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Ma. Slab rupture and adiabatic rise of this
accumulated mantle generated bimodal erup-
tions of flood basalt and rhyolite from 17 to
15 Ma, the latter driven by basalt injection
and melting of fertile crust near the center
of the Nevada–Columbia Basin Magmatic
Belt (e.g., Coble and Mahood, 2016; Benson
et al., 2017).
Silicic volcanism remained dispersed until
Figure 2. Palinspastic reconstruction of ca. 14 Ma when rhyolitic eruptions became
bimodal volcanism along the Nevada–
Columbia Basin magmatic belt from ca. more focused along the Yellowstone–Snake
17–15 Ma, with southernmost extension River Plain in SW Idaho (Fig. 1). Here,
based solely on aeromagnetic data. See
Figure 1 for definition of red and blue bimodal eruptions from ca. 14 Ma to 10 Ma
stars and volcanic fields HRCC, MVF, are thought to be associated with the transi-
LOVF, and NNR. Orange arrows depict
the orientation of mid-Miocene Basin- tion from volcanism above the broad accu-
and-Range extension; black arrows mulation of plume material to volcanism
depict the overall dilation direction of above the narrow plume tail, as the former
coeval mid-Miocene dikes. CJDS–Chief
Joseph dike swarm, where 85% of the was overridden by continental lithosphere of
Columbia River Basalt Group volume the North American craton (Pierce and
erupted. Area of 17–14 Ma extension
from Colgan and Henry (2009). WSRP— Morgan, 1992; Shervais and Hanan, 2008).
Western Snake River Plain. A systematic ENE progression of younger
inception ages for rhyolite fields in the cen-
tral Snake River Plain began between 12.5–
10.8 Ma, with the plume tail establishing a
well-defined hotspot-migration trend by ca.
10 Ma (Pierce and Morgan, 1992, 2009).

Coeval Rhyolite Migrations along
Opposing Trends (10 Ma to Recent)
Anders et al. (2019) calculated a migra-
tion rate of 2.27 ± 0.21 cm/yr along the
setting. Basin-and-Range extension began Could plume impingement be the main Yellowstone–Snake River Plain trend since
at 17–16 Ma (Colgan and Henry, 2009) cause of Basin-and-Range extension? This 10.41 Ma, which is close to independent
when torsional stress was fully imposed on also seems unlikely, based on the well-doc- estimates of plate motion along the same
the continental interior due to plate-bound- umented influence of plate-boundary con- ENE trend (Fig. 3). This is consistent with a
ary tectonics (Dickinson, 1997). ditions on regional stress and the influence fixed Yellowstone hotspot over this time-
Could the initiation of continental exten- of high gravitational potential energy on the frame, similar to the classic Hawaiian-type
sion at 17–16 Ma be the root cause of coeval uplifted orogenic plateau, the Nevadaplano. model of plate motion above a stationary
flood-basalt and related magmatism in the On the other hand, plume underplating may plume tail.
Nevada–Columbia Basin Magmatic Belt well have played a role in crustal extension Contemporaneous silicic migration since
(e.g., Dickinson, 1997)? Such a scenario con- through thermal weakening and mantle 10 Ma occurs across the Oregon High Lava
flicts with two observations: (1) the greatest traction at the base of the lithosphere (Pierce Plains from SE Oregon toward the Newberry
eruptive volume was in the area of least et al., 2002), thus providing a catalyst for volcano east of the Oregon Cascades arc
extension (e.g., the Chief Joseph dike swarm; extension of the high plateau that was already (e.g., Jordan et al., 2004). This WNW trend
CJDS on Fig. 2), while the smallest eruptive under stress and on the verge of regional col- (Fig. 3) is antithetical to the Yellowstone–
volume was in the Basin-and-Range region lapse (Camp et al., 2015). Snake River Plain trend and is often cited
of far greater extension (e.g., the NNR on as evidence against a plume origin (e.g.,
Fig. 2); and (2) early crustal extension in the Transition from Broad-Based Christiansen et al., 2002; Foulger et al., 2015).
northern and central Basin-and-Range gen- Volcanism to an Age-Progressive Several workers attribute the High Lava
erated structural elements with NNE trends, Hotspot Track (ca. 14–10 Ma) Plains trend to mantle upwelling associated
but coeval magmatic intrusion along the In the long-lived plume scenario, the with slab rollback (e.g., Long et al., 2009;
Nevada–Columbia Basin Magmatic Belt Yellowstone plume head arrived prior to Ford et al., 2013), but this may be difficult to
generated dikes with NNW trends, a 45° dif- Siletzia accretion, and not during the onset reconcile with evolving seismic data that
ference (e.g., Colgan, 2013). Camp et al. of flood-basalt volcanism. The plume com- reveal a shortened and highly fragmented
(2015) and Morriss et al. (2020) attributed ponent in the main-phase Columbia River slab in this region (Long, 2016). Slab frag-
the source of these magmatic trends instead Basalt Group eruptions is instead attributed mentation is described by Hawley and Allen
to a bottom-up process of forceful dike injec- to the large volume of plume material that (2019) as a propagating tear responsible for
tion due to high magma overpressure unre- collected beneath the Farallon slab by flux westward mantle flow beneath the High
lated to regional stress. of the feeding plume tail from ca. 34–17 Lava Plains trend. Following Jordan et al.
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