Neogene ignimbrites of the Nevsehir plateau


In Anatolia (Turkey), extensive calc-alkaline volcanism has developed along discontinuous provinces from Neogene to Quaternary times as a consequence of plate convergence and continental collision. In the Nevşehir plateau, which is located in the Central Anatolian Volcanic Province, volcanism consists of numerous monogenetic centres, several large stratovolcanoes and an extensive, mainly Neogene, rhyolitic ignimbrite field. Vent and caldera locations for the Neogene ignimbrites were not well known based on previous studies. In the Neogene ignimbrite sequence of the Nevşehir plateau, we have identified an old group of ignimbrites (Kavak ignimbrites) followed by five major ignimbrite units (Zelve, Sarımaden Tepe, Cemilköy, Gördeles, Kizilkaya) and two smaller, less extensive ones (Tahar, Sofular). Other ignimbrite units at the margin of the plateau occur as outliers of larger ignimbrites whose main distributions are beyond the plateau. Excellent exposure and physical continuity of the units over large areas have allowed establishment of the stratigraphic succession of the ignimbrites as, from bottom to top: Kavak, Zelve, Sarımaden Tepe, Cemilköy, Tahar, Gördeles, Sofular, Kizilkaya. Our stratigraphic scheme refines previous ones by the identification of the Zelve ignimbrite and the correlation of the previously defined "Akköy" ignimbrite with the Sarımaden Tepe ignimbrite. Correlations of distant ignimbrite remnants have been achieved by using a combination a field criteria:

  1. sedimentological characterisitics;
  2. phenocryst assemblage;
  3. pumice vesiculation texture;
  4. presence and characteristics of associated plinian fallout deposits; and
  5. lithic types.

The correlations significantly enlarge the estimates of the original extent and volume of most ignimbrites: volumes range between 80 km (super 3) and 300 km (super 3) for the major ignimbrites, corresponding to 2500-10.000 km (super 2) in areal extent. The major ignimbrites of the Nevşehir plateau have an inferred source area in the Derinkuyu tectonic basin which extends mainly between Nevşehir and the Melendiz Dağı volcanic complex. The Kavak ignimbrites and the Zelve ignimbrite have inferred sources located between Nevşehir and Derinkuyu, coincident with a negative gravity anomaly. The younger ignimbrites (Sarımaden Tepe, Cemilköy, Gördeles, Kizilkaya) have inferred sources clustered to the south between the Erdaş Dağı and the Melendiz Dağı volcanic complex. We found evidence of collapse structures on the northern and southern flanks of the Erdaş Dağı volcanic massif, and of a large updoming structure in the Şahinkalesi Tepesi massif. The present-day Derinkuyu tectonic basin is mostly covered with Quaternary sediments and volcanics. The fault system which bounds the basin to the east provides evidence that the ignimbrite volcanism and inferred caldera formation took place in a locally extensional environment while the basin was already subsiding. Drilling and geophysical prospecting are necessary to decipher in detail the presently unknown internal structure of the basin and the inferred, probably coalesced or nested, calderas within it.

Le-Pennec-J-L; Bourdier-J-L; Froger-J-L; Temel-A; Camus-G; Gourgaud-A
Universite Blaise Pascal, OPGC (Centre de Recherche Volcanologique), Clermont-Ferrand, France
Journal of Volcanology and Geothermal Research. 63; 1-2, Pages 59-87. 1994
GeoRef, Copyright 1998, American Geological Institute.
Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
Refs: 33; illus. incl. 3 tables, geol. sketch maps
Elsevier. Amsterdam, Netherlands. 1994