Polyphase tectonic reworking of serpentinites and chlorite‐tremolite‐talc rocks (SW Spain) from the subduction forearc to intracontinental emplacement

The petrostructural and geochronological study of a poorly known ultramafic unit from SW Spain (Badajoz–Córdoba belt) combined with previous structural data permits disclosure of a history of metasomatism, tectono‐metamorphism, reworking and isotopic resetting related to a poly‐orogenic evolution in...

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Bibliographic Details
Published in:Journal of metamorphic geology 2023-05, Vol.41 (4), p.491-523
Main Authors: Ábalos, Benito, Puelles, Pablo, Gil Ibarguchi, José Ignacio
Format: Article
Language:English
Subjects:
Aluminum
Apatite
apatite dating
Cadomian
Chlorite
Decoupling
Deformation
Geochronology
High pressure
Metamorphism
Ordovician
Orogeny
petrofabric
Plastic deformation
Recrystallization
Rocks
Schists
serpentinite
Serpentinization
Shear zone
Silicon
Subduction
Subduction (geology)
Talc
Tectonics
Tremolite
Ultramafic materials
Ultramafic rocks
Variscan
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Summary:The petrostructural and geochronological study of a poorly known ultramafic unit from SW Spain (Badajoz–Córdoba belt) combined with previous structural data permits disclosure of a history of metasomatism, tectono‐metamorphism, reworking and isotopic resetting related to a poly‐orogenic evolution in different geodynamic scenarios. The heterogeneous ultramafic unit studied contains antigorite‐serpentinites and metasomatized ultramafic rocks (chlorite‐talc schists, tremolite‐talc‐chlorite rocks and magnesio‐hornblende‐chlorite rocks). Mantle‐wedge serpentinization was followed by Si and Al pre‐ to syn‐metamorphic/tectonic metasomatism in a subduction realm. Petrofabrics of selected lithologies reveal variable syn‐metamorphic crystal‐plastic deformation and recrystallization (assisted by other mechanisms) under relative high pressure, concomitant with the conditions recorded by neighbouring tectonic units that were later intruded by Ordovician granites. The resultant ensemble was reworked and isotopically reset much later in an intracontinental ductile shear zone. Syn‐ to late‐tectonic apatite from chlorite‐talc schists provides an anchored Tera–Wassenburg isochron radiometric age of 342.8 ± 12.2 Ma that provides evidence for the decoupling between isotopic systems and microstructures. The results are discussed from a twofold perspective: with regard to the likely tectonic context of this ophiolite (the current analogue of the Mariana forearc) and with regard to regional geological implications.
ISSN:0263-4929
1525-1314
DOI:10.1111/jmg.12704