Upper mantle P wave velocity structure of the eastern Snake River Plain and its relationship to geodynamic models of the region

Abstract

Abstract. Tomographic inversions of ~5(• teleseismic P wave travel time residuals image a narrow, deep, low-velocity region centered beneath the eastern Snake River Plain, Idaho. Aligned in the direction of North American plate motion, the eastern Snake River Plain is the locus of time-progressive volcanism leading to the Yellowstone hotspot. The low-velocity anomaly extends to depths of at least 200 km and is flanked by high-velocity manfie to either side. These results are inconsistent with standard manfie plume models which predict a shallow, wide, low-velocity anomaly. By considering the effects of composition, partial me!t, and temperature on both P wave velocities and upper manfie densities (assnming local isostasy), we conclude that the low-velocity region is partially molten peridotitc and the high-velocity regions on either side are depletext residuum. Swell relief at hotspots has generally been attributed to thermal effects and is commonly used to estimate plume thermal buoyancy fluxes. However, we demonstrate that the compositional effects of manfie melting and depletion can account for at least one fifth and possibly all of the swell relief at Yellowstone. These results sa•est that melt generation and segregation are dominant pr•esses within the upper manfie of Yellowstone and allow for the possibility that the fundamental origin of the Yellowstone hotspot is something other than a deep-seated mantle plume.

Teleseismic studies of the lithosphere below the Abitibi-Grenville Lithoprobe transect

“…The interpretation of the high-velocity anomalies flanking the corridor are, at this point, highly speculative. They could either represent zones of depleted residuum produced by mantle melting (Saltzer and Humphreys 1997) or transitions in mantle fabric (i.e., anisotropy) related to the Cretaceous process discussed above. Subsequent analysis of the data and derivation of improved models will help constrain the location and interpretation of the low-velocity corridor.…”

Remediation Technologies at the INEEL

“…Instead variations seen in major elements and the -30-40 percent range in incompatible elements is related to variations in the amount of partial melting, phenocryst abundance in the samples, and possibly post-eruptive vapor-phase transport. After Smith and Braile (1993). Anders and Geissman (1989) and Hughes and others (1996).…”

Seismic Traveltime Tomography of the Crust and Lithosphere

“…However, if a large number of blocks are used and restrictions are placed on the size of the velocity changes between adjacent blocks, then a reasonable approximation to a continuously varying velocity field is possible. In teleseismic tomography, constant velocity blocks have been used by many authors including Aki et al (1977), Oncescu et al (1984), Humphreys & Clayton (1988), Humphreys & Clayton (1990), Benz et al (1992), Achauer (1994) and Saltzer & Humphreys (1997). In wide-angle traveltime inversions, the use of constant velocity blocks is not as common.…”

“…Most teleseismic studies are carried out in 3-D (e.g. Aki et al, 1977;Oncescu et al, 1984;Humphreys & Clayton, 1990;Benz et al, 1992;Glahn & Granet, 1993;Achauer, 1994;Seber et al, 1996;Saltzer & Humphreys, 1997;Ritsema et al, 1998;Steck et al, 1998;Graeber et al, 2002), with relatively few 2-D studies (e.g. Evans, 1982;McQueen & Lambeck, 1996) probably because of the difficulty in lining up an array of recorders on roughly the same great circle as a set of teleseismic earthquakes with good angular coverage.…”