Mineralogy and origin of Mlakawa albitite from Kurdistan region, northeastern Iraq

Abstract

For the first time, albitite was found in the Iraq Zagros thrust zone near the village of Mlakawa, 60 km northeast of Sulaimani City, Kurdistan region, northeastern Iraq. It occurs as a white pod within the massive tectonized and serpentinized part of the Penjwin ophiolite sequence. Based on the preserved texture and mineralogical, petrological, and geochemical data from the core of the albitite pod, a plagiogranite protolith of Mlakawa albitite was inferred. It has undergone rodingitization and blackwall formation along its rim. The occurrence of barium aluminosilicate (celsian), cymrite, barium muscovite, and a high Na2O concentration (11 wt%) of albitite suggests that barium-sodium–rich fluid was involved during the albitization process of plagiogranite. Evidence of the progressive albitization includes the metasomatic replacement of Caplagioclase to albite and grossular, celsian to cymrite, replacement of tremolite by edenite, and newly formed sheaf-like barium muscovite. The presence of analcime and multiple generations of chlorite suggests that the albitite protolith was accompanied by chloritization and retrograde metamorphism before and after the albitization process. Ca-amphibole thermobarometry and the occurrence of strontium apatite and cymrite suggest that the albitization of plagiogranite occurred at <650 °C and 1.5 GPa.