Petrography, Geochemistry, and Tectonic Significance of Walash Pillow Basalt in the Choman-Rayat Area, NE Iraq: Implications for the Neo-Tethyan Evolution

Abstract

The basaltic pillow lava and basalt at Choman-Rayat towns, Erbil City, Northeastern Iraq, were studied for their geochemistry, petrology, and morphology. The basalt of the Choman-Rayat area is a part of the Walash sequence in the Iraqi Zagros Suture Zone. Petrographically, the texture of basaltic pillow lava and basalt samples is revealed as amygdaloidal and vesicular aphanitic basalt, wherein plagioclase functions as a first mixing phase of the magma. A large phenocryst of pyroxene is located inside a matrix of extended quenching plagioclase. Numerous euhedral grains of opaque minerals are distributed in the very fine groundmass. Mineralogically, they predominantly consist of plagioclase, clinopyroxene, and opaque minerals, with other components as secondary and alteration minerals, including amphibole, spinel, epidote, calcite, serpentine, quartz, zeolite, and chlorite. Morphological properties indicate that the basaltic pillow lava samples range from 10 cm to 6 m in diameter, with spherical, tubular, friable red-coloured to firm green-colored isolated pillows with vesicle-rich interiors containing secondary minerals, and geochemically based on their magmatic affinity. The basaltic pillow lava and basalt samples are classified as part of the tholeiitic series. Numerous tectonic discriminating diagrams show that the majority of samples are linked to the magma of an oceanic island arc indicate that the pillow lavas were intruded in a shallow marine marginal within-plate basin. Consequently, the active subduction system in the Neo-Tethyan region during the Eocene-Oligocene age was crucial to the formation of an island-arc complex, distinguished by basaltic pillow lavas and related volcanic rocks.