https://vital.lib.tsu.ru/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://vital.lib.tsu.ru/vital/access/manager/Repository/vtls:000460402 Tue 12 Sep 2017 14:44:07 KRAT ]]> https://vital.lib.tsu.ru/vital/access/manager/Repository/vtls:000553121 Thu 04 May 2017 11:22:26 KRAT ]]> https://vital.lib.tsu.ru/vital/access/manager/Repository/vtls:000553111 Mon 23 Apr 2018 16:29:44 KRAT ]]> https://vital.lib.tsu.ru/vital/access/manager/Repository/vtls:000621319 70 wt. % SiO2, 10-14.4 wt. % Al2O3, 4-10 wt. % FeO) as compared to granulites of Group B (50-59 wt. % SiO2, 16.6-20.6 wt. % Al2O3, 12-16 wt. % FeO). Granulites are represented by various cordierite-biotite-sillimanite, garnet-hypersthene-sillimanite-cordierite, hypersthene-cordierite-sillimanite, garnet-cordierite-biotite-sillimanite gneisses. Opx-Sil-Qtz parageneses (Grt + Opx + Crd + Fsp + Sil + Qtz, Opx + Crd + Pl + Sil + Qtz) were found in granulites of Group A, which testify to UHT metamorphism. Other signs of UHT metamorphism are the presence of mesoperthitic K-Na feldspar and Al-orthopyroxene (up to 7-8 wt. % Al2O3). Granulites of Group B usually do not contain Opx-Sil-Qtz parageneses and are represented by the next associations: Grt + Crd + Bt + Pl + Kfs + Sil + Qtz (+ Sp), Crd + Kfs + Bt + Sil + Qtz. It should be noted that green spinel occurs only in the form of inclusions in garnet. Garnets from granulites of Group A (Alm58–65Py33–38Grs1–3Sps0–1) are more magnesian (XMg = 0.33-0.41) compared to garnets from granulites of Group B (Alm65–71Py25–30Grs2–3Sps1–2; XMg = 0.25-0.32). The content of Al2O3 in orthopyroxene of granulites of Group A varies from 8.0 to 4.5 wt. %, XMg = 0.57-0.66. Granulites of Group B don’t contain orthopyroxene, with the exception of a single sample containing orthopyroxene (Al2O3 = 1.6-2.8 wt. %, XMg = 0.64-0.66). Cordierite, like sillimanite, is found in all samples and is the most magnesian phase (XMg = 0.79-0.89). There are no significant differences in mineral composition between different types of rocks. Biotite from different groups of granulites differs sharply in composition. Granulites of Group A contain aggregates of finely scaly high-magnesian–low-titanium biotite (TiO2 = 3.6-0.9 wt. %, XMg = 0.74-0.86) replacing cordierite under amphibolite facies. Biotite of Group B is characterized by high contents of TiO2 = 4.1-5.1 wt. % and lower XMg = 0.62-0.66. Granulites of Group A contain mesoperthitic feldspar, while in granulites of Group B, in addition to K-Na feldspar, plagioclase is also found: oligoclase (An25-30) or andesine (An40-47). Green spinel occurs only inside the garnet crystals in B-type granulites and is a solid solution of hercinite (50-65 %) - spinel (22-38%) - ghanite (9-16 %). The content of ZnO in spinel is 4.7-8.0 wt. %. Estimates of P-T metamorphic conditions obtained using the Grt-Opx thermometer (Aranovich, Berman, 1997), Ti-in-Grt and Ti-in- Opx thermometers (Kawasaki, Motoyoshi, 2007), Grt-Crd-Sil-Qtz barometer (Wells, 1979), TWQ program (Berman, Aranovich, 1996), THERMOCALC (Holland, Powell, 1998) indicate high temperatures of the granulite formation (830-940 ° C) and moderate pressures 7.5-8.5 kbar. Simulation of phase equilibria using pseudosections plotted in the NCKFMASHTO system and mineral isoplets indicate a P-T path of subisobaric cooling (IBC) during exhumation of the Kaltygey granulites. The Al content in orthopyroxene decreasing from 0.29 to 0.19 p.f.u. and XCa in garnet varying from 0.009 to 0.013, were used as mineral isoplets. Peak values of the P-T metamorphic conditions are 950°C and ~9 kbar, indicating UHT metamorphism, were obtained on the basis of the analysis of pseudosections. The concordant weighted mean 206Pb/238U age obtained on zircons by the U-Pb (SHRIMP) isotope method is 1868 ± 6 Ma and 1866 ± 4 Ma, which is interpreted as the peak metamorphism time. The age of 1.94-1.91 Ga obtained on cores of rounded and irregular zircon grains is regarded as a minimum estimate of the formation time of the granulite protoliths. The formation of the Kaltygei granulites with the IBC evolutionary trend can be due to heating as a result of magmatic underplating along the continental margin and subsequent cooling to normal temperature during the post-collisional extension. The metamorphic age (~1.87 Ga) of the granulites is close to the age of completion of the main collision and post-collisional events that occurred in the Paleoproterozoic stage along the periphery of the Siberian Craton.]]> Fri 04 May 2018 16:19:10 KRAT ]]>