GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 flatirons at the base of the ridge just NE of Tirana (Fig. 2). West of Kruja, the shortening associated to the first buried thrust has originated the NW-SE trending Makaresh anticline, whose growth is shown by disruption of the hydrographic network, including small endorheic basins on its eastern flank. West of it, another smaller anticline is the surficial expression of the Fushë-Kruja thrust (Velaj 2011). Its recent growth has originated a kind of hummocky morphology, possibly suggestive of a slowing down of the folding process here. The course of the Ishëm River is determined by Holocene activity of the main tectonic structures. Notably, its right-side tributaries show a bend from ca. E-W to SE-NW due to the barrier effect created by the uplift of the Vora ridge and the concurrent subsidence of its footwall in the Tirana syncline (Fig. 2). The western side of the Ishëm river plain is bordered by the NW-SE striking Vora ridge, whose uplift results from the NE-vergent Vora backthrust, passively pushed up by the activity of the buried Kruja thrust system. The Vora backthrust runs for about 25 km with a rather continuous, rectilinear and steep scarp, despite the soft clastic lithologies (Fig. 2). The ridge top represents the uplifted and tilted paleosurface of the hangingwall of the thrust separating the Tirana-Thumana syncline from the coastal Shijak syncline. Quaternary and ongoing rise of the ridge is documented by the abandoned valley that today hosts the SH2 highway from Tirana to Durrës. Excavated in the Pleistocene first by the Terkuza River and later by the Tirana River, that joined the Erzen River near Sukth (Fig. 2), this valley was left almost dry by the flow diversion towards the Ishëm River. The valley from Yzberisht to SW of Vogel, across the Yzberisht ridge, is another major abandoned valley (windgap) used before by the Tirana and Lana Rivers to flow SW into what is now the lower Erzen River. Thus, both Vora and Yzberisht valleys once provided direct outflow to the sea for the rivers from the Dajti ridge. The still active high rate of tectonic uplift is possibly confirmed by reverse faulting/folding downthrowing recent alluvial deposits with a step of 8-9 meters in the SW outskirts of Tirana. In the sector south of the Tirana plain, there is morphotectonics evidence of the migration toward NE of the river courses emphasizing the direct relationship with the growing of the Vora ridge. Another evidence of the Vora backthrust activity is the westward diversion of the N-S Peza River (A in Fig. 2) carved into the uplifting front of the thrust. In addition, the rise of the Shijak thrust pushes the flow of the Erzen River along the eastern flank of the Shijak syncline, with a rather sharp deviation at Pejze (B in Fig. 2). Nearby, a narrow incision without active drainage is carved across the whole small anticline growing on the hangingwall of the Shijak thrust. Moreover, the growth of the anticline dams the Erzen River forcing its deviation from NE-SW to NW-SE downstream of the confluence of the Peza river (near A in Fig. 2). In addition, a splay of the Shijak thrust could cause the uplift of a few aligned hills that control the northeastern migration of the Erzen River avoiding the predictable capture by the near Juba River (C in Fig. 2).