HR: 08:45h
AN: T31E-04    [Abstracts]
TI: Oligocene - Miocene Rise of the Bolivian Altiplano and Eastern Cordillera: Implications for Andean Lithospheric Evolution
AU: * Garzione, C N
EM: garzione@earth.rochester.edu
AF: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627 United States
AU: Ghosh, P
EM: pghosh@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 United States
AU: Eiler, J M
EM: eiler@gps.caltech.edu
AF: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 United States
AU: Libarkin, J C
EM: libarkin@ohio.edu
AF: Department of Geological Sciences, Ohio University, Athens, OH 45701 United States
AU: MacFadden, B J
EM: bmacfadd@flmnh.ufl.edu
AF: Florida Museun of Natural History, University of Florida, Gainesville, FL 32611 United States
AU: Withers, S
EM: sw141403@ohio.edu
AF: Department of Geological Sciences, Ohio University, Athens, OH 45701 United States
AB: The siliciclastic sedimentary record, magnetostratigraphy, and isotopic composition of carbonate deposited in the northern Altiplano and Eastern Cordillera are used to reconstruct the Oligocene to Miocene paleoenvironment and paleoelevation of the Andean plateau. Based on relatively positive δ¹⁸O values (-7.4‰ to -6.2‰) for paleosol carbonates in the Salla Formation, the Eastern Cordillera resided at low elevation (<500 m) between ~26 and 29 Ma. By ~25 Ma, there is a negative shift in δ¹⁸O of carbonate to values ~2 to 5‰ more negative than Salla Formation paleosols. Paleoleaf physiognomy, δ¹⁸O paleoaltimetry, and Δ₄₇ paleothermometry suggest that the Altiplano had attained no more than ~1600 m of elevation between 11.3 Ma and 10.3 Ma. Both δ¹⁸O paleoaltimetry and Δ₄₇ paleothermometry suggest that the Altiplano was raised to its current elevation by ~6.8 Ma. These results suggest that the Andean plateau rose during two stages: early surface uplift on the order of ~1 to 1.5 km took place between ~25 and 11.3 Ma and later surface uplift of ~2 to 3 km, took place between ~10 and 7 Ma. An intriguing aspect of this elevation history is that the late Oligocene Salla Formation in the Eastern Cordillera suggests very low elevations despite evidence that most upper crustal shortening had already taken place in the Altiplano and Eastern Cordillera. Several possible mechanisms for maintaining low elevations at this time are 1) dynamic subsidence related to a shallow dip of the subducting Nazca slab and/or 2) distributed shortening of dense mantle lithosphere that counters the effect of upper crustal shortening. The former mechanism is supported by a shut down of the central Andean magmatic arc at ~30 Ma. This was followed by widespread eruption of mafic volcanics and ignimbrites in the northern and central Altiplano beginning at ~25 Ma indicating a change in the thermal structure of the lithosphere. The ~2 to 3 km of surface uplift that occurred between ~10 Ma and 7 Ma could have only been generated by removal of mantle lithosphere. The long-term elevation history of the central Andes suggests that most of the surface rise of Andean plateau occurred in discrete pulses associated with the removal of mantle lithosphere.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: Fall Meeting 2005