Bulletin du Service Géologique de l'Algérie
Volume 4, Numéro 1, Pages 3-24
1993-06-01

The Cap De Garde Pelites And Gneisses, Edough, Annaba, Ne Algeria: Their Petrology, Geochemistry And Origin

Authors : Ahmed -said Y. . Leake B.-e .

Abstract

The geochemistry of the Capde Garde kyanite -rich pelites shows that the rocks, which suffered high pres¬ sure (P=7-9kb) and medium temperature (T=60Q±30 *C) metamorphism, were well sorted illite-rich sediments with only a minor basic igneous component. Based on major and trace chemical analyses, the Edough biotite gneisses, whether augen-bearing or not, are shown to have been isochemically metamorphosed acidic calc-alkaline granitic rocks contai¬ ning country rock sheets and xenoliths and this is compatible with evidence deduced from whole rock Rb - Sr isotopic studies ((87Rb/86Sr)199=0.71448±19).The major tectonic shearing phase (N140E) which is very well developed in Cap de Garde probably took place at 199±30 MA. The volatile - rich muscovite gneisses and the aplites were probably more evolved acid igneous rocks whereas the leptynites are thought to have a similar origin to the biotite gneisses.

Keywords

Calc-alkaline, Edough, Isochemical, Leucosome, Migmatite, Tholeiite