SEDIMENT PROVENANCE AND STRUCTURAL RECORDS OF BASIN INVERSION IN THE NORTHERNMOST ANDES: EASTERN CORDILLERA AND MAGDALENA VALLEY, COLOMBIA

The Eastern Cordillera of Colombia recorded Mesozoic extension followed by Cenozoic basin inversion during Andean shortening. The evolution of sediment provenance and crustal structures is important to understanding the topographic development of the Eastern Cordillera (EC) and Middle Magdalena Valley (MMV) intermontane basin. The Rio Ermitaño study area along the EC-MMV boundary displays structures that pre-date and post-date a well-exposed regional unconformity of the late Eocene age. The contrasting sedimentary successions below and above the unconformity define a major transition from organic-rich clastic marine strata to coarse-grained fluvial and alluvial fan deposits. Synthesis of published and new detrital zircon U-Pb data from strata below the unconformity reveals multiphase variations in provenance in response to extensional deformation and post-extensional subsidence. Three major provenance signatures are identified: Triassic-Early Cretaceous (250-100 Ma) ages from Andean arc/Central Cordillera (CC); Neoproterozoic-early Paleozoic (650-350 Ma) ages from Andean/EC basement; and Precambrian (1200-700 Ma) ages from Brazilian cratonic sources. Multimodal zircon populations from Andean basement and cratonic sources characterize the latest Jurassic to earliest Cretaceous synextensional sedimentation. Subsequent upsection shifts among mainly Andean magmatic arc, Andean basement, and cratonic provenance within Cretaceous strata correspond to phases of drainage reorganization during post-extensional basin evolution. The latest Cretaceous to early Paleocene shift from Andean basement and cratonic sources to principally Andean magmatic arc sources recorded the onset of shortening and associated magmatism in the CC (western provenance) before initial uplift and unconformity development along the EC-MMV transition. The detrital zircon U-Pb results also provide constraints for structural modeling of Cenozoic shortening and basin inversion during EC uplift. Further structural analyses will assess the timing and kinematic sequence of deformation along the EC-MMV transition to identify the linkages between uplift and sediment dispersal across the EC, CC, and MMV, with attention to the role of stratigraphic and structural inheritance.