Diagenesis and very low-grade metamorphism of the Antalya unit: Mineralogical evidence of Triassic rifting, Alanya-Gazipaşa, central Taurus belt, Turkey

Abstract

The Paleozoic-Lower Mesozoic formations of the Antalya Unit in southern Turkey comprise diagenetic sediments, shale, mudstone, shale, siltstone, sandstone and scarce spiculite, together with very low-grade metamorphic lithologies, slate, metamudstone, metasiltstone, metasandstone and metalimestone. These diagenetic and metamorphic lithologies are dominant in the northern (Demirtaş-Alanya) and southern (Gazipaşa) parts of the unit, respectively. The main minerals of the meta-sedimentary rocks are phyllosilicates (2M1+1Md+1M illite, Ia chlorite, C-V, C-S, I-S), quartz, plagioclase, calcite and dolomite. The Cambrian-Cretaceous units of the Antalya Unit differ from the Devonian-Cretaceous northern Bolkardagi and Aladag units with respect to age, lithology and phyllosilicate assemblage, but show a considerable similarity to the metamorphic Permian-Triassic Mahmutlar Nappe of the Alanya Unit in their phyllosilicate paragenesis. Although the Antalya and Precambrian-Tertiary Geyikdagi units seem to have similar lithologies and phyllosilicate associations, there are some distinct mineralogical differences, such as phyllosilicate polytypes and degree of diagenetic/metamorphic alteration. Ophiolitic fragments, olistostromal lithologies, phyllosilicate parageneses, illite polytype variations, anchi-epimetamorphic illite crystallinity, and relatively low b values suggest that the Paleozoic-Lower Mesozoic parts of the Antalya Unit were metamorphosed in anticlockwise P-T-t paths in a rifting-associated extensional basin. The grade of diagenetic/metamorphic alteration increases from north to south in the Antalya Unit, related to the higher heat flow due to the southward deepening of the basin. Vertical diagenetic/metamorphic inversion between the Lower Paleozoic and Triassic units is related to higher the heat flux, which affected the Triassic sediments, rather than to thrust tectonics. © 2004 Elsevier Ltd. All rights reserved.