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

Abstract

The petrostructural and geochronological study of a poorly known ultramafic unit from SW Spain (Badajoz-C ordoba 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-hornblendechlorite rocks). Mantle-wedge serpentinization was followed by Si and Al preto 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.

Low–Ti Continental Tholeiite Origin of Magmas With Calc‐Alkaline Signature in Transcurrent Settings: The Mississippian Matachel Volcanic Field (SW Iberian Massif)

“…The latter alignment is spatially related to fault‐bounded volcano‐sedimentary basins (including the Matachel basin) filled with shallow marine and continental sediments as well as with bimodal volcanic and volcanosedimentary formations (Figures 14a and 14b). These basins developed at the site of a ductile and brittle/ductile Variscan intracontinental shear zone (Burg et al., 1981) that reworked an older suture (Ábalos, 1992; Ábalos et al., 2023) and during the late Paleozoic generated a flower structure with nested strike‐slip basins (Figures 14c and 14d).…”

“…These faults separate the Carboniferous record of this syncline from Late Ediacaran and earliest Cambrian units of the Badajoz‐Córdoba (or Coimbra‐Córdoba; e.g., Burg et al., 1981) ductile shear belt (Figure 2). The shear belt represents a reworked suture zone with a complex and protracted polyphase tectonothermal evolution (Ábalos et al., 1991, 2023). Geological maps of the Matachel basin (Apalategui et al., 1983; Arriola et al., 1983; Sánchez Cela et al., 1977) disclose a ∼2 km thick Mississippian volcano‐sedimentary succession made of conglomerates, slates, greywackes and limestones with interbedded volcanic rocks.…”

“…These include principally pillow‐lava flows that constructed a several km in areal extension (but volumetrically limited) lava field within an ephemeral Carboniferous continental marine basin regionally known as the Matachel basin. Its current tectonic context relates to a major lithospheric‐scale shear zone active during the Variscan orogeny (Burg et al., 1981) that reworked an older suture (Ábalos et al., 2023; Eguíluz et al., 2000). Continental tholeiitic volcanism also involved the coeval emission of calc‐alkaline basalts and basaltic andesites.…”

Introductory Chapter: Introduction to New Advances in Metamorphic Geology

“…Metamorphism in the context of geology (https://opengeology.org/petrology/ 9-intro-to-metamorphism/ -accessed on 25 February 2024) is a process that changes the mineralogy, microstructure, texture, and chemical compositions of any rocks, normally over long time scale (millions of years) and in a dominantly solid state [1]. Fluiddriven transition of rock textures and compositions are commonly viewed as a special part of metamorphism (or not even included at all within metamorphism) normally associated with some fluid migration controlled by magmatism such as metasomatism on a sea floor in small or lithospheric scales, including ophiolites [2][3][4][5][6][7]. In general, metamorphism is understood as a process that forms rock assemblages directly in response to gradually changing physical and chemical conditions.…”