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Geological evolution of the gediz graben, sw turkey: temporal and spatial variation of the graben

Çiftçi, Bozkurt N
Gediz Graben is a continental extensional basin filled with Neogene sediments. Its margins are controlled by active ~EW-trending fault systems with major system, in terms of total offset and duration of activity, located along the southern margin. The graben evolved as a half graben by the activity of the southern margin during the entire Miocene. Then, the northern margin-bounding structure initiated by PlioQuaternary to form the current configuration of the graben with an inherited asymmetry. The southern margin-bounding fault system forms a graben-facing step-like pattern from the horst block (~2000 m) down to the graben floor (~200 m). The faults become younger towards the graben and the structural maturity decreases in the same direction. Fault plane data suggest ~NS-oriented regional crustal extension through the entire graben history with no evidence of temporal change in the regional extension direction. Minor spatial variations are attributed to poorly defined s3-axis or local stress field anomalies caused by fault interactions. Evolution of the Gediz Graben is a dynamic process as indicated by pronounced changes in the geometry and lateral extend of the southern margin-bounding structures along strike and dip directions. This also influenced the lithofacies, depositional pattern and thickness of the graben fill units. The western Anatolian extension is episodic with earlier (Miocene) and later (PlioQuaternary) phases of extension and intervening short phase of contraction (Late MioceneEarly Pliocene). Despite of this fact, evidence for the short-term intervening contractional phase throughout the Gediz Graben is scarce and there is local observation of folds and thrust/reverse faults affecting the Alaşehir formation. These structures suggest that the short-term phase of contraction might have existed but most probably been absorbed by the high rates of extension. This data may further imply that graben evolution from half-graben phase (Miocene configuration) to full graben phase (present day configuration) might be a discontinuous process accompanied by a short-time break in-between.