Systematic variations of cosmogenic radionuclides in meteorite falls: Mocs, Ghubara, and members of possible H chondrite streams
Abstract
Cosmogenic radionuclides 10Be(t½ = 1.50 Ma), 26 Al(t½ = 705 ka), and 36Cl(t½ = 301 ka), measured by accelerator mass spectrometry, and other cosmic ray products were analyzed in multiple samples of 2 large L chondrites (Mocs and Ghubara) and individual samples of 47 H chondrites. Physical relationships of samples in parent meteoroids, exposure histories and statistical relationships of nuclides were construed. Cosmogenic stable and radio nuclide data suggest that Mocs (L6) was irradiated during a two-stage exposure history. In the first, 110 Ma, exposure it was shielded in a large (>300 cm) body. This was followed by a 10.5 Ma exposure in a smaller (65 cm) body. Relative shielding in the most recent stage of a 2-stage exposure was supported by 36Cln-capture production. Data for meteorites dispersed throughout the strewn field are consistent with a two-stage fragmentation in the atmosphere. Three orthogonal and mutually intersecting cores of the Ghubara (L5) regolith breccia were sampled to study systematic variations of cosmic ray products. Collaborative measurements of cosmogenic radionuclides, noble gases, thermoluminescence, and nuclear tracks indicate that Ghubara matrix and clasts represent two generations of asteroid regoliths followed by a 4.21 Ma exposure as an 85 cm meteoroid. A two-generation regolith and heating differences within the parent meteoroid (recorded by uneven loss of 4He and nuclear track erasure) are unprecedented in non crater-forming events. A group of 47 H chondrites including the previously designated “Cluster 1”, a set of 13 meteorites related in temporal history, were analyzed for cosmogenic radionuclides to determine exposure histories and multivariate statistical differentiation of various suites. H chondrite suites showing 3He loss due to close solar approach and those with normal levels of noble gases were determined to be statistically distinguishable using cosmogenic radionuclide levels.
Degree
Ph.D.
Advisors
Lipschutz, Purdue University.
Subject Area
Analytical chemistry|Geochemistry|Astronomy|Astrophysics
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