Mineral chemistry of mantle peridotites from Loghar ophiolite (Southweast of Kabul - Afghanistan)

The Loghar ophiolite is located in ophiolitic belt of Kabul block (southeast of Afghanistan) and it is a part of Neotethyan ophiolites in Alpine - Himalayan orogenic system with Eocene age. Olivine, orthopyroxene, clinopyroxene and spinel are rock forming minerals of Loghar ophiolite mantle peridotite. Most of the olivines from different rock types are serpentinized but some fresh are present with forsterite composition. Orthopyroxene and clinopyroxene are enstatite (Mg# 0.961-0.972) and diopside (Mg# 0.976-0.999) in composition. The Cr# of vermicular and unhedral spinels of lherzolite and subhedral reddish brown spinels of harzburgite are 0.547 and 0.625 respectively. The Cr# of subhedral to euhedral spinels of dunite is 0.477, induced by high content of Al2O3 and low level of Cr2O3. The Cr# of dark red and euhedral spinel of chromitite is 0.633. The peridotites of the studied area belong to sub-oceanic crust mantle. The low content of Al2O3 in pyroxenes (opx and cpx) and the low amount of Na2O in clinopyroxene indicate high degree of partial melting of mantle peridotites. The chemical composition of minerals in dunites are different from that of lherzolite and harzburgite but present considerable similarity with that of the pillow lavas. The dunites of Loghar mantle peridotite (LMP) do not share features with those derived by partial meltiny, but represent sub lithospheric melt channels.