity proposals range from small scale melting to near total fusion and the formation of deep magma oceans2 here we report a study of oxygen isotopes in two basaltic meteorite suites the heds howardites eucrites and diogenites which are thought to sample the asteroid 4 vesta6 and the angrites from an unidentified asteroidal source our results demonstrate that these meteorite suites formed during early global scale melting 50 per cent events we show that magma oceans were present on all the differentiated solar system bodies so far sampled magma oceans produced compositionally layered planetesimals the modification of such bodies before incorporation into larger objects can explain some anomalous planetary features such as earth s high mg si ratio

coda q estimates in the andaman islands using local earthquakes the attenuation property of andaman island has been investigated analyzing coda waves from 57 local earthquakes in the magnitude range of 2 0 4 9 using the single backscattering model these earthquakes waveforms recorded on five broadband seismographs sited over the island from north to south during nov 2003 to march 2004 have been used to calculate the frequency dependent coda q q c applying the time domain coda decay method the coda q computed at central frequencies from 0 5 12 hz and five lapse time windows from 40 to 80 s progressively increases from 105 f 0 88 in the north andaman to 135 f 0 79 in the south andaman with an average of 119 f 0 80 the average q c values vary from 75 42 at 0 5 hz to 697 54 at 12 hz central frequency for 40 s lapse time window while for 80 s lapse time window its variation is from 117 38 at 0 5 hz to 1256 115 at 12 hz the q c estimated at different lapse times manifests a significant variation from 122f 0 75 to 174f 0 73 corresponding to lapse time window lengths of 40 and 80 s respectively the variation of q c with frequency lapse time and also with the location of seismograph reflects the marked structural and compositional inhomogeneity with depth along the andaman islands these observations are well correlated with the seismicity pattern and distinct high angle subduction beneath the island

a local magnitude scale for the western great basin eastern sierra nevada from synthetic wood anderson seismograms abstract we have computed synthetic wood anderson seismograms for over 1100 arrivals at 10 three component broadband digital stations in the unr western great basin eastern sierra nevada network these represent all the available records from local earthquakes over magnitude 3 5 between 1990 and june of 1993 plus selected events of smaller magnitude there were 77 events ranging in magnitude from 2 2 to 5 9 including four events over magnitude 5 the distances considered ranged from 15 to 600 km with the best represented range being from 30 to 450 km we invert these measurements to determine distance and station corrections appropriate for a local magnitude scale constrained by richter9s original definition that an earthquake of m l 3 will cause a 1 mm zero to peak deflection of the wood anderson seismogram at 100 km from the epicenter the results between 30 and 450 km were essentially independent of choice of curve fitting parameters in the 30 to 500 km distance region the smooth distance correction curves were very similar to that determined by richter 1958 which is still used for southern california earthquakes we propose to use richter9s distance correction curve in reporting amplitude magnitudes from our digital network

the mesozoic victoria basin vanished link between antarctica and australia the transantarctic mountains tam are the largest non compressional mountain belt in the world their origin is traditionally related to crustal thickening during the jurassic ferrar magmatic event that was followed by episodic uplift in the early and late cretaceous and since the paleocene this concept of a long lived morphological high constitutes a base of virtually all gondwana reconstructions and global climate models here we demonstrate that crossover age relationships between thermochronological apatite fission track data and stratigraphic information contradict this established interpretation instead these data together with a wealth of independent thermal indicators and geological evidence require the existence of a vast intra gondwana basin between at least late triassic and late cretaceous times including during the ferrar magmatic event referred to here as the mesozoic victoria basin mvb this basin formed during crustal extension across the paleo pacific margin of antarctica and australia uplift of the tam with associated basin inversion commenced only with the development of the west antarctic rift system in paleogene times the recognition of the long lived mvb has primary consequences for the general understanding of the landscape of gondwana and the breakup between antarctica and australia west antarctic rifting and uplift of the tam and global long term climate evolution and faunal radiation

the importance of apatite composition and single grain ages when interpreting fission track data from plutonic rocks a case study from the coast ranges british columbia abstract fission track results determined from granitic rocks exposed within the coast ranges of british columbia indicate that significant variations in apatite chemistry may occur in small plutonic rock samples to test ages determined earlier by parrish using the population method of fission track dating new apparent apatite ages were completed using the external detector method so that single grain ages could be generated in most cases the new apatite ages were similar to the earlier ones within 2 however in many cases it was found that individual samples contained significant variations in single grain apatite ages microprobe analyses showed the spread in ages were directly related to variations in apatite chemistry such that chlorine rich apatites retained older ages than fluorine rich grains examination of the single grain age data suggested that the spread in single grain ages provided information which constrained the thermal history of the sample and that distributions of single grain ages reflected the temperatures at which they resided during cooling these results suggest that it is important to generate more than a few single grain fission track ages when dating apatite from granitic rocks since variations in the chlorine concentration in apatite grains may exist in kg sized granitic rock samples therefore it is no longer a valid assumption that each apatite grain separated from a small granite sample will have a similar chlorine concentration and in future apatite fission track studies of granitic terrains it is important to recognize that the apatite composition might be heterogeneous when interpreting results

implications of late eocene to early miocene clay mineral assemblages in mcmurdo sound ross sea antarctica on paleoclimate and ice dynamics abstract the clay mineral assemblages of upper eocene to lower miocene sediments recovered at the ciros 1 and mssts 1 drill sites on the mcmurdo sound shelf antarctica were analyzed in order to reconstruct the cenozoic antarctic paleoclimate and ice dynamics the assemblages are dominated by smectite and illite with minor amounts of chlorite and kaolinite the highest smectite amounts and best smectite crystallinities occur in the upper eocene part of ciros 1 below 425 445 mbsf they indicate that during their deposition chemical weathering conditions prevailed on the nearby continent large parts of east antarctica were probably ice free at that time but some glaciers reached the sea and contributed to the glaciomarine sedimentation in contrast only minor total amounts of smectite are present in oligocene and younger sediments due to the shift to mainly physical weathering on an ice covered antarctic continent however relative smectite percentages rise to more than 60 during two late oligocene intervals ca 27 5 26 2 and 25 0 24 5 ma and during one early miocene interval starting at ca 23 3 ma these intervals are characterized by ice masses coming probably from the south where volcanic rocks acted as a source as also indicated by the composition of the sand and gravel fractions during the other intervals the ice came from the west where the physical erosion of basement rocks and sedimentary rocks of the beacon supergroup in the transantarctic mountains provided high illite concentrations because the two drill sites are only 4 km apart their clay mineral records can be correlated this led to a new interpretation of the oligocene paleomagnetic data of the mssts 1 site and to a more detailed lithostratigraphic correlation of the miocene parts of the cores

the composition of the mantle of the eucrite parent body and the origin of eucrites abstract previous estimates of the composition of the epb have tacitly assumed chondritic abundances of refractory lil elements a model is presented here which utilizes refractory element ratios instead consideration of these ratios and of known olivine liquid partition coefficients for sc mg and si imply that the epb mantle may be accurately modeled as a simple mixture of 25 eucrite 75 olivine the model also implies that eucrites such as juvinas and sioux county were derived by large degrees of partial melting 20 30 comparison of the model epb mantle to known meteorite classes indicates a similarity between the element abundances of the epb and c3 chondrites

post mid cretaceous tectonic and topographic evolution of western marie byrd land westantarctica insights from apatite fissiontrack and u th sm he data

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

survey and evaluation of eucrite bulk compositions the purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting fractional crystallization and magma ocean theories for the eucrite parent body in order to evaluate bulk elemental abundances for the eucrites 296 peer reviewed articles monographs theses or books and 143 abstracts dating from 1938 to 1997 were surveyed of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature 20 were selected for in depth examination the selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist the mean bulk elemental abundance 1 standard deviation and the percent deviation were calculated for each element in a given eucrite in order to evaluate the quality of the mean abundances the elements were then grouped according to availability of data and percent deviations possible reasons for the different deviations in the different groups are briefly discussed from the major element abundances the normative cipw composition the molar compositions of pyroxene olivine and plagioclase and the bulk densities were calculated and compared to petrographic observations the calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not possible reasons for this are discussed unfortunately analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty therefore future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites especially those of key elements used for planetary modeling

aubrites and diogenites trace element clues to their origin we have analyzed by rnaa 25 aubrite and 9 diogenite samples for 13 to 29 siderophile volatile and lithophile trace elements both meteorite classes show a typically igneous siderophile element pattern with ir os re ge more depleted than au ni pd sb but aubrites tend to have about 10 higher abundances 10 3 10 4 cl for the first 4 and 10 2 10 3 cl for the last 4 siderophiles apparently reflecting smaller metal silicate distribution coefficients at lowerf o2 or less complete segregation of metal se is surprisingly abundant in aubrites up to 0 4 cl but te is less so sete 5 cl apparently due to its stronger siderophile character other volatiles ag zn in cd bi t1 show depletions intermediate between lunar dunite and the earth s mantle of 7 aubrites analyzed for ree ce nd eu tb yb lu 6 are depleted in ree 0 08 0 5 cl and 5 show negative eu anomalies the exceptions are bishopville and mt egerton silicate this supports an igneous origin as already noted by boynton and schmitt 1972 no samples of the complementary basaltic and feldspathic rocks have been found thus far but one of our samples of khor temiki dark is a candidate for the basalt it is 5 7 enriched in ree and only slightly less so in rb cs and u though shocked and enriched in siderophiles to 0 05 cl it apparently represents a new meteorite class three diogenites analyzed for ree show very diverse patterns from strongly depleted in light ree for tatahouine ce 0 01 cl to flat for garland 2 5 cl the data confirm the trends found by fukuokaet al 1977 as well as their interpretations factor analysis shows several parallel groupings for aubrites and diogenites siderophiles re ir os pd ge chalcophiles se te volatiles ag in tl and incompatibles u ree and cs or rb but there are some differences for elements such as ni sb cd bi au and zn most of which behave more sensibly in aubrites than in diogenites several element pairs that differ greatly in volatility cs u ge ir correlate closely in aubrites in approximately cl chondrite proportions these correlations and other lines of evidence suggest strongly that aubrites originated by igneous processes in their parent body not by direct nebular condensation the source material may have resembled el chondrites in oxidation state and depletion of refractories metal and volatiles

the formation of eucrites constraints from metal silicate partition coefficients this study explores the controls of oxygen fugacity and temperature on the solubilities of fe ni co mo and w in natural eucritic liquids to better constrain the formation of eucritic melts the solubilities of all five elements in molten silicate in equilibrium with fenico femo and fewalloys increase with increasingly oxidizing conditions and decrease with decreasing temperatures in applying these data to formation scenarios of the eucrite parent body we find that the siderophile element abundances in eucrites meteoritic basalts cannot be explained by a single step partialmelting process from a chondritic metal containing source the ni content of the partial melt is too high and the w and mo contents are too low compared to the abundances in eucritic meteorites but fe ni and co concentrations in eucrites can be modeled by metal silicate equilibrium during more or less complete melting of the eucrite parent body with subsequent fractional crystallization of olivine and orthopyroxene however the computed values of mo are still too low and those of w too high when compared with mo and w abundances in eucritic meteorites one possibility is that the mo and w partition coefficients strongly depend on pressure although the howardite eucrite diogenite hed parent body only had a minimal pressure gradient maximum interior pressure 0 1 gpa alternatively sulfides may have played some role in establishing mo abundances

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

the u pb systematics of angrite sahara 99555 abstract angrite sahara 99555 hereafter sah precisely dated by baker et al baker j bizzarro m wittig n connelly j and haack h 2005 early planetesimal melting from an age of 4 5662 gyr for differentiated meteorites nature 436 1127 1131 has been proposed as a new reference point for the early solar system timescale and for calculation of the revised minimum age of our solar system the pb pb age of sah of 4566 18 0 14 ma reported by baker et al differs from the pb pb age of d orbigny another basaltic angrite of 4564 42 0 12 ma amelin y 2008 u pb ages of angrites geochim cosmochim acta 72 221 232 despite the fact that the relative 53mn 53cr and 182hf 182w ages of these meteorites are identical here i report u pb data for 21 whole rock and pyroxene fractions from sah analyzed using the same approach as d orbigny amelin 2008 these fractions contain between 1 3 and 8 9 pg of total common pb slightly more than analytical blank measured 206pb 204pb ratios are between 625 and 2817 for d orbigny blank corrected 206pb 204pb ratios are between 1173 and 6675 eight acid washed whole rock fractions yielded an isochron age of 4564 86 0 38 ma mswd 1 5 data for pyroxene fractions plot mostly above the whole rock isochron and do not form a linear array in 207pb 206pb vs 204pb 206pb isochron coordinates the 207pb 206pb model dates of the pyroxene fractions vary from 4563 8 0 3 to 4567 1 0 5 ma the difference between whole rock and pyroxene u pb systematics may be a result of re distribution of radiogenic pb at a mineral grain scale several million years after crystallization complexities of sm nd lu hf and possibly 26al 26mg mineral systematics of sah described previously may be related to the same process that caused the re distribution of radiogenic pb disturbance of isotopic chronometers renders sah an imperfect anchor for the early solar system timescale the problems with age determination revealed by the studies of sah call for greater attention in pb isotopic dating of angrites and other achondrites

an experimental assessment of the potential of sulfide saturation of the source regions of eucrites and angrites implications for asteroidal models of core formation late accretion and volatile element depletions abstract the geochemistry of asteroidal magmas provides fundamental clues to the processes involved in the origin and early evolution of planetary bodies although sulfides are important reservoirs for a diverse suite of major and trace elements it is currently unclear whether the interiors of asteroid vesta and the angrite parent body were sulfide liquid saturated during petrogenesis of non cumulate eucrites and volcanic angrites to assess the potential of sulfide liquid saturation in the interiors of these bodies high pressure p temperature t experiments were used to quantify the sulfur concentrations at sulfide saturation scss for volcanic angrites and non cumulate eucrites the sulfide silicate partitioning behavior of various trace elements was simultaneously quantified to study their geochemical behavior at sulfide liquid saturation it was found that the measured scss values agree well with the scss values predicted from a previous thermodynamic model for high feo melts to assess the possibility of sulfide liquid saturation of the source regions of non cumulate eucrites and angrites their s abundances were compared with the calculated scss values for their source regions results show that if eucritic and angritic source regions were saturated with fes liquid significant degassing 50 80 of s must have occurred during or following their magmatic emplacement such loss is inconsistent with the s cl zn and rb isotopic compositions of non cumulate eucrites sulfide liquid saturation of eucrite and angrite source regions is also excluded from the strongly incompatible behavior of cu and hse in non cumulate eucrites and angrites riches et al 2012 additional calculations were performed to further explore the timing and extent of s loss during crystallization of the vestan magma ocean the assumption of chondritic bulk s abundances of bulk vesta would correspond with extremely high s contents of the eucrite source region s even after consideration of depletion of s due to core formation in light of the s cl zn and rb stable isotopic compositions of eucrites the s abundances in eucrites are most consistent with the hypothesis that the vestan mantle was already strongly depleted in s 70 80 by the time of vestan magma ocean crystallization resulting in more realistic s contents of the eucrite source region s the depletion of s could have been established during initial accretion of vesta or it could simply reflect accretion of volatile depleted components that experienced incomplete condensation wu et al 2018 modeling of the new experimentally determined sulfide silicate partition coefficients and previously reported vestan mantle depletions of the various chalcophile and siderophile elements suggests that sulfide liquid segregation during early vestan magma ocean crystallization is also unlikely the lack of sulfide liquid saturation in the source regions of non cumulate eucrites and angrites as well as during early vestan magma ocean solidification shows that current geochemical models of core formation and late accretion remain valid for these bodies

coda q in the eastern caribbean west indies summary coda q q has been estimated from seismograms of local earthquakes recorded on short period seismographs on some of the eastern caribbean islands of the lesser antilles arc west indies using the s s single scattering model the region was subdivided into four distinct subregions in order to investigate lateral variations in q the qc values exhibit a strong frequency dependence in the frequency band 1 5 to 16 hz with calculated coda q at 1 hz qo ranging from a minimum of 97 in the dominica area to a maximum of 145 in the leewards the degree of frequency dependence is also largest in the dominica area n 1 09 and smallest in the leewards n 0 82 although there appears to be some lateral and depth variation of both q and n in the region this variation does not seem to be very significant

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

comparative geochemistry of basalts from the moon earth hed asteroid and mars implications for the origin of the moon abstract most hypotheses for the origin of the moon rotational fission co accretion and collisional ejection from the earth including giant impact call for the formation of the moon in a geocentric environment however key geochemical data for basaltic rocks from the moon earth the howardite eucrite diogenite hed meteorite parent body probably asteroid 4 vesta and the shergottite nakhlite chassignite snc meteorite parent body likely mars provide no evidence that the moon was derived from the earth and suggest that some objects with lunar like compositions were produced without involvement of the earth the source region compositions of basalts produced in the moon mare basalts were similar to those produced in the hed asteroid eucrites with regard to volatile lithophile elements na k rb cs and tl siderophile elements ni co ga ge re and ir and ferromagnesian elements mg fe cr and v and less similar to those in the earth or mars mare and eucrite basalts differ in their mn abundances fe mn values and isotopic composition suggesting that the moon and hed asteroid formed in different nebular locations however previous claims that the moon and hed parent body differ significantly in the abundances of some elements such as ni co cr and v are not supported by the data instead cr mg fe ni co abundance systematics suggest a close similarity between the source region compositions and conditions involved in producing mare and eucrite basalts and a significant difference from those of terrestrial basalts the data imply that the moon and hed asteroid experienced similar volatile element depletion and similar fractionation of metallic and mafic phases among hypotheses of lunar origin rotational fission and small impact collisional ejection seem less tenable than co accretion capture or a variant of giant impact collisional ejection in which the moon inherits the composition of the impactor both the moon and hed asteroid may have been derived from a class of objects that were common in the early solar system the most plausible model for the origin of the moon in line with geochemical and cosmochemical constraints is an impact induced fission of the proto earth wanke and dreibus 1986 clearly the moon and eucrite parent body resemble each other to a high degree nature produced such a composition not once but at least twice this calls into question an entire class of models that invoke ad hoc processes to explain the moon by a unique chance event anders 1977 the similarity between eucrites and lunar mare basalts are remarkable were it not for the differences in age and oxygen isotope signature it might be difficult to distinguish them on petrological or geochemical grounds taylor 1986

chondritic models of 4 vesta implications for geochemical and geophysical properties simple mass balance and thermodynamic constraints are used to illustrate the potential geochemical and geophysical diversity of a fully differentiated vesta sized parent body with a eucrite crust e g core size and density crustal thickness the results of this analysis are then combined with data from the howardite eucrite diogenite hed meteorites and the dawn mission to constrain vesta s bulk composition twelve chondritic compositions are considered comprising seven carbonaceous three ordinary and two enstatite chondrite groups our analysis excludes ci and ll compositions as plausible vesta analogs as these are predicted to have a negative metal fraction second the melts thermodynamic calculator is used to show that the enstatite chondrites the cv ck and l groups cannot produce juvinas like liquids and that even for the other groups depletion in sodium is necessary to produce liquids of appropriate silica content this conclusion is consistent with the documented volatile poor nature of eucrites furthermore carbonaceous chondrites are predicted to have a mantle too rich in olivine to produce typical howardites and to have fe mn ratios generally well in excess of those of the heds on the other hand an na depleted h chondrite bulk composition is capable of producing juvinas like liquids has a mantle rich enough in pyroxene to produce abundant howardite diogenite and has a fe mn ratio compatible with eucrites in addition its predicted bulk silicate density is within 100 kg m 3 of solutions constrained by data of the dawn mission however oxidation state and oxygen isotopes are not perfectly reproduced and it is deduced that bulk vesta may contain approximately 25 of a cm like component values for the bulk silicate composition of vesta and a preliminary phase diagram are proposed

cenozoic erosion of the transantarctic mountains a source to sink thermochronological study abstract the formation of the transantarctic mountains tam is strictly related to the evolution of the west antarctic rift system but the timing of their exhumation is still not fully assessed in this work we provide new apatite fission track data collected on the region between the royal society range and the britannia range cooling ages are late eocene oligocene in the center of the region but they get older both northwards and southwards we infer that exhumation was strictly controlled by tam parallel fault strands that were active after the oligocene the royal society range and the britannia range represent transition zones corresponding to transverse structures probably inherited from early basement crustal discontinuities and reactivated as transfer regions during rift propagation the exhumation of the investigated region has been then modeled and predicted thermochronological ages have been compared with detrital data from the miocene sedimentary succession drilled in the victoria land basin results indicate that this sector of the tam is the most probable candidate for the source of sediments and that during the neogene 3 km but up to 5 km of rocks was exhumed

petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites petrology and geochemistry of d orbigny geochemistry of sahara 99555 and the origin of angrites

geochemistry and genesis of the angrites the angrites angra dos reis lew86010 and lew87051 are petrologically and compositionally similar achondrites all angrites have high feomno ratios of 80 94 and very low ci normalized na sm ratios of 0 001 0 003 high abundances of oxidized fe and low abundances of moderately volatile na most likely resulted from parent body processes such as magmatic outgassing rather than nebular processes all angrites have fractionated ca al ratios with angra dos reis exhibiting the most extreme ratio 3 1 ci this ca al fractionation may be due to small amounts of residual spinel in the source region after removal of the angrite melts or to crystallization of spinel from precursor melts for lew86010 and lew87051 the fractionated ca al ratios are not caused by the presence of significant cumulus material for angra dos reis cumulus material may be the cause of the high ca al ratio refractory element ca eu al sc la ce sm tb yb lu ti hf th and ta abundances of lew86010 and lew87051 show similar patterns while angra dos reis has both greater enrichments in these elements and more fractionated patterns compositional and petrologic constraints indicate that lew86010 and lew87051 are related via olivine control the refractory element abundances and mg of lew86010 can be approximated by removal of olivine from lew87051 suggesting that lew86010 may be a residual melt from a lew87051 like precursor alternatively lew87051 may have formed via olivine accumulation from a lew86010 like precursor the origin of the unusual refractory element pattern in angra dos reis remains obscure the differences between the lew86010 lew87051 duo and angra dos reis suggest that either the angrite parent body was heterogeneous or that angra dos reis was formed on a separate parent body based on feomno ratios and normative mineralogies the angrite parent body ies may be similar in bulk composition to one of the carbonaceous chondrite groups particularly ci cm co

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

applications of detrital geochronology and thermochronology from glacial deposits to the paleozoic and mesozoic thermal history of the ross embayment antarctica

low temperature thermochronology and modeling strategies for multiple samples 1 vertical profiles abstract low temperature thermochronology is a powerful method for constraining the time temperature history of rocks and provides constraints on denudation chronologies landscape evolution and tectonic history of geological terrains we present a strategy for modelling thermal histories constrained by thermochronological data from multiple samples in vertical profiles the thermal history is specified to be similar in form for each sample and we include extra parameters to determine the offset temperature between the uppermost and lowermost samples we combine the likelihood from each sample to produce a joint likelihood for all samples together and using initially stochastic search then directed search methods we try to identify a maximum likelihood solution we also implement a test bayesian information criterion which allows us to assess whether we have overparameterised the thermal history and potentially introduced unwarranted complexity this test allows us to simplify the thermal history model without compromising the acceptable data fit subsequently we use a sampling approach to determine the uncertainty or resolution of the thermal history markov chain monte carlo is straightforward to implement and is used to produce joint and marginal probability distributions and from these we can infer credible intervals on the model parameters we demonstrate that combining the samples is preferable in that the final model is easier to interpret and generally has smaller uncertainties than the case where we model all samples independently we consider both synthetic and real data examples focusing on apatite fission track analysis but the general approach is applicable to other analytical methods such as u th he dating and 40ar 39ar analysis and in principle it is straightforward to combine these different data types into one joint thermal history model

the oxygen isotope composition of diogenites evidence for early global melting on a single compositionally diverse hed parent body oxygen isotope measurements of a suite of 22 diogenites demonstrate that they have a restricted range of 17o values 0 246 0 014 2 these results indicate that the diogenites form a single population consistent with a single parent body source rather than multiple sources as has recently been suggested our previously published analysis of eucrites and cumulate eucrites n 34 give very similar results to the diogenites with o17 0 241 0 016 2 and confirm that diogenites and eucrites are from the same parent asteroid the isotopic homogeneity displayed by diogenites eucrites and cumulate eucrites provides strong evidence for an early large scale melting event on the hed parent body possibly resulting in the formation of a magma ocean the paradox whereby diogenites show isotopic evidence in favor of global melting but also geochemical features indicative of late stage interaction with eucritic crust may reflect a rapid transition from global to serial magmatism on their parent body the fact that all the lithologically varied hed units have an isotopically homogeneous composition supports the proposal that they are derived from a single large diverse asteroid most likely 4 vesta the recent suggestion that the heds are not from vesta but instead represent material from the same asteroidal source as the main group pallasites and iiiab irons can be excluded by our oxygen isotope data

record of s rich vapors on asteroid 4 vesta sulfurization in the northwest africa 2339 eucrite in the northwest africa nwa 2339 eucrite a few high fe pigeonite fragments were partially replaced by fine grained troilite mg rich augite silica with minor ilmenite and mg rich ferrosilite the relict pigeonite has distinctly lower fe mn values 17 18 than those 30 of augite and mg rich ferrosilite in the fine grained replacement textures and other eucritic pyroxenes in nwa 2339 the few plagioclase grains associated with these fe rich pigeonite fragments contain high albite components ab17 31 similar replacement textures are also present in a lithic clast consisting of pyroxene and na rich plagioclase ab20 25 in this lithic clast high fe subcalcic augite was replaced by troilite mg rich hedenbergite silica and minor ilmenite whereas mg rich pigeonite remains intact troilite also occurs as tiny inclusions in porous regions of plagioclase moreover the porous regions of plagioclase are enriched in si and depleted in al ca and na compared to relict plagioclase these textures indicate that the formation of troilite rich mineral assemblages is related to the reaction between fesio3 component in pyroxene and s rich vapors whereas the formation of tiny troilite in porous regions of plagioclase is related to the reaction between fe2 in plagioclase and s rich vapors x ray mapping results reveal that during sulfurization of pyroxene and plagioclase lithophile elements mn al ca na and mg were removed to various extents very likely by the s rich vapors based on our observations the s rich vapors could be dry s o p vapors which most likely have been formed by volatilization of pre existing s p bearing materials due to impact heating on the surface of asteroid 4 vesta

chalcophile elements in martian meteorites indicate low sulfur content in the martian interior and a volatile element depleted late veneer abstract it is generally believed that the martian mantle and core are rich in sulfur and that shergottites originated from sulfide saturated magma however recent work suggests that the high feo contents would require very high s concentrations in shergottite parent magmas at sulfide saturation here we combine new and published data on chalcophile elements in shergottites nakhlites and alh84001 to constrain the sulfide saturation state of the parent magmas and the chalcophile element concentrations in their mantle sources regardless of the mgo content and the long term depletion history of incompatible lithophile elements as indicated by initial e143nd different groups of shergottites display limited variations in ratios of pt pd re cu s se and te the emplacement of most shergottites within the crust and limited variations of ratios of chalcophile elements with substantial differences in volatility during eruption e g cu s cu se and pt re indicate little degassing losses of s se te and re from shergottites limited variations in ratios of elements with very different sulfide silicate melt partition coefficients and negative correlations of chalcophile elements with mgo require a sulfide undersaturated evolution of the parent magmas from mantle source to emplacement in the crust consistent with the feo based argument sulfide petrography and the komatiite like fractionation of platinum group elements pge in shergottites also support this conclusion the absence of accumulated sulfides in the ancient martian cumulate alh84001 results in very low contents of pge re cu se and te in this meteorite hinting that sulfide undersaturated magmas may have occurred throughout the martian geological history the negative correlation of cu and mgo contents in shergottites suggests approximately 2 0 4 1 s g g cu in the martian mantle the ratios of cu s se and te indicate 360 120 g g 1s s 100 27 ng g 1s se and 0 50 0 25 ng g 1s te in the martian mantle at such low s concentrations all s in martian mantle sources may dissolve in basaltic melts that form at 5 partial melting assuming equilibrium metal silicate partitioning and provided that the compositional model of the martian mantle based on snc meteorites is correct martian mantle inventories of cu s and se were mostly established by core formation and the martian core should contain