Geochemical and geochronological cross section of the deep Variscan crust: The Cabo Ortegal high-pressure nappe (northwestern Spain)

Peucat, Jean-Jacques; Bernard-Griffiths, J.; Ibarguchi, José Ignacio Gil; Dallmeyer, R. D.; Ménot, René-Pierre; Cornichet, J.; Léon, M. Iglesias Ponce de

doi:10.1016/0040-1951(90)90285-g

Cited by 143 publications

(116 citation statements)

References 48 publications

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“…This and similar units were underthrust between 390 and 380 Ma (peucat et aL, 1990;Dallmeyer et aL, 199 1, 1997), as deduced from 4°A r p o Ar ages of the arnphibolite-faeies foliation.…”

Section: P-t Valuessupporting

confidence: 58%

Shear stress in subducting continental margin from high-pressure, moderate-temperature metamorphism in the Ordenes Complex, Galicia, NW Spain

2005

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The Ordenes Complex, Galicia, NW Spain, preserves high-pressure, moderate-temperature metamorphism in continental margin rocks subducted during closure of the Rheic Ocean in the Variscan orogeny. The exposures extend across '" 90 km perpendicular to strike and include rocks that reached depths of 30 to 60 km. Estimates of P-T conditions of rocks found near the boundary between overriding and subducting plates range from 430 DC at 1.0 GPa to 520°C at 1.65 GPa. Structural reconstructions including these data indicate an angle of subduction between 15 and 30°.A mathematical solution and numerical models have been used to estimate shear heating experienced by this well-exposed paleo-subduction zone. Best fit of model to thermobarometric results occurs if shear stress in the upper reaches of the fault separating subducting and overriding slabs was'" 100 MPa (constant shear) or '" 10.0% of pressure (constant coefficient of friction) assuming a convergence rate of 6 cm year-I . At greater depths negative feedback between temperature and shear stress caused the system to approach steady state with decreasing shear stress and with little increase in temperature. The decrease in shear stress at temperatures above 400°C occurs as the rheological properties of the rock at higher temperature and (or) pressure allow more plastic behavior. This suggests that high-temperature metamorphism is unlikely to occur in subducting crust without special circumstances. A comparison of these results with estimates of shear stress infelTed from seismicity and heat flow at active convergent boundaries in the Pacific indicates that shear stress is best described as a pressure-dependent variable not as a constant shear stress.

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“…This and similar units were underthrust between 390 and 380 Ma (peucat et aL, 1990;Dallmeyer et aL, 199 1, 1997), as deduced from 4°A r p o Ar ages of the arnphibolite-faeies foliation.…”

Section: P-t Valuessupporting

confidence: 58%

Shear stress in subducting continental margin from high-pressure, moderate-temperature metamorphism in the Ordenes Complex, Galicia, NW Spain

2005

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“…A plateau isotopic correlation age of Ma represents a cooling age following 376.8 ‫ע‬ 0.4 the amphibolite facies metamorphism. This is slightly younger than 390-380 Ma reported from amphibolite facies metamorphism in equivalent ophiolitic units in Cabo Ortegal (Peucat et al 1990) and the Portuguese complexes (Dallmeyer et al 1991).…”

mentioning

confidence: 56%

Tectonic Evolution of the Careón Ophiolite (Northwest Spain): A Remnant of Oceanic Lithosphere in the Variscan Belt

García¹,

Arenas²,

Catalán³

et al. 1999

The Journal of Geology

105

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A B S T R A C TAnalysis of the Careó n Unit in the Ordenes Complex (northwest Iberian Massif) has supplied relevant data concerning the existence of a Paleozoic oceanic lithosphere, probably related to the Rheic realm, and the early subduction-related events that were obscured along much of the Variscan belt by subsequent collision tectonics. The ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse-grained and pegmatitic gabbros. An Early Devonian zircon age ( Ma, U-Pb) was obtained in a leucocratic gabbro. The 395 ‫ע‬ 2 whole section was intruded by numerous diabasic gabbro dikes. Convergence processes took place shortly afterward, giving rise to a mantle-rooted synthetic thrust system, with some coeval igneous activity. Garnet amphibolite, developed in metamorphic soles, was found discontinuously attached to the thrust fault. The soles graded downward to epidote-amphibolite facies metabasite and were partially retrogressed to greenschist facies conditions. Thermobarometric estimations carried out at a metamorphic sole ( ЊC; kbar) suggested that imbrications T ≈ 650 P ≈ 11.5 developed in a subduction setting, and regional geology places this subduction in the context of an early Variscan accretionary wedge. Subduction and imbrication of oceanic lithosphere was followed by underthrusting of the Gondwana continental margin.

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“…395 Ma (U-Pb, zircon; Díaz García et al 1999;Pin et al 2002), whereas the regional tectonic foliation that was developed under amphibolite facies conditions yields 40 Ar/ 39 Ar ages between 390 and 376 Ma in this and other upper ophiolitic units (hornblende concentrates; Dallmeyer and Gil Ibarguchi 1990;Peucat et al 1990;Dallmeyer et al 1991Dallmeyer et al , 1997. The amphibolite-facies fabric is related to ophiolite imbrication (Díaz García et al 1999;Arenas et al 2007a), and the narrow age interval between oceanic lithosphere generation and thrusting is consistent with a rapid deformation in a suprasubduction zone context.…”

Section: Geological Contextmentioning

confidence: 79%

“…Widely accepted results include 40 Ar/ 39 Ar ages that range between 390 and 376 Ma (hornblende concentrates; Dallmeyer and Gil Ibarguchi 1990;Peucat et al 1990;Dallmeyer et al 1991Dallmeyer et al , 1997. These ages are interpreted to date the last cooling through those temperatures required for intracrystalline retention of argon within hornblende ;Harrison 1981).…”

Section: Age Constraints and Geodynamic Implicationsmentioning

confidence: 99%

Fabric Development in a Middle Devonian Intraoceanic Subduction Regime: The Careón Ophiolite (Northwest Spain)

Barreiro

Catalán²,

Prior³

et al. 2010

The Journal of Geology

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Geochemical and geochronological cross section of the deep Variscan crust: The Cabo Ortegal high-pressure nappe (northwestern Spain)

Cited by 143 publications

References 48 publications

Shear stress in subducting continental margin from high-pressure, moderate-temperature metamorphism in the Ordenes Complex, Galicia, NW Spain

Shear stress in subducting continental margin from high-pressure, moderate-temperature metamorphism in the Ordenes Complex, Galicia, NW Spain

Tectonic Evolution of the Careón Ophiolite (Northwest Spain): A Remnant of Oceanic Lithosphere in the Variscan Belt

Fabric Development in a Middle Devonian Intraoceanic Subduction Regime: The Careón Ophiolite (Northwest Spain)

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