° Klepeis, K.A., Daczko, N.R. and Clarke, G.L. 1999. Kinematic vorticity and tectonic significance of superposed mylonites in a major lower crustal shear zone, northern Fiordland, New Zealand. Journal of Structural Geology, 21, 1385-1405.


New structural, metamorphic, finite strain and kinematic vorticity data from a 4 km-wide, subvertical shear zone in Fiordland, New Zealand reveal a history of deformation reflecting different tectonic regimes. An analysis of ductile fabrics within the shear zone and its wall rocks shows two distinctive stages of amphibolite facies mylonitic deformation (D2ASZ and D3ASZ) that are superimposed on older Paleozoic or early Mesozoic structures. Variations in strain intensity and well defined shear zone boundaries have allowed us to examine the progressive development of L2ASZ-S2ASZ and L3ASZ-S3ASZ fabrics and compare the types, kinematics and conditions of deformation that produced them. L2ASZ-S2ASZ formed under lower crustal conditions equilibrating at 11.9±1.1 kbars and 581±34°C; mineral assemblages defining L3ASZ-S3ASZ equilibrated at 8.7±1.2 kbars and 587±42°C. Finite strain and kinematic vorticity studies show that D2ASZ involved ductile normal faulting and crustal thinning leading to decompression and exhumation of lower crustal rocks, probably during the Cretaceous rifting of ancestral New Zealand from Australia. D3ASZ represents an episode of mid-crustal dextral transpression that may have resulted from late Mesozoic or Cenozoic oblique convergence. Reactivation of the subvertical S3ASZ foliation by cataclastic shear zones and brittle faults (D4ASZ) was accompanied by limited recrystallization at greenschist facies conditions. D4ASZ shear zones record upper crustal dextral strike-slip faulting that resembles late Tertiary deformation patterns associated with the Australian-Pacific transform plate boundary.


Dr Nathan R. Daczko
GEMOC ARC National Key Centre
Department of Earth and Planetary Sciences
Macquarie University NSW 2109

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