Study of Serpentinized Ultramafic Rocks of Bela Ophiolite, Balochistan, Pakistan

Mineralogical and petrological study of ultramafic rocks of Bela Ophiolite of Cretaceous age revealed serpentinization after harzburgite. It is further evident on SiO2/MgO vs. Al2O3, molar ratio Si/Mg+Fe vs. LOI and MgO-SiO2-LOI diagrams. The XRD analysis also showed occurrence of olivine, different members of pyroxene and serpentine groups. The three polymorphous of serpentines can be distinguished on (Fe2++ Mg2+)/(Fe3++A13+) vs. H2O diagram, reflecting thermal regime in the study area.

The analyzed samples of the study area showed relevance with Alpine peridotites. The plots MgO versus CaO and Ni show relation with average primitive mantle. The high amount of Ni and low content of Al2O3 in the study area indicates depleted-mantle peridotite. The parent rock is classified on the basis of Al/Si (av. 0.031) and Mg/Si (av. 1.05) ratios as harzburgite. The altered harzburgites displayed as serpentines on SiO2 vs. LOI plot and SiO2-(Al2O3+Fe2O3)-MgO triangular diagram.