Petrology of pseudotachylytes from the Alpine Fault of New Zealand

Bossière, Gérard

doi:10.1016/0040-1951(91)90295-4

Cited by 34 publications

(26 citation statements)

References 27 publications

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“…40 Ar/ 39 Ar geochronologic dating methods, as well as petrographic, scanning electron microscopy, geochemistry, palaeomagnetic and magnetic fabric studies, were applied to pseudotachylytes hosted in Permian granitic rocks of the Chiapas Massif, in southern Mexico. These techniques have been applied in different combinations to pseudotachylytes in a range of settings (Bossiere 1991; Nakamura et al 2002; DiToro & Pennacchiote 2004; Cosca et al 2005; Maurel et al 2006), but few studies have integrated a large number of such approaches. The focus of this contribution is on the magnetic properties of remanence and magnetic fabric of microscopically well‐characterized cataclasite‐dominated pseudotachylytes from a previously unknown locality.…”

Section: Introductionmentioning

confidence: 99%

An integrated magnetic and geological study of cataclasite- dominated pseudotachylytes in the Chiapas Massif, Mexico: a snapshot of stress orientation following slip

Molina-Garza¹,

Geissman

Wawrzyniec

et al. 2009

Geophysical Journal International

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S U M M A R YThe Permian age Chiapas Massif in southeast Mexico is locally host to well-exposed pseudotachylyte vein networks. The veins are black to dark grey and aphanitic in appearance, and consist mostly of microbreccia of angular fragments of plagioclase, K-feldspar, biotite and quartz, in a cryptocrystalline (microscopically irresolvable) matrix. Evidence of melting is present in the form of glass seams, dikelets, glass clasts included in cataclasite and a distinct chemistry in the pseudotachylite veins; pristine glass represents a relatively small volume of the pseudotachylite veins. At an exposure along the Tablón River valley, where the host rock is a medium to coarse-grained equigranular quartz diorite, individual veins are consistently oriented about 280 • , are up to 16 mm wide, tens of cm apart, display a consistent left-lateral offset and can be traced for several metres. Individual pseudotachylyte veins rarely cross each other, and they cannot be directly linked to a regional-scale fault. Pseudotachylytes are apparently formed by a combination of crushing, comminution and frictional melting, but they are cataclasite dominated. Textures indicate that cataclasis continued after frictional melting had ceased. A 40 Ar/ 39 Ar age determination from whole rock chips of one vein shows a climbing Ar release spectrum with a date of ∼114 Ma as the most reliable age estimate for Ar retention. This result is interpreted in the context of pseudotachylyte formation, recrystallization and resetting of K-bearing minerals for the K-Ar system in the late Early Cretaceous. Ten veins were sampled for palaeomagnetic and magnetic fabric studies, with samples collected from both the veins and their host rock. Remanence data give moderate natural remanent magnetization (NRM) intensities for both the veins (e.g. NRM mean 6.6 × 10 −3 A m −1 ; σ = 5.5) and host rock (mean 7.7 × 10 −3 A m −1 ; σ = 10.8). Many samples of host rock yield an ill-defined east-west directed and shallow magnetization, which we interpret as a Late Permian magnetization based on previous studies of the Chiapas Massif. This magnetization resides in haematite. Veins, as well as immediately adjacent host rock, typically have well-defined, single polarity magnetizations of north-northwest declination and moderate positive inclination and these resemble the Cretaceous expected field direction. The overall mean of the veins is of Dec = 348.7 • and Inc = 33.6 • (k = 30.5 and α 95 = 12.3 • ; n = 6 site means). Rock magnetic parameters suggest that the remanence in the veins principally resides in low-Ti pseudo-single domain magnetite and maghemite grains, but haematite, coarse-grained magnetite, rutile, Fe-Cr-Ni oxides and ilmenite are also present in the veins. Bulk magnetic susceptibility values range between ∼0.3 and 1.1 * 10 −3 SI volume units, and host rock values do not differ significantly from vein values. The orientations of the principal susceptibility axes in the host rock and the veins are indistinguishable. In both, magnetic foliations are near ...

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Section: Introductionmentioning

confidence: 99%

An integrated magnetic and geological study of cataclasite- dominated pseudotachylytes in the Chiapas Massif, Mexico: a snapshot of stress orientation following slip

Molina-Garza¹,

Geissman

Wawrzyniec

et al. 2009

Geophysical Journal International

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“…Stierman 1984) and the temperature during the earthquake may increase locally, even to produce partial rock melting and consequent post-seismic fault lubrication (e.g. Bossiere 1991).…”

Section: Discussion a N D Conclusionmentioning

confidence: 99%

Rheology heterogeneities on fault surfaces inferred from the time history of afterslip events

Belardinelli

Bonafede

1994

Geophysical Journal International

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S U M M A R YA model of shallow afterslip on transcurrent vertical faults is presented. The creeping region is represented with a 2-D, quasi-static crack, open to the Earth surface; the fault gouge is treated as a viscoplastic layer with vertically heterogeneous Bingham rheology and a deep earthquake is assumed to generate a two-level stress distribution on the fault plane: in the deeper level the stress drops to values less than the plastic threshold of the fault gouge while, in the shallower level, the earthquake concentrates stress to values greater than the plastic threshold; in this region aseismic slip takes place. Initially the creeping region is assumed to extend from the Earth surface to the depth of transition between stress levels, but subsequently it penetrates deeper, thanks to the stress concentration created by the crack beyond its tip. Slip at the Earth surface is computed for some stress-drop distributions and viscosity profiles, and the results are compared with afterslip observations on three California faults. The whole evolution is sensibly affected by the initial stress profile variations, mainly because the crack gradually extends to increasing depths. The initial part of the evolution is also affected by the viscosity profile assumed on the fault plane. In particular the advanced phase of the evolution is not affected by a shallow region with low viscosity on the fault plane. The fast relaxation of this region in fact provides a quick displacement superimposed from the beginning on a slip evolution very similar to that with a uniform viscosity. After removal from the data of this initial displacement, treated as a free parameter since it is not well constrained from data themselves, a suitable choice of the stress parameter values gives a good reproduction of the data in all the cases analysed even if a uniform viscosity on the fault plane is assumed. In all the analysed cases these parameter values are consistent with a temporal deepening of the creeping region, even if the computed displacement at the Earth surface along a direction orthogonal to the fault strike is scarcely sensitive to maximum depth of creep.

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“…The chemistry of both natural (for example, Bossière, 1991;Maddock, 1992;Spray, 1993;Jiang and others, 2015) and laboratory (for example, Spray, 1987Spray, , 1993Spray, , 2010Lin and Shimamoto, 1998;Lin, 2008) pseudotachylytes indicates that melting accompanying shear occurs as a nonequilibrium process, in which lower melting-point, typically hydrous minerals are the first to melt. Melt compositions are characteristically more basic (in other words, lower SiO 2 content) than the wall rocks, and are enriched in Fe with or without Mg from the preferred melting of hydrous mafic minerals such as biotite and amphibole.…”

Section: Temperature Estimatesmentioning

confidence: 99%

Gallery of melt textures developed in Westerly Granite during high-pressure triaxial friction experiments

Moore¹,

Lockner²,

Kilgore³

et al. 2016

Open-File Report

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Petrology of pseudotachylytes from the Alpine Fault of New Zealand

Cited by 34 publications

References 27 publications

An integrated magnetic and geological study of cataclasite- dominated pseudotachylytes in the Chiapas Massif, Mexico: a snapshot of stress orientation following slip

An integrated magnetic and geological study of cataclasite- dominated pseudotachylytes in the Chiapas Massif, Mexico: a snapshot of stress orientation following slip

Rheology heterogeneities on fault surfaces inferred from the time history of afterslip events

Gallery of melt textures developed in Westerly Granite during high-pressure triaxial friction experiments

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