A sensitive vorticity gauge using rotated porphyroblasts, and its application to rocks adjacent to the Alpine Fault, New Zealand

Holcombe, RJ and Little, TA (2001) A sensitive vorticity gauge using rotated porphyroblasts, and its application to rocks adjacent to the Alpine Fault, New Zealand. Journal of Structural Geology, 23 6-7: 979-989. doi:10.1016/S0191-8141(00)00169-3


Author Holcombe, RJ
Little, TA
Title A sensitive vorticity gauge using rotated porphyroblasts, and its application to rocks adjacent to the Alpine Fault, New Zealand
Journal name Journal of Structural Geology   Check publisher's open access policy
ISSN 0191-8141
Publication date 2001-01-01
Sub-type Article (original research)
DOI 10.1016/S0191-8141(00)00169-3
Volume 23
Issue 6-7
Start page 979
End page 989
Total pages 11
Editor J P Evans
Place of publication Oxford, United Kingdom
Publisher Elsevier Science
Collection year 2001
Language eng
Subject C1
260107 Structural Geology
780104 Earth sciences
Abstract Variable aspect ratio porphyroblasts deformed in non-coaxial flow. and internally containing rotated relicts of an external foliation, can be used to characterise plane strain flow regimes. The distribution obtained by plotting the orientation of the long axis of such grains, classified by aspect ratio, against the orientation of the internal foliation is potentially a sensitive gauge of both the bulk shear strain (as previously suggested) and kinematic vorticity number. We illustrate the method using rotated biotite porphyroblasts in the Alpine Schist: a sequence of mid-crustal rocks that have been ramped to the surface along the Alpine Fault. a major transpressional plate boundary. Results indicate that, at distances greater than or equal to similar to1 km from the fault, the rocks have undergone a combination of irrotational fattening and dextral-oblique, normal-sense shear, with a bulk shear strain of similar to0.6 and kinematic vorticity number of similar to0.2. The vorticity analysis is compatible with estimates of strongly oblate bulk strain of similar to 75% maximum shortening. Dextral-reverse transpressional flow characterises higher strain S-tectonite mylonite within similar to1 km of the Alpine Fault. These relationships provide insight into the kinematics of flow and distribution of strain in the hangingwall of the Alpine Fault and place constraints on numerical mechanical models for the exhumation of these mid-crustal rocks. (C) 2001 Elsevier Science Ltd. All rights reserved.
Keyword Geosciences, Multidisciplinary
Southern Alps
Island
Uplift
Strain
Zones
Constraints
Deformation
Boundary
Schist
Flow
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
 
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Created: Wed, 15 Aug 2007, 01:01:23 EST