The petrology of the Abu Zawal gabbroic intrusion, Eastern Desert, Egypt: An example of an island-arc setting

The Abu Zawal gabbroic intrusion consists of three gabbroic zones. Each of these zones has a distinctive mineralogical composition. Plagioclase and altered clinopyroxene are abundant in the lower zone gabbro (uralitized gabbro). Hornblende and Fe-Ti oxides occur in the middle and upper zone gabbros (hornblende and ferro-gabbros, respectively). Fe-Ti oxides are more abundant in the upper zone gabbro. The composition of the plagioclase cores ranges from A(158) (lower zone) to An(40) (upper zone). The primary clinopyroxene and calcic amphibole are augite and magnesio-hornblende, respectively. Application of the hornblende geobarometer indicates a pressure of crystallization ranging from 2.9 to 3.5 kbar. In addition, application of the amphibole-plagioclase geothermometer yields crystallization temperatures of about 1080-1100 degrees C. Major oxide, trace element and REE data are suggestive of an island-are evolved high alumina basalt as the parent for these gabbros. The differentiation of the gabbroic zones can be accounted for by low pressure, closed-system in situ crystallization under wet conditions.