PETROLOGY AND MAJOR ELEMENT GEOCHEMISTRY OF MANTLE ROCKS FROM KHANOZAI OPHIOLITE, NORTHERN BALOCHISTAN, PAKISTAN

The Khanozai Ophiolite Complex comprises of a thick mantle section which is divided into foliated peridotite and transition zone dunite. The foliated peridotite is dominantly harzburgite with minor dunite and mylonitized/banded lherzolite. The transition zone of the mantle section is dominantly dunite with minor harzburgite. Mineralogically, lherzolite consists of olivine, orthopyroxene, and clinopyroxene, harzburgite consists of olivine and clinopyroxene while dunite dominantly consists of olivine. All the rocks have a minor amount of Cr-Spinel grains and are serpentinized to variable degrees. The textures of the mantle rocks identified are porphyritic and porphyroclastic. The range of geochemical concentration in harzburgite in the major element (wt.%) and trace element (ppm) such as A12O3 (0.2–1.46), CaO (3–4), TiO2 (0.01–0.03), Cr (5-384), Co (23-35) and Ni (45-87) and in dunite is A12O3 (0.1–0.4), CaO (3–4), and TiO2 (0.01–0.03), Cr (12–321), Co (29–39) and Ni (59–75). The Khanozai harzburgite is poor in clinopyroxene while the dunite is poor in pyroxene indicating that the peridotite of the mantle section is refractory in nature and may be residual after a large number of partial melting of the lherzolitic source. The depleted mantle rocks are also possible to have been affected by melt–peridotite reaction. Therefore, the harzburgite may simply be residual from partial melting and combined with consequent fluid–peridotite interaction, and its dunite is the reactive conduits through which the partial melts were extracted. The transition zone of the mantle section may either have formed by olivine fractionation from picritic magma or may be residual in origin. The Khanozai Ophiolite mantle section may be residual from partial melting and/or a product of subsequent magma–mantle interaction while the transition zone is formed by a combination of the mantle and crustal processes which reveals mainly mantle processes at its base and crustal processes for the top. Major element geochemical signatures of Khanozai mantle rocks indicate that they are depleted in nature and are typical of ophiolitic peridotite and abyssal peridotite.   Download Full Paper