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Title: Strontium stable isotope behaviour accompanying melting and magmatism in the Earth-Moon system
Author: Sutcliffe, Nadine C.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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This thesis concerns the application of a new technique for measuring the stable isotopes of Sr, specifically pertaining to mass dependent fractionation in high temperature processes on the Earth and Moon. Processes such as mantle melting and differentiation on Earth and the formation of the Lunar Magma Ocean are investigated by the application of a double-spike TIMS method to terrestrial and lunar material to obtain high-precision 87Sr/86Sr, 88Sr/86Sr and 84Sr/86Sr data. Measurements of mantle-derived mafic material provide insights into the 88Sr/86Sr composition of the silicate mantle. Ocean Island Basalts possess restricted δ88Sr compositions, whilst Mid-Ocean Ridge Basalts from the Pacific, Atlantic and Indian ridges reveal variations in δ88Sr, the majority of which is seen within the FAMOUS section of the Mid-Atlantic Ridge. These variations are attributed partly due to the effects of plagioclase crystallisation and partly due to mantle source heterogeneity. Analyses of mineral separates from three different igneous systems provide an understanding of δ88Sr fractionation at a mineral-scale. The possibility of δ88Sr fractionation as a result of magmatic differentiation has also been assessed, and found to occur between the basalt and rhyolitic end-members of the Icelandic Hekla suite. Variations in the 87Sr/86Sr ratios of these rocks are also found, and considered most likely to be due to contamination. Analyses of lunar rocks indicate that the highland suite appears to be relatively uniform in δ88Sr, whilst significant fractionation to light δ88Sr compositions occurs in the mare basalts. Such variations are thought to be associated with the crystallisation of plagioclase during the differentiation of the lunar magma ocean. Lastly, precise 87Rb/86Sr and 87Sr/86Sr data yield a model age for the Moon of 4.523 ± 0.019 Ga.
Supervisor: Burton, Kevin W.; Halliday, Alex N.; Porcelli, Don Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geochemistry ; strontium ; non-traditional stable isotopes ; thermal-ionisation mass spectrometry ; cosmochemistry