WASATCH LINE (NEOGENE)/EAST PACIFIC RISE PLATE TECTONIC MODEL: VIABLE ALTERNATIVE TO SLAB GAP?

The Wasatch Line (Neogene)/East Pacific Rise plate tectonic model (Model) interprets current Cordilleran topography and late Cenozoic geology to be the result of the East Pacific Rise (EPR) operating under the North American Plate (NAP). The full plate tectonic cycle is evidenced under the NAP, from initial basalt plate generation to plate “subduction” (defined as basalt plate sinking into the mantle) and partial melting. The Wasatch Front (WF)/Mogollon Rim (MR) topography (topo) is an affect of the Wasatch/EPR spreading center (WSC), but the actual position of the WSC is the Intermountain Seismic Zone, typically east of the WF/MR. Utah’s “rift pillows” evidence WSC magma generation. The Yellowstone Hot Spot is an Icelandic analogue integral to the WSC.

The WSC generates two hot fast-moving divergent basaltic plates that slide horizontally away from the WSC immediately under the NAP. The West Basaltic Plate (WBP) moves southwesterly; the East Basaltic Plate (EBP) moves northeasterly. The WBP underrides the NAP more rapidly than the NAP overrides the WSC creating Basin & Range (B&R) extension, which therefore is concentrated in the eastern B&R. WBP subduction begins at the Walker Lane Belt (WLB)/Gulf of California trough (GoC); continued WBP subduction tilts the Sierra Nevada (SN)/Baja California (BC) batholiths and is evidenced by southwesterly SN “delamination” and Great Valley “mantle drips.” The Mojave Block plateau is a segment of the WBP that contacted the Pacific plate, locked in place, failed to subduct, remaining essentially horizontal, in contrast with WBP segments north of the Garlock fault and south in the Salton Trough. The resulting regional topo high creates the apparent north/south topo break in the SN/BC, WLB/GoC, B&R, and WF/MR; each of which would otherwise be singular topo features.

The Klamath-Blue Mountain Lineament (KBML) is the northwest (NW) edge of the WBP. The KBML is crudely co-spatial and on strike with the most recent line of Oregon’s 10 Ma. northwesterly lines of Time-Transgressive Rhyolite domes (Oregon TTR). The Oregon TTR evidences the rotation of the KBML (i.e., the WBP NW edge) under the NAP, starting at the Steens/Black Rock Range topo line about 12 Ma. WBP activity may explain Cascadia’s: lack of a trench, localized lack of Benioff zone; pattern of volcanic petrology, and Yakima Fold Belt.