STRUCTURE AND EVOLUTION OF THE FORELAND THRUST-FOLD BELT OF THE FUEGIAN ANDES, TIERRA DEL FUEGO, ARGENTINA

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 of the foreland thrust-fold belt is about 14.2 Km (~44%).

Morley C. K., 1986, A classification of thrust fronts: American Association of Petroleum Geologists Bulletin, v. 70, p. 12-25.