Ductile fabrics in the zone of active oblique convergence near the Alpine Fault, New Zealand: identifying the neotectonic overprint

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

doi:10.1016/s0191-8141(01)00059-1

Cited by 78 publications

(168 citation statements)

References 69 publications

Supporting

Mentioning

151

Contrasting

Order By: Relevance

“…Given these large offsets, it is possible that the large apparent shortening was a function of pre-Alpine Fault regional variations in geothermal gradient (i.e. a regional variability in initial Ti concentration at a given depth), and/or shallowing of the hypothesized deep, semi-horizontal 10 continuation of the Alpine Fault towards the east (Batt and Braun, 1997;Cox and Sutherland, 2007;Little et al, 2002a).…”

Section: Initial Ti-in-quartz Concentrations Were 2-4 Ppmmentioning

confidence: 99%

“…In particular, Little et al (2002a) Mesozoic D 3 fabrics. The present schist foliation outside of the Alpine mylonite zone is mostly S 3−4 .…”

Section: Deformation Historymentioning

confidence: 99%

“…Neogene deformation incurred a vertical thickening and clockwise rotation (when viewed from the SW) and dextral shearing of the schists. The mylonitic D 4 imprint is only perceptible within 5 km of the Alpine Fault, where it is expressed by a contractional finite shortening strain (post garnet growth) of <50% in a direction perpendicular to the foliation (Holm et al, 5 1989;Little et al, 2002a). The mylonitic foliation (S m ) that is clearly a product of Alpine Fault-related ductile shearing is subparallel to and strengthens these earlier fabrics, but results from higher strain and thus is aligned nearly parallel to the SEdipping Alpine Fault.…”

Section: Deformation Historymentioning

confidence: 99%

“…Holcombe and Little (2001); Little et al (2002a;2002b) and Little (2004) provide detailed microstructural descriptions of the 35 transition from the Alpine Schist to the Alpine Fault mylonite zone. In particular, Little et al (2002a) Mesozoic D 3 fabrics.…”

Section: Deformation Historymentioning

confidence: 99%

See 3 more Smart Citations

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

Kidder¹,

Toy²,

Prior³

et al. 2018

Preprint

View full text Add to dashboard Cite

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.

show abstract

Section: Initial Ti-in-quartz Concentrations Were 2-4 Ppmmentioning

confidence: 99%

“…In particular, Little et al (2002a) Mesozoic D 3 fabrics. The present schist foliation outside of the Alpine mylonite zone is mostly S 3−4 .…”

Section: Deformation Historymentioning

confidence: 99%

Section: Deformation Historymentioning

confidence: 99%

Section: Deformation Historymentioning

confidence: 99%

See 2 more Smart Citations

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

Kidder¹,

Toy²,

Prior³

et al. 2018

Preprint

View full text Add to dashboard Cite

show abstract

“…Aspiring terrane rocks of Otago are Late TriassicÁEarly Jurassic, based on detrital zircon ages (Adams et al 2009;Jugum et al 2009). Little et al (2002) recognised that in the vicinity of Franz Josef Glacier and the Whataroa River, the Alpine Schist is divisible into two components. A metabasite-pelite-rich sequence in the west occurs in a zone 7Á10 km wide adjacent to the Alpine Fault, whereas a more psammitic, Torlesselike (Rakaia terrane) sequence occurs farther east.…”

Section: Introductionmentioning

confidence: 99%

Cretaceous sedimentation and metamorphism of the western Alpine Schist protoliths associated with the Pounamu Ultramafic Belt, Westland, New Zealand

Cooper

Ireland

2013

New Zealand Journal of Geology and Geophysics

View full text Add to dashboard Cite

The Pounamu Ultramafic Belt (PUB), part of the Alpine Schists, comprises a metamorphosed ophiolitic sequence overlain by a thin pelagic unit, a massive quartzofeldspathic biotite rock and quartzofeldspathic turbidites derived from a Torlesse/Otago Schist source. Constituent zircon populations from the biotite rock are euhedral/prismatic and are unabraded. One sample is near unimodal, with a UÁPb SHRIMP age of 106.691.4 Ma (2s m ), while the other has two peaks at 108.091.6 Ma and 71.991.8 Ma. The older age is interpreted to represent the age of igneous activity and sedimentation, while the younger peak is interpreted to represent the age of subsequent metamorphism. The whole-rock geochemistry of the biotite rock, its field distribution and zircon morphology are consistent with an origin by eruption of a dacitic air-fall tuff. The base of the Pounamu sequence divides predominantly psammitic Triassic metasediments to the east from intensely deformed, but regionally west-facing, Cretaceous metasediments to the west. These Cretaceous metasediments have undergone multiphase deformation and metamorphism by 72 Ma, a timing that contrasts markedly with previous interpretations for Jurassic amalgamation of the Haast Schists.

show abstract

Are quartz LPOs predictably oriented with respect to the shear zone boundary?: A test from the Alpine Fault mylonites, New Zealand

Little

Prior

Toy

2016

Geochem Geophys Geosyst

View full text Add to dashboard Cite

The Alpine fault self‐exhumes its own ductile shear zone roots and has a known slip kinematics. Within ∼1 km of the fault, the mylonitic foliation is subparallel to the boundary of the amphibolite‐facies ductile shear zone in which it formed. Using EBSD, we analyzed quartz Lattice Preferred Orientations [LPOs) of mylonites along a central part of the Alpine Fault. All LPOs feature a strongest girdle of [c]‐axes that is forward‐inclined ∼28 ± 4° away from the pole to the fault. A maximum of axes is inclined at the same angle relative the fault. The [c]‐axis girdle is perpendicular to extensional (C') shear bands and the maximum is parallel to their slip direction. [c]‐axis girdles do not form perpendicular to the SZB. Schmid factor analysis suggests that σ1 was arranged at 60–80° to the Alpine Fault. These observations indicate ductile transpression in the shear zone. The inclined arrangement of [c]‐axis girdles, axes, and C' planes relative to the fault can be explained by their alignment relative to planes of maximum shear‐strain‐rate in a general shear zone, a significant new insight regarding shear zones and how LPO fabrics may generally develop within them. For the Alpine mylonite zone, our data imply a kinematic vorticity number (Wk) of ∼0.7 to ∼0.85. Inversions of seismic focal mechanisms in the brittle crust of the Southern Alps indicate that σ1 is oriented ∼60° to the Alpine Fault; that shear bands form at ∼30° to this direction, and that σ2 and σ3 flip positions between the brittle and ductile parts of the crust.

show abstract

Ductile fabrics in the zone of active oblique convergence near the Alpine Fault, New Zealand: identifying the neotectonic overprint

Cited by 78 publications

References 69 publications

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

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

Cretaceous sedimentation and metamorphism of the western Alpine Schist protoliths associated with the Pounamu Ultramafic Belt, Westland, New Zealand

Are quartz LPOs predictably oriented with respect to the shear zone boundary?: A test from the Alpine Fault mylonites, New Zealand

Contact Info

Product

Resources

About