Top-down structures of mafic enclaves within the Valle Fértil magmatic complex (Early Ordovician, San Juan, Argentina)

Authors

  • A. CASTRO Departamento de Geología, Universidad de Huelva, Campus del Carmen, E21071 Huelva, España.
  • R.D. MARTINO Departamento de Geología, Universidad Nacional de Córdoba Córdoba, Argentina
  • G. VUJOVICH Departamento de Geología, Universidad de Buenos AiresCiudad Universitaria, 1428 Buenos Aires, Argentina
  • J.E. OTAMENDI Departamento de Geología, Universidad Nacional de Río Cuarto Río Cuarto, Argentina
  • Eleonora PINOTTI Universitat de Barcelona (UB)
  • F. D'ERAMO Departamento de Geología, Universidad Nacional de Río Cuarto Río Cuarto, Argentina
  • A. TIBALDI Departamento de Geología, Universidad Nacional de Río Cuarto Río Cuarto, Argentina
  • A. VIÑAO Departamento de Geología, Universidad Nacional de Río Cuarto Río Cuarto, Argentina

DOI:

https://doi.org/10.1344/105.000000252

Keywords:

Enclaves, Synplutonic intrusions, Calc-alkaline batholiths, Argentina, Famatinian belt

Abstract

Magmatic structures related to the mechanical interaction between mafic magmas and granitoids have been studied in the Valle Fértil calc-alkaline igneous complex, Argentina. Excepcional outcrops with vertical walls of more than 300 m high allow us the study of three-dimensional geometries of individual blobs of mafic magma as well as the geometry of pipe-like structures in which mafic microgranular enclaves are concentrated in more than 50 times the normal abundance in the granodiorite mass. The shape of enclaves and pipe-like structures are interpreted as the ressult of top-to-down intrusions of a mafic magma into a granodiorite-tonalite mass. These sinking structures are the result of a reverselly stratified magma chamber with gabbros and diorites at the top and granodiorite-tonalite at the bottom. They may account for most of the structures found in microgranular enclaves and magma mingling zones that characterize calc-alkaline batholiths. Synplutonic intrusions from the top is the only plausible mechanism to account for the observed structures. The model may be of general application to calc-alkaline batholiths characterized by the presence of mafic microgranular enclaves. An implication of these reverselly stratified magma chambers is the presence of a petrological inversion which may be the consequence of cold diapirs emplaced below the mantle wedge in a suprasubduction setting.

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Any 2008 Vol.: 6 Núm.: 3

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2009-04-24

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Vol. 6 No. 3 (2008)

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