Direct precipitation of Pt alloys from basaltic magma in the 2.77 Ga Monts de Cristal Complex,Gabon
The Monts de Cristal Complex consists of several igneous bodies believed to be remnants of a tectonically dismembered > 100km long and 1-3 km wide intrusion in north-central Gabon.The Complex consists largely of massive orthopyroxenite,with less abundant olivine-orthopyroxenites,harzburgites,dunites and norites.Geochronology using U-Pb SHRIMP on baddeleyite and monazite indicates an age of 2776±10 Ma.The rocks have fractionated incompatible trace element patterns,showing strong relative enrichment in LILE and negative Nb-Ta and Ti anomalies,indicating a significant crustal component.Mineral compositions (Fool84,Mg#Opx 85,Anplag 82,Cr/Fe chromite 1-1.45) and whole rock data indicate that the magma was a basalt containing a minimum of 7-8% MgO.The intrusion shows an unusual pattern of strong Pt enrichment (10-150 ppb),at low concentrations of Pd (1-10 ppb),Au (1-2 ppb),and Cu (1-20 ppm).Platinum contents correlate positively with the concentrations of IPGE and Rh,consistent with direct crystallization of IPGE- and Rh- bearing PtFe alloys from a sulfur undersaturated magma derived largely from the sub-continental lithospheric mantle.
W.D.Maier B.Rasmussen I.Fletcher S.Yang
Department of Geosciences,University of Oulu,Finland Dept.of Geology,Curtin University,Perth,Australia
国际会议
贵阳
英文
104-107
2012-06-16（万方平台首次上网日期，不代表论文的发表时间）