Continental subduction during arc-microcontinent collision in the southern Siberian craton: Constraints on protoliths and metamorphic evolution of the North Muya complex eclogites (Eastern Siberia)

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Abstract

The eclogites of the North Muya complex (Eastern Siberia) are located within the Early Neoproterozoic metasedimentary and felsic rocks of the Baikal-Muya Fold Belt (BMFB). The eclogites show subduction-related affinity, with large-ion lithophile (LILE) and light rare-earth element (LREE) enrichment and high field-strength element (HFSE) depletion signatures, similar to the exposed plutonic and volcanic rocks of the Early Neoproterozoic (Early Baikalian) subduction setting in the BMFB. Coupled Nd (εNd(T) of +6 to −1.4) and Sr (87Sr/86Sr ratio of 0.705–0.708), along with key trace-element indicators, imply progressive crustal recycling (up to 5–10%) from the Early Precambrian continental rocks to a depleted mantle source or equivalent crustal contribution via intracrustal contamination. Mineral δ18O data (+3.9 − +11.5) indicate that the contaminant or recycled crustal substrate might be represented by rocks altered at both low and high-temperature, or result from variable fluid-rock interaction in the subduction channel. Pseudosection modelling of eclogites, coupled with zircon U–Pb geochronology (~630 Ma) suggest that the Ediacarian high-pressure metamorphic event for different rocks shared a maximum depth corresponding to 2.5–2.7 GPa with variable temperature range (560–760 °C), reflecting their potential relation to distinct slices of the subducted crust. The estimated metamorphic conditions for both the burial and exhumation of rocks indicate a continental subduction setting, but with a relatively cold geotherm (~20–25 °C/kbar). These conditions resulted from the continental subduction of the Baikal-Muya composite structure beneath the relatively thin and immature overlying arc lithosphere of southern Siberia. Some carbonate-bearing eclogites and garnet-pyroxene rocks, metamorphosed under T below 700 °C and a minimum P up to 1.4 GPa, exhibit LREE-enriched patterns and low εNd(T) values of −7 to −16. These rocks have Paleoproterozoic to Archean model ages and may support the existence of a Paleoproterozoic or older lithosphere in the Baikal-Muya Fold Belt, but their subduction history and origin remain uncertain due to geochemical and isotopic signatures probably overprinted by carbonate metasomatism.

Original languageEnglish
Pages (from-to)76-96
Number of pages21
JournalLithos
Volume342-343
DOIs
Publication statusPublished - 1 Oct 2019

Keywords

  • Ar-Ar dating
  • Central Asian Orogenic belt
  • Eclogites
  • Geochemistry
  • Metamorphic evolution
  • Zircon U–Pb geochronology
  • Zircon U-Pb geochronology
  • TRACE-ELEMENT MOBILIZATION
  • GARNET
  • ZIRCON U-PB
  • PHASE-EQUILIBRIA
  • CARBONATITE MAGMATISM
  • OXYGEN-ISOTOPE GEOCHEMISTRY
  • CRUST
  • LU-HF
  • Edogites
  • CHEMICAL-COMPOSITION
  • SM-ND

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