March-April GSA Bulletin media highlights

Boulder, CO, USA - Geology topics of interest include: landscape evolution of California's Sierra Nevada; Nevada's northwestern Basin and Range and its remarkable record of Cenozoic magmatism; turbidity currents and topography of Earth's submarine channels; sediment dynamics of the lower Mississippi River; microorganisms' catalytic effect on limestone formation; high-resolution topographic survey of offshore California's Eel Canyon; and impact of scoria-cone eruptions on nearby communities.

Representatives of the media may obtain complimentary copies of articles by contacting Ann Cairns, . Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GSA BULLETIN in stories published. Contact Ann Cairns for additional information or assistance.

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P-T-t data from central Nepal support critical taper and repudiate large-scale channel flow of the Greater Himalayn Sequence

Matthew J. Kohn et al., Department of Geosciences, Boise State University, Boise, Idaho 83725, USA. Pages 259-273.

Kohn et al. present a new synthesis of pressure-temperature conditions and pressure-temperature-time (P-T-t) paths for high-grade metamorphic thrust sheets associated with the Main Central Thrust, in the Langtang and Darondi regions, central Nepal. From structurally low to structurally high, major structures include the Lesser Himalayan Duplex, Munsiari Thrust, Main Central Thrust (thrust contact between the Greater and Lesser Himalayan Sequences), and Langtang Thrust. Overall, metamorphic and chronologic patterns are matched well by expectations of critical taper models, including (1) uniformly high pressures of metamorphism (8–12 kbar) for all structural levels and thrust movement along the paleo–Main Himalayan Thrust, (2) isobaric cooling from the peak of metamorphism for Greater Himalayan rocks (deep juxtaposition of thrust sheets), (3) “hairpin” P-T paths for Lesser Himalayan rocks, and (4) relatively slow cooling rates for Greater Himalayan rocks. However, observations contrast significantly with published channel flow models. Most generally, although channel flow may have initiated since ca. 10 Ma due to focused erosion above the Lesser Himalayan Duplex, it does not appear responsible for past transport and exhumation of the migmatitic core of the Himalaya.

Carson Pass–Kirkwood paleocanyon system: Paleogeography of the ancestral Cascades arc and implications for landscape evolution of the Sierra Nevada (California)

C.J. Busby et al., Department of Earth Science, University of California, Santa Barbara, California 93101, USA. Pages 274-299.