Origin and Tectonic History of Some Metamorphic Rocks From Southern Sinai, Egypt | Szegedi Tudományegyetem, Ásványtani, Geokémiai és Kőzettani Tanszék

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Origin and Tectonic History of Some Metamorphic Rocks From Southern Sinai, Egypt

Acta Mineralogica-Petrographica, Szeged 2002, Vol. 43, pp. 27-38

Aabdel-Aal Abdel-Karim
Puskás Zuárd
Jánosi Melinda

The Baba schists and gneisses, in the extremely northwestern part of the metamorphic belt of Sinai, have been discussed in terms of the mode of occurrence, evolution of mineral chemistry, major, trace and rare earth elements (REE) and age dating. They exhibit a trondhjemitic composition and comprise four metamorphic zones, namely the chlorite, biotite, almandine and cordierite zone. They are derived from pelitic + semi-pelitic rocks affected by three episodes of metamorphism. The first episode is a low-grade regional metamorphism of greenschist facies, the second episode is lower amphibolite facies metamorphism with higher temperature and similar pressure followed by the third episode of a retrograde metamorphism with decreasing temperature and pressure.Chemically, the schists and gneisses are similar to crustal sediments and evolved intermediate igneous rocks, which are the source of these sediments. We assume that, they represent metamorphosed pelitic and intermediate volcanoclastic sediments that underwent hydrothermal alteration and were affected by metamorphic differentiation and partial melting. The schists and gneisses have REE patterns analogous to the intermediate igneous rocks of island arc. There are minor but interesting differences between schists and gneisses. The gneisses are characterized by higher contents of TiO2 , Hf, Ta, U, Zr, Nb and REE and lower contents Sc, Cr and Co relative to the schists, probably due to the influence of the accessory zircon, apatite and monazite and/or the more pronounced effects of the metamorphic differentiation on the gneisses. K-Ar age dating of gneisses gives ages of 620 ± 24 Ma and 602 ± 23 Ma. The former age may represent the nearest estimated age for the formation of the protolith of the gneisses, meanwhile, the second one probably records the age of metamorphism. The schists yield an age of 549 ± 22 Ma, which may be represent the late retrograde metamorphism effected the schists.




acta2002, geochemistry, gneisses, K-Ar age dating, metamorphic evolution, mode of occurrence, origin, schists, Southern Sinai




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