Geodetic measurement of deformation in the Taupo Volcanic Zone, New Zealand: The north Taupo network revisited

151

130

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 semicontinuously 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 (8 > 60°). 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.

Section: Extensional Domainssupporting

confidence: 73%

Extensional fault kinematics within the Taupo Volcanic Zone, New Zealand: Soft‐linked segmentation of a continental rift system

Rowland

Sibson

2001

151

130

“…Geodetic data show extension rates of 9 ± 3 mm/yr north of Lake Taupo (Darby et al 2000). Inversion of GPS and fault slip data (Beanland & Haines 1998) and inversion of GPS velocities, earthquake slip vectors, and geological fault slip rates (Wallace et al 2004) depict extension of the Taupo Rift/Havre Trough gradually decreasing to a point of zero extension at the southern termination of the zone.…”

Section: The Taupo Riftmentioning

confidence: 99%

Evolution of the southern termination of the Taupo Rift, New Zealand

Villamor¹,

Berryman

2006

100

To understand the tectonic evolution of the southern termination of the Taupo Volcanic Zone (TVZ), New Zealand, we compare the late Quaternary structure and kinematics of the southern part of the Taupo Rift or Taupo Fault Belt (Mt Ruapehu Graben) with central parts of the rift (Ngakuru Graben), and with the South Wanganui Basin. We also investigate the differences between displacements of Pliocene and late Quaternary markers within the southern Taupo Rift. Comparison of fault displacement rates derived from displacements of late Quaternary and Pliocene markers yields a preliminary estimate of <400 000 yr for fault initiation of the majority of faults in the southern Taupo Rift. The timing of the onset of faulting in the southern TVZ appears to be younger than central parts of the TVZ and may indicate a step-wise southward propagation of the rift. Faulting also appears to be less evolved in the south than in the central parts of the Taupo Rift (thicker seismogenic crust and hence wider fault spacing), reinforcing the impression of a recent incremental propagation of the Taupo Rift to the south. The onset of faulting coincides with independent observations of the initiation of volcanism in the southern TVZ. We propose that the termination of the TVZ, geographically short of the limit of the Hikurangi margin, may only be temporary, and it is most likely to propagate southward in association with future major perturbations in the subduction margin, such as the occurrence of large ignimbrite volcanism.

“…The rates inri correspond to fan-like extension at 5, 10, and 20 mm/ / increasing to the north. Though this pattern is not incompatil >1 with available onshore geological and geodetic di.t (Berryman 1996;Darby 1996), the value of 20 mm/yr th; we chose for the offshore area covered by box 40 is especia 1 uncertain, and in inverting for the solutions presented belin it has been treated accordingly. The strain rate fitted then?…”

Section: Fault Slip Rates and Rates Of Extension In The Taupo Volcanimentioning

confidence: 99%

The kinematics of active deformation in the North Island, New Zealand, determined from geological strain rates

Beanland

Haines

1998

131

134

Kinematic modelling utilising the method of Haines & Holt extended to the case of cubic Bessel interpolation on curvilinear grids, allows analysis of presentday horizontal motions occurring in the Hikurangi margin, North Island, New Zealand. The velocity field solutions are derived from first order geological data; that is, rates and orientation of extension in the Taupo Volcanic Zone and rates and orientation of motion on the North Island Dextral Fault Belt, against the background of the pattern of uplift and subsidence in the margin.A basic (preferred) velocity field is presented, with four other solutions with different input data, to explain what controls features in the main solution. Every one of the five solutions is the best fitting solution for the input data in each case. All velocity fields are shown relative to the western boundary of the model, which is considered fixed, as part of the assumed non-deforming Australian plate.The velocity field in the main solution includes a strong clockwise rotation of the Hikurangi margin east of the Taupo Volcanic Zone in the north. Farther south, shear across the North Island Dextral Fault Belt facilitates the southwestward motion of the eastern part of the margin. An important boundary condition for the deformation in the North Island appears to be the higher rate of dextral shear in the Marlborough region, which accommodates the relative motion of the Australian and Pacific plates immediately south of the Hikurangi margin.The extension in the Taupo Volcanic Zone, with rates onshore of 5-10 mm/yr north of where the Taupo Volcanic Zone terminates in the centre of the North Island, and the strike-slip component of shear on the North Island Dextral Fault Belt, of c. 20 mm/yr in the south and <5 mm/yr in the north, account for most of the margin-parallel plate motion in the Hikurangi margin. No other major geological strains are required to be occurring in the North Island out of compatibility with these strains.