The Evolution of Deepwater Slope Systems on Retroarc Foreland Basin Margins: Insights From Detrital Zircon Geochronology, Tres Pasos Formation, Magallanes Basin, Chile

Abstract

Sedimentary systems in foreland basins transport large amounts of detritus over great distances, and contribute to some of the largest sediment accumulations on Earth. Because these systems often span large areas (100s of kms long and wide) and evolve continuously over their lifespans, the deduction of sediment dispersal patterns and depositional timing in foreland basins can prove difficult. Deep-water slopes, common in the deepest parts of some foreland basins, can provide unique insight, as they represent key sedimentary sinks towards the end of sediment routing systems. To add to the comprehension of sediment routing networks and timing of deposition in foreland basins, we present high-resolution maximum depositional ages (MDAs) and provenance data from a series of outcropping deep-water slope deposits from the Cretaceous Tres Pasos Formation, Magallanes foreland basin, southern Chile. Geochronological data for this study was derived from 13 sandstone samples and 6358 detrital zircon grains, which were obtained from numerous stratigraphic intervals over a 100 km-long depositional-dip-parallel transect of the Tres Pasos Formation. Zircon grains were isolated via standard mineral separation procedures and single-grain ages were determined via analysis of 238U/206Pb isotopic ratios acquired with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). MDAs calculated for each stratigraphic interval reveal that the deposition of distinct slope clinothems in the Tres Pasos system (700-1100 m thick) spanned 1-3 Myr in duration. Shelf-edge progradation rates associated with clinothem deposition range from 7-14 km/Myr, which is consistent with rates from other deep-water slope systems. Furthermore, the ages indicate that the entire slope system, which is represented by a ∼2500 m thick package of stratigraphy in the Magallanes Basin succession, was active for up to 10 Myr. Detrital zircon spectra illustrate that the majority of sediment routed through the system was derived from similar hinterland sources. These sources include: 1) adjacent Paleozoic metamorphic basement rocks; 2) the Tobífera Formation, a Jurassic-aged Andean volcanogenic unit; 3) 110-90 Ma-aged Andean volcanic arc material; and 4) 80-70 Ma-aged Andean volcanic arc material. These results can be used to add insight into slope system evolution on other basin margins, including analogous clinoform systems worldwide.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016