HR: 15:25h
AN: V23D-08    [Abstracts]
TI: Megacryst Petrogenesis in Southern Africa
AU: * Bell, D R
EM: David.R.Bell@asu.edu
AF: SESE, Arizona State University, Box 871404, Tempe, AZ 85287-1404, United States
AB: The Cr-poor megacryst suite is ubiquitous in kimberlites, but its origins are not well understood, including details of the relationship to kimberlite magma. Major and trace element and isotope data for >2000 megacrysts from ~50 kimberlites in southern Africa vary systematically with respect to host kimberlite type, geographic location and tectonic setting. Distinctive differences between Group I and Group II kimberlite megacryst suites confirm a broadly cognate origin. A large range of geochemical differentiation patterns is displayed by individual megacryst suites reflecting the varying influences of melt-rock interaction in the mantle prior to kimberlite eruption. Geographic variations in megacryst composition have been used to construct a deep mantle compositional and thermal structure for southern Africa. This structure suggests the intrusion of deep level mantle magmas in zones of previous tectonism. Variations in the interplay between chemical boundary layer thickness, mantle geotherm, melt-rock ratio, and inferred megacryst-magma phase relations can explain many features of the systematic mineralogical and compositional distribution of megacrysts, and other metasomatic products derived from megacryst parent magmas.
DE: 1025 Composition of the mantle
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 1065 Major and trace element geochemistry
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting