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• 41. [Article] Seamount morphology in the Bowie and Cobb hot spot trails, Gulf of Alaska

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Seamount morphology in the Bowie and Cobb hot spot trails, Gulf of Alaska Author: Dziak, Robert P., Keller, Randall A., Chaytor, Jason D., Duncan, Robert A. copyrighted by American Geophysical Union Title: Seamount morphology in the Bowie and Cobb hot spot trails, Gulf of Alaska Author: Dziak, Robert P., Keller, Randall A., Chaytor, Jason D., Duncan, Robert A. copyrighted by American Geophysical Union Close

• 42. [Article] Hotspots, mantle plumes, flood basalts, and true polar wander

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Hotspots, mantle plumes, flood basalts, and true polar wander Author: Duncan, Robert A., Richards, M. A. copyrighted by American Geophysical Union Title: Hotspots, mantle plumes, flood basalts, and true polar wander Author: Duncan, Robert A., Richards, M. A. copyrighted by American Geophysical Union Close

• 43. [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

• 44. [Article] Distribution of recent volcanism and the morphology of seamounts and ridges in the GLIMPSE study area: implications for the lithospheric cracking hypothesis for the origin of intraplate, non-hotspot volcanic chains

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Distribution of recent volcanism and the morphology of seamounts and ridges in the GLIMPSE study area: implications for the lithospheric cracking hypothesis for the origin of intraplate, non-hotspot volcanic chains Author: Scheirer, Daniel S., Forsyth, Donald W., Harmon, Nicholas, Duncan, Robert A. copyrighted by American Geophysical Union Title: Distribution of recent volcanism and the morphology of seamounts and ridges in the GLIMPSE study area: implications for the lithospheric cracking hypothesis for the origin of intraplate, non-hotspot volcanic chains Author: Scheirer, Daniel S., Forsyth, Donald W., Harmon, Nicholas, Duncan, Robert A. copyrighted by American Geophysical Union Close

• 45. [Article] ⁴⁰Ar/³⁹Ar geochronology of silicic and basic volcanic rocks on the margins of the North Atlantic

  At the submerged margins of the North Atlantic, andesitic to dacitic and basaltic volcanic rocks occur together. The silicic rocks were derived by processes requiring the presence of continental crust (crustal ...

  Citation × Citation Citation Abstract Copy Title: ⁴⁰Ar/³⁹Ar geochronology of silicic and basic volcanic rocks on the margins of the North Atlantic Author: Hitchen, K., Duncan, Robert A., Sinton, C. W. At the submerged margins of the North Atlantic, andesitic to dacitic and basaltic volcanic rocks occur together. The silicic rocks were derived by processes requiring the presence of continental crust (crustal anatexis and/or contamination of mafic magmas) while the majority of the basaltic lavas had little or no contact with continental crust. We report ⁴⁰Ar–³⁹Ar incremental heating ages for several dacitic and basaltic rocks recovered from three offshore localities of the North Atlantic Igneous Province. Dacitic lavas and tuffs at the southeast Greenland margin and trachytic lavas in the Scottish Hebrides erupted contemporaneously with basaltic lavas at 62–61 Ma. In contrast, the silicic lavas from the northern Rockall Trough (offshore western Scotland) and the Vøring Plateau (offshore Norway) erupted at ~ 55 Ma followed shortly by basaltic volcanism. At this time, silicic magmatism at the southeast Greenland margin had ceased and only oceanic basalts were erupted. Similarly, ~ 55 Ma lavas on the southwest Rockall Plateau are wholly basaltic. The compositions of all of the dated silicic volcanic rocks are consistent with derivation from partial melting of either continental crust or sediments. The heat necessary for partial melting appears to have been provided by basaltic magmas. Therefore, the existence of the silicic rocks indicates the presence of continental crust as well as a stable tectonic environment that allowed the stagnation and pooling of basaltic melts within the crust. With this in mind, it is apparent that at 62–60 Ma, both western and eastern sides of the present North Atlantic margins were characterized by extensional environments within continental crust that were restrictive to the passage of mafic magmas. By 55 Ma, at the time of continental breakup, the proximal margins at southeast Greenland and the Rockall Plateau were devoid of continental crust. But the presence of 55 Ma silicic magmatism on the eastern North Atlantic margin can be attributed to a broader zone of magmatism and sediment-filled Mesozoic rift basins. Title: ⁴⁰Ar/³⁹Ar geochronology of silicic and basic volcanic rocks on the margins of the North Atlantic Author: Hitchen, K., Duncan, Robert A., Sinton, C. W. At the submerged margins of the North Atlantic, andesitic to dacitic and basaltic volcanic rocks occur together. The silicic rocks were derived by processes requiring the presence of continental crust (crustal anatexis and/or contamination of mafic magmas) while the majority of the basaltic lavas had little or no contact with continental crust. We report ⁴⁰Ar–³⁹Ar incremental heating ages for several dacitic and basaltic rocks recovered from three offshore localities of the North Atlantic Igneous Province. Dacitic lavas and tuffs at the southeast Greenland margin and trachytic lavas in the Scottish Hebrides erupted contemporaneously with basaltic lavas at 62–61 Ma. In contrast, the silicic lavas from the northern Rockall Trough (offshore western Scotland) and the Vøring Plateau (offshore Norway) erupted at ~ 55 Ma followed shortly by basaltic volcanism. At this time, silicic magmatism at the southeast Greenland margin had ceased and only oceanic basalts were erupted. Similarly, ~ 55 Ma lavas on the southwest Rockall Plateau are wholly basaltic. The compositions of all of the dated silicic volcanic rocks are consistent with derivation from partial melting of either continental crust or sediments. The heat necessary for partial melting appears to have been provided by basaltic magmas. Therefore, the existence of the silicic rocks indicates the presence of continental crust as well as a stable tectonic environment that allowed the stagnation and pooling of basaltic melts within the crust. With this in mind, it is apparent that at 62–60 Ma, both western and eastern sides of the present North Atlantic margins were characterized by extensional environments within continental crust that were restrictive to the passage of mafic magmas. By 55 Ma, at the time of continental breakup, the proximal margins at southeast Greenland and the Rockall Plateau were devoid of continental crust. But the presence of 55 Ma silicic magmatism on the eastern North Atlantic margin can be attributed to a broader zone of magmatism and sediment-filled Mesozoic rift basins. Close

• 46. [Article] Basalts erupted along the Tongan fore arc during subduction initiation: Evidence from geochronology of dredged rocks from the Tonga fore arc and trench

  This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gc/.

  Citation × Citation Citation Abstract Copy Title: Basalts erupted along the Tongan fore arc during subduction initiation: Evidence from geochronology of dredged rocks from the Tonga fore arc and trench Author: Wright, Dawn J., Meffre, Sebastian, Bloomer, Sherman H., Duncan, Robert A., Hauff, Folkmar, Falloon, Trevor J., Hoernle, Kaj, Crawford, Tony J. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gc/. Title: Basalts erupted along the Tongan fore arc during subduction initiation: Evidence from geochronology of dredged rocks from the Tonga fore arc and trench Author: Wright, Dawn J., Meffre, Sebastian, Bloomer, Sherman H., Duncan, Robert A., Hauff, Folkmar, Falloon, Trevor J., Hoernle, Kaj, Crawford, Tony J. This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://www.agu.org/journals/gc/. Close

• 47. [Article] Evidence for diffuse exension of the Pacific plate from Pukapuka ridges and cross-grain gravity lineations

  copyrighted by American Geophysical Union

  Citation × Citation Citation Abstract Copy Title: Evidence for diffuse exension of the Pacific plate from Pukapuka ridges and cross-grain gravity lineations Author: Mammerickx, Jacqueline, Levitt, Daniel A., Johnson, Catherine L., Sandwell, David T., Lynch, Mary Ann, Duncan, Robert A., Winterer, Edward L. copyrighted by American Geophysical Union Title: Evidence for diffuse exension of the Pacific plate from Pukapuka ridges and cross-grain gravity lineations Author: Mammerickx, Jacqueline, Levitt, Daniel A., Johnson, Catherine L., Sandwell, David T., Lynch, Mary Ann, Duncan, Robert A., Winterer, Edward L. copyrighted by American Geophysical Union Close

• 48. [Article] Insights into mantle composition and mantle melting beneath mid‐ocean ridges from postspreading volcanism on the fossil Galapagos Rise

  This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by American Geophysical Union and can be found at: http://www.agu.org/journals/gc...

  Citation × Citation Citation Abstract Copy Title: Insights into mantle composition and mantle melting beneath mid‐ocean ridges from postspreading volcanism on the fossil Galapagos Rise Author: Grevemeyer, Ingo, Haase, Karsten M., Brandl, Philipp A., Duncan, Robert A., Stroncik, Nicole, Regelous, Marcel This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by American Geophysical Union and can be found at: http://www.agu.org/journals/gc/. Title: Insights into mantle composition and mantle melting beneath mid‐ocean ridges from postspreading volcanism on the fossil Galapagos Rise Author: Grevemeyer, Ingo, Haase, Karsten M., Brandl, Philipp A., Duncan, Robert A., Stroncik, Nicole, Regelous, Marcel This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by American Geophysical Union and can be found at: http://www.agu.org/journals/gc/. Close