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Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

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Title Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot
Names Wells, Ray (creator)
Bukry, David (creator)
Friedman, Richard (creator)
Pyle, Doug (creator)
Duncan, Robert (creator)
Haeussler, Peter (creator)
Wooden, Joe (creator)
Date Issued 2014-07-14 (iso8601)
Note To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Geological Society of America and can be found at: http://geosphere.gsapubs.org/.
Abstract Siletzia is a basaltic Paleocene and Eocene
large igneous province in coastal Oregon,
Washington, and southern Vancouver Island
that was accreted to North America in the
early Eocene. New U-Pb magmatic, detrital
zircon, and ⁴⁰Ar/³⁹Ar ages constrained by
detailed field mapping, global nannoplankton
zones, and magnetic polarities allow correlation
of the volcanics with the 2012 geologic
time scale. The data show that Siletzia was
rapidly erupted 56–49 Ma, during the Chron
25–22 plate reorganization in the northeast
Pacific basin. Accretion was completed
between 51 and 49 Ma in Oregon, based on
CP11 (CP—Coccolith Paleogene zone) coccoliths
in strata overlying onlapping continental
sediments. Magmatism continued in
the northern Oregon Coast Range until ca.
46 Ma with the emplacement of a regional
sill complex during or shortly after accretion.
Isotopic signatures similar to early Columbia
River basalts, the great crustal thickness of
Siletzia in Oregon, rapid eruption, and timing
of accretion are consistent with offshore
formation as an oceanic plateau. Approximately
8 m.y. after accretion, margin parallel
extension of the forearc, emplacement of
regional dike swarms, and renewed magmatism
of the Tillamook episode peaked at
41.6 Ma (CP zone 14a; Chron 19r). We examine
the origin of Siletzia and consider the possible
role of a long-lived Yellowstone hotspot
using the reconstruction in GPlates, an open
source plate model. In most hotspot reference
frames, the Yellowstone hotspot (YHS) is on
or near an inferred northeast-striking Kula-Farallon and/or Resurrection-Farallon ridge
between 60 and 50 Ma. In this configuration,
the YHS could have provided a 56–49 Ma
source on the Farallon plate for Siletzia,
which accreted to North America by 50 Ma.
A sister plateau, the Eocene basalt basement
of the Yakutat terrane, now in Alaska,
formed contemporaneously on the adjacent
Kula (or Resurrection) plate and accreted to
coastal British Columbia at about the same
time. Following accretion of Siletzia, the leading
edge of North America overrode the YHS
ca. 42 Ma. The voluminous high-Ti basaltic
to alkalic magmatism of the 42–35 Ma Tillamook
episode and extension in the forearc
may be related to the encounter with an active
YHS. Clockwise rotation of western Oregon
about a pole in the backarc has since moved
the Tillamook center and underlying Siletzia
northward ~250 km from the probable
hotspot track on North America. In the reference
frames we examined, the YHS arrives
in the backarc ~5 m.y. too early to match the
17 Ma magmatic fl are-up commonly attributed
to the YHS. We suggest that interaction
with the subducting slab may have delayed
arrival of the plume beneath the backarc.
Genre Article
Identifier Wells, R., Bukry, D., Friedman, R., Pyle, D., Duncan, R., Haeussler, P., & Wooden, J. (2014). Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot. Geosphere, 10(4), 692-719. doi:10.1130/GES01018.1

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