О ВОЗРАСТЕ И СОСТАВЕ ГНЕЙСОВ ИЗ ФУНДАМЕНТА СЕВЕРО-ЗАПАДНОЙ ЧАСТИ ЗАПАДНО-СИБИРСКОЙ ПЛИТЫ

The plagiogneiss mineralogy from the Yangiyuganskaya parametric borehole (the West-Siberia north-western part) has been studied. The rocks are composed of quartz-oligoclase aggregate with presence of mica (muscovite and phlogopite), amphibole (edenite-ferroedenite-ferropargasite), clinozoisite-epidote, garnet (almandine-grossular series), clinochlore, microcline, magnetite, titanomagnetite, rutile and fluorapatite. It is shown that plagiogneisses have been formed from leucocratic plagiogranites under the conditions of the metamorphism of amphibolite facies. U-Pb, Sm-Nd, Rb-Sr plagiogneiss datings point with the biggest possibility to the following main events of geological history of these rocks formation: 1) magmatic intrusion of plagiogranites in Vendian; Sm-Nd isochrone 691 ± 58 Ma also points to neoproterozoic age of the plagiogneiss initial substance; 2) the metamorphism of plagiogranites and its turning into plagiogneisses involved in early Ordovician (486 Ma); 3) the latest tectonothermal events (292 ± 23 Ma), fixed by Rb-Sr system are associated possibly with collision processes.