crustal structure across the transition from rifting to spreading the woodlark rift system of papua new guinea summary the woodlark rift system is one of the few places where active ocean basin formation can be studied within this rift system continental extension rates are some of the fastest on the planet and extension progresses eastwards to full seafloor spreading we use results from a recent passive seismic experiment to address the role of magmatism prior to the onset of seafloor spreading we invert local earthquake p and s traveltimes for 3 d structure around and ahead of the active spreading tip from the local earthquake tomography we observe three main structures seismic velocities in the crust show a sharp contrast between regions that resemble continental crust ahead of the spreading tip and oceanic crust to the east in the continental portion p velocities increase from 5 6 km s 1 to 6 9 km s 1 between 10 and 25 km depth indicating a bulk felsic to intermediate composition similar to other continental regions beneath the seismic moho 23 28 km depth as defined by receiver functions a 10 15 kmthick gradient zone exist locally with velocities from 7 0 to 7 9 km s 1 which may reflect an underplated mafic granulite facies lowermost crust or perhaps magmatic intrusion into the lithospheric mantle in contrast farther east and closer to the active spreading tip velocities rapidly increase from 6 5 to 7 2 km s 1 between 8 and 18 km depth these fast crustal velocities appear in a narrow zone roughly 60 km wide and indicate a mafic crust similar to oceanic crust our velocity results suggest that the transition from diffuse continental rifting to localized seafloor spreading likely occurs across a narrow zone magmatism prior to the onset of seafloor spreading may not play a significant role in altering crust until the onset of seafloor spreading except through underplating at the base of the crust

an observational search for carbonates on mars a search for carbonates and other salts exposed on the surface of mars was undertaken by observing areas of the surface in the 2 6 m to 4 2 m spectral region using the university of hawaii 2 2 m telescope at the mauna kea observatory hawaii observations of four mars areas syrtis major hellas arabia and an area northeast of hellas were made on the night of september 19 1986 the reflectance spectra for two partially overlapping areas show a weak absorption band in the 3 8 m to 3 9 m region which is in the spectral region where carbonate absorptions appear 3 8 m to 4 0 m the mars area of overlap contains syrtis planum the spectral feature from about 3 76 m to 3 95 m is clearly shortward of and broader than the calcium carbonate band about 3 9 m to 4 0 m and is at a slightly shorter wavelength position than magnesium carbonate magnesite bands about 3 8 m to 3 96 m as measured in this study positive identification of this band cannot be made by us at this time measurements for two other mars areas show no evidence of carbonate or other bands if the band is due to absorptions in the mars surface material spectrum and if it is due to carbonates then the results imply about 3 to 5 wt of a carbonate such as magnesite on average in the upper few millimeters of the mars surface material over the two areas where the weak spectral feature appears we can place an upper limit of 3 to 5 wt calcium carbonate and about 5 wt magnesite for all areas observed the interpretations are based on laboratory measurements of the reflectance spectra of calcite and magnesite and their mixtures with palagonite effects of thermal emission on the detection of carbonates were also explored for a wide range of temperatures thermal effects are not sufficient to mask the presence of calcite in the 3 to 5 wt range theoretical reasoning strongly supporting the presence of carbonates as a component of the mars surface is reviewed these and earlier observations do not rule out carbonates below the surface in other locations as small outcrops or in concentrations of less than 3 to 5 of the areas observed

loess and life out of earth abstract loess is a homogeneous typically nonstratified porous friable slightly coherent often calcareous fine grained silty pale yellow wind blown aeolian and often by water reworked sediment that is distributed on continents world wide recent studies have highlighted the importance of biological loess crusts in trapping and transforming aeolian material into loess and also in prevention from wind and water erosion of deposited material some planets and satellites in our solar system are characterized by conditions comparable to those related to loess formation in terrestrial environments given the requirements for loess deposition on earth this study aims to ask the following questions 1 if loess like sediment formation is possible outside earth what are the mechanisms of sediment deposition and preservation 2 could the possible loess like sediments be stabilized through the activity of extraterrestrial equivalents of biological loess crusts found on earth as loess formation on earth is related to biological activity we propose a new direction in the search for extraterrestrial life evidence about extraterrestrial loess might indicate extraterrestrial life connected to loess formation on the basis of comparative analysis of some astrophysical conditions of seven celestial bodies we propose mars and titan and possibly venus and io to be assessed for evidence of loess deposition and the possible presence of related life forms and their biomarkers following recent advances in our understanding of terrestrial loess deposition we propose new indicators of extraterrestrial life research biomarkers in loess cyanobacterial and other microbial

the early environment and its evolution on mars implication for life there is considerable evidence that the early climate of mars was very different from the inhospitable conditions there today this early climate was characterized by liquid water on the surface and a dense atmosphere composed predominantly of co2 the duration of these warm initial conditions on the surface of mars is uncertain but theoretical models suggest that they could have persisted for hundreds of millions up to a billion years from studies of the earth s earliest biosphere we know that by 3 5 gyr ago life had originated on earth and reached a fair degree of biological sophistication surface activity and erosion on earth make it difficult to trace the history of life before the 3 5 gyr time frame if mars did maintain a clement environment for longer than it took for life to originate on earth then the question of the origin of life on mars follows naturally the fossil evidence of early life on earth provides clues as to what form fossils on mars might take of particular interest are stromatolites macroscopic layered structures that result from the anchoring of sediments by microorganisms living in the photic zone since over two thirds of the martian surface is more than 3 5 gyr old the possibility exists that mars may hold the best record of the events that led to the origin of life even though there may be no life there today

the new athena alpha particle x ray spectrometer for the mars exploration rovers 1 the new alpha particle x ray spectrometer apxs is part of the athena payload of the two mars exploration rovers mer the apxs sensor head is attached to the turret of the instrument deployment device idd of the rover the apxs is a very light weight instrument for determining the major and minor elemental composition of martian soils rocks and other geological materials at the mer landing sites the sensor head has simply to be docked by the idd on the surface of the selected sample x ray radiation excited by alpha particles and x rays of the radioactive sources is recorded by a high resolution x ray detector the x ray spectra show elements starting from sodium up to yttrium depending on their concentrations the backscattered alpha spectra measured by a ring of detectors provide additional data on carbon and oxygen by means of a proper calibration the elemental concentrations are derived together with data from the two other athena instruments mounted on the idd the samples under investigation can be fully characterized key apxs objectives are the determination of the chemistry of crustal rocks and soils and the examination of water related deposits sediments or evaporates using the rock abrasion tool attached to the idd issues of weathering can be addressed by measuring natural and abraded surfaces of rocks

a spectroscopic method for identifying terrestrial biocarbonates and application to mars abstract searching for traces of extinct and or extant life on mars is one of the major objectives for remote sensing and in situ exploration of the planet in previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples in the form of fresh shells and fossils of different ages whose biotic origin is easily recognizable the goal was to discriminate them from their abiotic counterparts in general it is difficult to identify biotic signatures especially when the organisms inducing the carbonate precipitation have low fossilization potential i e microbes bacteria archaea a wide variety of microorganisms are implicated in carbonate genesis and their direct characterization is very difficult to evaluate by traditional methods both in ancient sedimentary systems and even in recent environments in the present work we apply our analysis to problematic carbonate samples in which there is no clear evidence of controlled or induced biomineralization this analysis indicates a very likely biotic origin of the aragonite samples under study in agreement with the conclusion previously reported by guido et al 2007 who followed a completely different approach based on a complex set of sedimentary petrographic geochemical and biochemical analyses we show that our method is reliable for discriminating between biotic and abiotic carbonates and therefore it is a powerful tool in the search for life on mars in the next generation of space missions to the planet

organism substrate interactions and astrobiology potential models and methods abstract organism substrate interactions and their products biogenic structures are important biosignatures on earth this study discusses the application of ichnology the study of organism substrate interactions to the search for present and past life beyond earth three main questions are addressed 1 why to look for biogenic structures i e traces and ichnofabrics beyond earth 2 what biogenic structures to expect on other planets moons and asteroids 3 how to study extraterrestrial biogenic structures review of terrestrial evidence highlights a set of properties that make traces and ichnofabrics important for the search of potential extraterrestrial life trace fossils preserve the activity of soft bodied organisms biogenic structures are resilient to processes that obliterate other biosignatures i e mechanical and chemical degradation diagenesis tectonism and metamorphism traces are very visible biosignatures traces indicate environment and behaviour traces can be universal biosignatures i e biosignatures ideally suited for detecting any type of life a model of organism substrate interactions beyond earth is here proposed expected extraterrestrial traces are those that manifest behaviours that allow to maintain homeostasis excavations meandering traces and biodeposition structures most of the existing rovers and orbiters provide basic instruments for searching these traces it is here suggested that the search for extraterrestrial biogenic structures by rovers would also benefit from artificial adjustable lighting gpr lidar and drilling equipment with optical televiewer in this study open access databases of rover and orbiter imagery have been searched for traces and ichnofabrics but no unquestionable evidence of biogenic structures beyond earth has been found besides those produced by humans this sounds along the lines of the famous fermi paradox if the universe is teeming with aliens where are their traces results of this search show that habitable environments are not the only place to look for biogenic structures non habitable environments such as moons without atmosphere can favour the preservation of shallow tier traces the better preservation potential of traces compared to other biosignatures greatly widens the issue of planetary protection including the interaction between astronauts or vehicles and the substrate may produce disturbances although this study highlights a new direction of study with the tools and concepts of ichnology dialogue between the astrobiological and ichnological communities is needed to use its full potential and possibly answer one of the major questions of science does life exist beyond earth

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

lithospheric structures and possible processes in phanerozoic eastern australia from deep seismic investigations abstract the eromanga basin in eastern australia developed during four major episodes on the rifted eastern margin of the australian precambrian craton seismic reflection profiling together with coincident wide angle reflection refraction profiling indicates structures and compositions in the crust which are dominant in various depth ranges some structural features seem to be limited to the upper crust other deep reflection events and high crustal velocities predominate in the lower crust with mafic intrusion from upper mantle sources being one preferred interpretation these features emphasize the difference in structures and composition between the upper and lower parts of the crust yet other structural and deep reflection features are interpreted as being truly lithospheric in scale because they seem to have seismic expression right from the surface to the upper mantle similar interpretations are made for other continental regions indicating that lithospheric processes affect different depth ranges of the crust and upper mantle in a variety of ways any modelling of such processes in the lithosphere must lead to these quite different end results at appropriate depth ranges

association of phyllosilicates and the inverted channel in miyamoto crater mars 1 the western floor of the miyamoto crater in sinus meridiani on mars exhibits both geomorphic and spectral evidence for aqueous history it contains a sinuous and narrow ridge that is interpreted to be an inverted channel and is suggestive of past fluvial activity phyllosilicates occur in materials that are proximal to the paleochannel but are not detected on top the ridge the simultaneous use of the spectroscopic data high resolution images and a digital elevation model show that fe mg smectites are exposed by erosion they are associated with polygonally fractured bedrock which occurs on the slopes of both sides of the sinuous ridge the observations provide direct evidence of the presence of water and possibly of multiple aqueous events throughout the area

measured and calculated elastic wave velocities for xenoliths from the lower crust and upper mantle jackson i rudnick r l o reilly s y and bezant c 1990 measured and calculated elastic wave velocities for xenoliths from the lower crust and upper mantle in j h leven d m finlayson c wright j c doohey and b l n kennett editors seismic probing of continents and their margins tectonophysics 173 207 210

global distribution composition and abundance of olivine on the surface of mars from thermal infrared data 1 we used spectral indexing and linear deconvolution to compare thermal infrared emission spectra of fo91 fo68 fo53 fo39 fo18 and fo1 olivine samples to mars global surveyor thermal emission spectrometer tes data over low albedo regions of mars the fo91 fo68 fo53 and fo39 spectral end members were confidently identified on mars a range of compositions wider than inferred from martian meteorites small less than hundreds of square kilometers occurrences of the fo91 spectral end member are present in the rims of the argyre and hellas impact basins and may represent martian mantle materials the fo68 spectral end member is common throughout the highlands chasmata outflow channels and nili fossae region the fo53 spectral end member occurs in eastern syrtis major the nili fossae region and smooth floored craters of the highlands although less abundant than fo68 and fo53 the distribution of the fo39 spectral end member suggests that some olivine on mars is more fe rich than olivine in martian meteorites global maps of olivine show that 1 materials containing 10 20 of olivine are common in the southern highlands of mars 2 olivine is most common near the topographic dichotomy boundary and 3 olivine becomes uncommon near the poles suggesting that it may be influenced by topography and or latitude climate olivine is found in early noachian to amazonian terrains some of which may be coeval with phyllosilicate and sulfate deposits detected by omega implying that any early noachian wet period of mars climate history may have been globally inhomogeneous or insufficient to weather the olivine that remains today

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

assessing hydrothermal alteration intensity in volcanic hosted massive sulfide systems using portable x ray fluorescence analysis of drill core an example from myra falls canada current portable x ray fluorescence pxrf technology can rapidly and inexpensively yield concentrations of geologically significant elements typically with instrument detection limits below several tens of parts per million based on conventional xrf whole rock geochemical data both the ishikawa alteration index and the chlorite carbonate pyrite index increase with proximity to sulfide mineralization at myra falls however available pxrf technology is typically unable to detect all the elements required to calculate these alteration indices as a result there is a need to utilize the elements that are readily detectable using pxrf and apply these to hydrothermal alteration assessment we propose that rb sr ratios provide a robust proxy for the ishikawa alteration index and demonstrate that conventional whole rock xrf analytical results for rb and sr can be reproduced using pxrf analysis from drill core surfaces at myra falls the rb sr ratios vary from 2 0 for intensely altered rocks downhole profiles of alteration intensity generated from systematic pxrf analysis of drill core surfaces can be used to inform drilling and targeting decisions the application of the rb sr ratio as a proxy for alteration intensity extends beyond this case study and can be applied to other hydrothermal systems that produce phyllosilicate minerals as alteration products of feldspar

refined data of alpha proton x ray spectrometer analyses of soils and rocks at the mars pathfinder site implications for surface chemistry 1 an extensive recalibration of the alpha proton x ray spectrometer apxs was performed to improve the data evaluation of the mars pathfinder mpf rock and soil in situ measurements many samples and geostandards were measured with an mpf identical spare apxs under simulated martian atmospheric pressure and low night temperature conditions precise calibration curves for major and minor elements were obtained using an improved spectral evaluation method for the original mpf spectra refined and new elemental compositions of the mpf rocks and soils were derived however all initial conclusions about soils and rocks remained valid the mpf soil composition revealed the mafic nature of the surface as inferred from the results of viking 1 and 2 data however the mpf rocks reflect a felsic composition for all samples linear correlations of sulphur with all other elements were noticed reflecting the fact that the rocks were covered with varying degrees of soil which compared to the rocks is rich in sulphur extrapolating to low sulphur abundance 0 3 the composition of a soil free rock was calculated the mpf rock composition is high in si and k and low in mg and fe compared to the soil using elemental data from mpf and martian meteorites a global estimation of the martian crust composition was derived the crust is of basaltic nature with a high abundance of incompatible elements k rb nd u th and volatile elements s cl while carbonates are lower or absent

measured and calculated elastic wave speeds in partially equilibrated mafic granulite xenoliths implications for the properties of an underplated lower continental crust ultrasonic compressional wave velocities measured at 1 0 gpa and room temperature are compared with calculated velocities based on single crystal data and modal mineralogy for a suite of mafic granulite xenoliths from the chudleigh volcanic province north queensland australia the xenoliths have nearly constant major element compositions but widely variable modal mineralogy reflecting recrystallization under variable pressure temperature conditions at depth in the continental crust 20 45 km they thus provide an excellent opportunity to investigate velocity variation with depth in a mafic lower crust measured p wave velocities corrected for the decompression induced breakdown of garnet range from 6 9 to 7 6 km sec and correlate with derivation depth these velocities are 5 12 lower than the calculated velocities 7 5 8 0 km sec apparently as a result of grain boundary alteration as well as irreversible changes that occurred in the xenoliths during rapid decompression calculated p wave velocities are similar to those estimated by furlong and fountain 1986 and sobolev and babeyko 1989 for mafic granulites formed through basaltic underplating of the continental crust depending upon in situ temperature p wave velocities in the deepest samples may be interpreted as crustal e g 7 3 7 6 km sec if heat flow is high or mantle 7 7 7 8 km sec in areas of low heat flow the range of velocities in the xenolith suite is larger than predicted for a fully equilibrated underplated basaltic layer highlighting the importance of kinetic effects in determining the ultimate velocity profile of magmatically underplated crust comparison of our results with seismic profiles illustrates that the lower crust rarely reaches such high velocities suggesting quartz bearing rocks country rocks are present within magmatically underplated layers of the deep crust

s type granitic magmas petrogenetic issues models and evidence abstract despite a perception that it represents a perverse divergence it is perfectly possible to believe in the existence of s and i type granites and the implications for the nature of their protoliths and to disbelieve in the applicability of the restite unmixing model for chemical variation in granitic magmas white and chappell erected the s i classification with impeccable validity the isotopic evidence demands contrasting source reservoirs for s and i type granitic magmas however the major advance was not the classification but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas the restite unmixing model is commonly seen as a companion to the s i classification but it is really a separate issue this model implies that the compositions of granites image those of their source rocks in a simple way however there are other equally valid models that can explain the data and none of them represents a unique solution the most cogent explanation for the high grade metasedimentary enclaves in most s type granites is that they represent mid crustal xenoliths restitic enclaves are either rare or absent inherited zircons in s type rocks are certainly restitic however the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock zircon and zirconium behaviours are controlled by disequilibrium and kinetics and zr contents of granitic rocks can rarely be used to infer magma temperatures since the dominant ages among inherited zircons in lachlan fold belt lfb s type granites are ordovician and proterozoic it seems likely that crust of this age but geochemically different from the exposed rocks not only underlies much of the lfb but also forms a component in the granite magma sources the evidence is overwhelming that the dark microgranular enclaves that occur in both s and i type granites are igneous in origin they represent globules of quenched more mafic magma mingled and modified by exchange with the host granitic magma however magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas likewise the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and in some cases violate constraints from isotopic studies s and i type magmas commonly retain their distinct identities this suggests limited source mixing limited magma mixing and limited wall rock assimilation though intermediate types certainly exist they are probably relatively minor in volume crystal fractionation probably plays the major role in the differentiation of very many granitic magmas including most s types especially those emplaced at high crustal levels or in the volcanic environment minor mechanisms include magma mixing wall rock assimilation and restite unmixing isotopic variations within plutons and in granite suites could be caused by source heterogeneities magma mixing assimilation and even by isotopic disequilibrium however source heterogeneity coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust and crustal thickening likewise fails to provide sufficient heat generally the mantle must be the major heat source this might be provided through mantle upwelling and crustal thinning and possibly through the intra and underplating of mafic magmas upper crustal extension seems to have been common in regions undergoing granitic magmatism migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid present reactions granitic magmas are mostly formed by fluid absent processes where we do see rare evidence for arrested fluid absent partial melting the melt fraction is invariably concentrated into small shear zones veinlets and small dykes thus it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels however one major missing link in the chain is the mechanism by which melt fractions in small scale segregations occurring over a wide area can be gathered and focused to efficiently feed much wider spaced major magma conduits answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones self organization almost certainly plays a role

exploring for a record of ancient martian life the immediate task facing exopaleontology is to define a strategy to explore mars for a fossil record during the decade long exploration program that lies ahead consideration of the quality of paleontological information preserved under different geological conditions is important if we are to develop a strategy with broad applicability the preservation of microbial fossils is strongly influenced by the physical chemical and biological factors of the environment which acting together determine the types of information that will be captured and retained in the rock record in detrital sedimentary systems preservation is favored by rapid burial in fine grained clay rich sediments in chemical sedimentary systems preservation is enhanced by rapid entombment in fine grained chemical precipitates for long term preservation host rocks must be composed of stable minerals that are resistant to chemical weathering and that form an impermeable matrix and closed chemical system to protect biosignatures from alteration during subsequent diagenesis or metamorphism in this context host rocks composed of highly ordered chemically stable mineral phases like silica e g cherts or phosphate e g phosphorites are especially favored such lithologies tend to have very long crustal residence times and along with carbonates and shales are the most common host rocks for the precambrian microfossil record on earth although we make the defensible assumption that mars was more like the earth early in its history clearly the geological and historical differences between the two planets are many such differences must be carefully considered when adapting an earth based strategy to mars

p wave velocity features of the lithosphere under the eromanga basin eastern australia including a prominent mid crustal conrad discontinuity abstract the crustal structure of the central eromanga basin in the northern part of the australian tasman geosyncline revealed by coincident seismic reflection and refraction shooting contrasts with some neighbouring regions of the continent the depth to the crust mantle boundary moho of 36 41 km is much less than that under the north australian craton to the northwest 50 55 km and the lachlan fold belt to the southeast 43 51 km but is similar to that under the drummond and bowen basins to the east the seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the north australian and lachlan provinces in particular there is a sharp velocity increase at mid crustal depths 21 24 km which has not been observed with such clarity elsewhere in australia the conrad discontinuity in the lower crust the many discontinuous sub horizontal reflections are in marked contrast to lack of reflecting horizons in the upper crust further emphasising the differences between the upper and lower crust the crust mantle boundary moho is characterised by an increase in velocity from 7 1 7 7 km s to a value of 8 15 0 04 km s the depth to the moho under the canaway ridge a prominent basement high is shallower by about 5 km than the regional moho depth there is also no mid crustal horizon under the canaway ridge but there is a very sharp velocity increase at the moho depth of 34 km the ridge could be interpreted as a horst structure extending to at least moho depths but it could also have a different intra crustal structure from the surrounding area the sub crustal lithosphere has features which have been interpreted from limited data as being caused by a velocity gradient at 56 57 km depth with a low velocity zone above it because of the contrasting crustal thicknesses and velocity gradients the lithosphere of the central eromanga basin cannot be considered as an extension of the exposed lachlan fold belt or the north australian craton the lack of seismic reflections from the upper crust indicates no coherent accoustic impedance pattern at wavelengths greater than 100 m consistent with an upper crustal basement of tightly folded meta sedimentary and meta volcanic rocks the crustal structure is consistent with a pericratonic or arc back arc basin being cratonised in an episode of convergent tectonics in the early palaeozoic the seismic reflections from the lower crust indicate that it could have developed in a different tectonic environment

the composition and petrogenesis of the lower crust a xenolith study granulite facies lower crustal xenoliths from a single basaltic vent hill 32 in the mcbride volcanic province north queensland australia illustrate the extreme lithologic diversity of the deep crust these xenoliths are dominantly mafic but intermediate and felsic granulites represent a significant proportion 20 of the xenolith population all xenoliths have high grade mineralogies and generally well equilibrated textures as well as decompression features which are indicative of derivation from deep crustal levels 0 7 1 0 gpa major and trace element chemistry for 12 xenoliths chosen to span the observed lithologic range are used to constrain the petrogenesis of these rocks in the smaller layered samples metamorphic differentiation may lead to nonrepresentative sampling however in most instances such secondary processes can be identified and the original chemical characteristics delineated the mafic xenoliths formed through a variety of processes including crystallization of mafic magma crystal accumulation from mafic and felsic magmas and partial melting of intermediate compositions to yield a mafic residuum the two analyzed intermediate xenoliths are metasediments based upon high alumina to alkali ratios and rare earth element patterns whereas the two felsic xenoliths have compositions similar to igneous rocks comparisons of noncumulate and or restite xenoliths with unmetamorphosed rock types show that k and rb are variably depleted whereas th and u are strongly depleted in all rock types the large ion lithophile element depletion patterns for xenoliths are similar to those of rocks from granulite facies terrains suggesting similar processes were operative suggestions of an anomalously ba and sr rich lower crust are not supported by the data by using the observed lithologic proportions of xenoliths at hill 32 and the chemical analyses presented here a weighted mean composition of the lower crust can be obtained and compared with recently proposed lower crustal compositions the weighted mean composition is mafic and formed through a combination of basaltic underplating crystal accumulation tectonic underplating and partial melting no simple model of lower crust formation through basaltic or andesitic underplating nor intracrustal melting is sufficient to explain lower crust formation in phanerozoic continental margin settings

lower crustal xenoliths from queensland australia evidence for deep crustal assimilation and fractionation of continental basalts abstract a suite of mafic granulite facies xenoliths from north queensland possesses petrographic and geochemical features of basaltic cumulates crystallized at lower crustal pressures negative correlations between incompatible trace elements and mg and positive correlations between compatible trace elements and mg suggest the xenoliths are genetically related and crystallized from a continuously evolving melt zr hf y hree ti and v do not correlate with mg but show excellent negative correlations with al2o3 content reflecting the proportion of cumulate plagioclase to clinopyroxene these chemical trends also suggest the trace element concentrations have not been affected by subsolidus recrystallization the xenoliths have a large range in sr and nd isotopic compositions 87 sr 86 sr 0 70239 to 0 71467 nd 9 5 to 6 1 which cannot be produced by crystal fractionation alone and excellent correlations between isotope ratios and mg suggest the variable isotope compositions are not due to mantle source heterogeneities these mafic xenoliths are proposed to be cumulate products from a melt undergoing simultaneous assimilation and fractional crystallization afc the data illustrate that only a few percent afc in lower crustal environments can dramatically change the sr and nd isotopic composition of a basaltic melt and suggest the use of caution when inferring mantle source isotopic compositions from continental basalts additionally the nd isotopic data plot on a positive trend on an sm nd isochron diagram with an age of 570 ma however if these xenoliths formed by afc the positive trend reflects mixing between two isotopic end members and has no age significance the correlations between sr and nd isotopic compositions with mg degrade as the isotopic ratios are back calculated to earlier times suggesting the xenoliths are relatively young the xenoliths may be related to the cenozoic igneous activity which occurs throughout eastern australia

garnet forming reactions in mafic granulites from enderby land antarctica implications for geothermometry and geobarometry

heterogeneous magnesium isotopic composition of the lower continental crust a xenolith perspective 1 we report 26 high precision whole rock mg isotopic analyses for two suites of well characterized granulite xenoliths from chudleigh and mcbride north queensland australia in order to constrain the behavior of mg isotopes during deep crustal processes and the mg isotopic composition of the lower continental crust previous studies suggest that the chudleigh granulites are a suite of cogenetic cumulates crystallized from mafic magmas that intruded into and assimilated the preexisting lower crust via combined assimilation and fractional crystallization afc the 26mg values of the xenoliths range from 0 31 to 0 21 and correlate with radiogenic isotopes reflecting mixing of mantle derived mafic magma 26mg 0 31 with preexisting isotopically heavy crustal materials 26mg 0 5 through the afc process the mcbride granulites range compositionally from mafic to felsic and originated as cumulates solidified mafic felsic melts and restites that formed during basaltic underplating and reworking of preexisting lower crust their 26mg values vary widely from 0 72 to 0 19 the large mg isotopic variation in the mcbride xenoliths reflects both distinct source compositions and metamorphic enrichment of garnet which is isotopically light based on these results the lower continental crust has a heterogeneous mg isotopic composition with a weighted average 26mg of 0 18 the bulk continental crust based on available data has an average mg isotopic composition of 0 19 and is slightly heavier than the mantle the highly heterogeneous mg isotopic distribution in the crust indicates that chemical weathering not only modifies the upper crust compositions but also significantly influences lower crust compositions through emplacement of upper crustal materials into the deep crust

surface and crater exposed lithologic units of the isidis basin as mapped by coanalysis of themis and tes derived data products 1 the stratigraphy and mineral heterogeneity of surface and crater exposed deposits in the southwestern portion of the isidis basin were investigated using spatial spectral visible and thermophysical data sets from both the mars global surveyor and odyssey missions four themis spectral surface units were identified progressing from the libya montes highlands to the inner lowland plains of isidis planitia lithologic determinations of these spectral units were made by linear deconvolution analysis of tes data olivine rich surface materials correlate with a well documented high thermal inertia unit based on spatial and stratigraphic relationships interpreted from both crater exposed and surface exposures the olivine rich unit was determined to have formed subsequent to the isidis basin forming event morphology occurrence and linear deconvolution of this unit suggests that it may represent noachian age to hesperian age picritic lavas that erupted as early stage lavas originating from sources such as syrtis major beneath isidis and as far as tyrrhena patera these lavas are suggested to have partially filled the basin based on crater exposed occurrences and were subsequently buried by further evolved olivine poor lavas later these lavas were exposed by erosion and subsequent impacts into the basin crater scaling suggests significant infilling of the basin by these lavas that may account for craters with very high d d ratios and the well developed positive mass anomaly associated with the basin this study also demonstrates that the remote sensing of impact craters in conjunction with surface mapping is a potent mapping tool for understanding stratigraphy and the petrogenesis of the martian crust

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

possible magmatic underplating beneath the west coast of india and adjoining dharwar craton imprint from archean crustal evolution to breakup of india and madagascar abstract the shear wave velocity of the crust along a 660 km profile from the west to the east coast of south india is mapped through the joint inversion of receiver functions and rayleigh wave group velocity the profile consisting of 38 broadband seismic stations covers the archean dharwar craton proterozoic cuddapah basin and rifted margin and escarpment the moho is mapped at a depth of 40 km beneath the mid archean western dharwar craton wdc cuddapah basin cb and the west and east coasts formed through the rifting process this is in contrast with a thin 35 km crust beneath the late archean eastern dharwar craton edc along the profile the average thickness of the upper middle and lower crust is 4 km 12 4 km and 24 4 km respectively above the moho we observe a high velocity layer hvl vs 4 km s of variable thickness increasing from 3 1 km beneath the edc to 11 3 km beneath the wdc and the cb and 18 2 km beneath the west coast of india the seismic wave velocity in this layer is greater than typical oceanic lower crust we interpret the high velocity layer as a signature of magmatic underplating due to past tectonic processes its significant thinning beneath the edc may be attributed to crustal delamination or relamination at 2 5 ga these results demonstrate the dual signature of the archean dharwar crust the change in the geochemical character of the crust possibly occurred at the end of archean when komatiite volcanism ceased the unusually thick hvl beneath the west coast of india and the adjoining region may represent underplated material formed due to india madagascar rifting which is supported by the presence of seaward dipping reflectors and a 85 90 ma mafic dyke in the adjoining island

developing a quantitative mudrock calibration for a handheld energy dispersive x ray fluorescence spectrometer abstract handheld energy dispersive x ray fluorescence hhedxrf spectrometers enable rapid and non destructive means of quantifying the elemental composition of rocks advances in hhedxrf technology have resulted in their widespread usage in the geological sciences currently most popular hhedxrfs lack lithology specific calibrations and in turn acquire datasets with high precision but in many cases with unknown or low accuracy this study derives a methodology to create an internal regression based mudrock calibration for a hhedxrf analyzer with the aim of increasing the analytical quality of elemental data collected from core and outcrop samples for this study we utilize 64 compositionally diverse middle devonian mudrock samples from four cored locations within the central appalachian basin samples were analyzed on both a hhedxrf and a quantitatively superior bench top wavelength dispersive xrf wdxrf spectrometer utilizing linear regressions hhedxrf values were calibrated to the values of the wdxrf for individual elements measurements from the two xrf modes record the following coefficients of determination zn mo and ca r2 0 99 al k ti fe ni v cu and pb r2 0 92 zr and si r2 0 78 and cr r2 0 56 to assess precision relative standard deviations rsd were calculated for each element based on repeated measurements collected on internal reference samples all elements recorded rsd values of 20 outside of the acceptable limit the internal mudrock calibration creates high analytical quality datasets for more robust analyses when compared to previous approaches

visible near infrared and mid infrared spectral characterization of hawaiian fumarolic alteration near kilauea s december 1974 flow implications for spectral discrimination of alteration environments on mars

atmospheric conditions on early mars and the missing layered carbonates 1 widespread massive layered sediments studied by surface rovers and mars orbiting spectrometers are found to be rich in sulfates no similarly massive carbonates have been detected we present the results of coupled atmospheric and geochemical calculations of the formation of the sulfate rich meridiani sediments and offer an explanation for why extensive layered carbonates are not found there or elsewhere on mars large scale volcanism from the build up of tharsis during the late noachian would have injected large amounts of so2 into the atmosphere efficient photochemical conversion of so2 to h2so4 would have caused widespread sulfuric acid water clouds similar to those seen on venus today precipitation from these clouds and acidification of surface water would have sustained a thick warm co2 atmosphere via carbonate inhibition such an atmosphere could have been subjected to loss to space via impact erosion and sputtering once atmospheric so2 gas production dropped and waters become more alkaline the remaining co2 in the atmosphere collapsed to form poorly consolidated carbonate patinas on rock surfaces and in open fractures

did bushmanland extensionally unroof namaqualand abstract the namaqua natal orogen evolved between about 2000 and 1000 ma as part of an orogenic system that assembled the rodinian supercontinent and wraps the archaean kaapvaal craton to the south and west the orogen includes the western ultra high temperature sapphirine hercynite granulite facies namaqualand terrane structurally overlain to the north by the low grade high level igneous richtersveld terrane 1900 1700 ma and to the east by the amphibolite facies granite gneiss pb zn rich supracrustal bushmanland terrane which is overthrust from the north along the groothoek thrust by the high pressure hom terrane west of the dextral tantalite valley pofadder shear zone the gently dipping contacts among these terranes have been considered to be thrusts with the exception of the groothoek thrust the contacts are low angle top down to the east or northeast folded extensional detachments with displacements of up to at least 100 km the namaqualand part of the namaqua natal orogen comprises two distinct event sequences a kibaran phase of crustal shortening and thickening and voluminous granitic sheets at about 1200 ma then a namaquan phase of mafic underplating ultra high temperature metamorphism granitic sheets dextral transtension constrictional fabrics and crustal thinning from about 1060 to 1030 ma a dominant constrictional ls fabric was developed in regionally sub horizontal layered pink granite gneisses and metasediments deformed by ene trending folds extensional detachments developed late in the namaquan phase when the ultra high temperature rocks were exhumed in the bushmanland terrane aggeneys metasediments have mainly constrictional fabrics and are deformed by giant upward facing downward closing sheath folds developed during transtension in which lie 1700 ma pb zn sedex deposits like those of broken hill and flin flon the namaqualand terrane may be the largest and oldest extensional core complex on earth the proterozoic era was characterized by transtensional ultra high temperature horizontally layered lineated pink gneiss terrains with corrugating fold hinges roughly parallel with the finite stretching direction

seismic properties of lower crustal xenoliths from el hoyazo se spain experimental evidence up to partial melting abstract seismic techniques provide unique tools to investigate the structure and in combination with petrological geochemical and petrophysical study the composition of the lower crust controversies can be solved with comparative study of metamorphic terrains or xenoliths that occur adjacent to areas where seismic refraction reflection data are available xenoliths represent a direct sampling of the inaccessible lower crust at the time of the volcanism whilst exposed crustal sections can only be used as analogue of present day lower crust the present study is focused on the measurements of compressional wave velocities up to conditions exceeding the beginning of melting 950 c at 500 mpa confining pressure on three garnet biotite sillimanite metapelitic xenoliths recovered from the neogene dacites of el hoyazo se spain they preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction and represent the best example of partially molten lower crust in the alboran domain the influence of glass on vp is primarily reflected by anomalous positive dvp dt while heating with velocity increasing at 500 mpa from 4 98 to 5 50 km s 1 at room temperature to 5 85 6 79 km s 1 at 650 700 c this corresponds to the glass transition where all the grain boundaries and most of the pores within the glass are closed after this point the velocity decreases to 6 2 6 5 km s 1 at 950 c where re melting of the glass is achieved and additional partial melt produced on cooling the behavior is normal with negative dvp dt after the thermal treatment velocities are 30 higher 6 07 7 21 km s 1 and reveal that in the presence of intergranular melt velocity measurements at room temperature cannot be extrapolated to high temperatures p waves measured at melting conditions are in agreement with deep seismic refraction data and tomography in the area and corroborate the hypothesis that partial melts are actually present in alboran lower crust

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

clay minerals in delta deposits and organic preservation potential on mars clay rich sedimentary deposits are often sites of organic matter preservation and have therefore been sought in mars exploration however regional deposits of hydrous minerals including phyllosilicates and sulphates are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early mars the compact reconnaissance imaging spectrometer for mars crism has recently identified phyllosilicates within three lake basins with fans or deltas that indicate sustained sediment deposition eberswalde crater holden crater and jezero crater here we use high resolution data from the mars reconnaissance orbiter mro to identify clay rich fluvial lacustrine sediments within jezero crater which has a diameter of 45 km the crater is an open lake basin on mars with sedimentary deposits of hydrous minerals sourced from a smectite rich catchment in the nili fossae region we find that the two deltas and the lowest observed stratigraphic layer within the crater host iron magnesium smectite clay jezero crater holds sediments that record multiple episodes of aqueous activity on early mars we suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material

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

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

mineralogical composition and total organic carbon quantification using x ray fluorescence data from the upper cretaceous eagle ford group in southern texas six southern texas eagle ford cores were investigated to quantify mineralogical composition and total organic carbon toc machine learning of the x ray fluorescence xrf data set was conducted using neural network analysis to predict mineralogies for l1 l2 and l3 and toc for l1 l2 l3 iona 1 innes 1 and well x inees 1 and well x were used as blind tests to check the quality of the developed models the online neural designer software was used to perform the training process and develop models quantitative laboratory measured x ray diffraction xrd mineralogies and toc were used to conduct the training and develop high resolution semiquantitative models and the derived mineralogic and organic matter models were found to be promising the modeled mineralogy and toc represent continuous relative abundances which are far more significant than scattered individual xrd and toc point measurements the significance of this study is that it allows for the use of relatively inexpensive and nondestructive xrf analysis that requires minimal sample preparation to construct high resolution mineral abundances and toc content with modern advances in technology xrf can now be measured on drill cuttings in real time while drilling is occurring allowing operators to use the proposed method to construct semiquantitative mineralogical and toc models for evaluating placement of laterals in prospective intervals and designing completion techniques accordingly

cambrian burgess shale animals replicated in clay minerals although the evolutionary importance of the burgess shale is universally acknowledged there is disagreement on the mode of preservation of the fossils after burial elemental mapping demonstrates that the relative abundance of elements varies between different anatomical features of the specimens these differences reflect the compositions of the minerals that replicated the decaying organism which were controlled by contrasts in tissue chemistry delicate morphological details are replicated in the elemental maps showing that authigenic mineralization was fundamental to preserving these fossils even though some organic remains are also present

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

hydrous carbonates on mars evidence from mariner 6 7 infrared spectrometer and ground based telescopic spectra absorption features at 2 28 and 5 4 m identified in mariner 6 7 infrared spectrometer and terrestrial telescopic spectra are consistent with the spectra of hydrous magnesium carbonates such as hydromagnesite and artinite spectral characteristics of these hydrous carbonates are different from those of the anhydrous carbonates as the former do not have the strong spectral features typically associated with anhydrous carbonates such as calcite and siderite theoretical mixing indicates that depending on the type of hydrous carbonate 10 20 wt can be incorporated into the regolith without contradicting the spectral observations or the viking x ray fluorescence chemical analysis hydrous carbonates form as weathering products of mafic minerals in the presence of h2o and co2 even in the antarctic their formation as evaporite minerals from either original magmas or hydrothermally altered rocks is consistent with the martian environment provided liquid water is or has been at least transiently present on earth formation of hydrous mg carbonates is associated with the production of amorphous iron oxides which is consistent with both the environment and the inferred surface mineralogy of mars these minerals are about 60 wt h2o co3 and oh if they are abundant everywhere at the 10 level then about 6 of the surface weight could be volatiles bound in this type of mineral although the stability of hydrous carbonates in a martian environment is uncertain there may be kinetic factors inhibiting the dehydration of these minerals which may persist metastably in the current environment although the spectroscopic evidence for anhydrous carbonates is scant the possible presence of hydrous carbonates provides an appealing mechanism for the existence of carbonates on mars

circum mediterranean oligo miocene biogeographic evolution the gastropods point of view based on studies in iran qom basin esfahan sirjan basin zagros mountains in turkey mut and sivas basins in the mesohellenic basin and in northeastern egypt a new palaeobiogeographic concept for the oligocene and miocene in the circum mediterranean area with special emphasis on the distribution patterns of gastropod faunas is presented a very strict biogeographic terminology is proposed to avoid the common fusion of geographic faunistic and geodynamic terms in the palaeontologists jargon our main interest focuses on the affinities and the faunistic interactions between the early mediterranean and the early indo pacific regions during the oligo miocene especially the role of the early indo pacific faunas as the mythic centre of origination of early neogene european mollusc faunas as often vaguely indicated in the literature is critically evaluated this leads to the establishment of a mediterranean iranian province and a western indian eastern african province as palaeobiogeographic subunits of the western tethys region during the oligocene due to major geodynamic and related biogeographic changes in the early miocene the western tethys region no longer existed and was replaced by the proto mediterranean atlantic region for the area of the paratethys the palaeobiogeographic unit danubian province which includes the protocaspian subprovince is proposed furthermore the underrated transatlantic communication of the oligo miocene nearshore mollusc faunas is demonstrated altogether this paper is a contribution to the discussion on the biogeographic concepts classification and nomenclature in palaeontology as initiated by westermann palaeogeogr palaeoclimatol palaeobiogeogr 158 2000 1 13 163 2000 49 68 2002 elsevier science b v all rights reserved

the lower crust of se belarus petrological geophysical and geochemical constraints from xenoliths abstract highly altered alkaline lamprophyre tuffs of devonian age from se belarus contain lower crustal xenoliths that vary from feldspar rich mafic granulites to rarer feldspar poor eclogitic granulites together with coarse grained hornblendites textural evidence mineral compositions and t p data 700 800 c 0 9 1 1 gpa of the garnet granulite xenoliths indicate that equilibration occurred in the lower crust and therefore we consider that these xenoliths represent samples of the in situ lower crust they are highly altered but the main primary minerals are almandine garnet diopside and andesine plagioclase k feldspar scapolite biotite apatite ilmenite ti magnetite and rutile are accessory minerals a subsequent metasomatic event post dating the granulite facies metamorphism has introduced widespread pargasitic amphibole the granulites are basic in composition are enriched in the most incompatible trace elements and have large negative nb anomalies la n nb n range from 3 to 12 inferring a subduction related origin ree patterns show variable lree enrichment la yb 6 27 and some positive eu anomalies indicating plagioclase accumulation trace element and ree patterns for one sample suggest a melt composition the granulites may represent a gabbroic underplate of unknown age and may be petrogenetically related to the osnitsk mikashevichi plutonic belt hornblendite xenoliths are relatively unaltered and consist of pargasite or pargasite plus magnetite and apatite amphibole compositions are very homogeneous and resemble those in the granulite xenoliths the 40 ar 39 ar plateau age is 381 2 ma lree enriched patterns low 87 sr 86 sr ratios and textural constraints suggest that these hornblendites precipitated from a magma formed from a small degree partial melt of a garnet bearing mantle they may be petrogenetically related to the host lamprophyres possibly as a cumulate from an earlier flux of magma and related to the metasomatic event that affected the granulites whole rock vp values calculated from modal mineralogies of the granulite xenoliths range from 6 7 to 7 5 km s assuming equilibration at 800 c 1 0 gpa they are compatible with seismic velocity measurements of the lower crust beneath se belarus which reach 7 2 km s xenoliths with the least modal plagioclase and to some extent the most modal clinopyroxene and garnet give the highest whole rock vp values calculated vp values for hornblendite xenoliths 6 75 km s at 800 c 1 0 gpa suggest that identification of hornblendite in the lower crust from vp values alone would be difficult

martian surface mineralogy from observatoire pour la mineralogie l eau les glaces et l activite on board the mars express spacecraft omega mex global mineral maps 1 after 2 years of operation the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer on board mars express has acquired data coverage of the martian surface with spatial resolution varying between 300 m and 4 8 km depending on the pericenter altitude of the spacecraft s elliptical orbit we report the global surface distributions of some minerals using the omega observations in the visible and near infrared vnir wavelength domains 0 35 2 5 m global maps of ferric phases mafic minerals pyroxenes and olivines and hydrated minerals have been derived from spectral parameters the limits of detection in terms of abundance for some minerals of different grain size distributions are given the distribution of pyroxenes is in general agreement with the mineral maps of previous telescopic and space observations the fe3 absorption feature in the visible wavelength region is present everywhere on the surface the spectra of the bright regions compare with anhydrous nanophase ferric oxides terrains with water bearing minerals cover a very small fraction of the martian surface olivine mg rich compositions is detected in more extensive regions of the pyroxene rich zones than previously reported olivine with higher iron content and or larger grain size 100 m is only detected in isolated areas the mineralogy of the northern low albedo regions is discussed in the light of these mineral maps chemical alteration or oxidation during extrusion producing a coating or varnish of anhydrous ferric phases over a dark basaltic surface best accounts for the vnir spectral properties of these regions although a glassy composition resulting from impact is also considered

orbital identification of carbonate bearing rocks on mars geochemical models for mars predict carbonate formation during aqueous alteration carbonate bearing rocks had not previously been detected on mars surface but mars reconnaissance orbiter mapping reveals a regional rock layer with near infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the nili fossae region the carbonate is closely associated with both phyllosilicate bearing and olivine rich rock units and probably formed during the noachian or early hesperian era from the alteration of olivine by either hydrothermal fluids or near surface water the presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering proposed to be characteristic of hesperian mars did not destroy these carbonates and thus did not dominate all aqueous environments

geological tectonic framework of solomon islands sw pacific crustal accretion and growth within an intra oceanic setting the solomon islands are a complex collage of crustal units or terrains herein termed the solomon block which have formed and accreted within an intra oceanic environment since cretaceous times predominantly cretaceous basaltic basement sequences are divided into 1 a plume related ontong java plateau terrain ojpt which includes malaita ulawa and northern santa isabel 2 a normal ocean ridge related south solomon morb terrain ssmt which includes choiseul and guadalcanal and 3 a hybrid makira terrain which has both morb and plume plateau affinities the ojpt formed as an integral part of the massive ontong java plateau ojp at c 122 ma and 90 ma respectively was subsequently affected by eocene oligocene alkaline and alnoitic magmatism and was unaffected by subsequent arc development the ssmt initially formed within a normal ocean ridge environment which produced a morb like basaltic basement through which two stages of arc crustal growth subsequently developed from the eocene onwards the makira terrain records the intermingling of basalts with plume plateau and morb affinities from c 90 ma to c 30 ma and a contribution from late miocene present day arc growth two distinct stages of arc growth occurred within the solomon block from the eocene to the early miocene stage 1 and from the late miocene to the present day stage 2 stage 1 arc growth created the basement of the central part of the solomon block the central solomon terrain cst which includes the shortland florida and south isabel islands stage 2 arc growth led to crustal growth in the west and south the new georgia terrain or ngt which includes savo and the new georgia and russell islands both stages of arc growth also added new material to pre existing crustal units within other terrains the solomon block terrane collage records the collision between the alaska sized ojp and the solomon arc initial contact possibly first occurred some 25 20 ma but it is only since around 4 ma that the ojp has more forcefully collided with the solomon arc and has been actively accreting since that time continuing to the present day we present a number of tectonic models in an attempt to understand the mechanism of plateau accretion one model depicts the ojp as splitting in two with the upper 4 10 km forming an imbricate stack verging to the northeast over which the solomon arc is overthrust whilst deeper portions of the ojp beneath a critical detachment surface are subducted the subduction of young 5 ma hot oceanic lithosphere belonging to the woodlark basin at the ssts has resulted in a sequence of tectonic phenomena including the production of unusual magma compositions e g na ti rich basalts and an abundance of picrites an anomalously small

evidence for extensive olivine rich bedrock on mars color infrared observations of an area around the nili fossae acquired by the mars odyssey thermal emission imaging system have been used to map the regional distribution and geologic context of olivine rich materials that first were identified from mars global surveyor thermal emission spectrometer data spectral thermal geomorphic and topographic data demonstrate that the majority of olivine rich material is in the form of inplace layered rock covering an area roughly four times larger than previously recognized some high olivine concentrations are associated with spatially small areas dominated by sediments we favor olivine rich basalts as the origin of the observed olivine enrichment although several hypotheses are viable

chemical variation of the large apollo 15 olivine normative mare basalt rock samples most chemical analyses of apollo 15 olivine normative mare basalts have been conducted on subsamples of 4 g to obtain greater whole rock representivity these subsamples were individually ground and homogenized and splits were taken for analysis furthermore we used both x ray fluorescence and neutron activation techniques to analyze for a comprehensive set of elements suitable for petrogenetic interpretation the analyses show that the samples form a single coherent suite with almost all of the variation corresponding with olivine control 15 range a few of the coarser rocks are not quite represented even at this sampling size the analyses show that the rocks are individually distinct and that analyses are not merely of unrepresentative pieces of a single rock undifferentiated rock unit or rocks differing only by short range unmixing of residual fluids the petrographic features including the low abundance of olivine and its small size and the vesicularity of even some of the coarser samples show that the olivine that controlled the chemical variation is not accumulated in any of the rocks the apollo 15 olivine normative mare basalts were extruded as a series of magmas from a shallow but not locally surficial olivine accumulating magma system and formed a sequence of thin flows a greater understanding of the relationships within and among other mare basalt sequences would be obtained by obtaining comprehensive chemical analyses on splits taken from subsamples of 5 g of all rocks large enough to obtain such subsamples

a 3 5 ga record of water limited acidic weathering conditions on mars abstract the secondary mineral budget on earth is dominated by clay minerals al hydroxides and fe oxides which are formed under the moderate ph high water to rock ratio conditions typical of earth s near surface environment in contrast geochemical analyses of rocks and soils from landed missions to mars indicate that secondary mineralogy is dominated by mg fe ca sulfates and fe oxides this discrepancy can be explained as resulting from differences in the chemical weathering environment of earth and mars we suggest that chemical weathering processes on mars are dominated by 1 a low ph sulfuric acid rich environment in which the stoichiometric dissolution of labile mineral phases such as olivine and apatite fe ti oxides is promoted and 2 relatively low water to rock ratio such that other silicate phases with slower dissolution rates e g plagioclase pyroxene do not contribute substantially to the secondary mineral budget at the martian surface under these conditions al mobilization is limited and the formation of significant al bearing secondary phases e g clays al hydroxides al sulfates is inhibited the antiquity of rock samples analyzed in situ on mars suggest that water limited acidic weathering conditions have more than likely been the defining characteristic of the martian aqueous environment for billions of years

study of terrestrial fossils in phyllosilicate rich soils implication in the search for biosignatures on mars abstract the search for biosignatures in the soil of mars is a major objective of the planet exploration but the detection of such structures is not straightforward due to the degradation of the organic material in a previous work our group has analyzed the spectral reaction to thermal processing of biomineral carbonate samples including fresh and fossil shells we found that two terrestrial fossil shells collected from clay deposits preserve their biomineral characteristics much better than coeval fossils not embedded in clay layers in the present paper we extend our analysis to a set of fossils found in three different terrestrial clay deposits our results confirm that the level of degradation may be much lower than the standard values if fossils are surrounded by clay minerals as a result these fossils have a spectroscopic response to thermal treatment which make them much more distinguishable from their abiotic counterparts than coeval fossils not collected from clay deposits this result implies that the phyllosilicates regions recently discovered on mars may represent very interesting environments that can provide conditions favorable to preserve evidence of biomarkers and hence can be regarded as good candidate locations for their detection

mineralogy at meridiani planum from the mini tes experiment on the opportunity rover the miniature thermal emission spectrometer mini tes on opportunity investigated the mineral abundances and compositions of outcrops rocks and soils at meridiani planum coarse crystalline hematite and olivine rich basaltic sands were observed as predicted from orbital tes spectroscopy outcrops of aqueous origin are composed of 15 to 35 by volume magnesium and calcium sulfates a high silica component modeled as a combination of glass feldspar and sheet silicates 20 to 30 and hematite only minor jarosite is identified in mini tes spectra mini tes spectra show only a hematite signature in the millimeter sized spherules basaltic materials have more plagioclase than pyroxene contain olivine and are similar in inferred mineral composition to basalt mapped from orbit bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites bright wind streak material matches global dust waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering

thermal emission spectra of mars 5 4 10 5 μm evidence for sulfates carbonates and hydrates we have obtained spectra of the thermal emission from mars in the 5 4 10 5 m wavelength domain at a resolving power of about 60 from the kuiper airborne observatory spectra were obtained for several large spots on mars whose ground temperatures and air masses through the martian atmosphere differed significantly these data were taken at two times during the flight by taking the ratio of the spectral flux from one spot to that of a second spot we obtained results that were independent of uncertainties in the instrument s spectral response and the transmission of the earth s atmosphere these data as well as spectral fluxes of single spots based using the star tau as a calibration standard show a number of emission and absorption features they are present in sets of spectra taken at two different times some of the absorption features are due to gaseous co2 in the martian atmosphere the remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface comparison of the strength of features seen at similar times but with three different air masses and ground temperatures suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere based on comparisons of the observed features with laboratory data for a broad ensemble of minerals spectra of other solar system bodies and relevant compositional information about mars we have made the following tentative identifications of the observed features emission features at 7 8 and 9 7 m are attributed to surface silicates an emission feature at 6 1 m is attributed to a molecular water component of the surface material an absorption band at 8 7 m as well as possibly one at 9 8 m is ascribed to sulfate or bisulfate anions probably located in a distorted crystalline site and an absorption band at 6 7 m is attributed to carbonate or bicarbonate anions located in a distorted crystalline site although we cannot totally rule out a nitrate origin for this feature we have simulated these spectra with radiative transfer programs for the atmosphere and surface these simulations indicate that the sulfate and carbonate bearing minerals are contained in the same particles of the airborne dust as the dominant silicate minerals that the dust optical depth was about 0 6 at a reference wavelength of 0 3 m over the area of the observed spots and that sulfates and carbonates constitute about 10 15 and 1 3 by volume of the airborne dust respectively these results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current mars

a chemical model for evaporites on early mars possible sedimentary tracers of the early climate and implications for exploration martian geomorphology seems to indicate extensive hydrological activity during the noachian era liquid water at the surface would require a large greenhouse effect that is widely hypothesized to have been caused by a high partial pressure of atmospheric carbon dioxide pco2 a sedimentation model driven by sequential evaporation is used to calculate the evaporite mineral sequence in a closed basin lake subject to high pco2 the initial fluid is derived from weathered igneous rock similar to martian meteorite basalts siderite feco3 is always the first major carbonate to precipitate thus siderite is predicted to be an important fades component in ancient martian sediments along with silica which is also an early precipitate these would form varves in lakes that undergo cycles of evaporation and water recharge after silica and siderite the sequence is magnesian calcite nearly pure hydromagnesite and gypsum followed by highly soluble salts like nacl the presence of siderite sediments generally requires an atmospheric pco2 level in excess of 0 1 bar otherwise iron silicates such as greenalite would form this may be used in exploration as an observational test on the past atmospheric composition of mars subject to consideration of the depositional environment at pco2 of approximately several bar gypsum precipitation could occur before calcite upon evaporation if the initial so42 ca2 ratio is high and there is no water recharge the predicted carbonate sequence upon evaporation is generally consistent with recent hypotheses suggesting traces of evaporite carbonates in some martian meteorites several mechanisms destroy or obscure carbonates at the martian surface consequently in situ analysis of the interior of ejecta from recent impact craters lying within sedimentary basins may offer the most practical approach to future exploration of ancient carbonate sediments

initial source evaluation of archaeological obsidian from the kuril islands of the russian far east using portable xrf obsidian artifacts recently have been recovered from 18 archaeological sites on eight islands across the kuril island archipelago in the north pacific ocean suggesting a wide ranging distribution of obsidian throughout the island chain over the last 2 500 years although there are no geologic sources of obsidian in the kurils that are known to have been used prehistorically sources exist in hokkaido japan and kamchatka russia the southern and northern geographic regions respectively from which obsidian may have entered the kuril islands this paper reports on the initial sourcing attempt of kuril islands obsidian through the analysis of 131 obsidian artifacts data from this research were generated through the application of portable xrf technology and are used to address research questions concerning prehis toric mobility exchange and social networking in the kuril islands

a review of the handheld x ray fluorescence spectrometer as a tool for field geologic investigations on earth and in planetary surface exploration x ray fluorescence xrf spectroscopy is a well established and commonly used technique in obtaining diagnostic compositional data on geological samples recently developments in x ray tube and detector technologies have resulted in miniaturized field portable instruments that enable new applications both in and out of standard laboratory settings these applications however have not been extensively applied to geologic field campaigns this study investigates the feasibility of using developing handheld xrf hxrf technology to enhance terrestrial field geology with potential applications in planetary surface exploration missions we demonstrate that the hxrf is quite stable providing reliable and accurate data continuously over a several year period additionally sample preparation is proved to have a marked effect on the strategy for collecting and assimilating hxrf data while the hxrf is capable of obtaining data that are comparable to laboratory xrf analysis for several geologically important elements such as si ca ti and k the instrument is unable to detect other elements such as mg and na reliably while this limits the use of the hxrf especially when compared to laboratory xrf techniques the hxrf is still capable of providing the field user with significantly improved contextual awareness of a field site and more work is needed to fully evaluate the potential of this instrument in more complex geologic environments

discovery of olivine in the nili fossae region of mars we have detected a 30 000 square kilometer area rich in olivine in the nili fossae region of mars nili fossae has been interpreted as a complex of grabens and fractures related to the formation of the isidis impact basin we propose that post impact faulting of this area has exposed subsurface layers rich in olivine linear mixture analysis of thermal emission spectrometer spectra shows surface exposures of 30 olivine where the composition of the olivine ranges from fo30 to fo70

silicate oxide and sulphide trends in neo archean rocks from the nilgiri block southern india the role of fluids during high grade metamorphism the nilgiri block southern india represents an exhumed section of lower late archean 2500 ma crust the northern highlands of the nilgiri block are characterized by metagabbros with pyroxenite inlayers a two pyroxene granulite zone acts as a transition between the metagabbros and charnockites which are exposed in the central and southern part of the nilgiri highlands thermobarometry results indicate a sw ne regional trend both in temperature similar to 650 800 degrees c and in pressure 700 1100 mpa over the nilgiri highlands in the charnockites composite rutile ilmenite grains are the dominant oxide assemblage in the two pyroxene granulites hemo ilmenite magnetite is dominant with coexisting rutile ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites in the metagabbros hemo ilmenite magnetite is the dominant oxide assemblage the principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite chalcopyrite exsolution lamellae or blebs in the two pyroxene granulites and the metagabbros the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite pyrrhotite chalcocopyrite associations from these observations a specific oxidation trend is seen the northern granulite facies metagabbros and two pyroxene granulites of the nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions this higher oxidation state is proposed to be the result of highly oxidizing agents probably as so3 in low h2o activity grain boundary nacl saline fluids with a dissolved caso4 component present during granulite facies metamorphism of the metagabbros and two pyroxene granulites eventually these agents became more reducing owing to the inherent buffering of the original tonalite granodiorite granitoids at the graphite co2 buffer such that s took the form of h2s during the granulite facies metamorphism of the charnockites at the same time these saline fluids were also responsible the solid state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro two pyroxene granulite and charnockite

cumulative effects of channel correction and regulation on floodplain terrestrialisation patterns and connectivity abstract one of the main drivers of overbank fine deposition and floodplain formation is the hydrological connectivity between the channel and the floodplain channel correction i e groyne field construction within the main flow channel and secondary channel disconnections and flow regulation can typically lead to a disconnection of riverine floodplains and disturbances that directly affect terrestrialisation channel correction and flow regulation can sometimes occur successively and it is challenging to distinguish the roles of each this work attempts to assess the respective effects of two phases of channel regulation correction versus flow regulation on floodplain terrestrialisation by comparing three bypassed reaches of the rhone france pierre benite peage de roussillon and donzere mondragon we applied a transversal methodology coupled with gis analysis old maps orthophotos dem s etc to understand processes of channel planform evolution conducted a sediment survey metal rod to assess floodplain terrestrialisation and performed sediment sampling manual auger to obtain surface sediment metal content levels x ray fluorescence and inductively coupled plasma mass spectrometry we found a general trend of channel narrowing within the three reaches among which approximately 40 was found to be associated with correction works while 20 was attributed to flow lowering caused by channel bypassing the number of flowing channels in all sections declined significantly and local anabranching reaches evolved into very stable single thread channels overbank sedimentation declined significantly over the period with very high sedimentation levels observed immediately after correction works and with very low sedimentation levels observed after diversion we also found overbank flooding in the number of days per year decreased while fine sediment thickness increased similarly the highest concentrations of metals zc pb and cu were found to be associated with a low connection frequency and vice versa when similar 2 staged terrestrialisation patterns are observed in all three reaches they differ in chronology and driving factors because of their longitudinal positioning and specific local conditions

seismic tomography with local earthquakes in costa rica abstract the costarican isthmus is located at the western limit of the caribbean oceanic plateau where the cocos plate subducts along the middle american trench this plate shows strong lateral variations in its morphology and structure the main objective of this study is to investigate the effects of subduction related magmatism as a function of morphology and structure of the subducting plate by performing a simultaneous inversion of the 3 d crustal velocity field and hypocenter locations from local earthquakes for that we used the traveltimes of p waves first arrivals from more than 5000 events recorded at the costarican seismic networks between 1991 and 1998 in order to prevent data and modeling inaccuracies we followed an inversion scheme consisting of four steps 1 selection of an adequate data subset for tomographic inversion 2 estimation of the best reference 1 d model 3 determination of the finest parameterization and 4 evaluation of resolution the results show that the uppermost levels of the crust 0 6 km are consistent with geology since the velocity anomalies reflect the most meaningful geological features observed in the surface below these levels 6 20 km deep we found two different zones separated by a sw ne seismic alignment the northern part is characterized by a highly heterogeneous velocity field and is seismically active while the southern part is much more homogeneous and practically inactive moreover the northern part shows a certain accumulation of low velocity material within the upper mantle we suggest and illustrate that the structural differences between the northern and southern zones can be a consequence of the differences on the geometry and structure of the subducting slab

infrared spectroscopy of microbially induced carbonates and past life on mars abstract a number of evidences as the past presence of water a denser atmosphere and a mild climate suggest that on early mars environmental conditions should have been favourable to the emergence of life therefore if life actually developed on mars a few hundreds of million years ago or even more recently some biomarkers may still be present in several previous papers based on laboratory analysis we have investigated the modifications induced by thermal processing in the mid infrared spectra of carbonate samples in the form of fresh shells and fossils of different ages skeletal remains of already complex terrestrial life whose biotic origin is not questionable in this way we have been able to develop a spectroscopic method for discriminating biotic samples from their abiotic counterparts in this work we show that our method can be successfully applied also to microbialites i e bio induced carbonates deposits and particularly to stromatolites the laminated fabric of microbialites some of which are among the most primitive and oldest traces of biological activity on earth this result is of valuable importance since such primitive living organisms can be considered good analogues for putative martian life forms

amphibole and lower crustal seismic properties abstract measurements of seismic anisotropy frequently offer insights of the deformation kinematics in situ within the earth in the continental crust seismic anisotropy is commonly ascribed to regionally aligned lattice preferred orientation lpo of mica crystals however determinations of composition suggest that the deep continental crust contains rather little mica in this contribution the role of amphibole a far more plausible constituent especially for deep continental crust of basic composition is assessed a field analogue approach is adopted where the lpo are measured correlated with the strain state of the rocks and used to calculate the seismic properties the seismic properties may be up scaled through the specimen using the modal proportions of the constituent mineral phases to examine the role of composition in controlling the intensity of seismic anisotropy seismic properties are computed using an array of modal compositions so called rock recipes the case history comes from the central block of the lewisian of nw scotland where a regional basic dyke swarm the scourie dykes is locally deformed within amphibolite facies shear zones conditions that are representative of the deep crust shear strain profiles across a 100 m wide shear zone using deflected banding in the host gneisses yield values of 0

phyllosilicates in the mawrth vallis region of mars 1 omega mars express has discovered large outcrops rich in phyllosilicates in the region of mawrth vallis mars around 20 w 25 n the region is located in noachian highly cratered terrains close to the limit of the martian dichotomy where the outflow channel mawrth vallis cuts the highlands we have examined this region using omega spectra of the surface from 0 9 m to 2 6 m with spatial sampling from 500 m to 3 km offering a full coverage of the region omega spectra show two broad bands centered at 1 m and 2 2 m revealing the presence of clinopyroxene on dark surfaces phyllosilicates have been identified by absorption bands at 1 4 m 1 9 m and 2 2 or 2 3 m comparison with laboratory spectra reveals similarities with al oh smectites such as montmorillonites or fe or mg oh smectites such as nontronite a precise location of the phyllosilicate rich areas on visible hrsc images indicates that they are placed exclusively on bright outcrops mostly on the plateaus dated to the noachian period on hrsc and moc images the phyllosilicate rich outcrops reveal strong erosional features such as numerous residual buttes composed of layers a few meters thick the phyllosilicate rich unit corresponds to a geological unit more than 100 m thick over a horizontal extension approximately of 300 km 400 km this unit implies a large volume of altered rocks either in situ or after transport and deposition in noachian terrains revealing a different climatic and geologic environment from the present one

comparison between a regional and semi regional crustal obs model in the voring basin mid norway margin semi regional ocean bottom seismograph obs data acquired in the central and northern part of the voring basin mid norway margin have been modeled by use of 2 d ray tracing the semi regional model derived from the study of twenty five obss deployed along a 120 km long profile is compared with a regional model consisting of five obss from the same profile the semi regional model is somewhat more detailed than the regional model due to the considerably closer receiver spacing the overall geometry and velocity distribution of the two models are remarkably similar however proving that the regional procedure with large obs spacing provides a reliable regional model intrusions of sills related to early tertiary continental rifting and break up are important at intermediate and deep sedimentary levels 2 10 km below sea floor in most parts of the area the semi regional modeling suggests that one of the deepest sills extends much further east and is substantially thicker locally more than 500 m than indicated in the regional model another important difference is a high velocity body within the upper crystalline crust at 11 12 km depth in the nw part of the area indicating that the closer obs spacing in the semi regional modeling allows detection of local intra crustal intrusions local differences are also inferred in the lower crust at about 20 km depth a structure is inferred within the lower crust from wide angle reflections this might suggest that the high velocity lower crustal layer interpreted as magmatic underplating consists of a mixture of underplated intruded magmatic material and blocks of continental lower crust

laboratory wave velocity measurements on lower crustal xenoliths from calcutteroo south australia abstract seismological and petrologic studies have suggested the presence of mafic granulite eclogite and amphibolite as the major components of the lower crust in southeastern australia elastic wave velocity measurements conducted to 400 mpa confining pressure of selected nodules from one kimberlite pipe in south australia range after corrections for estimated in situ crustal pressures and temperatures from v p 6 9 7 7 km s 1 and v s 3 9 4 3 km s 1 these values fall between previous measurements for more silicic crustal granulites and mafic eclogites and coincide with the published velocities determined by seismic studies for southeastern australia it is possible that these types of compositions may be widespread components of the lower continental crust and may require revision of currently accepted models of crustal evolution

lithospheric structure of the costa rican isthmus effects of subduction zone magmatism on an oceanic plateau we present the results of a multidisciplinary geophysical study conducted to investigate the lithospheric structure of the costa rican isthmus the physical properties of the lithosphere are resolved by three dimensional 3 d simultaneous inversion of velocity anomalies and hypocenter parameters using local earthquakes and 2 d forward modeling of onshore and offshore seismic refraction and gravity data according to our results the northern half of the costa rican isthmus is constituted by a 40 km thick crust with a 6 to 7 km thick oceanic crust subducting under it the uppermost level of the basement and most of the marginal wedge show intermediate velocities and high densities in good agreement with those described for flood basalts the midlevel shows velocities and densities representative of oceanic crust the bottommost level 20 40 km shows high velocities and densities typical of mafic rocks and the upper mantle displays anomalously low densities and velocities intracrustal heterogeneities at intermediate wavelengths are indicated by prominent velocity anomalies these results are consistent with a basement beneath the costa rican isthmus being part of the caribbean plateau originated at 85 90 ma with the onset of the galapagos hotspot the upper level corresponds to the flood basalts extruded during this phase and it includes most of the marginal wedge the second level represents the preexisting oceanic crust the mafic lower crust intracrustal heterogeneities and anomalous upper mantle are interpreted to be built up by underplating intrusion and crystallization of basaltic melts formed under the influence of subducting lithosphere dehydration