SHRIMP U-Pb zircon dating of the Katerina Ring Complex: Insights into the temporal sequence of Ediacaran calc-alkaline to peralkaline magmatism in southern Sinai, Egypt

摘要

SHRIMP U-Pb dating reveals that the hypabyssal Katerina Ring Complex formed over a ~. 9. Ma interval. The first rocks that formed were the alkaline to peralkaline granitoids that form the wall and the roof cap of the Ring Dike, emplaced at 602. ±. 8. Ma and 602±4. Ma respectively. These were closely followed by the Isbaiya calc-alkaline quartz-monzonites at 599±3. Ma, and by the main Katerina pluton at 596±3. Ma. The pluton is composed of A-type metaluminous fluorite-bearing granites that contain one inherited Archean zircon (~. 3.2. Ga). The Katerina magmatic cycle ended with the intrusion of another peralkaline body in the ring interior at 593±2. Ma; this body forms the summit of Gebel Musa (Mount Sinai). The Ring Dike encloses older rocks such as the 844±4. Ma Moneiga quartz-diorites and the 622±3. Ma Rutig volcanic rocks. The conglomerates interbedded with these contain boulders of granites with ages of 735±6. Ma and 748±11. Ma. Outcrops of igneous rocks with these ages are currently unknown in the Sinai, probably because they were recycled into the late ~. 590-625. Ma granites and volcanic rocks, as is revealed by zircon inheritance. The alternating formation of calc-alkaline and alkaline granite magmas during the short time frame of the Katerina magmatic cycle (~. 9. Ma) poses the problem to understand which mechanisms have controlled the production of coeval calc-alkaline and alkaline magmas, the magma sources of which remain poorly constrained as identical Sr and Nd isotope compositions cannot distinguish between mantle melting and reworking of juvenile crust. Additionally, the diachronism of peralkaline magmas from the Katerina magmatic cycle with respect to other areas of the Sinai suggests that the magmatic focus migrated in space and time which may be related to alkaline metasomatism processes in the crust.