Calc-silicates from Wadi Solaf region, Sinai, Egypt

Abstract

Calc-silicates have proved to be important rock types to place constraints on the fluid behaviour in high grade metamorphic rocks. Here we describe amphibolite facies calc-silicate rocks of Wadi Solaf, Egypt which is one of the highest grade basement complexes of Egypt and was exhumed in close connection with the Najd fault system – one of the largest pre-Mesozoic fault systems on the Earth. Calc-silicates formed around 7–8 kbar in temperature range of 600–720 °C and can be classified into three groups (CS 1, CS 2 and CS 3). CS 1 and CS 2 are characterized by the presence of garnet porphyroblasts which contain concentrically arranged wollastonite inclusions. CS 3 has a similar paragenesis but is characterized by the presence of clinozoisite/epidote and the absence of wollastonite as well as a pervasive late overgrowth of prehnite. Garnet in CS 1 lies along a grossular–andradite solid solution, while the garnet composition of CS 2 and CS 3 is hydrogrossular and hydroandradite. There is a positive correlation between Al 2O 3 and Na 2O as well as between Al 2O 3 and Fe 2O 3 from CS 2 through CS 1 to CS 3 possibly indicating a successive increase in fluid flow between the different calc-silicate types. During the peak metamorphism, the XCO 2 is 0.02–0.08 and 0.2–0.44 for the CS 1 and CS 3, respectively. The mineral assemblage of CS 1 and CS 2 buffered the composition of the fluids along the reaction: q + cc = wo + CO 2. During post-peak metamorphism the rocks were intruded by syn-tectonic granites. CS 2 records the contact metamorphic conditions. The rocks reached a peak contact metamorphism conditions at temperature 790–828 °C and XCO 2 = 0.22–0.41. Finally, the rocks reached a temperature range 296–311 °C during the cooling path.