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Imaging Pacific lithosphere seismic discontinuities – Insights from SS Precursor modeling

Imaging Pacific lithosphere seismic discontinuities – Insights from SS Precursor modeling
Imaging Pacific lithosphere seismic discontinuities – Insights from SS Precursor modeling
Oceanic lithosphere provides an ideal location to decipher the nature of the lithosphere–asthenosphere system which is vital to our understanding of plate tectonics. It is well established that oceanic lithosphere cools, thickens and subsides as it ages according to the conductive cooling models. Yet, this simple realization fails to explain various observations. For example, old oceanic lithosphere does not subside as predicted. Further, precise imaging of the lower boundary of the oceanic lithosphere has proven challenging. Here we use SS precursors to image the discontinuity structure across the Pacific Ocean using 24 years of teleseismic data. We image a sharp pervasive velocity discontinuity (3 – 15% drop over < 21 km) at 30 – 80 km depth that increases in depth with age from the ridge to at least 36 ± 9 My along the 1100 °C conductive cooling isotherm. Beneath seafloor > 36 My, there is no age–depth dependence, and we image the discontinuity at an average depth of 60 ± 1.5 km. The amplitude and sharpness of the boundary suggests a compositional variation and/or layered carbonatitic melt may be required to explain our observations rather than temperature alone. The strength and pervasiveness of the boundary suggests that it is likely related to the lithosphere–asthenosphere boundary. An additional deeper discontinuity at 80 – 120 km depth is imaged intermittently that in most cases likely represents a continuing negative velocity gradient in depth.
2169-9356
2131–2152
Tharimena, Saikiran
9e95dff0-7044-43d4-ac5e-51e72468b719
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
White, Paul
2dd2477b-5aa9-42e2-9d19-0806d994eaba
Tharimena, Saikiran
9e95dff0-7044-43d4-ac5e-51e72468b719
Rychert, Catherine
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Harmon, Nicholas
10d11a16-b8b0-4132-9354-652e72d8e830
White, Paul
2dd2477b-5aa9-42e2-9d19-0806d994eaba

Tharimena, Saikiran, Rychert, Catherine, Harmon, Nicholas and White, Paul (2017) Imaging Pacific lithosphere seismic discontinuities – Insights from SS Precursor modeling. Journal of Geophysical Research: Solid Earth, 122 (3), 2131–2152. (doi:10.1002/2016JB013526).

Record type: Article

Abstract

Oceanic lithosphere provides an ideal location to decipher the nature of the lithosphere–asthenosphere system which is vital to our understanding of plate tectonics. It is well established that oceanic lithosphere cools, thickens and subsides as it ages according to the conductive cooling models. Yet, this simple realization fails to explain various observations. For example, old oceanic lithosphere does not subside as predicted. Further, precise imaging of the lower boundary of the oceanic lithosphere has proven challenging. Here we use SS precursors to image the discontinuity structure across the Pacific Ocean using 24 years of teleseismic data. We image a sharp pervasive velocity discontinuity (3 – 15% drop over < 21 km) at 30 – 80 km depth that increases in depth with age from the ridge to at least 36 ± 9 My along the 1100 °C conductive cooling isotherm. Beneath seafloor > 36 My, there is no age–depth dependence, and we image the discontinuity at an average depth of 60 ± 1.5 km. The amplitude and sharpness of the boundary suggests a compositional variation and/or layered carbonatitic melt may be required to explain our observations rather than temperature alone. The strength and pervasiveness of the boundary suggests that it is likely related to the lithosphere–asthenosphere boundary. An additional deeper discontinuity at 80 – 120 km depth is imaged intermittently that in most cases likely represents a continuing negative velocity gradient in depth.

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Accepted/In Press date: 15 February 2017
e-pub ahead of print date: 18 February 2017
Published date: 11 March 2017
Organisations: Ocean and Earth Science, Geology & Geophysics, Inst. Sound & Vibration Research, Signal Processing & Control Grp

Identifiers

Local EPrints ID: 406228
URI: http://eprints.soton.ac.uk/id/eprint/406228
ISSN: 2169-9356
PURE UUID: a5224262-19ea-4e54-b2a4-ddc99372cc4f
ORCID for Saikiran Tharimena: ORCID iD orcid.org/0000-0002-1841-1911
ORCID for Nicholas Harmon: ORCID iD orcid.org/0000-0002-0731-768X
ORCID for Paul White: ORCID iD orcid.org/0000-0002-4787-8713

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Date deposited: 10 Mar 2017 10:43
Last modified: 17 Dec 2019 02:02

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Contributors

Author: Nicholas Harmon ORCID iD
Author: Paul White ORCID iD

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