TWO STAGES OF ASSEMBLY OF THE PANGEA SUPERCONTINENT IN THE POLAR URALS: FIRST U/Pb (LA-ICP-MS) AND <sup>40</sup>Ar/<sup>39</sup>Ar AGES OF THE YARKEU COMPLEX

Abstract

In the Polar Urals, there are few small granitoid intrusions (Yarkeu, Yayu and Pogurei complexes), which are usually associated with the Ural collision. Their Carboniferous-Early Permian age, in most cases, is based on methodologically outdated K/Ar dates, and is also assumed from field geological relationships. We have studied the monzonitoids of the Yarkeu petrotypical pluton, one of the largest such intrusions, and for the first time obtained Late Precambrian U–Pb LA-ICP-MS (zircon) and 40Ar/39Ar (amphibole) ages of 687 ± 3, 669 ± 8 Ma years, respectively. Water-saturated fluid regime (presence of magmatic amphibole and high water content in it, 4.5–5.6 wt %,), hypabyssal formation conditions (P = 2.1–3.5 kbar, T = 871–960°C), features of the chemical composition of monzonitoids (low TiO2 (0.6–0.8 wt %) and CaO (3.6–6.3 wt %) contents, high Al2O3 (16.6–18.0 wt %) and K2O (1.7–4.6 wt %), enrichment in large-ion lithophile elements relatively high field strength and rare earth elements, Ta-Nb minimum and Pb maximum), as well as metallogenic specialization in Cu and Mo (±Pb, Hg, Au), indicate the formation of the rocks of the Yarkeu complex in a subuction-related setting in a fairly thick continental crust. Isotopic clocks in these monzonitoids captured two stages of the assembly of the Pangea supercontinent: the earliest stage in the Late Precambrian, when monzonitoids were formed on the active Bolshezemel margin of Arctida, and one of the final stages in the Middle to Late Carboniferous, when the rocks underwent metamorphism due to the closure of the Paleo-Ural ocean and the onset of collision between Arkt-Laurussia and Siberia.