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Book Chapter

Application of magnetic fabrics to the emplacement and tectonic history of Devonian granitoids in central Argentina

By
M. G. López De Luchi
M. G. López De Luchi
Instituto de Geocronología y Geología Isotópica, Pabellón INGEIS, Giudad Universitaria, C1428EHA, Buenos Aires, Argentina
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A. E. Rapalini
A. E. Rapalini
Instituto de Geofísica Daniel Valencio (INGEODAV), Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, CONICET, Pabellón 2, Ciudad Universitaria, C1428EHA, Buenos Aires, Argentina
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S. Siegesmund
S. Siegesmund
Geoscience Centre of the University of Göttingen (GZG), Department of Structural Geology and Geodynamics, University of Göttingen, 37077 Göttingen, Goldschmidtstrasse 3, Germany
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A. Steenken
A. Steenken
Geoscience Centre of the University of Göttingen (GZG), Department of Structural Geology and Geodynamics, University of Göttingen, 37077 Göttingen, Goldschmidtstrasse 3, Germany
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Published:
January 01, 2004

Abstract

Regional considerations on the tectonic regime during the emplacement of the Early Devonian magmatic units in the Sierra de San Luis are inferred from combined field, petrographic and AMS observations. Devonian granitoids of the Sierra de San Luis, in central Argentina, constitute elliptical composite batholiths and make up the most voluminous magmatism that appears in the Sierra. Detailed fabric studies have been carried out on the La Totora batholith (33°09′S, 65°42′W), which complement previous studies on two of the largest plutons in the Sierra de San Luis: The Renca and Las Chacras-Potrerillos batholiths. The studies comprised systematic field surveys, petrographic observations and anisotropy of magnetic susceptibility (AMS) measurements. Microstructural studies indicate that the batholith rocks are mainly characterized by magmatic microstructures with limited sub-magmatic to high-temperature solid-state deformation. All three batholiths possess concentric foliation patterns. The average magnetic foliation patterns in the studied plutons agree well with the macroscopic fabrics measured in the field indicating that the AMS-data can be used to study the orientation of fabric elements. Bulk susceptibility indicates a predominance of ferromagnetic contributions, although some paramagnetic sub-units are also present. Most foliations and lineations reflect magmatic flow and their attitude is linked to the interference between regional deformation and batholith inflation, i.e. fabrics may be due to regional strain in combination with the internal dynamics of the magma bodies. Rock fabrics are mainly described by oblate magmetic fabric ellipsoids. Magnetic lineations generally show a NNE-SSW trend that is interpreted to be controlled by the opening transtensional pull-apart structures during batholith inflation. It turns out that the Devonian batholiths intruded the basement syn-kinematically with respect to the Achalian deformational cycle.

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Contents

Geological Society, London, Special Publications

Magnetic Fabric: Methods and Applications

F. Martín-Hernández
F. Martín-Hernández
Faculty of Geosciences, Utrecht University, The Netherlands
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C. M. Lüneburg
C. M. Lüneburg
Department of Geology and Geophysics, University of New Orleans, USA
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C. Aubourg
C. Aubourg
Laboratoire de Tectonique, Université de Cergy-Pontoise, France
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M. Jackson
M. Jackson
Institute for Rock Magnetism, University of Minnesota, USA
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Geological Society of London
Volume
238
ISBN electronic:
9781862394865
Publication date:
January 01, 2004

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