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TECTONICS, VOL. 27, TC5006, doi:10.1029/2008TC002306, 2008

Rheic Ocean ophiolitic remnants in southern Iberia questioned by SHRIMP U-Pb zircon ages on the Beja-Acebuches amphibolites

A. Azor

Departamento de Geodinámica, Universidad de Granada, Granada, Spain


D. Rubatto

Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia


J. F. Simancas

Departamento de Geodinámica, Universidad de Granada, Granada, Spain


F. González Lodeiro

Departamento de Geodinámica, Universidad de Granada, Granada, Spain


D. Martínez Poyatos

Departamento de Geodinámica, Universidad de Granada, Granada, Spain


L. M. Martín Parra

Instituto Geológico y Minero de España, Madrid, Spain


J. Matas

Instituto Geológico y Minero de España, Madrid, Spain


Abstract

The Rheic Ocean was a major oceanic domain between Avalonia and Gondwana in Ordovician-Silurian times. Most of the Paleozoic plate reconstructions assume that the Rheic Ocean suture lies within southern Iberia, coinciding with the contact between the South Portuguese Zone and the Ossa-Morena Zone. This paper reports four Sensitive High Resolution Ion Micro-Probe (SHRIMP) U-Pb zircon ages from mid-ocean ridge basalt (MORB)-featured rocks of the Beja-Acebuches Amphibolite unit, which crops out along the boundary between the Ossa-Morena and the South Portuguese Zone, and is considered its most conspicuous suture unit. The obtained ages range from 332 ± 3 to 340 ± 4 Ma, corresponding to the crystallization of the mafic protoliths. These Early Carboniferous ages for the Beja-Acebuches amphibolites imply that this unit can no longer be viewed as an ophiolite belonging to the Rheic Ocean suture, since this oceanic domain was presumably closed in Devonian times. Tectonic reconstructions joining in a single suture line the Beja-Acebuches Amphibolite unit in southern Iberia to either the Devonian Lizard ophiolite in southern England or the root zone of the Devonian/Ordovician ophiolitic units in northwest Iberia must be therefore reconsidered because of the age difference. We interpret the Beja-Acebuches Amphibolite unit to represent a narrow and very ephemeral realm of oceanic-like crust that opened in Early Carboniferous times, after total consumption of the Rheic Ocean. We suggest that a mantle plume underneath southern Iberia in Early Carboniferous times is the most plausible large-scale geodynamic scenario for the formation of these MORB-featured rocks.

Received 10 April 2008; accepted 15 July 2008; published 4 October 2008.

Keywords: U-Pb zircon geochronology; suture contact; Variscan Orogen.

Index Terms: 8102 Tectonophysics: Continental contractional orogenic belts and inversion tectonics; 8157 Tectonophysics: Plate motions: past (3040); 1115 Geochronology: Radioisotope geochronology.

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Citation: Azor, A., D. Rubatto, J. F. Simancas, F. González Lodeiro, D. Martínez Poyatos, L. M. Martín Parra, and J. Matas (2008), Rheic Ocean ophiolitic remnants in southern Iberia questioned by SHRIMP U-Pb zircon ages on the Beja-Acebuches amphibolites, Tectonics, 27, TC5006, doi:10.1029/2008TC002306.