Collision of the Mocha fracture zone and a less than 4 Ma old wave of orogenic uplift in the Andes (36º-38ºS)

FOLGUERA, A. Y RAMOS, V.A.

Lithosphere

GSA

Año: 2009 vol. 1 p. 1 - 6

1941-8264

The Southern Central and Northern Patagonian Andes (34º-45ºS) are characterized by low to no crustal seismicity at the retroarc fold and thrust belt, in contrast to the Pampean flat subduction zone located immediately to the north (27º-33º30´S). Detailed examination of this area shows no indication of contractional neotectonics with the exception of the segment located between 36º and 38ºS. There, out of sequence transpressional deformation, initially developed in the 1.7-1.4 Ma interval, affects the western retroarc between 36º and 38ºS next to the arc zone. It is between these latitudes that contractional deformation less than 3.6 Ma old developed in the forearc region. Oblique collision of the Mocha fracture zone and its associated rise explains the distribution, extent and timing of less than 3.6 Ma contractional deformations from the forearc to the foreland, as well as incipient shallowing of the Nazca plate beneath the South American plate, which has been inferred from seismic, gravimetric, and arc dynamics studies.