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Geological Society, London, Special Publications; 1992; v. 60; p. 203-217;
DOI: 10.1144/GSL.SP.1992.060.01.12
© 1992 Geological Society of London

Influence of the partial melting regime on the formation of ophiolitic chromitite

Stephen Roberts

Department of Geology, The University, Highfield, Southampton, SO9 5NH, UK

The mantle sequence of the Vourinos ophiolite is composed of a highly depleted peridotite. Indices of depletion including the MgO content of the whole rock (40 wt% MgO), the CaO and Al2O3 contents of the orthopyroxene (<3.00 and 1.5 wt% respectively) and the Cr# value (100Cr/(Cr + Al)) of the spinels (54–80) all indicate a high degree of depletion, consistent with the removal of one or more melt fractions. The extensive chromite mineralization of the mantle sequence also shows a highly restricted chemistry with all but one chromite segregation falling in the range Cr# 75–82. By comparing the geochemistry of the Vourinos mantle sequence with other depleted (Semail) and more fertile mantle (Appenine) sequences, it can be shown that the melting of increasingly depleted residua results in chromium-rich magmas due to the DCrperidotite-melt of 1 or less. These chromium-rich magmas undergo extensive olivine plus spinel fractionation and result in chromium-rich chromite segregations partly due to the chromium content of the liquid but also to the relatively high silica content of the magmas concerned. Although chromite mineralisation is unlikely to be taking place within the ocean basins at the present time, modern oceans do contain evidence of sites of likely former chromite mineralisation within the oceanic crust.





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A. H. E. Rassios and E. M. Moores
Heterogeneous mantle complex, crustal processes, and obduction kinematics in a unified Pindos-Vourinos ophiolitic slab (northern Greece)
Geological Society, London, Special Publications, 2006; 260: 237 - 266.
[Abstract] [PDF]