The Northern Central Andes and Andean tectonic evolution revisited: An integrated stratigraphic and structural model of three superimposed orogens

Abstract

The mechanism for crustal thickening and superposition of several orogens is critical for understanding the growth of mountain ranges. Our study focuses on a trans-orogen crustal cross-section to revisit the Andean tectonic evolution in the Northern Central Andes (5°-8°S). It is based on a review of the geological setting, the definition of long-term tectono-sedimentary successions, and for the first time, a crustal balanced cross-section 895 km long through the entire orogen. We show that the Northern Central Andes were born in the Jurassic, and correspond to the superposition of several orogens representing a minimum total shortening of ∼207 km. They were built over 180 Ma during three orogenic periods (180–140 Ma; 100–50 Ma; 30–0 Ma), separated by two post-orogenic periods during which most Andean relieves were erased (140–100 Ma; 50–30 Ma). Each post-orogenic period was recorded by 1) a major regional erosional unconformity sealed by a widespread marine transgression, and 2) extensional tectonics in the forearc. Crustal shortening was driven by westward South America Plate displacement and continental crustal underthrusting, and not by oceanic subduction. The propagation of the Andean wedge has been controlled by successive inversions of two pre-existing rifts. The sequential restoration of the trans-orogen balanced cross-section, constrained by the sedimentary record, provides a realistic picture of each orogenic and post-orogenic stage. For the first time, the pre-Neogene basins are reconstructed respecting the Andean shortening. The first-order factors that have controlled the complex growth evolution of Northern Central Andes are South America Plate dynamics changes associated with shifts in the geometry of the subducting oceanic slab. Some correlations can be established with Phanerozoic climate changes.