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South America |
School of Oceanography, Oregon State University, Corvallis, Oregon 97331, U.S.A.
Hawaii Institute of Geophysics, 2525 Correa Road, Honolulu, Hawaii 96822, U.S.A.
The central Peru forearc (6°–14°S) is characterized by a variety of structural and tectonic styles. Continental shelf basins, Sechura, Salaverry, and East Pisco, are floored by a block faulted Precambrian to Palaeozoic massif and accumulated as much as 3 km of Cenozoic and probably Mesozoic sediment. The massif rises to form an Outer Shelf High (OSH) covered with disrupted Neogene strata. Structural and stratigraphic relationships suggest several pulses of uplift and subsidence for the massif with the most recent uplift detected on the positive massif features.
Upper slope basins are cradled between the OSH and a seaward Upper Slope Ridge (USR) of deformed sediment. Late Eocene and younger clastic sediments, with minor limestone beds, occupy the eastern Trujillo Basin, whereas late Miocene to Pleistocene dolomicrite, micrite and glauconitic micrite are prominent in the western part of the basin. Both the Trujillo and Yaquina Basins (7°–9°30'S) exhibit severe internal disruption caused by compressional stresses. To the south, the Lima Basin (9°30'–13°S) contains similar carbonate lithologies, but this basin and underlying massif have subsided 275 to 500 m Ma–1 since Pliocene-Pleistocene time, indicating tensional stresses.
Geological and geophysical data show the subducting plate is rupturing by thrust faulting of layer 2 basalts which may form a sediment-basalt mélange in the overlying subduction complex. Because the seaward boundary of the arc massif is not well-defined, several forearc models are presented which allow the subduction complex to range in width from 15 to 60 km.
The Peru forearc off Lima (12°S) exhibits many of the tectonic characteristics of the Japan forearc off Honshu, especially the subsiding slope basin and contemporaneous accreting subduction complex.
