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Major disruption of D″ beneath Alaska

Sun, Daoyuan and Helmberger, Don and Miller, Meghan S. and Jackson, Jennifer M. (2016) Major disruption of D″ beneath Alaska. Journal of Geophysical Research: Solid Earth, 121 (5). pp. 3534-3556. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20160623-120036564

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Abstract

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 the 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.


Item Type:Article
Related URLs:
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http://dx.doi.org/10.1002/2015JB012534DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2015JB012534/fullPublisherArticle
Additional Information:© 2016 American Geophysical Union. Received 16 SEP 2015. Accepted 21 APR 2016. Accepted article online 23 APR 2016. Published online 12 MAY 2016. The authors would like to thank Editor Paul Tregoning, Associate Editor Sebastien Chevrot, Kenji Kawai, and an anonymous reviewer. Their suggestions and comments were greatly appreciated and made significant improvements to the manuscript. Data are provided by IRIS Data Center and Earthscope USArray, which are available at http://www.iris.edu. All maps in this paper were produced using GMT developed by Paul Wessel and Walter H.F. Smith. This work was supported by National Natural Science Foundation of China 41574037; Chinese MOST 973 program 2014CB845901; and the Fundamental Research Funds for the Central Universities in China WK2080000078, NSF EAR-345015, and CSEDI EAR-1161046.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
National Natural Science Foundation of China41574037
Ministry of Science and Technology (China) 973 Program2014CB845901
Fundamental Research Funds for the Central Universities in China WK2080000078
NSFEAR-345015
NSFEAR-1161046
Record Number:CaltechAUTHORS:20160623-120036564
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160623-120036564
Official Citation:Sun, D., D. Helmberger, M. S. Miller, and J. M. Jackson (2016), Major disruption of D″ beneath Alaska, J. Geophys. Res. Solid Earth, 121, 3534–3556, doi:10.1002/2015JB012534.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:68635
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:23 Jun 2016 19:49
Last Modified:03 Nov 2016 20:04

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