Measurement of elastic properties of silicates at realistic mantle pressures
type: CreativeWork
description: Measurements of seismic wave travel times through the Earth’s interior provide one of the few sources of information on the properties of deep mantle rocks. These travel times can be interpreted in terms of their implications for the mineralogy, chemistry and temperature of the mantle if they can be compared with models determined from laboratory measurements for the elastic properties of mantle minerals at high pressures and temperatures. In this study MHz ultrasonic measurements have been used to determine the velocities of P and S acoustic waves in mantle minerals at mantle conditions. These results are used to constrain the properties of the mantle through comparison with seismic data. Subduction zones exhibit faster seismic wave velocities compared to the surrounding mantle due to the recycling of relatively cold oceanic lithosphere. In certain subduction zones, however, a 5-10 km thick low velocity layer (LVL) has been inferred to exist along the top surface of the subducting slab at depths of up to 250 km. Shear-wave velocities, in particular, within these layers have been estimated as up to 10% slower than in the surrounding mantle. High-pressure ultrasonic interferometric measurements were performed to gain insight into the elastic properties of lawsonite [CaAl2(Si2O7)(OH)2.H2O], a hydrous mineral phase stabilized under cold subduction zone conditions. It was found that lawsonite has an unusually low shear modulus at high pressure and its formation in subducted oceanic crust can explain some seismic evidence for LVL at depths exceeding 100 km. To approach estimated LVL velocities requires lawsonite to form in the subducting crust as a result of a fluid influx due to the breakdown of other hydrous minerals such as serpentine. The formation of lawsonite additionally lowers seismic velocities because it forms at the expense of garnet, a mineral with relatively fast seismic velocities. LVL observations may therefore be used to place constraints on the amount of…
abstract: Measurements of seismic wave travel times through the Earth’s interior provide one of the few sources of information on the properties of deep mantle rocks. These travel times can be interpreted in terms of their implications for the mineralogy, chemistry and temperature of the mantle if they can be compared with models determined from laboratory measurements for the elastic properties of mantle minerals at high pressures and temperatures. In this study MHz ultrasonic measurements have been used to determine the velocities of P and S acoustic waves in mantle minerals at mantle conditions. These results are used to constrain the properties of the mantle through comparison with seismic data. Subduction zones exhibit faster seismic wave velocities compared to the surrounding mantle due to the recycling of relatively cold oceanic lithosphere. In certain subduction zones, however, a 5-10 km thick low velocity layer (LVL) has been inferred to exist along the top surface of the subducting slab at depths of up to 250 km. Shear-wave velocities, in particular, within these layers have been estimated as up to 10% slower than in the surrounding mantle. High-pressure ultrasonic interferometric measurements were performed to gain insight into the elastic properties of lawsonite [CaAl2(Si2O7)(OH)2.H2O], a hydrous mineral phase stabilized under cold subduction zone conditions. It was found that lawsonite has an unusually low shear modulus at high pressure and its formation in subducted oceanic crust can explain some seismic evidence for LVL at depths exceeding 100 km. To approach estimated LVL velocities requires lawsonite to form in the subducting crust as a result of a fluid influx due to the breakdown of other hydrous minerals such as serpentine. The formation of lawsonite additionally lowers seismic velocities because it forms at the expense of garnet, a mineral with relatively fast seismic velocities. LVL observations may therefore be used to place constraints on the amount of…
author: Chantel, Julien
date published: 2013-11-27
date modified: 2026-07-27T18:49:02Z
provider: Universität Bayreuth
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Universität Bayreuth