Abstract:
In the Transangarian region of the Yenisey Ridge in eastern Siberia (Russia), Fe- and Al-rich metapelitic schists of the Korda plate show field and petrological evidence of two superimposed metamorphic events. An early middle Proterozoic event with age of c.1100 Ma produced low-pressure, andalusite-bearing assemblages at c. 3.5–4 kbar and 540–560 °C. During a subsequent late Proterozoic event at c. 850 Ma, a medium-pressure, regional metamorphic overprint produced kyanite-bearing mineral assemblages that replaced minerals formed in the low-pressure event. Based on the results of geothermobarometry and P–T path calculations it can be shown that pressure increased from 4.5 to 6.7 kbar at a relatively constant temperature of 540–600 °C towards a major suture zone called the Panimba thrust. In order to produce such nearly isothermal loading of 1–7 °C km −1, we propose a model for the tectono-metamorphic evolution of the study area based on crustal thickening caused by south-westward thrusting of the 5–7 km-thick upper-plate metacarbonates over lower-plate metapelites with velocity of c. 350 m Myr−1. A small temperature increase (up to 20 ± 15 °C) of the upper part of the overlapped plate is explained by specific behaviour of steady-state geotherms calculated using lower radioactive heat production of metacarbonates as compared with metapelites. The suggested thermal-mechanical model corresponds well with P–T paths inferred from obtained thermobarometric data and correlates satisfactorily with P–T trajectories predicted by other two-dimensional thermal models for different crustal thickening and exhumation histories.
