Petrological and geochemical constraints on the origin of the granitoid suite of the Homret Mikpid area, south Eastern Desert, Egypt

Abstract

The granitoid suite of the Homret Mikpid area is categorized as quartz-diorite, granodiorite and adamellite. Quartz-diorite and granodiorite are predominantly metaluminous, whereas adamellite is peraluminous and displays some of the S-type characteristics. While Quartz-diorite and granodiorite are classified respectively as being intrusives in a pre-plate collision and late orogenic tectonic settings, the adamellite is correlated with syn-collision setting. Granodiorite shows the highest values of REE, which could be attributed to the presence of accessory minerals. Quartz-diorite shows irregular chondrite-normalized REE pattern without significant europium anomaly, hi contrast, the adamellite is characterized by slightly steep LREE and a flat HREE pattern, with little negative europium anomaly (Eu/Eu* = 0.652-0.826), and LaN/YbN ratios of 3.4-5.3. Uranium and potassium contents show gradual increase from quartz-diorite to adamellite. This is in harmony with the relatively mafic nature of quartzdiorite and the crustal source of adamellite. On the other hand, thorium shows a relative enrichment in granodiorite. This enrichment is attributed to the presence of accessory minerals particularly allanite. The Homret Mikpid granitoids provide an example for demonstrating partial melting from different magma sources. The quartz-diorite formed separately as a result of partial melting of the lower crust that formed mainly of amphibolites. At different crustal level, the granodiorite was formed from dacites-tonalites and metagreywackes through the same process. The adamellite could be generated at shallower depth by anatexis of crustal source such as metapelites and metagreywackes.