Platinum-group elements distribution and spinel composition in podiform chromitites and associated rocks from the upper mantle section of the Neoproterozoic Bou Azzer ophiolite, Anti-Atlas, Morocco

Enrichment of Rh, Ru, Ir and Os in Cr spinels from oxidized magmas: Evidence from the Ambae volcano, Vanuatu

“…The correlation between whole rock Cr and PGE contents observed in various magmatic suites (Hamlyn et al, 1985;Crocket and Macrae, 1986;Brugmann et al, 1987), and the enrichment of PGEs in chromitites from the layered intrusions, ophiolites and alpine-type peridotites (Peck et al, 1992;Zhou et al, 1998;Ahmed and Arai, 2002;Buchl et al, 2004;Ahmed et al, 2009), suggest a genetic link between PGE concentrations and Cr spinels. Whether the observed trends are controlled mainly by PGEs in solid solution in the Cr spinels or platinum group minerals (PGMs) and PGE-bearing sulfides that are entrapped in Cr spinels during their crystal growth remains unresolved.…”

Compositional variations and tectonic settings of podiform chromitites and associated ultramafic rocks of the Neoproterozoic ophiolite at Wadi Al Hwanet, northwestern Saudi Arabia

“…Their PGE contents (100-500 ppb) and (Pd/Ir) N ratios (0.8-0.1) are highly variable (Page and Talkington, 1984;Barnes et al, 1985;Leblanc, 1991) and display gentle-negatively sloped PGE patterns (Leblanc, 1991;Ahmed and Arai, 2002). In some other cases, the PGE-poor chromitites display steep-negatively sloped PGE patterns (highly depleted in PPGE), and high Cr# (>0.7) of chromian spinels reflecting their formation from a melt produced by high degrees of partial melting in arc settings (Page and Talkington, 1984;Leblanc, 1991;Zhou et al, 1998;Ahmed and Arai, 2002;Ahmed et al, 2009). The PGE-rich chromitites, on the other hand, are often IPGE-rich and sometimes Pt-Pd rich, or show a combination of both types.…”

“…Podiform chromitites and their possible associated platinum-group elements (PGEs) are mostly concentrated in the upper mantle section of ophiolites. They are important as geochemical monitors of deep-seated mantle processes that provide us with constraints on the physico-chemical conditions and evolution of mantle lithosphere (Lago et al, 1982;Leblanc and Ceuleneer, 1992;Liipo et al, 1995;Ahmed and Arai, 2002;Ahmed et al, 2001Ahmed et al, , 2005Ahmed et al, , 2009. It is now widely accepted that ophiolitic chromitites are dominated by Ir-subgroup (IPGE = Os, Ir, Ru) and depleted in Pd-subgroup (PPGE = Rh, Pt and Pd) of PGE (Page et al, 1982a,b;Page and Talkington, 1984;Talkington et al, 1984;Augé, 1986;Prichard et al, 1996;Zhou et al, 1998;Ahmed and Arai, 2003).…”

“…This may be due to the extensive dismembering and metamorphism of the ophiolitic rocks of older ages. Few petrological studies, on the other hand, have been carried out on the Precambrian ophiolites, in general (Quick, 1990;Bonavia et al, 1993;Liipo et al, 1995;Vuollo et al, 1995;Zimmer et al, 1995;Suita and Strieder, 1996;Ahmed et al, 2001Ahmed et al, , 2005Ahmed et al, , 2009Azer and Stern, 2007;Farahat et al, 2010), and on the late Proterozoic ophiolite of the Arabian Shield, Saudi Arabia, in particular (Bakor et al, 1976;Nassief et al, 1984;Pallister et al, 1988;Al-Shanti and El-Mahdy, 1988;Al-Saleh et al, 1998;Dilek and Ahmed, 2003;Johnson et al, 2003Johnson et al, , 2004Stern et al, 2004;Ahmed and Harriri, 2008). Although several ophiolite belts in the Arabian Shield of Saudi Arabia have a good exposure of their upper mantle section, only few studies were focused on the petrology of these mantle components.…”

Geochemistry of platinum-group elements and mineral composition in chromitites and associated rocks from the Abdasht ultramafic complex, Kerman, Southeastern Iran

“…Strong depletion of PPGE in the Abdasht peridotites coupled with the high Cr# values determined for spinels (> 0.80), strongly indicate that either a high-degree of partial melting or partial melting of an already depleted mantle peridotite (second-stage melting) was responsible for the formation of the Abdasht chromitites. These conditions are believed to develop in suprasubduction zone settings similar to the podiform chromitites from Bou Azzer ophiolite in Morroco (Ahmed et al, 2009). This also implies that the Abdasht chromitites have been derived A C C E P T E D M A N U S C R I P T…”