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Unraveling the origins and P-T-t evolution of the allochthonous Sobrado unit (Órdenes Complex, NW Spain) using combined U–Pb titanite, monazite and zircon geochronology and rare-earth element (REE) geochemistry

Benítez-Pérez, José Manuel; Castiñeiras, Pedro; Gómez-Barreiro, Juan; Martínez Catalán, José R.; Kylander-Clark, Andrew; Holdsworth, Robert E.

Unraveling the origins and P-T-t evolution of the allochthonous Sobrado unit (Órdenes Complex, NW Spain) using combined U–Pb titanite, monazite and zircon geochronology and rare-earth element (REE) geochemistry Thumbnail


Authors

José Manuel Benítez-Pérez

Pedro Castiñeiras

Juan Gómez-Barreiro

José R. Martínez Catalán

Andrew Kylander-Clark



Abstract

The Sobrado unit, within the upper part of the Órdenes Complex (NW Spain) represents an allochthonous tectonic slice of exhumed high-grade metamorphic rocks formed during a complex sequence of orogenic processes in the middle to lower crust. In order to constrain those processes, U–Pb geochronology and rare-earth element (REE) analyses of accessory minerals in migmatitic paragneiss (monazite, zircon) and mylonitic amphibolites (titanite) were conducted using laser ablation split stream inductively coupled plasma mass spectrometry (LASS-ICP-MS). The youngest metamorphic zircon age obtained coincides with a Middle Devonian concordia monazite age (∼380 Ma) and is interpreted to represent the minimum age of the Sobrado high-P granulite facies metamorphism that occurred during the early stages of the Variscan orogeny. Metamorphic titanite from the mylonitic amphibolites yield a Late Devonian age (∼365 Ma) and track the progressive exhumation of the Sobrado unit. In zircon, cathodoluminescence images and REE analyses allow two aliquots with different origins in the paragneiss to be distinguished. An Early Ordovician age (∼490 Ma) was obtained for metamorphic zircons, although with a large dispersion, related to the evolution of the rock. This age is considered to mark the onset of granulite facies metamorphism in the Sobrado unit under intermediate-P conditions, and related to intrusive magmatism and coeval burial in a magmatic arc setting. A maximum depositional age for the Sobrado unit is established in the late Cambrian (∼511 Ma). The zircon dataset also record several inherited populations. The youngest cogenetic set of zircons yields crystallization ages of 546 and 526 Ma which are thought to be related to the peri-Gondwanan magmatic arc. The additional presence of inherited zircons older than 1000 Ma is interpreted as suggesting a West African Craton provenance.

Citation

Benítez-Pérez, J. M., Castiñeiras, P., Gómez-Barreiro, J., Martínez Catalán, J. R., Kylander-Clark, A., & Holdsworth, R. E. (2020). Unraveling the origins and P-T-t evolution of the allochthonous Sobrado unit (Órdenes Complex, NW Spain) using combined U–Pb titanite, monazite and zircon geochronology and rare-earth element (REE) geochemistry. Solid Earth, 11(6), 2303-2325. https://doi.org/10.5194/se-11-2303-2020

Journal Article Type Article
Acceptance Date Oct 2, 2020
Online Publication Date Nov 30, 2020
Publication Date 2020
Deposit Date May 26, 2021
Publicly Available Date Mar 28, 2024
Journal Solid Earth
Print ISSN 1869-9510
Publisher European Geosciences Union
Peer Reviewed Peer Reviewed
Volume 11
Issue 6
Pages 2303-2325
DOI https://doi.org/10.5194/se-11-2303-2020

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