The paleotectonic evolution of the western Mediterranean: provenance insights from the internal Betics, southern Spain

Abstract

Since the early Cenozoic, the closure of the Alpine Tethys in the Western Mediterranean has been accomplished by protracted subduction, followed by collision and orogenic collapse. The internal zones of the Betic Cordillera (southern Spain) and Rif (northern Morocco) experienced subduction metamorphism and subsequent exhumation due to the westward migration of the orogenic system. The detrital provenance of these meta-sedimentary units contains crucial insights into their pre-subduction stratigraphic arrangement, which is essential to constrain the pre-Cenozoic paleogeography and tectonic evolution of the Western Mediterranean. This study focuses on the Nevado-Filábride Complex (NFC) and the Eastern Alpujárride Complex in the Internal Betic Cordillera. New depth-profile zircon U-Pb LA-ICP-MS data from the NFC (N = 72) and Alpujárride (N = 21) and in situ apatite U-Pb data from a metabasite within the NFC allow us to establish the pre-subduction stratigraphy, sedimentary provenance, and paleotectonic configuration of the Iberian rifted margin during the Paleozoic–Early Mesozoic. Our dataset demonstrates that the NFC represents an intact Devonian to Early Jurassic stratigraphic sequence that records the evolution of the Western Mediterranean from the Variscan orogeny to rifting and opening of the Alpine Tethys. Detrital zircon U-Pb age modes of the NFC remain remarkably similar for over 200 Myr with only the differences being the progressive addition of new zircon modes related to depositional ages. Additionally, a comparison between the provenance record of the NFC and Alpujárride reveals notably similar zircon signatures of Carboniferous and Permian strata. This study reports the first data from the Triassic–Jurassic strata that record the opening of the Alpine Tethys. Additional evidence for rifting is present in the metabasites from the Veleta unit yielding in situ apatite U-Pb ages of 197 Ma, recording CAMP magmatism and Early Jurassic rifting in the Alpine Tethys. The data demonstrate a palinspastic connection between the NFC and the Alpujárride. Based on these extensive new provenance data, we propose a pre-subduction tectonic configuration in which the NFC and Alpujárride both represent adjacent attenuated continental fragments that are separated from the southern Iberian rifted margin by a narrow oceanic domain of the Alpine Tethys in the early Mesozoic.

Pre‐Subduction Architecture Controls Coherent Underplating During Subduction and Exhumation (Nevado‐Filábride Complex, Southern Spain)

“…Thrust relationships, similar to those in the NFC, have also been identified in the adjacent Alpujárride Complex by field observations (Balanyá et al., 1997; Booth‐Rea et al., 2005; Rossetti et al., 2005) and recent geochronologic data (Poulaki & Stockli, 2022), showing Carboniferous graphitic schist structurally overlaying Permian phyllites and schists. Hence, both the NFC and Alpujárride units have experienced subduction imbrication and subsequent underplating and exhumation.…”

“…The Carboniferous and Jurassic metamorphic ages of the Veleta unit reveal that it has previously experienced metamorphism and hence dehydration prior to entering the subduction system. Additionally, the apparent unconformities with missing Permian strata and overall thicker stratigraphic sequence in the Veleta unit could indicate that it was deposited in a more proximal domain to the Variscan Orogeny and Pangea rifting events than the overlying NFC units (Poulaki & Stockli, 2022) despite subsequent minor thinning due to extension and detachment faulting during the latest Miocene. These conditions would result in a more buoyant succession that would provide resistance to deep subduction.…”

“…Even though the P / T conditions of Alpujárride and the NFC are different, the timing of the metamorphic events is similar (Bessière et al., 2022; Bessière, Augier, et al., 2021; Bessière, Jolivet, et al., 2021). Additionally, Poulaki & Stockli (2022) showed that the NFC and Alpujárride have nearly identical sedimentary provenance signatures and were likely deposited nearby in similar tectonic settings, showing a close affinity between the Internal Betic terranes.…”

“…Additionally, Laborda-López et al (2015) identified Early Devonian fossil assemblages in graphite marbles intercalated in the graphite schist of the Veleta unit. In contrast, detrital zircon data show that the overlying Mulhacén succession is Late Carboniferous/Early Permian to Early Jurassic (Jabaloy-Sánchez et al, 2018, 2021Poulaki & Stockli, 2022). More recently, Poulaki & Stockli (2022) performed abundant detrital zircon dating and found that the NFC is Paleozoic to Early Jurassic metasedimentary sequence preserving the record of sedimentation from the Variscan orogeny to Neo-Tethys opening.…”

“… Geologic map of the Nevado‐Filábride Complex illustrating the main lithologic units, sample locations, and presence/absence of Cenozoic metamorphic zircon and apatite. Light blue shows Eocene ages, yellow shows Miocene ages, and black colors show the absence of zircon rims or non‐Cenozoic apatite (from IGME Spain maps, and modified after Poulaki and Stockli (2022)). …”