The accretionary history of ureilites: A systematic re-evaluation.
Final Report Abstract
One of the three objectives detailed in the original proposal – namely, the analysis of the isotopic Ni compositions of ureilite olivines and metal – could not be finished. The other two objectives, however, were successfully executed. Using FeO diffusion data from ten ureilites, I could constrain the debris size produced in the catastrophic disruption of the UPB to a relatively tight absolute range of 0.5-3 m in radius. In addition, I showed that the time needed for the average fragments (approximately 1-2 m in radius) to cool to 1100 K in their cores was on the order of 3-14 days. Thus, the time span of the UPB disruption and reassembly could have comprised as little as about 2 weeks. My second objective addressed the elemental Ni and Co compositions of ureilite olivines vs. those of the interstitial metal. I could show that olivines and intergranular metal are in disequilibrium, in support of an earlier study that came to the same conclusion. My data also strongly support my working hypothesis that the vast majority of metal in ureilites, namely the intergranular metal, is of exogenous origin and was, most likely, injected into the ureilite rubble upon the catastrophic disruption of the UPB. In addition to this exogeneous metal, my results unanimously led to the distinction of two additional populations of metal: a) occasional indigenous metal spherule inclusions, and b) metal inclusions generated during reduction and pyroxene-selective impact smelting.
Publications
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EVIDENCE AGAINST CHONDRULE-MATRIX COMPLEMENTARITY AS SEEN IN CO, CM and CR CHONDRITES. 52nd LPSC, The Woodlands, TX, USA
A. Patzer, E. S. Bullock & C. M. O’D. Alexander
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Testing models for the compositions of chondrites and their components: I. CO chondrites. Geochimica et Cosmochimica Acta, 304, 119-140.
Patzer, Andrea; Bullock, Emma S. & Alexander, Conel M. O.'D.
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THE NON-COMPLEMENTARY COMPOSITIONS OF CHONDRULES AND MATRICES IN CO, CM AND CR CHONDRITES. 84th Meteoritical Society Meeting, Chicago, IL, USA
A. Patzer, E. S. Bullock & C. M. O’D. Alexander
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Testing models for the compositions of chondrites and their components: II. CR chondrites. Geochimica et Cosmochimica Acta, 319, 1-29.
Patzer, Andrea; Bullock, Emma S. & Alexander, Conel M.O.'D.
