Origin and metamorphism of corundum-rich metabauxites at mt. ısmail in the southern menderes massif, sw Turkey

Abstract

The corundum-rich metabauxites, found at the northwest limb of an NESW-trending isoclinal recumbent fold at Mt. Ismail, are enclosed in thick-bedded platform-type marbles of Late Cretaceous age, surrounding the polymetamorphic core series in the southern part of the Menderes Massif (SW Turkey). The metabauxite horizons observed as typically boudine-like structure, extend laterally over c. 3 km and are 1 to 5 m thick. These rocks have dominant mineral assemblages of corundum (similar to 50 modal %), chloritoid (similar to 30 modal %), white mica (margarite, muscovite), diaspore, FeTi-Oxides (ilmenite, ilmenohematite, rutile), and goethite, limonite, pyrite, tourmaline (uvite, schorl) as minor phases. Chemical analyses of whole rock samples and the mineral assemblage indicate that coexisting minerals of metabauxites are highly aluminous. A number of minerals (e.g. chloritoid and margarite) display a large compositional variation reflecting the initial chemical inhomogenetiy of the karstbauxites. The field observations, trace-element accumulation coefficients, concentration of elements such as Cr, Zr, Ga and Ni and low amounts of immobile elements all suggest that the studied corundum-rich metabauxites can be classified as karstbauxites, and are more likely to be a product of weathering of intermediate igneous or argillaceous parental rocks, similar to the karstic Tauric bauxites in the Central Taurides (Seydi sehir region) and probably are similar in age (CenomanianTuronian). In respect of tectono-metamorphic evolution, the studied corundum-rich metabauxites were regionally metamorphosed at similar to 56 kbar pressure and 500-600 degrees C as a consequence of the Barrovian metamorphism referred to as the Main Menderes Metamorphism related to the ophiolitic obduction onto the Menderes platform from the IzmirAnkara Suture during the Middle Eocene.