UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

Extrinsic elastic anisotropy in a compositionally heterogeneous Earth’s mantle

Faccenda, M; Ferreira, AMG; Tisato, N; Lithgow-Bertelloni, C; Stixrude, L; Pennacchioni, G; (2019) Extrinsic elastic anisotropy in a compositionally heterogeneous Earth’s mantle. Journal of Geophysical Research , 124 (2) pp. 1671-1687. 10.1029/2018JB016482. Green open access

[thumbnail of Ferreira Extrinsic Elastic Anisotropy in a compositionally heterogeneous earth's mantle published.pdf]
Preview
Text
Ferreira Extrinsic Elastic Anisotropy in a compositionally heterogeneous earth's mantle published.pdf - Published version

Download (7MB) | Preview

Abstract

Several theoretical studies indicate that a substantial fraction of the measured seismic anisotropy could be interpreted as extrinsic anisotropy associated with compositional layering in rocks, reducing the significance of strain‐induced intrinsic anisotropy. Here, we quantify the potential contribution of grain‐scale and rock‐scale compositional anisotropy to the observations by (i) combining effective medium theories with realistic estimates of mineral isotropic elastic properties, and (ii) measuring velocities of synthetic seismic waves propagating through modelled strain‐induced microstructures. It is shown that for typical mantle and oceanic crust sub‐solidus compositions, rock‐scale compositional layering does not generate any substantial extrinsic anisotropy (<1%) because of the limited contrast in isotropic elastic moduli among different rocks. Quasi‐laminated structures observed in subducting slabs using P‐ and S‐ wave scattering are often invoked as a source of extrinsic anisotropy, but our calculations show that they only generate minor seismic anisotropy (<0.1‐0.2% of Vp and Vs radial anisotropy). More generally, rock‐scale compositional layering, when present, cannot be detected with seismic anisotropy studies, but mainly with wave scattering. In contrast, when grain‐scale layering is present, significant extrinsic anisotropy could exist in vertically limited levels of the mantle such as in a MORB‐rich lower transition zone or in the uppermost lower mantle where foliated basalts and pyrolites display up to 2‐3% Vp and 3‐6% Vs radial anisotropy. Thus, seismic anisotropy observed around the 660 km discontinuity could be possibly related to grain‐scale SPO. Extrinsic anisotropy can form also in a compositionally homogeneous mantle, where velocity variations associated with major phase transitions can generate up to 1% of positive radial anisotropy.

Type: Article
Title: Extrinsic elastic anisotropy in a compositionally heterogeneous Earth’s mantle
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2018JB016482
Publisher version: http://doi.org/10.1029/2018JB016482
Language: English
Additional information: This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10066549
Downloads since deposit
53Downloads
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item