Title:
  Terrane stations: Seismic tomography explains where the North American
  Cordillera came from.

Abstract:
  The western quarter of North America consists of accreted terranes,
  crustal blocks that were added to the margin in a series of collisions
  over the past 200 million years - but why? The most widely accepted
  explanation posits a scenario analogous to Andean subduction, with these
  terranes conveyed to the continental margin while the oceanic Farallon
  plate subducted under it. Yet purely Andean-style subduction under North
  America is questionable as a terrane delivery mechanism, since no
  comparable accretion sequence took place along the South American
  margin, and since North American terranes are of very varied provenance.

  I consider this geological question directly related to a geodynamical
  one: Why has it been so difficult to reconcile - even on the largest
  scale - the geometries and locations of slabs in the lower mantle, as
  imaged by seismic tomography, with Cretaceous plate reconstructions of
  the North American west coast (unless anomalous mantle rheology or ad
  hoc shifts of absolute reference frame are invoked)? This problem was
  recognized soon after the discovery of the massive, lower-mantle
  "Farallon slabs" by Grand (1994), but has recently been aggravated.
  Thanks to a worldwide unequaled coverage of the continent by seismic
  broadband stations (USArray), and their exploitation in finite-frequency
  waveform inversion, we discovered more westerly slabs in the lower
  mantle. Contrary to the widely held assumption, not all of these slabs
  can be Farallon, unless very non-vertical and/or uneven slab sinking
  behavior is allowed for.

  As a joint solution, I offer a radical reinterpretation of
  paleogeography and test it quantitatively: The seas west of Cretaceous
  North America must have resembled today's western Pacific. The Farallon
  and two more plates subducted into the intra-oceanic trenches of a vast
  archipelago in the eastern Panthalassa (proto-Pacific) ocean, both from
  the east and the west. The trenches remained stationary throughout much
  of Jurassic and Cretaceous times, depositing the massive, near-vertical
  slab walls imaged in the lower mantle today. On their overriding plates,
  island arcs and subduction complexes nucleated, and assembled with
  exotic fragments.

  The archipelago was gradually overridden by North America on its
  westward journey away from Pangaea. Episodes of crustal accretion and
  Cordilleran mountain building (Sevier, Canadian Rocky Mountains,
  Laramide) occurred when the continental margin collided with various
  parts of the archipelago. Geodynamically, this scenario is simpler than
  previous models in that it is consistent with purely vertical slab
  sinking. Sinking rates can be quantified from slab and plate geometries,
  and range between 9 and 12 mm/yr.