Erhan Akay

Geology of the Yozgat Region and Evolution of the Collisional Cankiri Basin

The Cankiri Basin evolved as a detrital basin during the Late Tertiary in Central Anatolia between the Pontides (Sakarya continent) and the Kirsehir block. It is E-W trending, and along its southern border it overlies the Kirsehir block unconformably. The Kirsehir block consists of two tectonic belts. Structurally, the lower unit is the Kirsehir Massif, consisting of a platform sequence and a marble association; the upper unit is the Cicekdag belt. The Cicekdag belt consists of thick mafic volcaniclastic rocks and interbedded sediments and rare gabbro masses. This belt probably was developed as a primitive island-arc in the Neotethys ocean. During the Late Cretaceous period, the Cicekdag belt was thrust southward onto the Kirsehir platform. Consequently, the overburden of the nappes caused metamorphism of the Kirsehir platform and the lower parts of the Cicekdag belt. The Yozgat magmatics, consisting of granitic plutons and dacitic rhyolitic lavas, intruded into the Kirsehir block, which was formed by the...

Early Miocene post-collisional magmatism in NW Turkey: geochemical and geochronological constraints

The Alaçam region of NW Turkey lies within the Alpine collision zone between the Sakarya continent and the Menderes platform. Four different tectonic zones of these two continents form imbricated nappe packages (including the Afyon zone), intruded by the Alaçam granite. Newly determined U-Pb zircon ages of this granite are 20.0 ± 1.4 and 20.3 ± 3.3 Ma, indicating early Miocene emplacement. Rb-Sr biotite ages of the granite are 20.01 ± 0.20 and 20.17 ± 0.20 Ma, suggesting fast cooling at a shallow crustal level. Geochemical characteristics show that the Alaçam granite is similar to numerous EW-trending plutons in NW Anatolia. Gneissic granites of the Afyon tectonic zone were intruded by the Miocene Alaçam granite and have been interpreted in earlier studies as sheared parts of the Alaçam granite, which formed along a crustal-scale detachment zone under an extensional regime. We determined a U-Pb zircon age of 314.9 ± 2.7 Ma for a gneissic granite sample of the Afyon zone, demonstrating that these rocks are unrelated to the Miocene Alaçam granite. The early Miocene granitic plutons bear post-collisional geochemical features and are interpreted as products of Alpine-type magmatism along the Izmir–Ankara suture zone in NW Turkey, and seem to have no genetic relation to the detachment zone.

Formation of Subaqueous Felsic Domes and Accompanying Pyroclastic Deposits on the Foça Peninsula (Izmir, Turkey)

In western Anatolia, a thick volcanic succession of andesitic to rhyolitic lavas and volcaniclastic rocks crops out extensively. On Foça Peninsula, the westernmost part of the region, a dominantly rhyolitic sequence is exposed where massive rhyolites occur as dome or domelike stubby lava flows. These rhyolite domes vertically and laterally pass into blanketing volcaniclastic sequences. The gradational boundary relations and the facies characteristics of the surrounding volcaniclastic sequences indicate that the silicic domes directly intruded a subaqueous environment and were shattered upon sudden contact with water to form hyaloclastic blankets. In and around these rhyolite domes, we have defined six different volcanic and volcaniclastic facies, consisting of: (1) massive rhyolite; (2) massive perlite; (3) hyaloclastic breccias; (4) rhyolite pumice and lithic fragment-bearing volcaniclastic rocks; (5) subaqueous welded ignimbrites; and (6) brecciated perlite. The massive rhyolite facies have distinct structures from the centers to the peripheries of the domes and stubby lava flows. Massive lava facies gradually pass into hyaloclastic breccias and massive perlite facies, indicating water-magma interaction during the emplacement. Phreatomagmatic explosive activity and doming caused the subaqueous pyroclastic flows on the flanks of the volcanic center. Welding in the upper parts of these pyroclastic flow deposits indicates the high-temperature emplacement of the pyroclastic material and relatively slow cooling caused by the cushioning effect of the gas-vapor mixture and rapid deposition of younger pyroclastic units.