Inference of thermodynamic state in the asthenosphere from anelastic properties, with applications to North American upper mantle

abstract Early reflections of the phase P′P′ recorded at North American seismograph stations from nuclear explosions in Novaya Zemlya are used to examine the crust and upper mantle beneath a region of eastern Antarctica. Many reflections are observed from depths less than 120 km, indicating considerable inhomogeneity at these depths in the Earth. No regular horizons were found throughout the area, but some correlation was observed among reflections at closely-spaced stations, and, at many stations, reflections were observed from depths of between 60 and 80 km, corresponding to a likely upper boundary of the low-velocity channel. Deeper reflections were found at depths of near 420 and 650 km. The latter boundary was particularly well-observed and appears to be sharply defined at a depth that is constant to within a few kilometers. The boundary at 420 km is not so well defined by reflections of P′P′, but reflects well longer-period PP waves, arriving at wider angles of incidence. This boundary appears to be at least as pronounced, but not so sharp as that near 650 km. The deep structure beneath Antarctica presents no obvious difference from that beneath other continental areas.

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The North American upper mantle: Density, composition, and evolution

Journal of Geophysical Research Atmospheres ◽

10.1029/2010jb000866 ◽

2010 ◽

Vol 115 (B12) ◽

Cited By ~ 81

Author(s):

Walter D. Mooney ◽

Mikhail K. Kaban

Keyword(s):

North American ◽

Upper Mantle ◽

The North

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Electromagnetic images of the Trans-Hudson orogen: the North American Central Plains anomaly revealed

Canadian Journal of Earth Sciences ◽

10.1139/e05-018 ◽

2005 ◽

Vol 42 (4) ◽

pp. 457-478 ◽

Cited By ~ 47

Author(s):

Alan G Jones ◽

Juanjo Ledo ◽

Ian J Ferguson

Keyword(s):

Electrical Properties ◽

North American ◽

Upper Mantle ◽

Lithospheric Mantle ◽

Three Dimensional ◽

Conductivity Anomaly ◽

Central Plains ◽

Slave Craton ◽

The North ◽

Kimberlite Field

Magnetotelluric studies of the Trans-Hudson orogen over the last two decades, prompted by the discovery of a significant conductivity anomaly beneath the North American Central Plains (NACP), from over 300 sites yield an extensive database for interrogation and enable three-dimensional information to be obtained about the geometry of the orogen from southern North Dakota to northern Saskatchewan. The NACP anomaly is remarkable in its continuity along strike, testimony to along-strike similarity of orogenic processes. Where bedrock is exposed, the anomaly can be associated with sulphides that were metamorphosed during subduction and compression and penetratively emplaced deep within the crust of the internides of the orogen to the boundary of the Hearne margin. A new result from this compilation is the discovery of an anomaly within the upper mantle beginning at depths of ~80100 km. This lithospheric mantle conductor has electrical properties similar to those for the central Slave craton mantle conductor, which lies directly beneath the major diamond-producing Lac de Gras kimberlite field. While the Saskatchewan mantle conductor does not directly underlie the Fort à la Corne kimberlite, which is associated with the Sask craton, the spatial correspondence is close.

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