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Book Chapter

Evolution of the middle and lower crust during the transition from contraction to extension in Fiordland, New Zealand

By
Keith A. Klepeis
Keith A. Klepeis
Department of Geology, University of Vermont, Burlington, Vermont 05405-0122, USA
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Daniel S. King
Daniel S. King
Department of Geology, University of Vermont, Burlington, Vermont 05405-0122, USA
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Published:
January 01, 2009

A deeply eroded orogen in southwest New Zealand preserves a record of changing flow patterns in the middle and lower crust during a transition from contraction and crustal thickening to extension and crustal thinning. The New Zealand exposures show that deformation patterns at mid-lower crustal depths were strongly influenced by local variations in crustal structure, temperature, composition, magmatic activity, and rheology. Kinematic parameters, including the orientation of shear zone boundaries, the degree of non-coaxiality and kinematic partitioning, strain symmetry, and whether shear zones were thickening or thinning in different planes of observation, were extremely variable spatially and changed repeatedly over an 8–10 Ma period. However, despite this variability, several aspects of superposed deformations remained constant and can be assigned to distinctive tectonic settings. All shear zones that formed during the 119–111 Ma period in Northern Fiordland record flow involving bulk horizontal (layer-parallel) shortening, vertical (layer-perpendicular) thickening, and >50% pure shear regardless of shear zone orientation, degree of non-coaxiality, strain symmetry, and temperature conditions. In contrast, all shear zones that formed during the 114–90 Ma period in Central Fiordland record flow involving vertical thinning, subhorizontal stretching, and 40%–50% pure shear. These patterns are correlative with regional contraction and regional extension, respectively. The data suggest that at length scales of ~100 km and time scales of ca. 10 Ma, the effects of changing plate boundary dynamics on deformation patterns in the middle and lower crust can be distinguished from the effects of changing local boundary conditions, including steep temperature gradients and variable rheology.

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GSA Special Papers

Crustal Cross Sections from the Western North American Cordillera and Elsewhere: Implications for Tectonic and Petrologic Processes

Robert B. Miller
Robert B. Miller
San José State University, San José, California, USA
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Arthur W. Snoke
Arthur W. Snoke
University of Wyoming, Laramie, Wyoming, USA
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Geological Society of America
Volume
456
ISBN print:
9780813724560
Publication date:
January 01, 2009

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