Extrusive Members of Postcollisional A-Type Magmatism in Central Anatolia: Karahidir Volcanics, Idis Dagi-Avanos Area, Turkey

Abstract

The Idis Dagi Igneous Complex is one of a number of late-stage plutonic bodies within the Central Anatolian Crystalline Complex. It intrudes Paleozoic-Mesozoic metamorphic basement rocks and Late Cretaceous granitoids. The complex comprises mainly quartz syenites and alkali-feldspar quartz syenites known as the Idis Dagi Syenitoids. Trachydacitic, trachyandesitic, and dacitic rocks (Karahidir Volcanics) have been recently found as dikes cutting the Idis Dagi Syenitoids or as huge blocks within an olistostromal unit of latest Cretaceous(?)-Early Paleocene age that immediately overlies the Idis Dagi Igneous Complex. Petrographic and geochemical data indicate that the Idis Dagi Syenitoids and the Karahidir Volcanics display similar humped patterns on chondrite- and MORB-normalized spider diagrams, with peaks at Rb, Th, and Ce, and also negative Nb anomalies. These features are similar to patterns considered typical of postcollisional, A-type igneous rocks. A postcollisional setting is also suggested by the distribution of data on tectonic discrimination diagrams involving Nb, Y, and Rb. As a whole, the geochemical data suggest that the Idis Dagi Syenitoids and Karahidir Volcanics are cogenetic. Thus, the Karahidir Volcanics represent the shallow intrusive and volcanic equivalents of the deeper-level Idis Dagi Syenitoids. The syenitoid rocks are considered the final phase of the magmatism in the Central Anatolian Crystalline Complex and are classified as post-orogenic alkaline rocks. Their chemical features suggest a largely mantle-derived magma contribution, together with a noticeable crustal component in their genesis. They were formed during postcollisional uplift that followed crustal thickening related to the southward emplacement of ophiolitic nappes during closure of the Izmir-Ankara-Erzincan Oceanic strand of Neotethys. The Karahidir Volcanics were exposed during regional extension that resulted in the formation of latest Cretaceous(?)-Early Paleocene extensional basins, and were emplaced as huge blocks into the continental clastic rocks by gravity sliding. This extension phase is characteristic of the development of all the other latest Cretaceous-Early Tertiary intracratonic basins in central Anatolia.