THE GEOLOGY OF THE SOUTH OF MANYAS (BALIKESİR) AND TECTONIC SIGNIFICANCE OF BLUESCHISTS

Abstract

The study area comprises mainly Karakaya complex units of Sakarya zone, a granodioritic pluton which cuts the Karakaya complex and unconformably overlying Neogene sedimentary and volcanic rocks. Apart from these, a small blueschist klippe rests on the Karakaya complex. The Karakaya complex in the area studied is made up of Nilüfer unit and tectonically overlying Triassic detritics (Hodul unit and Orhanlar greywacke). Nilüfer unit consists of metabasite-metapelite-marble intercalation at the base and monotonous marbles at the top. Nilüfer unit has undergone greenschist fades metamorphism probably during Late Triassic. Nilüfer unit is in tectonic contact with detritic rocks bearing neritic limestone blocks of Carboniferous-Permian age and rare spilite blocks. A blueschist klippe, which consists of metabasites, is observed on the Nilüfer unit and on the Triassic detritics to the south of Manyas. The metamorphic age of the blueschist is Late Cretaceous as reported from south of Mustafakemalpaşa. The exhumation of blueschists mainly occurred during the latest Cretaceous. Thus, the thrusting of blueschist onto Karakaya complex units took place probably during the Paleocene continent-continent collision. Main blueschist belt is located to the south of klippe which indicates a northward vergence. This shows that back-thrusting occurred during continent-continent collision in the western Anatolia.