摘要

The Late Cretaceous closure of the Late Jurassic-Early Cretaceous Rocas Verdes basin-resulted in the development of the Patagonian fold-and-thrust belt and Magallanes foreland basin between 50 degrees S and 54.5 degrees S. New geologic maps, structural data, and two retrodeformed, line-balanced cross sections from the Magallanes region of Chile (53 degrees S-54 degrees S) constrain the kinematic evolution and along-strike correlations of deformation that occurred at the base of the fold-and-thrust belt near the brittle-ductile transition. The stratigraphic architecture of the predecessor basin controlled the position of regional decollement levels. During the initial stage of closure (Albian-Campanian), the floor of the Rocas Verdes basin was imbricated and thrust onto the continental margin to form a regional decollement within Jurassic-Lower Cretaceous shale. Continued shortening resulted in the deepening of the decollement to a ductile shear zone that formed <1 km below the basement-cover contact. Ductile polyphase folding accommodated basement shortening and was mechanically decoupled from the overlying fold-and-thrust belt below-the lower decollement. Ramps that cut Jurassic volcanic deposits linked the lower and upper decollements and transferred displacement into the nascent foreland basin. A second stage of shortening, characterized by basement-involved reverse faults that cut the early decollements, reflects complete closure of the Rocas Verdes basin by the Maastrichtian-Eocene. Coniacian to Eocene shortening estimates indicate a northwest-southeast increase from 26% to 37% over 100 km along strike and are consistent with regional models of the Patagonian fold-and-thrust belt. The results provide an important example of the kinematic evolution of the base of a retroarc fold-and-thrust belt in an "Andean-style" orogen.

  • 出版日期2015-7