Kinematic model of triclinic transtension zonesThe case of the Boa Fé shear zone (Ossa-Morena Zone, Iberian Variscan Massif)

  1. Carlos Fernández 1
  2. Manuel Díaz-Azpiroz 2
  3. M. Francisco Pereira 3
  4. Martim Chichorro 4
  5. Dyanna Czeck 5
  1. 1 Universidad de Huelva
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    Universidad de Huelva

    Huelva, España

    ROR https://ror.org/03a1kt624

    Geographic location of the organization Universidad de Huelva
  2. 2 Universidad Pablo de Olavide
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    Universidad Pablo de Olavide

    Sevilla, España

    ROR https://ror.org/02z749649

    Geographic location of the organization Universidad Pablo de Olavide
  3. 3 Universidade de Évora
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    Universidade de Évora

    Évora, Portugal

    ROR https://ror.org/02gyps716

    Geographic location of the organization Universidade de Évora
  4. 4 Universidade Nova de Lisboa
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    Universidade Nova de Lisboa

    Lisboa, Portugal

    ROR https://ror.org/02xankh89

    Geographic location of the organization Universidade Nova de Lisboa
  5. 5 University of Wisconsin–Milwaukee
    info
    University of Wisconsin–Milwaukee

    Milwaukee, Estados Unidos

    ROR https://ror.org/031q21x57

    Geographic location of the organization University of Wisconsin–Milwaukee
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Journal:
Geotemas (Madrid)

ISSN: 1576-5172

Year of publication: 2016

Issue Title: IX CONGRESO GEOLÓGICO DE ESPAÑA

Issue: 16

Pages: 9-12

Type: Article

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More publications in: Geotemas (Madrid)

Abstract

A kinematic model of triclinic transtension with oblique coaxial shortening is presented in this work. The main parameters controlling the model are the simple-shear obliquity angle (), the angle between the infinitesimal shortening axis of the coaxial flow component and the true-dip line of the shear zone boundary (), and the kinematic vorticity number (Wk). It includes, as special cases, previous models of monoclinic and triclinic transtension. Our theoretical results allow predicting the shape of the finite strain ellipsoid and the orientation of the principal finite strain axes for the distinct combinations of the controlling parameters and increasing finite strain intensity. Testing of the plano-linear fabric of the sinistral transtensional Boa Fé shear zone (Ossa-Morena Zone, Iberian Variscan belt) against the model yielded a satisfactory fit for a horizontal to moderately SE-plunging simple-shear direction (=0 to -60º), coaxial shortening near the true-dip of the shear zone boundary (10º>>170º), and a pure-shear dominated flow (Wk<0.81). Measurement of the shape of the finite strain ellipsoid is needed in this and other natural shear zones to rigorously check them against the theoretical model presented here.

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