Abstract

The highly evolved Kuradawe granitic pegmatite dike is hosted in a harzburgite-dunite succession of the Mawat ophiolite in northeastern Iraq. It consists mainly of quartz, orthoclase, albite, tourmaline, and muscovite. Accessory minerals include cordierite, andalusite, monazite-(Ce), biotite, zircon, Nb-rich rutile, chlorapatite, chlorite, Sc-bearing columbite-(Fe), uraninite, U-rich thorite, and xenotime-(Y). The internal structure of the pegmatite consists of border, wall, intermediate, and core zones. Plagioclase composition increases from Ab92 to Ab97 towards the core. Whole rock major oxides such as MgO, Al2O3, and CaO decrease and SiO2 increases toward the core. Na2O, K2O, and total FeO are enriched in specific zones. Among the trace elements, incompatible elements such as Sr, Ba, and Zr decrease and the compatible elements Ni and Cr slightly increase toward the core. The pegmatite is characterized by the dominance of tourmaline; muscovite as the dominant mica; normative corundum; high contents of SiO2, Al2O3, A/CNK, and Rb; low contents of CaO and Sr; and a high total FeO/MgO ratio in biotite. These features suggest an affinity with calc-alkaline peraluminous S-type granite in a subduction-related, syncollisional setting. The pegmatite is classified as beryl-columbite subtype of the LCT family. The restricted occurrence of high-temperature cordierite in the border zone may suggest that the pegmatite was overprinted by modal metasomatism during intrusion into the mantle rocks. Zircon saturation geothermometry indicates inward crystallization at temperatures of 782 °C in the border zone, 717 °C in the wall zone, and 550 °C in the intermediate zones. Geochemical data suggest that inward crystallization typified the formation of the pegmatite.

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