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Low-P metamorphism following a Barrovian-type evolution. Complex tectonic controls for a common transition, as deduced in the Mondon˜edo thrust sheet (NW Iberian Massif)

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Arenas Martín, Ricardo and Martínez Catalán, José Ramón (2003) Low-P metamorphism following a Barrovian-type evolution. Complex tectonic controls for a common transition, as deduced in the Mondon˜edo thrust sheet (NW Iberian Massif). Tectonophysics, 365 . pp. 143-164. ISSN 0040-1951

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Official URL: http://www.journals.elsevier.com/tectonophysics/



Abstract

The Mondoñedo thrust sheet has been studied to investigate the complex dynamic relationships that may be involved in the
development of low- and medium-P metamorphic domains. This unit underwent an initial medium-P event during the initial
stages of Variscan convergence, related to crustal thickening. Subsequently, the thrust sheet evolved to a low-P baric type of
metamorphism, related to syn-convergence thinning and exhumation. Its footwall, cropping out in two tectonic windows,
registered a different evolution, with a low-P history that evolved from low- to high-T under a high geothermal gradient. Several
different P–T paths of the Mondon˜edo thrust sheet and its relative autochthon are traced and interpreted according to the
structural evolution of the area. Following the initial crustal thickening, two main syn-convergence extensional shear zones
developed. One of them occurs in the hangingwall, whereas the other affects the footwall unit. Both extensional shear zones were
contemporaneous with ductile thrusting in the inner parts of the thrust sheet, and their activity is viewed as a consequence of the
need for gravitational re-equilibration within the orogenic wedge.
The most commonly accepted models of tectonothermal evolution in regions of thickened continental crust assume that low-P
metamorphism is essentially a late phenomenon, and is linked to late-orogenic tectonic activity. In the Mondon˜edo thrust sheet,
our conclusions indicate that low-P metamorphism may also develop during convergence, and that this may occur in at least two
cases. One is tectonic denudation of an allochthonous unit during its emplacement, and the other, thinning and extension at the
footwall unit of an advancing thrust sheet. As a consequence, the low-P evolution may show different characteristics in different
units of an orogenic nappe pile.


Item Type:Article
Uncontrolled Keywords:Variscan metamorphism; Barrovian to low-P evolution; NW Iberian Massif
Subjects:Sciences > Geology > Petrology
Sciences > Geology > Geodynamics
ID Code:17382
Deposited On:11 Dec 2012 11:40
Last Modified:11 Dec 2012 11:40

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