Paleointensity and paleodirection of the geomagnetic field in the middle Miocene: Evidence from late cenozoic volcanites of primorye |
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| Authors: | V V Shcherbakova V P Shcherbakov Yu S Bretshtein G V Zhidkov |
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| Institution: | 1.Borok Geophysical Observatory, Schmidt Institute of Physics of the Earth,Russian Academy of Sciences,Borok, Yaroslavl Region,Russia;2.Kosygin Institute of Tectonics and Geophysics, Far East Division,Russian Academy of Sciences,Khabarovsk,Russia |
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| Abstract: | We present the results of analyzing a representative collection of the middle Miocene 12.4–10.0 Ma basalts that compose the
volcanic cover of the Shufan and Sovgavan plateaus, namely the Nikolo-L’vovsk (NL) and Sovetskaya Gavan (SG) volcanic fields.
Preliminary data are obtained about the relicts of some volcanic edifices within the West and East Sikhote-Alin volcanic belts,
namely the Shishlovskii, Malyshevo, and Truzhenik objects. It is established that the volcanic rocks from these localities
are characterized by similar petrologic and magnetic properties. Thermal cleaning of the samples is carried out, and the coordinates
of the paleomagnetic pole are determined as Λ = 190.2°E, Φ = 71.3°N for basalts of the Nokolo-L’vovsk area and Λ = 180.4°E,
Φ = 71.9°N for rocks from the Sovgavan locality. These values are consistent with the data for coeval volcanics from other
regions of Eurasia. Reliable determinations of the paleointensity H
pal for a representative collection of samples were obtained using the Thellier method. The corresponding values of the virtual
dipole moment (VDM) are almost half its present-day value. The analysis of the Miocene VDM values available from the world
database revealed a low average field 5.06 × 1022 Am2 characterized by high variance σ = 2.13 × 1022 Am2 at that time. The similarity of VDM values for the Miocene characterized by frequent inversions and for the Cretaceous Superchron
supports the hypothesis of the lack of a correlation between the VDM values and the frequency of geomagnetic inversions. |
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