The paper summarizes results of work on the geochronological confirmation of the age of metamorphic structures occurring at the base of the Precambrian of the north of the Urals and the age of overlying Upper Precambrian basal sediments. It is shown that the occurrences of early stages of metamorphism of rocks of metamorphic (polymetamorphic) complexes date back to about 2.1 Ga. Their substrate is unambiguously related to the Lower Precambrian. We determined that Mesoproterozoic strata are absent Upper Precambrian sections of the north of the Urals, in contrast to more southern regions of the Urals. The basal strata in the Lyapin and Kharbey-Marunkeu anticlinoria, according to the data obtained, are dated to the Middle Neoproterozoic (cryogenian). The established fact of the absence of deposits of a huge age interval (Mesoproterozoic — at least 600 Ma) in the north of the Urals can be explained by a high standing of the territory of the northeast (in modern coordinates) of the Baltic craton, a fragment of which at that time was the Timan-Northern Ural lithospheric segment, and the location in the interiors of the Columbia (Nuna) supercontinent.
Throughout most of the exposed Timanide Orogen, the grade of regional metamorphism does not exceed greenschist facies. Only on the Kanin Peninsula and in the northernmost Timan and in a few of the drillcores that sample basement beneath the Pechora Basin, are amphibolite facies rocks present. This study presents new P-T estimates by garnet-biotite geothermometry and GASP geobarometry from the high-grade rocks of the Kanin Peninsula, together with a new structural interpretation of the SE-Kanin area. Thick metaturbiditic successions show an increase of metamorphic grade downwards from low greenschist to high amphibolite facies. On the SE Kanin Peninsula, peak metamorphic conditions are estimated to have reached c. 0.72 GPa and c. 610 °C. These inferred Late Proterozoic successions were thickened by thrust-stacking and emplaced southwestwards onto low-grade metamorphic pericratonic sedimentary rocks of the East European Craton during the Timanian Orogeny. Timing of metamorphism is inferred to be late Neoproterozoic, but radiometric ages are not well constrained and more work is needed. The new field observations and analytical results suggest that high-grade regional metamorphism is not confined to the Timan-Kanin area. This is of importance when considering the geophysical data over the Pechora Basin and Barents Sea, particularly the interpretation of crustal velocity structure. Higher velocities, often inferred to represent pre-Riphean basement, may well be related to Neoproterozoic and Mesoproterozoic complexes.
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.
Ââåäåíèå Äëÿ öèðêîíîâ èç ãðàíèòîèäîâ õàðàêòåðíî áîëüøîå ðàçíîîáðàçèå ôîðì è âíóòðåííåãî ñòðîåíèÿ êðèñòàëëîâ, áîãàòàÿ öâåòîâàÿ ãàììà, íàëè÷èå ìèíåðàëüíûõ è ãàçîâî-aeèäêèõ âêëþ÷åíèé. Áëàãîäàðÿ ðàçíîîáðàçèþ ìîðôîëîãè÷åñêèõ îñîáåííîñòåé è óñòîé÷èâîñòè öèðêîíà ê íàëîaeåííûì ïðîöåññàì ïðåîáðàçîâàíèÿ ìàãìà-òè÷åñêèõ ïîðîä îí øèðîêî èñïîëüçóåòñÿ äëÿ ðàñ÷ëåíåíèÿ è êîððåëÿöèè ãðàíèòîèäîâ, äëÿ óñòàíîâëåíèÿ ôèçèêî-õèìè÷åñêèõ óñëîâèé èõ ôîðìèðîâàíèÿ è äëÿ îïðåäåëåíèÿ èçîòîïíîãî âîçðàñòà. Íàèáîëåå ïîëíûå ñâåäåíèÿ î ìîðôîëîãè÷åñêèõ îñîáåííîñòÿõ öèðêîíîâ èç ãðàíèòîâ è äðóãèõ èçâåðaeåííûõ ïîðîä Òèìàíà è ñåâåðà Óðàëà, è â òîì ÷èñëå Ïðèïîëÿðíîãî Óðàëà, ïðèâîäÿòñÿ â ìîíîãðàôèè Ì. Â. Ôèøìàíà è åãî êîëëåã [19]. Ïåðâàÿ ïîïûòêà èñïîëüçîâàòü òèïîìîðôíûå îñîáåííîñòè öèðêîíîâ äëÿ ðàçäåëåíèÿ ðàçíîâîçðàñòíûõ ãðàíèòîèäíûõ êîìïëåêñîâ áûëà ïðåäïðèíÿòà â íàøèõ ïðåäûäóùèõ ðàáîòàõ [5, 16 è äð.].  ïîñëåäíèå ãîäû ñîáðàí äîïîëíèòåëüíûé ìàòå
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