Episodic two-stage extensional evolutionary model for southwestern Anatolian graben–horst system: New field data from the Erdoğmuş-Yenigediz graben (Kütahya)

Abstract

The study area is the Erdoğmuş-Yenigediz graben, located along the western section of the Akşehir-Simav normal fault system in western Turkey. The Erdoğmuş-Yenigediz graben development commenced on the erosional surface of the northern Menderes Massif, under the control of several normal fault zones such as the Simav, Şaphane and Yelşilova fault zones during the late Early Miocene (Burdigalian). Later it gained its present-day configuration under the control of both older and younger normal faults. Three graben fills accumulated in the Erdoğmuş-Yenigediz graben. These are, from oldest to youngest, the Arıca formation of Burdigalian age; the Akdere formation of Late Miocene–Early Pliocene age; and the Erdoğmuş formation of Plio-Quaternary age. The first two fills are termed pre-modern graben fills, while the third one is named a modern (neotectonic) graben fill. The pre-modern graben fills are deformed (folded and reverse to strike-slip faulted) and overlain with an angular unconformity by the nearly flat-lying (non-deformed) modern graben fill. The Erdoğmuş-Yenigediz graben experienced three phases of deformation. These are, in turn, the first phase of extension (D1), the first phase of contraction (D2), and the second phase of extension or neotectonic extension (D3). D1 corresponds to the extensional exhumation mode of the Menderes Massif while D3 represents the rifting mode of the Southwest Anatolian graben–horst system (SWAGHS). These phases of deformation are evidenced by a series of reactivated older faults, folds, overturned contacts, reverse to strike-slip faults, angular unconformities, the young (neotectonic) normal faults (e.g., the Muratdağı, Dörtdeğirmen, Gümüşlü, and Yenigediz faults) and more than one overprinted sets of slip-lines recorded on both the boundary faults and in the graben fills. Analyses of slip-plane data and the folds reveal that the D1 and D2 deformation phases occurred in an approximately NW–SE direction, while the D3 deformation phase occurred in the NE–SW extension direction, confirmed by the fault plane solution diagram of the March 28, 1970 Gediz earthquake of Ms=7.2. These three phases of deformation strongly support the episodic two-stage extensional evolutionary history but precludes the uniform and continuous evolutionary model for the SWAGHS.