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The Case for a Long-Lived

and Robust Yellowstone Hotspot

Victor E. Camp, San Diego State University, Dept. of Geological Sciences, 5500 Campanile Drive, San Diego, California 92182, USA;
and Ray E. Wells, U.S. Geological Survey, 2130 SW 5th Street, Portland, Oregon 97201, USA

ABSTRACT mantle plume (e.g., Hooper et al., 2007, and Although alternative models for the origin of
The Yellowstone hotspot is recognized as a references therein), an origin reinforced by Siletzia have been proposed, including conti-
whole-mantle plume with a history that recent seismic tomography that resolves the nental margin rifting (Clowes et al., 1987;
extends to at least 56 Ma, as recorded by off- Yellowstone hotspot as a high-temperature, Wells et al., 1984); slab window magmatism
shore volcanism on the Siletzia oceanic low-density conduit that extends through the (Babcock et al., 1992; Madsen et al., 2006);
plateau. Siletzia accreted onto the North lower mantle and is sourced at the core- and microplate accretion (McCrory and
American plate at 51–49 Ma, followed by mantle boundary (Nelson and Grand, 2018; Wilson, 2013), proximity to a hotspot seems
repositioning of the Farallon trench west of Steinberger et al., 2019). An energetic plume to be required to produce the large volume of
Siletzia from 48 to 45 Ma. North America is suggested by peak excess temperatures of basalt. Such an origin is supported by a vari-
overrode the hotspot, and it transitioned from 650–850 °C through the lower mantle ety of more recent studies; for example:
the Farallon plate to the North American plate (Nelson and Grand, 2018), and by an esti- (1) plate reconstruction models supporting
from 42 to 34 Ma. Since that time, it has been mated range in volume flux through the the location of a Paleocene to Eocene
genetically associated with a series of aligned upper mantle of 15 m s to 31 m s (Camp, Yellowstone hotspot in position to produce
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volcanic provinces associated with age- pro- 2019). Here, we examine the enduring Siletzia offshore of the northwestern U.S.
gressive events that include Oligocene high-K strength and evolution of this feature by (Engebretson et al., 1985; McCrory and
calc-alkaline volcanism in the Oregon back- summarizing and connecting previous stud- Wilson, 2013; Wells et al., 2014; Müller et al.,
arc region with coeval adakite volcanism ies to reveal a linear progression of magmatic 2016); (2) field and geochronological data
localized above the hot plume center; mid- provinces lying along the track of a fixed constraining the composition, age, and tim-
Miocene bimodal and flood-basalt volcanism Yellowstone hotspot that has been active at ing of Siletzia’s accretion (Wells et al., 2014;
of the main-phase Columbia River Basalt least since 56 Ma. Eddy et al., 2017); (3) volume calculations of
Group; coeval collapse of the Nevadaplano 1.7 × 10 km to 2.6 × 10 km for the unsub-
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associated with onset of Basin and Range PROVENANCE AND KINSHIP OF ducted part of the Siletzia terrane (Trehu et
extension and minor magmatism; and late SILETZIA TO THE YELLOWSTONE al., 1994; Wells et al., 2014), classifying it as
Miocene to recent bimodal volcanism along HOTSPOT a large igneous province typical of other oce-
two coeval but antithetical rhyolite migration Debate on the earliest manifestation of the anic hotspots (Bryan and Ernst, 2008);
trends—the Yellowstone–Snake River Plain Yellowstone hotspot has focused on tradi- (4) elevated Os/ Os in Siletzia mafic lavas
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hotspot track to the ENE and the Oregon High tional models that equate the generation of and He/ He on olivine phenocrysts, consis-
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Lava Plains to the WNW. continental flood-basalt provinces to melting tent with a mantle plume source (Pyle et al.,
of starting plume heads at the base of conti- 2015); (5) trace-element and Sr-Pb-Nd-Hf
INTRODUCTION nental lithosphere (e.g., Campbell, 2005). isotopic data delineating a heterogeneous
Most workers agree that rhyolite migra- This paradigm has led several workers to mantle source with a plume component simi-
tion along the Yellowstone–Snake River conclude that the Yellowstone starting plume lar to early Columbia River Basalt Group
Plain hotspot track is driven by mantle head arrived at ca. 17 Ma, contemporaneous lavas (Pyle et al., 2015; Phillips et al., 2017);
upwelling and basaltic magmatism, but they with the earliest flood-basalt eruptions of the and (6) mantle potential temperature calcula-
disagree on the mechanism of mantle ascent. Columbia River Basalt Group (Pierce and tions that are well above ambient mantle and
Proponents of a shallow-mantle origin for the Morgan, 1992; Camp and Ross, 2004; consistent with melts derived from a hot
Yellowstone hotspot have suggested a vari- Shervais and Hanan, 2008; Smith et al., mantle plume (Phillips et al., 2017).
ety of mechanisms that include rift propaga- 2009). Duncan (1982), however, was an early Murphy (2016) suggested a still earlier
tion (Christiansen et al., 2002), the lateral supporter of an older Yellowstone hotspot period of offshore magmatism, with the
migration of lithospheric extension (Foulger responsible for Paleocene to Eocene volca- Yellowstone swell entering the Farallon
et al., 2015), and eastward mantle flow driven nism that created an oceanic plateau, now trench at ca. 80–75 Ma and contributing
by sinking of the Farallon slab (Zhou et al., preserved as mafic rocks accreted to the to the Laramide orogeny. The cause of the
2018). Other workers attribute the hotspot Coast Ranges of Oregon, Washington, and Laramide orogeny remains controversial and
trend to plate motion over a deep-seated Vancouver Island—the Siletzia terrane. is not addressed here.

GSA Today, v. 31, https://doi.org/10.1130/GSATG477A.1. CC-BY-NC.

4 GSA Today | January 2021