Publication Type:Journal Article
Source:Geochimica et Cosmochimica Acta, Pergamon, Oxford, International, Volume 62, Number 4, p.677-688 (1998)
Keywords:Asia, back-arc basins, basalts, basins, China, chromite ores, chromitite, Far East, geochemistry, igneous rocks, island arcs, mantle, metal ores, metals, mid-ocean ridge basalts, mineral deposits, genesis, models, orogenic belts, partial melting, peridotites, platinum group, plutonic rocks, podiform deposits, tectonics, ultramafics, volcanic rocks
Analyses are presented of podiform chromitites from two major Phanerozoic orogenic belts - the Qilian-Qiangling-Kunlun-Himalaya tectonic domain, and the th Asiatic orogenic belt. Data presented include average chromite compositions for major and minor oxides, and PGE, Cr (sub 2) O (sub 3) , V, Co, Ni, Cu, Zn for the podiform chromitites which range in texture from disseminated, nodular to massive. The results show two types of mantle-normalized PGE patterns with negative slopes: Type I (high-Cr) chromitites have higher Os, Ir, Ru and Rh than Type II (high-Al) chromitites; most of both types have lower Pd and Pt than upper mantle peridotites in which they occur. The PGE distributions in the podiform chromitites were produced by combined partial melting and/rock interaction in the mantle; the chromite deposits are in part metasomatic replacements of the mantle peridotites in which they developed. Type I chromitites formed by the interaction of depleted harzburgite upper mantle with S-undersaturated boninitic magmas enriched in Pd, Pt and perhaps Ir. Type II chromitites formed by the interaction of depleted harzburgite mantle with S-saturated tholeiitic magmas and lost their PGE before formation of the chromitites. All the PGE in these deposits were inherited from the upper mantle in which the chromite deposits formed.
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