Geología del Mesozoico en Bahía Ensenada, Tierra del Fuego.

E. B. OLIVERO; R. D. ACEVEDO; D. R. MARTINIONI

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 1997 vol. 52 p. 169 - 179

0004-4822

GEOLOGY OF THE MESOZOIC OF BAHÍA ENSENADA, TIERRA DEL FUEGO. - ABSTRACT: The small area surrounding Bahía Ensenada is critical for the geological and structural understanding of the Andes Fueguinos. The accompanying 1:20.000 map shows the following units. 1.- Strongly cleaved, polyphase deformed fine-grained Quartz-sericite-garnet-schists that could be part of the basement or of the Lemaire (Tobífera) Formation. 2.- Quartz porphyries associated with acidic breccias and tuffs; tuffaceous turbidites; cherts; slates; and tuffaceous schists. Similar facies associations are typical for the Tobífera Formation in the adjacent Chilean area. Bedding is only preserved in the coarser rocks and a careful survey demonstrates that the beds are folded in overturned, E-SE plunging folds. 3.- Rhythmically interbedded black slates; silty sandstones; limestones; and light-coloured tuffaceous rocks. The succession, assigned to the Yahgan Formation, is folded in asymmetrical, north vergent folds with well developed axial plane cleavage. 4.- Massive to schistose subvolcanic and volcanic rocks similar to basaltic spilites. The original assemblage of plagioclase-clinopyroxene is altered to actinolite-amphibolite facies. At one locality the melanocratic rocks cross-cut tuffaceous schists of the Lemaire Formation. The Lemaire Formation and the associated melanocratic rocks were up-thrusted against the Yahgan Formation. The north-vergent thrusts parallel the lithological boundaries and coincide with major NW-SE lineaments. In the nearby Chilean area these lineaments are continuous with a major, north-vergent fault that uplifts the basement against rocks similar to the Yahgan Formation.