Strain within the ultrahigh-pressure Western Gneiss region of Norway recorded by quartz CPOs

Barth, Nicolas C.; Hacker, Bradley R.; Seward, Gareth; Walsh, Emily O.; Young, D. J.; Johnston, Scott M.

doi:10.1144/sp335.27

Cited by 33 publications

(54 citation statements)

References 55 publications

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“…Late sense of shear data are mostly top-W in the western three-fourths of the field area and top-E in the eastern quarter (stereonets show shear-band data from six sites). Some data from Chauvet and Séranne (1989), Robinson (1995), Labrousse et al (2002), and Barth et al (2010). indicate early, mostly top-E sense of shear (Fig. 10).…”

Section: Structural Domainsmentioning

confidence: 94%

“…4). They consist mostly of gently plunging ENE-WSW to ESE-WNW lineations, isoclinal lineationparallel folds, and generally symmetrical fabrics implying coaxial strain histories with a constrictional component (Andersen et al, 1994;Dransfield, 1994;Krabbendam and Wain, 1997;Krabbendam and Dewey, 1998;Labrousse et al, 2002;Hacker et al, 2003a;Terry and Robinson, 2003;Engvik et al, 2007;Barth et al, 2010). Along the western edge of the WGR, these fabrics are overprinted by or merge into the Nordfjord-Sogn Detachment Zone (NSDZ), an amphibolite-to greenschist-facies, W-dipping, top-W shear zone that formed toward the end of the Scandian orogeny (Norton, 1987;Andersen and Jamtveit, 1990; see summary in Johnston et al, 2007a).…”

Section: Structural Overview Of the Wgrmentioning

confidence: 99%

“…Sense-of shear data are mostly top-W in the west and top-E in the east (stereonets show shear-band data from five sites). Some sense of shear data from Chauvet and Séranne (1989), Robinson (1995), Labrousse et al (2002), Terry and Robinson (2003), and Barth et al (2010). Red sense of shear indicators show displacement of shallower structural levels toward the foreland (east) and blue show displacement of shallower rocks toward the hinterland (west).…”

Section: Structural Domainsmentioning

confidence: 99%

“…In situ 'melts' that are moderately to strongly deformed increase in abundance northwestward (Fig. 6j); some quartz CPOs show prism-[c] slip (Barth et al, 2010), typical of granulite-facies temperatures (Lister and Dornsiepen, 1982). Significant zones of mylonitic gneiss and mylonite are present (Fig.…”

mentioning

confidence: 99%

“…Typical are medium-grained rocks formed of coarsened symplectite that overprints an earlier strong lineation; some quartz CPOs show prism-[c] slip (Barth et al, 2010). Asymmetric structures are abundant and show both sinistral and dextral shear.…”

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confidence: 99%

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Ultra High Pressure Metamorphism☆

Massonne

2016

Reference Module in Earth Systems and Environmental Sciences

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A new dataset for the high-pressure to ultrahigh-pressure Western Gneiss Region allows the definition of distinct structural and petrological domains. Much of the study area is an E-dipping homocline with E-plunging lineations that exposes progressively deeper, more strongly deformed, more eclogite-rich structural levels westward. Although eclogites crop out across the WGR, Scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area. The Scandian reworking increases westward, culminating in strong Scandian fabrics with only isolated pockets of older structures; the dominant Scandian deformation was coaxial E-W stretching. The sinistrally sheared Møre-Trøndelag Fault Complex and Nordfjord Mylonitic Shear Zone bound these rocks to the north and south. There was moderate top-E, amphibolite-facies deformation associated with translation of the allochthons over the basement along its eastern edge, and the Nordfjord-Sogn Detachment Zone underwent strong lower amphibolite-facies to greenschist-facies top-W shearing. A northwestward increase in exhumation-related melting is indicated by leucosomes with hornblende, plagioclase, and Scandian sphene. In the western 2/3 of the study area, exhumation-related, amphibolite-facies symplectite formation in quartzofeldspathic gneiss postdated most Scandian deformation; further deformation was restricted to slip along biotite-rich foliation planes and minor local folding. That the Western Gneiss Region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation, implies that continental crust in general need not undergo pervasive deformation during subduction.

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Section: Structural Domainsmentioning

confidence: 94%

Section: Structural Overview Of the Wgrmentioning

confidence: 99%

Section: Structural Domainsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Ultra High Pressure Metamorphism☆

Massonne

2016

Reference Module in Earth Systems and Environmental Sciences

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Partially melted, mica-bearing crust in Central Tibet

2014

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Surface wave tomography shows that the central Tibetan Plateau (the Qiangtang block) is characterized by S wave speeds as slow as 3.3 km/s at depths from 20-25 km to 45-50 km and S wave radial anisotropy of at least 4% (V SH > V SV ) that is stronger in the west than the east. The depth of the Curie temperature for magnetite inferred from satellite magnetic measurements, the depth of the α-β quartz transition inferred from V P /V S ratios, and the equilibration pressures and temperatures of xenoliths erupted from the middle to deep crust indicate that the Qiangtang crust is hot, reaching 1000°C at the Moho. This inferred thermal gradient crosses the dehydration melting solidi for crustal rocks at 20-30 km depth, implying the presence or former presence of melt in the Tibetan middle to deep crust. These temperatures do not require the wholesale breakdown of mica at these depths, because F and Ti can stabilize mica to at least 1300°C. Petrology suggests, then, that the Qiangtang middle to deep crust consists of a mica-bearing residue from which melt has been extracted or is being extracted. Wave speeds calculated for mica-bearing rocks with a subhorizontal to gently dipping foliation and 2% silicate melt are a good match to the wave speeds and anisotropy observed by seismology.

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Thermo‐kinematic evolution of theAnnapurna‐DhaulagiriHimalaya, centralNepal: TheCompositeOrogenicSystem

Parsons

Law

Lloyd

et al. 2016

Geochem Geophys Geosyst

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The Himalayan orogen represents a ''Composite Orogenic System'' in which channel flow, wedge extrusion, and thrust stacking operate in separate ''Orogenic Domains'' with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >7008C to 550-6508C), to rigid wedge extrusion (Stage 2, 400-6008C) and duplexing (Stage 3, <280-4008C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems.

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Strain within the ultrahigh-pressure Western Gneiss region of Norway recorded by quartz CPOs

Cited by 33 publications

References 55 publications

Ultra High Pressure Metamorphism☆

Ultra High Pressure Metamorphism☆

Partially melted, mica-bearing crust in Central Tibet

Thermo‐kinematic evolution of theAnnapurna‐DhaulagiriHimalaya, centralNepal: TheCompositeOrogenicSystem

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