Mineralogy of the Neoproterozoic epidote-bearing TTG suite, Mons Claudianus batholith (Egypt) and implications for synorogenic magmatism

Abstract

AbstractThe Neoproterozoic, epidote-bearing Mons Claudianus Batholith (MCB), Egypt, consists of tonalite-trondhjemite-granodiorite (TTG) lithologies, containing variable contents of quartz, feldspars, amphiboles, biotite, and magmatic epidote, with accessory titanite, zircon, allanite, apatite, opaque magnetite and ilmenite. Plagioclase varies from An49 to An19, and K-feldspars possess near end-member compositions (Or97 to Or91). Amphiboles are calcic (Ca = 1.88–1.92 atoms per formula unit (apfu)), Al-rich (average AlT = 1.84 apfu), having an average Fe/(Fe + Mg) ratio of 0.50, and are edenite, ferro-edenite and ferropargasite. The Al-in-Hb barometer produced an average crystallization pressure of 5.5 kbar, consistent with the presence of magmatic epidote; the association epidote – Al-rich-Hb suggests mesozonal crustal levels, and thus a possible average rate of regional uplift for the Nubian Shield would have been in the order of 0.03 mm/yr. Calculated temperatures (using the Hb-Plag geothermometer) range from 729 to 754°C (average 747°C). The calculated P / T values of epidote-bearing MCB rocks fall within the experimentally-determined P-T range of stability of magmatic epidote with fO2 buffered from NNO to HM. Biotites in the MCB are moderately Mg-rich (Fe/(Fe + Mg) = 0.42 to 0.50), and are type 'C'-biotite, typical of calcalkaline orogenic suites, which are distinct from types 'A' and 'P' biotites occurring in anorogenic alkaline, and peraluminous lithologies, respectively. The minor secondary chlorite phases, with their Fe/(Fe + Mg) ratios of 0.37–0.52, are pycnochlorite and ripidolites, and belong to group 'c' chlorites. Minerals of the MCB reflect a petrogenetic history involving a wet, subsolvus, typically orogenic magmatic system. Results of this study could have wide implications for mineralogical characterization, level of emplacement and evolution of magmatic systems of TTG suites occurring in other orogenic belts.