Resumen
Lago Yehuin, a WNW-ESE elongated basin located in the outer fold-and-thrust belt of the Fuegian Andes, occupies a compartmented structural depression originated along a segment of the left-lateral Lago Deseado fault system. This paper describes the first geophysical survey performed within the lake. New acquired high-resolution single-channel seismic data, integrated with geological information in the surroundings of the Lago Yehuin, allowed to: (i) produce a complete bathymetric map of the lake, (ii) reconstruct the basement surface of the lake, and (iii) analyze the geometry, distribution, and thickness of the sedimentary infill. Two sub-basins were recognized within Lago Yehuin: A western sub-basin, 7.5 km long, with a maximum depth of 118 m; an eastern sub-basin, 7.2 km long with a maximum depth of 80 m. Both sub-basins are limited by a set of normal faults which overprint NE-verging thrusts. Three seismo-stratigraphic units have been identified in the seismic records: (1) a lower unit with wedged geometry interpreted as a mass flow deposits; (2) a thick (up to 120 m) intermediate unit of glacio-lacustrine nature and irregularly distributed in the Yehuin basin; (3) a thin (generally <10 m) upper lacustrine unit which drapes the entire basin. Lago Yehuin is considered a Neogene basin generated by strike-slip tectonics that was later affected by glacial and glacio-lacustrine deposition. Interpreted submerged ridge moraines within Lago Yehuin are correlated with onland moraine arcs built by the complete recessional paths of Fuego and Ewan ice lobes. A significant structural control is proposed not only for the formation of Lago Yehuin, but also for the general paths of the northern arms of the Fagnano palaeo-glacier.