HR: 16:45h
AN: T14C-04    [Abstracts]
TI: The role of basement relief in the structural evolution of the Naryn intramontane basin, Kyrgyz Tian Shan
AU: * Oskin, M
EM: oskin@email.unc.edu
AF: Department of Geological Sciences, University of North Carolina at Chapel Hill, 104 South Rd., Chapel Hill, NC 27599, United States
AU: Burbank, D
EM: burbank@crustal.ucsb.edu
AF: Department of Earth Science, University of California at Santa Barbara, Webb Hall, Santa Barbara, CA 93106, United States
AU: Bookhagen, B
EM: bodo@pangea.Stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Braun Hall, Stanford, CA 94305, United States
AU: Phillips, F
EM: phillips@nmt.edu
AF: Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
AU: Marrero, S
EM: shastamarrero@gmail.com
AF: Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802, United States
AU: Selander, J
EM: selander@unc.edu
AF: Department of Geological Sciences, University of North Carolina at Chapel Hill, 104 South Rd., Chapel Hill, NC 27599, United States
AU: Goode, J
EM: jgoode@crustal.ucsb.edu
AF: Department of Earth Science, University of California at Santa Barbara, Webb Hall, Santa Barbara, CA 93106, United States
AB: We examine the emergence of basement topographic relief and the distribution of shortening through time in the Naryn intramontane basin, located within the Tian Shan orogen. At present the entire basin is undergoing erosion by the Nayrn River system, resulting in remarkable exposures of its structural architecture. The basin is bounded by basement-cored uplifts with 1500-2500 m of topographic relief above the Naryn River. Growth strata shed into a Neogene lacustrine basin record the activity of these basement-cored uplifts. This setting differs markedly from Late Quaternary deformation, which largely occurs on folds and thrust faults that deform the Neogene lacustrine strata and Quaternary stream gravels. Rates of uplift, erosion, and resulting landscape evolution differ significantly between structures hosted in basement versus Neogene strata. Despite rates of relative rock uplift approaching ~2 mm/yr, easily eroded Neogene strata sustain topographic relief of at most 300-500 m above river level. In contrast, relief production on basement is dominated by erosional stripping of pre-existing structures; evidence of Late Quaternary deformation of the basement is sparse. We calibrate a ~1 mm/yr vertical rate of exposure of basement from cosmogenic ³⁶Cl dating of a progressively exposed, pristine unconformable contact with Neogene cover strata. Patterns of river incision into this surface are also consistent with sustained rapid erosional stripping of the unconformity surface. We conclude that (1) exhumation of pre- existing, largely inactive basement massifs dominates relief production in the Naryn basin and (2) the presently rapid rate of convergence (~5 mm/yr) across the basin is almost completely focused on structures hosted in Neogene strata with modest topographic relief where shortening is largely balanced by erosion. This pattern is consistent with mechanical models of thrust-belt evolution where topographic relief above reverse faults exerts a first-order control on the loci of shortening.
DE: 1856 River channels (0483, 0744)
DE: 8002 Continental neotectonics (8107)
DE: 8108 Continental tectonics: compressional
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting