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Research title The oldest carbonate minerals on Earth: insights into the early history of the Solar System . Summary of research Carbonaceous chondrite meteorites are the oldest and least-altered rocks available for study and record processes that took place during the birth and early history of our Solar System. The CM2 carbonaceous chondrites are of particular interest because they contain a mixture of mineral grains that formed at high temperatures in the solar nebula (for example olivine-pyroxene chondrules) with other minerals including clays, phyllosilicates and carbonates whose origin is controversial. Although most workers believe that these minerals were produced by low temperature water-mediated alteration of anhydrous minerals within the asteroidal parent body of carbonaceous chondrites, some have suggested that the phyllosilicates and carbonates may have formed from a nebula gas or within an earlier-formed asteroid. The definitive evidence that will enable us to unambiguously distinguish between these two models has been hard to find, but a resolution to this debate has far-reaching implications for our understanding of the early history of the Solar System.
This project will use the carbonate cements that are commonplace in CM2 meteorites as a tool for unlocking the mechanisms by which the suite of hydrous minerals were formed. These carbonates predominantly comprise calcite, but dolomite and aragonite have also been reported, and the crystals are scattered throughout the phyllosilicate-rich matrices of the meteorites. Investigation of the mineralogy, chemical composition, microstructure and petrographic relationships of the carbonate cements will potentially convey information on the temperature, pressures and chemical conditions during crystal growth. This work will use state of the art microscopy techniques including electron backscatter diffraction and scanning cathodoluminescence imaging, making extensive use of the Division's newly installed FEI Quanta 200 field-emission environmental Scanning Electron Microscope, which is one of the most sophisticated SEM's in any UK geoscience department. This project is especially timely as results will help to build upon new models for the composition and origin of asteroids and comets coming from the recent successful American and Japanese sampling missions.
Supervisors Dr Martin Lee
Dr Caroline Smith, Natural History Museum (London) Recent publications Sofe, M.R.; Lee, M.R. and Smith, C. L. 2010. Mg-phyllosilicate pseudomorphs after calcite in the pollen (CM2) carbonaceous chondrite: new insights into aqueous alteration.Meteoritics & Planetary Science. V. 45, A193-A193.
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