Evidence from Fe- and Al-rich metapelites for thrust loading in the Transangarian region of the Yenisey Ridge, eastern Siberia

n 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 degreesC. 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 degreesC towards a major suture zone called the Panimba thrust. In order to produce such nearly isothermal loading of 1-7 degreesC 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 degreesC) 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.