| Summary: | We have developed a fast, simple, and accurate ICPMS method for quantification of 45 elements in cosmochemical samples (chondrites). These elements in conjunction with those of our 14 element RNAA suite cover nearly the entire geo and cosmochemical behavior range. With these methods, we investigate thermal histories of chondrites through their trace element contents. Carbonaceous chondrite compositions reflect only primary processes (condensation and accretion) in the solar nebula. We characterized a freshly fallen meteorite, Tagish Lake, and 8 other carbonaceous chondrites using our methods: elemental data reveal that each of 9 carbonaceous chondrites of different type exhibit the Orgueil-normalized plateaus expected for members of such types. Trends evident in Tagish Lake differ from those of all other carbonaceous chondrites, including CI and CM. Samples of Tagish Lake collected later show similar patterns affected by weathering. We used our analytical techniques for the analysis of a large suite (62) of L4-6 chondrite falls to investigate post-accretionary thermal processes, especially shock-related reheating. During analysis, we discovered unusual elemental patterns in 14 chondrites, some of which were grouped by others as L/LL. These atypical patterns are likely the result of sampling heterogeneity: we excluded these samples from further consideration. We used graphical and statistical methods to analyze the 48 remaining L4-6 chondrites for shock-induced compositional trends due to open-system thermal metamorphism and found moderate- to highly-significant evidence for a difference in composition between mildly- and highly-shocked L4-6 chondrite falls. No evidence was found for compositional fractionation during thermal metamorphism in the L4-6 parent(s).
|
|---|