TRACE ELEMENT EVIDENCE FOR CONTRASTIVE THERMAL HISTORIES OF H4-6 AND L4-6 CHONDRITE PARENT BODIES
Abstract
Earlier studies at Purdue revealed that tertiary shock (impact) heating is the main post-accretionary fractionation process for mobile and siderophilic trace elements in L4-6 chondrites. Lower contents of these elements in samples evidencing shock are attributable to loss (transport in an Fe-Ni-S eutectic or volatilization from collisional debris) upon breakup of the L parent body 500-650 Myr ago. Reported here are new radiochemical neutron activation analysis results for Ag, As, Au, Bi, Cd, Co, Cs, Ga, In, K, Rb, Sb, Se, Te, Tl and Zn in H4-6 chondrites as a function of $\sp{40}$Ar retention (a reliable shock indicator in L chondrites). Mobile element depletion in H chondrites with undisturbed $\sp{40}$Ar vs. unshocked L chondrites indicates a hotter environment (a shock event or higher accretion temperatures) for the former. Siderophiles are enriched in H relative to L chondrites, as expected. Within the H chondrite population, trace element relationships with $\sp{40}$Ar retention and petrologic type are complex and puzzling. These are discussed in detail in light of several proposed parent body models.
Degree
Ph.D.
Subject Area
Geochemistry
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