Shallow reworking of magmatic zircon grains of latest Neoproterozoic (Timanian) age in serpentinite of the Voykar Massif, Polar Urals: new constraints from U-Pb isotopic data, and first trace elements and Lu-Hf isotopic data

ABSTRACT

The Voykar Massif of the Polar Urals in Russia consists of an ultramafic complex (mantle section) in the northwest, followed by a late Cambrian to Silurian mafic complex (intra-oceanic primitive island arc) and early Devonian intrusive rocks of an evolved island arc to the southeast. These complexes represent tectonic nappes thrust over the East European continental margin during the late Palaeozoic Uralian Orogeny. LA-ICP-MS U-Pb dating of zircon grains (n = 42) from an antigorite-serpentinite lens within the mafic complex yielded a Concordia age of 542 ± 2 Ma with an age range of 549–527 Ma. Additionally, few grains contain inherited domains with ages between ~990 and 3277 Ma. Hafnium isotopic data of the main age group show ¹⁷⁶Hf/¹⁷⁷Hf_t from 0.28242 to 028249 and εHf_t ranging from +1.9 to −6.5. The evolved Hf isotope data and the trace-element composition of the zircon grains point to an involvement of a continental crustal component in the parental magma. The zircon grains originate from igneous rocks formed during the Timanian Orogeny that affected the East European margin in the latest Neoproterozoic. During the Timanian or Uralian Orogeny, the magmatic zircons were eroded and shallowly recycled into the serpentinised mantle above the subduction zone. Finally, Uralian thrusting led to juxtaposition and imbrication of the zircon-bearing serpentinite and intra-oceanic volcanic rocks of the mafic complex.

KEYWORDS:

• Ophiolite
• mantle
• Uralides
• Timanides
• Baltica
• antigorite serpentinite
• island arc
• LA-ICP-MS U-Pb zircon dating

Acknowledgments

Linda Marko is thanked for her comprehensive support in zircon separation and analyses at the LA-ICP-MS at the Goethe-University, Frankfurt. We thank Marina Luchitskaya and Andrei Khudoley for their constructive reviews and Victoria Ershova for editorial handling of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed online here: https://doi.org/10.1080/11035897.2019.1621371