Petrochemistry and Petrogenesis of Bulfat Mafic Intrusion, Qala Dizeh, Iraqi Kurdistan

Abstract

Bulfat mafic intrusion was studied at Noba and Benas peaks at southeastern Hero at Qaladizeh area is located at the Zagros thrust fault. The studied rocks consist of troctolite, olivine gabbro, gabbro, amphibole pyroxene gabbro. In Noba peak the olivine gabbro is dominant rock while in Benas peak amphibole pyroxene gabbro is a dominant. Textural study reflected that Noba peak rocks had suffered tectonic deformation more than Benas peak rocks. The chemical composition of minerals changes from bottom to top as plagioclase from An60 to An57, olivine from Fo79 to Fo75 clinopyroxene from Wo46 En46 Fs8 to Wo47 En44 Fs9 of diopside type and amphibole Mg+2/(Mg+2 + Fe+2)x100 from 84 to 75. Benas peak plagioclase are An57, olivine changes from Fo59 to Fo53, clinopyroxene from Wo43 En42 Fs15 to Wo45 En39 Fs16 of (augite) type, amphibole Mg+2/(Mg+2 + Fe+2)x100 changes from 72 to 65. These changes reflected the control of crystal fractionation in creation of different rocks. In addition the Benas rocks represent more progressive stage of crystal fractionation. Benas rocks are rich in iron, titanium and vanadium and poor in chromium and nickel because of the governing of crystallization of olivine, Cr-spinel and clinopyroxene at earlier stages. Low ratios of strontium isotopes in Bulfat rocks indicate that it had been formed from magmas derived from upper mantle. Geochemical indication of elements and isotopes revel the variation in the degree of partial melting for source rocks. As Benas rocks formed from depleted source with a partial melting of more than 30% while Noba rocks formed from sources with partial melting of about 15%. Depending on the magmatic affinity, the studied rocks are classified to low-K calc-alkaline type associated with magma of Island arcs.