Abstract-The trapped noble gas record of 57 enstatite chondrites (E chondrites) has been investigated. Basically, two different gas patterns have been identified dependent on the petrologic type. All E chondrites of type 4 to 6 show a mixture of trapped common chondritic rare gases (Q) and a subsolar component (range ofelemental ratios for E4-6 chondrites: 36Ar/132Xe = 582 ± 270 and 36Ar/84Kr= 242 ± 88). E3 chondrites usually contain Q gases, but also a composition with lower 36Ar/132Xe and 36Ar/84Kr ratios, which we call sub-Q (36Ar/132Xe = 37.0 ± 18.0 and 36Ar/84Kr= 41.7 ± 18.1). The presence of either the subsolar or the sub-Q signature in particular petrologic types cannot be readily explained by parent body metamorphism as postulated for ordinary chondrites. We therefore present a different model that can explain the bimodal distribution and composition of trapped heavy noble gases in E chondrites.Trapped solar noble gases have been observed only in some E3 chondrites. About 30% of each group, EH3 and EL3 chondrites, amounting to 9% ofall analyzed E chondrites show the solar signature. Notably, only one of those meteorites has been explicitly described as a regolith breccia.

In general, our study strongly supports the widely accepted idea that acapulcoites and lodranites evolved through partial melting and melt migration of metal/sulfide phases and plagioclase. Furthermore, we concur with previous researchers that the original bimodal classification scheme for acapulcoites and lodranites proves to be too simple. Based on our data set, we introduce an alternative, extended scheme. With respect to their elemental distribution patterns, we distinguish 5 subtypes comprising primitive, typical, transitional, and enriched acapulcoites on one hand and lodranites on the other. The chemical distinction between the primitive, typical, and transitional acapulcoites is rather subtle and gradual. It stands in contrast to the clear modifications observed for the signatures of the enriched acapulcoites and the lodranites. The definition of subcategories basically reflects the concentrations of 2 key elements: K and Se. We note, however, that the assignment of subgroups may not be exclusively inferred from elemental abundances but should also consider additional petrographic information.

Abstract-Itqiy is a unique coarse-grained, metal-rich enstatite meteorite that was found in the Western Sahara and consists of two rocks together weighing 4.72 kg, which are both completely coated with fusion crust. We report results from our electron microprobe and instrumental neutron activation analysis techniques.Itqiy consists of subhedral, equigranular, millimeter-sized enstatite, -25 vol% of millimeter-sized kamacite and a few tiny intergrowths of sulfides and kamacite. Relic chondrules are absent. Pyroxene (Fs0.2) is chemically similar to enstatite in EL chondrites, but the metal is closer in composition to that in EH chondrites. Sulfides resemble those in E chondrites but their compositions are distinct from those in both EL and EH chondrites. Itqiy clearly formed under very reducing conditions, but it does not appear to have formed from EH or EL chondrites.Two thermal events can be distinguished. Silicate compositions including rare earth element abundances indicate loss of partial melt and slow cooling. Heterogeneous sulfides indicate a subsequent reheating and quenching event, which may have been due to shock as many enstatite grains show shock stage S3 features.

Several E chondrites yield significantly lower 38Ar ages compared to those calculated from cosmogenic 3He and 21Ne. For these E chondrites, we suggest a reduction of cosmogenic 38Ar as a result of weathering. In order to prove the possible influence of terrestrial alteration on the cosmogenic noble gas record of E-chondritic material, we simulated terrestrial weathering in an experiment of 12 weeks duration. The treatment showed that a significant amount of cosmogenic 38Ar is lost on Earth by the influence of water.