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• 1. [Article] Evolution of the Walvis Ridge-Rio Grande rise hot spot systen : implications for African and South American plate motions over plumes

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Evolution of the Walvis Ridge-Rio Grande rise hot spot systen : implications for African and South American plate motions over plumes Author: O'Connor, John M., Duncan, Robert A. copyrighted by American Geophysical Union Title: Evolution of the Walvis Ridge-Rio Grande rise hot spot systen : implications for African and South American plate motions over plumes Author: O'Connor, John M., Duncan, Robert A. copyrighted by American Geophysical Union Close

• 2. [Article] Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor

  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 ...

  Citation × Citation Citation Abstract Copy Title: Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor Author: Mahoney, J. J., Pyle, D. G., Duncan, Robert A., Christie, David M. 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 remains a matter of speculation. To determine if Pacific-type upper mantle has migrated westward beneath the eastern Indian Ocean basin as Australia and Antarctica drifted apart during the last 70 m.y., we present new Sr-Nd-Pb isotope data, combined with trace element and 40Ar-39Ar radiometric age determinations, for samples from Legs 28 and 29 of the Deep Sea Drilling Project (DSDP). Basaltic basement at these DSDP sites provides a record of their upper mantle source composition and shows regional variations consistent with upper mantle flow in this region. East of the South Tasman Rise, all DSDP basalts have 87SR/86SR (0.7025-0.7029) and 206Pb/204Pb (18.80-19.48) ratios typical of Pacific-type MORB indicating that Pacific-type upper mantle existed east of the Australian-Antarctic continental margin and beneath the Tasman Sea during the early stages of seafloor spreading in this region. Basalts from DSDP sites west of the AAD have high 87Sr/86Sr (0.7030-0.7035), low 206Pb/204Pb (17.99-18.10) and trace element characteristics typical of present day Indian-type SEIR MORB. Between these two regions, DSDP basalts recovered along the western margin of the South Tasman Rise have isotopic characteristics that are, in one case consistent with Indian-type MORB source (Site 280A) and, in the second case, transitional between Pacific-type and Indian-type mantle sources. The occurrence of seafloor basalts with transitional or Indian-type isotopic characteristics well to the east of the present Indian-Pacific MORB isotopic boundary within the AAD strongly implies that Pacific-type upper mantle has migrated westward into the region since the South Tasman Rise separated from Antarctica circa 40 Ma. Title: Geochemistry and geochronology of ancient southeast Indian and southwest Pacific seafloor Author: Mahoney, J. J., Pyle, D. G., Duncan, Robert A., Christie, David M. 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 remains a matter of speculation. To determine if Pacific-type upper mantle has migrated westward beneath the eastern Indian Ocean basin as Australia and Antarctica drifted apart during the last 70 m.y., we present new Sr-Nd-Pb isotope data, combined with trace element and 40Ar-39Ar radiometric age determinations, for samples from Legs 28 and 29 of the Deep Sea Drilling Project (DSDP). Basaltic basement at these DSDP sites provides a record of their upper mantle source composition and shows regional variations consistent with upper mantle flow in this region. East of the South Tasman Rise, all DSDP basalts have 87SR/86SR (0.7025-0.7029) and 206Pb/204Pb (18.80-19.48) ratios typical of Pacific-type MORB indicating that Pacific-type upper mantle existed east of the Australian-Antarctic continental margin and beneath the Tasman Sea during the early stages of seafloor spreading in this region. Basalts from DSDP sites west of the AAD have high 87Sr/86Sr (0.7030-0.7035), low 206Pb/204Pb (17.99-18.10) and trace element characteristics typical of present day Indian-type SEIR MORB. Between these two regions, DSDP basalts recovered along the western margin of the South Tasman Rise have isotopic characteristics that are, in one case consistent with Indian-type MORB source (Site 280A) and, in the second case, transitional between Pacific-type and Indian-type mantle sources. The occurrence of seafloor basalts with transitional or Indian-type isotopic characteristics well to the east of the present Indian-Pacific MORB isotopic boundary within the AAD strongly implies that Pacific-type upper mantle has migrated westward into the region since the South Tasman Rise separated from Antarctica circa 40 Ma. Close

• 3. [Article] Geochronology of age-progressive volcanism of the Oregon High Lava Plains : implications for the plume interpretation of Yellowstone

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Geochronology of age-progressive volcanism of the Oregon High Lava Plains : implications for the plume interpretation of Yellowstone Author: Deino, Alan L., Grunder, Anita L., Duncan, Robert A., Jordan, Brennan T. copyrighted by American Geophysical Union Title: Geochronology of age-progressive volcanism of the Oregon High Lava Plains : implications for the plume interpretation of Yellowstone Author: Deino, Alan L., Grunder, Anita L., Duncan, Robert A., Jordan, Brennan T. copyrighted by American Geophysical Union Close

• 4. [Article] The Cobb-Eickelberg seamount chain : hotspot volcanism with mid-oean ridge basalt affinity

  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 ...

  Citation × Citation Citation Abstract Copy Title: The Cobb-Eickelberg seamount chain : hotspot volcanism with mid-oean ridge basalt affinity Author: Desonie, Dana L., Duncan, Robert A. 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 the hotspot and a westward increase in the age difference between the seamounts and the crust on which they formed. These results are consistent with movement of the Pacific plate over a fixed Cobb hotspot and eventual encroachment by the westwardly migrating Juan de Fuca ridge. CES lavas are slightly enriched in alkalies and incompatible elements relative to those of the Juan de Fuca ridge but they have Sr. Nd, and Pb isotopic compositions virtually identical to those found along the ridge. Therefore, Cobb hotspot is a stationary, upper mantle melting anomaly whose volcanic products show strong mid-ocean ridge basalt (MORB) affinity. These observations can be explained by low degrees of partial melting of entrained heterogeneous upper mantle MORB source material within a thermally driven lower mantle diapir or by an intrinsic MORB-like composition of the deeper mantle source region from which northeast Pacific plumes rise. Title: The Cobb-Eickelberg seamount chain : hotspot volcanism with mid-oean ridge basalt affinity Author: Desonie, Dana L., Duncan, Robert A. 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 the hotspot and a westward increase in the age difference between the seamounts and the crust on which they formed. These results are consistent with movement of the Pacific plate over a fixed Cobb hotspot and eventual encroachment by the westwardly migrating Juan de Fuca ridge. CES lavas are slightly enriched in alkalies and incompatible elements relative to those of the Juan de Fuca ridge but they have Sr. Nd, and Pb isotopic compositions virtually identical to those found along the ridge. Therefore, Cobb hotspot is a stationary, upper mantle melting anomaly whose volcanic products show strong mid-ocean ridge basalt (MORB) affinity. These observations can be explained by low degrees of partial melting of entrained heterogeneous upper mantle MORB source material within a thermally driven lower mantle diapir or by an intrinsic MORB-like composition of the deeper mantle source region from which northeast Pacific plumes rise. Close

• 5. [Article] A captured island chain in the coast range of Oregon and Washington

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: A captured island chain in the coast range of Oregon and Washington Author: Duncan, Robert A. copyrighted by American Geophysical Union Title: A captured island chain in the coast range of Oregon and Washington Author: Duncan, Robert A. copyrighted by American Geophysical Union Close

• 6. [Article] Temporal and geochemical variability of volcanic products of the Marquesas hotspot

  copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Temporal and geochemical variability of volcanic products of the Marquesas hotspot Author: Desonie, Dana L., Duncan, Robert A., Natland, J. H. copyrighted by American Geophysical Union. Title: Temporal and geochemical variability of volcanic products of the Marquesas hotspot Author: Desonie, Dana L., Duncan, Robert A., Natland, J. H. copyrighted by American Geophysical Union. Close

• 7. [Article] Seismic and seafloor evidence for free gas, gas hydrates, and fluid seeps on the transform margin offshore Cape Mendocino

  Copyrighted by American Geophysical Union.

  Citation × Citation Citation Abstract Copy Title: Seismic and seafloor evidence for free gas, gas hydrates, and fluid seeps on the transform margin offshore Cape Mendocino Author: Goffredi, Shana K., Stakes, Debra S., Salamy, Karen A., Bartlett, Cindy D., Potter, Susan M., Duncan, Robert A., Chevallier, Johanna, Tréhu, Anne Martine Copyrighted by American Geophysical Union. Title: Seismic and seafloor evidence for free gas, gas hydrates, and fluid seeps on the transform margin offshore Cape Mendocino Author: Goffredi, Shana K., Stakes, Debra S., Salamy, Karen A., Bartlett, Cindy D., Potter, Susan M., Duncan, Robert A., Chevallier, Johanna, Tréhu, Anne Martine Copyrighted by American Geophysical Union. Close

• 8. [Article] Age progressive volcanism in the New England seamounts and the opening of the Central Atlantic Ocean

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Age progressive volcanism in the New England seamounts and the opening of the Central Atlantic Ocean Author: Duncan, Robert A. copyrighted by American Geophysical Union Title: Age progressive volcanism in the New England seamounts and the opening of the Central Atlantic Ocean Author: Duncan, Robert A. copyrighted by American Geophysical Union Close