Petrogenetic Aspects of Wadi Akhdar-Wadi El-Sheikh Granitoid Rocks, Central Southern Sinai, Egypt: Evidence from the Chemistry of Ampiholes and Biotite PDF

Keywords

Granitoid rocks, Wadi Akhdar-Wadi El-Sheikh, Sinai, Egypt. Chemistry amphiboles and biotites

Abstract

Amphiboles and biotites from some calcalkaline granitoid rocks ranging in composition from quartz-diorite (QD), through tonalite (TON), granodiorite (GD) to monzogranite (MGR) exposed at Wadi Akhdar Wadi El-Sheikh area have been analysed for major, trace and REE. Both the amphiboles and biotites cover a wide compositional range which reflects the magmatic evolution of their host rocks. The amphiboles belongs to the calcic-type, ranging from magnesio-hornblende in QD and TON, actinolite hornblende in GD, and actinolite in MGR. Biotite varies from 45 to 64 mol % phlogopite and classified as Fe-rich in QD, TON and GD and Fe-poor lepidopmelane in MGR. The proposed conditions of crystallization range from <1-3Kb and 650°-850°C for the amphibole and a lower pressure and 800-600°C for the biotite equilibrium Generally, the amphibole and biotite are characterized by an increase in Si, Fe, K and HFSE, a decrease in Ti, Ca, Mg and the third transitional element contents relative to Fe/(Fe+Mg) ratios. They also show a good parallelism with the successive enrichment of both the total REE contents and negative Eu anomalies, suggesting a progressive crystal fractionation from the more mafic melt to constitute the felsic QD- TON-GD-MGR crystallization trend. The examined amphiboles and biotites from Wadi Akhdar-Wadi El-Sheikh granitoid complex chemically similar to those from the orogenic calcalkaline (L-type) suites