Large volumes of anhydrous pseudotachylyte in the Woodroffe Thrust, eastern Musgrave Ranges, Australia

Camacho, Alfredo; Vernon, R. H.; Gerald, John Fitz

doi:10.1016/0191-8141(94)00069-c

Cited by 144 publications

(87 citation statements)

References 27 publications

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“…The results outlined above are consistent with both experimental work (Spray 1987(Spray , 1988(Spray , 1990(Spray , 1995 and geochemical analyses of pseudotachylyte from impact craters (Killick 1994;Thompson & Spray 1996) and fault-hosted pseudotachylyte (Maddock 1992;Magloughlin & Spray 1992;O'Hara 1992;Camacho et al 1995;O'Hara & Sharp 2001). These previous studies suggested that the formation of pseudotachylyte is accomplished by the preferential melting of hydrous phases (e.g., micas, amphibole) and the preferential retention, as lithic clasts, of plagioclase and quartz.…”

Section: Pseudotachylyte Geochemistrysupporting

confidence: 78%

Cretaceous age, composition, and microstructure of pseudotachylyte in the Otago Schist, New Zealand

Barker

Sibson

Palin

et al. 2010

New Zealand Journal of Geology and Geophysics

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At Tucker Hill, in Central Otago, New Zealand, a series of pseudotachylyte veins are hosted in quartzofeldspathic schist. Chilled margins, microlites, flow banding, and the crystallisation of mineral phases absent from the host rock provide unequivocal evidence for melting during pseudotachylyte formation. Whole rock analyses of pseudotachylyte reveal c. 3 ) enrichment of K 2 O, Ba, and Rb, and similar depletion of Na 2 O, CaO, Sr, and Eu, as compared to host schist. Formation age of pseudotachylyte is 95.991.8 Ma as measured by total fusion 40 Ar/ 39 Ar analyses. Stepwise heating of pseudotachylyte matrix yields an excellently defined 40 Ar/ 39 Ar plateau age of 96.090.3 Ma. These well-defined ages are attributed to the presence of potassium feldspar, low abundance of inherited lithic material from the host rock, and few fluid inclusions containing extraneous Ar. We propose that formation of these pseudotachylyte veins was related to Cretaceous extensional uplift and exhumation of the Otago Schist.Keywords: pseudotachylyte; schist; Otago; Ar-Ar; geochronology; friction melting IntroductionThe presence of pseudotachylyte (former friction melt) in a fault zone is commonly attributed to frictional melting of rock during seismic slip (Sibson 1975). As such, pseudotachylytes are valuable indicators that an exhumed fault zone was seismically active. Pseudotachylytes have been described from inactive, ancient fault zones (e.g., Outer Hebrides Fault Zone: Sibson 1975;Maddock 1983;Kelley et al. 1994) and present day seismically active fault zones (e.g., the Alpine Fault: Sibson et al. 1981;Bossiere 1991;Warr et al. 2003). Determining the formation age of pseudotachylyte can reveal when a fault was seismically active, and provide information on the significance of a pseudotachylytebearing fault zone relative to the timing of other regional deformation events (Kelley et al. 1994;Magloughlin et al. 2001;Sherlock & Hetzel 2001;Mueller et al. 2002;Warr et al. 2003).In Central Otago, New Zealand, a series of pseudotachylyte veins are found in schist outcropping on Tucker Hill (1698 24?23??E; 458 15?16?S), near the township of Alexandra (Fig. 1). The pseudotachylyte veins are hosted in the garnet-biotite-albite zone of the greenschist facies of the Otago Schist, which forms the basement rocks of much of the Otago region (Mortimer 1993a, b). Tucker Hill is approximately 15 km to the east of the Cromwell Gorge Shear Zone and approximately 20 km to the south of the Rise and Shine Shear Zone, which are two Cretaceous age extensional shear zones (Deckert et al. 2002).Previous studies that have attempted to determine the age of pseudotachylyte utilising 40 Ar/ 39 Ar geochronology in various localities have met with varying degrees of success. In particular, accurate and geologically meaningful 40 Ar/ 39 Ar age determinations are negatively influenced by the presence of variable amounts of inherited crystals (i.e., incompletely melted) from host rocks (Magloughlin et al. 2001;Warr et al. 2007), argon loss by diffusion or alteration ...

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Section: Pseudotachylyte Geochemistrysupporting

confidence: 78%

Cretaceous age, composition, and microstructure of pseudotachylyte in the Otago Schist, New Zealand

Barker

Sibson

Palin

et al. 2010

New Zealand Journal of Geology and Geophysics

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“…The upper side of pseudotachylyte veins has a wider alteration rind than the lower side, which is interpreted to suggest that it results from percolation of meteoric fluids. The general lack of alteration in the center of veins argues against alteration by deuteric fluids [Boullier et al, 2001] or by breakdown of hydrous phases [Camacho et al, 1995]. The oxidation of magnetite into hematite is likely to preferentially affect small grains and therefore it is possible that if SP magnetite had been present along margins it has been preferentially oxidized.…”

Section: Chemical Remanent Magnetization (Crm)mentioning

confidence: 99%

“…In contrast, frictional melting is in general incongruent, in that it is a phase-selective mechanism through which minerals that have a low melting temperature preferentially melt [e.g., Maddock, 1992;Magloughlin, 1992;Lin, 1994;Camacho et al, 1995;Andersen et al, 2008]. Pseudotachylytes formed by frictional melting are generally Fe-, K-and Mg-enriched, and Si-and Na-depleted, suggesting that phyllosilicates melt preferentially, and quartz remains refractory [Camacho et al, 1995;Lin and Shimamoto, 1998;Wenk et al, 2000;Di Toro and Pennacchioni, 2004;Allen, 2005;Zechmeister et al, 2007;Lin, 2008;Molina Garza et al, 2009]. This can be explained by segregation of an Ferich melt from unmolten refractory clasts.…”

Section: Chemical Constraints On Pseudotachylyte Formationmentioning

confidence: 99%

“…[20] Geochemical studies on pseudotachylytes have typically addressed two main issues: (1) whether melts were locally derived or transported along the veins and (2) whether frictional melting was congruent or incongruent [Maddock, 1992;Magloughlin and Spray, 1992;Camacho et al, 1995;Lin and Shimamoto, 1998;O'Hara and Sharp, 2001;Moecher and Sharp, 2004;Warr and van der Pluijm, 2005].…”

Section: Geochemistry Of the Pseudotachylyte Veins And Host Rocksmentioning

confidence: 99%

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Magnetic properties of fault pseudotachylytes in granites

Ferré¹,

Geissman²,

Zechmeister³

2012

J. Geophys. Res.

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[1] We investigate the petrographic, geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from Southern California, the Italian Alps and Kyushyu, Japan. The main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite. These ferrimagnetic grains record a stable, multicomponent magnetization that consists of one or more of the following: coseismic thermal remanent magnetization, coseismic lightning isothermal remanent magnetization and post-seismic chemical remanent magnetization. Fault pseudotachylytes from the three localities display contrasting magnetic properties, which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage.

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“…Along the northern margin of the orogen, differential denudation across largescale thrust faults resulted in important structuring of the crust. The major structural feature is the Woodroffe Thrust; a south-dipping mylonite zone up to 3 km thick (Edgoose et al 1993;Camacho et al 1995;Stewart 1995) offsetting the Moho by c. 20 km (Lambeck & Burgess 1992) and associated with a prominent gradient in the gravity field. South of the Woodroffe Thrust, deformation produced an imbricate thrust stack in which levels of denudation decrease northward from c. 40 km to 30 km in the immediate hanging wall of the Woodroffe Thrust (Scrimgeour & Close 1998).…”

mentioning

confidence: 99%

Tectonic feedback, intraplate orogeny and the geochemical structure of the crust: a central Australian perspective

Sandiford

Hand

McLaren

2001

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The geological record of intraplate deformation in central Australia implies that past tectonic activity (basin formation, deformation and erosion) has modulated the response of the lithosphere during subsequent tectonic activity. In particular, there is a correspondence between the localization of deformation during intraplate orogeny and the presence of thick sedimentary successions in the preserved remnants of a formerly widespread intracratonic basin. This behaviour can be understood as a kind of 'tectonic feedback', effected by the longterm thermal and mechanical consequences of changes in the distribution of heat producing elements induced by earlier tectonism. From a geochemical point of view, one of the most dramatic effects of intraplate orogeny in central Australia has been the exposure, in the cores of the orogens, of deep crustal rocks largely depleted in the heat producing elements. The geochemical structuring of the crust associated with the erosion of the heat-producing upper crust resulted in long-term cooling of the deep crust and upper mantle with associated lithospheric strengthening. This is illustrated here by mapping the consequences of deformation and associated tectonic responses onto the h-q c plane, where h is the characteristic length-scale for heat production distribution, and q c is the total crustal heat production.

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Large volumes of anhydrous pseudotachylyte in the Woodroffe Thrust, eastern Musgrave Ranges, Australia

Cited by 144 publications

References 27 publications

Cretaceous age, composition, and microstructure of pseudotachylyte in the Otago Schist, New Zealand

Cretaceous age, composition, and microstructure of pseudotachylyte in the Otago Schist, New Zealand

Magnetic properties of fault pseudotachylytes in granites

Tectonic feedback, intraplate orogeny and the geochemical structure of the crust: a central Australian perspective

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