Unraveling burial heating and sediment recycling in retroarc foreland basins: Detrital thermochronologic insights from the northern Magallanes Basin, Patagonian Andes

Monday, 15 December 2014: 8:00 AM
Julie C Fosdick, Indiana University Bloomington, Bloomington, IN, United States, Marty J Grove, Stanford University, Geological and Environmental Sciences, Stanford, CA, United States, Stephan A Graham, Stanford University, Stanford, CA, United States, Jeremy K Hourigan, UC Santa Cruz, Santa Cruz, CA, United States, Oscar M Lovera, University of California Los Angeles, Earth and Space Sciences, Los Angeles, CA, United States and Brian Romans, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
Sediment recycling is expected in many tectonic settings, such as foreland basins, where the path followed by grains initially derived from erosion of a basement source region typically involves significant intermediate stages of crustal evolution before the detritus is finally incorporated into tectonically stable basin strata. The shallow-crustal thermal histories experienced by eroded sediment may go undetected by traditional provenance methods but are potentially recoverable by thermochronologic methods. The Patagonian Magallanes retroarc foreland basin affords an excellent case study of sediment burial and recycling within a thrust belt setting. Combined detrital zircon U-Pb geochronology and (U-Th)/He thermochronology data and thermal modeling results confirm delivery of both rapidly cooled, first-cycle volcanogenic sediments from the Patagonian magmatic arc and recycled sediment from deeply buried and exhumed Cretaceous foredeep strata to the Cenozoic Magallanes basin depocenter. Numerical models of temperature-time histories indicate that ca. 54-45 Ma burial of the Maastrichtian Dorotea Formation produced 164-180°C conditions and heating to within the zircon He partial retention zone. Such deep burial is unusual for Andean foreland basins and may have resulted from combined effects of high basal heat flow and high sediment accumulation within a rapidly subsiding foredeep that was floored by basement weakened by previous Late Jurassic rifting. In this interpretation, Cenozoic thrust-related deformation deeply eroded the Dorotea Formation and underlying strata from ~5 km burial depths and may be associated with the development of a regionally extensive Paleogene unconformity. Results from the Cenozoic Río Turbio and Santa Cruz formations confirm that they contain both Cenozoic first-cycle zircon from the Patagonian magmatic arc and highly outgassed recycled zircon. This work suggests that Middle Miocene sediments were most likely derived from recycling of deeply buried Upper Cretaceous strata in the Patagonian thrust belt. These findings contribute new understanding to Patagonian foreland basin evolution and provide insight into the broader interactions between tectonics and sedimentation and signals of sediment recycling in convergent basins.