the shape and internal structure of the moon from the clementine mission global topographic and gravitational field models derived from data collected by the clementine spacecraft reveal a new picture of the shape and internal structure of the moon the moon exhibits a 16 kilometer range of elevation with the greatest topographic excursions occurring on the far side lunar highlands are in a state of near isostatic compensation whereas impact basins display a wide range of compensation states that do not correlate simply with basin size or age a global crustal thickness map reveals crustal thinning under all resolvable lunar basins the results indicate that the structure and thermal history of the moon are more complex than was previously believed

dynamical fault rupture processes in heterogeneous media abstract the fault rupture processes in a horizontally layered medium and also in a three dimensionally heterogeneous structure are investigated on three dimensional spontaneous dynamic shear crack models the wave equations for three dimensional space are solved numerically by a finite difference scheme under the appropriate boundary conditions and the finite stress fracture criterion the heterogeneous properties of the elastic medium particularly the existence of low velocity zones give remarkable effects on the rupture process yielding appreciably decelerated rupture velocities and large fault displacements in and around the zones and strong motions in the near field the large fault displacements are enhanced when the rupture breaks the ground surface the static seismic moment in the case with a low velocity zone is essentially the same as in a homogeneous half space an attempt is made to simulate the rupture process of a moderate size earthquake by applying the above shear crack model in a heterogeneous medium with depth dependent and laterally heterogeneous stress drop the model appears to explain the observed features to a satisfactory degree

defining seismogenic sources from historical earthquake felt reports abstract we present a method that uses macroseismic intensity data to assess the location physical dimensions and orientation of the source of large historical earthquakes intensity data contain a great deal of information that can be used to constrain the essential characteristics of the seismic source in particular both the seismological theory and its practice suggest that the orientation of the source of significant earthquakes is reflected in the elongation of the associated damage pattern a plausible and easily manageable way of describing a seismic source is by representing it as an oriented rectangle the length and width of which are obtained from moment magnitude through empirical relationships this rectangle is meant to represent either the actual surface projection of the seismogenic fault or at least the projection of the portion of the earth crust where a given seismic source is likely to be located the systematic application of this method to all the m 5 5 earthquakes that occurred in the central and southern apennines italy in the past four centuries returned encouraging results that compare well with existing instrumental direct geological and geodynamic evidence the method is quite stable for different choices of the algorithm parameters and provides elongation directions that in most cases can be shown to be statistically significant in particular the resulting pattern of source orientations is rather homogeneous showing a consistent appennines parallel trend that agrees well with the ne sw extension style of deformation active in the central and southern portions of the italian peninsula

outgassed water on mars constraints from melt inclusions in snc meteorites the snc shergottite nakhlite chassignite meteorites thought to be igneous rocks from mars contain melt inclusions trapped at depth in early formed crystals determination of the pre eruptive water contents of snc parental magmas from calculations of the solidification histories of these amphibole bearing inclusions indicates that martian magmas commonly contained 1 4 percent water by weight when combined with an estimate of the volume of igneous materials on mars this information suggests that the total amount of water outgassed since 3 9 billion years ago corresponds to global depths on the order of 200 meters this value is significantly higher than previous geochemical estimates but lower than estimates based on erosion by floods these results imply a wetter mars interior than has been previously thought and support suggestions of significant outgassing before formation of a stable crust or heterogeneous accretion of a veneer of cometary matter

source inversion of intensity patterns of earthquakes a destructive shock in 1936 in northeast italy 1 we demonstrate that it is possible to retrieve geometric and kinematic information about the source of a destructive past earthquake by inverting its regional macroseismic intensity patterns in fact in the case study the inversion results agree with the seismological instrumental measurements of the 1930s and with neotectonic evidence this leads to the hope that more knowledge about preinstrumental events can be obtained a key toward improving the calculation of seismic hazard mostly in the old world after validating our technique on the 1987 whittier narrows california earthquake pettenati and sirovich 2003 gentile et al 2004 we achieve the present results by investigating an earthquake that happened in 1936 in northeast italy the automatic inversions were performed by using a simplified formula for body waves that radiate from a linear source the inversion shows two minima on the hypersurface of the minimum residuals calculated observed intensity at all sites in the multiparameter model space these two minimum variance source models resemble the two auxiliary planes of the same theoretical fault plane solution similar to that given by the standard use of the first p wave arrivals the present result encourages us to treat more cases and to explore new inversion techniques for quantitatively treating the intensity patterns of earthquakes because at least in some cases they carry geometric and kinematic information about their source

a model for the thermal and chemical evolution of the moon s interior implications for the onset of mare volcanism crystallization of the lunar magma ocean creates a chemically stratified moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior within the magma ocean cumulates the last liquids to crystallize form dense ilmenite rich cumulates that contain high concentrations of incompatible radioactive elements the underlying olivine orthopyroxene cumulates are also stratified with later crystallized denser more fe rich compositions at the top this paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy rayleigh taylor instability causes the dense ilmenite rich cumulate layer and underlying fe rich cumulates to sink toward the center of the moon forming a dense lunar core after this overturn radioactive heating within the ilmenite rich cumulate core heats the overlying mantle causing it to melt in this model the source region for high tio2 mare basalts is a convectively mixed layer above the core mantle boundary which would contain small and variable amounts of admixed ilmenite and kreep this deep high pressure melting as required for the generation of mare basalts occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the moon regardless of details implied by particular model parameters gravitational overturn driven by the high density of magma ocean fe rich cumulates should concentrate high tio2 mare basalt sources and probably a significant fraction of radioactive heating toward the center of the moon this will have important implications for both the thermal evolution of the moon and for mare basalt genesis

earth and mars water inventories as clues to accretional histories abstract the earth has 2 7 km of water on its surface its mantle contains at least 150 ppm water and probably significantly more depending on the amount of undepleted mantle and subducted crustal water that is present geologic evidence suggests that a few hundred meters of water are close to the martian surface but evidence from snc meteorites indicates that the martian mantle is very dry containing no more than about 35 ppm water part of the difference in water content of the mantles of the two planets is attributed to plate tectonics however the earth s mantle appears to contain at least several times the water content of the martian mantle even accounting for plate tectonics we attribute the difference to two possible causes the first possibility is that melting of the earth s surface during accretion as a result of the development of a steam atmosphere allowed impact devolatized water at the surface to dissolve into the earth s interior in contrast because of mars smaller size and greater distance from the sun the martian surface may not have melted so that the devolatilized water could not dissolve into the surface a second and preferred possibility is that mars like the earth acquired a late volatile rich veneer but it did not get folded into the interior as with the earth but instead remained as a water rich veneer the perception of mars as having a wet surface but a dry interior is consistent with what we know of the geologic history of mars which can be viewed as the progressive intrusion and overplating of a water rich crust by dry mantle derived volcanic rocks

s type asteroids ordinary chondrites and space weathering the evidence from galileo s fly bys of gaspra and ida new observations of the s type asteroids gaspra and ida especially by the galileo spacecraft demonstrate that a space weathering process operates which modifies the reflectance spectra of fresh material to be redder straighter and have shallower absorption bands the weathering process appears similar to but less potent than that observed on the moon it operates in the sense that it would tend to convert spectra of ordinary chondrites oc to having the spectral traits of s type asteroids these results appear to resolve the major obstacles of the long standing s type conundrum about the provenance of ordinary chondrite meteorites a wide body of recent research which is reviewed here builds on previous meteoritical evidence to support a new developing consensus that the larger s type asteroids are a diverse assortment of silicaceous assemblages which includes the ordinary chrondite parent bodies recent fairly realistic laboratory simulations of space weathering processes have changed oc spectra to resemble s type spectra j f bell s highly regarded earlier paradigm that oc parent bodies would be found only among sub 10 km main belt asteroids has been tested by an extensive observational survey by r binzel and his proteges the result is that no small main belt analog for the ocs has been found not even the somewhat oc like object boznemcova this article reviews the history of the s type conundrum which set the stage for galileo s historic flybys i review the findings about gaspra and ida including results about their geology their geophysical structure and probable origins and about ida s small moonlet dactyl density constraints on ida set by dactyl s orbit rule out for ida at least the classic view of s types as metallic stripped cores of differentiated precursor asteroids new analysis of the galileo spectral images of ida is presented that provides strong evidence that space weathering occurs on ida and that ida and the koronis family asteroids in general are plausibly oc like in composition after reviewing 1990s developments on the s type conundrum i advocate a new perspective that the ordinary chondrite parent bodies are among the s type asteroids a diverse grouping that also contains other silicaceous and silicate metal assemblages presumably including various stony irons and primitive achondrites represented in meteorite collections gaspra may be such a metal rich assemblage

lunar highland meteorites and the composition of the lunar crust abstract major minor and trace element data obtained by neutron activation techniques and by spark source mass spectrometry ssms on two lunar meteorites mac88104 and mac88105 are reported both mac samples were also analysed for their contents and isotopic compositions of rare gases additional ssms data were obtained on four lunar highland meteorites previously found in antarctica alha81005 y791197 y82192 and y86032 mac88104 and mac88105 are very similar in chemistry suggesting that they are pieces of a single fall event the bulk chemical composition of mac88104 5 is not very different from the other lunar highland meteorites highly aluminous with relatively low contents of ree and siderophile element concentrations slightly above 1 of a ci chondritic level however mafic element concentrations mg cr mn etc are slightly lower in mac88104 5 than in the other lunar highland meteorites the contents of solar rare gases in the two mac samples are low indicating only a small regolith contribution in agreement with rare petrographically identifiable regolith components the mac samples and also y82192 and y86032 are classified as fragmental breccias with negligible regolith components in contrast to alha81005 and y791197 which are regolith breccias with high solar wind derived rare gas contents there is no correlation among lunar meteorites between peak shock pressures and solar gas contents indicating that peak shock pressures of up to 25 gpa do not lead to gas loss a low 26al activity vogt et al 1990 and high contents of cosmogenic rare gases in mac88104 5 suggest a long exposure 400 000 years in the lunar sub surface k ar ages are in excess of 3 9 by lunar highland meteorites and compositionally similar granulitic rocks from the apollo 16 and 17 landing sites contain about 1 of a ci chondritic component according to siderophile and volatile element contents but independent of the amount of regolith components apparently the major fraction of meteoritic elements in these rocks was not provided by micrometeorites impacting the regolith the abundances of siderophile e g ir and volatile elements may therefore reflect the last spike of accretion of the moon after the formation of the anorthositic crust lunar meteorites of highland origin are chemically different from the bulk of the apollo 16 highland samples in having higher fe mg ratios and lower contents and less fractionated patterns of incompatible and siderophile elements since lunar highland meteorites are associated with at least three but probably four different fall events and since they are not derived from chemically exotic front side terranes they may represent a better sampling of the average chemical composition of the lunar crust than previous estimates based on returned lunar samples and remote sensing data a comparison between an average highland composition derived by taylor 1982 and an estimate based on lunar highland meteorites shows that the taylor composition contains higher concentrations and more fractionated incompatible elements mainly because of a substantial amount of kreep a trace element rich highly fractionated component from the front side of the moon not present at the sites from which the lunar meteorites come

multispectral studies of western limb and farside maria from galileo earth moon encounter 1 new visible and near infrared multispectral images of the moon obtained by the galileo solid state imaging system along with lunar orbiter images for crater counts and spectral mixing analyses were used to characterize western limb and eastern farside maria and determine compositional and age relationships in selected regions results indicate that 1 western limb mare deposits have less variability in titanium content 6 wt tio2 mare basalts were observed on the western limb and farside which may reflect the inability of such denser magmas to penetrate the thicker farside crust

the environmental seismic intensity scale esi 2007 in greece addition of new events and its relationship with magnitude in greece and the mediterranean preliminary attenuation relationships abstract the environmental seismic intensity esi scale has been officially released in 2007 and is based on the quantification of earthquake environmental effects due to its quantitative nature the scale improves the process of assessing macroseismic intensities particularly in the epicentral area of those cases in which sole traditional intensity scales prove to be ineffective following a large number of publications that applied this relatively newly established scale there is some need for parametrization this is because this intensity scale can offer new insights to seismic hazard assessment and has the potential to reduce the uncertainties that stem from traditional macroseismic scales this study has three main goals firstly to enrich and compile an esi 2007 database from earthquakes in greece by adding 4 new events secondly to extract a relationship between magnitude and the esi 2007 for greece and the mediterranean thirdly to offer a preliminary estimate of how the intensity attenuates with distance after developing a code in python language to assist this process the esi 2007 scale was applied in the 1995 ms 6 6 kozani grevena earthquake the 1978 mw 6 5 thessaloniki earthquake the historic 1894 atalanti earthquake sequence m 6 4 and m 6 8 and the 365ad event in crete m 8 4 these events were selected because they have well documented and extensive co seismic effects including primary and secondary surface ruptures rockfalls landslides and liquefaction phenomena for the kozani earthquake extracted results were correlated with sar interferograms in order to provide a complete and high spatial resolution of the ground deformation both the kozani grevena and the thessaloniki events produced a maximum intensity ix on the esi 2007 scale the atalanti earthquake produced a maximum intensity x and the 365ad crete earthquake a maximum intensity xii overall the esi 2007 scale compares fairly well with the traditional macroseismic scales except for some villages in the kozani grevena epicentral area where due to the poor quality of buildings existing scales overestimated the intensity by one degree compared to the esi 2007 it is interesting to note that both for greece and the mediterranean area a strong correlation exists between mw and the esi 2007 scale in particular the following relationships between the mw and the esi scale have been extracted i for greece io esi 2007 3 1427 exp 0 1643mw and ii for the mediterranean io esi 2007 3 3543exp 0 1557mw however more events and more data regarding the intensity distributions are required to establish the intensity attenuation with distance

revised model calculations for the thermal histories of ordinary chondrite parent bodies recent measurements of ordinary chondrite physical and thermal properties along with new geothermometry studies have provided the necessary parameters for updating a previously proposed model miyamoto et al 1981 for the thermal evolution and internal structure of ordinary chondrite parent bodies model calculations assumed a heat source term derived from the decay of 26al justification is provided differences from the previous model include varying the thermal diffusivity parameter with increasing temperature and decreasing porosity using variable physical and thermal parameters to provide end member models and incorporating a shortened thermal history of 60 ma obtained from new pb pb chronology of phosphates rather than 100 ma times of isotopic closure in chondrite phosphates overlap the thermal model estimates and postmetamorphic cooling rates from the model approximately coincide in both trend and magnitude with metallographic and fission track cooling rate data model calculations attempt to match peak metamorphic conditions in the central portions of these bodies and yield accretion ages between 1 4 to 3 1 ma after calcium aluminum inclusion cai formation model calculations also predict that both the h and the l chondrite parent asteroids consisted of 80 equilibrated and 20 unequilibrated chondritic material and that their original radii ranged from 80 to 95 km

incompletely transformed serpentine type phyllosilicates in the matrix of antarctic cm chondrites abstract recent hrem high resolution electron microscopy investigation has shed light on the characterization of matrix phyllosilicates in cm chondrites in examining the antarctic cm chondrite yamato 793321 by hrem mineral grains which show an ed electron diffraction pattern consisting of both olivine and serpentine spots show disordered and defect structures in patchy hrem images these data are interpreted as representing an intermediate phase in the transformation from serpentine to olivine this is the first description of such an intermediate phase in belgica 7904 phyllosilicates seem to have been almost completely transformed to olivine it is suggested that it formed by heating of matrix phyllosilicates preliminary heating experiments on murchison also a cm chondrite showed that the matrix phyllosilicates transformed to a phase which gave an ed pattern and hrem image similar to those for yamato 793321 the results of these heating experiments support the formation of the intermediate phase by transformation from phyllosilicate to olivine during a heating event at a late stage

mineralogy of chondritic interplanetary dust particles from a mineralogical survey of approximately 30 chondritic micrometeorites collected from the lower stratosphere and studied in detail using current electron microscopy techniques it is concluded that these particles represent a unique group of extraterrestrial materials these micrometeorites differ significantly in form and texture from components of carbonaceous chondrites and contain some mineral assemblages which do not occur in any meteorite class electron microscope investigations of chondritic micrometeorites have established that these materials 1 are extraterrestrial in origin 2 existed in space as small objects 3 endured minimal alteration by planetary processes since formation and 4 can suffer minimal pulse heating 600 c on entering earth s atmosphere the probable sources for chondritic interplanetary dust particles idps are cometary and asteroidal debris and perhaps to a lesser extent interstellar regions these sources have not been conclusively linked to any specific mineralogical subset of idp although the chondritic porous cp aggregate is considered of likely cometary origin chondritic idps occur in two predominant mineral assemblages 1 carbonaceous phases and phyllosilicates and 2 carbonaceous phases and nesosilicates or inosilicates although particles with both types of silicate assemblages are observed olivines pyroxenes layer silicates and carbon rich phases are the most commonly occurring minerals in many chondritic idps other phases often observed in variable proportions include sulphides spinels metals metal carbides carbonates and minor amounts of sulphates and phosphates individual mineral grain sizes range from micrometers primarily pyroxenes and olivines to nanometers with the predominant size for all phases less than 100 nm specific mineral characteristics for particular chondritic idps provide an indication of processes which may have occurred prior to collection in the earth s stratosphere for example pyroxene mineralogy in some chondritic aggregates is consistent with condensation from a vapor phase and we consider with condensation in a turbulent solar nebula at relatively low temperatures 1000 c carbonaceous phases present in other cp aggregates have been used to imply low temperature formation processes such as fischer tropsch synthesis 530 c or carbonization and graphitization 315 c alteration processes have been implicated in the formation of some layer silicates in cp aggregates and may have involved hydrocryogenic alteration at 0 c in general interpretations of transformation processes on submicrometer size minerals in chondritic idps are consistent with formation at a radius equivalent to the asteroid belt or greater during the later stages of solar nebula evolution using currently available models

evidence for komatiite type lavas on mars from phobos ism data and other observations data from the phobos 2 imaging spectrometer for mars ism compiled by mustard et al 1993 and other observations support the existence of komatiitic lavas on mars mustard et al 1993 determined from ism data that the composition of the low albedo materials covering the syrtis major plateau originally consisted of augite bearing basalt containing both augite and pigeonite with no appreciable amount of olivine this description is consistent with a komatiitic basalt komatiite is significant for the earth because it contains a high amount of mgo implying generation under unique circumstances compared to more typical basaltic compositions and may be similarly important for mars

a 4 gyr shock age for a martian meteorite and implications for the cratering history of mars analyses of meteorites that originated on mars provide important insights into the geological and atmospheric evolution of the planet such analyses have hitherto been restricted to relatively young martian rocks1 the oldest martian meteorites have an age of approximately 1 3 billion years but the recently recognized2 martian meteorite allan hills 84001 which is distinct from the other martian meteorites2 4 shows evidence for a much older age5 6 here we report an analysis of the shock alteration history of this meteorite based on argon isotope dating from which we derive a shock age of 4 0 0 1 billion years the age and geological history of this meteorite suggest that it came from the heavily cratered noachian age terrains of mars s southern hemisphere and it may thus provide an absolute chronology for this region of the planet independent of that inferred from the cratering record the shock age of the meteorite also coincides with that of the so called lunar cataclysm a relatively short period during which many of the craters on the moon are believed to have formed supporting the idea7 that intense bombardment was widespread throughout the inner solar system between 3 9 and 4 1 billion years ago

lunar meteorites siderophile element contents and implications for the composition and origin of the moon abstract six lunar meteorites have thus far been discovered in antarctica although these meteorites are of undocumented lunar geographic provenance all other available lunar samples obtained from the apollo and luna programs came from a relatively minuscule region of the central nearside around which a polygon could be drawn covering just 4 7 of the lunar surface the five lunar meteorites that are now well studied represent at least two but probably three separate lunar source craters alha81005 and y791197 are probably from separate craters and compound meteorite y82192 6032 is certainly from a crater of its own at least alha81005 and y791197 and probably also at least in a loose sense y82192 6032 are highlands regolith breccias thus their compositions may be appropriately compared with compositions of apollo and luna highlands regolith samples compared with average highlands regolith samples from the central nearside apollo sites lunar meteorites have lower concentrations of siderophile elements in general and especially au ge and ni among anorthositic apollo samples i e mainly those from apollo 16 au ir and to a lesser extent ge ir ratios tend to be hyperchondritic most previous models for lunar regolith siderophile geochemistry assumed that the apollo 16 samples are representative of the overall lunar highlands such models tended to conclude that the hyperchondritic au ir and ge ir ratios were consequences of variations in the compositions of moon striking projectiles as a function of time it was even speculated that these temporal variations were consequences of the heterogeneous accretion of a moon with a general enrichment in refractory elements the lunar meteorites suggest that hyperchondritic au ir and ge ir are not general features of the highlands but peculiarities of the apollo 16 region or more generally the central nearside the high ni contents of the apollo 16 megaregolith substantially in excess of the ni implied by a model in which all meteoritic debris has an h chondritic ni ir ratio have been interpreted to imply that the mg rich fraction of the lunar crust is extremely ni rich and thus similar in siderophile geochemistry to terrestrial komatiites this coincidence has been interpreted as confirmation that the moon formed by modified fission from the earth s mantle after core formation plus late accretion effects had established the final siderophile pattern of the earth s mantle however the lunar meteorites and a survey of data for the luna 20 highlands regolith sample suggest that the high ni content of the apollo 16 regolith is strictly a peculiarity of the apollo 16 region and not a general feature of the moon s crust the anomalous siderophile composition of the central nearside regolith probably stems from a combination of regional heterogeneity in cratering projectile compositions plus regional enrichments in relatively labile siderophile elements most notably au ge and perhaps to a certain extent ni which might be loosely correlated with the anomalously high concentration of kreep over the central nearside

spectral properties and rotational spectral heterogeneity of 433 eros composite spectra of different rotational aspects of the s asteroid 433 eros were assembled from previous studies covering the wavelength range 0 33 2 5 m these data allow us to measure significant attributes of eros s spectrum its mafic mineral absorptions and the degree and nature of compositional heterogeneity of its surface we also evaluated previous s asteroid taxonomies using independent methods and from this test determined that the taxonomy of gaffey et al 1993 provides a sound basis for relating eros to other s asteroids on average eros resembles the s iv asteroids which bear the closest resemblance to ordinary chondrites in mafic mineralogy however eros also exhibits distinct rotational spectral variations comparable to the greatest yet recognized on an s asteroid one side of the asteroid has a shorter wavelength 1 m absorption and a stronger 2 m absorption than the global average and is interpreted to be richer in pyroxene the opposite face has a longer wavelength 1 m absorption and a weaker 2 m absorption and is interpreted to be richer in olivine the pyroxene rich side coincides with a facet like face identified in radar studies and the olivine rich side coincides with a convex shaped face each side of the asteroid exhibits spectral affinities with a different spectral class of s asteroids demonstrating that such subdivisions of s asteroids represent different parts of a compositional continuum high spatial resolution measurement of the mineralogic and elemental compositions and especially the geologic settings of these different materials by the near earth asteroid rendezvous mission will provide a great advance in the understanding of the origin and evolution of a candidate ordinary chondrite parent body

the geology of gaspra the surface of gaspra can be divided into several facets separated by ridges superimposed on the facets and ridges are two populations of craters type 1 craters are crisply defined and constitute a production function of impact origin type 2 craters are mostly irregular shallow depressions and probably of various origins some of the type 2 craters may have formed by impact and be remnants of a crater population that predates the type 1 population the number of type 1 craters suggests that they started to accumulate 2 107 to 3 108 years ago the freshest craters have a depth diameter ratio of 1 7 as compared with 1 5 typically observed on other bodies the craters appear to have become shallower with age at a rate of 10 6 to 10 7 m year the shallow depth of newly formed craters and the progressive degradation with age are ascribed to downslope movement of poorly coherent surface materials the movement being aided by seismic shaking as a result of impact the surface shows subtle color differences the most prominent differences are observed around craters on ridges where the surface has a stronger 1 m absorption than elsewhere the contrast is not observed around craters on the facets the color differences are attributed to alteration of the materials brought to the surface the unaltered material is estimated to be located at least 50 m below the surface on the facets only on the ridges is unaltered material at a shallow enough depth to be excavated by the observed craters the rate of degradation of craters the rounded form of the ridges the depth of altered material on the facets and the presence of old degraded craters all suggest that gaspra is covered with a regolith a few tens to several tens of meters thick

normal alkanes in meteorites molecular δ13c values indicate an origin by terrestrial contamination in the time period since 1961 n alkanes straight chain hydrocarbons have been detected in varying amounts in many meteorites proposed origins for these compounds have included extraterrestrial biotic extraterrestrial abiotic and terrestrial contamination processes to help establish the source of these compounds we determined the carbon isotopic compositions of individual n alkanes in meteorites of several different classes and terrestrial histories orgueil ci1 cold bokkeveld cm2 murchison cm2 vigarano cv3 allende cv3 ornans co3 and bishunpur ll3 the efficiency of supercritical fluid extraction sfe was exploited to provide extractable non polar organic matter from the meteorites the n alkanes in these extracts were then identified with gas chromatography mass spectrometry gc ms and the carbon isotopic composition of individual molecules was determined using isotope ratio monitoring gas chromatography mass spectrometry irm gc ms n alkanes were found in all but one of the meteorites analysed allende but carbon number distributions varied between samples pristane and phytane were also detected in five of the seven meteorites 13c values for the individual n alkanes occupied a range from 25 3 to 38 7 the 13c values for the meteoritic n alkanes have a similar range as those for n alkanes measured from petroleum in the literature therefore the n alkanes in meteorites appear to be terrestrial contaminants which may have originated from fossil hydrocarbons or petroleum products this type of contamination is analogous to that which will be threatening future meteorite falls and the samples returned from spaceflight missions over the next two decades and beyond for falls already contaminated irm gc ms appears useful in discriminating between indigenous compounds and those introduced by terrestrial contamination

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

defining biominerals and organominerals direct and indirect indicators of life abstract by introducing the new term organomineral to apply to minerals that are affected by organics mostly life related but not directly produced by living cells we hope to increase the accuracy of the terminology in present usage we believe that the term biomineral does not describe all mineral deposits precisely enough and offer case studies to support instances where the use of the new term organomineral is more appropriate we provide examples of some materials that are biominerals such as those in diatoms and human bones and which perform a functional purpose we then attempt to show that terminology can sometimes mislead investigators drive the direction and prejudice interpretations of scientific investigation this is achieved by presenting case studies of minerals that have been investigated as biominerals although they may not actually be directly controlled by biology for this reason we pay special attention to desert varnish hot spring siliceous deposits stromatolites and bacterial encrustations we go on to explain why we regard biominerals as direct indictors of life whereas organominerals should be treated as indirect indicators of life that require careful characterization to establish the origin of contained organics and whether these are biotic in origin how organic compounds are preserved and transformed in sedimentary environments and in the mineral matrix is as highly relevant to the study of modern earth environments as it is in the search for the oldest evidence of life in the terrestrial rock record it is also important to many disciplines such as microbiology and archaeology and especially to scientists planning missions to look for evidence of life on other planetary surfaces

geology of 243 ida abstract the surface of 243 ida is dominated by the effects of impacts no complex crater morphologies are observed a complete range of crater degradation states is present which also reveals optical maturation of the surface darkening and reddening of materials with increasing exposure age regions of bright material associated with the freshest craters might be ballistically emplaced deposits or the result of seismic disturbance of loosely bound surface materials diameter depth ratios for fresh craters on ida are 1 6 5 similar to gaspra results but greater than the 1 5 ratios common on other rocky bodies contributing causes include rim degradation by whole body ringing relatively thin ejecta blankets around crater rims or an extended strength gradient in near surface materials due to low gravitational self packing grooves probably represent expressions in surface debris of reactivated fractures in the deeper interior isolated positive relief features as large as 150 m are probably ejecta blocks related to large impacts evidence for the presence of debris on the surface includes resolved ejecta blocks mass wasting scars contrasts in color and albedo of fresh crater materials and albedo streaks oriented down local slopes color data indicate relatively uniform calcium abundance in pyroxenes and constant pyroxene olivine ratio a large relatively blue unit across the northern polar area is probably related to regolith processes involving ejecta from azzurra rather than representing internal compositional heterogeneity a small number of bluer brighter craters are randomly distributed across the surface unlike on gaspra where these features are concentrated along ridges this implies that debris on ida is less mobile and or consistently thicker than on gaspra estimates of the average depth of mobile materials derived from chute depths 20 60 m grooves 30 m and shallowing of the largest degraded craters 20 50 m minimum 100 m maximum suggest a thickness of potentially mobile materials of 50 m and a typical thickness for the debris layer of 50 100 m

interplanetary dust particles collected in the stratosphere observations of atmospheric heating and constraints on their interrelationships and sources abstract the majority of the interplanetary dust particles idps collected in the stratosphere belong to one of three major classes the first two dominated by the anhydrous minerals olivine and pyroxene and the third by hydrous layer lattice silicates infrared spectroscopy and transmission electron microscopy studies show that the different idp classes represent different types of dust that exist as individual particles in interplanetary space the majority of the collected idps smaller than 30 m in diameter in the layer lattice silicate and pyroxene classes appear not to have been heated to temperatures above 600 c during atmospheric entry the relatively low maximum temperatures experienced by these idps during atmospheric entry imply that they arrive at the top of the atmosphere with low geocentric encounter velocities this limits the possible encounter trajectories for these particles to relatively circular prograde orbits as a result it is unlikely that these idps are from earth crossing comets or asteroids asteroids and comets having low inclinations and perihelia outside 1 2 ua appear to be the best candidates for the parent bodies of the pyroxene and layer lattice silicate particles chemical and mineralogical information suggests that the pyroxene rich idps are from comets and layer lattice silicate rich idps are from asteroids the collected idps dominated by olivine appear to include a larger fraction of particles heating above 600 c suggesting that these particles were captured from more eccentric orbits this and the observation of the infrared spectral features of olivine in several comets suggest these particles have a cometary origin since much of the collected dust has apparently been captured from nearly circular prograde orbits and since there are no appropriate parent bodies presently in such orbits these results provide an experimental confirmation that the poynting robertson effect exists as a nongravitational force important in the orbital evolution of dust in the solar system

petrologic study of the belgica 7904 carbonaceous chondrite hydrous alteration oxygen isotopes and relationship to cm and ci chondrites abstract seven components were separated from the belgica 7904 b7904 carbonaceous chondrite in order to learn more about the genetic relationships between the petrology hydration reactions and the oxygen isotopic compositions these components include two partially altered chondrules two phyllosilicate clasts two olivine fragments and one matrix sample the partially altered chondrules have a core rim structure cores have igneous textures and are unaltered and rims consist mainly of talc component bearing phyllosilicates and unaltered olivine clear textural evidence indicates that the phyllosilicates in the rims were produced by replacing pyroxene and plagioclase while the olivine remained unaltered during the process on the other hand the phyllosilicate clasts consist mainly of fine grained serpentine produced from olivine as well as the pyroxene and plagioclase the olivine fragments derived by disaggregation of large porphyritic olivine chondrules are unaltered the matrix sample consists mainly of fine grained phyllosilicates if the hydration reactions took place with liquid water in the parent body olivine would have produced talc component free phyllosilicates before pyroxene and plagioclase reacted this is not the case for the phyllosilicates in the chondrule rims therefore we suggest that the chondrule rims formed by hydration in the nebula prior to accretion rather than with liquid water in the parent body thermodynamic calculations show that the reactions of pyroxene and plagioclase with a gas would produce the talc component bearing phyllosilicates at temperatures higher than that at which olivine reacts to produce serpentine assuming that total gas pressure was 10 3 bars the chondrule rims may have been produced by reactions with a nebular gas having an h 2 o h 2 ratio of 0 052 at temperatures ranging from 560 to 330 k the phyllosilicate clasts where olivine also reacted may have been produced by reactions with this nebular gas at temperatures near 300 k and the matrix phyllosilicates may have been in equilibrium with the gas at temperatures higher than 250 k there is no evidence for liquid water interacting with the chondrite the cm mixing line in the three oxygen isotope plot mayeda et al 1991 which includes the separated components and whole rock composition of b7904 is explained by hydration in nebular gas ci chondrites may have formed from materials similar to the b7904 matrix by reactions with liquid water in a parent body cm chondrites have experienced two stage alteration including both hydrous reactions with a gas in the nebula and aqueous alteration with liquid water in their parent body

the role of meteoritics in spaceflight missions and vice versa research on extraterrestrial materials plays a critical role in formulating the science rationale and design for spacecraft missions and conversely spaceflight holds great promise for solving perplexing problems in meteoritics the connections between meteoritics and sample return missions are obvious meteorite research can define sampling strategies the capabilities of sampling devices acceptable levels of chemical contamination and physical alteration of samples and the conditions under which samples are stored prior to and during recovery for their part sample return missions can provide geologic context for meteorites increased sampling diversity including materials not sampled as meteorites such as unconsolidated regolith ices and atmosphere calibration for crater counting chronology and ground truth for remote sensing measurements of meteorite parent bodies meteoritics also relates to spacecraft flyby rendezvous and lander missions that do not necessarily return samples specific illustrations of this mutual relationship based on a selection of recent or planned spacecraft missions include identifying source asteroid classes for ordinary and carbonaceous chondrites and reconstructing their thermal and collisional histories galileo near clementine ii and muses c determining the extent to which cometary dust and interstellar grains are found as interplanetary dust particles and assessing volatile abundances isotopic compositions and molecular species in cometary nuclei stardust and rosetta understanding the compositions of ancient martian crust and the mantle sources for snc meteorites as well as inventorying the planet s volatile reservoirs and interactions mars pathfinder mars global surveyor and mars volatiles and climate surveyor assessing whether lunar meteorites provide a more representative chemical sampling of the highlands crust and of mare volcanism than do apollo samples galileo clementine and lunar prospector spaceflight is the first priority of the space agencies that fund most research on extraterrestrial materials and the continued level of support for such research may be linked in part to its use in exploration by spacecraft

analysis of the ground accelerations radiated by the 1980 livermore valley earthquakes for directivity and dynamic source characteristics the strong motion accelerograph recordings of the 24 january 1980 main shock and the 27 january 1980 aftershock of the livermore valley earthquake sequence are analyzed for systematic variations with azimuth or station location the variation of the peak accelerations with epicentral azimuth is apparently reversed for the two events the main shock accelerations are larger to the south and the aftershock accelerations are larger to the northwest we eliminate the site effects by forming the ratio of the peak accelerations recorded at the same station after correcting for the epicentral distance this analysis indicates that source directivity caused a total variation of a factor of 10 in the peak accelerations comparison of this variation with the spatial extent of the aftershock sequences suggests that the strong directivity in the radiated accelerations is the result of unilateral ruptures in both events the accelerograms recorded at 10 stations within 35 km of the events were digitized to analyze the azimuthal variation of the rms acceleration the peak velocity and the radiated energy flux the variation of rms acceleration correlates almost exactly with the variation of the peak accelerations this correlation is analyzed using both deterministic and stochastic models for the acceleration waveforms the peak velocities corrected for epicentral distance vary with azimuth by a factor of 5 for both events while the radiated energy flux varies by a factor of 30 for the main shock and 15 for the aftershock the peak velocities are strongly correlated with the radiated energy flux the radiated seismic energies are estimated to be 2 6 0 9 1020 dyne cm for the main shock and 1 5 0 3 1020 dyne cm for the aftershock

source geometry of historical events retrieved by synthetic isoseismals abstract the possibility of computing complete synthetic signals for laterally homogeneous structural models in an exact efficient and computationally rapid way allows an investigation of the effects of given source and structural models on the macroseismic field synthetic isoseismals are computed by first adding vectorially in the horizontal plane the sh wave and p sv wave displacement fields the maximum zero to peak value of displacement is then calculated at points distributed in space in such a way that it is easy to contour the isolines automatically this methodology developed mainly in the point source approximation and used to investigate the macroseismic field of some instrumentally recorded earthquakes can also be applied to historical events

the campania lucania southern italy earthquake of 23 november 1980 abstract we present the main seismological results of our study of the campania lucania earthquake of 23 november 1980 a complete set of far field and local data has been analysed from long period body waves data we determine the fault plane solution 1 140 1 60 2 75 2 54 a depth of 15 km and calculate a seismic moment of 6 1025 dyne cm and a source duration of 6 s from data of a local network deployed immediately after the event we determine aftershock locations they are aligned in a direction nw se that fit extremely well with the focal solution determined above we can choose as fault plane the plane striking 140 and dipping at 60 and the event is a normal event with a large component of left lateral strike slip the source area evaluated from this aftershock distribution 14 km 40 km is quite suitable for an earthquake of a seismic moment of 6 1025 dyne cm

archean komatiites and geotherms solution to an apparent contradiction the high liquidus temperatures of archean komatiites and the low geothermal gradients in archean continents appear to give contradictory indications of temperatures in the archean mantle we resolve this contradiction in terms of an idealized model of convection in the archean mantle we suggest that temperatures in the archean mantle were no more than 100 c higher than at present that komatiites originate from the hot lower boundary layer of a non steady convection cell and that archean continents were formed near subduction zones where near surface temperature gradients were lower than elsewhere in the convecting mantle

aftershocks of the campania lucania italy earthquake of 23 november 1980 abstract the result of a study of 1130 aftershocks of the 1980 campania lucania earthquake are presented the data were collected primarily with a dense array of portable smoked drum seismographs deployed in the epicentral region a few days after the main shock tests performed on subsets of the data to establish the location accuracy are described in detail and epicentral maps and cross sections are presented and discussed one hundred and sixty well constrained fault plane solutions using upward traveling rays are presented the distribution of aftershocks forms an elongate cloud which does not define a plane this is not because the events are poorly located a subset of events located with epicentral errors of less than 1 km and depth errors less than 2 km forms a similar cloud to the complete aftershock set the aftershock mechanisms are very varied some are similar to the main event but many differ profoundly these include events on shallow or vertical planes and thrust events the latter include some events which require contraction in the direction in which the main event indicates extension the aftershocks of all mechanisms are intermixed in space in such a way that no simple system of faults can explain them a model to explain the aftershocks and the lack of surface ruptures in the main event is offered it is proposed that the main shock cuts between two aseismic detachment surfaces and that the aftershocks are a consequence of the complicated deformation that such a geometry demands whatever interpretation is adopted the results are a challenge to the commonly accepted view that aftershocks even approximately define simple fault planes or that aftershock mechanisms replicate the mechanism of the main shock defects in interpretations of the main shock and aftershocks process arise largely from a lack of information about the geometry of structures at depth in the epicentral region suitable deep reflection profiles could help to resolve this problem

carbon oxygen and nitrogen isotopic compositions of possible martian weathering products in eeta 79001 abstract carbon and oxygen isotopic analyses of carbonate rich white druse material isolated from a contact between lithologies a and c of the eeta 79001 shergottite indicate that this component is probably extraterrestrial in origin and not simply an antarctic weathering product the 13c 6 8 and 18o 21 1 values of the calcium carbonate predominantly calcite are unlike 13 c 18 o combinations of most common terrestrial carbonates whether biogenic or abiogenic however 13c and 18o of the carbonates in eeta 79001 are very similar to the corresponding values for carbonates analysed from nakhla a meteorite closely allied to shergottites it seems apparent that the carbonate minerals in these snc meteorites were formed on the meteorites parent body mars isotopic analysis of nitrogen liberated during combustion of a carbonate rich fraction of eeta 79001 does not give any clear evidence for the 15n enriched component isolated from eeta 79001 lithology c glass and postulated as trapped martian atmosphere however substantial amounts of nitrogen were present the origin of these components is unclear but the low temperature of release poses some constraints

attenuation of peak horizontal acceleration and velocity from italian strong motion records italian strong motion data were used to study attenuation characteristics of horizontal peak ground acceleration and velocity the data base consisted of 190 horizontal components of accelerograms recorded in italy since 1976 from 17 earthquakes of magnitudes 4 6 to 6 8 the resulting equations are log a 1 562 0 306 m log r 2 5 8 2 1 2 0 169 s log v 0 710 0 455 m log r 2 3 6 2 1 2 0 133 s where a is peak horizontal acceleration in g v is peak horizontal velocity in centimeters second m is magnitude r is the closest distance to the surface projection of the fault rupture in kilometers and s is a variable taking the values of 0 and 1 according to the local site geology peak acceleration and velocity were found to be lognormally distributed with a standard error representing respectively a 49 and 64 per cent increase in the median estimate we considered a magnitude dependent shape of the attenuation curves but we found no basis for it in the data attenuation relationships developed using epicentral distance in place of fault distance gave similar results with higher standard errors and higher predicted values for short distances and high magnitudes sensitivity studies performed with the analysis of the residuals showed that predictions based on our relatiaons are stable with respect to reasonable variations of the model and the seismic areas providing the data comparisons with attenuation relationships proposed for western north america showed differences of the same order of magnitude as the statistical prediction uncertainty

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

tests of source parameter inversion of the u s geological survey intensities of the whittier narrows 1987 earthquake we validated the source inversions of the intensity data set of the whittier narrows m l 5 9 1987 earthquake by comparing the source characteristics retrieved by our inversion technique with those already known from instrumental measurements in our grid search technique the squared residuals calculated minus observed intensity at the sparse sites are weighted by the voronoi polygons tessellation and then the sum of the weighted squared residuals is minimized for comparison we also minimize the sum of the unweighted squared residuals the intensities are calculated by our kinematic kf function twelve source parameters are involved in the inversions the most sensitive of which are the epicentral coordinates and the fault plane solution to find the minimum variance model we explore the whole space of the angular values that control the fault plane solution and place some reasonable constraints on the other parameters two minimum variance models were determined by the inversions one source that is in agreement with that already known from instrumental measurements and one almost coinciding with its auxiliary plane in the fault plane solution this finding confirms that notwithstanding the introduction of more source parameters the nature of the problem of the inversion of an almost pure dip slip earthquake is still close to bimodality it is demonstrated that it is possible to get an approximate idea of the source of the studied earthquake by inverting the u s geological survey intensities this result encourages us to validate our inversion technique with more well documented earthquakes and to treat intensities of preinstrumental earthquakes which are the principal target of our work manuscript received 10 february 2001

a case of the influence of radiation pattern on peak accelerations abstract the strong ground shaking of the 23 november 1980 earthquake in southern italy seems to have been conditioned by the dimension of the source its focal mechanism and by the distance from the shallow portion of the source there was only a low and doubtful directivity effect these results come from a comparison of the azimuthal distribution of the recorded peak ground horizontal accelerations with that of the total dimensionless radiation pattern of s waves in the horizontal plane at each site radiation from the closest point of the fault and appropriate azimuth and take off angles were considered the recorded maxima were obtained from hodogram plots of each couple of automatically digitized horizontal components in 13 stations with negligible local site effects at a distance of up to 78 km from the epicenter the analysis indicates the strong influence of the strike slip component on the azimuthal distribution of motion the fault mechanism best fitting the recorded maxima is as follows strike 318 dip 64 rake 317 this picture does not change if acceleration maxima in the frequency bands 0 1 to 5 hz 1 to 5 hz or 1 to 2 hz are used in a segment of the southern apennines where the strong motion energy radiation in the near intermediate field of a repetitive series of shocks from the seventeenth century up to 1980 seems to be controlled by the gross features of the source it could be useful to include radiation patterns into algorithms for regional seismic hazard calculations conversely because of the fact that drawing isoseismal lines results in a smoothing of at least the very local site effects it might be possible to infer information about the gross features of the sources of historical earthquakes from macroseismic data

sm nd age and isotopic systematics of the bimodal suite ancient gneiss complex swaziland studies of the development and stabilization of the archaean crust often focus on the relative temporal relationships between the metamorphosed basaltic to ultramafic volcanic units greenstone belts and the sialic gneiss terrains that make up the oldest sections of the terrestrial crust at the heart of this interest are the questions of the processes responsible for crust formation in the archaean and whether or not the various units of an archaean crustal section represent new additions to the crust from the mantle or are products of the reprocessing of even older crustal materials one area where this controversy has been particularly pronounced is the archaean crustal section of south west africa1 6 the oldest rocks in the kaapvaal craton consist of the onverwacht group of mafic to ultramafic metavolcanics of the barberton greenstone belt and a grey gneiss complex termed the ancient gneiss complex agc of swaziland we report here the results of a whole rock sm nd isotopic study of the agc and the implications these data may have for crustal evolution in the kaapvaal craton

focal mechanism of an earthquake of baroque age in the regno delle due sicilie southern italy abstract a new kinematic function kf which incorporates fault dimension mean variation in velocity of rupture v r radiation pattern and mean depth from which the majority of the damaging energy is radiated is able to model the shape of isoseismals of the 1694 earthquake the focal mechanism of this earthquake is estimated to be a normal fault of apenninic direction dipping 60 70 towards the ne with a left lateral strike slip component due to the similarity with isoseismals of other earthquakes in the southern apennines it is argued that similar mechanisms could be responsible for other earthquakes in the region

assessing biomarker syngeneity using branched alkanes with quaternary carbon baqcs and other plastic contaminants biomarker molecules are valuable for the elucidation of ancient microbial ecosystems and the characterization of petroleum source rocks for such studies acquisition of reliable hydrocarbon data and proof of their syngeneity are essential however contamination of geological samples with anthropogenic petroleum products during drilling storage and sampling can be particularly problematic because these hydrocarbons may over print an original indigenous biomarker profile to evaluate the extent of contamination of drill core and outcrop material we studied the distribution of hydrocarbons in 26 rocks from different locations in the world all rocks had petroleum products on their exterior surfaces twenty two samples also contained surficial hydrocarbons derived from polyethylene plastic including branched alkanes with quaternary carbon centers baqcs and alkylcyclopentanes with pronounced even over odd carbon number preference using three examples from the paleoproterozoic tawallah and mcarthur groups in northern australia we show how indigenous biomarkers can be recognized by comparing hydrocarbon distributions between exterior rock surfaces and the rock interior and how infiltration of allochthonous hydrocarbons can be assessed through the spatial distribution of characteristic polyethylene derived hydrocarbons in the rock the methods outlined in this paper give confidence in the interpretation of biomarkers in particularly sensitive applications such as the first occurrences of certain organisms in the geological record and the provenance of organic matter in meteorites

precise u pb zircon ages from the gamitagama greenstone belt southern superior province volcanism in the gamitagama lake greenstone belt 50 km south of wawa ontario on the east shore of lake superior took place ago at the same time as similar volcanism in the much larger abitibi greenstone belt to the east two post orogenic intrusions in the metavolcanic metasedimentary terrain are coeval at and and could very well be comagmatic as suggested by ayres a granitic sill in a metasedimentary granitic migmatite terrain that borders the greenstone belt to the southwest has an age of 2615 10 ma and is much younger than the post orogenic plutons to the northeast this migmatite region represents either an uplifted deep zone that remained hot long after volcanism or a region that accumulated heat as a result of its sedimentary cover

carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles we have studied nineteen anhydrous chondritic interplanetary dust particles idps using analytical electron microscopy we have determined a method for quantitative light element edx analysis of small particles and have applied these techniques to a group of idps our results show that some idps have significantly higher bulk carbon abundances than do carbonaceous chondrites we have also identified a relationship between carbon abundance and silicate mineralogy in our set of anhydrous idps in general these particles are dominated by pyroxene olivine or a subequal mixture of olivine and pyroxene the pyroxene dominated idps have a higher carbon abundance than those dominated by olivines members of the mixed mineralogy idps can be grouped with either the pyroxene or olivine dominated particles based on their carbon abundance the high carbon pyroxene dominated particles have primitive mineralogies and bulk compositions which show strong similarities to cometary dust particles we believe that the lower carbon olivine dominated idps are probably derived from asteroids based on carbon abundances the mixed mineralogy group represents particles derived from either comets or asteroids we believe that the high carbon pyroxene rich anhydrous idps are the best candidates for cometary dust

correlated alteration effects in cm carbonaceous chondrites three parameters are proposed to determine the relative extent of alteration in cm chondrites the mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to mg serpentine and increases with increasing alteration to calculate values of this index an algorithm has been developed to estimate the average matrix phyllosilicate composition in individual cm chondrites the second parameter is the volume percent of isolated matrix silicates which decreases with progressive alteration due to mineral hydration finally the volume percent of chondrule alteration monitors the extent of chondrule phyllosilicate production and increases as alteration proceeds these parameters define the first cm alteration scale that relies on multiple indicators of progressive alteration the following relative order of increasing alteration is established by this model murchison bells pollen murray mighei nogoya cold bokkeveld the relative degree of aqueous processing cochabamba and boriskino experienced is less precisely constrained although both fall near the middle of this sequence a comparison between the mineralogic alteration index and literature values for the whole rock chemistry of cm chondrites reveals several correlations a positive nearly linear correlation between bulk h content and progressive cm alteration suggests an approximately constant production rate of new phyllosilicates relative to the mineralogical transition from cronstedtite to mg serpentine the abundance of trapped planetary 36ar decreases systematically in progressively altered cm chondrites suggesting the wholesale destruction of primary noble gas carrier phase s by aqueous reactions because low temperature fluid rock reactions are generally associated with large isotopic mass fractionation factors we also compared our model predictions with 18o values for bulk cm samples although some of these data are poorly resolved the order of increasing 18o values approximates the order of increasing alteration predicted by our model parameters multiple correlations between diverse alteration parameters strongly suggest that a different cm chondrites experienced similar kinds of processes and conditions and b cm materials experienced in situ alteration on the cm parent body or bodies

abundance and distribution of iron on the moon the abundance and distribution of iron on the moon is derived from a near global data set from clementine the determined iron content of the lunar highlands crust 3 percent iron by weight supports the hypothesis that much of the lunar crust was derived from a magma ocean the iron content of lower crustal material exposed by the south pole aitken impact basin on the lunar farside is higher 7 to 8 percent by weight and consistent with a basaltic composition this composition supports earlier evidence that the lunar crust becomes more mafic with depth the data also suggest that the bulk composition of the moon differs from that of the earth9s mantle this difference excludes models for lunar origin that require the earth and moon to have the same compositions such as fission and coaccretion and favors giant impact and capture

magnetic properties of antarctic shergottite meteorites eeta 79001 and alha 77005 possible relevance to a martian magnetic field abstract the possibility that the parent body of the snc meteorites is mars implies that the magnetic properties of these meteorites may provide evidence concerning ancient martian magnetic fields eeta 79001 possesses a weak very stable primary magnetization the properties of which are consistent with its acquisition in an ambient magnetic field either during the meteorite s formation or during the severe shock event later in its history the samples of alha 77005 studied possessed no measurable primary magnetization the observed remanence appears to be a viscous magnetization acquired in local laboratory fields the magnetic carriers in the meteorites are fine grained magnetite and a lower curie point mineral probably titanomagnetite or pyrrhotite present to the extent of less than 0 1 by weight estimates of the strength of the magnetizing field for eeta 79001 are in the range 1 10 t

origin and early growth rate of continents abstract data suggest that early continents formed over mantle sinks and grew rapidly between 2 7 and 3 0 ga ago nd isotopic results indicate that archean tonalites which are largely responsible for early continental growth are derived chiefly from ancient depleted mantle sources trace element and oxygen isotope data however indicate enriched sources for such tonalites these constraints can be explained if the mantle is fractionated into depleted dmr and enriched emr reservoirs during early degassing of the earth 4 4 ga blocks of emr are recycled back into the mantle and the emr dmr mixtures serve as sources for archean basalts these basalts are enriched in incompatible elements by deep sea alteration metasomatism in sinks or by other mantle processes and then undergo wet partial melting to produce tonalite magmas enrichment must occur not more than 150 ma prior to tonalite production basalt plateaus accumulate at sinks and as cooling continues geotherms at sinks pass into the eclogite stability field dense eclogite roots form on the basalt plateaus which pulls them into the mantle between 2 7 and 3 0 ga ago resulting in rapid tonalite production and thus in rapid continental growth

the irpinia italy 1980 earthquake detailed analysis of a complex normal faulting a detailed analysis of near source strong motion and leveling data together with the results of teleseismic waveform modeling by westaway and jackson 1987 and aftershock studies by deschamps and king 1984 allows a satisfactory kinematic description of the complex normal faulting associated with the magnitude ms 6 9 november 23 1980 irpinia earthquake southern italy the three main rupture episodes starting at about 0 20 and 40 s are here associated with better constrained source parameters than in previous studies we first evaluated the triggering time for the 11 closest accelerometers by using the well recorded 40 s strong motion phases this gave the absolute time and location of the dominant episodes of faulting the first rupture propagated mainly toward the northwest on a ne dipping normal fault at a mean velocity close to 3 km s for about 20 km and continued 15 km further on smaller subfaults it was associated with surface breakage in the southeastern part the second rupture started from the southeastern end of the first rupture about 18 s after it and propagated about 20 km toward the southeast on a low angle normal fault dipping 20 ne it was associated with secondary faulting on steeper planes reaching the surface the third and last episode at 39 s nucleated near the first hypocenter at shallower depth and the rupture possibly propagated on a 10 to 15 km long normal fault striking se antithetic to the first activated fault a clear correlation appears between the strength of the geological formations and the existence of surface breakage and shallow aftershock activity

source complexity of the 1980 southern italian earthquake from the analysis of strong motion s wave polarization strong motion records from 23 november 1980 earthquake in irpinia basilicata southern italy recorded less than 59 km to the source show strong s wave phases coherent up to 10 hz at more distant stations the signal is only coherent up to 5 hz even when recordings contain signal up to 10 hz hodogram plots of the coherent signal in the 5 to 10 hz range show lissajous figures of sh and sv waves radiated by the nearest point with strong seismic radiation by the terminations of the rupture or by other relatively compact features the largest acceleration recorded at the sturno station is due to high frequency pulses radiated by a source south of the station and 25 km from the epicenter hodogram plots of low frequencies show polarizations due to the propagation of the large scale rupture along the fault lissajous figures help to discriminate p and s arrivals and reveal their direction of propagation on the basis of this kind of analysis it is confirmed that the 1980 irpinia basilicata earthquake ml 6 5 was composed of three main sub events at 0 sec 19 sec and 39 sec in relative time the first and second events broke the same structure striking nw there is also evidence of bilateral propagation the third event broke a second smaller structure also striking nw and placed very close to the alignment of the previous ones

original structures and fragmentation and reassembly histories of asteroids evidence from meteorites abstract if chondritic meteorites were internally heated after accretion had ended then the hottest material would have been buried the deepest and should have cooled the slowest if this is correct there ought to be a correlation between cooling rate and petrographic type a measure of the extent to which chondrites were metamorphosed i e heated published and new cooling rates derived from the compositions of metallic iron nickel grains do not display this correlation implying either that chondrite parent asteroids never had onion shell structures or that bodies with onion shell structures were broken up and reassembled prior to cooling to below 500 c the temperature at which cooling rate information is recorded in metallic iron nickel chondritic regolith breccias formed from materials that resided on the surfaces of their parent asteroids metallic iron nickel grains in h and l chondrite regolith breccias indicate that the breccia constituents cooled at rates ranging from 1 to 1000 k myr based on thermal calculations these cooling rates suggest that the materials spread out on the surfaces of h and l chondrite parent asteroids originated at depths ranging from about one kilometer to several tens of kilometers craters deep enough to excavate tens of kilometers cannot form on typical asteroidal bodies only 100 to 300 km in diameter without disrupting them therefore it appears that at least some asteroids namely the parent bodies of h and l chondrites were disrupted after cooling to below 300 c and then reassembled to create surfaces containing rocks that originated at a wide range of depths these results support theoretical calculations suggesting that many asteroids were broken up and subsequently reassembled into gravitationally bound rubble piles

upb systematics of phosphates from equilibrated ordinary chondrites u pb systematics were determined from fifteen phosphate separates from equilibrated ordinary chondrites and from small bulk fragments of the same meteorites the high 238u204pb ratios of thirteen of these phosphate separates lead to extremely radiogenic pb whose 206pb204pb ratios range from 250 up to 3500 the pb pb model ages for these phosphates range from 4 563 to 4 502 ga with an analytical precision of 106 y and the u pb system is apparently concordant the time interval observed 60 106 y reflects the thermal processing of the equilibrated chondrites and is consistent with that previously derived from the rb sr k ar and pu chronologies the pb pb ages of the phosphates from the seven h chondrites show a negative correlation versus their metamorphic grade this is the first clear relationship ever observed between a long lived chronometer and the intensity of metamorphism as reflected by metamorphic grade assuming that the pb pb age indicates the accurate u pb closure time in phosphates the pb pb chronology is compatible with the model of a layered h chondrite parent body however this interpretation of the u pb systematics is not unique it postulates a slow cooling of the equilibrated materials at high temperature in apparent conflict with petrological observations except for the h chondrites which agree rather well with pu systematics comparison of the pb pb chronology with published radiochronometric data does not reveal simple correlations in the present debate concerning the thermal history of chondrites the chronometric information derived from each isotope system is interpreted as the time of its thermal closure however this basic assumption may not be correct for all the radiochronologies and must be evaluated before the radiochronometric data can be applied as compelling time constraints for the period of 4 56 4 4 ga of proto planetary history

lunar impact basins and crustal heterogeneity new western limb and far side data from galileo multispectral images of the lunar western limb and far side obtained from galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution the data reveal that the ejecta from the orientale impact basin 900 kilometers in diameter lying outside the cordillera mountains was excavated from the crust not the mantle and covers pre orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts the inside of the far side south pole aitken basin 2000 kilometers in diameter has low albedo red color and a relatively high abundance of iron and magnesium rich materials these features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta

contamination by sesquiterpenoid derivatives in the orgueil carbonaceous chondrite the free organic components of the orgueil carbonaceous chondrite have been the subject of much controversy several proposals for their source have been put forward including extraterrestrial abiotic processes extraterrestrial life and terrestrial contamination in this study we have analysed the free components to assess their distribution and possible sources compounds suggestive of terrestrial contamination by essential plant oil derivatives are evident their distribution suggests a source such as cleaning products disinfectant and air freshener where they are present in refined form this study strongly highlights the need for extreme care when interpreting organic data from meteorites with long curational histories future meteorites falls and extraterrestrial sample returns should be stored so as to avoid being compromised by similar terrestrial substances

a contamination assessment of the ci carbonaceous meteorite orgueil using a dna directed approach the orgueil meteorite has become one of the most well studied carbonaceous meteorites after it fell in france 150 yr ago extraterrestrial organic compounds such as amino acids and nucleobases in the parts per billion ranges were identified in orgueil samples with supporting isotopic analyses however speculations of terrestrial contamination such as organic inclusions in the form of microbes and seeds accompanied the analyses of the orgueil meteorite ever since its fall by using molecular analysis we performed dna extractions and spiking experiments combined with 16s and 18s rrna gene targeted pcr amplification to quantify the level of terrestrial biocontamination our results indicate that terrestrial contamination with dna was insignificant in the investigated meteorite fraction we also remeasured and confirmed concentrations of amino acids found in previous studies and conclude that their rather high concentrations and distribution cannot be explained by terrestrial contamination with microorganisms alone these results represent the first analysis using dna directed tools in the analysis of the orgueil meteorite to determine trace levels of biomarkers

archean mantle fractionation nd isotopic data require that most archean igneous rocks are derived from depleted or undepleted mantle sources while geochemical model stuides necessitate enriched sources for most archean tonalites this apparent contradiction can be reconciled if the enriched sources are produced by short lived 150 m y enrichment of depleted sources extensive depleted mantle reservoirs were probably produced during early degassing of the upper mantle 4 4 b y ago and complementary enriched reservoirs collected at the base of the lithosphere sources for tonalites may be produced from short lived enrichment of basalt above convective downcurrents by metasomatic and magmatic components derived chiefly from depleted mantle and by degassing of sinking short lived komatiitic lithosphere

the mean life of continents estimates of continent recycling rates from nd and hf isotopic data and implications for mantle structure an analysis of the initial neodymium and hafnium isotopic compositions of modern and ancient mantle derived rocks shows that the divergence of the mantle 143nd 144nd and 176hf 177hf ratios from the chondritic ratios over the past 2 billion years has been much less than would be expected based on the sm nd and lu hf ratios of the mantle source of mid ocean ridge basalt the most likely explanation is that rock material from the continents has been recycled semi continuously back into the mantle over this time period the required rate of return of continents to the mantle calculated from a simple transport model is about 0 35 0 15 of the continental mass per billion years 2 5 km year this result is consistent with the hypothesis that the mass of the continents has been approximately constant since the late archean and implies that recycled continental material must be an important component of the upper mantle

the macalpine hills lunar meteorite and implications of the lunar meteorites collectively for the composition and origin of the moon the mac88104 mac88105 meteorite is a lunar highlands regolith breccia even more anorthositic than previously available samples of highlands regolith clasts studied include two unusual pristine rocks one a 2 5 mm slightly granulitic clast rated as probably pristine contains extraordinarily fe rich fo40 olivine the other a 5 mm clast with clear vestiges of a poikilitic cumulate texture has silicate compositions that extend the range of the mg suite in the direction of the high mg end of the ferroan anorthositic suite the pyroxene of the latter clast is relatively ca rich and poorly equilibrated by lunar cumulate standards suggesting that it may have formed in an uncommonly shallow intrusion the four lunar highlands meteorites are all regolith breccias or in one case a marginal type between regolith breccia and ordinary polymict breccia and they probably represent three to four separate lunar source craters the proportion of regolith breccias is higher among lunar highlands meteorites than among rock samples from the classic highlands site apollo 16 9 regolith breccias for the majorelement composition of the crust the highlands meteorites confirm that the two low th central nearside sites luna 20 and especially apollo 16 are approximately representative the consistently high al2o3 composition indicated for the upper crust supports the magmasphere hypothesis for the trace element composition of the crust the highlands meteorites indicate that the central nearside apollo and luna sites are in several respects grossly unrepresentative concentrations of siderophile elements are far lower in highlands meteoritic regolith breccias than in their central nearside counterparts the high overall siderophile levels and hyperchondritic niir and auir ratios characteristic of highlands materials from apollo 16 and apollo 14 are evidently idiosyncracies of the central nearside concentrations of incompatible elements including k th and u are far lower in the highlands meteorites than in regolith samples from the central nearside this trend implies that certain lower limits on the bulk moon content of u and associated refractory lithophile elements should be relaxed models of lunar origin implying large enrichments of refractory lithophile elements are not favored by the new constraints from these meteorites

molecular and isotopic indicators of alteration in cr chondrites the cr group of carbonaceous chondrites may represent some of the most primitive extraterrestrial materials available for analysis however in contrast to other chondrite groups the cr organic fraction is poorly characterized the carbonaceous chondrite literature shows that relatively anhydrous thermal processing results in a condensed poorly alkylated o poor macromolecular material while for aqueous processing the converse is true such characteristics can be used to discern the alteration histories of the carbonaceous chondrites we have performed bulk elemental and isotopic analysis and flash pyrolysis on four cr chondrites renazzo al rais elephant moraine eet 87770 and yamato y 790112 to determine the nature of their organic component renazzo al rais and y 790112 release qualitatively similar pyrolysis products although there are some variations al rais macromolecular structure contains substantially higher relative abundances of alkylated and oxidized species and relatively lighter 15n suggesting that it has endured more extensive aqueous processing than the other cr chondrites renazzo appears relatively unprocessed with a low degree of alkylation a lack of detectable nitrogen bearing components and low methylnaphthalene ratio eet 87770 s low abundance of alkylated species suggests its macromolecular structure may be relatively condensed with condensation potentially assisted by a period of mild thermal alteration

mineralogy petrology chronology and exposure history of the chelyabinsk meteorite and parent body three masses of the chelyabinsk meteorite have been studied with a wide range of analytical techniques to understand the mineralogical variation and thermal history of the chelyabinsk parent body the samples exhibit little to no postentry oxidation via mossbauer and raman spectroscopy indicating their fresh character but despite the rapid collection and care of handling some low levels of terrestrial contamination did nonetheless result detailed studies show three distinct lithologies indicative of a genomict breccia a light colored lithology is ll5 material that has experienced thermal metamorphism and subsequent shock at levels near s4 the second lithology is a shock darkened ll5 material in which the darkening is caused by melt and metal troilite veins along grain boundaries the third lithology is an impact melt breccia that formed at high temperatures 1600 c and it experienced rapid cooling and degassing of s2 gas portions of light and dark lithologies from chel 101 and the impact melt breccias chel 102 and chel 103 were prepared and analyzed for rb sr sm nd and ar ar dating when combined with results from other studies and chronometers at least eight impact events e g 4 53 ga 4 45 ga 3 73 ga 2 81 ga 1 46 ga 852 ma 312 ma and 27 ma are clearly identified for chelyabinsk indicating a complex history of impacts and heating events finally noble gases yield young cosmic ray exposure ages near 1 ma these young ages together with the absence of measurable cosmogenic derived sm and cr indicate that chelyabinsk may have been derived from a recent breakup event on an neo of ll chondrite composition

topographic compositional units on the moon and the early evolution of the lunar crust the distribution of elevations on the moon determined by clementine deviates strongly from a normal distribution suggesting that several geologic processes have influenced the topography the hypsograms for the near side and far side of the moon are distinctly different and these differences correlate with differences in composition as determined by apollo orbital geochemistry clementine global multispectral imaging and ground based spectroscopy the hypsograms and compositional data indicate the presence of at least five compositional altimetric units the lack of fill of the south pole aitken basin by mare basalts suggests poor production efficiency of mare basalt in the mantle of this area of the moon

discovery and physical properties of dactyl a satellite of asteroid 243 ida observations of stellar occultations by asteroids have suggested that some may have satellites1 but given the absence of any confirmatory evidence the prevailing view has been that although such satellites probably do exist they are likely to be rare2 here we report the discovery3 by the galileo spacecraft of a satellite associated with the asteroid 243 ida although the satellite dactyl is only 1 6km across it has been imaged with sufficient resolution for geological analysis we describe the physical properties of dactyl with emphasis on its notably smooth shape its crater population which includes a crater chain and its photometric properties we find that spectroscopically dactyl resembles both ida and the other members of the koronis asteroid family implying a similar composition small spectral differences may reflect a space weathering process that slightly alters the colours with time we argue that dactyl originated during the breakup of the koronis parent body and that satellites could be common around other asteroids particularly members of asteroid families

an open system fractional crystallization model for very early continental crust formation abstract a model is discussed which seeks to explain the origin of archaean tonalitic trondhjemitic granodioritic ttg crust by an open system fractional crystallization mechanism following the assumption that in the pre and early archaean the melt which formed above sites of large scale mantle upwelling was too voluminous and too hot to solidify an almost global near surface partially molten zone could form the magma in this layer would converge above mantle sinks and undergo fractional crystallization recharged fractionating reservoirs would form at sites of convergence the major element composition of the magma in such reservoirs would evolve towards one resembling that of ttg rocks provided that amphibole was a significant fractionating phase from such reservoirs their incompatible as well as compatible trace element abundances would also become similar to those of ttg terrains it is proposed that such terrains resulted from the consolidation of these recharged fractionating reservoirs it is shown that the reservoirs would remain indistinguishable from the primitive mantle in terms of radiogenic isotopes so that model ages cannot be greater than the age of their consolidation consideration of the main aspects of greenstone belts and archaean high grade terrains indicates no contradictions with the model the intrusion of late archaean adamellites and granites is interpreted as an indirect effect of pressure induced breakdown of amphibole in the cumulate underlying the ttg crust which in turn resulted from crustal shortening cratonization is seen as the result of consolidation not only of the crust but also of the underlying cumulate as subcontinental lithosphere

role of a thin komatiite rich oceanic crust in the archean plate tectonic process in the archean tectonic regime the time available for oceanic lithosphere to cool on its journey from ridge to convergent plate boundary was far less than at present under these conditions only an inherently dense lithosphere could have acquired the negative buoyancy necessary for it to subduct at this time plate tectonics could have operated only if 1 the oceanic crust was rich in komatiite lava and 2 the thickness of this crust was not much greater than the thickness of modern oceanic crust

geochemistry of the archean low to high grade transition zone southern india the transition zone between archean low and high grade rocks in southern india represents eroded crustal levels representative of 15 20 km it is comprised chiefly of tonalitic gneisses with some varieties showing incipient charnockitization and of minor amounts of granitic gneiss and charnockite both of which appear to have developed from the tonalitic gneisses