Computer Science
Scientific paper
Jul 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53.1551m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 7, pp.1551-1561
Computer Science
2
Scientific paper
Three new varieties of aluminous assemblages from the Jagersfontein kimberlite are recognized as xenoliths consisting of garnet + spinel (alkremite), corundum + garnet (corganite) and corundum + garnet + spinel (corgaspinite). Accessory minerals include phlogopite, K-pargasite, fassaitic pyroxene and secondary spinel. Bulk-rock major elements are depleted in SiO 2 and enriched in Al 2 O 3 and MgO relative to basalt. The compatible trace elements Ni, Cr, Zn, Ga and V reflect the modal mineralogy, and the incompatible trace elements K, Rb and Ba vary as a function of metasomatism. Chondrite normalized REE patterns are characterized by fanning light and heavy REE variations. Calculations show that the patterns are consistent with partial melting of pelitic rocks from which a granitic low temperature portion has been removed by anatexis to produce a restite containing the observed geochemical variations. Sr isotopic ratios of garnet separates are high (0.780-0.804) and also indicate a sedimentary origin for the assemblages. A two-stage process involving partial melting of Archean sediments followed by prograde metamorphism of the residual restite is tentatively proposed, initiated by exotic terrain accretion or subduction at the edge of the Kaapvaal craton.
Haggerty Stephen E.
Mazzone Peter
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