Pattern Formation in Schist Rocks of the Bulfat Igneous Complex, Iraqi Kurdistan Region: Field Observations and Mineral Chemical Constraints

Abstract

This paper presents the initial detailed petrographic and mineral chemical study of the outcrops of schist rock in the villages of Beklo and Dawzjan within the Qandil region, northeast of Iraq. The bottom of the Bulfat Igneous Complex reveals schist and adjoins the Walash volcano-sedimentary group, while the upper layer of the schist is tectonically juxtaposed with the Naopurdan Nummulitic limestone. In some of the localities, it seems to form part of the lower allochthonous unit of the volcano-sedimentary succession of the Walash group. According to field investigations, the schist rock body contains remnants of the Walash group, including pelitic rocks, limestone, and serpentinite blocks. The schist has a well-evolved pattern formation represented by alternating dark and light compositional layers and continues over the millimeter-to-decimeter scale, perpendicular to the primary foliation. Plagioclase (albite and oligoclase), feldspar (orthoclase and microcline), and quartz dominate the light layers, and amphibole (tremolite-actinolite, Mg-Fe hornblende, and Mg-Fe hastingsite) with chlorite dominates the dark layers. Mineral chemistry demonstrates metamorphic conditions ranging from greenschist to upper amphibolite facies, with temperatures ranging between 300 and 650 °C under moderate pressure regimes, which is consistent with progressive regional metamorphism. Textural relationships and mineral assemblages record prograde metamorphic evolution accompanied by intense deformation structures, including boudinage, foliation, folding, and faulting, suggesting a strong tectonic influence. Petrogenetic evidence suggests a sedimentary protolith, derived mainly from mafic mud (mud rich in mafic sediments) source rocks including basalt, gabbro, and volcanic detritus within the Walash volcano-sedimentary group. These lithologies underwent progressive regional metamorphism associated with intensive deformation in an island arc fragment (lower allochthonous sheet) of the northeastern Iraqi segment of the Zagros Suture Zone.