Cyprych, D, Piazolo, SC orcid.org/0000-0001-7723-8170 and Almqvist, BSG (2017) Seismic anisotropy from compositional banding in granulites from the deep magmatic arc of Fiordland, New Zealand. Earth and Planetary Science Letters, 477. pp. 156-167. ISSN 0012-821X
Abstract
We present calculated seismic velocities and anisotropies of mafic granulites and eclogites from the Cretaceous deep lower crust (∼40–65 km) of Fiordland, New Zealand. Both rock types show a distinct foliation defined by cm-scale compositional banding. Seismic properties are estimated using the Asymptotic Expansion Homogenisation – Finite Element (AEH-FE) method that, unlike the commonly used Voigt–Reuss–Hill homogenisation, incorporates the phase boundary network into calculations. The predicted mean P- and S-wave velocities are consistent with previously published data for similar lithologies from other locations (e.g., Kohistan Arc), although we find higher than expected anisotropies (AVPAVP ∼ 5.0–8.0%, AVSAVS ∼ 3.0–6.5%) and substantial S-wave splitting along foliation planes in granulites. This seismic signature of granulites results from a density and elasticity contrast between cm-scale pyroxene ± garnet stringers and plagioclase matrix rather than from crystallographic orientations alone. Banded eclogites do not show elevated anisotropies as the contrast in density and elastic constants of garnet and pyroxene is too small. The origin of compositional banding in Fiordland granulites is primarily magmatic and structures described here are expected to be typical for the base of present day magmatic arcs. Hence, we identify a new potential source of anisotropy within this geotectonic setting.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2017, Elsevier B. V. This is an author produced version of a paper published in Earth and Planetary Science Letters. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | seismic anisotropy; lower crust; compositional banding; EBSD; granulite; Fiordland |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 18 Sep 2017 12:57 |
Last Modified: | 09 Sep 2018 00:38 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.epsl.2017.08.017 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:121214 |