Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (15) Citing Articles via Google Scholar Google Scholar Articles by Davis, A. S. Articles by Greene, H. G. Search for Related Content GeoRef GeoRef Citation

Seamounts at the continental margin of California: A different kind of oceanic intraplate volcanism

¹ Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95039-9644, USA
² Department of Geological Sciences, Central Washington University, Ellensburg, Washington 98926, USA
³ College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331-5503, USA
⁴ Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95039-9644, USA, and Moss Landing Marine Laboratory, Moss Landing, California 95039, USA

Davidson, Guide, Pioneer, Gumdrop, and Rodriguez Seamounts, located at the continental margin offshore California between latitudes 37.5°N and 34.0°N, may represent a previously unrecognized type of intraplate oceanic volcanism. Morphologically unlike typical oceanic-island volcanoes or near-ridge seamounts, they are complex, northeast-trending ridges that reflect the ridge-parallel structure of the underlying oceanic crust. ⁴⁰Ar/³⁹Ar laser fusion ages of mineral separates indicate at least two episodes of volcanism at ca. 16 and ca. 12 Ma, younger by 7–11 m.y. than the underlying ocean crust. Volcanic rocks are predominantly differentiated alkalic basalt, hawaiite, and mugearite. The lack of coherent liquid- lines-of-descent is consistent with small batches of magma forming, fractionally crystallizing, and erupting in isolation from the previous and subsequent batches. The presence of mantle xenoliths suggests that magmas originated in the upper mantle. Xenoliths of alkalic cumulates and xenocrysts of feldspar, amphibole, and titanomagnetite are consistent with fractionation in the upper mantle as well. Sr, Nd, and Pb isotope ratios of some samples are from depleted-mantle sources like those of MORB (mid-oceanic-ridge basalt); others indicate more variably enriched mantle sources. Magmas formed by small- percentage partial melting of variably enriched MORB-source-type mantle, according to the samples' high abundances of incompatible elements such as Nb, Ta, and Th. Coeval middle Miocene basalts in onshore coastal California have a similar isotopic range, but their trace elements show a subduction-related signature. If the coeval volcanic rocks offshore originated in a slab window, as proposed for those onshore, they were not influenced by a slab component. Although a slab-window origin is plausible for the middle Miocene volcanism, later episodes of small, sporadic eruptions on- and offshore probably resulted from decompression melting of mantle rising along existing zones of weakness undergoing extension related to continued movement along transform-fault systems.

Key Words: central California • continental margin • geochronology • isotope geochemistry • petrology • submarine volcanoes

This article has been cited by other articles:

				G. Shanmugam Comment on "Late Holocene Rupture of the Northern San Andreas Fault and Possible Stress Linkage to the Cascadia Subduction Zone" by Chris Goldfinger, Kelly Grijalva, Roland Burgmann, Ann E. Morey, Joel E. Johnson, C. Hans Nelson, Julia Gutierrez-Pastor, Andrew Ericsson, Eugene Karabanov, Jason D. Chaytor, Jason Patton, and Eulalia Gracia Bulletin of the Seismological Society of America, August 1, 2009; 99(4): 2594 - 2598. [Full Text] [PDF]

				B. Cousens, J. Prytulak, C. Henry, A. Alcazar, and T. Brownrigg Geology, geochronology, and geochemistry of the Miocene-Pliocene Ancestral Cascades arc, northern Sierra Nevada, California and Nevada: The roles of the upper mantle, subducting slab, and the Sierra Nevada lithosphere Geosphere, October 1, 2008; 4(5): 829 - 853. [Abstract] [Full Text] [PDF]

				P. R. Castillo Origin of the adakite-high-Nb basalt association and its implications for postsubduction magmatism in Baja California, Mexico Geological Society of America Bulletin, March 1, 2008; 120(3-4): 451 - 462. [Abstract] [Full Text] [PDF]

				G. Pe-Piper, D. J.W. Piper, L. F. Jansa, and A. de Jonge Early Cretaceous opening of the North Atlantic Ocean: Implications of the petrology and tectonic setting of the Fogo Seamounts off the SW Grand Banks, Newfoundland Geological Society of America Bulletin, May 1, 2007; 119(5-6): 712 - 724. [Abstract] [Full Text] [PDF]

				A. S. Davis, D. A. Clague, and J. B. Paduan Diverse Origins of Xenoliths from Seamounts at the Continental Margin, Offshore Central California J. Petrology, May 1, 2007; 48(5): 829 - 852. [Abstract] [Full Text] [PDF]

				J. G. Fitton The OIB paradox Geological Society of America Special Papers, January 1, 2007; 430(0): 387 - 412. [Abstract] [Full Text] [PDF]

				J.M. Kela, D.S. Stakes, and R.A. Duncan Geochemical and age constraints on the formation of the Gorda Escarpment and Mendocino Ridge of the Mendocino transform fault in the NE Pacific Geological Society of America Bulletin, January 1, 2007; 119(1-2): 88 - 100. [Abstract] [Full Text] [PDF]