Reconstructing the stratigraphy and structure of the Alaşehir Graben (Western Anatolia): Evidence for a high-angle origin of the Alaşehir detachment fault and layer-parallel shortening during the Miocene time

Abstract

Western Anatolia is a well-known continental extension province in the world. The most distinctive structural elements of the region are E-W trending grabens. The Alaşehir Graben forms the boundary between the northern and central parts of the Menderes Massif. It trends E-W from Ahmetli to Turgutlu and NW-SE from Salihli to Alaşehir. This paper documents the outcomes of fieldwork along the southern margin of the Alaşehir Graben between the Salihli and Alaşehir areas. The tectonostratigraphy of the southern margin of the Alaşehir Graben is divided into the footwall and hanging wall of the Alaşehir detachment fault. The footwall comprises the Bayındır and Bozdağ Nappes and the syn-extensional Salihli granitoid intruding the Bayındır Nappe. The hanging wall consists of the Çine Nappe and Neogene-Quaternary sedimentary rocks, and Miocene fills tectonically overlying the Çine Nappe, which is above the Alaşehir detachment fault in the Alaşehir area. Structural data show three types of master fault sets, including (i) the low-angle Alaşehir detachment fault, which is composed of cataclastic rocks; (ii) low-angle normal faults, which are devoid of any cataclastic rocks; and (iii) Plio-Quaternary high-angle normal faults cutting them. Two different low-angle normal faults were coeval and active during the Miocene, and low-angle normal faults were synthetic and antithetic faults of the Alaşehir detachment fault. Their initial position was high-angle and the original position had 55°-75° dip during the Miocene. In the Salihli and Alaşehir segments, several major fold geometries are defined in the footwall and hanging wall of the Alaşehir detachment fault. The fold axis is NE-trending and plunges mainly northeast in the Salihli segment in the footwall of the Alaşehir detachment fault. The other is ~ E–W-trending and plunges mainly west in the Alaşehir segment in the footwall and hanging wall of the Alaşehir detachment fault. They are associated with extensional structures formed by layer-parallel shortening during the Miocene. The Alaşehir detachment fault, as indicated by the difference in fold axes between the Salihli and Alaşehir segments, was cut and back-rotated by Plio-Quaternary high-angle normal faults and tilted to the south.