Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........9m&link_type=abstract
Thesis (PhD). OPEN UNIVERSITY (UNITED KINGDOM), Source DAI-C 65/03, p. 765, Fall 2004, pages.
Mathematics
Logic
2
Scientific paper
This thesis describes the use of Mössbauer spectroscopy and X-ray diffraction (XRD), and the development of a new Microsource XRD technique to quantify the modal mineralogy of primitive chondrites and their components. The modal mineralogy is used to interpret early Solar System processes that shaped the evolution of ordinary chondrites, carbonaceous chondrite matrix, dark inclusions (DIs) and calcium-, aluminium- rich inclusions (CAIs). Despite being a fundamental tool in the interpretation of geological systems, no modal mineralogical data has hitherto been available for these materials. This is due to their fine-grained nature and heterogeneous mineralogy, making accurate modal mineralogy difficult to acquire by conventional techniques. A correlation was found to exist between Mössbauer quadrupole splitting and olivine Fe content. This has implications for determining bulk compositions of silicates in heterogeneous chondrites and for in situ analysis with Mössbauer spectrometers on planetary landers. The unequilibrated ordinary chondrites (UOCs) were found to contain a significant proportion of phyllosilicates that were converted during metamorphism to ferromagnesian silicates. Mössbauer spectroscopy has revealed evidence of increasing reduction with metamorphism in the UOCs. An integrated model of redox conditions on equilibrating ordinary chondrite parent bodies has been developed. The development of a novel, high brightness Microsource XRD technique has allowed modal mineralogy to be obtained for samples with volumes of 0.018mm 3, i.e. rare chondrites and chondritic inclusions. Matrix and DIs from Allende were found to lie on a continuum, in terms of mineral abundance, suggesting that they have a related origin. DIs are shown to contain less equilibrated olivine suggesting that they experienced less intense metamorphism than Allende matrix. CAIs from Allende were found to contain high abundances of alteration minerals. Conversion of modal mineralogy to bulk chemical data has shown that different CAI types experienced different styles of alteration, but similar amounts of Fe-metasomatism.
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