Яндекс.Метрика

Nikolai Dobretsov

: 32nd International Geological Congress, Florence, Italy, August 20-28, 2004: Abstracts Volume

The Permo-Triassic (250 Ma) superplume is recorded in Asia as (i) Siberian and Emeishan traps formed under the cold lithosphere and as (ii) syenites and A-granites formed under the thickened lithosphere formed due to collisions. Intrusion of Siberian traps is an important event in the Earth's history. Four mln km3 of Siberian traps occur in the Siberian platform and 10-16 million km3 of basalts occur beneath the sediments of the West Siberian Plain, the Kara Sea and the Barents Sea, totally 10-16 mln km3 (Dobretsov, 1997). The effusion reached its peak at 249-251 Ma and a volume of 8*106 km3. The composition and volume of the Siberian traps are similar to those of the lavas and sills of the Ontong Java Plateau (Dobretsov and Vernikovskiy, 2001). The 1.5*106 km3 Emeishan traps intruded the Yangze Craton at 253 Ma (Chung and Jahn, 1995). The associated syenitic and granitic plutons are distributed around the Siberian and Emeishan traps as wide belts between them. The associated granites and syenites have been found in the West Taimyr (Vernikovskiy et al., 2001), Tom'- Kolyvan foldbelt in Siberian and Semeutau-Irtysh area in East Kazakstan (Dobretsov, 2003). Those syenites and A-granites show negative to positive еNd and 87Sr/86Sr=0.704-0.706, and high K2O. In general, the granitoids have Nd-Sr trends similar to those of the traps. The Permian -Triassic syenite-granite plutons located around the Siberian traps and between the Siberian and Emaishan traps record 4 important events.1. Bimodal alkaline volcanic rocks and syenites in Transbaikalia and collisional granites and metamorphic rocks of the Taimyr, Urals and Altay Sayan (260-280 Ma). 2. Basaltic and alkaline sills and dikes associated with granitic syenitic plutons and related to the main intrusion of Siberian traps (245-255 Ma).3. Alkaline volcanic rocks and small alkaline granitic plutons formed during the latest Siberian traps formation (225-235 Ma).4. Granitic plutons and basic dikes surrounding the Emeishan area (210±5 Ma).Superplumes mark the periods of global synchronization of tectonic events. The superplumes were active at 120 and 250 Ma and, possibly, at 360 and 480 Ma. The interval of 120 Ma can be also suggested for Late Precambrian superplumes, which were active at 610, 730 and 850 Ma. Smaller local plumes were active at a periodicity of 30 Ma (Larson, Olson, 1991; Dobretsov, 2003).
индекс в базе ИАЦ: 024345