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⁴⁰Ar-³⁹Ar ages of lavas from the Southeast Greenland margin, ODP leg 152, and the Rockall Plateau, DSDP leg 81

Creator:: Sinton, Christopher W. and Duncan, Robert A.
Abstract:: ⁴⁰Ar-³⁹Ar incremental heating experiments were performed on volcanic rocks recovered by drilling during Ocean Drilling Program Leg 152, southeast Greenland Margin (63°N), and Deep Sea Drilling Project Leg 81, southwest Rockall Plateau (56°N). Both of these legs drilled into thick sections of submerged lava flows, known as seaward-dipping reflector sequences,...
Resource Type:: Article
Full Text:: ., Jr. (Eds.), 1998 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 152 32. 40Ar

Age progressive volcanism in the New England seamounts and the opening of the Central Atlantic Ocean

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...
Resource Type:: Article
Full Text:: alkaline intrusions along the For the central At•lantic Ocean the pattern of northeast coast of

Tillamook volcanic series : further evidence for tectonic rotation of the Oregon Coast Range

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...
Resource Type:: Article
Full Text:: Oregon and Washington. Arrows indicate the mean paleomagnetic directions found for the re- spective

Tahiti: Geochemical evolution of a French Polynesian volcano

Creator:: Duncan, Robert A., Fisk, Martin R., White, William M., and Nielsen, Roger L.
Abstract:: The island of Tahiti, the largest in French Polynesia, comprises two major volcanoes aligned NW-SE, parallel with the general trend of the Society Islands hotspot track. Rocks form this volcanic system are basalts transitional to tholeiites, alkali basalts, basanites, picrites, and evolved lavas. Through K-Ar radiometric dating we have established...
Resource Type:: Article
Full Text:: center of the island. Few of these were fresh enough for dating; zeolites, clays and carbonate have

Precise dating of the Holmatindur cooling event in eastern Iceland: Evidence for mid-Miocene bipolar glaciation

Creator:: Duncan, Robert A. and Helgason, J.
Abstract:: A succession of basaltic lavas, volcaniclastic sediments, and lignite beds in the Holmatindur region of eastern Iceland provides the means for tying magnetic reversal stratigraphy and a record of major North Atlantic cooling to a precise radiometric timescale. A prominent part of the section is the Holmatindur classic bed, which...
Resource Type:: Article
Full Text:: ., vol. 77, edited by M. Pringle et al., pp. 233-261, AGU, Washington, D.C., 1995. Mathews, W. H

Evidence for diffuse exension of the Pacific plate from Pukapuka ridges and cross-grain gravity lineations

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...
Resource Type:: Article
Full Text:: Evidence for diffuse extension of the Pacific plate from

Temporal and geochemical variability of volcanic products of the Marquesas hotspot

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...
Resource Type:: Article
Full Text:: in 87Sr/86Sr for ocean islands yet found, but they have consistently higher Pb-isotope ratios than

Petrology and Geochemistry of the Galápagos Islands : portrait of a pathological mantle plume

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...
Resource Type:: Article
Full Text:: , New York ALEXANDER R. McBIRNEY Center for Volcanology, University of Oregon, Eugene ROBERT A

Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor

Creator:: Pyle, D. G., Christie, David M., Mahoney, J. J., and Duncan, Robert A.
Abstract:: Within the Australian-Antarctic Discordance (AAD), a boundary exists between isotopically defined “Pacific-type” and “Indian-type” mid-ocean ridge basalt (MORB) erupted along the Southeast Indian Ridge (SEIR). This boundary has migrated westward beneath the easternmost AAD spreading segment at a minimum rate of 25 mm/yr since 4 Ma; however, its long-term history...
Resource Type:: Article
Full Text:: The Australian-Antarctic Discordance (AAD) lies in the center of the Southern Ocean between Australia

Geochronology of Galapagos seamounts

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...
Resource Type:: Article
Full Text:: Spreading Center (GSC) in the eastern Pacific Ocean (Figure 1), is the present volcanic expression of the

The Cobb-Eickelberg seamount chain : hotspot volcanism with mid-oean ridge basalt affinity

Creator:: Desonie, Dana L. and Duncan, Robert A.
Abstract:: Cobb hotspot, currently located beneath Axial seamount on the Juan de Fuca ridge, has the temporal but not the isotopic characteristics usually attributed to a mantle plume. The earlier volcanic products of the hotspot, from eight volcanoes in the Cobb-Eickelberg seamount (CES) chain, show a westward age progression away from...
Resource Type:: Article
Full Text:: with Mid‐Ocean Ridge Basalt Affinity JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. B8, PAGES

The timing and duration of the Karoo igneous event, southern Gondwana

Creator:: Duncan, Robert A., Hooper, P. R., Rehacek, J., Marsh, J. S., and Duncan, A. R.
Abstract:: A volcanic event of immense scale occurred within a relatively short period in early Jurassic time over large regions of the contiguous Gondwana supercontinent. In southern Africa, associated remnants of thick volcanic successions of lava flows and extensive dike and sill complexes of similar composition have been grouped together as...
Resource Type:: Article
Full Text:: A1 tubes and irradiated for 6-10 hours at 1 MW power in the center ring of the TRIGA reactor at

Origin of the Louisville ridge and its relationship to the Eltanin Fracture Zone System

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...
Resource Type:: Article
Full Text:: sufficiently for a portion of the ridge to have been emplaced on crust with an offset. After about 12 Ma

Hotspots, mantle plumes, flood basalts, and true polar wander

Creator:: Duncan, Robert A. and Richards, M. A.
Abstract:: Persistent, long‐lived, stationary sites of excessive mantle melting are called hotspots. Hotspots leave volcanic trails on lithospheric plates passing across them. The global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions, through the orientations and age distributions of volcanic trails left by these melting...
Resource Type:: Article
Full Text:: . Modeled hotspot tracks for the northern Atlantic Ocean basin (see Figure 3 for details). The text

ScholarsArchive@OSU

⁴⁰Ar-³⁹Ar ages of lavas from the Southeast Greenland margin, ODP leg 152, and the Rockall Plateau, DSDP leg 81

Age progressive volcanism in the New England seamounts and the opening of the Central Atlantic Ocean

Tillamook volcanic series : further evidence for tectonic rotation of the Oregon Coast Range

Tahiti: Geochemical evolution of a French Polynesian volcano

Precise dating of the Holmatindur cooling event in eastern Iceland: Evidence for mid-Miocene bipolar glaciation

Evidence for diffuse exension of the Pacific plate from Pukapuka ridges and cross-grain gravity lineations

Temporal and geochemical variability of volcanic products of the Marquesas hotspot

Petrology and Geochemistry of the Galápagos Islands : portrait of a pathological mantle plume

Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor

Geochronology of Galapagos seamounts

The Cobb-Eickelberg seamount chain : hotspot volcanism with mid-oean ridge basalt affinity

The timing and duration of the Karoo igneous event, southern Gondwana

Origin of the Louisville ridge and its relationship to the Eltanin Fracture Zone System

Hotspots, mantle plumes, flood basalts, and true polar wander

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