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Re-interpreting the Devonian ophiolites involved in the Variscan suture: U–Pb and Lu–Hf zircon data of the Moeche Ophiolite (Cabo Ortegal Complex, NW Iberia)

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Abstract

New U–Pb zircon data of a mylonitic greenschist from the Moeche Ophiolite, one of the mafic units involved in the Variscan suture in the Cabo Ortegal Complex (NW of the Iberian Massif), yielded an age of 400 ± 3 Ma. Consequently, this unit can be considered one of the Devonian ophiolites, the most extended group of oceanic units in the Variscan belt. The mafic rocks show transitional compositions between N-MORB and island-arc tholeiites, although Lu–Hf isotope signatures of its zircons clearly indicate contribution from an old continental source. εHf values in the analysed zircons are negative (generally below εHf = −5), and thence, they are not compatible with their generation from a juvenile mantle source. Accordingly, the igneous protoliths were generated in a setting where juvenile mafic magmas interacted with an old continental crust. The Devonian ophiolites from the Variscan suture have been repeatedly interpreted as remnants of the Rheic Ocean. However, the presence of a continental source in the origin of the mafic rocks of the Moeche Ophiolite allows discarding an intraoceanic setting for their generation, at least for the NW Iberian counterparts. The tectonic setting for the Devonian ophiolites of NW Iberia is very likely represented by an ephemeral oceanic basin opened within a continental realm. Herein, the real Rheic Ocean suture could only be located west of the terrane represented by the upper units of the allochthonous complexes. Apparently that suture is not represented in NW Iberia.

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Acknowledgments

Financial support for this research has been provided by Spanish projects CGL2007-65338-CO2-01 and CGL2012-34618 (Ministerio de Economía y Competitividad). Jürgen Von Raumer and an anonymous reviewer are gratefully acknowledged for insightful reviews of the manuscript.

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  1. Departamento de Petrología y Geoquímica and Instituto de Geociencias (UCM, CSIC), Universidad Complutense de Madrid, 28040, Madrid, Spain

    R. Arenas, S. Sánchez Martínez, R. Albert, R. Díez Fernández & P. Andonaegui

  2. Institut für Geowissenschaften, Mineralogie, J. W. Goethe Universität, Frankfurt am Main, Germany

    A. Gerdes

  3. Department of Earth Sciences, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa

    A. Gerdes

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  1. R. Arenas
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Arenas, R., Sánchez Martínez, S., Gerdes, A. et al. Re-interpreting the Devonian ophiolites involved in the Variscan suture: U–Pb and Lu–Hf zircon data of the Moeche Ophiolite (Cabo Ortegal Complex, NW Iberia). Int J Earth Sci (Geol Rundsch) 103, 1385–1402 (2014). https://doi.org/10.1007/s00531-013-0880-x

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