Evidence from Fe- and Al-rich metapelites for thrust loading in the Transangarian region of the Yenisey Ridge, eastern Siberia |
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| Authors: | I I Likhanov O P Polyansky V V Reverdatto I Memmi |
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| Institution: | Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences, Pr. Acad. Koptyuga 3, Novosibirsk 630090, Russia (); University of Siena, Via Laterina 8, 53100 Siena, Italy |
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| 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. |
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| Keywords: | andalusite–kyanite phase transition Fe- and Al-rich metapelites tectono-thermal model thermobarometry Yenisey Ridge |
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