The early Precambrian history of rock metamorphism in the Urals segment of crust

Abstract

Early Precambrian rock units in the Urals are present in several polymetamorphic complexes, which are exposed in the Urals in the form of small (<1500 km 2 ) tectonic blocks. Their ages are Archaean (as old as 3.5 Ga) and Palaeoproterozoic. During the formation of these complexes in the early Precambrian, two stages of ultra-high-temperature (granulite) metamorphism occurred. The maximum age of the early Neoarchaean stage of metamorphism is 2.79 Ga. Evidence of this metamorphic event includes the dating of the Taratash gneiss-granulite complex of the South Urals. Gneiss-migmatite complexes, which dominate the lower Precambrian section of the Urals, were formed in the Palaeoproterozoic during the sequential appearance of granulite facies metamorphism followed by amphibolite facies metamorphism and accompanying granitization. The maximum age of the Palaeoproterozoic stage of granulite metamorphism in the Alexandrov gneissmigmatite complex, the most well-studied complex in the South Urals, is 2.08 Ga.

Provenance and sedimentation age of the Proterozoic clastic succession of the Garhwal‐Kumaon Lesser Himalaya, NW‐India: Clues from U–Pb zircon and Sr–Nd isotopes

“…It is generally regarded the Th/U ratio ≥0.5 is of magmatic origin (Skublov et al, 2009). Whereas, Th/U ratio in between 0.1 and 0.3 generally considered as metamorphic in origin (Armstrong‐Altrin, 2020; Pystin & Pystina, 2015; Saha et al, 2016). In the present study, the Th/U ratio exhibits a wide range from 0 to 4.2.…”

Paleoproterozoic Rock Metamorphism of the Nyartin Complex, the Subpolar Urals

“…Note that the analogous age of similar zircons was established by us in the Aleksandrov gneissmigmatite complex of the Southern Urals (2081 ± 14 Ma, SHRIMP-II, [6]). A significant error for the lower intersection of discord with concordia (555 ± 120 Ma) results from the fact that figurative age points are localized mainly near the upper intersection.…”

“…Despite the early Precambrian rock ages of the most complexes shown in figure 1, belonging of only two South Ural complexes: the Taratash gneiss-granulite and Alexandrov gneiss-migmatite (figure 1) to the Archean-Paleoproterozoic section does not cause much controversy. They are framed by poorly metamorphosed Lower Riphean deposits, and reliable geochronological data are obtained on them, which unambiguously indicate the early Precambrian age of rock metamorphism [3,4,5,6]. Available Early Precambrian dates (with the prevalence of Late Precambrian and Paleozoic ages) for other Ural polymetamorphic complexes are interpreted in different ways.…”

Archean to Paleoproterozoic crustal evolution in the Sassandra-Cavally domain (Côte d’Ivoire, West Africa): Insights from Hf and U-Pb zircon analyses

“…All the zircons belonging to younger age clusters including the four analyses that were obtained from zircons rims were associated with overall low Th/U ratios < 0.50. Magmatic zircons present Th/U > 0.50 (Skublov et al, 2009;Pystin and Pystina, 2015;Rubatto, 2002)., while metamorphic zircons have Th/U comprised between 0.10 and 0.30 (Pystin and Pystina, 2015), or even < 0.10 (Rubatto, 2002). The age of 2076 ± 7 Ma has been obtained on a large euhedral overgrowth crystallized around an inherited zircon core with an age of 2748 ± 11 Ma (Fig.…”