Structure and evolution of the foreland thrust-fold belt of the Fuegian Andes, Tierra del Fuego, Argentina.

TORRES CARBONELL, PABLO J.; OLIVERO, EDUARDO B.; DIMIERI, LUIS V.

Mendoza

Congreso; Backbone of the Americas; 2006

Asociación Geológica Argentina y Geological Society of America

Field work in the frontal part of the foreland thrust and fold belt of the Fuegian Andes reveals complex relationships between stratigraphy and structure. An early-Eocene detachment propagated below Paleocene to earliest-Eocene foredeep mudstones of the Austral Basin forming a detachment fold over its tip. Thick sequences up to ~1500 m of quartz-rich sandstones filled a piggy-back basin bounded by this fold. Less thick sequences of the same lithologies were deposited concomitantly in the Eocene-Oligocene foredeep formed northwards of this structural high. In the late-Eocene a backthrust branching from the detachment delaminated the clastic sequence of the piggy-back basin. Later sticking of the backthrust leaded to a foreland propagation of the deformation, manifested by a sequence of low-angle thrusting that affected the foredeep. The original detachment ramped to a higher stratigraphic level a few kilometers behind the deformation front. The foreland propagation of the deformation front ended in the uppermost Oligocene-lowermost Miocene with the development of growth strata within the foredeep mudstones deposited unconformably over the frontal fault tip. Following Morley (1986) the thrust front can be classified as a Type 2 Buried Thrust Front, ending abruptly in a blind thrust (Castor thrust). The total shortening calculated for the frontal 18 km (kilometers) of the foreland thrust-fold belt is about 13 km (kilometers) (~72%).