Fine-grained, heavily-hydrated lithic clasts in the metal-rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe-Mn-Mg-bearing Ca-carbonates set in a phyllosilicate-rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of ~0.73 nm, and saponite, with basal spacings of about 1.1-1.2 nm. Chondrules and FeNi-metal grains in CB and CH chondrites are believed to have formed at high temperature (>1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi-metal grains after these high-temperature components had been transported from their hot formation region to a much colder region of the solar nebula.

Active capture is a new process for the incorporation of large quantities of heavy noble gases into growing surfaces. Adsorption in the conventional sense involves surface bonding by polarization (Van der Waals forces). What is referred to as "anomalous adsorption" of heavy noble gases involves chemical bonds and can occur when other (more chemically active) species are not available to preempt sites with unfilled bonds. Anomalous adsorption has been observed under conditions of fracture, vacuum deposition and ionizing radiation. Active capture depends upon anomalous adsorption to retain noble gases on a surface long enough to be captured in a growing surface film as it is deposited. The fundamental principle may be the impingement onto the growing film with sufficient energy to liberate surface electrons (work function energy of a few electronvolts) so that they are retained by anomalous adsorption long enough to be entrapped in the growing surface. Trapping efficiencies of ~1% have been observed for Kr and Xe in laboratory experiments, implying a fundamentally new mechanism for the incorporation of heavy noble gases onto surfaces. It may play a role in explaining the large concentrations of planetary noble gases contained in phase-Q.

The Frontier Mountain blue ice field is an important Antarctic meteorite trap which has yielded 472 meteorite specimens since its discovery in 1984. Remote sensing analyses and field campaigns from 1993 to 1999 have furnished new glaciological data on ice flow, ice thickness, bedrock topography, ice ablation and surface mass transport by wind, along with detailed descriptions of the field situation at the trap. This solid set of data combined with an updated meteorite distribution map and terrestrial ages available from literature allows us to better describe the nature of the concentration mechanism. In particular, we observe that the meteorite trap forms in a blue ice field (1) located upstream of an absolute and a shallow sub-ice barriers; (2) characterized by compressive ice flow with horizontal velocities decreasing from 100 to <10 cm/year on approaching the obstacle; (3) undergoing mean ablation rates of 6.5 cm/year; (4) nourished by a limited snow accumulation zone extending ~20 km upstream of the blue ice area. We also draw the following conclusions: (1) the origin of the meteorite trap can be explained according to the present‐day glaciological situation; (2) the meteorite concentration develops according to the general principles of the “ice flow model”; (3) the accumulation model can be described as “stagnant ice or slow‐moving ice against an absolute and submerged barriers”, according to the descriptive schemes present in literature; (4) the Frontier Mountain ice field is an effective trap for meteorites weighing more than ~200 g; for smaller masses, the combination of wind and glacial drift may remove meteorites in less than a few tens of thousands of years; (5) although the activation age of the Frontier Mountain trap is not yet constrained, we infer that one of the most important findsites may be as old as 50 ka, predating the last glacial maximum.

Antarctic CM meteorites Allan Hills (ALH) 81002 and Lewis Cliff (LEW) 90500 contain abundant fine-grained rims (FGRs) that surround a variety of coarse-grained objects. FGRs from both meteorites have similar compositions and petrographic features, independent of their enclosed objects. The FGRs are chemically homogeneous at the 10 micrometer scale for major and minor elements and at the 25 micrometer scale for trace elements. They display accretionary features and contain large amounts of volatiles, presumably water. They are depleted in Ca, Mn, and S but enriched in P. All FGRs show a slightly fractionated rare earth element (REE) pattern, with enrichments of Gd and Yb and depletion of Er. Gd is twice as abundant as Er. Our results indicate that those FGRs are not genetically related to their enclosed cores. They were sampled from a reservoir of homogeneously mixed dust, prior to accretion to their parent body. The rim materials subsequently experienced aqueous alteration under identical conditions. Based on their mineral, textural, and especially chemical similarities, we conclude that ALH 81002 and LEW 90500 likely have a similar or identical source.

Plagioclase-rich chondrules (PRCs) in the reduced CV chondrites Efremovka, Leoville, Vigarano and Grosvenor Mountains (GRO) 94329 consist of magnesian low-Ca pyroxene, Al-Ti-Cr-rich pigeonite and augite, forsterite, anorthitic plagioclase, FeNi-metal-sulfide nodules, and crystalline mesostasis composed of silica, anorthitic plagioclase and Al-Ti-Cr-rich augite. The silica grains in the mesostases of the CV PRCs are typically replaced by hedenbergitic pyroxenes, whereas anorthitic plagioclase is replaced by feldspathoids (nepheline and minor sodalite). Some of the PRCs contain regions that are texturally and mineralogically similar to type I chondrules and consist of forsterite, low-Ca pyroxene and abundant FeNi-metal nodules. Several PRCs are surrounded by igneous rims or form independent compound objects. Twelve PRCs contain relic calcium-aluminum-rich inclusions (CAIs) composed of anorthite, spinel, high-Ca pyroxene, +/- forsterite, and +/- Al-rich low-Ca pyroxene. Anorthite of these CAIs is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules. This suggests that either the alteration predated formation of the PRCs or that anorthite of the relic CAIs was more susceptible to the alteration than anorthitic plagioclase of the host chondrules. These observations and the presence of igneous rims around PRCs and independent compound PRCs suggest that the CV PRCs may have had a complex, multistage formation history compared to a more simple formation history of the CR PRCs. Relatively high abundances of moderately-volatile elements such as Cr, Mn and Si in the PRCs suggests that these chondrules could not have been produced by volatilization of ferromagnesian chondrule precursors or by melting of refractory materials only. We infer instead that PRCs in carbonaceous chondrites formed by melting of the reduced chondrule precursors (magnesian olivine and pyroxene, FeNi-metal) mixed with refractory materials (relic CAIs) composed of anorthite, spinel, high-Ca pyroxene, and forsterite. The mineralogical, chemical and textural similarities of the PRCs in several carbonaceous chondrite groups (CV, CO, CH, CR) and common presence of relic CAIs in these chondrules suggest that PRCs may have formed in the region(s) intermediate between the regions where CAIs and ferromagnesian chondrules originated.