The upper mantle geoid: Implications for continental structure and the intraplate stress field

Coblentz, David; van Wijk, Jolante; Richardson, Randall M.; Sandiford, Mike

doi:10.1130/SPE514

Title: The upper mantle geoid: Implications for continental structure and the intraplate stress field

Abstract

We use the fact that geoid anomalies are directly related to the local dipole moment of the density-depth distribution to help constrain density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the upper mantle geoid contribution from the full geoid (which is dominated by sources in the lower mantle). Here, we address this issue by using a high-pass spherical harmonic filtering of the EGM2008–WGS 84 geoid to produce an “upper mantle” geoid. The tectonic implications of the upper mantle are discussed in terms of plate tectonics and intraplate stresses. We find that globally there is a ~9 m geoid step associated with the cooling oceanic lithosphere that imparts a net force of ~2.5 × 10¹² N/m in the form of “ridge push”—a magnitude that is consistent with one-dimensional models based on first-order density profiles. Furthermore, we find a consistent 6 m geoid step across passive continental margins which has the net effect of reducing the compressive stresses in the continents due to the ridge push force. Furthermore, we use the upper mantle geoid to reevaluate the tectonic reference state which previous studies estimated using an assumption of Airy-based isostasy. Our evaluationmore »« less

Authors:

^[1]; van Wijk, Jolante ^[2]; Richardson, Randall M. ^[3]; Sandiford, Mike ^[4]

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
New Mexico Inst. of Mining and Technology, Socorro, NM (United States). Dept. of Earth and Environmental Science
Univ. of Arizona, Tucson, AZ (United States). Dept. of Geosciences
Univ. of Melbourne (Australia). School of Earth Sciences

Publication Date:: Thu Oct 01 00:00:00 EDT 2015

Research Org.:: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:: National Science Foundation (NSF); USDOE

OSTI Identifier:: 1526946

Report Number(s):: LA-UR-17-22883
Journal ID: ISSN 0072-1077

Grant/Contract Number:: 89233218CNA000001; EAR-0607808

Resource Type:: Accepted Manuscript

Journal Name:: Geological Society of America, Special Paper

Additional Journal Information:: Journal Volume: 514; Journal ID: ISSN 0072-1077

Country of Publication:: United States

Language:: English

Subject:: 58 GEOSCIENCES; Earth Sciences

Citation Formats


                    Coblentz, David, van Wijk, Jolante, Richardson, Randall M., and Sandiford, Mike. The upper mantle geoid: Implications for continental structure and the intraplate stress field.  United States: N. p., 2015. 
Web.  doi:10.1130/SPE514.

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                    Coblentz, David, van Wijk, Jolante, Richardson, Randall M., & Sandiford, Mike. The upper mantle geoid: Implications for continental structure and the intraplate stress field.  United States.  https://doi.org/10.1130/SPE514

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                    Coblentz, David, van Wijk, Jolante, Richardson, Randall M., and Sandiford, Mike. Thu .  
"The upper mantle geoid: Implications for continental structure and the intraplate stress field".  United States.  https://doi.org/10.1130/SPE514.  https://www.osti.gov/servlets/purl/1526946.

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@article{osti_1526946,

  title        = {The upper mantle geoid: Implications for continental structure and the intraplate stress field},

  author       = {Coblentz, David and van Wijk, Jolante and Richardson, Randall M. and Sandiford, Mike},

  abstractNote = {We use the fact that geoid anomalies are directly related to the local dipole moment of the density-depth distribution to help constrain density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the upper mantle geoid contribution from the full geoid (which is dominated by sources in the lower mantle). Here, we address this issue by using a high-pass spherical harmonic filtering of the EGM2008–WGS 84 geoid to produce an “upper mantle” geoid. The tectonic implications of the upper mantle are discussed in terms of plate tectonics and intraplate stresses. We find that globally there is a ~9 m geoid step associated with the cooling oceanic lithosphere that imparts a net force of ~2.5 × 1012 N/m in the form of “ridge push”—a magnitude that is consistent with one-dimensional models based on first-order density profiles. Furthermore, we find a consistent 6 m geoid step across passive continental margins which has the net effect of reducing the compressive stresses in the continents due to the ridge push force. Furthermore, we use the upper mantle geoid to reevaluate the tectonic reference state which previous studies estimated using an assumption of Airy-based isostasy. Our evaluation of the upper mantle geoid confirms the near-equivalence of the gravitational potential energy of continental lithosphere with an elevation of ~750 m and the mid-ocean ridges. This result substantiates early conclusions about the tectonic reference state and further supports the prediction that continental regions are expected to be in a slightly extensional state of stress.},

  doi          = {10.1130/SPE514},

  journal      = {Geological Society of America, Special Paper},

  number       = ,

  volume       = 514,

  place        = {United States},

  year         = {Thu Oct 01 00:00:00 EDT 2015},

  month        = {Thu Oct 01 00:00:00 EDT 2015}

}

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Figures / Tables:

Figure 1: A) The complete (unfiltered) geoid height anomaly, relative to WGS 84 Ellipsoid, based on the EGM2008 model (degree/order up to 2159). B) Upper mantle geoid anomaly derived from a harmonic filter passing coefficients between degree/order 9 and 355 with a cosine taper between degree/order 6-9 and 355-360. Seemore »

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