Provenance Record of Renewed Mafic Sediment Contribution to the Magallanes Basin 50-52°S: Hinterland Thrusting or Plateau Magmatism?
Abstract
Integrated sediment provenance analysis of synorogenic deposits preserve records of mountain-belt growth and long-term evolution of orogenic divides. Here we characterize changes to the Magallanes retroarc foreland basin in response to Cenozoic tectonic and climate processes in the southern Patagonian Andes. Stratigraphy, clast compositions, sandstone petrography, and detrital zircon U/Pb LA-ICPMS data were collected from Eocene-Early Miocene deposits along the frontal monocline of the Patagonian thrust-belt. Sandstone petrography and clast lithology counts reveal the appearance of mafic sediment in the Eocene-Oligocene Río Turbio Fm., signaling a rejuvenated mafic input to the basin. These sources could be the Sarmiento Ophiolitic Complex, gabbro intrusions within the southern Patagonian Batholith, and/or eroded plateau basalts similar to the Eocene Posadas plateau basalts. The lower Río Turbio Fm. contains upper deltaic deposits characterized by fossiliferous planar to trough cross-bedded sandstone and matrix-supported conglomerate. These strata contain mostly mafic volcanic and metamorphic clasts with increasing quartz upsection. Zircon U/Pb age distributions from the lower Río Turbio yield Late and Early Cretaceous, and Late Jurassic age peaks. The overlying upper Río Turbio Fm. is comprised of bioturbated and fossiliferous upper delta front and subaqueous delta plain deposits with upsection increasing terrestrial input and interbedded coal deposits. Sandstone petrography data show mafic volcanic lithics as an important sediment component. Zircon U/Pb age distributions from the upper Río Turbio include Late Eocene/early Oligocene, mid-Cretaceous, and very small Late Jurassic age peaks. Youngest age peaks constrain timing of deposition to ca. 38 to 27 Ma. Age-correlative units north in the Sierra Baguales share similar provenance signatures, with larger Late Jurassic and Paleozoic age peaks within the Eocene-Oligocene basin-fill. The renewed mafic sediment contribution indicates a source that may reflect hinterland thrusting of the Sarmiento Ophiolitic Complex or a yet unidentified phase of Cenozoic mafic magmatism at this latitude in the Patagonian Andes. Ongoing geochemical and geochronological studies will resolve potential mafic sources and orogenic implications.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.T23D0645V
- Keywords:
-
- 7218 Lithosphere;
- SEISMOLOGY;
- 8108 Continental tectonics: compressional;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS