TECTONIC SIGNIFICANCE OF LATE PRECAMBRIAN CALC-ALKALINE AND ALKALINE MAGMATISM IN SAINT KATHERINA AREA, SOUTHERN SINAI, EGYPT

Abstract

Two magmatic rock suites are distinguished in the Late Precambrian basement of the Southern Sinai (NW Arabian-Nubian Shield, Egypt), namely (a) a calc-alkaline suite, and (b) an alkaline suite. The former includes Rutig Volcanics, quartz-diorite, quartz-monzonite and monzogranite, while the latter includes Katherina Volcanics and A-type granites. The minerals and textural features (kink, decussate and foliated textures) of the quartz-diorite reveal that it was subjected to deformation and thermal metamorphism. The Rutig Volcanics and quartz-diorite represent subduction related I-type magma, generated from anatexis of older crust with contribution of mantle-wedge magma. The quartz-monzonite and monzogranite are evolved from hybrid magma due to injection of the partly crystallized granitic magma by more basic melts. The mineralogical and geochemical characteristics of these granites indicate a mildly alkaline character and belonging to transitional magma type on the borderline between the calc-alkaline and alkaline magma. The mafic microgranular enclaves (MME) in the quartz-monzonite and monzogranite represent cooled globules from a dioritic magma mingled with the partly crystalline granitic magma. The association of rapakivi texture with the MME confirms the genetic link between the rapakivi texture and magma mixing. The overall characteristics of the Katherina Volcanics and Atype granite are consistent with within-plate tectonic setting. The Katherina Volcanics are derived from a crustal source with a mantle contribution, whereas A-type granites represent residual melts derived from deeper magma chamber through extreme fractional crystallization process.