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Magnetic anisotropy of the common rock-forming minerals (amphibole, pyroxene and feldspar) and ultrabasic rocks

English title Magnetic anisotropy of the common rock-forming minerals (amphibole, pyroxene and feldspar) and ultrabasic rocks
Applicant Hirt Ann M.
Number 143438
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2012 - 30.09.2014
Approved amount 133'459.00
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All Disciplines (3)

Discipline
Geophysics
Mineralogy
Geology

Keywords (6)

ultrabasic rocks; EBSD; pyroxene; anisotropy of magnetic susceptibility; feldspar; amphibole

Lay Summary (English)

Lead
Lay summary

This project has two main parts. The first part is interested in gaining a deeper understanding of how anisotropy of magnetic susceptibility (AMS) arises in minerals from the amphibole, pyroxene and feldspar groups and olivines. This will involve evaluating the magnetic properties in relationship to chemical composition and the spatial distribution of Fe in the crystal structure, and modeling dipolar interactions between Fe cations. The second part of the project will involve modeling AMS of mantle rocks from the AMS of single crystal of constituent minerals and their distribution. Modeled results will be compared to measurements. This work will involve determining high-field AMS in order to isolate the paramagnetic fabric, as well as the preferred crystallographic orientation with EBSD for minerals that contribute to the susceptibility; lithologies will include deformed peridotites, amphibolites and pryoxenites.


Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Anisotropy of magnetic susceptibility in alkali feldspar and plagioclase
Biedermann Andrea R. Pettke Thomas Angel Ross J. Hirt Ann M. (2016), Anisotropy of magnetic susceptibility in alkali feldspar and plagioclase, in Geophysical Journal International, 205, 479-489.
Magnetic anisotropy in natural amphibole crystals
A.R. Biedermann C. Bender-Koch T. Pettke A.M. Hirt (2015), Magnetic anisotropy in natural amphibole crystals, in The American Mineralogist, 100, 1940-1951.
Origin of magnetic fabrics in ultramafic rocks
Biedermann A.R., Kunze K., Zappone A.S., Hirt A.M. (2015), Origin of magnetic fabrics in ultramafic rocks, in IOP Conf. Series: Materials Science and Engineering, 82, 012098.
Anisotropy of magnetic susceptibility in natural olivine single crystals
Biedermann A.R. Pettke T. Reusser E. and Hirt A.M (2014), Anisotropy of magnetic susceptibility in natural olivine single crystals, in Geochemistry, Geophysics, Geosystems , 15(7), 3051-3065.
Low-temperature magnetic anisotropy in micas and chlorit
Biedermann A.R. Bender Koch C. Lorenz W.E.A. and Hirt A.M (2014), Low-temperature magnetic anisotropy in micas and chlorit, in Tectonophysics , 629, 63-74.
Magnetic study of a late Alpine dike crosscutting the regional foliation
Hirt A.M. Biedermann A.R. Mancktelow N.S. (2014), Magnetic study of a late Alpine dike crosscutting the regional foliation, in Tectonophysics, 629, 250-259.
Magnetic anisotropy in clinopyroxene and orthopyroxene single crystals
A.R. Biedermann T. Pettke C. Bender-Koch A.M. Hirt, Magnetic anisotropy in clinopyroxene and orthopyroxene single crystals, in Journal of Geophysical Research.

Collaboration

Group / person Country
Types of collaboration
Department of Earth Sciences, Nanjing University China (Asia)
- in-depth/constructive exchanges on approaches, methods or results
- Exchange of personnel
Dept. Chemistry, Univ. Copenhagen Denmark (Europe)
- Publication
Department of Geology, University of Bern Switzerland (Europe)
- Publication

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
ICOTOM17 Talk given at a conference Origin of magnetic fabrics in ultrabasic rocks 29.08.2014 Dresden, Germany Hirt Ann M.;
Short Course on Magnetic Susceptibility Individual talk High-field magnetic anisotropy/ Applications in Environmental Magnetism 29.08.2014 Évora, Portugal Hirt Ann M.;
European Geosciences Union General Assembly 2014 Talk given at a conference Magnetic anisotropy in pyroxene single crystals 02.05.2014 Vienna, Austria Hirt Ann M.;
European Geosciences Union General Assembly 2014 Talk given at a conference Influence of deformation on the magnetic fabric and remanence of magnetic nanoparticles in an elastic matrix 02.05.2014 Vienna, Austria Hirt Ann M.;
European Geosciences Union General Assembly 2013 Poster Understanding the source of magnetic and seismic anisotropy in peridotites 10.04.2013 Vienna, Austria Hirt Ann M.;
European Geosciences Union General Assembly 2013 Talk given at a conference Single-crystal magnetic anisotropies of rock-forming minerals 08.04.2013 Vienna, Austria Hirt Ann M.;
Swiss Geoscience Meeting Talk given at a conference Seismic and magnetic anisotropy of the Finero Peridotite (Ivrea Zone) 17.11.2012 Bern, Switzerland Hirt Ann M.;


Awards

Title Year
Outstanding Student Presentation AGU Fall Meeting 2013

Associated projects

Number Title Start Funding scheme
129806 Magnetic anisotropy of the common rock-forming minerals: amphibole, pyroxene and feldspar 01.10.2010 Project funding (Div. I-III)

Abstract

The proposed project is a continuation of a two-year project, which started in October, 2010, that is examining the magnetic anisotropy in single crystals of pyroxene, amphibole and feldspar. A consistent anisotropy that is related to crystallographic structure has been identified in each group. Most amphibole minerals have their minimum susceptibility normal to the crystallographic b-c plane and the maximum axis along [010]. Clinopyroxene has its intermediate axis of susceptibility close to [010], and the maximum and minimum axes in the a-c crystallographic plane. Feldspars, which possess a weak intrinsic anisotropy, have their minimum axes associated with the b-crystallographic axis. The continuation project has two goals: 1) to obtain a better physical understanding of the origin of anisotropy in amphibole, pyroxene and feldspar, based on the distribution of chemical elements within the crystal structure; and 2) to apply the results of the single crystal study to understand factors that contribute to physical anisotropies in ultrabasic rocks. The intrinsic magnetic anisotropy of a crystal is strongly dependent on the arrangement of atoms in the lattice structure. The distribution of iron in defined planes or along specific crystallographic axes, can lead to higher susceptibility in those directions. We propose to do high-resolution chemical mapping, using scanning transmission X-ray microspectroscopy (STXM) (PolLUX beamline) at PSI, to evaluate the distribution of iron cations in single crystals. This method has a spatial resolution of 10 - 15 nm, and can distinguish between ferric and ferrous iron, which is an important aspect due to the fundamental difference in their magnetic anisotropies. This method, however, cannot distinguish coordination between atoms. For this purpose we want to explore the use of X-ray magnetic circular dichroism to test for exchange coupling of spins of the iron atoms. To date, only a few studies have been conducted on paramagnetic minerals; however, the ability to use high fields and low temperature has potential to provide new insights into the origin of magnetic anisotropy in paramagnetic minerals. In the second part of the project we propose to use the intrinsic anisotropy of single crystals to examine how these contribute to the overall magnetic anisotropy in ultrabasic rocks. Rock samples will be selected to cover different compositions that are composed of minerals whose intrinsic anisotropy has been measured in the first part of the project. Lithologies will include peridotite (olivine), gabbros (olivine and pyroxenes), pyroxenite, amphibolites and anorthosite (plagioclase). The magnetic anisotropy of these rocks will be modeled based on the orientation distributions of their constituent phases and single crystal properties; modeled values will be compared to AMS measurements of the bulk rock.
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