Affiliation:
1. 1Department of Geological Sciences, California State University Northridge, 18111 Nordhoff Street, Northridge, California 91330-8266, USA
2. 2Department of Geography and Earth Sciences, University of Vermont, 94 University Place, Burlington, Vermont 05405-0114, USA
Abstract
Abstract
We present a new method of linking microstructures, electron backscatter diffraction (EBSD)–derived crystallographic vorticity axis (CVA) analysis, and titanite petrochronology to directly link fabric development to specific deformation events in shear zone rocks with complex histories. This approach is particularly useful where overprinting is incomplete, such that it is unknown which fabric is being dated by the petrochronometer. Here, we compared single-phase CVA patterns of fabric-forming minerals with those of synkinematic petrochronometers (e.g., titanite) to associate the timing of fabric development with deformational events in the middle crust of the George Sound shear zone, Fiordland, New Zealand. The host rocks to the George Sound shear zone include the Carboniferous Large Pluton, where titanite petrochronology demonstrates an unequivocally Cretaceous age of metamorphic titanite growth within mylonitic foliation. However, the host rocks show two distinct CVA patterns: a transtensional deformation event recorded by quartz and plagioclase, and a pure-shear–dominated transpressional deformation event recorded by biotite and titanite. Therefore, the transpressional CVA pattern of the titanite, coupled with its Cretaceous age, shows that it cannot be used to date the quartz and plagioclase fabric developed in response to an older transtensional deformation event. These results demonstrate the necessity of combining EBSD and CVA analysis with petrochronology to demonstrate that synkinematic accessory phase petrochronometers show the same kinematic deformation geometry (i.e., CVA pattern) as the fabric being dated.
Publisher
Geological Society of America
Cited by
3 articles.
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