Articles | Volume 6, issue 3
Solid Earth, 6, 957–970, 2015

Special issue: The Lithosphere-Asthenosphere Boundary (LAB) Dilemma

Solid Earth, 6, 957–970, 2015

Research article 31 Jul 2015

Research article | 31 Jul 2015

Structure of the upper mantle in the north-western and central United States from USArray S-receiver functions

R. Kind1,2, X. Yuan1, J. Mechie1, and F. Sodoudi1 R. Kind et al.
  • 1Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany
  • 2Freie Universität, Fachrichtung Geophysik, Berlin, Germany

Abstract. We used more than 40 000 S-receiver functions recorded by the USArray project to study the structure of the upper mantle between the Moho and the 410 km discontinuity from the Phanerozoic western United States to the cratonic central US. In the western United States we observed the lithosphere–asthenosphere boundary (LAB), and in the cratonic United States we observed both the mid-lithospheric discontinuity (MLD) and the LAB of the craton. In the northern and southern United States the western LAB almost reaches the mid-continental rift system. In between these two regions the cratonic MLD is surprisingly plunging towards the west from the Rocky Mountain Front to about 200 km depth near the Sevier thrust belt. We interpret these complex structures of the seismic discontinuities in the mantle lithosphere as an indication of interfingering of the colliding Farallon and Laurentia plates. Unfiltered S-receiver function data reveal that the LAB and MLD are not single discontinuities but consist of many small-scale laminated discontinuities, which only appear as single discontinuities after longer period filtering. We also observe the Lehmann discontinuity below the LAB and a velocity reduction about 30 km above the 410 km discontinuity.

Short summary
We observed with seismic data the lithosphere–asthenosphere boundary (LAB) in the western United States and the mid-lithospheric discontinuity (MLD) in the central United States. In the northern and southern United States, the western LAB (probably of the Farallon plate) is weakly east dipping. There are indications of a west-dipping MLD in between. We interpret this interfingering structure of the mantle lithosphere as a result of the collision of the Farallon and the Laurentia plates.