Cenozoic deformation history of the Andean plateau in southern Peru : stratigraphic, structural, and geochronologic constraints

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2015-08

Authors

Perez, Nicholas David

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Abstract

Cenozoic shortening in the central Andes of southern Peru was accommodated by thin- and thick-skinned deformation that governed hinterland/foreland basin dynamics, the timing and location of exhumation, and development of modern high topography. A new line length balanced cross section estimates 130 km of shortening (38%) across the Eastern Cordillera and Subandean Zone. I propose the location of a pre-Andean graben in the Eastern Cordillera, and a kinematic model that links selectively inverted basement-involved normal faults to shallow detachments that accommodate thin-skinned deformation across the orogen. New U-Pb zircon geochronology from synrift deposits establishes Triassic age deposition, and suggests compartmentalized rift basins were filled with local Eastern Cordillera sediment sources.

Eocene exhumation in the Eastern Cordillera represents reactivation of Triassic normal faults and the onset of Andean deformation. In-sequence deformation was transferred from the Eastern Cordillera to the Altiplano by the thin-skinned Central Andean Backthrust Belt and induced flexural subsidence in the Ayaviri hinterland basin beginning at ~30 Ma. Facies analyses, sediment provenance, geochronology, and structural mapping define multiple phases of basin reorganization that are temporally correlative with motion along basin margin thrust faults. Major middle Miocene reorganization of the Ayaviri basin is linked to ~17 Ma out-of-sequence thrust fault motion in the Western Cordillera. Oligocene-Miocene hinterland basin evolution in the northern Altiplano was driven by thrust tectonics.

U-Pb detrital zircon geochronology from Cretaceous through Cenozoic stratigraphy in hinterland and foreland basins record distinct provenance differences since the Cretaceous. This is the detrital record of either an inherited structural high in the Eastern Cordillera that predated Eocene shortening and created two depocenters with distinct provenance, or lateral provenance variations across a large retroarc foreland basin. Existing K/Ar, ⁴⁰Ar/³⁹Ar, and new zircon (U-Th)/He thermochronology suggest Eocene-Oligocene exhumation in the Eastern Cordillera was synchronous ~400 km along strike. New apatite (U-Th)/He data from the Eastern Cordillera demonstrate a change to localized, diachronous exhumation and uplift events in the Miocene-Pliocene. Apatite (U-Th)/He thermochronology demonstrates onset of deformation in the Subandean Zone by ~15 Ma, after shortening and exhumation in the Eastern and Western Cordillera ceased.

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