Slab‐plume interaction beneath the Pacific Northwest

Abstract

[1] The Pacific Northwest has undergone complex plate reorganization and intense tectono-volcanic activity to the east during the Cenozoic (last 65 Ma). Here we show new high-resolution tomographic images obtained using shear and compressional data from the ongoing USArray deployment that demonstrate first that there is a continuous, wholemantle plume beneath the Yellowstone Snake River Plain (YSRP) and second, that the subducting Juan de Fuca (JdF) slab is fragmented and even absent beneath Oregon. The analysis of the geometry of our tomographic models suggests that the arrival and emplacement of the large Yellowstone plume had a substantial impact on the nearby Cascadia subduction zone, promoting the tearing and weakening of the JdF slab. This interpretation also explains several intriguing geophysical properties of the Cascadia trench that contrast with most other subduction zones, such as the absence of deep seismicity and the trench-normal fast direction of mantle anisotropy. The DNA velocity models are available for download and slicing at http://dna.berkeley. edu. Citation: Obrebski, M., R. M. Allen, M. Xue, and S.-H.

Evidence for Cyclical Fractional Crystallization, Recharge, and Assimilation in Basalts of the Kimama Drill Core, Central Snake River Plain, Idaho: 5.5-Million-Years of Petrogenesis in a Mid-crustal Sill Complex

“…These relatively low pressures imply that melting must occur within the sublithospheric conduit that has been imaged seismically (Schutt and Dueker, 2008;Stachnik et al, 2008;Obrebski et al, 2010) beneath the eastern Snake River Plain as inferred by Hanan et al (2008).…”

Drilling the solid earth: global geodynamic cycles and earth evolution

“…Project Hotspot was designed to explore the impact of deep-seated mantle plumes on continental crust and lithosphere, and the influence of continental lithosphere on plume-derived magmas (Shervais et al 2013a). The Snake River Plain (SRP) of southern Idaho records the track of the Yellowstone hotspot, a deep-seated mantle plume that has been imaged seismically to depths of over 1,000 km and forms a curtain of hot mantle that penetrates the subducting Farallon slab (Obrebski et al 2010;James et al 2011). Magmas associated with melting of the plume head erupted under eastern Oregon and Washington circa 17 Ma, forming the Columbia River basalts and related rhyolite eruptive centers under northern Nevada and southwestern Idaho.…”

The Yellowstone “hot spot” track results from migrating basin-range extension

“…They rule out a deeper body wider than 50 km and stronger than -1.5% in V S and -0.75% in V P . In a paper published just nine days later, the same group report an inversion showing a continuous, corkscrew-shaped 'whole-mantle plume' bottoming at 900 km depth in both V P and V S (Obrebski et al, 2010). They report good recovery of structure down to 1200 km depth.…”

“…They attribute the time-progressive Newberry volcanic chain to upper-mantle processes. Obrebski et al (2010) interpret the low-velocity anomaly beneath the ESRP as part of a plume head, whereas Tian and Zhao (2012) attribute it to hydrated minerals. Obrebski et al (2010) suggest a Yellowstone plume rose opportunistically through a preexisting tear in the downgoing Farallon slab.…”

“…Since inception of the USArray project in 2004 a vast database of seismic recordings has accumulated which has been used by numerous research groups to study the structure of the mantle beneath the contiguous 48 states James et al, 2011;Obrebski et al, 2010;Schmandt and Humphreys, 2010;Tian et al, 2009;Tian and Zhao, 2012;e.g., Xue and Allen, 2010). Beginning with the installation of ~ 400 stations in a swath covering Washington, Oregon and California, USArray migrated progressively east and has now almost completed its sweep across the continent.…”