EFFECTS OF PRIMARY CONDENSATION, SECONDARY METAMORPHISM AND TERTIARY SHOCK REHEATING ON THE CHEMISTRY OF L AND LL CHONDRITES AND A MINERALOGICAL SURVEY OF THE CUMBERLAND FALLS CHONDRITIC INCLUSIONS
Abstract
Neutron activation analysis was used to determine 13 trace elements (Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn) in 14L and 3LL chondrites. Additional aliquots of these samples had previously been analyzed for Fe, Ni and S and were petrographically classified into one of six shock facies. Based on elemental correlations and average elemental abundances, two subclasses of the L-group chondrites have been identified and designated as the normal and depleted iron subclasses. The two subclasses in the L-group and the LL-group chondrites are suggested to have been derived from a siderophile-lithophile fractionation during or before primary condensation and accretion. Correlation profiles suggest that the L and LL-group chondrites have not experienced an open system metamorphic episode. The two-element correlation diagrams for Bi:Tl and In:Tl agree well with the theoretical condensation curves previously calculated employing the two-component condensation theory. However, correlations of strongly depleted In and Zn with the shock classifications indicates that the volatile elements are mobilized as a result of a shock induced reheating event. Co-variation of Fe, Ni and S in the normal and depleted iron subclasses indicates that sulfides have been mobilized and lost following condensation and accretion. The appearance of a siderophile-chalcophile fractionation process in the heavily shocked depleted iron subclass indicates that the observed Fe, Ni and S co-variation resulted from shock reheating event. New mineralogical and petrological data are presented for nine chondritic inclusions and one sample of the aubrite host of the Cumberland Falls polymict breccia. The chondritic inclusions represent a range of petrologic characteristics, the most primitive of which apparently belongs to petrologic grade 2. The matrix is chiefly fine-grained, considerably more opaque than other chondritic inclusions and lacks chondrules normally observed in petrologic grades 2-6. Other criteria indicating its very primitive nature are the presence of water-clear glass, the absence of taenite, the presence of high-Ni sulfides, and the heterogeneous low-Ca clinopyroxene compositions. All other chondritic inclusions are apparently type 3 chondrites, in that clinopyroxene is the dominant pyroxene and they contain chondrules with sharp to diffuse margins. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI
Degree
Ph.D.
Subject Area
Geochemistry|Analytical chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.