Geology and petrography of gabbroic rocks from Khanozai Ophiolite, Northwestern Pakistan
- 1Centre of Excellence in Mineralogy, University of Balochistan, Quetta, Pakistan
- 2Centre of Excellence in Mineralogy, University of Balochistan, Quetta, Pakistan
- 3Department of Earth and Environmental Sciences, Bahria University Karachi Campus, Pakistan
Int. Res. J. Earth Sci., Volume 7, Issue (3), Pages 10-22, September,25 (2019)
The geology of Khanozai area is comprised of Indian Platform Sediments, the Suture Zone and Flysch Zone. The Khanozai Ophiolite Complex is a fragment of Zhob Valley ophiolites is marking the Suture Zone in the area and consists of mantle peridotite overlain by crustal ultramafic to mafic cumulate which is underlain by metamorphic sole rocks and mélange. The crustal section of the ophiolite comprises of both ultramafic to mafic cumulates. Ultramafic cumulates comprise repeated successions of dunite, pyroxenite and wehrlite while mafic cumulates consist of foliated to layered gabbros. The Khanozai gabbros cover about 60% area of the crustal plutonic rocks and have a lower transitional contact with the ultramafic cumulates. The gabbros (sensu lato) are classified as olivine gabbro, gabbronorite, olivine gabbronorite, norite and gabbro. The mineralogy of the gabbros indicates that they have both primitive and evolved components. The geochemistry indicates that the Khanozai gabbros are tholeiitic in nature and comprise both cumulate and non-cumulate mineral phases with olivine, pyroxenes and plagioclase being involved in fractionation. The cyclic series of ultramafic cumulates and gabbros has a different order, thickness, and structure in the crustal part of ophiolite and this possibly results from a variable supply of different magma compositions to the chamber. The structure of Khanozai Ophiolite' crustal section, with a well-developed plutonic sequence and absence of sheeted dyke indicate that these rocks may have formed in a tectonic setting with a slow spreading rate over different periods of time as a consequence of episodic low magma supply rates. These gabbros may have formed in a similar manner to the Semail Ophiolite' gabbros and imply that a well-developed ophiolitic sequence is rarely formed in a tectonic setting where the spreading and magma supply rates are not balanced.
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