Unraveling the pre-subduction stratigraphy and tectonometamorphic evolution of deeply subducted and exhumed rocks using zircon U-Pb geochronology
Abstract
The structural and metamorphic processes operating along the deeper plate interface in subduction zones remain elusive as much of the geologic record is typically recycled deep into the mantle. However, in some cases metamorphosed subducted crustal rocks are underplated and exhumed back to the surface, containing important clues regarding the structural, thermal, and rheological evolution of convergent margins. The closure of the Neo-Tethys in the Mediterranean is characterized by Cenozoic HP/LT subduction complexes that were exhumed during back-arc extension and/or collision, including the Nevado-Filábride Complex (NFC) in Southern Spain. In this study, we present new detrital zircon (DZ) U-Pb depth profile data from the four principle tectonic units of the NFC to resolve the pre-subduction paleogeography, maximum depositional ages, the juxtaposition history during subduction underplating, and the timing of metamorphism.
DZ U-Pb analyses (N=98) reveal that the two structurally lowest metasedimentary units are Carboniferous in age and overlain by Triassic metasedimentary rocks. While previously subdivided, our data suggest that these two lower Carboniferous units are indistinguishable in terms of lithology and age and behaved as a coherent 4-km thick basement succession with no evident large-scale structural duplication. The highest tectonic unit (Bedar-Macael) consists of Permian metasedimentary and granitoid rocks, but structurally overlies Triassic-Jurassic rocks (Tahal unit). This presents both the first unequivocal evidence for early Mesozoic margin strata and structural repetition of coherent crustal slices. This repetition, coupled with structural and metamorphic observations, points to imbrication of coherent tectonic slivers during subduction underplating, forming the large-scale, imbricated tectono-metamorphic sequence of the NFC. Zircons from all units exhibit both Eocene and Miocene rims, demonstrating that structural stacking occurred during subduction prior to early Cenozoic metamorphism. This study also demonstrates that this novel analytical approach in combination with field data can unravel the pre- and syn-subduction evolution and the structural stacking of HP/LT terranes, which is critical for the fundamental understanding of subduction processes.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMV041...02P
- Keywords:
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- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGY;
- 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY;
- 8104 Continental margins: convergent;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS