HR: 08:45h
AN: V31G-04    [Abstracts]
TI: New high-precision 40Ar/39Ar ages and geochemical data from the greater Siberian large igneous province: The Biggest gets Bigger.
AU: * Reichow, M K
EM: mkr6@le.ac.uk
AF: Department of Geology, University of Leicester, University Rd., Leicester, LE1 7RH, United Kingdom
AU: Pringle, M S
EM: mpringle@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Av., MIT, Cambridge MA, 02139-4307, United States
AU: Saunders, A D
EM: ads@le.ac.uk
AF: Department of Geology, University of Leicester, University Rd., Leicester, LE1 7RH, United Kingdom
AU: Puchkov, V N
EM: puchkv@anrb.ru
AF: Institute of Geology, Ural Branch RAS, Karl Marx Street 16/2, Ufa, 45000, Russian Federation
AU: Safonova, I Y
EM: inna@uiggm.nsc.ru
AF: Institute of Geology and Mineralogy, SB RAS, Koptyuga Avenue 3, Novosibirsk, 630090, Russian Federation
AU: Millar, I L
EM: ilm@bgs.ac.uk
AF: NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, NG12 5GG, United Kingdom
AU: Buslov, M M
EM: misha@uiggm.nsc.ru
AF: Institute of Geology and Mineralogy, SB RAS, Koptyuga Avenue 3, Novosibirsk, 630090, Russian Federation
AU: Fedoseev, G S
EM: fedoseev@sbras.nsc.ru
AF: Institute of Geology and Mineralogy, SB RAS, Koptyuga Avenue 3, Novosibirsk, 630090, Russian Federation
AU: Scott, R A
EM: robert.scott@casp.cam.ac.uk
AF: CASP (Cambridge Arctic Shelf Programme), 181A Huntingdon Road, Cambridge, CB3 ODH, United Kingdom
AU: Inger, S
EM: S.Inger@bath.ac.uk
AF: CASP (Cambridge Arctic Shelf Programme), 181A Huntingdon Road, Cambridge, CB3 ODH, United Kingdom
AB: The Siberian Traps (ST) represent the remnants of the largest Phanerozoic continental flood basalt province, with an estimated original size of 4 x 106 km2 and an original combined volume of at least 2 x 106 km3 (Milanovskiy, 1976). The province may also be responsible for the Permo-Triassic mass extinction at 251 Ma. Despite recent intensive research on the province, the extent and duration of extrusive and related magmatism are still controversial. Although several areas surrounding the Siberian craton have been attributed to the ST volcanic activity, the full extent remains conjectural as precise age determinations and chemical correlations between units are missing. Basaltic, gabbroic and rhyolitic rocks occur throughout the West Siberian Basin beneath a thick succession of Mesozoic and Cenozoic sediments. Thicknesses of the lava sequences vary but exceed 2 km in places. Areas with basalt and dolerite rocks supposedly related to the ST are also reported further to the north of the Siberian craton, on the Taimyr Peninsula, along the eastern border of the Urals (Chelyabinsk) and in the polar Urals (Vorkuta), and to the south within the Kuznetsk Basin (Kuzbass) and Semeitau (Kazakhstan) areas. We have obtained widespread sample material from across Siberia, and show that the majority of basalts and gabbros have ages indistinguishable from the Traps on the craton. Plagioclase (from basalt) and biotite (from gabbros) have 40Ar/39Ar ages of 248.7 ± 0.6 Ma to 251.7 ± 0.6 Ma (relative to FC sanidine at 28.02 Ma). Early to mid-Triassic ages obtained on Chelyabinsk basalts demonstrate that volcanic activity in Siberia occurred in at least two episodes and that not all volcanism may be contemporaneous with the main Traps activity. An assessment of published and new geochemical and isotopic data demonstrate that basalts from the West Siberian Basin, and the Chelyabinsk, Kuzbass, Vorkuta regions have chemical characteristics typical of evolved, crustally-contaminated continental flood basalts (e.g., low Mg#, negative Nb anomaly) showing affinities with the Nadezhdinsky suite of the main Traps from the Noril'sk area. The Nadezhdinsky suite is known to immediately precede the supposedly main pulse of volcanism that extruded over large areas of the craton. Our data emphasize that basalts surrounding the ST exposed on the Siberian craton are likely to be a part of a greater Siberian LIP, but it is not yet possible, with the currently available data, to closely define the duration of activity. It also stresses the importance of correlating igneous units in Siberia using both chemical and radiometric age determinations.
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 1115 Radioisotope geochronology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting