Authors: SABAH YILMAZ ŞAHİN, DURMUŞ BOZTUĞ
Abstract: Central Anatolia typically represents well-preserved geological features of a collision zone. This collision zone is characterized by some geological events occurred in the Anatolide passive margin of the Anatolide-Pontide collision along the Ankara Erzincan suture zone. This suture zone is commonly known to be formed by the pre-Maastrichtian northward subduction of the northern branch of Neo-Tethys beneath the Pontides which was constituting the southernmost tip of Eurasiain plate at that time. These geological occurrences are inverted metamorphism; ophiolitic slabs derived from main suture zone; syn-collisional and S/C ST type magmatism; post-collisional, high-K calcalkaline, hybrid and I/H LO type magmatism; post-collisional, within-plate, A-type alkaline magmatism; and post-collisional Central Anatolian basins. Among these geological occurrences, the ophiolitic slabs derived from Ankara-Erzincan suture zone; post-collisional, high-K calcalkaline, hybrid I/H LO type magmatism; and post-collisional, within-plate, A-type alkaline magmatism are observed as a good association in space and time in the Çiçekdağ region in Central Anatolia. The ophiolitic slab, named as Central Anatolian ophiolite, is composed of two mapable units which are called Çökelik volcanics and Akçakent gabbro. There are some gabbroic intrusions within the Çökelik volcanics in some localities, however, the major boundary between these two units is a thrust fault along which the Akçakent gabbro thrusted onto the Çökelik volcanics from east to west. The rocks of Akçakent gabbro possess a preserved ophitic texture and mineralogical composition which can lead one to call them uralite-gabbro. Some major and trace element geochemical data determine a depleted mantle and low-K tholeiitic characteristics in composition. The Halaçli monzogranite, characterizing the post-collisional, high-K calcalkaline, hybrid I/H LO type magmatism, intrudes the Central Anatolian Ophiolite by forming some contact metamorphic hornfelses derived particularly from the Çökelik volcanics. The phaneritic-porphyritic texture is a recognizing feature in the rocks of Halaçli monzogranite due particularly to existence of common K-feldspar megacrysts. The major rock forming minerals are composed of quartz+K-feldspar + plagioclase (An 32-44 )+hornblende + augite +biotite association. The Egrialan syenite, part of post-collisional, within-plate, A-type alkaline magmatism, is seen to intrude both of the Central Anatolian Ophiolite and Halaçli monzogranite. The rocks of this syenitic body can be subdivided into medium to coarse-grained and medium-grained rocks on the basis of texture. The major rock forming minerals consist of orthoclase+plagioclase(An 32-40 ) ± nepheline + riebekite / arfvedsonite+aegirine+biotite±melanite garnet; as for the accessory constituents they are composed of sphene+apatite+xenotime+monazite+allanite+zircon+fluorite minerals. The Egrialan syenite includes some fluorite mineralizations within the syenitic body itself, and also at the contact with gabbros.
Keywords: Çiçekdağ igneous complex, high-K calcalkaline, alkaline magmatism, Central Anatolian ophiolite, igneous petrogenesis, collision zone magmatism.
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