Pre‐Subduction Architecture Controls Coherent Underplating During Subduction and Exhumation (Nevado‐Filábride Complex, Southern Spain). (14th March 2023)

• Record Type: Journal Article
• Authors: Poulaki, Eirini M.; Stockli, Daniel F.; Shuck, Brandon D.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 24:Number 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-14
• Subjects: subduction zones -- underplating -- metamorphic apatite -- Nevado‐Filabride Complex -- subduction complex -- Mediterranean subduction; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2022GC010802
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The interplay between structural and metamorphic processes operating along the deep plate interface in subduction zones remains elusive as much of the geologic record is recycled into the mantle. In some cases, metamorphosed subducted rocks are underplated and exhumed to the surface, providing critical constraints on structural processes and the rheological evolution of subduction interfaces at convergent margins. One such exhumed high‐pressure/low‐temperature subduction complex is the Cenozoic Nevado‐Filábride Complex (NFC) in Southern Spain. This study presents new data from the NFC that elucidate the syn‐metamorphic deformation, stacking, and underplating of continental slivers along the subduction interface. The structurally lowest NFC dominantly comprises lithologically monotonous Paleozoic metamorphic basement rocks recorded by apatite U‐Pb ages and shows no evidence for large‐scale internal duplications suggesting it behaved as a coherent basement succession during subduction. In contrast, structurally higher levels of the NFC are characterized by the stacking of older‐on younger coherent slices and distinctly different metamorphic ages. These relationships document syn‐subduction structural repetitions and tectonic stacking of imbricate thin slivers (∼100s m) during subduction underplating. Structurally higher levels of the NFC exhibit both Eocene and Miocene metamorphic zircon rims and apatite ages, along with microstructures indicative of relatively higher temperature metamorphism. Large‐scale underplating and antiformal stacking of slivers in the subduction channel can provide buoyancy forces to underplate and assist exhumation. We demonstrate that the presubduction stratigraphic architecture is a key control on the style and timing of deformation and metamorphism, facilitating coherent subduction underplating. Plain Language Summary: Subduction zones are tectonic boundaries where one rigid lithospheric plate sinks underneath another. At the interface between the two plates, rocks experience intense temperature, pressure, and stress conditions during metamorphism, causing deformation. The geologic record of these processes is often not accessible unless these rocks return to the surface. Our study targets one such exposure in Southern Spain, the Nevado‐Filábride Complex, which records deformation and structural mixing from subduction and subsequent transfer to the overriding plate. We perform geochronologic analyses to determine the age of zircon overgrowths that reveal the timing of metamorphism. Additionally, we date apatite minerals and examine deformation relationships at the microscopic scale to approximate the temperature conditions that these rocks experienced. We synthesize these new results with previously established geochronology of zircon grains from the same region that collectively show evidence for the large‐scale structural stacking of coherent rock slivers during deformation. The stacking pattern is observed only in the weak upper stratigraphic successions, while the deeper unit remained internally intact and experienced a lesser degree of metamorphism. Our results argue that the style and distribution of deformation during subduction are strongly influenced by the original stratigraphic architecture and properties prior to subduction. Key Points: Two main Cenozoic metamorphic events were recorded in the Betic subduction zone in Eocene and Miocene by zircon and apatite Imbrication and thrust faults coeval with underplating developed along the subduction interface Subduction of thick coherent metamorphic basement enhances buoyancy forces and contributes to exhumation