Seismic cycles recorded in late Quaternary calcite veins: Geochronological, geochemical and microstructural evidence I. Tonguç Uysal a, ⁎, Yue-xing Feng b , Jian-xin Zhao b , Robert Bolhar b , Veysel Işik c , Kim A. Baublys d , Anya Yago b , Suzanne D. Golding d a Queensland Geothermal Energy Centre of Excellence, The University of Queensland, Queensland 4072, Australia b Radiogenic Isotope Facility, Centre for Microscopy and Microanalysis, The University of Queensland, Queensland 4072, Australia c Ankara University, Faculty of Engineering, Department of Geological Engineering, Tectonics Research Group, TR-06100 Ankara, Turkey d School of Earth Sciences, The University of Queensland, Queensland 4072, Australia abstract article info Article history: Received 8 February 2010 Received in revised form 13 December 2010 Accepted 18 December 2010 Available online 2 February 2011 Editor: R.D. van der Hilst Keywords: active tectonism CO 2 geochronology Quaternary Turkey vein Southwest Turkey is seismically active as a result of the Hellenic subduction process in the Eastern Mediterranean. We conducted high-resolution micro-sampling, high-precision U-series dating and micro- chemical analysis on an extensional vein system in a tectonically active but non-hydrothermal area. U/Th age data and microscopic observations provide evidence of repeated fracturing of a previously sealed crack system followed by a new increment of veining. Repeated injection of veinlets suggests that the vein system was formed by the crack-seal mechanism. Four major U/Th age groups for the emplacement of the vein system fall between 23.9 ± 0.2 ka and 23.2 ± 0.4 ka, 21.7 ± 0.4 ka and 19.2 ± 0.2 ka, 17.3 ± 0.1 ka and 16.2 ± 0.3 ka, and at 11.8 ± 0.2 ka. Stable and Sr isotope geochemistry of the calcite vein samples indicates that surface water interacting with the soil cover was the major component of the groundwater system from which the extensional veins precipitated. Trace element and O isotope data of the vein system are interpreted to reflect carbonate precipitation associated with seismic cycles involving fluids with different trace element compositions and CO 2 contents. Initial carbonate precipitation during a single seismic cycle occurred from CO 2 -dominated fluids that were degassed from the original CO 2 –water mixture. This was followed consecutively by carbonate precipitation from the remaining water, which was relatively impure with higher trace element contents. Millimetre to submillimetre-scale U-series dating in conjunction with geochemistry of carbonate veins related to active tectonism offers an innovative means of constraining the absolute timing of late Quaternary seismic and inter-seismic events. © 2010 Elsevier B.V. All rights reserved. 1. Introduction It has been widely recognised that vein formation in tectonically active regions is linked with fluid pressure cycling and fault reactivation (e.g., Ramsay, 1980; Sibson, 1981, 1987). High pressure fluids play an important role in faulting and vein formation (Cox, 2007; Sibson, 1996). These fluids reduce the effective shear stress that allows slip on faults and gives rise to generation and propagation of breccia and fracture networks. High-pressure fluids trapped within active fault systems are released intermittently through fault rupture that is followed by rapid sealing through mineral precipitation. Mineral precipitation as fracture and breccia filling is attributed to sudden pressure drops and fluid unmixing immediately after earthquake induced rupture (Robert et al., 1995). The development of veins is associated with the circulation of fluids in rocks, both for transport of material and for propagation and opening of the vein (Nuriel et al., 2011; Passchier and Trouw, 1996). Thus vein systems in actively deforming regions bear important records of multiple episodes of fault reactivation manifested by crack-seal extension veins (cf. Ramsay, 1980). In this context, microchemical analyses on millimetre- to submillimetre-thick quartz and carbonate crack-seal veins provide information about vein growth history and vein-forming fluids (Barker et al., 2006; Kirschner et al., 1993; Lee et al., 1997; and Rye and Bradbury, 1988). These studies concluded that crack-seal increments occur in a discontinuous flow regime as a result of multiple pulses of chemically distinct external fluids. Precise dating of the crack-seal process is of special importance to our understanding of the complex interplay between seismic event cycles and fluid flow events. However, crack-seal vein growth of pre- Quaternary systems that were investigated by previous studies could not be dated precisely because of the limitations of relatively old quartz and carbonate minerals for radiometric dating techniques. Conversely, carbonate veins related to late Quaternary active faulting Earth and Planetary Science Letters 303 (2011) 84–96 ⁎ Corresponding author. E-mail address: t.uysal@uq.edu.au (I.T. Uysal). 0012-821X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2010.12.039 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl