Geodetic strain determinations from the Okarito and Godley‐Tekapo regions, central South Island, New Zealand

Pearson, Chris

doi:10.1080/00288306.1994.9514623

Cited by 11 publications

(6 citation statements)

References 19 publications

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“…In each case the direction of horizontal principal contraction is within a few degrees of 110 ø, in good agreement with other measurements in the central South Island [Walcott, 1978[Walcott, , 1979Bibby et al, 1986;Reilly, 1990;Pearson, 1991Pearson, , 1994. Pearson [1994] showed that the 110 ø orientation is consistent with the Pacific-Australian plate motion predicted by the NUVEL-1 (and by implication the NUVEL-1A) plate velocity model. In order to better define the spatial distribution of strain, we magnitude and orientation of the axis of maximum relative contraction, together with its 95% confidence region.…”

Section: Results Of the Strain Determinationssupporting

confidence: 87%

Strain distribution across the Australian‐Pacific plate boundary in the central South Island, New Zealand, from 1992 GPS and earlier terrestrial observations

Pearson¹,

Beavan²,

Darby³

et al. 1995

J. Geophys. Res.

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As part of a geodetic experiment aimed at understanding the deformation associated with the Australian‐Pacific plate boundary in the South Island of New Zealand, in 1992 we reoccupied using Global Positioning System (GPS) techniques a first‐order triangulation and trilateration network established in 1978 between Christchurch on the east coast and Hokitika on the west. The network crosses the South Island a few tens of kilometers southwest of the region where the plate boundary changes from a single, throughgoing oblique slip fault, the Alpine fault, to a series of subparallel strike‐slip faults, the Marlborough faults. The GPS data have been analyzed as daily network solutions, with about 12 stations in each solution. RMS repeatabilities for stations with multiple occupations are 4 mm, 8 mm, and 15 mm in the north, east, and vertical components, respectively. The observed strain across the network is consistent with the entire NUVEL‐IA Pacific‐Australia plate velocity being accommodated on land across this part of the South Island. Shear strain rates derived from the GPS and terrestrial data show that the highest strain rate (> 0.4 μrad/yr) occurs in the region of the Southern Alps and Alpine fault. This rate is about two thirds of the rate predicted from the NUVEL‐IA plate velocity model assuming that all the plate boundary deformation occurs across this region, implying that about two thirds of the plate motion is accommodated in the vicinity of the Alpine fault. Significant shear strain rates greater than 0.2 μrad/yr are also observed farther east, particularly in the region of the Porters Pass‐Amberley fault zone, demonstrating that this zone accommodates a significant part of the plate boundary deformation. Using dislocation modeling, we show that the variation in fault‐parallel shear strain rates across the Alpine fault is reasonably consistent with a nonoptimized dislocation model involving a 50° dipping fault that is presently locked to a depth of ∼12 km. One explanation for this observation is that the upper ∼12 km of the crust in this area is storing most of the right‐lateral shear component of the relative plate motion as elastic energy that will be released in a future major earthquake. The variation in the other component of shear strain, which may be interpreted as fault‐normal relative contraction, is not explained by a simple dislocation model, implying that the normal component of plate motion is taken up in other ways.

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Section: Results Of the Strain Determinationssupporting

confidence: 87%

Strain distribution across the Australian‐Pacific plate boundary in the central South Island, New Zealand, from 1992 GPS and earlier terrestrial observations

Pearson¹,

Beavan²,

Darby³

et al. 1995

J. Geophys. Res.

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“…This direction is consistent within errors o: geodetically measured principal strains at 116° ± 14 in a survey network 30 km northeast of this study (Pearson 1994) Slickenside orientations on reverse faults in the duplex structures are oblique, with a mean rake of 55° (Fig. 7B) The shortening direction across the duplex can be estimated from the slickenside and fault orientations.…”

Section: Structural Summary and Interpretationsupporting

confidence: 87%

“…Seismicity and geodetie surveys confirm that deformation does currently occur east of the Alpine Fault (e.g., Rynn & Scholz 1978;Wood &. Blick 1986;Anderson & Webb 1994;Pearson 1994;Eberhart-Phillips 1995;Pearson et al 1995). However, offset marker horizons and datable surfaces are not common in the rapidly eroding and monotonous greywacke-schist sequences in the central Southern Alps.…”

Section: Geology Of Main Divide Regionmentioning

confidence: 99%

Structure and fluid migration in a late Cenozoic duplex system forming the Main Divide in the central Southern Alps, New Zealand

Cox¹,

Craw²,

Chamberlain³

1997

New Zealand Journal of Geology and Geophysics

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The Alpine Schist immediately west of the Main Divide of the Southern Alps is a west-dipping duplex system consisting of an imbricated stack of rock slabs, each c. 250-1000 m thick. The imbricated stack has low grade, little deformed pumpellyite-actinolite facies semischists at the base, overlain by progressively higher grade and more deformed schists. The structurally highest slab mapped consists of multiply-deformed biotite zone schist. The duplex lies on the hanging wall of the northwest-dipping Main Divide Fault Zone, which separates semischist from structurally underlying greywacke. Rock slabs are internally disrupted by faults subparallel to layering, and consist of lozenge-shaped blocks of 10-100 m. Fault zones separating rock slabs consist of <50 cm thick zones of weakly lithified cataclasite and soft gouge. Slickensides on fault surfaces plunge northwest. The duplex formed during late Cenozoic rise of the Southern Alps.Four generations of postmetamorphic veins cut rock slabs of the duplex system. The earliest veins contain quartz, chlorite, calcite, and sulphides and lie subparallel to foliation in the higher grade slabs only. A distinctive set of openspace-filling fissure veins in a lower greenschist facies slab contains euhedral quartz, adularia, bladed calcite, and chlorite. The whole duplex system is cut by steeply dipping shears and fractures containing quartz and ankerite infilling and breccia cementation. Late stage iron oxy-hydroxidecoated fractures, generally steeply dipping, cut all rock slabs. Pyrite and, locally, arsenopyrite accompanies quartz and ankerite veins in extensional sites of steeply dipping late stage fractures, and gold contents up to 850 ppb occur. This G96031Received 2 September 1996; accepted 9 May 1997 gold mineralisation occurred within c. 1 km of the surface and had epithermal affinities.Hydrothermal fluids mineralising the various fractures range in temperature between 350°C and near-ambient temperatures. The quartz-adularia-calcite veins formed at 0.5-2.5 km depth before duplex formation, and later veins formed at shallower levels after duplex formation. Vein carbonates have δ 18 O(SMOW) between 11.4 and26.1%o, and Δ 13 C(PDB) between -0.6 and -11.4%o. Calculated isotopic ratios for the mineralising fluids show little evidence for meteoric origin. The fluid may be meteoric water which has undergone isotopic exchange with host rocks, metamorphic water, or a mixture of these, and mineralisation occurred during rise of the fluids from depth.

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“…Late Quaternary strike-slip displacement rates along the Alpine Fault (27 ± 5 mm/yr) make up 70-75% of the fault-parallel interplate motion, and are relatively constant compared with dip-slip rates (0 to >10 mm/yr) which are greatest adjacent to the highest mountains (Norris & Cooper 2001). Geodetic surveys show that rocks in the immediate vicinity of the Alpine Fault are currently storing elastic strain energy that corresponds to 50-70% of the plate motion rate (Pearson 1994;Pearson et al 1995;Beavan et al 1999). …”

Section: Tectonic Settingmentioning

confidence: 99%

Upper crustal structure beneath the eastern Southern Alps and the Mackenzie Basin, New Zealand, derived from seismic reflection data

Long

Cox

Bannister

et al. 2003

New Zealand Journal of Geology and Geophysics

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Geodetic strain determinations from the Okarito and Godley‐Tekapo regions, central South Island, New Zealand

Cited by 11 publications

References 19 publications

Strain distribution across the Australian‐Pacific plate boundary in the central South Island, New Zealand, from 1992 GPS and earlier terrestrial observations

Strain distribution across the Australian‐Pacific plate boundary in the central South Island, New Zealand, from 1992 GPS and earlier terrestrial observations

Structure and fluid migration in a late Cenozoic duplex system forming the Main Divide in the central Southern Alps, New Zealand

Upper crustal structure beneath the eastern Southern Alps and the Mackenzie Basin, New Zealand, derived from seismic reflection data

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