Geochemistry of diogenites: Still more diversity in their parental melts

Abstract

Abstract-We report on the major and trace element abundances of 18 diogenites, and O-isotopes for 3 of them. Our analyses extend significantly the diogenite compositional range, both in respect of Mg-rich (e.g., Meteorite Hills [MET] 00425, MgO = 31.5 wt%) and Mg-poor varieties (e.g., Dhofar 700, MgO = 23 wt%). The wide ranges of siderophile and chalcophile element abundances are well explained by the presence of inhomogeneously distributed sulfide or metal grains within the analyzed chips. The behavior of incompatible elements in diogenites is more complex, as exemplified by the diversity of their REE patterns. Apart from a few diogenite samples that contain minute amounts of phosphate, and whose incompatible element abundances are unlike the orthopyroxene ones, the range of incompatible element abundances, and particularly the range of Dy/Yb ratios in diogenites is best explained by the diversity of their parental melts. We estimate that the FeO/MgO ratios of the diogenite parental melts range from about 1.4 to 3.5 and therefore largely overlap the values obtained for non-cumulate eucrites. Our results rule out the often accepted view that all the diogenites formed from parental melts more primitive than eucrites during the crystallization of a magma ocean. Instead, they point to a more complex history, and suggest that diogenites were derived from liquids produced by the remelting of cumulates formed from the magma ocean.

Evidence for K‐rich terranes on Vesta from impact spherules

“…SiO 2 , TiO 2 , Al 2 O 3 , CaO, Na 2 O, and K 2 O (wt%) versus 100 × Mg/(Mg + Fe) (atomic) plots for impact glasses from howardites (Noonan [1974]; Desnoyers and Jérome [1977]; Yagi et al [1978]; Hewins and Klein [1978]; Klein and Hewins [1979]; Noonan et al [1980]; Delaney et al [1982]; Ikeda and Takeda [1984], and this study). The fields for eucrites (E), cumulate eucrites (CE), diogenites (D), and howardites (H) are drawn from a compilation of literature data (see references in Mittlefehldt et al [1998] and Barrat et al [2007Barrat et al [ , 2008). Al 2 O 3 abundances (about 18 wt% compared to 8.8-13 wt% in the lunar granites).…”

Oxygen isotopic constraints on the origin and parent bodies of eucrites, diogenites, and howardites

“…e See http://metdb.nipr.ac.jp/am_db_public. Wiechert et al (2004), Greenwood et al (2005), Floss et al (2005), Barrat et al (2006Barrat et al ( , 2007Barrat et al ( , 2008 and this study. Analyses in abstracts and the Meteoritical Bulletin were excluded.…”

Geochemistry of CI chondrites: Major and trace elements, and Cu and Zn Isotopes

“…The concentrations of trace elements were determined by ICP-SFMS (inductively coupled plasma-sector field mass spectrometry) using a Thermo Element 2 spectrometer following the procedures described by Barrat et al (2007Barrat et al ( , 2008. Two aliquots of each mother solutions containing the equivalent of 15 mg of sample were weighted in dry screw-top Teflon vessels.…”