Upper Mantle Discontinuity Topography from Thermal and Chemical Heterogeneity

Science ◽  
2007 ◽  
Vol 318 (5850) ◽  
pp. 623-626 ◽  
Author(s):  
Nicholas Schmerr ◽  
Edward J. Garnero
Keyword(s):  
Upper Mantle ◽  
Phase Changes ◽  
Chemical Heterogeneity ◽  
Multiple Reflections ◽  
Partial Melt ◽  
Tectonic Processes ◽  
Seismic Discontinuities ◽  
Mineralogical Phase ◽  
Mantle Discontinuity ◽  
Upper Mantle Discontinuity

Using high-resolution stacks of precursors to the seismic phase SS, we investigated seismic discontinuities associated with mineralogical phase changes approximately 410 and 660 kilometers (km) deep within Earth beneath South America and the surrounding oceans. Detailed maps of phase boundary topography revealed deep 410- and 660-km discontinuities in the down-dip direction of subduction, inconsistent with purely isochemical olivine phase transformation in response to lowered temperatures. Mechanisms invoking chemical heterogeneity within the mantle transition zone were explored to explain this feature. In some regions, multiple reflections from the discontinuities were detected, consistent with partial melt near 410-km depth and/or additional phase changes near 660-km depth. Thus, the origin of upper mantle heterogeneity has both chemical and thermal contributions and is associated with deeply rooted tectonic processes.

Upper-mantle discontinuity from amplitude data of P′P′ and its precursors

1973 ◽  
Vol 63 (2) ◽  
pp. 587-597
Author(s):  
Ta-Liang Teng ◽  
James P. Tung
Keyword(s):  
Upper Mantle ◽  
Body Waves ◽  
P Wave ◽  
Specific Reference ◽  
Amplitude Data ◽  
Surface Displacements ◽  
Short Period ◽  
Mantle Velocity ◽  
Mantle Discontinuity ◽  
Upper Mantle Discontinuity

abstract Recent observations of P′P′ and its precursors, identified as reflections from within the Earth's upper mantle, are used to examine the structure of the uppermantle discontinuities with specific reference to the density, the S velocity, and the Q variations. The Haskell-Thomson matrix method is used to generate the complex reflection spectrum, which is then Fourier synthesized for a variety of upper-mantle velocity-density and Q models. Surface displacements are obtained for the appropriate recording instrument, permitting a direct comparison with the actual seismograms. If the identifications of the P′P′ precursors are correct, our proposed method yields the following: (1) a structure of Gutenberg-Bullen A type is not likely to produce observable P′P′ upper-mantle reflections, (2) in order that a P′P′ upper-mantle reflection is strong enough to be observed, first-order density and S-velocity discontinuities together with a P-wave discontinuity are needed at a depth of about 650 km, and (3) corresponding to a given uppermantle velocity-density model, an estimate can be made of the Q in the upper mantle for short-period seismic body waves.

Upper mantle discontinuity structure in the region of the Tonga Subduction Zone

2001 ◽  
Vol 28 (9) ◽  
pp. 1855-1858 ◽  
Author(s):  
Hersh J. Gilbert ◽  
Anne F. Sheehan ◽  
Douglas A. Wiens ◽  
Kenneth G. Dueker ◽  
LeRoy M. Dorman ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Upper Mantle ◽  
Tonga Subduction Zone ◽  
Discontinuity Structure ◽  
Mantle Discontinuity ◽  
Upper Mantle Discontinuity
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