GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 5 THE IONIAN BATTLEFIELD: THE (TOO) MANY FAULTS OF A “LAZY” SUBDUCTION ZONE A. Argnani CNR, ISMAR-Bologna, Italy 1. Rationale. The Ionian sea and its margins have attracted a great deal of interest from various research groups in the last ten years or so. In spite of this effort the tectonic complexity of this vast region, and the difficulty to acquire good quality data, still hamper a full understanding of the tectonic evolution, and of the active tectonics in particular. The progressive south-eastward migration of the Calabrian Arc during the opening of the Tyrrhenian basin was likely related to large-scale tears in the subducted lithosphere (e.g., Wortel and Spakman, 2000; Argnani, 2009; Argnani et al. , 2016), making this area a relevant case study for this kind of tectonic process (STEP Fault; Govers and Wortel, 2005). Following up from this idea a school of thought has emphasized the role of lithospheric tears in shaping the present CalabrianArc accretionary wedge, with the aim of characterizing its active tectonics and seismicity (Fig. 1). I argue that in this approach the role of lithospheric tears has been sometimes overemphasized, and in some instances, data and literature have been used in a selective way. Whereas hypothesis-driven interpretations can be acceptable when data are scanty, the selective use of data and literature have lead to contrasting interpretations, often driven by pre-defined conclusions, which in many instances are litlle or not supported by evidence. Fig. 1 - Simplified tectonic map of the western Ionian region, showing the main structural features that are encountered in the literature. The structures in red are from Argnani (2014), those in black are from Gutscher et al. (2017). The inferred location of the continent-ocean boundary in the southern Ionian Sea (light orange), the region supposed to undergo transtension (gray pattern), and a large field of serpentinite diapirs (orange spots) are also indicated (after Polonia et al. , 2017). The gray line is one of the refraction profiles in Dellong et al. (2108), with the segment of thinned continental crust indicated in bold. The bluish bands in NE Sicily indicate inferred locations of lithospheric tears. The structures are superimposed on the morpho-bathymetry of Gutscher et al. (2017).