RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 8, ES1004, doi:10.2205/2006ES000191, 2006
[34] The aim of this study was to generalize the data available for the paleointensity, reversal frequency, and the variation of the direction of the geomagnetic field in the vicinity of the Paleozoic-Mesozoic boundary, which was marked by the peak of the igneous activity of the Siberian traps (251 Ma). For this purpose I used the data, available in the Data Base and the geomagnetic polarity time-scale. However, I did not find any specific features in the behavior of the geomagnetic field for that period of time.
[35] 1. The paleointensity of the field was found to be elevated in the time interval of 330-280 Ma and then declined abruptly (averagely twice as much), remaining the same up to 200 Ma. The time interval of the igneous activity of the Siberian traps was situated within the time interval of low paleointensity values and "lagged" 30 million years behind the abrupt changes in the paleointensity.
[36] 2. The Paleozoic-Mesozoic boundary and the time of the maximum trap activity coincided with the period of frequent reversals and, hence, with the frequent changes of the geomagnetic polarity, without being recorded in the specific features of the geomagnetic field. The peak of the biota change, coinciding with the peak of the highest Siberian trap activity, lagged 15 million years behind the boundary between the Kiama hyperchron of the stable reversed polarity field and the Illawara hyperchron of frequent polarity changes.
[37] 3. The global changes of the average magnitude variations of the field direction from its unstable state with oscillations of 6o-10o to 6o-7o fell on the lower and upper boundaries of the Kiama hyperchron. As the Kiama hyperchron was superseded by the Illawara hyperchron, the variation magnitude began to grow from 6o (265 Ma) to 8o-9o (240 Ma). The P/T boundary proper did not show any specific features in the field variation magnitude. Therefore, the Paleozoic-Mesozoic boundary is not recorded in the paleomagnetic data.
[38] 4. With approaching to the center of the Siberian traps, the field variation magnitude showed a regular growth of the field direction variation magnitude from its normal state (7o-8o) to the average value of 11o-12o. This can be explained by a connection between the local excitation in the outer core of the Earth and the formation of the Siberian superplume. This growth of the variation magnitude occurred during the period of 20-50 million years before the Paleozoic-Mesozoic boundary and the maximum activity of the Siberian traps. This "retardation" seems to have been the time of the Siberian superplume rise from the core-mantle boundary to the Earth surface. This long time lagging can be explained by the inexact dating of the objects of the paleomagnetic studies and/or by the NRM age, yet, the most probable explanation is the formation of a series of plumes at that time, in the same region of the core and mantle boundary. This interpretation is validated by the existence of the compact concentrations of the high-magnitude magnetic field directions, as the potential regions of the formation of world magnetic anomalies and plumes in the time interval between 300 Ma and 200 Ma. Main part of such groups concentrated relatively close to one another, between the longitudes of 0o E and 80o E and between the latitudes of 10o N and 60o N. It is possible that the region of the exited state of the upper part of the Earth core (270-300 Ma), which was situated south of the region underlain by the Siberian traps, was the region of the Siberian superplume generation.
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Figure 17 |
Citation: 2006), Geomagnetic field in the vicinity of the Paleozoic-Mesozoic boundary and the Siberian superplume, Russ. J. Earth Sci., 8, ES1004, doi:10.2205/2006ES000191.
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