The relative abundances of the highly siderophile elements (HSE) Os, Ir, Ru, Pt, Rh, and Pd in relatively pristine lherzolites differ from solar abundance ratios and are several orders of magnitude higher than predicted for equilibrium distribution between metal/silicate (core-mantle). The samples are characterized by a mean Ca/Al ratio of 1.18 +/- 0.09 sigma-M and a mean Ca/Si ratio of 0.10 +/- 0.01 sigma-M, overlapping with a mean Ca/Al of 1.069 +/- 0.044 sigma-M and a mean Ca/Si of 0.081 +/- 0.023 sigma-M found in chondrites (Wasson and Kallemeyn 1988). Interestingly, the CI-normalized abundance pattern shows decreasing solar system normalized abundances with increasing condensation temperatures. The abundance of the moderately volatile element Pd is about 2x higher than those in the most refractory siderophiles Ir and Os. Thus, the HSE systematics of upper mantle samples suggest that the late bombardment, which added these elements to the accreting Earth, more closely resembles materials of highly reduced EH or EL chondrites than carbonaceous chondrites. In fact, the HSE in the Earth mantle are even more fractionated than the enstatite chondritesan indication that some inner solar system materials were more highly fractionated than the latter.

U, Th, and Pb isotopes and rare earth elements (REEs) in individual phosphate grains from martian meteorites Lafayette and Yamato-000593/000749 were measured using a sensitive highresolution ion microprobe (SHRIMP). Observed U-Pb data of 12 apatite grains from Yamato (Y-) 000593/000749 are well represented by linear regressions in both conventional 2D isochron plots and the 3D U-Pb plot (total Pb/U isochron), indicating that the formation age of this meteorite is 1.53 +/- 0.46 Ga (2-sigma). On the other hand, the data of nine apatite grains from Lafayette are well represented by planar regression rather than linear regression, indicating that its formation age is 1.15 +/- 0.34 Ga (2-sigma) and that a secondary alteration process slightly disturbed its U-Pb systematics as discussed in the literature regarding Nakhla. The observed REE abundance patterns of the apatites in Lafayette and Yamato-000749, normalized to CI chondrites, are characterized by a progressive depletion of heavy REEs (HREEs), a negative Eu anomaly, similarity to each other, and consistency with previously reported data for Nakhla. Considering the extensive data from other radiometric systems such as Sm- Nd, Rb-Sr, Ar-Ar, and trace elements, our results suggest that the parent magmas of the nakhlites, including the newly found Y-000593/000749, are similar and that their crystallization ages are ~1.3 Ga.

We have investigated the mineralogy, petrography, bulk chemistry, and light element isotope composition of the ungrouped chondrites North West Africa (NWA) 1152 and Sahara 00182. NWA 1152 contains predominantly type 1 porphyritic olivine (PO) and porphyritic olivinepyroxene (POP) chondrules. Chondrule silicates are magnesium-rich (Fo98.8 +/- 1.2, n = 36; Fs2.3 +/- 2.1 Wo1.2 +/- 0.3, n = 23). Matrix comprises ~40 vol% of the sample and is composed of a micron sized silicate groundmass with larger silicate, sulfide, magnetite, and Fe-Ni metal (Ni ~50 wt%) grains. Phyllosilicates were not observed in the matrix. Refractory inclusions are rare (0.3 vol%) and are spinel pyroxene aggregates or amoeboid olivine aggregates; melilite is absent from the refractory inclusions. Sahara 00182 contains predominantly type 1 PO chondrules, POP chondrules are less common. Most chondrules contain blebs of, and are often rimmed with, Fe-Ni metal and sulfide. Chondrule phenocrysts are magnesium-rich (Fo92.2 +/- 0.6, n = 129; Fs4.4 +/- 1.8 Wo1.3 +/- 1.1, n = 16). Matrix comprises ~30 vol% of the meteorite and is predominantly sub-micron silicates, with rare larger silicate gains. Matrix Fe-Ni metal (mean Ni = 5.8 wt%) and sulfide grains are up to mm scale. No phyllosilicates were observed in the matrix. Refractory inclusions are rare (1.1 vol%) and melilite is absent. The oxygen isotope composition of NWA 1152 falls within the range of the CV chondrites with delta-17O = -3.43 ppm delta-18O = 0.70 ppm and is similar to Sahara 00182, delta-17O = -3.89 ppm, delta-18O = -0.19 ppm (Grossman and Zipfel 2001). Based on mineralogical and petrographic characteristics, we suggest NWA 1152 and Sahara 00182 show many similarities with the CR chondrites, however, oxygen isotopes suggest affinity with the CVs. Thus, neither sample can be assigned to any of the currently known carbonaceous chondrite groups based on traditionally recognized characteristics. Both samples demonstrate the complexity of inter- and intra-group relationships of the carbonaceous chondrites. Whatever their classification, NWA 1152 and Sahara 00182 represent a source of relatively pristine solar system material.

Isotopic signatures and concentrations of xenon have been measured in Shergotty mineral separates by laser step heating. Martian atmosphere and martian interior xenon are present, as is a spallation component. Martian atmospheric xenon is 5-10 times more concentrated in opaque minerals (magnetite, ilmenite, and pyrrhotite) and maskelynite than in pyroxenes, perhaps reflecting grain size variation. This is shown to be consistent with shock incorporation. A component consisting of solar xenon with a fission contribution, similar to components previously identified in martian meteorites and associated with the martian interior, is best defined in the pyroxene-dominated separates. This component exhibits a consistent 129Xe (129Xe/132Xe ~1.2) excess over solar/planetary (129Xe/132Xe ~1.04). We suggest that gas present in the melt, perhaps a mixture of interior xenon and martian atmosphere, was incorporated into the pyroxenes in Shergotty as the minerals crystallized.

The outer portions of many type I chondrules (Fa and Fs <5 mol%) in CR chondrites (except Renazzo and Al Rais) consist of silica-rich igneous rims (SIRs). The host chondrules are often layered and have a porphyritic core surrounded by a coarse-grained igneous rim rich in low-Capyroxene. The SIRs are sulfide-free and consist of igneously-zoned low-Ca and high-Ca pyroxenes, glassy mesostasis, Fe, Ni-metal nodules, and a nearly pure SiO2 phase. The high-Ca pyroxenes in these rims are enriched in Cr (up to 3.5 wt% Cr2O3) and Mn (up to 4.4 wt% MnO) and depleted in Al and Ti relative to those in the host chondrules, and contain detectable Na (up to 0.2 wt% Na2O).Mesostases show systematic compositional variations: Si, Na, K, and Mn contents increase, whereas Ca, Mg, Al, and Cr contents decrease from chondrule core, through pyroxene-rich igneous rim (PIR), and to SIR; FeO content remains nearly constant. Glass melt inclusions in olivine phenocrysts in the chondrule cores have high Ca and Al, and low Si, with Na, K, and Mn contents that are below electron microprobe detection limits. Fe, Ni-metal grains in SIRs are depleted in Ni and Co relative to those in the host chondrules. The presence of sulfide-free, SIRs around sulfide-free type I chondrules in CR chondrites may indicate that these chondrules formed at high (>800 K) ambient nebular temperatures and escaped remelting at lower ambient temperatures. We suggest that these rims formed either by gas-solid condensation of silica-normative materials onto chondrule surfaces and subsequent incomplete melting, or by direct SiO (gas) condensation into chondrule melts. In either case, the condensation occurred from a fractionated, nebular gas enriched in Si, Na, K, Mn, and Cr relative to Mg. The fractionation of these lithophile elements could be due to isolation (in the chondrules) of the higher temperature condensates from reaction with the nebular gas or to evaporation-recondensation of these elements during chondrule formation. These mechanisms and the observed increase in pyroxene/olivine ratio toward the peripheries of most type I chondrules in CR, CV, and ordinary chondrites may explain the origin of olivine-rich and pyroxene-rich chondrules in general.

Forty-eight bottle-green microtektites (BGMTs) were found in a core sample recovered from Ocean Drilling Program Site 1169, located along the western flank of the South Tasman Rise in the southeastern Indian Ocean. Biostratigraphic evidence loosely constrains the age of the Site 1169 BGMTs to an interval spanning the late-middle Miocene to earliest Pliocene (12.1-4.6 Ma); an incomplete core recovery and a major stratigraphic hiatus prevented a more precise age determination. This broad range of biostratigraphic ages indicates that these microtektites predate the Australasian strewn layer by at least 3.83 Ma, and perhaps by as much as 11.33 Ma. Furthermore, the REE signatures of the Site 1169 BGMTs are incongruent with those of typical Australasian ejecta, indicating that the Site 1169 BGMTs are not part of the larger Australasian strewn field. Among the various australite subgroups, the Site 1169 BGMTs are most similar in age to the HNa/K australites. However, numerous compositional discrepancies indicate that these two ejecta populations are also unrelated; the great distances separating Site 1169 from HNa/K australite-bearing localities also makes a shared provenance unlikely. Therefore, we conclude that the Site 1169 BGMTs were formed by a late Miocene impact that is distinctly separate from the Australasian and HNa/K australite events, though the location of this impact is unknown.