TRACE ELEMENT ANALYSIS OF ANTARCTIC H CHONDRITES: CHEMICAL WEATHERING AND COMPARISONS WITH THEIR NON-ANTARCTIC COUNTERPARTS
Abstract
Large numbers of meteorites have been discovered in Antarctica over the last decade (7000 fragments probably representing over 1200 separate events). They are important for their numbers and for their complement of unique or rare specimens; they also have long terrestrial ages (up to 1,000,000 years) compared to non-Antarctic falls (usually < 200 years).
We report compositional data for mobile/volatile trace elements Ag, Au, Bi, Cd, Co, Cs, In, Rb, Sb, Se, Te, Tl, U, and Zn in a suite of Antarctic H chondrites. Our data show that heavily oxidized H chondrites are leached of a portion of their trace elements and, therefore, have been chemically compromised by their stay in Antarctica. The less oxidized specimens seem to have retained their chemical integrity. We suggest possibilities for using chemical data to measure the degree of a chondrite's chemical weathering. We compare our data to that obtained previously for non-Antarctic H chondrites (Lingner et al., 1986), by petrologic type (H4, H5, H6, H4-6) and shock-loading (moderately shocked facies a-c, heavily shocked facies d-f). Many statistically significant differences are found between non-Antarctic and Victoria Land, Antarctica H chondrites of each petrologic type and of shock facies d-f. Leaching of the Victoria Land chondrites is not a viable explanation for these differences because many mean elemental concentrations are higher in the Victoria Land population. Two-element scatter plots of Bi, In, and Tl also reveal remarkable differences which cannot be due to shock-heating or leaching of Victoria Land chondrites, even though this population has a higher percentage of heavily shocked chondrites than the non-Antarctic population. After ruling out alternate explanations, we believe these differences to be preterrestrial and attribute them to a changing meteoroid flux to Earth with time.
Degree
Ph.D.
Subject Area
Chemistry
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