A near-ridge origin for seamounts at the southern terminus of the Pratt-Welker Seamount Chain, Northeast Pacific Ocean

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doi: 10.1139/e99-008
Authors:Cousens, Brian; Dostal, Jarda; Hamilton, T. S.
Author Affiliations:Primary:
Carleton University, Department of Earth Sciences, Ottawa, ON, Canada
Other:
Saint Mary's University, Canada
Wichita State University, United States
Volume Title:Canadian Journal of Earth Sciences Revue Canadienne des Sciences de la Terre
Source:Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, 36(6), p.1021-1031. Publisher: National Research Council of Canada, Ottawa, ON, Canada. ISSN: 0008-4077
Publication Date:1999
Note:In English with French summary. 53 refs.; illus., incl. 1 table
Summary:Three seamounts close to the south end of the Pratt-Welker Seamount Chain, Gulf of Alaska, have been sampled to test whether or not mantle plume-related volcanism extends south of Bowie Seamount. Lavas recovered from Oshawa, Drifters, and Graham seamounts are weathered, Mn-encrusted pillow lavas and sheet-flow fragments, commonly with glassy rims. The glasses and holocrystalline rocks are tholeiitic basalts, with light rare earth element depleted to flat primitive mantle normalized incompatible element patterns and radiogenic isotope compositions within the ranges of mid-ocean ridge and near-ridge seamount basalts from the Explorer and northern Juan de Fuca ridges. Chemically, the seamount lavas strongly resemble older, "shield-phase" tholeiitic rocks dredged from the flanks of southern Pratt-Welker seamounts, but are distinct from the younger alkaline intraplate lavas that cap Pratt-Welker edifices. The weathered, encrusted basalts were most likely erupted in a near-ridge environment, adjacent to Explorer Ridge, between 11 and 14 Ma. No evidence of plume-related activity is found in this area. Compared with northeast Pacific mid-ocean ridge and alkaline intraplate basalts, Graham seamount lavas have anomalously high 206Pb/204Pb, which does not appear to be a function of sea-floor alteration, magma contamination, or mixing between previously identified mantle components. All near-ridge seamounts in the northeast Pacific exhibit isotopic heterogeneity that does not correlate with major or trace element composition, suggesting that the mantle sources of all near-ridge seamounts have been variably depleted by prior, but recent melting events.
Sections:Petrology
Subsections:Oceanic petrology
Subjects:Alkaline earth metals; Basalts; Crust; Geochemistry; Glasses; Igneous rocks; Isotope ratios; Isotopes; Lava; Lead; Lithogeochemistry; Major elements; Mantle; Metals; Mid-ocean ridges; Nd-144/Nd-143; Neodymium; Ocean floors; Oceanic crust; Pb-206/Pb-204; Pb-207/Pb-204; Pillow lava; Radioactive isotopes; Rare earths; Seamounts; Sr-87/Sr-86; Stable isotopes; Strontium; Tholeiitic basalt; Trace elements; Volcanic glass; Volcanic rocks; East Pacific; Explorer Plate; Gulf of Alaska; Juan de Fuca Ridge; North Pacific; Northeast Pacific; Pacific Ocean; Drifters Seamount; Graham Seamount; Oshawa Seamount; Pratt-Walker Seamounts
Coordinates:N520000 N533000 W1333000 W1350000
Abstract Numbers:00M/2159
Record ID:2000009830
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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