Whole Rock Geochemistry and Petrography of Pyroxenite Veins within Cumulate Dunite, Mawat Ophiolite: Implication for Classification and Petrogenesis, Kurdistan Region, NE Iraq

Abstract

The Mawat ophiolite is situated in the Kurdistan region of Iraq. Pyroxenite veins are crossed cut ultramafic Mawat ophiolite. Petrographic study and new geochemical data suggest that Pyroxenite veins in ultramafic units can be classified into two main rock types: websterite and pyroxenite. The websterite veins have a width ranging from 10 to 25 cm and a length of 300 m inside dunite. The pyroxenite veins, on the other hand, have a width of up to 10 cm and extend for around 150 m along dunite rock. Their major element geochemical characteristics emphasized that the websterite has relatively higher contents of SiO2 (49.01–53.02 wt%), CaO (15.3–19.35 wt%), Al2O3 (1.06–1.36 wt%), Σrare earth elements (1.09–2.09 ppm), and low MgO (21.07–23.06 wt%). Pyroxenite rock samples are characterized by relatively low SiO2 (41.01–48.09 wt%), CaO (1.49–12.3 wt%), Al2O3 (0.65–1.29 wt%), Σrare earth elements (0.3–3 ppm), and high MgO (24.04–39.07 wt%). The result of Trace and rare earth elements suggests that pyroxenite veins are formed by partial melting from the extensively depleted mantle. The rare earth element in dunite normalized to chondrite shows a flat to concave trend, whereas chondrite normalized rare earth elements in pyroxenite rock samples are highly depleted (SmN/CeN ~2) and display a negative light rare earth elements trend in comparably flattened positive middle rare earth elements and heavy rare earth elements patterns. This suggests that the vein is generated from supra-subduction zone settings. The enrichment in Ba, Th, and U provides further constraints on re-fertilization mechanisms. The research samples even showed a wide range of high partial melting degrees from the mantle source.