abstract: Boron concentrations and isotopic composition of phlogopite mica, amphibole, and selected coexisting anhydrous phases in mantle-derived xenoliths from the Kaapvaal Craton were measured by secondary ion mass spectrometry in an effort to better understand the B isotope geochemistry of the subcontinental lithospheric mantle (SCLM) and its implications for the global geochemical cycle of B in the mantle. These samples display a wide, and previously unrecognized, range in their boron contents and isotopic compositions reflecting a complex history involving melt depletion and metasomatism by subduction- and plume-derived components, as well as late stage isotopic exchange related to kimberlite emplacements. Micas from ancient lithospheric harzburgite metasomatized by slab-derived fluids suggest extensive B-depletion during subduction, resulting in low-B, isotopically light compositions whereas kimberlite-related metasomatic products and a sample from the 2 Ga Palabora carbonatite have boron isotopic compositions similar to proposed primitive mantle. The results suggest that subduction of oceanic lithosphere plays a limited role in the B geochemistry of the convecting mantle. / Dissertation/Thesis / Masters Thesis Geological Sciences 2014
| Identifer | oai:union.ndltd.org:asu.edu/item:25881 |
| Date | January 2014 |
| Contributors | Guild, Meghan R. (Author), Hervig, Richard L (Advisor), Bell, David R (Committee member), McNamara, Allen (Committee member), Arizona State University (Publisher) |
| Source Sets | Arizona State University |
| Language | English |
| Detected Language | English |
| Type | Masters Thesis |
| Format | 69 pages |
| Rights | http://rightsstatements.org/vocab/InC/1.0/, All Rights Reserved |
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