INFLUENCE OF THE STRUCTURAL GEOMETRY ON THE STREAM NETWORK IN

ABASCAL, L.; GONZÁLEZ BONORINO, G; RICARDO MON; ANTONIO GUTIERREZ

Congreso; 22nd LAK 2011; 2011

The Lerma Valley is an intramontane structural depression within the Central Andes in northwestern Argentina. The Lerma Valley initiated its formation in relation to Tertiary crustal shortening along the Andes. The studied area is located in the Eastern Cordillera, linked to blockfaulted uplifts underlain by moderately to highly indurated metasedimentary and sedimentary rocks (Turner and Mon, 1979). The highest topographic elevations occur in the Lesser and Obispo Ranges along the west with 4200 m a.s.l. The Lerma Valley is limited in the north by Vaqueros Range (1900 m), and to the east by the Mojotoro (1900 m) and Castillejo (1600 m) ranges. The Obispo, Lesser and Mojotoro ranges are dominantly underlain by Precambrian-lower Paleozoic basement rocks. Southward, this substrate dips beneath Mesozoic-Cenozoic sedimentary strata in the Castillejo Range and southern Obispo Range. In the north, the Vaqueros Range interposes a wedge of Cenozoic strata of the Pliocene-Pleistoce Piquete Formation. During the Quaternary, the Lerma basin had a particular evolution. In the Pleistocene this basin became landlocked to the east by the elevation of the Mojotoro and Castillejo ranges. An endorheic fluvial network delivered sediments to an internal basin characterised by lacustrine deposition. The tectonic deformation in the region has been suggested to play a relevant role in theposition. The tectonic deformation in the region has been suggested to play a relevant role in the configuration and evolution of the drainage. It is our purpose to show that drainage basin evolution and geometry, and structural development have affected each other. The courses of the rivers have been forced to migrate to a position at, or near its presenttion and geometry, and structural development have affected each other. The courses of the rivers have been forced to migrate to a position at, or near its present eastward courses, flowing across the future site of the Mojotoro Range. In northern Lerma Valley, four wind gaps cross the Mojotoro Range indicating incision into the emerging topographic barrier; visual analysis supports correlation of river courses west of the Mojotoro Range with the wind gaps. The Mojotoro water gap may have persisted due to the effect of the Mojotoro transverse fault in decreasing the resistance to erosion of the substrate by the time Medeiros terracesley, four wind gaps cross the Mojotoro Range indicating incision into the emerging topographic barrier; visual analysis supports correlation of river courses west of the Mojotoro Range with the wind gaps. The Mojotoro water gap may have persisted due to the effect of the Mojotoro transverse fault in decreasing the resistance to erosion of the substrate by the time Medeiros terraces developed underlain the Vaqueros anticline influence. In southern Lerma Valley, the Juramento River issues from the Lerma Valley along synclinal and fault-related lows. The ancient Juramento River outlet developed as a subsequent stream.