Mathematics – Logic
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.539t&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 539
Mathematics
Logic
Abundance, Meteoritic Composition, Mineralogy, Rare Earth Elements, Solar System Evolution, Anomalies, Metamorphism (Geology), Radioactive Age Determination, Radioactive Isotopes
Scientific paper
The diogenites have been regarded as igneous products in the early solar system and they have been considered to have genetically close relationship with eucrites. Depsite their simple mineralogical compositions and narrow range for major-element compositions, diogenites have been known to show wide Rare Earth Elements (REE) variations in absolute concentration and in mutual abundance ratios. Furthermore, some diogenites have peculiar Rb-Sr isotope systematics (ages younger than 4.5 b.y.). The Shalka meteorite belongs to the diogenites, and a unique REE abundance pattern has been reported. We performed Rb-Sr isotopic analyses and measured REE abundances in the Shalka diogenite with several other diogenites to discuss their genesis. Roughly speaking, REE patterns in diogenites are characterized by the negative Eu anomaly and the depletion of light REE. For Shalka, some heterogeneity in REE abundance patterns have been observed. While one sample chip shows the REE pattern with a large negative Eu anomaly and depleted light REE, particularly characterized by the concave curvature for the La-Nd span, other samples show the pattern nearly flat or the pattern enriched in light REE. These variations could not be explained easily by the simple mixing process of LREE-depleted components and LREE-enriched melt, but they imply some metamorphism process. The Rb-Sr isotopic data for Shalka are shown with the data for other several diogenites. These observations indicate that Shalka would undergo a significant extent of metamorphism followed by redistribution of REE and the disturbance of the Rb-Sr systematics. We are going to do further studies on Shalka to discuss the metamorphic process and compare it with other diogenites.
Kagi Hiroyuki
Masuda Akimasa
Takahashi Keitaro
Yabuki Sadayo
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