The University of Southampton
University of Southampton Institutional Repository
Warning ePrints Soton is experiencing an issue with some file downloads not being available. We are working hard to fix this. Please bear with us.

A comparison of oceanic and continental mantle lithosphere

A comparison of oceanic and continental mantle lithosphere
A comparison of oceanic and continental mantle lithosphere
Over the last decade, seismological studies have shed new light on the properties of the mantle lithosphere and their physical and chemical origins. This paper synthesizes recent work to draw comparisons between oceanic and continental lithosphere, with a particular focus on isotropic velocity structure and its implications for mantle temperature and partial melt. In the oceans, many observations of scattered and reflected body waves indicate velocity contrasts whose depths follow an age-dependent trend. New modeling of fundamental mode Rayleigh waves from the Pacific ocean indicates that cooling plate models with asymptotic plate thicknesses of 85-95 km provide the best overall fits to phase velocities at periods of 25 s to 250 s. These thermal models are broadly consistent with the depths of scattered and reflected body wave observations, and with oceanic heat flow data. However, the lithosphere-asthenosphere velocity gradients for 85-95 km asymptotic plate thicknesses are too gradual to generate observable Sp phases, both at ages less than 30 Ma and at ages of 80 Ma or more. To jointly explain Rayleigh wave, scattered and reflected body waves and heat flow data, we propose that oceanic lithosphere can be characterized as a thermal boundary layer with an asymptotic thickness of 85-95 km, but that this layer contains other features, such as zones of partial melt from hydrated or carbonated asthenosphere, that enhance the lithosphere-asthenosphere velocity gradient. Beneath young continental lithosphere, surface wave constraints on lithospheric thickness are also compatible with the depths of lithosphere-asthenosphere velocity gradients implied by converted and scattered body waves. However, typical steady-state conductive models consistent with continental heat flow produce thermal and velocity gradients that are too gradual in depth to produce observed converted and scattered body waves. Unless lithospheric isotherms are concentrated in depth by mantle upwelling or convective removal, the presence of an additional factor, such as partial melt at the base of the thermal lithosphere, is needed to sharpen lithosphere-asthenosphere velocity gradients in many young continental regions. Beneath cratons, numerous body wave conversions and reflections are observed within the thick mantle lithosphere, but the velocity layering they imply appears to be laterally discontinuous. The nature of cratonic lithosphere-asthenosphere velocity gradients remains uncertain, with some studies indicating gradual transitions that are consistent with steady-state thermal models, and other studies inferring more vertically localized velocity gradients.
0031-9201
Fischer, Karen M.
5acb751d-c894-4a40-b944-cea48b0ad966
Rychert, Catherine A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Dalton, Colleen A.
ca990c1e-ed70-4ad2-96cc-f2ec91a5bc1b
Miller, Meghan S.
d9aa01fc-e48f-494d-9eda-5e9c60f60266
Beghein, Caroline
c190f49e-963e-471c-831d-e4efd96e062d
Schutt, Derek L.
4ad87ffc-fefd-4d46-8e1e-ad566e38cbec
Fischer, Karen M.
5acb751d-c894-4a40-b944-cea48b0ad966
Rychert, Catherine A.
70cf1e3a-58ea-455a-918a-1d570c5e53c5
Dalton, Colleen A.
ca990c1e-ed70-4ad2-96cc-f2ec91a5bc1b
Miller, Meghan S.
d9aa01fc-e48f-494d-9eda-5e9c60f60266
Beghein, Caroline
c190f49e-963e-471c-831d-e4efd96e062d
Schutt, Derek L.
4ad87ffc-fefd-4d46-8e1e-ad566e38cbec

Fischer, Karen M., Rychert, Catherine A., Dalton, Colleen A., Miller, Meghan S., Beghein, Caroline and Schutt, Derek L. (2020) A comparison of oceanic and continental mantle lithosphere. Physics of the Earth and Planetary Interiors, 309, [106600]. (doi:10.1016/j.pepi.2020.106600).

Record type: Article

Abstract

Over the last decade, seismological studies have shed new light on the properties of the mantle lithosphere and their physical and chemical origins. This paper synthesizes recent work to draw comparisons between oceanic and continental lithosphere, with a particular focus on isotropic velocity structure and its implications for mantle temperature and partial melt. In the oceans, many observations of scattered and reflected body waves indicate velocity contrasts whose depths follow an age-dependent trend. New modeling of fundamental mode Rayleigh waves from the Pacific ocean indicates that cooling plate models with asymptotic plate thicknesses of 85-95 km provide the best overall fits to phase velocities at periods of 25 s to 250 s. These thermal models are broadly consistent with the depths of scattered and reflected body wave observations, and with oceanic heat flow data. However, the lithosphere-asthenosphere velocity gradients for 85-95 km asymptotic plate thicknesses are too gradual to generate observable Sp phases, both at ages less than 30 Ma and at ages of 80 Ma or more. To jointly explain Rayleigh wave, scattered and reflected body waves and heat flow data, we propose that oceanic lithosphere can be characterized as a thermal boundary layer with an asymptotic thickness of 85-95 km, but that this layer contains other features, such as zones of partial melt from hydrated or carbonated asthenosphere, that enhance the lithosphere-asthenosphere velocity gradient. Beneath young continental lithosphere, surface wave constraints on lithospheric thickness are also compatible with the depths of lithosphere-asthenosphere velocity gradients implied by converted and scattered body waves. However, typical steady-state conductive models consistent with continental heat flow produce thermal and velocity gradients that are too gradual in depth to produce observed converted and scattered body waves. Unless lithospheric isotherms are concentrated in depth by mantle upwelling or convective removal, the presence of an additional factor, such as partial melt at the base of the thermal lithosphere, is needed to sharpen lithosphere-asthenosphere velocity gradients in many young continental regions. Beneath cratons, numerous body wave conversions and reflections are observed within the thick mantle lithosphere, but the velocity layering they imply appears to be laterally discontinuous. The nature of cratonic lithosphere-asthenosphere velocity gradients remains uncertain, with some studies indicating gradual transitions that are consistent with steady-state thermal models, and other studies inferring more vertically localized velocity gradients.

Text
Text_8_8_20 - Accepted Manuscript
Download (50kB)
Text
References_8_8_20-2
Download (41kB)
Text
Figures_8_8_20_1-3
Download (10MB)

More information

Accepted/In Press date: 23 October 2020
e-pub ahead of print date: 4 November 2020
Published date: 1 December 2020

Identifiers

Local EPrints ID: 446071
URI: http://eprints.soton.ac.uk/id/eprint/446071
ISSN: 0031-9201
PURE UUID: 934acaa6-6725-4d82-98b7-e135833e5988

Catalogue record

Date deposited: 20 Jan 2021 17:30
Last modified: 26 Nov 2021 05:39

Export record

Altmetrics

Contributors

Author: Karen M. Fischer
Author: Colleen A. Dalton
Author: Meghan S. Miller
Author: Caroline Beghein
Author: Derek L. Schutt

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×