Diagenesis and low grade metamorphism of Karakaya complex units in the NW Anatolia [KB anadolu'daki Karakaya karmaşi{dotless}?i{dotless} birimlerinin diyajenezi-düşük dereceli metamorfizmasi{dotless}]

Abstract

The aim of this study is contribute to discussions concerning the formation of the Paleotethyan Permo-Triassic Karakaya Complex by revealing the diagenetic-metamorphic properties of the units within the Sakarya Composite Terrane in Northwestern Anatolia. The Nilüfer unit from the Lower Karakaya unit is represented by rocks of blueschist in the lower parts and greenschist facies in the upper parts. The Upper Karakaya unit has limestone blocks, made up of psammite, pelite and carbonate rocks associated with volcanics. In NW Anatolia, various mi- nerals have been determined, in order of abundance, as phyllosilicates (illite, chlorite, stilpnomelane, smectite, kaolinite, C-S, I-S, C-V), feldspar, calcite, quartz, dolomite, pyroxene (augite, Ti-augite), amphibole (hornblende, glaucophane, tremolite/actinolite, anthophyllite), hematite, epidote and goethite in the Lower Karakaya unit, and quartz, phyllosilicates (illite, chlorite, I-S, C-V, C-S, I-C, kaolinite, vermiculite, smectite), calcite, dolomite, feldspar, epidote, augite, hornblende, natrolite, hematite and goethite in the Upper Karakaya units. Trioctahedral chamozitic chlorites and phengitic dioctahedral illites have, respectively, IIb polytypes and 2M1+1M +1Md in the Nilüfer, Orhanlar and Çal units. Kübler index (KI) and Arkai index (AI) data correspond to low-grade anchizone and epizone for the Nilüfer Unit, high grade diagenesis for the Hodul Unit, high grade diagenesis and low grade anchizone for the Orhanlar Unit, and low grade diagenesis for the Çal Unit. The b0 values of illites show as moderate to high for the Lower Karakaya units, but mostly as a moderate pressure facies series for the Upper Karakaya units. According to the textural features, mineral associations, clay/phyllosilicate transformations, typical index minerals and crystallochemical data of phyllosilicates, the Lower Karakaya units were formed in high pressure/low temperature conditions in a compressional basin, whereas the Upper Karakaya units reflect the diagenetic/metamorphic characteristics of an extensional basin dominated by low heat flow.