HR: 0800h
AN: V31A-1411    [Abstracts]
TI: Processes and Timing estimate of Metasomatism in peridotitic xenoliths from Orapa kimberlites, Botswana
AU: * Uehara, Y
EM: yuehara@geo.titech.ac.jp
AF: Depertment of Earth and Planetary Sciences, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo, 152-8551 Japan
AU: Koimya, T
EM: tkomiya@geo.titech.ac.jp
AF: Depertment of Earth and Planetary Sciences, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo, 152-8551 Japan
AU: Hirose, K
EM: kei@geo.titech.ac.jp
AF: Depertment of Earth and Planetary Sciences, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo, 152-8551 Japan
AB: The evolution of cratonic lithosphere has been of debate for a long time. High SiO2 contents in whole rock, presence of hydrous minerals and enrichment in magmaphile elements suggest the important role of metasomatism in the history. Peridotitic xenoliths from Orapa kimberlites, Botswana, mainly classified into three main groups (Coarse Low-T type, Mid-T type and Deformed High-T type). Some peridotitic xenoliths from these groups include garnets which show well preserved chemical heterogeneities resulting prior to kimberlite entrapment and its intrusion. These Garnets show several zonation patterns regarding major elements like Cr, Ca, Ti, Fe and Mg. Most of such zonations are along the lherzolite trend defined by CaO and Cr203 contents especially in Deformed High-T type xenoliths. In addition, Cr2O3 and TiO2 line profiles show well-developed U-shape or S-shape zonation patterns which are taken as prototype of resorption or regrowth of garnet. These zonation patterns indicate resorption or growth by metasomatic fluid infiltrated through cratonic lithosphere beneath Orapa. Because ideal resorption patterns depend on diffusion coefficiencys and the timing of infiltration of fluid, we estimate the timing of the infiltration of metasomatic fluids by comparison with the analyzed chemical patterns and ideal simple simulations. REE patterns of coexisting garnet and clinopyroxene suggest that the rims of these minerals are well equilibrated but cores are not always so. This fact indicates the process of garnet-clinopyroxene equilibration by metasomatic fluid (silicate, carbonate or kimberlitic melt). Using these new data, we constructed one of possible rough story about metasomatism in cratonic lithosphere beneath Orapa
DE: 9305 Africa
DE: 3670 Minor and trace element composition
DE: 1749 Volcanology, geochemistry, and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting