Thrust tectonics, deep structure and crustal subduction in the Alps and Himalayas

Butler, Rob

doi:10.1144/gsjgs.143.6.0857

Cited by 112 publications

(39 citation statements)

References 60 publications

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“…The eclogite-facies rocks occur 30-150 m thick shear zones surrounded by uneclogitized to partially eclogitized granulite-facies gabbroic anorthosites. The terrain, therefore, represents an example of deep continental crust partially converted to eclogite-facies during continental collision in the sense envisioned by Butler (1986) and Laubscher (1990) and affords an opportunity to study the variation of physical properties associated with this process. Austrheim and Msrk (1988) suggested that eclogite shear zones could be deep crustal reflectors because of their juxtaposition against lowervelocity granulite-facies rocks.…”

Section: "Ose I "3snmentioning

confidence: 99%

“…Crustal material may be converted to eclogite when portions of the continental crust are forced into the mantle during collisional orogenies, such as the Alpine orogeny (e.g. Butler, 1986;Laubscher, 1990;Austrheim, 1991). Laubscher (1990) cited the wellknown occurrences of eclogites with continental crustal affinities within Phanerozoic erogenic belts such as the Alps (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Eclogite-facies shear zones—deep crustal reflectors?

et al. 1994

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Strongly foliated eclogite-facies rocks in 30-150 m thick shear zones of Caledonian age occur within a Grenvillian garnet granulite-facies gabbro-anorthosite terrain in the Bergen Arcs of Norway. The predominant eclogite-facies mineral assemblages in the shear zones are omphacite + garnet + zoisite + kyanite in gabbroic anorthosite and omphacite + garnet in gabbro. Eclogite-facies rocks in shear zones are generally fine-grained; alternating omphacite/ garnet-and kyanite/ clinozoisite-rich layers define gneissic layering. A strong shape preferred orientation of omphacite, kyanite, and white mica (phengitic muscovite and/or paragonite) define the foliation. The anorthositic eclogites show omphacite b-axis maxima approximately normal to the foliation and c-axis girdles within the foliation plane. P-wave velocities (V,) determined at confining pressures to 600 MPa for samples from eciogite-facies shear zones range from 8.3 to 8.5 km s-l and anisotropy ranges from 1 to 7%. The few samples with more pronounced anisotropy tend to be approximately transversely isotropic with minimum velocities for propagation directions normal to foliation and maximum velocities for propagation directions parallel to foliation. The fast propagation direction lies within the c-axis girdles (parallel to foliation) and the slow propagation direction is parallel to the b-axis concentration (normal to foliation) in samples for which omphacite crystallographic preferred orientation was determined, V, for the granulite-facies protoliths average about 7.5 km s -'. High calculated reflection coefficients for these shear zones, 0.04-0.14, indicate that they are excellent candidates for deep crustal reflectors in portions of crust that experienced high-pressure conditions but escaped thermal reactivation.

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Section: "Ose I "3snmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Eclogite-facies shear zones—deep crustal reflectors?

et al. 1994

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“…Their detection is therefore fundamental in the understanding of the earth's dynamic. In particular, the pres-ence of eclogite bodies within the continental lithosphere could explain high velocity patches detected in seismic tomography models or bright seismic reflectors on deep seismic reflection profiles (Butler, 1986;Laubscher, 1990;Nicolas et al, 1990;Austrheim, 1991;Warner et al, 1996). Laboratory measurements of P-and S-wave velocities (e.g.…”

Section: Introductionmentioning

confidence: 99%

EBSD-measured lattice-preferred orientations and seismic properties of eclogites

Bascou¹,

Barruol²,

Vauchez³

et al. 2001

Tectonophysics

133

102

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measured lattice-preferred orientations and seismic properties of eclogites. Tectonophysics, Elsevier, 2001, 342, pp.61 -80. <10.1016/S0040-1951 AbstractWe investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities (Alps, Norway, Mali and eastern China) through the analysis of their microstructures and lattice-preferred orientations (LPO). These samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions. Omphacite and garnet LPO were determined from electron backscatter diffraction (EBSD) technique. Garnet appears to be almost randomly oriented whereas omphacite develops strong LPO, characterized by the [001]-axes concentrated sub-parallel to the lineation, and the (010)-poles concentrated sub-perpendicular to the foliation. In order to analyze the deformation mechanisms that produced such omphacite LPO, we compare our observations to LPO simulated by viscoplastic selfconsistent numerical models. A good fit to the measured LPO is obtained for models in which the dominant slip systems are 1/2h110i{110}, [001] {110} and [001] (100). Dominant activation of these slip systems is in agreement with TEM studies of naturally deformed omphacite. Seismic properties of eclogite are calculated by combining the measured LPO and the single crystal elastic constants of omphacite and garnet. Although eclogite seismic anisotropies are very weak (less than 3% for both P-and S-wave), they are generally characterized by a maximum P-wave velocity sub-parallel to the lineation and by a minimum velocity approximately normal to foliation. The mean P-and S-wave velocities are high (respectively, 8.6 and 4.9 km/s). The S-wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation. Calculated reflection coefficients show that an eclogite/crust interface is generally a good reflector (Rc > 0.1), whereas an eclogite body embedded in the upper mantle would be hardly detectable. D

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“…At high strain rates, the increased strength of the lower crust couples upper crust and mantle, resulting in deformation to become more distributed. Patterns of distributed deformation appear to be in disagreement with structures in recent orogens (Butler 1986), but might apply to Archean or Proterozoic tectonics (e.g. Shackleton 1993;Brun 2002).…”

Section: T E C T O N I C M O D E L Smentioning

confidence: 86%

Current issues and new developments in deformation mechanisms, rheology and tectonics

Meer

Drury

Bresser

et al. 2002

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Abstract:We present a selective overview of current issues and outstanding problems in the field of deformation mechanisms, rheology and tectonics. A large part of present-day research activities can be grouped into four broad themes. First, the effect of fluids on deformation is the subject of many field and laboratory studies. Fundamental aspects of grain boundary structure and the diffusive properties of fluid-filled grain contacts are currently being investigated, applying modern techniques of light photomicrography, electrical conductivity measurement and Fourier Transform Infrared (FTIR) microanalysis. Second, the interpretation of microstructures and textures is a topic of continuous attention. An improved understanding of the evolution of recrystallization microstructures, boundary misorientations and crystallographic preferred orientations has resulted from the systematic application of new, quantitative analysis and modelling techniques. Third, investigation of the theology of crust and mantle minerals remains an essential scientific goal. There is a focus on improving the accuracy of flow laws, in order to extrapolate these to nature. Aspects of strain and phase changes are now being taken into account. Fourth, crust and lithosphere tectonics form a subject of research focused on large-scale problems, where the use of analogue models has been particularly successful. However, there still exists a major lack of understanding regarding the microphysical basis of crust-and lithosphere-scale localization of deformation.

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Thrust tectonics, deep structure and crustal subduction in the Alps and Himalayas

Cited by 112 publications

References 60 publications

Eclogite-facies shear zones—deep crustal reflectors?

Eclogite-facies shear zones—deep crustal reflectors?

EBSD-measured lattice-preferred orientations and seismic properties of eclogites

Current issues and new developments in deformation mechanisms, rheology and tectonics

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