GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.1 191 Pleistocene (140 ka B.P.) lavas rests on the sands of the of the OIS 7 marine terrace (240-200 ka). The Holocene lava flows seem to conceal the structure. The vertical offset of the Middle Pleistocene lavas reaches about the 110 m. More to the east (see profile 4) the hanging wall of the ramp consists of a culmination of the lower portion of the marly clays succession that overthrust the top levels, containing the tholeiitic lavas. Surface data are insufficient to estimate the total vertical displacement of the structure. Discrete portions of the E-W oriented San Gregorio thrust are reactivated by dextral motion due to the accommodation of recent tectonic motions from a series of NW-SE oriented normal faults, affecting the southern flank of Mt. Etna. The reactivated segments show evidence of active motion, mostly due to aseismic creeping. Catania Old Town thrust. In the southern sector of the Catania town (Fig. 2), a N80, NNW- dipping thrust ramp was temporarily exposed in an excavation front of a quarry. The hanging wall of the thrust consists of an asymmetric anticline deformingMiddle Pleistocene sands. These levels ramp over the alluvial deposits referred to the 80 ka terrace (Monaco et al. , 2000) that show an almost horizontal attitude. The elevation of the base of the 80 ka conglomerates of the hanging wall suggests more than 10 m of vertical offset. More to the east, a geological section (1 in Fig. 3) based on several boreholes data, images the possible prolongation of the structure, just beneath downtown. The geometry of the ramp is partially obscured by the occurrence of a paleo-valley, which is infilled with lava flows and the associated alluvial deposits. The buried valley undercuts the terraced marine deposits of the OIS 3.3 (60 ka) (Monaco et al. , 2000) and it is deeply entrenched within the Middle Pleistocene marly clays substratum. The depth of the valley axis (36 m b.s.l.), corrected for the mean vertical uplift rate estimated in the Catania region at 1.2-1.3 mm/a (Monaco et al. , 2002), constrains the river incision at about 50 ky B.P., when the base level was 80 m below than the present one. This estimation is consistent with the presence of Plagioclase-rich lava flows within the valley, which are typical of the etnean activity between 56 to 15 ky B.P. (Volcano Ellittico; Branca et al. , 2011). On the two sides of the valley, a different attitude and elevation of the 60 ka-old marine terraced deposits (OIS 3.3; Monaco et al. , 2000) can be appreciated. In the southern flank of the valley, the marine terrace is gently dipping towards the south and the basal abrasion surface rests at an elevation of about 5 m a.s.l.. Across the valley, the basal surface of the marine terrace is vertically displaced for about 20 m and is markedly dipping to the north. Within the valley, a sharp discontinuity of the lava and alluvial horizons is compatible with the occurrence of a N-dipping ramp, coherent with the deformation of the morphological horizons on the two sides of the valley. The extension of the fault trace towards the Ionian coast is undetermined. The absence of any evidence of the thrust along the E-W oriented geological Profile 2 (Fig. 3) suggests to extend the ramp to the south of the trace of the geological section. Discussion and conclusions. The new geological data collected in the town of Catania provide precious information to identify Late Quaternary contractional tectonics. These consist in the continuation of the main Middle Pleistocene and Late Pleistocene tectonic features that are widely exposed to the south of the city. However the active tectonic picture deriving from the inversion of geodetic data (De Guidi et al. , 2015) and by seismic investigation (Gross et al. , 2016) shows a precise relation with the distribution of these tectonic features, along which impressive surface deformation is still now cumulating. References Branca, S., Coltelli, M., Groppelli, G., Lentini, F.; 2011: Geological map of Etna volcano, 1:50.000 scale . ��� �� It. J. Geosci. (Boll. Soc. Geol. It.), 130 (3), 265-291. doi: 10.3301/IJG.2011.15 Bousquet J.C., Lanzafame G. and Paquin C. ; 1988: Tectonic stresses and volcanism: in-situ stress measurements and neotectonic investigations in the Etna area (Italy) . Tectonophysics, 149 , 219-231. Catalano S., De Guidi G., Monaco C., Tortorici G. and Tortorici L.; 2008: Active faulting and seismicity along the Siculo-Calabrian rift zone . Tectonophysics, 453 , 177–192.