27-10 Linking Central US drip-like mantle anomalies to bulldozed craton lithosphere from the Laramide

Session: Evolution of Cordilleran-type orogenic systems

Presenting Author:

Authors:

Abstract:

The recent P- and S-wave full waveform tomography SATONA (Hua et al., 2025) revealed high velocity, drip-like features under the Central US at 300 to 500 km depths under South Dakota to Alabama (100°W to 85°W and 32°N to 47°N).  Based on rock physics modeling, Hua et al. (2025) propose the drip-like bodies have a craton-like composition and slightly elevated (~60°C) temperature compared to ambient mantle.  The ‘drips’ were interpreted to originate from active thinning of the North American craton due to downwelling generated by Farallon slab sinking.  We newly mapped the uppermost 1000 km of mantle structure under North America from SATONA.  We discuss our mapping in terms of Farallon subduction history and provide an alternative origin for the Central US drips.   

We mapped two slab-like anomalies north of the Mendocino triple junction and downdip of the Juan de Fuca trench down to depths of 550 km that are interpreted to represent Cascadia slabs.  The Cascadia slabs are separated by an E-W tear at ~46°N latitude. When reconstructed in a plate model, the Cascadia slabs account for Cascadia subduction since ~30 Ma. At depths greater than 550 km and east of 110°W (roughly from Colorado to Alabama), discontinuous fast velocity anomalies are interpreted as heavily fragmented Farallon slabs that subducted prior to 30 Ma.  We re-map the Central US drips using 3D isosurfaces and place the anomalies within a quantitative plate reconstruction. The drips restore beneath the region of New Mexico and Colorado during Laramide time. Given this position inboard the corridor of very flat-slab Farallon subduction, we interpret them to be derived from cratonic lithosphere that was metasomatized/weakened and bulldozed inboard in response to flat-slab subduction. The weak bulldozed keel was subsequently foundered in the form of drips as the slab foundered around 50 Ma. Dynamic surficial responses in the Rocky Mountains and Great Plains recorded by the Miocene-aged Ogallala Formation potentially corroborate drips associated with keel removal following slab foundering.   

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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