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Title: Origins of ultralow velocity zones through slab-derived metallic melt

Abstract

Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.

Authors:
 [1];  [1]; ORCiD logo [2];  [2]
  1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Earth and Environmental Sciences
  2. Carnegie Inst. of Washington, Argonne, IL (United States). Geophysical Lab.
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
National Science Foundation (NSF); National Aeronautic and Space Administration (NASA)
OSTI Identifier:
1257473
Resource Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 20; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Liu, Jiachao, Li, Jie, Hrubiak, Rostislav, and Smith, Jesse S. Origins of ultralow velocity zones through slab-derived metallic melt. United States: N. p., 2016. Web. doi:10.1073/pnas.1519540113.
Liu, Jiachao, Li, Jie, Hrubiak, Rostislav, & Smith, Jesse S. Origins of ultralow velocity zones through slab-derived metallic melt. United States. doi:10.1073/pnas.1519540113.
Liu, Jiachao, Li, Jie, Hrubiak, Rostislav, and Smith, Jesse S. Tue . "Origins of ultralow velocity zones through slab-derived metallic melt". United States. doi:10.1073/pnas.1519540113. https://www.osti.gov/servlets/purl/1257473.
@article{osti_1257473,
title = {Origins of ultralow velocity zones through slab-derived metallic melt},
author = {Liu, Jiachao and Li, Jie and Hrubiak, Rostislav and Smith, Jesse S.},
abstractNote = {Understanding the ultralow velocity zones (ULVZs) places constraints on the chemical composition and thermal structure of deep Earth and provides critical information on the dynamics of large-scale mantle convection, but their origin has remained enigmatic for decades. Recent studies suggest that metallic iron and carbon are produced in subducted slabs when they sink beyond a depth of 250 km. Here we show that the eutectic melting curve of the iron-carbon system crosses the current geotherm near Earth’s core-mantle boundary, suggesting that dense metallic melt may form in the lowermost mantle. If concentrated into isolated patches, such melt could produce the seismically observed density and velocity features of ULVZs. Depending on the wetting behavior of the metallic melt, the resultant ULVZs may be short-lived domains that are replenished or regenerated through subduction, or long-lasting regions containing both metallic and silicate melts. Slab-derived metallic melt may produce another type of ULVZ that escapes core sequestration by reacting with the mantle to form iron-rich post-bridgmanite or ferropericlase. The hypotheses connect peculiar features near Earth’s core-mantle boundary to subduction of the oceanic lithosphere through the deep carbon cycle.},
doi = {10.1073/pnas.1519540113},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 20,
volume = 113,
place = {United States},
year = {2016},
month = {5}
}

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