Reconstructing Farallon Plate Subduction Beneath North America Back to the Late Cretaceous

Abstract

Using an inverse mantle convection model that assimilates seismic structure and plate motions, we reconstruct Farallon plate subduction back to 100 million years ago. Models consistent with stratigraphy constrain the depth dependence of mantle viscosity and buoyancy, requiring that the Farallon slab was flat lying in the Late Cretaceous, consistent with geological reconstructions. The simulation predicts that an extensive zone of shallow-dipping subduction extended beyond the flat-lying slab farther east and north by up to 1000 kilometers. The limited region of flat subduction is consistent with the notion that subduction of an oceanic plateau caused the slab to flatten. The results imply that seismic images of the current mantle provide more constraints on past tectonic events than previously recognized.

Understanding a critical basinal link in Cretaceous Cordilleran paleogeography: Detailed provenance of the Hornbrook Formation, Oregon and California

“…90 Ma. With shallowing of the subducting Farallon slab to near horizontal (e.g., Saleeby, 2003;Dickinson, 2004;Liu et al, 2008), magmatism in the Sierran arc ceased by 82 Ma (Stern et al, 1981;Chen and Moore, 1982), and a peraluminous magmatic fl ux event occurred in the Idaho Batholith from 80 to 67 Ma (Gaschnig et al, 2010). Inverse mantle convection modeling predicts that Farallon slab fl attening began at ca.…”

“…1). We suggest that this provenance change occurred as magmatism and deformation shifted to the east with shallowing of Farallon plate subduction (Dickinson, 2004;Liu et al, 2008), and as the Kula plate separated from the Farallon plate and began moving north through oblique subduction (Woods and Davies, 1982;Engebretson et al, 1985). Similar provenance and provenance changes in the Late Cretaceous Great Valley Group suggest that the sedimentary strata of both basins record regional tectonic events of the Late Cretaceous Cordillera, and that these basins formed one, single depositional system during the Late Cretaceous, from Santonian through Maastrichtian time.…”

Facies architecture and provenance of a boulder-conglomerate submarine channel system, Panoche Formation, Great Valley Group: A forearc basin response to middle Cretaceous tectonism in the California convergent margin

“…100 Ma) in the Cretaceous arc-forearc-prism history of California led to the unique Cenomanian SLR deposits. Furthermore, these mid-Cretaceous events most likely resulted from an abrupt increase in plate-motion rates parallel to the arc (obliquity) between the Farallon plate and North American plate (Page and Engebretson, 1984;Engebretson et al, 1985;Liu et al, 2008). Page and Engebretson (1984) report convergence normal to the margin was 5 cm/yr prior to 100 Ma and nearly doubled to 9 cm/yr during 100-85 Ma.…”

“…Page and Engebretson (1984) report convergence normal to the margin was 5 cm/yr prior to 100 Ma and nearly doubled to 9 cm/yr during 100-85 Ma. In addition, Liu et al (2008) display plate-motion vectors that shift counterclockwise 38° between 100 Ma and 90 Ma. This change from nearly head-on convergence to oblique transpression likely triggered large-scale effects throughout the arcforearc-prism system.…”

“…100 Ma) has received particular attention as an opportunity to examine how a convergent system responded to changes in plate motion rates and direction. Many studies have documented an overall increase in plate convergence rate and plate motion parallel to the arc (obliquity) occurring 100-90 Ma (Page and Engebretson, 1984;Engebretson et al, 1985;Liu et al, 2008). Others suggest that these plate motion changes led to induced deformation in the eastern Sierran arc, resulting in increased rates of magmatism (Glazner, 1991;Tikoff and Teyssier, 1992;McNulty, 1995;Greene and Schweickert, 1995;Tikoff and Greene, 1997;Tobisch et al, 2000;Memeti et al, 2014;Paterson and Ducea, 2015), as well as accelerated phases of accretion in the prism (Wakabayashi, 2015).…”