Publications
° 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.
Abstract
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.
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ARC Centre of Excellence for Core to Crust Fluid Systems