EH3 matrix mineralogy with major and trace element composition compared to chondrules

Abstract

Abstract-We investigated the matrix mineralogy in primitive EH3 chondrites Sahara 97072, ALH 84170, and LAR 06252 with transmission electron microscopy; measured the trace and major element compositions of Sahara 97072 matrix and ferromagnesian chondrules with laser-ablation, inductively coupled, plasma mass spectrometry (LA-ICPMS); and analyzed the bulk composition of Sahara 97072 with LA-ICPMS, solution ICPMS, and inductively coupled plasma atomic emission spectroscopy. The fine-grained matrix of EH3 chondrites is unlike that in other chondrite groups, consisting primarily of enstatite, cristobalite, troilite, and kamacite with a notable absence of olivine. Matrix and pyroxenerich chondrule compositions differ from one another and are distinct from the bulk meteorite. Refractory lithophile elements are enriched by a factor of 1.5-3 in chondrules relative to matrix, whereas the matrix is enriched in moderately volatile elements. The compositional relation between the chondrules and matrix is reminiscent of the difference between EH3 pyroxene-rich chondrules and EH3 Si-rich, highly sulfidized chondrules. Similar refractory element ratios between the matrix and the pyroxene-rich chondrules suggest the fine-grained material primarily consists of the shattered, sulfidized remains of the formerly pyroxene-rich chondrules with the minor addition of metal clasts. The matrix, chondrule, and metal-sulfide nodule compositions are probably complementary, suggesting all the components of the EH3 chondrites came from the same nebular reservoir.

The formation conditions of enstatite chondrites: Insights from trace element geochemistry of olivine‐bearing chondrules in Sahara 97096 (EH3)

“…This is consistent with the average chondrule composition for Sahara 97072 (paired with Sahara 97096) given by Lehner et al. ().…”

“…, ), these compositions are too enriched in refractory lithophile elements to match bulk chondrules (see Lehner et al. ; Fig. b), as in a fractional crystallization scenario, and appear more consistent with a mesostasis composition.…”

“…; Lehner et al. ). Although our geochemical focus on REE has led us hitherto to consider solely oldhamite, the opaque nodules of course generally contain other sulfides, metal, schreibersite, etc.…”

“…() in the case of a Sm anomaly (like chondrule S19 mesostasis, or bulk chondrule S39; see also Lehner et al. and the anomalous ordinary chondrite chondrule analyses of Pack et al. ).…”

“…; Lehner et al. ), previous trace element analyses on enstatite chondrite have included SIMS measurements of sulfides and in particular oldhamite (Crozaz and Lundberg ; Gannoun et al. ) as well as pyroxene (Weisberg et al.…”