Paper No. 213-8
Presentation Time: 10:40 AM
DISPLACED CAMBRIAN BASINS AND CAMBRIAN STRIKE-SLIP EMPLACEMENT OF THE AREQUIPA TERRANE IN SOUTHERN PERU
Early to Middle Cambrian sedimentary basins have not been documented from the Arequipa terrane in southern Peru. In contrast, volcanically active basins of this age have been well-documented on correlative terranes in NW Argentina that were involved in the Early Cambrian Pampean Orogeny. Here, we present new mapping, stratigraphy, zircon geochronology, and depositional models for volcanically active Early and Middle Cambrian basins from the Arequipa terrane in southern Peru. From our work on these basins and additional geological constraints, we propose Cambrian strike slip displacement of the Arequipa terrane from NW Argentina and late Cambrian emplacement in southern Peru. In the >1000 meter-thick fine-grained siliciclastic turbidite sequence of the San Fernando Formation in coastal southern Peru, LA-ICPMS and CA-TIMS analyses from ash beds and detrital zircon samples are dominated by Early Cambrian ages. This is in sharp contrast with detrital zircon from the underlying carbonate-dominated Neoproterozoic passive margin deposits of the Marcona Group, dominated by >1 Ga basement ages. Rapid subsidence and high sedimentation rates in this tectonically active early Cambrian basin are supported by load coasts, flute clasts, climbing ripples, cobble beds of self-cannibalized units, and geochronological constraints. The Umachiri Formation in the Altiplano of southern Peru is a >1000 meter-thick package of siltstone and wackestone containing lapilli and outsized igneous clasts that is dominated by Early to Middle Cambrian detrital zircon dated by LA-ICPMS and CA-TIMS. Both the San Fernando and Umachiri basins bear sedimentological evidence in support of local uplift, consistent with a regional transpressional regime, and structural indicators in these units are consistent with a dextral transpressional regime. We correlate the San Fernando and Umachiri formations with the Puncoviscana Formation and Meson Group of NW Argentina and suggest that these basins were dextrally translated on the Arequipa terrane and emplaced in southern Peru in the late Cambrian.