The origin of the Late Paleozoic remagnetization in the Bashkirian megazone(the Southern Urals).

The research objects are magmatic bodies from the southern, central and northern parts of the Bashkirian megazone (the Southern Urals tectonic domain which extends from the south-east to the north-west for 300 km). Most of the studied intrusions have the Riphean age. In the Riphean the Bashkirian megazone (BM) was a part of the East European craton (2). The emplacement of most studied bodies is associated with the Mashak magmatic event (the Lower Riphean-Middle Riphean boundary), which marks the breakup of the super-continent Nuna (2). During the Late Paleozoic the rocks of the Bashkirian megazone were involved in the collision. During this process most of BM rocks was remagnetized.

Paleomagnetic analysis showed that the Late Paleozoic secondary remanence component present in 28 intrusive bodies from different parts of BM. In general, calculated paleomagnetic directions form a tight group in the geographic coordinate system, but the mean directions for some districts are statistically different. These differences may be related to: 1) local tectonic movements of the individual blocks within the Bashkirian megazone; 2) slightly different time of remagnetization; 3) insufficient averaging of secular variations of the geomagnetic field. To resolve this issue, further studies and more paleomagnetic data are required.

Given that paleomagnetic directions are more tightly grouped in a geographic coordinate system than in a stratigraphic coordinate system, the Late Paleozoic component is post-folding.

Distribution of this component does not reveal any regular features (for example, continuous trend from south to north, etc.) Thus, the differences of the mean paleomagnetic directions for various localities can not be explained by the migration of the remagnetization front. Also, the mean pole for all studied regions is close to the mean for 18 poles of Stable Europe with an age of 279-299 Ma (1).

We suggest that the component has a thermoviscous nature. Different minerals-carriers of magnetization show the same directions, evenly distributed over the magmatic rocks of the entire BM. Probably, the studied component of remanence was formed at the moment of partial stress relief at the final stage of collision and collapse of orogen in the Southern Urals. Also, this component could have formed during the exhumation of the BM to the surface at the time of formation of the South Ural thrust faults system.

Based on the obtained data, we can conclude that remagnetization in the Bashkirian megazone occurred approximately in the same time (279-299 Ma) and after the end of the main Late Paleozoic fold deformations in this area. By this time, the Bashkirian megazone was stable relative to the East European craton.

References:

1."Global Paleomagnetic Database" (GPMDB, v. 4.6, 2005), Pisarevsky S.A.

2. Puchkov V.N., Bogdanova S.V, Ernst R.E., Kozlov V.I., Krasnobaev A.A., Söderlund U., Wingate M.T.D., Postnikov A.V., Sergeeva N.D. The ca. 1380 Ma Mashak igneous event of the Southern Urals // Lithos. - 2013. - V.174. – P. 109-124.