flood volcanism in the northern high latitudes of mercury revealed by messenger messenger observations from mercury orbit reveal that a large contiguous expanse of smooth plains covers much of mercury s high northern latitudes and occupies more than 6 of the planet s surface area these plains are smooth embay other landforms are distinct in color show several flow features and partially or completely bury impact craters the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement these characteristics as well as associated features interpreted to have formed by thermal erosion indicate emplacement in a flood basalt style consistent with x ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites the plains formed after the caloris impact basin confirming that volcanism was a globally extensive process in mercury s post heavy bombardment era

concentration of h si cl k fe and th in the low and mid latitude regions of mars 1 we report maps of the concentrations of h si cl k fe and th as determined by the gamma ray spectrometer grs on board the 2001 mars odyssey mission for 45 latitudes the procedures by which the spectra are processed to yield quantitative concentrations are described in detail the concentrations of elements determined over the locations of the various mars landers generally agree well with the lander values except for fe although the mean of the grs fe data agrees well with that of martian meteorites the water equivalent concentration of hydrogen by mass varies from about 1 5 to 7 5 by mass with the most enriched areas being near apollinaris patera and arabia terra cl shows a distribution similar to h over the surface except that the cl content over medusae fossae is much greater than elsewhere the map of fe shows enrichment in the northern lowlands versus the southern highlands silicon shows only very modest variation over the surface with mass fractions ranging from 19 to 22 over most of the planet though a significant depletion in si is noted in a region west of tharsis montes and olympus mons where the si content is as low as 18 k and th show a very similar pattern with depletions associated with young volcanic deposits and enrichments associated with the tes surface type 2 material it is noted that there appears to be no evidence of significant globally distributed thick dust deposits of uniform composition

volcanism on mercury evidence from the first messenger flyby for extrusive and explosive activity and the volcanic origin of plains the first messenger flyby of mercury obtained images of 21 of the surface not seen by mariner 10 including the center and western half of the caloris basin and regions near the terminator that show details of the nature of smooth and intercrater plains these new data have helped to address and resolve a series of longstanding questions on the existence and nature of volcanism on mercury and the distribution of volcanic materials data from the mercury dual imaging system mdis on the messenger spacecraft have shown the following 1 numerous volcanic vents in the form of irregularly shaped rimless depressions are concentrated around the interior edge of the caloris basin 2 these vents appear to be sources for effusive volcanism that in one case built a shield in excess of 100 km in diameter and in some cases formed bright haloes around the vents that are interpreted to represent pyroclastic eruptions 3 lobate margins of plains units seen previously in mariner 10 data are documented in messenger images with more clarity and are often distinctive in morphology and color properties supporting the interpretation that these features are the edges of lava flow units 4 the interior of the caloris basin is filled with plains units spectrally distinctive from the rim deposits and comparison with the lunar imbrium basin and superposed impact crater stratigraphy provide evidence that these units are volcanic in origin detailed differences in the mineralogy of lava flow units so prominent in imbrium are not seen in the caloris interior 5 some of the smooth plains surrounding the exterior of the caloris basin show distinct differences in color and morphological properties supporting a volcanic origin 6 some smooth and intercrater plains units distant from the caloris basin show evidence of flooding and embayment relations unrelated to caloris ejecta emplacement local and regional geological and color relationships support a volcanic origin for these plains 7 large impact craters show a sequence of embayment of interior floor and exterior ejecta deposits that supports a volcanic origin for the embayment and filling processes 8 crater embayment and flooding relationships in selected areas suggest volcanic plains thicknesses of many hundreds of meters and local thicknesses inside impact craters of up to several kilometers 9 impact crater size frequency distributions for caloris exterior deposits including the facies of the caloris group and relatively high and low albedo smooth plains show that they are younger than plains interior to caloris and thus must be dominantly the product of post caloris volcanism these new data provide evidence that supports and confirms earlier hypotheses from mariner 10 data that volcanism was important in shaping the surface of mercury the emerging picture of the volcanic style of mercury is similar to that of the moon the other small one plate planetary body there are no major shield volcanoes e g comparable to tharsis montes on mars shallow magma reservoirs are rare and there is little evidence for surface deformation or long lived volcanic sources related to sites of upwelling mantle the close association of volcanic plains and surface deformation features suggests that future observations and analyses can help document the relation between the volcanic flux and the evolving state and magnitude of stress in the lithosphere of mercury

the oldest uhp eclogites of the world age of uhp metamorphism nature of protoliths and tectonic implications coesite bearing eclogitic rocks from the pan african belt in northern mali were dated by multichronological methods rb sr sm nd and ar ar rb sr and sm nd isotope analyses on whole rock and mineral separates of an omphacite kyanite micaschist and a mafic eclogite yielded concordant ages of about 620 ma this is interpreted as the time of the eclogitisation which represents the oldest ultrahigh pressure uhp metamorphic event so far recorded in the continental crust the nearly identical rb sr and sm nd ages suggest very rapid exhumation as observed in many phanerozoic uhp rocks 40ar 39ar dating of phengites from two uhp micaschists gave much older ages of 1045 and 760 ma phengite from a quartzite collected from the same site yielded a plateau date of 623 3 ma which is in agreement with the rb sr and sm nd dates the two 40ar 39ar ages older than 625 ma testify once more the recurrent problem of excess ar in ultrahigh pressure phengites the occurrence of the mali uhp eclogites indicates that by the late precambrian the earth has cooled enough to sustain the formation and preservation of deeply subducted uhp metamorphic rocks the new ages of ca 620 ma also constrain the amalgamation in nw gondwana to have occurred in the latest proterozoic but not in the middle cambrian this is supported by several recent chronological data for the southern segment of the major suture zone in the dahomeyide orogenic belt

thermal erosion by komatiites at kambalda western australia and the genesis of nickel ores huppert et al 1 calculated that komatiites flow turbulently transfer heat efficiently to their substrate and thus potentially produce thermal erosion channels in sequences onto which they were erupted their suggestion that komatiite hosted kambalda type2 nickel ores reside in such channels has led to resurgence of interest in volcanic models for ore emplacement3 5 and caused controversy6 7 such models have important implications not only to ore genetic studies but also to interpretation of the geochemistry of komatiites8 and their sm nd systematics9 10 here we demonstrate that interspinifex fe ni cu sulphide ores which underlie some hanging wall massive sulphide ores at kambalda the site of one of the world s major nickel deposits formed through thermal erosion of underlying komatiite flows and possibly also sediments providing proof of thermal erosion however we caution against the general application of thermal erosion models to the eruption of komatiites it seems that significant thermal erosion occurred rarely and only where basal concentrations of highly thermally conductive sulphide liquid were present at the base of localized lava channels isotope data11 12 and theoretical considerations13 suggest that the komatiites were contaminated by crustal rocks before eruption although there is limited evidence that localized contamination including sulphide assimilation4 may also have occurred below lava channels localized in pre existing embayments or troughs

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

possible detachment zone in precambrian rocks of kanjamalai hills cauvery suture zone southern india implications to accretionary tectonics abstract existence of a possible detachment zone at elampillai region nw margin of kanjamalai hills located in the northern part of cauvery suture zone csz southern india is reported here for the first time detailed structural mapping provides anatomy of the zone which are rarely preserved in precambrian high grade terranes the detachment surface separates two distinct rock units of contrasting lithological and structural characters the upper and lower units the detachment zone is characterized by a variety of fold styles with the predominance of tight isoclinal folds with varied plunge directions limb rotations and the hinge line variations often leading to lift off fold like geometries and deformed sheath folds presence of parasitic folding and associated penetrative strains seem to be controlled by differences in mechanical stratigraphy relative thicknesses of the competent and incompetent units and the structural relief of the underlying basement our present study in conjunction with other available geological geochemical and geochronological data from the region indicates that the structures of the detachment zone are genetically related to thrust tectonics forming a part of subduction accretion collision tectonic history of the neoproterozoic gondwana suture

visible and near infrared reflectance spectroscopy of pyroxene bearing rocks new constraints for understanding planetary surface compositions 1 laboratory visible and near infrared reflectance spectra of solid rock slabs mineral separates and systematic mixtures were simultaneously investigated we apply an empirical approach to evaluate spectra in order to achieve qualitative and quantitative information we use cumulates mostly norites leuconorites melanorites and anorthosites belonging to the bjerkreim sokndal layered intrusion a sequence of genetically related rocks with simple textures laboratory spectra are measured on slightly polished rock slabs in the 350 to 2500 nm interval and directional hemispherical reflectance geometry composition is determined using traditional techniques other than reflectance spectroscopy we find that 1 band minima measured on rock spectra are strongly influenced by the concurrent effects due to modal abundance of the spectroscopically active mineral and mineral chemistry 2 band depths can be used for semiquantitative analyses limited to the set of rocks investigated 3 the spectral parameters derived from powdered pyroxene are in agreement with previously published calibrations 4 the mineral mixture systematics can be reasonably considered as linear when pyroxene is mixed with neutral components and 5 the empirical evaluation of solid rock surface spectra needs further insights to give a great improvement to planetary researches in addition genetic sequences of rocks should be investigated in detail to help the geological interpretation of planetary evolution therefore more laboratory and analytical studies are required in order to understand the influence of composition and petrographic textures on the spectral analysis

a multi data stream assimilation framework for the assessment of volcanic unrest abstract active volcanoes pose a constant risk to populations living in their vicinity significant effort has been spent to increase monitoring and data collection campaigns to mitigate potential volcano disasters to utilize these datasets to their fullest extent a new generation of model data fusion techniques is required that combine multiple disparate observations of volcanic activity with cutting edge modeling techniques to provide efficient assessment of volcanic unrest the purpose of this paper is to develop a data assimilation framework for volcano applications specifically the ensemble kalman filter enkf is adapted to assimilate gps and insar data into viscoelastic time forward finite element models of an evolving magma system to provide model forecasts and error estimations since the goal of this investigation is to provide a methodological framework our efforts are focused on theoretical development and synthetic tests to illustrate the effectiveness of the enkf and its applicability in physical volcanology the synthetic tests provide two critical results 1 a proof of concept for using the enkf for multi dataset assimilation in investigations of volcanic activity and 2 the comparison of spatially limited but temporally dense gps data with temporally limited insar observations for evaluating magma chamber dynamics during periods of volcanic unrest results indicate that the temporally dense information provided by gps observations results in faster convergence and more accurate model predictions however most importantly the synthetic tests illustrate that the enkf is able to swiftly respond to data updates by changing the model forecast trajectory to match incoming observations the synthetic results demonstrate a great potential for utilizing the enkf model data fusion method to assess volcanic unrest and provide model forecasts the development of these new techniques provides 1 a framework for future applications of rapid data assimilation and model development during volcanic crises 2 a method for hind casting to investigate previous volcanic eruptions including potential eruption triggering mechanisms and precursors and 3 an approach for optimizing survey designs for future data collection campaigns at active volcanic systems

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 2 petrological implications abstract the primary objectives of this paper are to determine the modal mineralogy of selected low albedo terrains of different ages ranging from noachian to amazonian exposed on the surface of mars this analysis is conducted using the spectral modeling of the observatoire pour la mineralogie l eau les glaces et l activite omega reflectance data results from this work are consistent with the major results of previous spectroscopic studies plagioclase 40 60 in volume and high calcium pyroxene 20 40 hcp are the dominant minerals of the most regions low calcium pyroxene 10 15 lcp and minor amounts of olivine are also present the oldest terrains are characterized by the largest amount of lcp and the lowest concentration of plagioclase these overall compositions are consistent with two pyroxene basalts the particle sizes are in the range of a few hundreds of micrometers which is in good agreement with the thermal inertia of the martian low albedo regions in the region around the nili fossae localized concentrations of olivine up to 40 with millimeter particle size similar to picritic basalts observed in situ by the spirit rover in the gusev crater are inferred chemical compositions are calculated for the first time from omega spectra they are quite consistent with gusev rocks and shergottite compositions but they appear to be significantly sio2 poorer than thermal emission spectrometer data a decreasing low calcium pyroxene abundance with the decreasing age of the low albedo regions is reported this may be indicative of decreasing degree of partial melting as thermal flux decreases with time we propose that the ancient noachian aged lcp rich terrains could have been formed from h2o bearing melts then dry basaltic volcanism occurred leading to decreasing lcp abundance with time due to decreasing degree of partial melting the olivine bearing material modeled in nili fossae resembles the composition of alh77005 and chassigny meteorites consistent with prior studies implications on the formation of the basaltic shergottites are discussed

thermobarometric constraints on burial and exhumation of 2 billion year old eclogites and their metapelitic hosts abstract one of the first appearances of eclogite facies mineral assemblages in the geological record occurs in the c 2000 ma palaeoproterozoic usagaran belt in central tanzania where the extended margin of the tanzanian craton is interpreted to have been subducted mafic rocks are interpreted to have contained the mineral assemblage garnet omphacite rutile quartz amphibole this high pressure assemblage has been overprinted by a secondary mineral assemblage containing clinopyroxene plagioclase hornblende ilmenite orthopyroxene mineral equilibria forward modelling indicates that the eclogite facies assemblages reached minimum peak pressure temperature p t conditions of 17 kbar and 700 c inclusions in garnet document a prograde p t history consistent with burial through upper amphibolite facies conditions and possible partial melting petrological and compositional evidence from garnet suggests that following peak metamorphism the eclogite facies rocks were heated while stalled at approximate peak pressures temperature estimates derived from zr concentrations in interpreted texturally retrograde rutile support a near isothermal post peak p t evolution for the eclogite facies rocks an evolution that terminates at retrograde p t conditions of approximately 7 6 8 2 kbar and 680 790 c the relict eclogite domains form part of a larger assemblage with enclosing migmatitic metapelitic lithologies the isimani suite the metapelitic gneisses contain garnet kyanite biotite staurolite hornblende plagioclase muscovite rutile quartz and preserve minimal evidence of a high pressure history conceivably due to post peak mineralogical recrystallisation p t modelling inclusion assemblages and compositional zonation patterns in porphyroblastic garnet suggests the metapelitic gneisses similarly to the relict eclogites experienced burial to minimum peak pressures of approximately 16 5 17 kbar compositional zoning patterns in eclogitic garnet suggest the isimani system was buried reached peak metamorphic conditions and was subsequently exhumed within a timeframe of up to 20 myr a tectonic regime involving crustal thickening and subduction followed by extensional exhumation of the entire isimani suite is our preferred model for the development of the c 2000 ma usagaran belt

modern style plate subduction preserved in the palaeoproterozoic west african craton the timing of onset of modern style plate tectonics on earth is debated analysis of rocks in the west african metamorphic province which is more than 2 gyr old reveals that some minerals formed under conditions similar to those in modern day subduction zones suggesting that subduction occurred on the palaeoproterozoic earth

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

eruption constraints on tube fed planetary lava flows we examine the role of pressure and gravity as driving forces in planetary lava tubes for newtonian and power law rheologies the tubes are assumed to have been filled with lava that was emplaced in constant diameter circular tubes in the laminar flow regime and had constant density heat capacity thermal conductivity and viscosity our model provides relationships between tube dimensions driving forces and effusion rates and rheology parameters in general the pressure term in the driving force dominates for very small slopes but the gravity term eclipses the pressure term as the slope increases applying the model to alba patera tube flows suggests effusion rates somewhere between 2 and 105 m3 s and viscosities between 102 and 106 pa s with tighter constraints 2 to 4 orders of magnitude for specific tube sizes and travel times these effusion rate results are lower and the viscosity ranges are higher than those found in previous studies this allows eruptions that are closer in style to terrestrial basaltic eruptions although the flows are still considerably larger in scale than the hawaiian tube flows we find that very low lava viscosities are not essential for alba patera lava tubes and that tube formation may be a better indicator of the steadiness of the eruption and the presence of low slopes than it is of low viscosities e g 102 pa s in addition this analysis suggests that the tube systems on the steep flanks of olympus mons are fundamentally different from those at alba patera the olympus mons flows could not have roofed over been continuously full or maintained a continuous lava tube transport system in the assumed full steady and fully developed conditions

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

pyroxene spectroscopy revisited spectral compositional correlations and relationship to geothermometry the authors wish to thank the various agencies which have provided the necessary support for this project including grants in aid of research from sigma xi the scientific research society to e a c the geological society of america grant 3741 87 to e a c and nasa planetary geology and geophysics grant nagw 642 to m j g

paleozoic hp granulite facies metamorphism and anatexis in the dulan area of the north qaidam uhp terrane western china constraints from petrology zircon u pb and amphibole ar ar geochronology abstract hp mafic and felsic adakitic granulite bodies in the dulan area of the north qaidam ultrahigh pressure uhp terrane record high pressure hp granulite facies metamorphism and anatexis and provide temporal and tectonic constraints on deep subduction of continental crust and its subsequent exhumation mafic hp granulite components dominate the main outcrop and preserve features diagnostic of anatexis and locally may be described as migmatite the hp mafic granulites comprise garnet clinopyroxene plagioclase and quartz the felsic granulite leucosome is mainly composed of k feldspar plagioclase quartz kyanite garnet detailed zircon u pb and amphibole ar ar geochronology combined with trace element geochemistry indicate peak metamorphism for the mafic hp granulite at 434 3 to 435 3 ma and peak metamorphism and partial melting for the felsic hp granulite at 433 5 to 438 4 ma which overlaps the ages of uhp metamorphism for adjacent eclogite 430 446 ma 40 ar 39 ar amphibole ages of 423 to 432 ma represent amphibolite facies retrograde metamorphism and indicate rapid cooling during exhumation of the hp granulite bodies our geochronological data combined with field relationships petrology and geochemistry suggest that hp granulite facies metamorphism and the partial melting that produced adakitic melts represent the same tectonic event in this case the felsic hp granulites leucosome formed from an adakitic melt derived from partial melting of mafic hp granulite in the overriding plate in a relatively higher geothermal gradient 15 18 c km leaving garnet cumulate and or meta ultramafic mainly garnet pyroxenite as the residual component in contrast the nearby uhp eclogite is thought to have formed in the subducted plate in a relatively lower geothermal gradient 6 10 c km penecontemporaneous metamorphic ages but different geothermal gradients between hp granulites and related uhp eclogite define a possible paired metamorphic belt generated in a subduction collision setting associated with the north qaidam continental collisional orogeny during the late ordovician early silurian

constraints on mercury s surface composition from messenger neutron spectrometer data abstract the composition of mercury s surface is poorly known but the messenger mercury surface space environment geochemistry and ranging mission has provided a wealth of new data from three flybys in particular messenger neutron spectrometer ns observations reveal a surface enriched in neutron absorbing elements consistent with interpretations of color and albedo observations suggesting a surface composition enriched in fe mg ti oxides in this study we have computed the neutron absorption cross sections for all of the available proposed surface compositions of mercury and evaluated the plausibility of each surface composition based on the neutron absorption cross section observed by messenger for identified plausible compositions the implications for the thermal and magmatic evolution of mercury are discussed the measured macroscopic neutron absorption cross section of mercury is inconsistent with a crust formed from partial melting of plausible bulk mantle compositions flotation in a magma ocean or adiabatic melting of upwelling cumulates during magma ocean overturn however the observed neutron absorption is consistent with model compositions of late stage magma ocean cumulates and some proposed compositions from spectral modeling and equilibrium modeling this suggests that the enrichment of neutron absorbing elements may be indicative of the processes that acted to form mercury s crust the enrichment in neutron absorbing elements in combination with spectral observations that constrain feo in silicates

ion microprobe u pb age determinations on zircon from the late archean granulite facies transition zone of southern india abstract the southern dharwar craton of karnataka and tamil nadu states in south india exposes a depth profile of late archean crust amphibolite facies felsic to intermediate peninsular gneiss of protolith ages 3 4 2 9 ga with subordinate infolded supracrustal relics and the large closepet granite body give way southward to granulite facies orthopyroxene bearing gneisses over a transition zone about 40 km wide with mineralogic pressure indicators increasing from about 4 kbar corresponding to about 15 km paleodepth to about 7 kbar corresponding to near 25 km paleodepth previous whole rock and zircon geochronology have established that amphibolite facies metamorphism migmatization and granite intrusion took place in the latest archean at 2 53 2 51 ga however some workers have considered the foliated granulites as products of an earlier metamorphism distinct from the terminal archean events this work presents whole rock geochemical studies coupled with ion microprobe 207pb 206pb ages and th u

shonkinites from salem southern india implications for cryogenian alkaline magmatism in rift related setting abstract alkaline and potassic igneous rocks although minor components of the continental crust provide important constraints on magma processes and tectonic settings here we report petrology mineral chemistry whole rock geochemistry zircon u pb and lu hf data on shonkinites from the salem block in the southern granulite terrane of india the shonkinite is composed mainly of porphyritic clinopyroxene k feldspar and olivine and intrudes into the surrounding ultramafic rocks composed of wehrlite clinopyroxene and olivine and dunite mostly olivine with minor spinel the geochemical data on shonkinites from salem show alkaline and ultrapotassic features with marked enrichment in incompatible elements and high k 2 o and k 2 o na 2 o ratios suggesting magma derivation from metasomatized lithospheric mantle their hfse depletion relative to lile compositions coupled with positive nb anomalies suggests continental rift setting the zircon grains in shonkinite show typical magmatic crystallization features and their la icp ms u pb data yield weighted mean age of 818 6 3 ma mswd 0 32 the zircon e hf values range between 11 1 and 12 7 consistent with magma derivation from an enriched mantle with depleted mantle model ages t dm in the range of between 2406 and 2513 ma indicating the involvement of neoarchean paleoproterozoic subduction related components together with similar aged alkaline plutons with comparable geochemical features we envisage a major alkaline magmatic event associated with rifting during cryogenian in the northern part of the southern granulite terrane

high pressure granulites at the dawn of the proterozoic abstracthigh pressure metamorphism is uncommon in the ancient geo logical record kanja malai in the salem crustal block southern india contains high pressure kyanite garnet bearing felsic granu lites that equilibrated at 14 16 kbar and 820 860 c laser abla tion inductively coupled plasma mass spectrometry u pb zircon and in situ monazite geochronology indicate that these assemblages grew ca 2490 ma these pressure temperature time constraints pro vide a rare record indicating that thickened crust and low apparent thermal gradient conditions existed during the archean proterozoic transition a period of earth history for which the rock record com monly preserves evidence for comparatively high apparent thermal gradients the thermal regimes required to generate these metamor phic conditions are typical of collisional orogenesis and suggest that the continental lithosphere was capable of supporting crustal thick ening to 45 50 km such crustal thickening provides supporting evi dence that tectonic regimes similar to modern earth style tectonics were in operation at the archean proterozoic transition introduction

characterization of the 1 2 μm m1 pyroxene band extracting cooling history from near ir spectra of pyroxenes and pyroxene dominated rocks the 1 2 m band in near infrared spectra of pyroxenes results from fe2 in the m1 crystallographic site the distribution of fe and mg between the m1 and m2 sites is in part a function of the cooling rate and thermal history of a pyroxene combining near infrared and mssbauer spectra for a series of compositionally controlled synthetic mg fe ca pyroxenes we quantify the strength of the 1 2 m band as a function of fe2 in the m1 site near infrared spectra are deconvolved into component absorptions that can be assigned to the m1 and m2 sites using the modified gaussian model the relative strength of the 1 2 m band is shown to be directly related to the amount of fe2 in the m1 site measured by mossbauer spectroscopy the strength of the 1 2 m band relative to the combined strengths of the 1 2 and 2 m bands or the m1 intensity ratio is calculated for 51 howardite eucrite and diogenite hed meteorites diogenites and cumulate eucrites exhibit the lowest m1 intensity ratios consistent with their formation as slowly cooled cumulates basaltic eucrites exhibit a large range of m1 intensity ratios all of which are consistently higher than the diogenites and cumulate eucrites this example illustrates how the m1 intensity ratio can be a used as a tool for characterizing the cooling history of remotely detected pyroxene dominated rocks

the distribution and origin of smooth plains on mercury 1 orbital images from the messenger spacecraft show that 27 of mercury s surface is covered by smooth plains the majority 65 of which are interpreted to be volcanic in origin most smooth plains share the spectral characteristics of mercury s northern smooth plains suggesting they also share their magnesian alkali basalt like composition a smaller fraction of smooth plains interpreted to be volcanic in nature have a lower reflectance and shallower spectral slope suggesting more ultramafic compositions an inference that implies high temperatures and high degrees of partial melting in magma source regions persisted through most of the duration of smooth plains formation the knobby and hummocky plains surrounding the caloris basin known as odin type plains occupy an additional 2 of mercury s surface the morphology of these plains and their color and stratigraphic relationships suggest that they formed as caloris ejecta although such an origin is in conflict with a straightforward interpretation of crater size frequency distributions if some fraction is volcanic this added area would substantially increase the abundance of relatively young effusive deposits inferred to have more mafic compositions smooth plains are widespread on mercury but they are more heavily concentrated in the north and in the hemisphere surrounding caloris no simple relationship between plains distribution and crustal thickness or radioactive element distribution is observed a likely volcanic origin for some older terrain on mercury suggests that the uneven distribution of smooth plains may indicate differences in the emplacement age of large scale volcanic deposits rather than differences in crustal formational process

spectroscopic characterization of mineralogy and its diversity across vesta the mineralogy of vesta based on data obtained by the dawn spacecraft s visible and infrared spectrometer is consistent with howardite eucrite diogenite meteorites there are considerable regional and local variations across the asteroid spectrally distinct regions include the south polar rheasilvia basin which displays a higher diogenitic component and equatorial regions which show a higher eucritic component the lithologic distribution indicates a deeper diogenitic crust exposed after excavation by the impact that formed rheasilvia and an upper eucritic crust evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta this is broadly consistent with magma ocean models but spectral variability highlights local variations which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates overall vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle

effects of glass content and oxidation on the spectra of snc like basalts applications to mars remote sensing 1 we have investigated the effects of crystallization and oxidation on the visible and near infrared visnir and mid infrared mid ir spectra of materials with a shergotty nakhla chassigny snc basaltic composition in order to investigate potential links between martian visnir spectra martian mid ir spectra and snc meteorite data snc basalt samples of varying crystallinities were synthesized and subsequently oxidized in air at 700 c for 1 7 days and reflectance spectra of both fine 75 m and coarse 75 500 m basalt samples were obtained before and after oxidation the effects of crystallization on the spectral properties are readily observed in the unoxidized products in the visnir increasing crystallization is accompanied by an increasing influence of pyroxene absorptions and decreasing influence of glass absorptions in the mid ir changes in spectral properties with crystallization are due to the variations in relative amounts of glass pyroxene and plagioclase oxidation alters the glass and pyroxenes within the samples leading to changes in visnir and mid ir spectral shapes although distinct signatures of oxidation products are not always observed both spectral and electron microscopy data indicate that hematite is the dominant oxidation product in the pigeonite and glass of the samples in pigeonite hematite is present in nanophase form and leads to the diminishment of the diagnostic 1 and 2 m pyroxene absorptions in the visnir as well as pyroxene absorptions expressed between 800 and 1100 cm 1 in the mid ir in glass hematite forms a near surface layer that is detected with varying efficiencies in the visnir and mid ir depending on the crystallinity and particle size of the analyzed sample oxidized snc basalt samples of various crystallinities and fine grain sizes provide the best analogs to mars remote sensing data in the visnir and mid ir in the visnir partially crystalline oxidized snc basalts can reproduce martian dark region characteristics in the mid ir similarities exist between the spectra of a partially crystalline oxidized snc basalt and the basalt lithology detected by the thermal emission spectrometer tes the andesite lithology detected by tes is best matched by the spectrum of a fully crystalline oxidized snc basalt these results imply that plagioclase rich lithologies are not required by tes data and that observed variations in spectral character of dark regions across the martian surface can be explained by snc basalts influenced by oxidation coupled with variations in degree of crystallization

progressive metamorphism of mafic rocks from greenschist to granulite facies in the dharwar craton of south india in the archean dharwar craton of southern india n s trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2 5 ga ago the progressive changes in the assemblages and mineral chemistry of metabasites was studied in a n s traverse covering the chitradurga and nagaman gala belts the sargur area and the nilgiri hills towards the south with increasing metamorphic grade greenschists chl act ab ep pm carb qtz give way to amphibolites hbl plag pm qtz gar cumm and mafic granulites pyx plag gar pm hbl qtz the amphibole composition changes from actinolite in the greenschist zone to tschermakitic hornblende in the amphibolite zone and pargasitic hastingsitic hornblende in the granulite zone the ti content of the amphiboles systematically increases in this direction the plagioclase composition changes from albite in the greenschist zone to oligoclase andesine in the amphibolite zone and andesine labradorite in the granulite zone almandin

the geological history of nili patera mars nili patera is a 50 km diameter caldera at the center of the syrtis major planum volcanic province the caldera is unique among martian volcanic terrains in hosting i evidence of both effusive and explosive volcanism ii hydrothermal silica and iii compositional diversity from olivine rich basalts to silica enriched units we have produced a new geological map using three mosaicked 18 m pixel context camera digital elevation models supplemented by compact remote imaging spectrometer for mars hyperspectral data the map contextualizes these discoveries formulating a stratigraphy in which nili patera formed by trapdoor collapse into a volcanotectonic depression the distinctive bright floor of nili patera formed either as part of a felsic pluton exposed during caldera formation or as remnants of welded ignimbrite s associated with caldera formation both scenarios deriving from melting in the noachian highland basement after caldera collapse there were five magmatic episodes 1 a basaltic unit in the caldera s north 2 a silica enriched unit and the associated nili tholus cone 3 an intrusive event forming a 300 m high elliptical dome 4 an extrusive basaltic unit emplaced from small cones in the east and 5 an extreme olivine bearing unit formed on the western caldera ring fault the mapping together with evidence for hydrated materials implies magmatic interaction with subsurface volatiles this in an area of elevated geothermal gradient presents a possible habitable environment sampled by the hydrothermal deposits additionally similarities to other highland volcanoes imply similar mechanisms and thus astrobiological potential within those edifices

olivine in an unexpected location on vesta s surface although olivine was expected to occur within the deep south pole basins of asteroid vesta which are thought to be excavated mantle rocks spectral data from nasa s dawn spacecraft show that it instead occurs as near surface materials in vesta s northern hemisphere between july 2011 and september 2012 nasa s dawn spacecraft was in orbit around the asteroid vesta in this paper dawn s visible and infrared mapping spectrometer vir team presents a surprising finding the signature of olivine on the asteroid s surface olivine is a major component of the mantle of differentiated bodies including earth vesta is a large asteroid large enough to have differentiated into an earth like layered structure and the expectation was that olivine would be found within vesta s deep south pole basins thought to be excavated mantle rocks yet the spectroscopic data reveal olivine rich material close to the surface in the northern hemisphere an understanding of the differentiation processes that have occurred on vesta will be invaluable as a window on the primordial solar system but these latest findings show that vesta s evolutionary history is more complicated than was thought olivine is a major component of the mantle of differentiated bodies including earth howardite eucrite and diogenite hed meteorites represent regolith basaltic crust lower crust and possibly ultramafic mantle samples of asteroid vesta which is the lone surviving large differentiated basaltic rocky protoplanet in the solar system1 only a few of these meteorites the orthopyroxene rich diogenites contain olivine typically with a concentration of less than 25 per cent by volume2 olivine was tentatively identified on vesta3 4 on the basis of spectral and colour data but other observations did not confirm its presence5 here we report that olivine is indeed present locally on vesta s surface but that unexpectedly it has not been found within the deep south pole basins which are thought to be excavated mantle rocks6 7 8 instead it occurs as near surface materials in the northern hemisphere unlike the meteorites the olivine rich more than 50 per cent by volume material is not associated with diogenite but seems to be mixed with howardite the most common7 9 surface material olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area the size of the olivine exposures and the absence of associated diogenite favour a mantle source but the exposures are located far from the deep impact basins the amount and distribution of observed olivine rich material suggest a complex evolutionary history for vesta

downflow width behavior of martian and terrestrial lava flows examination of the downflow width behavior of 59 terrestrial lava flows at puu oo hawaii and glass mountain california and 86 martian flows at alba patera tyrrhena patera elysium and olympus mons was completed using aerial photographs topographic maps previously published flow maps and viking orbiter images the examined lava flows exhibit diverse width behavior from which information about flow processes and conditions was assessed for puu oo flows no significant correlation was found between the average width of a flow and flow length or average underlying slope a significant but weak relationship was found between average width and average flow thickness in analyses of the downflow width behavior of individual flows no consistent correlations were observed between width and thickness or underlying slope when width was analyzed as a function of distance from the source for all flows a variety of flow width behavioral trends were recognized and quantitatively classified the most common behavior observed on earth and mars involved variations of width sometimes significant about a mean without a significant downflow narrowing or widening trend the distributions of width behavior trends for the alba patera and puu oo flows examined were similar with this type of constant behavior dominating in contrast tyrrhena patera flows showed a tendency to widen with distance downflow and silicic flows at glass mountain were more likely to narrow flows were also subdivided by distance from the vent and the width behavior of each division classified subdivision of flows resulted in significant changes in the classification of width behavior while width behavior in the medial regions of flows was similar to that over entire flow lengths proximal regions show more variability possibly due to greater fluidity of lavas near the vent and distal regions tend to uniformly narrow possibly due to limited supply in certain cases classification and subdivision analysis can be used to link flow emplacement processes to the resulting morphology in particular width behavior can be correlated to the presence or absence of lateral levees

combined use of visible reflected infrared and thermal infrared images for mapping hawaiian lava flows the weathering of hawaiian basalts is accompanied by chemical and physical changes of the surfaces these changes have been mapped using remote sensing data from the visible and reflected infrared and thermal infrared wavelength regions they are related to the physical breakdown of surface chill coats the development and erosion of silica coatings the oxidation of mafic minerals and the development of vegetation cover these effects show systematic behavior with age and can be mapped using the image data and related to relative ages of pahoehoe and aa flows the thermal data are sensitive to silica rind development and fine structure of the scene the reflectance data show the degree of oxidation and differentiate vegetation from aa and cinders together data from the two wavelength regions show more than either separately the combined data potentially provide a powerful tool for mapping basalt flows in arid to semiarid volcanic environments

alkaline volcanic rocks from the columbia hills gusev crater mars 1 irvine backstay and wishstone are the type specimens for three classes of fine grained or fragmental relatively unaltered rocks with distinctive thermal emission spectra found as float on the flanks of the columbia hills chemical analyses indicate that these rocks are mildly alkaline basalt trachybasalt and tephrite respectively their mineralogy consists of na and k rich feldspar s low and high ca pyroxenes ferroan olivine fe ti and possibly cr oxides phosphate and possibly glass the texture of wishstone is consistent with a pyroclastic origin whereas irvine and backstay are lavas or possibly dike rocks chemical compositions of these rocks plot on or near liquid lines of descent for most elements calculated for adirondack class rocks olivine rich basalts from the gusev plains at various pressures from 0 1 to 1 0 gpa we infer that wishstone backstay and irvine class magmas may have formed by fractionation of primitive oxidized basaltic magma similar to adirondack class rocks the compositions of all these rocks reveal that the gusev magmatic province is alkaline distinct from the subalkaline volcanic rocks thought to dominate most of the planet s surface the fact that differentiated volcanic rocks were not encountered on the plains prior to ascending husband hill may suggest a local magma source for volcanism beneath gusev crater

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

earliest paleoproterozoic high grade metamorphism and orogenesis in the gawler craton south australia the southern cousin in the rae family neoarchean earliest paleoproterozoic rocks of the gawler craton preserved within the mulgathing complex south australia record metamorphism and deformation during an earliest paleoproterozoic tectonothermal event known as the sleafordian orogeny we present metamorphic data from pelitic gneisses of the mulgathing complex from three locations challenger mt christie and blackfellow hill in order to constrain the pressure temperature time p t t evolution of this orogeny in situ u pb dating via laser ablation inductively coupled plasma mass spectrometry shows that monazites within garnet porphyroblasts have ages ca 2470 ma providing an estimate of the timing peak p t conditions monazite crystallisation from melt occurred at ca 2460 ma in the presence of peritectic garnet either late on the prograde path during biotite dehydration melting or immediately following peak t lobate and patchy rims in leucosome hosted monazite suggest a dissolution reprecipitation process occurred during cooling across the elevated dry solidus at ca 2440 ma monazite younger than ca 2430 2420 ma that is located at grain boundaries between matrix minerals likely reflects monazite crystallisation during cooling across the dry solidus and or subsolidus mineral breakdown during the waning stages of the thermal event phase diagram modelling of pelitic gneisses suggests peak metamorphic conditions at the three localities overlap at 7 kbar and 850 c with apparent thermal gradients in the order of 125 135 c kbar 35 45 c km metamorphism involved a tight anticlockwise p t t path based on mineral assemblage paragenesis and indicates a slow shallow decompressive cooling path sub parallel to the apparent thermal gradient in the order of few degrees per myr a protracted magmatic history involving bimodal magmatism associated with a thinned and underplated extensional basin in the mulgathing complex was likely a thermal precursor to the high thermal gradient metamorphism and convergent transpressive deformation a significant period of post 2 4 ga quiescence in the gawler craton subsequent to basin inversion suggests that this orogenesis may have occurred interior to a plate margin the similarity in timing and style between the sleafordian orogeny in the gawler craton and the 2 5 2 28 ga arrowsmith orogeny of the rae craton supports the notion that these terranes together with the broader gawler adelie craton of the mawson continent the north australia craton elements of the north china sino korean and dharwar cratons formed part of a family of neoarchean terranes described as the rae family of cratons with a distinctive tectono metamorphic record as compared with other archean cratons we suggest the mawson continent is the southern member of this family dominated as it is by terranes now present in the northern hemisphere

volcanism on the marius hills plateau observational analyses using clementine multispectral data we have studied the marius hills region and mapped the spectrally distinct flows present for the first time using photographic and clementine multispectral data the basalts on the plateau are varied in age and composition but are dominated by a high titanium eratosthenian basalt most likely from the same source as the flamsteed basalt further south the thickness of the basalts across the plateau is consistently greater than 120 m and is considerably thicker in some areas a lower limit of 5320 km3 of basalts has been erupted onto the plateau the domes and cones in the region do not appear to be related to any specific basalt or volcanic episode but occur at all levels in the stratigraphy that can be derived in the region the eruption conditions required to form these constructs indicate that they must represent a series of separate volcanic episodes occurring throughout the history of the plateau cones on the marius plateau are dominated by a strong glassy signature and often have an associated microlitic structure examples are shown of localized microlitic or glassy materials in regions where no cone is evident in the photographic data these features are proposed to represent short lived pyroclastic episodes that have deposited glassy and microlitic units on the plateau but have not been maintained for long enough to develop a cone the volcanic history of the marius hills region is extremely complex and most likely involved several separate episodes of volcanism with a large contrast in eruption styles and characteristics

return to mercury a global perspective on messenger s first mercury flyby in january 2008 the mercury surface space environment geochemistry and ranging messenger spacecraft became the first probe to fly past the planet mercury in 33 years the encounter revealed that mercury is a dynamic system its liquid iron rich outer core is coupled through a dominantly dipolar magnetic field to the surface exosphere and magnetosphere all of which interact with the solar wind messenger images confirm that lobate scarps are the dominant tectonic landform and record global contraction associated with cooling of the planet the history of contraction can be related to the history of volcanism and cratering and the total contractional strain is at least one third greater than inferred from mariner 10 images on the basis of measurements of thermal neutrons made during the flyby the average abundance of iron in mercury s surface material is less than 6 by weight

plate tectonics on the early earth limitations imposed by strength and buoyancy of subducted lithosphere the tectonic style and viability of modern plate tectonics in the early earth is still debated field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the archean continue to accumulate here we present the first numerical modeling results that address for a hotter earth the viability of subduction one of the main requirements for plate tectonics a hotter mantle has mainly two effects 1 viscosity is lower and 2 more melt is produced which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation our modeling results show that eclogitization significantly relaxes this limitation for a developed ongoing subduction process furthermore the lower viscosity leads to more frequent slab breakoff and sometimes to crustal separation from the mantle lithosphere unlike earlier propositions not compositional buoyancy considerations but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter earth these results suggest a new explanation for the absence of ultrahigh pressure metamorphism uhpm and blueschists in most of the precambrian early slabs were not too buoyant but too weak to provide a mechanism for uhpm and exhumation

flow and convective cooling in lava tubes tube fed basaltic lava flows with lengths ranging from 10 to 200 km are inferred to exhibit similar amounts of cooling to explain the wide range of implied cooling rates we consider forced convection as a dominant cooling process in lava tubes and present solutions that express mean temperature versus distance down the tube as a function of flow rate and flow cross section our models treat forced convective thermal losses in steady laminar flow through a lava tube with constant temperature walls and constant material properties we explore the effects of different wall temperature and heat flux rate boundary conditions for circular tube and parallel plate flows over a range of tube sizes plate spacings eruption temperatures and volume flow rates results show that nonlinear cooling rates over distance are characteristic of constant wall temperature for a piecewise parallel plate circular tube model this provides the best fit to temperature observations for hawaiian tubes such a model may also provide an explanation for the very low 10 c cooling observed in 10 km long hawaii tube flows and inferred in longer 50 to 150 km tube fed flows in queensland the forced convective cooling model may also explain similar flow morphologies for long tube fed basaltic lava flows in a wide variety of locations since small variations in eruption temperature or flow rate can accommodate the entire range of flow lengths and cooling rates considered our results are consistent with previous suggestions that long basaltic flows may be a reflection of low slopes a particularly steady moderate eruption rate and well insulated flow rather than of high discharge rates

basaltic rocks analyzed by the spirit rover in gusev crater the spirit landing site in gusev crater on mars contains dark fine grained vesicular rocks interpreted as lavas pancam and mini thermal emission spectrometer mini tes spectra suggest that all of these rocks are similar but have variable coatings and dust mantles magnified images of brushed and abraded rock surfaces show alteration rinds and veins rock interiors contain 25 megacrysts chemical analyses of rocks by the alpha particle x ray spectrometer are consistent with picritic basalts containing normative olivine pyroxenes plagioclase and accessory feti oxides mossbauer pancam and mini tes spectra confirm the presence of olivine magnetite and probably pyroxene these basalts extend the known range of rock compositions composing the martian crust

lithospheric scale gravitational flow the impact of body forces on orogenic processes from archaean to phanerozoic in the archaean the combination of warmer continental geotherm with a lighter sub continental lithospheric mantle suggests that gravitational forces played a more signifi cant role in continental lithospheric deformation to test this hypothesis we compare the evolution of the deformation and the regional state of stress in archaean like and phanerozoic like lithospheres submitted to the same boundary conditions in a triaxial stress field with imposed convergence in one direction for plausible physical parameters thickening of normal to cold phanerozoic lithospheres produces relatively weak buoyancy forces either extensional or compressional in contrast for archaean continental litho spheres or for anomalously warm phanerozoic lithospheres lateral gravitationally driven flow prevents significant thickening this conclusion is broadly consistent with 1 the rela tive homogeneity of the erosional level now exposed at the surface of archaean cratons 2 the sub aerial conditions that prevailed during the emplacement of up to 20 km of green stone cover 3 the relatively rare occurrence in the archaean record of voluminous detrital sediments 4 the near absence of significant tectonic metamorphic and magmatic age gra dients across archaean cratons 5 the relative homogeneity of strain across large areas and 6 the ubiquitous presence of crustal scale strike slip faults in many late archaean cratons

importance of space weathering simulation products in compositional modeling of asteroids 349 dembowska and 446 aeternitas as examples based on recent progress in simulating space weathering on asteroids using pulse laser irradiation onto olivine and orthopyroxene samples detailed analyses of two of the a and r type asteroid reflectance spectra have been performed using reflectance spectra of laser treated samples the visible near infrared spectrum of olivine is more altered than that of pyroxene at the same pulse laser energy suggesting that olivine weathers more rapidly than orthopyroxene in space the same trend can be detected from reflectance spectra of the asteroids where the more olivine an asteroid has the redder its 1 m band continuum can become comparison of the 1 m band continuum slope and the 2 1 m band area ratio between the asteroids and olivine and pyroxene samples including the laser treated ones suggests that asteroids may be limited in the degree of space weathering they can exhibit possibly due to the short life of their surface regolith their pyroxenes may also have a limited chemical composition range fitting the visible continuum shape and other parts of the spectra especially the 2 m part has been impossible with any combination of common rock forming minerals such as silicates and metallic irons however this study shows for the first time excellent fits of reflectance spectra of an a asteroid aeternitas and an r asteroid dembowska including their visible spectral curves band depths and shapes and overall continuum shapes our results provide estimates that aeternitas consists of 2 fresh olivine 93 space weathered olivine 1 space weathered orthopyroxene and 4 chromite and that dembowska consists of 1 fresh olivine 55 space weathered olivine and 44 space weathered orthopyroxene these results suggest that space weathering effects maybe important to the interpretation of asteroid reflectance spectra even those with deep silicate absorption bands modified gaussian model deconvolutions of the laser irradiated olivine samples show that their identity as olivine remained the most recent submicroscopic mineralogical analyses have revealed that the laser irradiated olivine samples contain nanophase iron particles similar to those in space weathered lunar samples

imprints of diverse mantle deformational episodes in the cauvery suture zone south india abstract this study attempts to understand the upper mantle deformation pattern beneath the northern part of southern granulite terrain sgt located to the south of archean dharwar craton in south india the study region comprises the tectonic blocks nilgiri biligiri rangan shevaroy and madras blocks separated from the northern part of madurai block by the cauvery suture zone csz associated with subduction accretion collision tectonics shear wave splitting observed on high quality xk k s sks skks pks waveforms from 119 teleseismic events recorded by 19 broadband seismic stations mostly within the csz and the northern part of madurai block is utilized in this study the 122 splitting measurements obtained show an average delay time of 0 8 s between the fast and slow waves strong lateral variations in the fast polarization azimuths fpa are observed with the splitting parameters at the majority of stations showing a dependence on back azimuth importantly excluding the madras block a poor correlation between the fpa and the present day absolute plate motion apm direction is observed this dominance of non apm strain reflects complex anisotropy preserved in the lithosphere by plotting the fast polarization trends based on the ray piercing points at a depth of 150 km three distinct splitting patterns associated with the i biligiri rangan block and the eastern part of the nilgiri block ii eastern part of the csz and the northern madurai block nmb and iii madras block and its vicinity within the csz are observed the strong lateral heterogeneity in the deformation of the continental lithosphere might be either related with the shear zones that are associated with frozen magmatic intrusions two episodes of ocean closure and the collision that followed plate motion related strain or a combination of these similar deformation patterns in the northern part of madurai block might be related to remnants of subducted oceanic lithosphere

analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy 2 application to martian surface spectra from the mars global surveyor thermal emission spectrometer atmospherically corrected thermal infrared spectra of large regions of the martian surface from the mars global surveyor thermal emission spectrometer mgs tes previously have been interpreted to represent two general spectral classes one class represents a basalt to basaltic andesite composition and the other class represents a basaltic andesite to andesite composition we have performed new linear deconvolutions of the two martian surface type spectra with an end member set tailored to represent volcanic rock types our preparatory study of laboratory spectra of terrestrial volcanic rocks acquired at 2 cm 21 sampling convolved to tes spectral sampling 10 cm 21 shows little degradation in deconvolution results when compared to results acquired using the higher spectral resolution data indicating that the deconvolution technique is valid for analyzing data at tes resolution our spectral fits to the martian data agree well with previous models and do not exhibit any notable deviations from the martian spectra that would indicate the absence of any significant end members in our model modal mineralogies obtained with these new spectral fits also compare favorably within the previously stated uncertainties to prior results the newly derived modal mineralogies are used with new and traditional classification schemes for volcanic igneous rocks introduced in a companion paper wyatt et al this issue to classify the martian compositions our results substantiate the previously proposed hypothesis that these two spectral classes on the martian surface represent volcanic compositions with distinguishable differences in silica content ranging from basalt to andesite

vnir spectral variability of the igneous stratified stillwater complex a tool to map lunar highlands lunar highlands are plagioclase rich terrains produced by crystal floating in a magma ocean system lunar samples revealed the presence of anorthositic plagioclase 90 samples from the highlands associated to more mafic rocks recently remote sensing data permit mapping those terrains with high spatial and spectral resolution allowing detection of plagioclase and mafic crystal field c f absorptions in this paper we have studied bidirectional spectral characteristics in the visible near infrared vnir of rocks from the stillwater complex a cumulitic igneous stratified complex with composition varying from mafic to sialic e g pyroxenite anorthosite we investigated both slabs and powders of these rocks to give indication of the spectral variability of rock analogs of lunar crust from a mineralogical point of view samples have been spectrally separated in four main groups considering the different c f absorption association reflectance and spectral shape for both slab and powder spectra more spectral details can be obtained from the analysis of powder spectra than from the slab spectra the composition of rocks can be addressed by studying spectral parameters such as the position and the intensity of the absorption e g band center and band depth the analysis of our plagioclase pyroxene bearing samples indicates that mafic composition can be clearly obtained for samples characterized by one pyroxene phase even for few amounts of pyroxene from powder spectra on the other hand slab spectra show clear pyroxene absorptions only for rocks with mafic abundance at least 20 the intensity of the mafic absorptions of these samples shows a linear trend with respect to the abundance of pyroxenes orthopyroxene clinopyroxene for samples with ferrosilite amount less than ca 25 considering all pyroxene bearing samples the band depth of slab spectra are linearly related to the volumetric distribution of ferrous iron in pyroxenes

neoarchean lithospheric strengthening and the coupling of earth s geochemical reservoirs this paper explores the secular evolution of the height of an isostatically balanced collisional mountain belt in the context of ongoing convergence we show that until the neoarchean continents were unable to sustain topography 2500 m during the neoarchean the continental lithosphere evolved through a rheological threshold allowing for the development of signifi cant topography the consequence of the strengthening of the continental lithosphere is fundamental for the coupling of the earth s geochemical reservoirs the neoarchean was a period of global changes during which exogenic envelopes recorded major shifts in composition toward modern values we propose that during the neoarchean the exogenic envelopes which were until then coupled to the mantle through hydrothermal processes and volcanism also became coupled to the continental crust through reliefgenerating tectonics processes and erosion hence changing the balance between mantle versus crustal interaction with the exogenic earth

petrogenesis of mare basalts a record of lunar volcanism returned rock and soil samples from our nearest planetary neighbor have provided the basis for much of our understanding of the origin and evolution of the moon of particular importance are the mare basalts which have revealed considerable information about lunar volcanism and the nature of the mantle as well as post magma generation processes this paper is a critical review of the petrogenetic models for the generation of mare basalts formulated over the last twenty years we have used all available mare basalt analyses to define a six fold classification scheme using tio2 contents as the primary division i e 1 wt very low ti or vlt 1 6 wt low ti 6 wt high ti a secondary division is made using al2o3 contents i e 11 wt low al 11 wt high al and a tertiary division is defined using k contents i e 2000 ppm low k 2000 ppm high k such divisions and subdivisions yield a classification containing twelve categories of which six are accounted for by the existing apollo and luna collections therefore we present our discussions in the form of six mare basalt rock types 1 1 high ti low al low k referred to as high ti low k 2 2 high ti low al high k referred to as high ti high k 3 3 low ti low al low k referred to as low ti 4 4 low ti high al low k referred to as high alumina 5 5 low ti high al high k referred to as vhk 6 6 vlt low al low k basalts referred to as vlt a variety of post magma generation processes have been invoked such as fractional crystallization either alone or combined with wallrock assimilation to explain the compositional ranges of the various mare basalt suites in order to evaluate these proposed petrogenetic processes this review is by rock type and is non site specific but for each rock type reference to particular lunar sample return missions is brought forth this permits a comparison of similarities and differences of broadly similar rock types correlated with geography on the moon which in turn allows a more thorough petrogenetic evaluation high ti mare basalts i e high ti low al low k are found at apollo 11 and apollo 17 sites however the a 11 basalts contain lower tio2 abundances a considerably larger range in trace element contents and the only occurrence of high ti high k mare basalts fractional crystallization and source heterogeneity within each site are the keys to understanding the petrogenesis of the high ti basalts low ti basalts including both low al k and high al k varieties are found at apollo 12 14 and 15 and luna 16 sites the low ti basalts exhibit a wide range of major and trace element compositions and require source heterogeneity fractional crystallization and some assimilation the high alumina mare basalts i e low ti high al low k are found at apollo 14 and luna 16 sites and exhibit a wide range of major and trace element compositions however in these examples source heterogeneity is not a major factor indeed fractional crystallization coupled with kreep assimilation particularly for the apollo 14 variants can explain the compositional ranges of these high alumina basalts the vhk mare basalts i e low ti high al high k have been sampled only at the apollo 14 locale and are products of a parental highalumina magma assimilating lunar granite very low ti vlt mare basalts i e vlt low al low k are found at apollo 17 and luna 24 sites fractional crystallization has had a major influence upon the range in vlt compositions but luna 24 vlt basalts have been derived from a source slightly different in composition from that for apollo 17 vlt varieties for example the luna 24 vlt basalts generally exhibit positive eu anomalies a unique property for mare basalts which almost always have negative eu anomalies the concept of a lunar magma ocean lmo is generally accepted and source modelling of all basalts invokes a mafic lmo cumulate source this is the only unifying model for mare basalt petrogenesis but the semantics and logistics of it are and will be debated for many years for example major convective overturn of the lmo appears plausible but whether this occurred on a local or planet wide scale to produce source heterogeneity remains to be determined

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

spectral characteristics of lunar impact melts and inferred mineralogy abstract two suites of lunar impact melt samples have been measured in nasa s reflectance experiment laboratory relab at brown university suite 1 comprises seven apollo 17 crystalline impact melt breccias and seven quenched glass equivalents suite 2 is made up of 15 additional impact melt samples from apollo 12 15 16 and 17 which exhibit a range of textures and compositions related to cooling conditions and glass abundance a few of these samples have cooled slowly and fully crystallized and thus have the same spectral properties as igneous rocks of similar texture and composition they cannot be uniquely distinguished without geologic context however most of the impact melts and melt breccias contain either quantities of quenched glass and or have developed microcrystalline nonequilibrium textures with well defined diagnostic spectral properties the microcrystalline textures are associated with a distinctive 600 nm absorption feature apparently due to submicroscopic ilmenite inclusions in a transparent host typically fine grained plagioclase the reflectance properties of these lunar sample suites contribute to and constrain the identification and characterization of impact melts in remote sensing data

crustal architecture and tectonic evolution of the cauvery suture zone southern india abstract the cauvery suture zone csz in southern india has witnessed multiple deformations associated with multiple subduction collision history with incorporation of the related accretionary belts sequentially into the southern continental margin of the archaean dharwar craton since neoarchean to neoproterozoic the accreted tectonic elements include suprasubduction complexes of arc magmatic sequences high grade supracrustals thrust duplexes ophiolites and younger intrusions that are dispersed along the suture the intra oceanic neoarchean neoproterozoic arc assemblages are well exposed in the form of tectonic melanges dominantly towards the eastern sector of the csz and are typically subjected to complex and multiple deformation events multi scale analysis of structural elements with detailed geological mapping of the sub regions and their structural cross sections geochemical and geochronological data and integrated geophysical observations suggest that the csz is an important zone that preserves the imprints of multiple cycles of precambrian plate tectonic regimes

optical effects of space weathering the role of the finest fraction the optical properties of lunar softs are different than those of rocks from which they are derived as a consequence of lunar space weathering soils are darker and exhibit a distinctive red sloped continuum and weaker mineral absorption bands the accumulation of dark glass welded aggregates agglutinates has been thought to account for these optical effects of space weathering on lunar soils spectroscopic analyses of agglutinate separates and size fractions for a suite of lunar softs presented here indicate that the agglutinate paradigm is insufficient to fully account for lunar optical alteration it is the finest fraction of lunar soils 25 gm which constitute 25 wt that dominates the optical properties of the bulk soil unlike size fractions of most silicates for which the finest fraction is the brightest the lunar soil size fractions all have comparable albedos in the short wavelength visible in the near infrared however it is the finest fraction that exhibits the steep red continuum and weak absorption bands the properties of the finest fraction cannot be duplicated by preparing a fine fraction by grinding larger agglutinate rich soil particles these results suggest space weathering on airless bodies is dominated by surface correlated processes perhaps associated with the development of fine grained fe o on or near the surface of grains and the accumulation of the larger agglutinates is not necessarily required to account for lunar optical alteration

orthopyroxene sillimanite quartz assemblages distribution petrology quantitative p t x constraints and p t paths granulite facies magnesian metapelites commonly preserve a wide array of mineral assemblages and reaction textures that are useful for deciphering the metamorphic evolution of a terrane quantitative pressure temperature and bulk composition constraints on the development and preservation of characteristic peak granulite facies mineral assemblages such as orthopyroxene sillimanite quartz are assessed with reference to calculated phase diagrams in nckfmash and its chemical subsystems peak assemblages form mainly in high variance fields and most mineral assemblage changes reflect multivariant equilibria the rarity of orthopyroxene sillimanite quartz bearing assemblages in granulite facies rocks reflects the need for bulk rock xmg of greater than approximately 0 60 0 65 with pressures and temperatures exceeding c 8 kbar and 850 c respectively cordierite coronas mantling peak minerals such as orthopyroxene sillimanite and quartz have historically been used to infer isothermal decompression p t paths in ultrahigh temperature granulite facies terranes however a potentially wide range of p t paths from a given peak metamorphic condition facilitate retrograde cordierite growth after orthopyroxene sillimanite quartz indicating that an individual mineral reaction texture is unable to uniquely define a p t vector therefore the interpretation of p t paths in high grade rocks as isothermal decompression or isobaric cooling may be overly simplistic integration of quantitative data from different mineral reaction textures in rocks with varying bulk composition will provide the strongest constraints on a p t path and in turn on tectonic models derived from these paths

thermal and magmatic evolution of the moon as with all science our continually developing concepts of lunar evolution are firmly tied to both new types of observations and the integration of these observations to the known pool of data this process invigorates the intellectual foundation on which old models are tested and new concepts are built just as the application of new observational tools to lunar science in 1610 galileo s telescope and 1840 photography yielded breakthroughs concerning the true nature of the lunar surface the computational and technological advances highlighted by the apollo and post apollo missions and associated scientific investigations provided a new view of the thermal and magmatic evolution of the moon 1 1 pre apollo view of the thermal and magmatic evolution of the moon many of the early views of the moon manifested in mythology and art throughout the world were primarily tied to lunar and terrestrial cycles and the relationships between the sun and the moon prophetically myths involving the lunar deities mwuetsi from zimbabwe and coyolxauhqui from mexico told of rather violent or catastrophic events in which the moon was expunged from the earth numerous ancient scientific observations were made about the nature of the moon ranging from those uncovered in early neolithic sites that correctly identified mare crisium and mare humorum to the insights made by greek philosophers such as anaxagoras ca 500 428 b c and democritus ca 460 370 b c who attached terrestrial analogues to its character stone mountains with the advent of the telescope 1610 and photography 1840 as scientific tools for lunar exploration semiquantitative data could be collected that would provide an intellectual foundation for scientific interpretation initially modern terrestrial geological analogs were extended to the moon lunar highlands volcanic craters seas combined with the rigors of computational modeling these observational data were extended to predict the original thermal state of the moon and its thermal and magmatic history its proximity to the earth

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

chemical multispectral and textural constraints on the composition and origin of rocks at the mars pathfinder landing site rocks at the mars pathfinder site are probably locally derived textures on rock surfaces may indicate volcanic sedimentary or impact generated rocks but aeolian abration and dust coatings prevent unambiguous interpretation multispectral imaging has resolved four spectral classes of rocks gray and red which occur on different surfaces of the same rocks pink which is probably soil crusts and maroon which occurs as large boulders mostly in the far field rocks are assigned to two spectral trends based on the position of peak reflectance the primary spectral trend contains gray red and pink rocks maroon rocks constitute the secondary spectral trend the spatial pattern of spectral variations observed is oriented along the prevailing wind direction the primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks the secondary spectral trend is apparently due to coating by a different mineral probably maghemite or ferrihydrite a chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit a flood deposit succeeded by smaller cobbles possibly deposited by impact and followed by aeolian erosion and deposition nearly linear chemical trends in alpha proton x ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust a conclusion supported by a correlation between sulfur abundance and red blue spectral ratio extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock the chemistry and normative mineralogy of the sulfur free rock resemble common terrestrial volcanic rocks and its classification corresponds to andesite igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias however the spectral mottling expected on conglomerates or breccias is not observed in any apxs analyzed rocks interpretation of the rocks as andesites is complicated by absence of a 1 m pyroxene absorption band plausible explanations include impact glass band masking by magnetite or presence of calcium and iron rich pyroxenes and olivine which push the absorption band minimum past the imager s spectral range the inferred andesitic composition is most similar to terrestrial anorogenic icelandites formed by fractionation of tholeiitic basaltic magmas early melting of a relatively primitive martian mantle could produce an appropriate parent magma supporting the ancient age of pathfinder rocks inferred from their incorporation in hesperian flood deposits although rocks of andesitic composition at the pathfinder site may represent samples of ancient martian crust inferences drawn about a necessary role for water or plate tectonics in their petrogenesis are probably unwarranted

chemical heterogeneity on mercury s surface revealed by the messenger x ray spectrometer 1 we present the analysis of 205 spatially resolved measurements of the surface composition of mercury from messenger s x ray spectrometer the surface footprints of these measurements are categorized according to geological terrain northern smooth plains deposits and the plains interior to the caloris basin differ compositionally from older terrain on mercury the older terrain generally has higher mg si s si and ca si ratios and a lower al si ratio than the smooth plains mercury s surface mineralogy is likely dominated by high mg mafic minerals e g enstatite plagioclase feldspar and lesser amounts of ca mg and or fe sulfides e g oldhamite the compositional difference between the volcanic smooth plains and the older terrain reflects different abundances of these minerals and points to the crystallization of the smooth plains from a more chemically evolved magma source high degree partial melts of enstatite chondrite material provide a generally good compositional and mineralogical match for much of the surface of mercury an exception is fe for which the low surface abundance on mercury is still higher than that of melts from enstatite chondrites and may indicate an exogenous contribution from meteoroid impacts

final chemical results from the mars pathfinder alpha proton x ray spectrometer 1 the calibrated pathfinder alpha proton x ray spectrometer apxs instrument is capable of measuring concentrations of all major and minor rock forming elements ranging from carbon through zirconium in atomic number therefore it is capable of constraining the petrology of the measured samples in particular the pathfinder data are the first in situ measurements of martian rocks and may be compared with previous remote sensing measurements as well as with the compositions of snc meteorites pathfinder soil and rock sample abundances from the alpha proton and x ray modes have been quantified the abundances suggest that 1 the rocks are covered with various amounts of soil 2 the soil free rocks on a volatile free basis have some element ratios similar to mars meteorites yet have different bulk chemistry indicative of more evolved rocks with higher silica abundances 3 the carbon and nitrogen contents are below detection limits and 4 the alpha mode oxygen reveals excess amounts of oxygen in some samples which is indicative of sample bound water contained within minerals or glasses in samples

an assemblage of lava flow features on mercury 1 in contrast to other terrestrial planets mercury does not possess a great variety of volcanic features its history of volcanism instead largely manifest by expansive smooth plains however a set of landforms at high northern latitudes on mercury resembles surface flow features documented on earth the moon mars and venus the most striking of such landforms are broad channels that host streamlined islands and that cut through the surrounding intercrater plains together with narrower more sinuous channels coalesced depressions evidence for local flooding of intercrater plains by lavas and a first order analysis of lava flow rates the broad channels define an assemblage of flow features formed by the overland flow of and erosion by voluminous high temperature low viscosity lavas this interpretation is consistent with compositional data suggesting that substantial portions of mercury s crust are composed of magnesian iron poor lithologies moreover the proximity of this partially flooded assemblage to extensive volcanic plains raises the possibility that the formation of these flow features may preface total inundation of an area by lavas emplaced in a flood mode and that they escaped complete burial only due to a waning magmatic supply finally that these broad channels on mercury are volcanic in nature yet resemble outflow channels on mars which are commonly attributed to catastrophic water floods implies that aqueous activity is not a prerequisite for the formation of such distinctive landforms on any planetary body

mesoarchean subduction processes 2 87 ga eclogites from the kola peninsula russia the nature of tectonic processes on the early earth is still controversial the scarcity of high pressure metamorphic rocks such as eclogite the high pressure equivalent of basalt in archean cratons has been used to argue that plate tectonics did not operate until earth had cooled to a critical point perhaps around the 2 5 ga archean proterozoic transition however eclogites occur as meter to kilometer sized lenses enclosed in archean gneisses of the belomorian province of the fennoscandian shield geochemistry and internal features suggest that the protoliths of the eclogites were interlayered olivine gabbros troctolites and fe ti oxide gabbros greenschist facies mineral parageneses are enclosed in prograde zoned eclogite garnets and peak metamorphic conditions define an apparent thermal gradient 12 15 c km consistent with metamorphism in a warm archean subduction zone we show here that these eclogites represent the oldest known high pressure metamorphic rocks u pb dating and hf isotope analyses of zircons from the eclogites and a crosscutting felsic vein define a minimum age of 2 87 ga for the uzkaya salma eclogite a 2 70 ga age for the shirokaya salma eclogite is interpreted as the age of a granulite facies overprint thermal overprinting and growth of new zircon also occurred during the svecofennian 1 9 1 8 ga orogeny these new data imply that plate tectonic processes operated at least locally in late mesoarchean time the adakitic nature of the felsic vein suggests that partial melting of hydrated eclogites could produce archean tonalite trondhjemite granodiorite type magmas

paleomagnetism and geochronology of mafic dykes from the southern granulite terrane india expanding the dharwar craton southward abstract the southern granulite terrane sgt of india is a collage of archean to neoproterozoic crustal blocks hosting several generations of mafic dykes we report new paleomagnetic and geochronologic results from mafic dykes in the salem block of the sgt the 2370 ma bangalore dyke swarm is confirmed in this area with a u pb zircon age of 2363 6 6 ma on dykes with steep dual polarity paleomagnetic directions yielding a pole at 2 n and 73 e a95 14 these results precisely place the dharwar craton and northern sgt at high latitudes in the early paleoproterozoic the episodic paleoproterozoic magmatic record of india is also recovered from the sgt several groupings of sgt paleomagnetic directions compare favorably with the 2 21 ga 2 18 ga and 1 88 ga dharwar craton dykes we also report a grand mean pole of 81 n and 259 e a95 11 that we attribute to a widespread ediacaran age remagnetization associated with the final stages of gondwana assembly these paleomagnetic and geochronologic data permit a better resolved reconstruction of indian crustal elements from the paleoproterozoic onward

large shield volcanoes on the moon 1 the volcanic style of the moon has long been understood to consist almost exclusively of flood basalts erupted from fissures along with minor pyroclastic activity large central vent shield volcanoes that characterize basaltic volcanism on the other terrestrial planets appeared to be absent small few kilometers diameter central vent constructs have long been recognized in the lunar maria and often are found clustered in fields throughout the lunar maria new global topographic data from the lola and lroc instruments on lro reveal that almost all of these volcanic complexes on the moon occur on large regional topographic rises in the lunar maria tens to hundreds of kilometers in extent and between several hundred to several thousand meters high we propose that these topographic swells are shield volcanoes and are the lunar equivalents of the large basaltic shields found on the earth venus and mars the newly recognized lunar shields are found peripheral to the large deeply flooded impact basins imbrium and serenitatis suggesting a genetic relation to those features loading of the lithosphere by these basalt filled basins may be responsible for inducing a combination of flexural and membrane stress inducing a pressure distribution on vertically oriented dikes favorable to magma ascent this condition would occur in a zone annular to the large circular loads produced by the basins where the shield volcanoes occur

smiles and frowns in migration velocity analysis reliable seismic depth migrations require an accurate input velocity model inaccurate velocity estimates will distort point diffractors into smiles or frowns on a depth section for both poststack and prestack migrated sections high velocities cause deep smiles while low velocities cause shallow frowns on migrated gathers however for prestack images in the offset domain high velocities cause deep frowns while low velocities cause shallow smiles if the velocity is correct there will be no variation in the depth migration as a function of offset and no smiles or frowns in the offset domain we explain migration responses both mathematically and graphically and thereby provide the basis for depth migration velocity analysis

spectral analysis and geological mapping of the daedalia planum lava field mars using omega data abstract the great variety of morphologies observed in the daedalia planum lava flows mars encouraged a detailed study of their spectral characteristics in order to obtain information about lava composition and detect possible differences in the spectra of the flows the omega spectral data collected from the lava field appear rather similar with absorptions between 0 8 and 1 4 m and 1 8 and 2 5 m suggesting the presence of mafic minerals which are typical primary mineral phases of volcanic rocks moreover after the subtraction of the background absorption continuum removal we highlighted the presence of two classes of spectra both compatible with tholeiitic basalts but with different proportions of ca in the pyroxene despite the similar absorption bands daedalia spectra show differences in albedo and spectral slope by employing the average spectra of the different flow units as end members a sam spectral angle mapper classification was performed the resulting spectral map reveals a relationship between spectral behavior and flow surface textures