New Zealand Journal of Geology and Geophysics abstracts
Extensional fault kinematics within the Taupo Volcanic Zone, New Zealand:
soft-linked segmentation of a continental rift system
J. V. ROWLAND
R. H. SIBSON
Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand
Abstract The Taupo Volcanic Zone (TVZ) is a young (<=2 Ma)
arc-backarc system in continental crust at the southern end of the Havre Trough
characterised by intense volcanism and geothermal activity. An extensional
fault belt (known locally as the Taupo Fault Belt) can be traced
semi-continuously within the TVZ from Ruapehu in the southwest to the Bay of
Plenty coast in the northeast. Contained within the belt are numerous active
volcanic centres (andesitic, basaltic, rhyolitic) and geothermal systems.
Kinematic studies demonstrate that normal faulting predominates within the
fault belt, which we interpret as a distributed rift system (here termed the
Ruaumoko Rift System), within which rift axes are locally defined by
crudely symmetric dispositions of northwest- and southeast-dipping faults. The
entire fault belt is partitioned along-strike into offset rift segments defined
by association with discrete rift axes. Fault dips, where measurable, are
generally steep (δ > 60deg.). Systematic fracture sets occur in all
rock types in the TVZ and generally show a strong northeast-southwest trend,
indicating a component of extensional strain distributed throughout the rock
mass. Extension is predominantly orthogonal to the rift axes except in
"accommodation zones" where interaction between offset rifting segments
perturbs the stress field, locally enhancing permeability. The varying trends
of extensional structures lie perpendicular to least principal stress
trajectories in a locally heterogeneous stress field with normal dip-slip as
the predominant fault mechanism.
Keywords Ruaumoko Rift System; orthogonal extension; Taupo
Volcanic Zone; Taupo Fault Belt; accommodation zone; normal fault; rift
segmentation
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
271-283
0028-8306/01/4402-0271 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (6176K); (scanned from paper original: notes about this process)
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