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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.