<![CDATA[The Garba Formation constitutes part of the Woyla volcanic arc system, which is interpreted as an inter-oceanic volcanic arc that later accreted onto the Sundaland margin. This study evaluates the mineralogical characteristics and geochemistry of volcanic rocks from the Garba Formation in the Gilas River section to provide petrogenetic constraints on their origin. Mineral characterization was conducted using petrographic analysis under a polarizing microscope, whereas geochemical analysis was performed using X-ray fluorescence (XRF). Field observations reveal lava-related structures including autobreccia, platy joints, and pillow lava. Based on mineral proportions, the samples are classified as andesite, exhibiting porphyritic, glomerocrystic, trachytic, pilotaxitic, hyalopilitic, and intergranular textures. Geochemically, the volcanic rocks range from andesite to dacite and belong to the subalkaline medium-K calc-alkaline series. Tectonic discrimination diagrams indicate calc-alkaline basalt affinity associated with a continental arc setting. The observed rock structures, mineral assemblages, and textures indicate emplacement as lava flows. Moreover, the occurrence of pillow lava and quenched textures suggests lava–water interaction in a submarine environment consistent with inter-oceanic arc volcanism. However, the geochemical signatures suggest that the associated subduction system had evolved into a relatively mature continental arc prior to its accretion onto the Sundaland margin.]]>
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