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Andean Forearc Dynamics, As Recorded By Detrital Zircon From the Eocene Talara Basin, Northwest Peru
Eocene strata of the Talara forearc basin of northwest Peru contain detrital-zircon (DZ) populations that, when integrated with other provenance indicators, record paleogeographic shifts in the Andean forearc that can be linked to larger-scale tectonic drivers such as subduction erosion, plate convergence rate, and regional accretion events. Because forearc basins along the western margin of South America are particularly difficult to preserve, the new DZ results provide rare insight into the trench–arc dynamics associated with the Andean orogenic cycle. The Talara basin tapped into both the Andean volcanic arc and older basement, and the DZ populations subsequently reflect long-lived plate interactions and progressive crustal growth along the northwestern edge of Amazonia, Gondwana, and South America. Dominant U–Pb zircon age populations include: 36–110 Ma (Andes convergence); 215–285 Ma (western Gondwana extension); 460–625 Ma (Rodinia extension and western Gondwana convergence); 950–1250 Ma (Grenville orogeny); and > 1250 Ma (Amazonia assembly). The data corroborate previous geochronology on pre-Andean basement and support the existence of a Famatinian arc (∼ 480 Ma) and Carboniferous–Triassic magmatism along northwestern Gondwana. Pre-Andean and Amazonian DZ likely was recycled from Paleozoic metasedimentary rocks of the Andean Cordillera and Amotape terrane, although the data do not preclude delivery of Amazonian detritus directly into the forearc via a large-scale, westward drainage. The Andean DZ population constrains the timing of arc activity and quiescence, with two peaks at ∼ 75 Ma and ∼ 50 Ma, and a gap at ∼ 70 Ma, linked to accretion of the Caribbean Oceanic Plateau against northwest South America. Arc volcanism was concurrent with Eocene forearc deposition, and syndepositional DZ is used to revise maximum depositional age for the upper Eocene Helico Member and Verdun Formation. Progressive subsidence and arc shut-down in the late Eocene coincide with arc collision to the north, uplift of the Amotape block, subduction erosion, and slab shallowing.
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