Petrogenetic study of diorite and Fe-Mg diorite from the Samar Bagh Complex: insights from petrographic and geochemical analyses

This study presents petrographic and geochemical investigations, in conjunction with field observations of the diorite and Fe-Mg diorite of the Samar Bagh Complex, located in the north-western part of the Kamila Amphibolite Belt in Northern Pakistan. The field investigations classify these rocks into dark grey to brownish diorite having quartz veins, alternating sheared and compacted zones, dark brown Fe-Mg diorite consisting of azurite and malachite, quartz veins, and oxidation of quartz veins in association with copper ores. The petrographic observations indicate these rocks primarily consist of plagioclase, clinopyroxene, amphiboles, quartz, alkali feldspar, magnetite, hornblende, biotite, sericite, olivine, orthopyroxene, hematite, and minor flakes of muscovite. The geochemical discrimination plots indicate tholeiitic magma series, with the ferron nature for diorite and magnesium-rich traits for Fe-Mg diorite. The tectonic classification of the Samar Bagh Complex, with rocks ranging from peraluminous to metaluminous, indicates that diorite, Fe-Mg diorite in mantle fractionates, island arc, and continental arc origins. This high-potassium to low-potassium rock is linked with the early intraoceanic subduction of the Neo-Tethys beneath the Asian Plate, intrusion of the Chilas Complex, interaction of the Indian Plate and the Kohistan Island Arc, resulting in the formation of diorite, Fe-Mg diorite, granodiorite, porphyry quartz monzonite, monzonite, and trachy andesite respectively. These findings contribute to the understanding of the magmatic and tectonic evaluation of the unsolved questions regarding the intermediate to felsic portion of the Kamila Amphibolite Belt.