South-American plate advance and forced Andean trench retreat as drivers for transient flat subduction episodes.

ABSTRACT: At two trench segments below the Andes, the Nazca Plate is subducting sub-horizontally over ?200-300?km, thought to result from a combination of buoyant oceanic-plateau subduction and hydrodynamic mantle-wedge suction. Whether the actual conditions for both processes to work in concert existed is uncertain. Here we infer from a tectonic reconstruction of the Andes constructed in a mantle reference frame that the Nazca slab has retreated at ?2?cm per year since ?50?Ma. In the flat slab portions, no rollback has occurred since their formation at ?12?Ma, generating 'horse-shoe' slab geometries. We propose that, in concert with other drivers, an overpressured sub-slab mantle supporting the weight of the slab in an advancing upper plate-motion setting can locally impede rollback and maintain flat slabs until slab tearing releases the overpressure. Tear subduction re-establishes a continuous slab and allows the process to recur, providing a mechanism for the transient character of flat slabs.

SUBMITTER: Schepers G 

PROVIDER: S-EPMC5440808 | biostudies-other | 2017 May

REPOSITORIES: biostudies-other