The age and genetic identification of the Khorasyur massif rocks: Sm-Nd ID-TIMS & U-Pb Shrimp-II constrains

It has been studied Sm-Nd (platiniferous association rocks) and «in situ» U-Pb (zircon granitoid) systems of the Khorasjur massif, being the northern termination of meridionally focused sequence from 14 mafic-ultramafic complexes presenting the Urals Platinum-bearing belt. The Sm-Nd data for olivine gabbro, gabbro-norite and amphibole gabbro of the platiniferous association exposed isochron dependence (MWSD = 0.29) defining isotope age as 565 ± 50 Ma (95 % confidential level) with probability of fit 0.75. The age obtained is sufficiently older than the earlier supposed one according to the results of geological observations and correlation with analogical formations of other provinces of Late Ordovician — Late Silurian time. The calculated for 9 whole rocks samples high values of ε Nd = +8.8 ÷ +9.0 impose certain constrains to the available modelling constructions concerning the formation of the platiniferous association rocks of the Cispolar Urals sector assuming as a substratum a considerably depleted source. The obtained U-Pb data for the zircons of the Verkhnetagil subcomplex granitoids at the plot in coordinates 206Pb/ 238U — 207Pb/ 235U demonstrate the presence of a number of age clusters within the range of 257—2022 Ma as relate to 206Pb/ 238U and 207Pb/ 206Pb accordingly. The revealed multimodal character of zircon ages testifies to the fact that the formations considered had much more complicated geological history than it had been supposed earlier.