Neogene To Quaternary Extensional Reactivation Of A Fold And Thrust Belt: The Agrio Belt In The Southern Central Andes And Its Relation To The Loncopué Trough (38°- 39ºS).

ROJAS VERA, EMILIO; FOLGUERA, ANDRES; ZAMORA VALCARCE, G.; GIMENEZ, MARIO E; RUÍZ, FANCISCO; MARTINEZ, M PATRICIA; BOTTESI, GERMAN; RAMOS, VICTOR

Tectonophysics

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Lugar: United States; Año: 2010 vol. 492 p. 279 - 294

0040-1951

The Andean orogenic front between 38 and 39ºS is formed by extensional structures delimiting the Loncopué trough. These structures are superimposed to Late Cretaceous-Late Miocene compressive structures that formed the Agrio fold and thrust belt. Detailed structural mapping together with gravity and magnetic data, and limited borehole and seismic data were used to construct two structural cross sections across the area of Neogene extensional deformation and remnants of the previous compressive structure. A structural cross section was restituted for the two stages when the Loncopué trough was developed, Late Oligocene-Early Miocene to Pliocene to Quaternary related to extensional structures; and the previous stage related to the inversion of the previous structures related to the Late Cretaceous prior to extensional relaxation. Different modeling techniques and filters particularly for gravity anomalies show that i) a series of deeper and larger depocenters, where Late Oligocene to Early Miocene sequences are buried, were located particularly at the Present trough boundaries; while ii) smaller and probably shallower depocenters were concentrated at the axial-eastern trough following structures at surface with young morphological expression. The former are interpreted as representative of the initial extensional stage when Late Cretaceous compressional basement structures were relaxated, while the latter could be the product of incipient-young collapse of the Agrio fold and thrust belt. General coincidence between both areas of extensional relaxation at the western Agrio fold and thrust belt implies that a common basement discontinuity is recurrently being reactivated through time, probably in coincidence with the eastern main Loncopué fault boundary.