Step-over fault zones controlling geothermal fluid-flow and travertine formation (Denizli Basin, Turkey)

• Published in: Geothermics 2021-01, Vol.89, p.101941, Article 101941
• Main Authors: Brogi, Andrea, Alçiçek, M. Cihat, Liotta, Domenico, Capezzuoli, Enrico, Zucchi, Martina, Matera, Paola Francesca
• Format: Article
• Language: English
• Subjects: Banded Ca-carbonate veins; Dismantling; Extensional tectonics; Fault lines; Fluid dynamics; Fluid flow; Fractures; Geological faults; Geothermal power; Geothermal resources; Geothermal systems; Hydrothermal systems; Kinematics; Localization; Permeability; Pleistocene; Regional development; Relay zones; Slip; Stretching; Tectonics; Travertine; Veins (geology); Western Anatolia
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/j.geothermics.2020.101941

[Display omitted] •We document a permeable step-over zone in a normal fault setting.•Meters-thick (6,5 m) banded Ca-carbonate veins filled the fractures in the step-over zone.•We describe the root of an hydrothermal system feeding travertine deposits.•Fissure ridge-type travertine deposits are related to the step-over zone. In the Honalilar area (Denizli Basin, Turkey), the occurrence of banded Ca-carbonate veins and travertine deposits, represented by a dismantled fissure ridge-type depositional system, are the evidence of a middle-late Pleistocene exhumed, shallow, hydrothermal system. Their occurrence offers the best opportunity to: (i) reconstruct the fluid paths from the underground to the palaeo-surface, and (ii) analyse the role of fault zones in controlling the permeability and fluids circulation. Permeability developed in overstepping regional scale normal faults, with a slight left-lateral oblique-slip component. At the surface, faults favored the localization and development of a fissure ridge-type travertine deposit. At depth, the root of the hydrothermal system consists of W-E oriented fractures filled of up to 6.5 m thick Ca-carbonate veins, developed in a high dilatation zone. It corresponds to the step-over determined by the oblique-slip kinematics of the NW-striking main faults. The high dilatation step-over zone contrasted the progressive sealing induced by the concomitant Ca-carbonate deposition within the fractures, thus favoring permeability maintenance and fluids circulation for at least 200 ka. This evidence adds key inputs for predicting permeable volumes during geothermal exploration in areas affected by extensional tectonics. The main NW-oriented faults remained active even after the hydrothermal fluid flow, causing the dismantlement and progressive exhumation of the upper part of the hydrothermal system.