Microstructural, chemical and textural records during growth of snowball garnet

Details

Serval ID
serval:BIB_53BD5F8EC277
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
Microstructural, chemical and textural records during growth of snowball garnet
Journal
Journal of Metamorphic Geology
Author(s)
Robyr M., Carlson W.D., Passchier C.W., Vonlanthen P.
ISSN
0263-4929
Publication state
Published
Issued date
2009
Peer-reviewed
Oui
Volume
27
Pages
423-437
Language
english
Abstract
The growth history of two populations of snowball garnet from the Lukmanier Pass area (central Swiss Alps) was examined through a detailed analysis of three-dimensional geometry, chemical zoning and crystallographic orientation. The first population, collected in the hinge of a chevron-type fold, shows an apparent rotation of 360 degrees. The first 270 degrees are characterized by spiral-shaped inclusion trails, gradual and concentric Mn zoning and a single crystallographic orientation, whereas in the last 90 degrees, crenulated inclusion trails and secondary Mn maxima centred on distinct crystallographic garnet domains are observed. Microstructural, geochemical and textural data indicate a radical change in growth regime between the two growth sequences. In the first 270 degrees, growth occurred under rotational non-coaxial flow, whereas in the last 90 degrees, garnet grew under a non-rotational shortening regime. The second population, collected in the limb of the same chevron-type fold structure, is characterized by a spiral geometry that does not exceed 270 degrees of apparent rotation. These garnet microstructures do not record any evidence for a modification of the stress field during garnet growth. Concentric Mn zoning as well as a single crystallographic orientation are observed for the entire spiral. Electron backscatter diffraction data indicate that nearly all central domains in the snowball garnet are characterized by one [001] axis oriented (sub-)parallel to the symmetry axis and by another [001] axis oriented (sub-)parallel to the orientation of the internal foliation. These features suggest that the crystallographic orientation across the garnet spiral is not random and that a relation exists among the symmetry axis, the internal foliation and the crystallographic orientation.
Keywords
electron backscatter diffraction, lukmanier, snowball garnet, tomography
Create date
03/07/2009 15:01
Last modification date
20/08/2019 15:08
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