Geophysical exploration and dynamics of the Alpine Fault Zone

Stern, T. A.; Okaya, D. A.; Kleffmann, Stefan; Scherwath, Martin; Henrys, S. A.; Davey, F. J.

doi:10.1029/175gm11

Cited by 66 publications

(125 citation statements)

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“…As part of this project, activesource multifold crustal seismic reflection data were acquired across the Southern Alps orogen. The data recorded east of the Main Divide have been discussed by Long et al (2003) and Stern et al (2007). West of the divide, the profile (Whataroa profile) starts about 5 km southeast of the Alpine Fault and crosses the fault and the adjacent coastal plain to the northwest (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…The Alpine Fault dips at the surface at about 458 and 40Á608 at depths of about 15Á30 km (e.g. Cooper & Norris 1994;Stern et al 2007). Northwest, the seismic profile is underlain by basement inferred to be dominantly formed of Ordovician Greenland Group quartz-rich metasediments of the Buller terrane and gneissic intrusions of Palaeozoic and Cretaceous granitoids.…”

Section: Introductionmentioning

confidence: 99%

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Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Davey

2010

New Zealand Journal of Geology and Geophysics

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Crustal seismic reflection data recorded across the Alpine Fault and coastal plain at Whataroa in 1998 are used to derive shallow (4 seconds two-way time or s twt) and deep (14 s twt) seismic reflection images and a simple refraction model. A single 25 km long, 636 channel receiver array recorded energy from 50 kg shots fired at 1 km intervals with intervening shots of 2.5 kg at about 300 m intervals along the profile. Record quality varied from good to poor. Across the Alpine Fault, basement lies at about 300Á500 m (0.2Á0.5 s twt), and a weak basement reflection may be attributed the Alpine Fault. Basement deepens sharply at about 6 km to the northwest of the fault, and a 3 km section of probably Miocene and younger sediments is imaged to the northwest. The southern boundary of the coastal basin probably corresponds to the South Westland Fault. The deeper section images a distinct band of strong reflectivity at a depth of about 9Á10 s twt, the base of which is inferred to be Moho. Depth conversion gives a horizontal Moho across the whole profile at a depth of about 27 km.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Davey

2010

New Zealand Journal of Geology and Geophysics

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“…Geodetic studies are consistent with a shallow (5-10 km) depth for full fault locking (Beavan et al, 1999), though some degree of interseismic coupling may persist to as deep as ~18 km . In the mid-crust, the fault zone exhibits low seismic wave speeds and high attenuation (Stern et al, 2001;Eberhart-Phillips and Bannister, 2002;Stern et al, 2007 and references therein) and high electrical conductivity (Wannamaker et al, 2002), suggesting interconnected saline fluids at high pressures within the ductile regime.…”

Section: Tectonic Settingmentioning

confidence: 99%

“…It also provides a mechanism of calibrating and interpreting remote observations, such as those provided by the South Island Geophysical Transect project (SIGHT; Okaya et al, 2002;Stern et al, 2007), and linking these to surface data and rupture models. Laboratory measurements made on samples retrieved from depth, as well as measurements of the conditions under which those samples were collected, are required to more accurately describe the physical characteristics of fault rocks during coseismic rupture, and to account for strong ground motions (Beeler, 2006;Rice and Cocco, 2007).…”

Section: Why the Alpine Fault?mentioning

confidence: 99%

Deep Fault Drilling ProjectAlpine Fault, New Zealand

Townend

Sutherland

Toy

2009

Scientific Drilling

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The Alpine Fault, South Island, New Zealand, constitutes a globally significant natural laboratory for research into how active plate-bounding continental faults work and, in particular, how rocks exposed at the surface today relate to deep-seated processes of tectonic deformation, seismogenesis, and mineralization. The along-strike homogeneity of the hanging wall, rapid rate of dextral-reverse slip on an inclined fault plane, and relatively shallow depths to mechanical and chemical transitions make the Alpine Fault and the broader South Island plate boundary an important international site for multi-disciplinary research and a realistic target for an ambitious long-term program of scientific drilling investigations.

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“…Mylonitization began at depths of up to 35 km (Grapes, 1995;Little et al, 2005;Stern et al, 2007;Sutherland et al, 2007;Vry et 10 al., 2004). Simple shear strains are >150 in the ultramylonites, as high as 120 in the mylonites, and 12-22 in the protomylonites.…”

Section: Deformation Historymentioning

confidence: 99%

Constraints on Alpine Fault (New Zealand) Mylonitization Temperatures and Geothermal Gradient from Ti-in-quartz Thermobarometry

Kidder¹,

Toy²,

Prior³

et al. 2018

Preprint

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Abstract.We constrain the thermal state of the central Alpine Fault using approximately 750 Ti-in-quartz SIMS analyses from a 10 suite of variably deformed mylonites. Ti-in-quartz concentrations span more than an order of magnitude from 0.24 to ~5 ppm, suggesting recrystallization of quartz over a 300° range in temperature. Most Ti-in-quartz concentrations in mylonites, protomylonites, and the Alpine Schist protolith are between 2 and 4 ppm and do not vary as a function of grain size or bulk rock composition. Analyses of 30 large, inferred-remnant quartz grains (>250 µm), as well as late, cross-cutting, chlorite-bearing quartz veins also reveal restricted Ti concentrations of 2-4 ppm. These results indicate that the vast majority of Alpine Fault 15 mylonitization occurred within a restricted zone of pressure-temperature conditions where 2-4 ppm Ti-in-quartz concentrations are stable. This constrains the deep geothermal gradient from the moho to about 8 km to a slope of 5 °/km. In contrast, the small grains (10-40 µm) in ultramylonites have lower Ti concentrations of 1-2 ppm, indicating a deviation from the deeper pressuretemperature trajectory during the latest phase of ductile deformation. These constraints suggest an abrupt, order of magnitude change in the geothermal gradient to an average of about 60 °/km at depths shallower than about 8 km, i.e. within the 20 seismogenic zone. Anomalously, the lowest-Ti quartz (0.24-0.7 ppm) occurs away from the fault in protomylonites, suggesting that the outer fault zone experienced minor plastic deformation late in the exhumation history when more fault-proximal parts of the fault were deforming exclusively by brittle processes.

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Geophysical exploration and dynamics of the Alpine Fault Zone

Cited by 66 publications

References 66 publications

Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Deep Fault Drilling ProjectAlpine Fault, New Zealand

Constraints on Alpine Fault (New Zealand) Mylonitization Temperatures and Geothermal Gradient from Ti-in-quartz Thermobarometry

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Geophysical exploration and dynamics of the Alpine Fault Zone

Cited by 66 publications

References 66 publications

Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Crustal seismic reflection profile across the alpine fault and coastal plain at Whataroa, South Island

Deep Fault Drilling ProjectAlpine Fault, New Zealand

Constraints on Alpine Fault (New Zealand) Mylonitization Temperatures and Geothermal Gradient from Ti-in-quartz Thermobarometry

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Deep Fault Drilling ProjectAlpine Fault, New Zealand