HR: 0800h
AN: GP11C-0836    [Abstracts]
TI: The Intensity of the Earth's Magnetic Field in the Earliest Triassic: Results from the East Siberian Trap Basalts in the Maimecha-Kotuy Region, Russia.
AU: * Heunemann, C
EM: heunem@geophysik.uni-muenchen.de
AF: Department for Earth and Environmental Sciences, Geophysics Section, Ludwig-Maximilians-Universit\"at, Theresienstr. 41, Munich, 80333 Germany
AU: Gurevitch, E
EM: egourev@rambler.ru
AF: VNIGRI, Laboratory of Paleomagnetism, Liteiny Avenue 39, St. Petersburg, 191104 Russian Federation
AU: Kr\'asa, D
EM: david@geophysik.uni-muenchen.de
AF: Department for Earth and Environmental Sciences, Geophysics Section, Ludwig-Maximilians-Universit\"at, Theresienstr. 41, Munich, 80333 Germany
AU: Soffel, H C
EM: soffel@geophysik.uni-muenchen.de
AF: Department for Earth and Environmental Sciences, Geophysics Section, Ludwig-Maximilians-Universit\"at, Theresienstr. 41, Munich, 80333 Germany
AU: Bachtadse, V
EM: valerian@geophysik.uni-muenchen.de
AF: Department for Earth and Environmental Sciences, Geophysics Section, Ludwig-Maximilians-Universit\"at, Theresienstr. 41, Munich, 80333 Germany
AB: A reliable and detailed record of the variation of the Earth's virtual dipole moment (VDM) provides important constraints for the understanding of geodynamo processes. However, the dataset available is very scarce. This holds true especially for the Mesozoic. An excellent opportunity to study the behaviour of the Earth's magnetic field with high temporal resolution are the Siberian Trap basalts, erupted at the Permo-Triassic boundary. So far, most studies of this large igneous province (LIP) and the palaeomagnetic information recorded by this huge pile of extrusives are limited to the sequence exposed in the Noril'sk area. The study presented here focuses on the East Siberian Trap basalts of the Maimecha-Kotuy region. The section sampled (21 flows) covers the Kogotoksky suite (upper Onkuchaksky to Tyvankitsky suite). Recent radiometric dates suggest that the section was emplaced in the earliest Triassic, postdating the main volcanic activity of this LIP. A transition from normal to reversed polarity is observed within the section. Therefore, it probably corresponds to the very upper part of the volcanics of the Noril'sk area implying that volcanism remained active significantly longer in the Maimecha-Kotuy region. From the paleomagnetic point of view, flows yield reliable directional information (overall VGP: 152.5\ensuremath{^{\circ}}/ 48.7\ensuremath{^{\circ}} with d$_\mathrm{p}$/d$_\mathrm{m}$: 8.5 / 9.6) carried by Ti-rich titanomagnetites of variable composition. Secondary overprints are rare and restricted to blocking temperatures below 150\ensuremath{^{\circ}} C. Extracting paleointensities using the Thellier-Thellier method showed to be more difficult. Reliable values were obtained from 9 flows. The mean VDM calculated on the basis of the data obtained from this section is $1.6 \pm 0.3 \times 10^{22} \;\mathrm{Am}^2$. This value suggests that the Earth's magnetic field was very weak around the Latest Paleozoic/Earliest Mesozoic for a considerable time as it is comparable to data from the western (and older) part of the Traps ($2.2 \pm 0.9 \times 10^{22}\;\mathrm{Am}^2$).
DE: 9320 Asia
DE: 9609 Mesozoic
DE: 1510 Dynamo theories
DE: 1521 Paleointensity
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting