GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 135 The best exposure of the LCDF is a a low-angle east-dipping plane (15°-30°) cropping out along the eastern slope of Serra la Limpida (Lao valley, Fig. 2a) referred to as the Gada- Ciagola LANF (GCL). There, it puts in contact the ligurian unit (topmost allochthon unit of the southern Apennines) on the Triassic dolostones of the Verbicaro unit (placed some km below, in the tectonic pile). Some spectacular mirrors of the GCL, on which we performed a detailed structural analysis, display normal, dip-slip kinematics. Conservative assessment of its associate displacement provide a value of ~ 2 km (Fig. 2b). On these same outcrops it was possible to define the relative temporal sequence of the observed faulting-related brittle structures. They show an articulated deformation history ended with the progressive flattening and doming of the original fault plane, due to exhumation processes. Moreover, fieldwork highlighted that the GCL is the westernmost structure belonging to a set of synthetic sub-parallel normal faults whose dip-angles increases from west to east (Fig. 2b), whereas their associated offset decreases eastward. The aforesaid geometrical pattern is compatible with a tectonic model in which the whole fault set branches from a common east- dipping detachment surface (LCDF) gently dipping toward east and whose break-away zone coincides with the GCL itself. The distribution of the seismicity recorded during the 2010-2014, “Pollino” seismic sequence, as shown by Brozzetti et al. (2017a) provides an indirect confirmation of our reconstruction. A geologically-constrained estimate of the cumulative displacement, occurred on the LCDF and on its major synthetic splays, gives a value of nearly 3300 m. This value results considerably higher than the offset associated to the antithetic, west-dipping, faults along a regional section extending eastward to the Mt Pollino ridge (Fig. 2b). Fig. 2 - Detailed geological map (a) in a 2 km-wide strip centered in the section trace A-B and its interpretative section (b). Stratigraphy of the three major superimposed units (Ligurian allochthon = LGU, Verbicaro = Ve and Pollino = Po units) are reconstructed through literature data integrated with original surveys; key: T1 = Middle-Late Triassic; T2 = Late Triassic; J = Jurassic; K = Cretaceous; Pg = Paleogene; Mc = Miocene. SFL = “Scisti del Fiume Lao Fm”; thick red and blues lines = east- and west-dipping Quaternary normal faults; thin grey dashed line = pre-existing thrust structure.