Petrochemical Significance of Biotite Schist Xenolith from Jabal Fezzan, Southern Libya

Abstract

The Jabal Fezzan's xenolith has been intruded during Pan-African metamorphism, characterized by (high pressure and medium temperature), this process results in the formation of the biotite, muscovite, and kyanite metamorphic zones. There is a slight increase in the degree of metamorphism as it reaches the biotite zone. It consists of foliated, medium- to coarse-grained schists, mostly biotite, muscovite, and kyanite, additionally plagioclase and quartz, as well as zircon, rutile, and Fe oxides. The microscopical evidence indicates that iron-rich biotite in pelitic schists undergoes a series of chemical reactions that cause it to be formed and transformed into other minerals. P-T diagrams suggest that rocks in the study area might have been formed during collisions and decompressions of thickened continental crust. They are derived from sedimentary rocks such as greywacke, which contain high levels of Si4⁺ and Al3⁺. As P-T conditions pass through, the biotite isograd and biotite forms. This study highlighted the oldest metamorphic rocks in southern Libya, enhancing the understanding of the mantle source protolith metasomatism, and reducing the information gap between petrochemical significance and the evolutionary stage of Pan-African metamorphism in southern Libya through study xenolith outcrops in more detail.