Diagenetic to low-grade metamorphic evolution of clay mineral assemblages in Palaeozoic to early Mesozoic rocks of the Eastern Taurides, Turkey

Abstract

Palaeozoic to early Mesozoic rocks of both autochthonous and allochthonous units of the Eastern Tauride Belt have different textural and mineralogical features related to their varying deposition regimes and thermal histories. The Devonian and Carboniferous formations in the allocthonous units have anchizonal to epizonal grades of metamorphism, whereas those of the autochthon experienced only early diagenetic conditions. A well-developed penetrative slaty cleavage is also found in Devonian formations of the allocthonous units, which is not observed in equivalent rocks of the autochthon. Phyllosilicates of the uncleaved diagenetic assemblages consist mainly of illite, chlorite, kaolinite, mixed-layer illite-smectite, chlorite-vermiculite and chlorite-smectite, whereas in addition to these, metamorphic allochthonous units contain some index minerals such as dickite, paragonite, Na and K mica, pyrophyllite, stilpnomelane and chloritoid. These latter assemblages show a higher degree of textural and mineralogical maturation and lower b cell dimensions than the autochthonous rocks, suggesting that they originated in a relatively high heat flow basin Such as an extensional setting.