Example of large volume loss in ductile shear zones
- Univ. of Minnesota, Minneapolis, MN (United States)
The authors have studied strain and fabric development in small ductile shear zones produced under amphibolite facies conditions in the Eastern Amphibolites of the Seve-Koeli nappe complex in the northern Swedish Caledonides. These rocks are particularly favorable for such a study because three independent measures of aspects of the deformation can be obtained. These are the shape and size of aggregates of plagioclase feldspar, and the orientation of the foliation defined by the elongate aggregates. Isogons of foliation trace on sections perpendicular to the shear zones and parallel to the displacement direction indicate a monoclinic geometry requiring simple shear, simple shear plus volume change, or simple shear and volume change plus constant deformation imposed upon the whole system. Both size of the feldspar aggregates as a function of position across the shear zones and aspect ratio of the aggregates plotted against orientation indicate significant volume decrease towards the centers of the zones. The data is consistent with constant shear strain across the zones and variable volume change, which seems implausible, and also with progressive loss of volume with increasing shear, which seems much more likely. Maximum volume loss is more than 50% in the centers of the zones. The addition of a weak homogeneous deformation affecting shear zones and wall rocks provides the best fit to the data. Recrystallization in the most highly deformed rock has caused a dispersal of the feldspar aggregates and a more homogeneous texture. Thus much of the deformational history has been erased in the most strongly deformed rock.
- OSTI ID:
- 5881660
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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