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Title: Major disruption of D'' beneath Alaska: D'' Beneath Alaska

D'' represents one of the most dramatic thermal and compositional layers within our planet. In particular, global tomographic models display relatively fast patches at the base of the mantle along the circum-Pacific which are generally attributed to slab debris. Such distinct patches interact with the bridgmanite (Br) to post-bridgmanite (PBr) phase boundary to generate particularly strong heterogeneity at their edges. Most seismic observations for the D'' come from the lower mantle S wave triplication (Scd). Here we exploit the USArray waveform data to examine one of these sharp transitions in structure beneath Alaska. From west to east beneath Alaska, we observed three different characteristics in D'': (1) the western region with a strong Scd, requiring a sharp δVs = 2.5% increase; (2) the middle region with no clear Scd phases, indicating a lack of D'' (or thin Br-PBr layer); and (3) the eastern region with strong Scd phase, requiring a gradient increase in δVs. To explain such strong lateral variation in the velocity structure, chemical variations must be involved. We suggest that the western region represents relatively normal mantle. In contrast, the eastern region is influenced by a relic slab that has subducted down to the lowermost mantle. In themore » middle region, we infer an upwelling structure that disrupts the Br-PBr phase boundary. Such an interpretation is based upon a distinct pattern of travel time delays, waveform distortions, and amplitude patterns that reveal a circular-shaped anomaly about 5° across which can be modeled synthetically as a plume-like structure rising about 400 km high with a shear velocity reduction of ~5%, similar to geodynamic modeling predictions of upwellings.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2]
  1. Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei Anhui China; National Geophysics Observatory at Mengcheng, Anhui China
  2. Seismological Laboratory, California Institute of Technology, Caltech, Pasadena California USA
  3. Department of Earth Sciences, University of Southern California, Los Angeles California USA
Publication Date:
OSTI Identifier:
1324803
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Geophysical Research. Solid Earth; Journal Volume: 121; Journal Issue: 5
Publisher:
American Geophysical Union
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES