Microgranular enclaves in the Pan-African I-type granites from the Sinai Massif: petrology, mineralogy and geochemistry

A geological, petrological and geochemical study involving mineral chemistry and whole-rock major and trace element data has been carried out on the microgranular enclaves hosted in the Sinai Massif I-type granites. Enclave specimens were collected from two separated plutons along the western margin of the Sinai Massif: the northern pluton (NP) and southern pluton (SP).

Enclaves consist of monzogabbros, monzodiorites and diorites, as well as, rare monzonites, syenogabbros and syenodiorites. They are characterized by wide compositional range (48–62% SiO₂). Mineral chemistry and whole-rock chemistries both suggest that enclaves from SP and NP were derived from two to three magmas. Enclaves provide microstructural evidence pertaining to magmatic source material. The origin of present microgranular enclaves hosted in the I-type metaluminous granitoids is best explained by mixing/mingling of hot basic magmas with relatively cooler acidic magma in a plutonic environment. Substantial changes in rheological properties of magmas occur due to thermal diffusion at the interfaces of these globules and increase the undercooling rate. Magma mingling occurs instead of through mixing and homogenization. The mafic globules are dispersed randomly or concentrated into swarms by flow of the hotter magma.