Kinematics of oblique collision and ramping inferred from microstructures and strain in middle crustal rocks, central Southern Alps, New Zealand

Little, Timothy A.; Holcombe, R. J.; Ilg, Bradley R.

doi:10.1016/s0191-8141(01)00060-8

Cited by 102 publications

(120 citation statements)

References 58 publications

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“…Large strains in the more deformed mylonites are indicated by the parallelism of all features with the foliation and the destruction of most of the original schist fabric. Shear sense indicators on both mesoscopic and microscopic scales consistently record oblique dextralreverse shear in accordance with the recent slip on the fault (Prior, 1988;Little et al, 2002). A strong convergent component developed on the fault around 5-6 Ma (Sutherland, 1995), since when there has been at least 70 km of convergence across the whole plate boundary .…”

Section: Alpine Fault Mylonite Zonementioning

confidence: 87%

Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand

Norris

2014

Earth Planet Sp

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The Alpine Fault accommodates around 60-70% of the 37 mm/yr oblique motion between the Australian and Pacific plates in the South Island of New Zealand. Uplift on the fault over the past 5 Ma has led to the exhumation of the deep-seated mylonite zone alongside the present surface trace. Shear strain estimates in the mylonites reach 200-300 in the most highly strained rocks, and provide an integrated displacement across the zone of 60-120 km. This is consistent with the amount of displacement during the last 5 Ma, suggesting that displacement on the fault is localised within a 1-2 km wide ductile shear zone to depths of 25-30 km. Existing geodetic data, together with Late Quaternary slip rate and paleoseismic data, are consistent with the steady build-up and release of elastic strain in the upper crust driven by ductile creep within a narrow mylonite zone at depth. Faults of the Otago Fault System form a parallel array east of the Alpine Fault and accommodate c. 2 mm/yr contraction. Long periods of quiescence on individual structures suggest episodic, or "intermittently characteristic", behaviour. This is more consistent with failure on faults within an elastico-frictional upper crust above a ductile lower crust. Localisation of crustal deformation may be initiated by inherited weaknesses in the upper crust, with downward propagation of slip causing strain weakening within the ductile zone immediately beneath. Inherited structures of great length focus a greater amount of displacement and hence more rapidly develop underlying zones of ductile shear.

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Section: Alpine Fault Mylonite Zonementioning

confidence: 87%

Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand

Norris

2014

Earth Planet Sp

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“…Correlation with a local low seismic velocity zone (EberhartPhillips & Bannister 2002) suggests the antiform strikes 040, agreeing well with geodetic shortening directions and formation by contemporary deformation. However, this direction is also parallel to the strike of regional schistosity in Alpine Schist that contains only a weak neotectonic overprint (Little et al 2002), which may be a counter argument of an actively growing fold of the first interpretation. The Alpine Schist fabric is probably Mesozoic, with mounting evidence for mid-late Cretaceous recrystallisation, although an early Miocene age cannot be entirely ruled out (Grapes 1995;Mortimer 2000;Vry et al 2000;Little et al 2002).…”

Section: Interpretation 2: Mesozoic Architecture With Cenozoic Overprintmentioning

confidence: 99%

“…The metamorphic peak in adjacent Alpine Schist, and corresponding development of pervasive foliation and isograds, also occurred before the modern phase of oblique convergence and uplift (Little et al 2002 and references therein). Although the Alpine Schist was tilted and structurally reorganised during the late Cenozoic (Cox et al 1997), schist fabrics contain only a minor penetrative neotectonic overprint (Little et al 2002).…”

Section: Contextmentioning

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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“…A large temperature anomaly can result in a weak zone with low seismic velocity that can be observed as a heterogeneous velocity structure in the seismic tomography data (Wittlinger et al 1998). Furthermore, mylonite outcrops of exhumed faults (White et al 1980) provide direct evidence for the existence of ductile shear zones in the lower crust under interplate (e.g., Rutter 1999;Little et al 2002) and intraplate faults (e.g., Shimada et al 2004;Fusseis et al 2006;Takahashi 2015).…”

Section: Introductionmentioning

confidence: 99%

Shear strain concentration mechanism in the lower crust below an intraplate strike-slip fault based on rheological laws of rocks

Zhang

Sagiya

2017

Earth Planets Space

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We conduct a two-dimensional numerical experiment on the lower crust under an intraplate strike-slip fault based on laboratory-derived power-law rheologies considering the effects of grain size and water. To understand the effects of far-field loading and material properties on the deformation of the lower crust on a geological time scale, we assume steady fault sliding on the fault in the upper crust and ductile flow for the lower crust. To avoid the stress singularity, we introduce a yield threshold in the brittle-ductile transition near the down-dip edge of the fault. Regarding the physical mechanisms for shear strain concentration in the lower crust, we consider frictional and shear heating, grain size, and power-law creep. We evaluate the significance of these mechanisms in the formation of the shear zone under an intraplate strike-slip fault with slow deformation. The results show that in the lower crust, plastic deformation is possible only when the stress or temperature is sufficiently high. At a similar stress level, ∼100 MPa, dry anorthite begins to undergo plastic deformation at a depth around 28-29 km, which is about 8 km deeper than wet anorthite. As a result of dynamic recrystallization and grain growth, the grain size in the lower crust may vary laterally and as a function of depth. A comparison of the results with constant and nonconstant grain sizes reveals that the shear zone in the lower crust is created by power-law creep and is maintained by dynamically recrystallized material in the shear zone because grain growth occurs in a timescale much longer than the recurrence interval of intraplate earthquakes. Owing to the slow slip rate, shear and frictional heating have negligible effects on the deformation of the shear zone. The heat production rate depends weakly on the rock rheology; the maximum temperature increase over 3 Myr is only about several tens of degrees.

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Kinematics of oblique collision and ramping inferred from microstructures and strain in middle crustal rocks, central Southern Alps, New Zealand

Cited by 102 publications

References 58 publications

Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand

Strain localisation within ductile shear zones beneath active faults: The Alpine Fault contrasted with the adjacent Otago fault system, New Zealand

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

Shear strain concentration mechanism in the lower crust below an intraplate strike-slip fault based on rheological laws of rocks

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