MINERALOGY OF ANDALUSITE-KYANITE-SILLIMANITE ROCKS OF THE SAITOVO SERIES IN ILMENY MOUNTAINS, THE SOUTH URALS
Blocks of quartzite-gneisses with andalusite, kyanite, and sillimanite have been found in metapelites of the Saitovskaya series in the Vishnyevo-Ilmenogorsk shear zone. Petrographic analysis of these garnet-sillimanite-andalusite-kyanitic quarzite-gneisses allows suggesting their metastable crystallization in the andalusite-kyanite stability field. The appearance of sillimanite is explained by further increase in temperature. The marginal part of the blocks, composed of kyanite-sillimanite-garnet-biotite schists with tourmaline, was formed in the kyanite-sillimanite stability field. The zoning in garnets from center to rim in quarzite-gneisses is as following: Py<sub>11.7</sub>Alm<sub>47.2</sub>Spess<sub>33.7</sub>Ca<sub>comp7.4</sub> → Py<sub>9.7</sub>Alm<sub>42.8</sub>Spess<sub>27.6</sub> · Ca<sub>comp19.9</sub> → Py<sub>13.5</sub>Alm<sub>50.2</sub>Spess<sub>24.8</sub>Ca<sub>comp11.5</sub> → Py<sub>16.6</sub>Alm<sub>52.0</sub>Spess<sub>26.2</sub>Ca<sub>comp5.2</sub>; and in schists: Py<sub>16.6</sub>Alm<sub>72.2</sub>Spess<sub>6.6</sub>Ca<sub>comp4.3</sub> → Py<sub>13.6</sub>Alm<sub>71.2</sub>Spess<sub>11.2</sub>Ca<sub>comp4.0</sub>. This zoning and alteration of mineral composition of inclusions in garnets and the host rocks (micas of the biotite group, feldspar and ilmenite) assumes the «clockwise» development of metamorphism. The rock-forming conditions correspond to the low-temperature amphibolite facies of moderate pressures (530 ± 20 °С, 4.5 kbar).