T23A-2932
Detrital Zircon Provenance Record of Pre-Andean to Modern Tectonics in the Northern Andes: Examples from Peru, Ecuador, and Colombia

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Sarah W.M. George, University of Texas at Austin, Austin, TX, United States, Lily Josephine Jackson, University of Arizona, Tucson, AZ, United States and Brian K Horton, University of Texas at Austin, Department of Geological Sciences and Institute for Geophysics, Austin, TX, United States
Abstract:
Detrital zircon U-Pb age distributions from modern rivers and Mesozoic-Cenozoic basin fill in the northern Andes provide insights into pre-Andean, Andean, and active uplift and exhumation of distinctive sediment source regions. Diagnostic age signatures enable straightforward discrimination of competing sediment sources within the Andean magmatic arc (Western Cordillera-Central Cordillera), retroarc fold-thrust belt (Eastern Cordillera-Subandean Zone), and Amazonian craton (composed of several basement provinces). More complex, however, are the mid/late Cenozoic provenance records generated by recycling of basin fill originally deposited during early/mid Mesozoic extension, late Mesozoic thermal subsidence, and early Cenozoic shortening. Although subject to time-transgressive trends, regionally significant provenance patterns in Peru, Ecuador, and Colombia reveal: (1) Triassic-Jurassic growth of extensional subbasins fed by local block uplifts (with commonly unimodal 300­–150 Ma age peaks); (2) Cretaceous deposition in an extensive postrift setting fed by principally cratonic sources (with common 1800–900 Ma ages); and (3) Cenozoic growth of a broad flexural basin fed initially fed by magmatic-arc rocks (100–0 Ma), then later dominance by thrust-belt sedimentary rocks with progressively greater degrees of basin recycling (yielding diverse and variable age populations from the aforementioned source regions).

U-Pb results from modern rivers and smaller subbasins prove useful in evaluating source-to-sink relationships, downstream mixing relationships, hinterland-foreland basin connectivity, paleodrainage integration, and tectonic/paleotopographic reconstructions. Most but not all of the elevated intermontane basins in the modern hinterland of the northern Andes contain provenance records consistent with genesis in a broader foreland basin developed at low elevation. Downstream variations within modern axial rivers and Cenozoic axial basins inform predictive models of Andean contributions from the >1500 km Marañon river to the broader Amazon drainage system, and help pinpoint the late Miocene birth of the >1500 km Magdalena river and associated submarine fan along the southern Caribbean margin.