Ph.D. Tezi Görüntüleme | |||||||||||||||||||||
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Summary: subgroups, namely Cpx-harzburgite, depleted harzburgite and dunite, on the basis of their modal mineralogy, geochemical features and mineral chemistry. Cpx-harzburgites are characterized by their higher Ca, Al and REE contents, and contain Al-rich orthopyroxeneand clinopyroxene with lower Cr# spinel compared to depleted harzburgite and dunite. Cpx-harzburgites are thought to be the residua left after extraction of MORB-type basalt,produced by %10 partial melting of fertile upper mantle, from which high-Al chromitite with high radiogenic Os content crystallized. However, depleted harzburgites are assumedto be residua left after extraction of hydrous boninitic melt, produced by second stage partial melting of already depleted mantle due to subducting slab, from which high-Crchromitites with lower radiogenic Os content were crystallized as a result of melt-rock interaction in a suprasubduction environment. Dunites around the chromite deposits areconsidered to be the product of melt-peridotite interaction. Most of the chromitites contain high-Cr chromite and display enrichment in IPGE(Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with concentrations of PGE between 61 and 1305 ppb. Consistently, laurite-erlichmanite serie minerals with various Os contents are found tobe the most abundant PGM in chromite. In addition to Os-Ir-Ru and Ru-Fe-Os alloys, irarsite and kashinite, Pt-Fe alloys (isoferroplatinum) which is not common in ophioliticchromitites were also detected as primary inclusions in chromite. In partly altered chromitite sample, laurite grains were found to be affected by alteration and transformed tothe Ru-oxide phases. The presence of olivine and clinopyroxene as well as hydrous silicate inclusions such as amphibole and phlogopite in high-Cr chromitite support the idea thathigh-Cr chromitites were formed in a suprasubduction environment. Key Words: Muğla, Mantle peridotites, Melt-peridotite interaction, Ophiolitic chromitites,Platinum-Group Elements, Platinum-Group Minerals, Re-Os isotope. |