Fracture Patterns and Structural History in the Sub-Andean Belt of Southernmost Chile

Abstract

Intensive transverse fracturing occurs in the sub-Andean fold belt east of the high Cordillera, at about lat. 51° S. Some of this fracturing is contemporaneous with the folding. Wrench faults, some with right-lateral displacement, originated during a later stage of compression. The oldest folding occurred between Maestrichtian and Eocene times. Thus Laramian movements are of principal importance in the evolution of the present-day Cordillera. Of Miocene age is a second, gentle folding which reached farther to the east. Granite intrusions occurred in the early Tertiary or Miocene. During Pliocene to early Pleistocene times the uprising high mountain belt in the west exerted lateral pressure on the adjacent area to the east, which produced a wrench-fault pattern oblique to the previous structures. Westward tilting during post-Pliocene times caused reversal of the drainage system; originally east-flowing rivers were captured and their courses deviated into Pacific waters. The new drainage pattern reflects the intensive transverse fracturing of the area.