Age and PT-parameters of the early-stage metamorphism of the Angara-Kan block (Yenisey Ridge)

A study was conducted on garnet-cordierite gneisses from the northeastern part of the Angara-Kan block (Yenisey Ridge), which belong to the Atamanova Series. It was established that the peak metamorphic PT conditions corresponded to the granulite facies at moderate pressure (T = 820 °C, P = 6 kbar) and were followed by a clockwise retrograde P-T path. This path evolved from near-isothermal decompression to near-isobaric cooling at a pressure of around 3 kbar. New U-Pb SHRIMP and LA-ICP-MS age data for zircon and monazite indicates the timing of the granulite-facies metamorphism at 1865 ± 5 Ma. The age data, metamorphic mineral assemblages, and microtextures demonstrate that the garnet-cordierite sillimanite gneisses were not affected by the later ultrahigh-temperature (UHT) metamorphic event (1.78–1.76 Ga), which was widespread across the Angara Kan block. Consequently, the block of garnet-cordierite-sillimanite gneisses of the Atamanova Series can be considered as a fragment of an early granulite-facies metamorphic complex. The findings support the two-stage metamorphic history concept for the Angara-Kan block and indicate a collisional event at approximately 1.86 Ga, which is characteristic of the amalgamation of the Siberian Craton. This metamorphic episode led to the generation of a large volume of post-collisional granitoids and likely played a key role in preconditioning the crust to achieve UHT conditions during the subsequent metamorphic event.