40Ar/39AR AGE, Petrology, and Tectonic Significance of Some Seamounts in the Gulf of Alaska

  1. Barbara H. Keating,
  2. Patricia Fryer,
  3. Rodey Batiza and
  4. George W. Boehlert
  1. G. Brent Dalrymple1,
  2. David A. Clague1,
  3. Tracy L. Vallier1 and
  4. H. William Menard2

Published Online: 18 MAR 2013

DOI: 10.1029/GM043p0297

Seamounts, Islands, and Atolls

Seamounts, Islands, and Atolls

How to Cite

Dalrymple, G. B., Clague, D. A., Vallier, T. L. and Menard, H. W. (1987) 40Ar/39AR AGE, Petrology, and Tectonic Significance of Some Seamounts in the Gulf of Alaska, in Seamounts, Islands, and Atolls (eds B. H. Keating, P. Fryer, R. Batiza and G. W. Boehlert), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM043p0297

Author Information

  1. 1

    U.S. Geological Survey, Menlo Park, California 94025

  2. 2

    Scripps Institution of Oceanography, La Jolla, California 92093

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1987

ISBN Information

Print ISBN: 9780875900681

Online ISBN: 9781118664209



  • Seamounts;
  • Coral reefs and islands


New petrographic, geochemical, and 40Ar/39Ar age data on Welker Guyot, Patton Seamount, Murray Guyot, Miller Seamount, and Pathfinder Seamount, when considered with previously published data, show that the majority of seamounts in the Gulf of Alaska formed by mid-plate, rather than ridge associated, volcanic processes. Lavas recovered by dredging from Welker, Patton, Murray, and Pathfinder include alkalic basalt, hawaiite, mugearite, benmoreite, and trachyte, which are typical of mid-plate volcanoes. Lavas from Miller Seamount are tholeiitic basalt and basalt transitional between tholeiitic and alkalic basalt, which are typical of volcanoes associated with accretionary processes at spreading ridges. These genetic associations are confirmed by the age data, which show that Miller was constructed on younger crust than the other four seamounts. 40Ar/39Ar age spectra show the following ages for the five seamounts: Welker 14.9±0.3 m.y., Patton 29.7±0.3 m.y., Murray 27.6±0.2 m.y., Miller 25.8±2.1 m.y., and Pathfinder 23.1±0.2 m.y. Welker Guyot is too old to be part of the hot spot trace proposed by Turner et al. [1980] for other dated volcanoes in the Pratt Welker chain unless the velocity of volcanic propagation changed just before and after Welker formed. It seems more likely that the volcanoes in this chain were formed by at least two episodes of mid-plate volcanism as well as volcanism associated with spreading ridges. The 40Ar/39Ar ages of Patton and Murray are much older than the 2–8 m.y. age suggested by their shallow depth and basement swell height; they apparently sit on crust that has been recently thermally rejuvenated. The volcanic “chains” in the Gulf of Alaska were formed by multiple episodes of intermittent mid-plate volcanism and by volcanism associated with spreading ridges rather than by the persistent volcanic activity typically associated with hot-spot chains elsewhere on the Pacific Plate. Their apparent alignment is in part fortuitous.