The Vila de Cruces Ophiolite: A Remnant of the Early Rheic Ocean in the Variscan Suture of Galicia (Northwest Iberian Massif)

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. A B S T R A C TThe Vila de Cruces ophiolite is one of the ophiolitic units involved in the Variscan suture of the northwest Iberian Massif. This ophiolite consists of a tectonically repeated succession of greenschist facies volcanic rocks, common alternations of metasediments of pelitic or siliceous character, and scarce orthogneisses, metagabbros, and serpentinites. The protolith age of a granitic orthogneiss that intruded the mafic rocks is dated at Ma (U-Pb in 497 ‫ע‬ 4 zircons). This age can be considered a reference for the generation of the ophiolite. According to their contents of some of the most immobile trace elements, the greenschist and the metagabbros are derived from basaltic magmas with compositions similar to those of island-arc tholeiites. The influence of a subduction zone in the generation of the original basaltic magmas can be deduced from the marked negative Nb anomaly observed in all the metabasic rocks of this ophiolite. The granitic orthogneisses can also be genetically related to the basic rocks because they are similar to granitic rocks generated in volcanic arcs. The Vila de Cruces ophiolite is interpreted as a suprasubduction zone ophiolite generated in Late Cambrian times, during the early stages of the opening of the Rheic Ocean. The ophiolite was probably generated in a back-arc basin developed during the first stages of the pulling apart and later drift of one or more peri-Gondwanan terranes, one of them represented by the upper allochthon of the northwest Iberian Massif.

The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

“…500 Ma) and Devonian (ca. 395 Ma) ages respectively, and they are considered to represent the opening and closure of the Rheic Ocean Arenas et al, 2007;Sánchez Martínez et al, 2007. The basal units represent a section of the most external Gondwanan margin, subducted at ca.…”

Fabric Development in a Middle Devonian Intraoceanic Subduction Regime: The Careón Ophiolite (Northwest Spain)

“…It is accepted that the Rheic Ocean started opening between the Late Cambrian and Early Ordovician (Cocks and Torsvik 2002;Murphy et al 2006;Arenas et al 2007aArenas et al , 2007b. Remnants of this ocean (in the form of ophiolites) and its continental margins have been identified in many parts of the Variscan-Appalachian belt, which was produced by the Laurussia-Gondwana collision ( fig.…”

“…These ophiolites are key elements to understanding the final stages of evolution of the Rheic Ocean as well as the early stages of convergence between Laurussia and Gondwana (Sá nchez Martínez et al 2007;Arenas et al 2007aArenas et al , 2007bMartínez Catalá n et al 2009). …”

“…365 Ma ( 40 Ar/ 39 Ar, muscovite; Dallmeyer et al 1997), while orthogneiss yielded an age of ca. 500 Ma (U-Pb, zircon; Arenas et al 2007b).…”

Extensional Flow during Gravitational Collapse: A Tool for Setting Plate Convergence (Padrón Migmatitic Dome, Variscan Belt, NW Iberia)

“…2, 3). The upper units are pieces of a Cambro-Ordovician ensialic island arc detached from Gondwana (Abati et al 1999), while the middle units are ophiolitic and represent the Rheic Ocean Arenas et al 2007; Sá nchez Martínez et al 2009). The basal units represent the most external part of the Gondwana margin , which was subducted beneath Laurussia at the onset of the Variscan collision (Arenas et al 1995Díez Ferná ndez et al 2012b) and exhumed by crustal-scale thrusting accompanied by recumbent folding and tectonic denudation (Martínez Catalá n et al 1996;Díez Ferná ndez and Martínez Catalá n 2009;Díez Ferná ndez et al 2011).…”