title: Fossil slabs attached to unsubducted fragments of the Farallon plate.
abstract: As the Pacific-Farallon spreading center approached North America, the Farallon plate fragmented into a number of small plates. Some of the microplate fragments ceased subducting before the spreading center reached the trench. Most tectonic models have assumed that the subducting oceanic slab detached from these microplates close to the trench, but recent seismic tomography studies have revealed a high-velocity anomaly beneath Baja California that appears to be a fossil slab still attached to the Guadalupe and Magdalena microplates. Here, using surface wave tomography, we establish the lateral extent of this fossil slab and show that it is correlated with the distribution of high-Mg andesites thought to derive from partial melting of the subducted oceanic crust. We also reinterpret the high seismic velocity anomaly beneath the southern central valley of California as another fossil slab extending to a depth of 200 km or more that is attached to the former Monterey microplate. The existence of these fossil slabs may force a reexamination of models of the tectonic evolution of western North America over the last 30 My.
authors.affiliation: Department of Geological Sciences, Brown University, Providence, RI 02865, USA. nubeyun@gmail.com
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.forename: Donald W
authors.initials: DW
authors.lastname: Forsyth
authors.forename: Christina J
authors.initials: CJ
authors.lastname: Rau
authors.forename: Nina
authors.initials: N
authors.lastname: Carriero
authors.forename: Brandon
authors.initials: B
authors.lastname: Schmandt
authors.forename: James B
authors.initials: JB
authors.lastname: Gaherty
authors.forename: Brian
authors.initials: B
authors.lastname: Savage
mesh_terms: D019419:Evolution, Planetary; D005844:Geology; D008800:Mexico; D008962:Models, Theoretical; D014054:Tomography