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Creator:: Sinton, Christopher W., Christie, David M., and Duncan, Robert A.
Abstract:: Lavas from seamounts of the central Galápagos Platform and the Carnegie Ridge increase in age with distance from the western edge of the platform, consistent with a hotspot model for the generation of these features. The areal distribution of seamount ages suggests that the pattern of dispersed volcanism seen on...
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Full Text:: the northwest of the Galfipagos Platform are young (<1 Ma), with the youngest measured ages closest

Creator:: Duncan, Robert A.
Abstract:: Radiometric ages (K-Ar and ⁴⁰Ar- ³⁹Ar methods) have been determined on dredged volcanic rocks from seven of the New England Seamounts, a prominent northwest-southeast trending volcanic lineament in the northwestern Atlantic Ocean. The ⁴⁰Ar-³⁹Ar total fusion and incremental heating ages show an increase in seamount construction age from southeast to...
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Full Text:: the New England Seamounts, a prominent northwest-southeast trend- ing volcanic lineament in the

Creator:: Sandwell, David T., Winterer, Edward L., Mammerickx, Jacqueline, Duncan, Robert A., Lynch, Mary Ann, Levitt, Daniel A., and Johnson, Catherine L.
Abstract:: Satellite altimeter measurements of marine gravity reveal 100 to 200-km wavelength lineations over a wide area of the Pacific plate oriented roughly in the direction of absolute plate motion. At least three mechanisms have been proposed for their origin: smallscale convective rolls aligned in the direction of absolute plate motion...
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Full Text:: marine gravity reveal 100 to 200-km wavelength lineations over a wide area of the Pacific plate oriented

Creator:: Magill, James, Cox, Allan, and Duncan, Robert A.
Abstract:: Paleomagnetic directions from the Eocene Tillamook Volcanic Series of the Oregon Coast Range point 460 clockwise from the expected Eocene field direction. Potassium argon dating of six dikes and flows from this formation yields a mean age of 44.3 ± 0.6 m.y. These results establish that the Oregon coastal block...
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Full Text:: to northwest occur in the western part of the area (Figure 3) near Pinochle Peak and Cedar Butte

Creator:: Desonie, Dana L., Duncan, Robert A., and Natland, J. H.
Abstract:: The Marquesas archipelago is a short. NW-SE trending cluster of islands and seamounts that formed as a result of volcanic activity over a weak hotspot. This volcanic chain lies at the northern margin of a broad region of warm and compositionally diverse mantle that melts to build several other subparallel...
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Full Text:: age from northwest to southeast. The new sample age distribution yields a volcanic migration rate

Creator:: VanLaningham, Sam, Duncan, Robert A., and Pisias, Nicklas G.
Abstract:: We use Ar-40-Ar-39 incremental heating to fingerprint bulk fluvial sediment entering the northeast Pacific Ocean, with the long-term intent of tracking sediment source and transport changes from the terrestrial system to the marine environment through time. We show reproducible age spectra from individual rivers accounting for the majority of sediment...
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Full Text:: spectra. A second model predicts bulk sediment ages from integrated bedrock cooling age-area estimates in

Creator:: Duncan, Robert A.
Abstract:: K-Ar and ⁴⁰Ar-³⁹Ar geochronologic data reveal the Paleocene to Eocene eruptive history of volcanic centers which produced the basaltic basement rocks of the Coast Range of Oregon and Washington. Volcanism was short lived at each center and migrated with time from the northern and southern ends toward the center, near...
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Full Text:: Plain and the Yellowstone area. 1. The Coast Range, Oregon and Washington Recently much interest

Creator:: Watts, A. B., Weissel, J. K., Duncan, Robert A., and Larson, R. L.
Abstract:: We have combined shipboard and Seasat altimeter derived data in an intergrated geological and geophysical study of the Louisville Ridge; a 3500-km-long seamount chain extending from the Tonga trench to the Eltanin Fracture Zone. A break in the smooth trend of the ridge at latitude 37.5°S has been recognized in...
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Full Text:: quarter of a revolu- tion of Seasat. Thus over the study area in which 800-km-long profiles of altimeter

Creator:: White, William M., McBirney, Alexander R., and Duncan, Robert A.
Abstract:: We report new major element, trace element, isotope ratio, and geochronological data on the Galapagos Archipelago. Magmas erupted from the large western volcanos are generally moderately fractionated tholeiites of uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic basanitoids. While these volcanoes do not...
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Full Text:: about 25% of the island's surface. One flow in the James Bay area at the northwest end contains

Creator:: Kruse, Sarah E., Liu, Zhengrong J., Naar, David F., and Duncan, Robert A.
Abstract:: Bathymetry and gravity data collected during Legs 5, 6, and 7 of the 1993 GLORIA Expedition and the recently released 2-min altimetry-derived global gravity grid are used to determine the effective elastic thickness of the lithosphere along the Easter Seamount Chain (ESC). Forward modeling, admittance, and coherence methods yield consistent...
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Full Text:: wavelengths long enough to capture the peak in the admittance curve and (2) restricting the study area to a

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