AN: T11B-18TI: P-T-t Constraints on Mechanisms of Vertical Tectonic Motion in a    Contractional OrogenAU: D L WhitneyAF: Geology and Geophysics, Univ of Minnesota, Minneapolis, MN    55455EM: Donna.L.Whitney-1@umn.eduAU: R B MillerAF: Geology, SJSU, San Jose, CA 95192EM: AU: S R PatersonAF: Earth Sciences, USC, Los Angeles, CA 90089EM: AB: Although most plate tectonic models for the development of orogens    emphasize the importance of large-scale lateral motions, the final    configuration of orogens (topography, distribution of metamorphic    rocks and structures) is strongly affected by vertical motion (burial,    exhumation). Deciphering the mechanisms of vertical motion requires    examining rocks and structures representing a range of crustal depths.    The Coast Mountains-North Cascades belt, extending from Washington    state to SE Alaska, represents a mid-Cretaceous arc with rocks and    structures formed at depths ranging from near-surface to 40 km.    Despite diachronous loading and unroofing involving many structures    along the length of the orogen, maximum depth of burial (40 km), peak    metamorphic T (650-700 C), P-T paths (clockwise with isothermal    decompression), and the relation (timing, style) among metamorphism,    deformation, and magmatism are similar in many parts of the belt,    indicating a common mechanism for burial and unroofing. The overall    shape of P-T paths and the relative timing and regional extent of the    high-P event are consistent with thrusting and/or pure shear    thickening as primary loading mechanisms. This interpretation is    further supported by comparison with thermal models which demonstrate    that the P-T paths are consistent with simultaneous thrusting and    folding at a high initial geothermal gradient (35-40 C/km) in much of    the orogen. A high geothermal gradient supports tectonic models    invoking intra-arc contraction and suggests that magmatism played an    important role in regional temperature-time paths. This    tectonic-thermal history is typical of other contractional orogens    (Sierra Nevada; Fiordland, NZ) and illustrates the importance of    large-scale vertical displacement of crust in these    systems.SC: TDE: 8102DE: 8110DE: 8099MN: 1997 Fall Meeting