الفهرس | Only 14 pages are availabe for public view |
Abstract This study deals with geologic setting, petrography, geochemistry, zircon typology, and radioactivity of some younger granite plutons of southwestern Sinai, Egypt. Four localities are chosen to carry out the present study, namely Wadi Akhdar, Wadi Nisriyin, Wadi E-Sahu, and Wadi Seih areas. Based on field setting and petrographic description, the studied areas comprise three phases of granites, which are distinguished from the oldest to the youngest into monzogranite, syenogranite, and alkali granite (or alkali feldspar granite). Geochemical investigation of the studied granites reveals that monzogranite is peraluminous S-type granite derived from a source dominated by metasediments. Syenogranite is metaluminous I-type granite crystallized from a highly differentiated feldspar-rich magma. Both types of granites were further identified as volcanic arc granites (VAG) emplaced under a compressional regime. Alkali granite, on the contrary, is identified as peralkaline A-type granite derived from a highly fractionated feldspar-rich magma. It is also recognized as a within plate granite (WPG) emplaced under an extensional regime. Based on zircon typology, the crystallization temperatures of monzogranite, syenogranite, and alkali granite zircons have mean values of 481˚C, 600˚C, and 665˚C, respectively. Zircons of the three types of granites are products of magmatic crystallization, where those of syenogranite are extensively affected by hydrothermal alterations. On the (I.A, I.T) parameters diagram, monzogranites, syenogranites, and alkali granites plot in the field of intrusive aluminous monzogranite and granodiorite (3), subalkaline series granite – granites of mantle or mainly mantle origin (5), and alkaline series granite (6), respectively. Two types of radiometric anomalies are detected in the studied areas. The first anomaly is associated with shear zones that affected by hydrothermal solutions and the second anomaly is associated with stream sediments. Uranium and thorium minerals, either along the shear zones or in the stream sediments, include kasolite and thorite. Associated mineral assemblages include spangolite, barite, fluorite, which suggest the same origin of these anomalies. Zircon is proposed as the preferred source of these anomalies. |