Structural styles of the Tierra del Fuego fold-thrust belt foothills, Argentina

Abstract

Regional structural cross-sections based on seismic, borehole and surface data portray the foothills geometry of the Tierra del Fuego fold-thrust belt. Andean contraction was accommodated by two main deformation mechanisms: 1) A lower duplex thrust system that involves mainly Cretaceous deposits, with floor and roof thrusts at the base of the Cretaceous and close to the base of the Cenozoic, respectively; and 2) A series of detachment and faulted detachment anticlines in the Cenozoic, detached in mudstones above the roof thrust of the underlying duplex thrust system. Less common structures include fault bend and fault propagation folds. Basement fault reactivation is only locally important, with most Jurassic grabens and half-grabens preserved without inversion. Shortening along the foothills is modest, with values ranging from ∼8 to 4.6 kilometers. This region of the fold-thrust belt has hydrocarbon exploration interest; however, it is largely underexplored. Several large anticlines preserving Cenozoic clastic rocks have not been tested to date. The key risk for these structures is the charge, as the thick mudstone package forming their detachment isolates potential Cenozoic reservoirs from the Lower Cretaceous source rocks. Duplex thrust systems at depth may constitute a potential exploration play, provided brittle intervals were naturally fractured.