Platinum-group element abundances and Os isotope composition of mantle peridotites from the Mamonia complex, Cyprus

Platinum-group element (Os, Ir, Ru, Pt and Pd) abundances and Re–Os isotopic composition of fifteen peridotites (eleven spinel lherzolites and four spinel harzburgites) from the Mamonia complex, Cyprus, were determined as well as major and trace element compositions of bulk-rocks and minerals. Spinel lherzolites show excellent correlation between parameters indicating the degree of melting — e.g. Fo content in olivine, Cr# (Cr/(Cr + Al)) of Cr-spinel, Al and Yb concentrations in clinopyroxene. The degree of partial melting, calculated using Cr-spinel compositions, range from 1% to 9%. The PGE contents in spinel lherzolites show correlation with each other and with the spinel compositions, and thus can be related to the partial melting of the mantle source. The PGE abundances of the mantle source are estimated using the least depleted spinel lherzolite samples: Os 3.6 ± 0.5, Ir 3.4 ± 0.5, Ru 6.5 ± 0.9, Pt 6.1 ± 0.2, Pd 3.9 ± 0.2 (in ppb). Spinel harzburgites, despite a good correlation between the whole rock major element abundances and mineral compositions (e.g., Yb in clinopyroxene and Cr# of spinel), indicate no relationship between the Fo content of olivine and the Cr# of spinel. Hence, the harzburgites cannot be the residuum of simple partial melting, but have a more complex origin (e.g. melt percolation). Pt/Ir ratios increase in the harzburgites as Pt increases. Similar behavior of Pt and Pd is observed in abyssal and SCLM harzburgites, and explained by sulfide precipitation during melt percolation. Rhenium concentrations in most Mamonia peridotites are significantly higher than in the primitive mantle and does not show correlations with PGE. Indeed Re concentrations tend to increase with the Cr# of spinel. Thus its distribution is not governed by partial melting and we suggest that Re addition to the peridotites of Mamonia occurred during serpentinization. The Re–Os model ages of peridotites form three age clusters at 250 Ma, 600–800 Ma and > 1000 Ma. The youngest age is consistent with the age of magmatic rocks in the Mamonia Complex, whereas the “oldest” peridotites may belong to remnants of the subcontinental mantle.