CONSTRAINING MANTLE DISCONTINUITY STRUCTURE BENEATH THE LARAMIE ARRAY IN SE WYOMING

The transition zone 'water – filter' model of Bercovici and Karato predicts that a layer of depleted mantle melt may pool above the 410 – km discontinuity, causing a persistent lateral negative velocity gradient above the discontinuity. Previous receiver function analysis of the mantle transition zone [Dueker, Fee in review] from the Billings Array (Montana) is suggestive of such a velocity gradient. We will present a receiver function analysis of the 410 and 660 km discontinuities underneath the Laramie Teleseismic Array (SE Wyoming) and examine evidence for the existence of the negative velocity gradient above the 410 discontinuity. The Laramie Array consisted of a dense (2 – km station spacing) deployment of 30 broadband seismometers in operation from Sept. 2000 to May 2001. Previous work with the Laramie Array data examined the Archean-Proterozoic Cheyenne Belt suture zone [Dueker, Yuan in preparation] as part of the CD-ROM project [Karlstrom et al., 2002].