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GEOREF RECORD

The Querigut Complex (Pyrenees, France) re-examined using the AMS technique; a syntectonic pluton of Hercynian dextral transpression

Jean-Baptiste Aurejac, Gerard Gleizes, Herve Diot and Jean-Luc Bouchez
Le complexe granitique de Querigut (Pyrenees, France) re-examine par la technique de l'ASM; un pluton syntectonique de la transpression dextre hercynienne
Bulletin de la Societe Geologique de France (2004) 175 (2): 157-174

Abstract

The Variscan Querigut Pluton (eastern Axial Zone, Pyrenees), recently dated at 307+ or -2 Ma, is a classical example for the structural study of granitoids. We present a new structural analysis of this pluton using the powerful technique of magnetic susceptibility anisotropy (AMS). A model of pluton emplacement is proposed on the basis of complementary microstructural analyses allowing the determination of the temperatures of fabric acquisition in the magmatic units, and of the shear sense criteria in the surrounding country rocks. This pluton is constituted by two main units that have intruded metasedimentary rocks where regional metamorphic conditions decrease from southwest to northeast. A well-foliated southern granodioritic unit, rich in Devonian marble xenoliths, is bounded to the south by Cambro-Ordovician metapelites. A weakly foliated northern monzogranitic unit, bounded to the north by Devonian marbles, comprises tow sub-types: an outer biotite-monzogranite and an inner biotite-muscovite leucomonzogranite. Abundant basic stocks of variable sizes and lithologies outcrop in the granodioritic unit and in the southern part of the monzogranitic unit. Mean magnetic susceptibility and magnetic foliation maps show a very good agreement with the previous compiled petrographic and structural maps, strengthening the validity of the AMS technique. The northern monzogranitic units display two unevenly distributed structural patterns: (a) a NE-SW-trending pattern of weakly to steeply dipping foliations, dominant in the outer biotite monzogranite, is associated to subhorizontal NE-SW lineations; and (b) a NW-SE-trending pattern of steeply dipping foliations, dominant in the inner biotite-muscovite monzogranite, is concentrated in NW-SE elongated corridors, associated to subhorizontal NW-SE lineations. In the southern granodiorite unit, foliation patterns follow roughly both the main regional foliation pattern and the pluton boundary, with foliation dips increasing to the south. Subhorizontal NW-SE trending magnetic lineations in the inner parts of this unit, are progressively verticalized toward the southern pluton boundary. A progressive increase in total magnetic anisotropy is observed toward the border of the pluton, correlated with both an increase in solid-state deformation and a decrease of the final temperature of fabric acquisition. These features result from a pluri-kilometric shear zone localized in the western half of the granodioritic unit, decreasing in thickness in its eastern half and along N060 degrees E trending contacts with the country rocks. In the northern monzogranitic unit, one can roughly correlate the magmatic microstructures to the NE-SW trending fabric, and the superimposed subsolidus microstructures to the NW-SE-trending corridors, where rather low-temperature (<300 degrees C) fluid-assisted cataclastic microstructures may also appear. The country-rocks, half kilometer away from the pluton border, display the D2 regional Variscan pattern, with subvertical and N110 degrees E-striking foliation and subhorizontal and E-W-trending stretching lineations associated to a dextral shear. Closer to the pluton, the country-rocks are subjected to the pluton influence, particularly along the southern border where a strong flattening is associated to subvertical lineations related to local thrusting of the pluton into its country rocks. An emplacement model is proposed through the injection of three principal magma batches (granodiorite, biotite-monzogranite and biotite-muscovite monzogranite) that successively and progressively built up the pluton while the whole region was subjected to a dextral and compressive deformation regime, in agreement with AMS results obtained from several other plutons of the Pyrenees.


ISSN: 0037-9409
EISSN: 1777-5817
Coden: #02538
Serial Title: Bulletin de la Societe Geologique de France
Serial Volume: 175
Serial Issue: 2
Title: Le complexe granitique de Querigut (Pyrenees, France) re-examine par la technique de l'ASM; un pluton syntectonique de la transpression dextre hercynienne
Translated Title: The Querigut Complex (Pyrenees, France) re-examined using the AMS technique; a syntectonic pluton of Hercynian dextral transpression
Affiliation: Universite Paul-Sabatier, Equipe de Geodynamique, Toulouse, France
Pages: 157-174
Published: 2004
Text Language: French
Summary Language: English
Publisher: Societe Geologique de France, Paris, France
References: 64
Accession Number: 2004-061136
Categories: Structural geologyIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N42°34'60" - N43°25'00", E00°49'60" - E02°10'00"
Secondary Affiliation: Universite de La Rochelle, FRA, France
Country of Publication: France
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200418
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