Stacking of nappes with different pressure-temperature paths: An example from the menderes nappes of western Turkey

Abstract

Pressure-temperature (P-T) paths have been estimated from metapelitic rocks in the lowermost Çine nappe and the directly underlying Bozdaǧ nappe of the Anatolide belt in western Turkey. Peak-metamorphic conditions in the lowermost Çine nappe are 670° to 730°C/∼6.2 to 6.3 kb. Prograde garnet (grt I) growth occurred largely before and during the formation of the regional SPA foliation (the suffix 'PA' indicates a pre-Alpine age). Formation of a second garnet generation (grt II), which discordantly overgrew grt I, followed at 550° to 620°C/∼6.4 to 6.5 kb. Peak-metamorphic conditions in the underlying Bozdaǧ nappe vary from 480° to 540°C/6.1 to 7.6 kb at the base to 610° to 660°C/8.5 to 10.8 kb at the top of the nappe and attest to an inverted metamorphic field gradient in the Bozdaǧ nappe. Differential thermodynamic modelling (Gibbs method) yielded a prograde path for garnet growth during the formation of SPA. Because DPA structures formed during prograde metamorphism, we relate them to crustal shortening, which was associated with a top-to-the-north-northeast shear sense (in present-day coordinates). This event caused deformation of the Çine and Bozdaǧ nappes under different metamorphic conditions. We propose that the Çine nappe was heated by granitoid intrusions before being emplaced above a foreland unit. We speculate that the Bozdaǧ nappe belonged to the lower parts of this foreland unit. Cross-cutting relationships of DPA structures with dated granites indicates an age of ∼540 to 550 Ma for this tectonometamorphic event. The final juxtaposition of the Çine nappe and Bozdaǧ nappes and also the inversion of the metamorphic field gradient in the Bozdaǧ nappe occurred during greenschist-facies conditions during the Alpine orogeny in the Eocene.