Crustal collapse at the retroarc zone (2-0 Ma): Tromen volcanic plateau, Southern Central Andes (36º40´-37º30´S).

FOLGUERA, A., BOTTESI, G., RAMOS, V., ZAPATA, T.

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Año: 2008 vol. 459 p. 140 - 160

0040-1951

Analysis of seismic lines and gravity data show the existence of Quaternary extensional depocenters beneath thick covers of less than 1 Ma volcanic rocks in the Tromen volcanic plateau retroarc region(36º40´-37º30´S). Dating and mapping of pre, post-extensional volcanic units and structure in this area indicate that the main phase of crustal collapse corresponded to the 1.7-0.7 Ma time interval. However, Late Quaternary reactivations of the extensional structure show that this process is still ongoing, perhaps with decreasing intensity. Moreover, identification of “mechanical” rift zones and the potential related main thermal anomaly have led to propose an east dipping detachment beneath the Late Cretaceous to Late Miocene fold and thrust belt, controlling crustal collapse at these latitudes. The Southernmost Central Andes (35º-37º30´S) have recorded a period of shallow subduction (13-5 Ma) with consequent expansion of the arc to the foreland, generation of ductile-fragile crustal transitions and consequent foreland imbrications, more than 550 kilometers away from the trench. This framework shifted to a normal Andean subduction type after 5 Ma, with the re-establishment of the arc front in the Present-western position. The immediate consequences of such a readjustment were a) widespread volcanic eruptions of intra-plate melts in the eastern retroarc foreland plateau and b) a major trough located between the arc front and the foreland plateau sequences (Las Loicas trough). This extensional basin controlled the emplacement of crustal melts as well as primary mantle-derived products, masterly represented in the Tromen volcanic plateau.