Evolución del relieve de un frente montañoso y respuesta del sistema erosivo fluvial ante el forzamiento causado por la actividad tectónica (Andes centrales, provincia de San Juan, Argentina)

Abstract

In the eastern piedmont of the Central Precordillera, in central western Argentina, relief is subject to recurrent Quaternary tectonic activity, which impacts the fluvial system. The goal of the present study is to analyze the relief evolution of a mountain front and to understand how the erosive river system responds to tectonic forcing, using geomorphology and morphometric indices. The analyzed indices are: Stream Length-gradient (SL), Strahler Integral, and Asymmetry Indices (F). These indices were applied to three sectors of the northeastern piedmont of cerro Zonda , one before the escarpment system, another one between escarpments, and a third one in the post-escarpment sector. Longitudinal profiles were analyzed for seven streams that are part of this piedmont basin. Image analysis and fieldwork allowed proposing a morphometric index, called Exposure Index, which results from the existing quotient between areas of exposed Miocene outcrops and areas of Quaternary cover (EI).

Results of the indices (SL, EI) indicate that the fluvial power of water flows in the headwall block is twice that in the footwall block, differences that arise when channels cross the escarpments from west to east. The post-seismic piedmont relief evolved differentially on both sides of the escarpment system. In the headwall block, the Miocene basement was uplifted, exhumed and eroded, whereas there are no geomorphic markers in the footwall block. Tectonic deformation occurred in the Zonda valley during the Quaternary, causing regional tilting to the north, with the main watercourses turning 45° north. The system of the northern Zonda mountain front is not in balance because of neotectonic activity.