Petrogenesis of Amphibolite/Hornblendite Dikes in Qala-Diza Area, Iraqi Kurdistan Region

Abstract

The amphibolite and hornblendite dikes occur as part of the igneous complexes of Bulfat Ophiolite within the Zagros Suture Zone, NE Iraq. The igneous complex is part of the upper allochthonous ophiolite terrane within the second unit of the Penjween-Walash Subzone. This article discusses the petrogenetic characteristics and tectonic setting of the amphibolite rocks based on their petrography, mineral chemistry, and whole-rock geochemistry. Petrographically, both banded and massive amphibolites reveal that the main mineral constituents are amphibole and plagioclase with accessory clinopyroxene, opaques, sphene, apatite, rutile, zircon, sericite, epidote and chlorite; meanwhile the hornblendites consist of >90% amphibole with minor amounts of pyroxene, opaques, plagioclase, titanite, quartz, apatite, zircon, and chlorite. The amphibolites are divided into two types, banded (foliated) and massive, (non-foliated). The dominat textures of amphibolites are porphyroblastic, granoblastic, poikiloblastic, nematoblastic, and blasto-ophitic; meanwhile those of hornblendites are equigranular, poikilitic, cataclastic, and intergranular. The electron microprobe analysis (EPMA) showed that the amphiboles of the banded amphibolite range between tschermakite, magnesio-hornblende and pargasite; and those of the massive amphibolites range between magnesio-hornblende and actinolite; meanwhile those of hornblendites are dominantly tschermakite with minor magnesio-hornblende and pargasite. The plagioclase of the banded amphibolites is mainly oligoclase and andesine; and those of the massive amphibolites are mostly anorthite. Chemical classification diagrams indicated that the studied rocks are had low alkalies (Na2O+K2O), tholeiitic, ultrabasic to basic, alkaline to subalkaline and divided between foidite, picrobasalt and basalt. Various tectonic discriminating diagrams showed that most of studied rocks are mid-ocean ridge basalt (MORB). The studied amphibolites have been subjected to amphibolite facies metamorphism.