Universität zu Köln

Wagner, Johannes ORCID: 0000-0002-0247-562X, Adjaoud, Omar, Marquardt, Katharina ORCID: 0000-0002-5924-3061 and Jahn, Sandro ORCID: 0000-0002-2137-8833 (2016). Anisotropy of self-diffusion in forsterite grain boundaries derived from molecular dynamics simulations. Contrib. Mineral. Petrol., 171 (12). NEW YORK: SPRINGER. ISSN 1432-0967

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Abstract

Diffusion rates and associated deformation behaviour in olivine have been subjected to many studies, due to the major abundance of this mineral group in the Earth's upper mantle. However, grain boundary (GB) transport studies yield controversial results. The relation between transport rate, energy, and geometry of individual GBs is the key to understand transport in aggregates with lattice preferred orientation that favours the presence and/or alignment of specific GBs over random ones in an undeformed rock. In this contribution, we perform classical molecular dynamics simulations of a series of symmetric and one asymmetric tilt GBs of Mg2SiO4 forsterite, ranging from 9.58 degrees to 90 degrees in misorientation and varying surface termination. Our emphasis lies on unravelling structural characteristics of high-and low-angle grain boundaries and how the atomic structure influences grain boundary excess volume and self-diffusion processes. To obtain diffusion rates for different GB geometries, we equilibrate the respective systems at ambient pressure and temperatures from 1900 to 2200 K and trace their evolution for run durations of at least 1000 ps. We then calculate the mean square displacement of the different atomic species within the GB interface to estimate self-diffusion coefficients in the individual systems. Grain boundary diffusion coefficients for Mg, Si and O range from 10(-18) to 10(-21) m(3)/s, falling in line with extrapolations from lower temperature experimental data. Our data indicate that higher GB excess volumes enable faster diffusion within the GB. Finally, we discuss two types of transport mechanisms that may be distinguished in low- and high-angle GBs.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Wagner, Johannes UNSPECIFIED orcid.org/0000-0002-0247-562X UNSPECIFIED Adjaoud, Omar UNSPECIFIED UNSPECIFIED UNSPECIFIED Marquardt, Katharina UNSPECIFIED orcid.org/0000-0002-5924-3061 UNSPECIFIED Jahn, Sandro UNSPECIFIED orcid.org/0000-0002-2137-8833 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-254023
DOI:	10.1007/s00410-016-1308-y
Journal or Publication Title:	Contrib. Mineral. Petrol.
Volume:	171
Number:	12
Date:	2016
Publisher:	SPRINGER
Place of Publication:	NEW YORK
ISSN:	1432-0967
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language HIGH-PRESSURE; UPPER-MANTLE; PHASE-TRANSITIONS; MG2SIO4 LIQUID; LOW-ANGLE; RHEOLOGY; TRANSPORT; DEFORMATION; CONSTRAINTS; WADSLEYITE Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/25402