Head of the Laboratory - Doctor of science A.N. Didenko

Laboratory was founded in 1939.

Main field of research include geomagnetic field changes during Neogea, paleotectonic and fine structure of geomagnetic field.

Main results of the Laboratory for the last four years run as follows.

The mean level of magnetic moment ( VADM ) for the last ~200 Ka was 0,5-0,6 of modern M, according to continuous paleointensity records of 6 curves longer than 200 Ka averaged records by sliding window of 20 Ka.

All curves have a clear sharp minimum of 180-190 Ka ( Biva I age). 15 shorter curves have maximum at about 55 Ka and a deep minimum near ~45-20 Ka as against the background of recorded Mono and Lashamp excursion [Petrova, 1998a]. The correlation coefficient for pairs of paleointensity curves varies in the range of 0.5-0.7 for the last 200 Ka. In some time interval K decreases. All excursions that these curves illustrate fit decreasing K, but the process of K decrease is remarkably longer than excursions themselves. [Petrova, 1999].

The variation of T=(95± 10) yr. was revealed as well as (60± 10) yr. and (120± 10) yr. in four different Karelian varves sections for time interval 16-9 Ka [Petrova et al, 1997, Petrova et al 1998b]. This variation does not exist neither in present spectrum of torsion oscillations nor in the spectrum of archaeological section for the age 4-5 Ka (Mesopotamia) [Nachasova, Burakov, 1993]. Supposedly, the presence of this variation is connected with the low magnetic moment of the Earth; 16-9 Ka ago it was ~0.5 of the present M [Petrova, 1998a].

The spectrum of variations with T 300-10000 yr. ( MAC-waves) was studied in two different sections (Jangiyul - Tashkent region and Kostenki - Dnepr river) for time interval 52-19 Ka. It is the same as spectrum known in archeomagnetic data, although the magnetic moment of the Earth during that time interval was 0.3-0.5 of present M. [Pospelova et al, 1998]

The analysis of long archaeointensity curves for the last 8000 years (Bulgaria, Georgia, Central Asia, China, Japan) allows to conclude that intensity variations may be approximated by harmonics with periods from 500 to 8000 years, which have both westward and eastward longitudinal drift with the same velocity about 0.2 degree per year.

The main waves have period 8000- and 1600-years. The 8000-years variation has the eastward drift and amplitude, changing with longitude from 6 to 10 A/m. The 1600-years variation is in the main responsible for the phenomena of the "westward drift" of geomagnetic field.

Archaeomagnetic data for Middle Asia and the Caucasus for the last four millennia (thousand years) allows us to identify variations with T=1800 and 1200 years. The 1200-yr. variation for the Caucasus has more pronounced and clear character. The 1800-yr. variation for Middle Asia is two times greater than that for the Caucasus [Burlatskaya, 1997]. The amplitude of 300-600-yr. variations increased abruptly (as a “splash”) in VIII century BC and fall in IV century BC [Burlatskaya, 1999a]. The amplitude of ~200 yr. increased gradually in mid second millennium and decreased abruptly in mid first millennium [Burlatskaya, 1999b].

The combined analysis of variations in geomagnetic reversal frequency, ratio in marine carbonate sediments, and drift velocity of the East European continent in the Paleozoic time indicates these quantities to be correlated and controlled by a general evolutionary process having a period of about 100 Ma. Surface effects of the Paleozoic activation periods of global tectonic-magmatic processes are likely to be related to the spreading activity in paleooceanic basins, an increase in the volume of newly formed oceanic crust, and the opening of new oceans. The Paleozoic stage of enhanced tectonic-magmatic activity at the Earth’s surface, accelerating the continental plate motion and decreasing the Sr in marine carbonate deposits of the Paleozoic, are preceded by quiet periods of the geomagnetic field, when its reversals are rare or totally absent during 40-60 Ma. The delay time of extremums in the plate velocity and Sr, associated with the tectonic-magmatic activation, amounts to about 28 Ma relative to the middle of a quiet geomagnetic field period.

The Urals is a Hercynian fold-nappe structure, have been resulted of the collision between the Baltia and Siberia continent. According to paleomagnetic data from ophiolites of the Polar Urals, paleooceanic basin was located at 8-14°S. The spreading zone had strike to the NNW direction. The present Northern margin of Siberia bordered the paleoocean from the East. Comprehensive geological and geophysical research in the west part of the Omolon massif and in the Sugoi folded zone suggests significant lateral displacements of these units relative to one another and with respect to the Siberian continent in Late Mesozoic time.

The data on changes in geomagnetic field reversals, intensity and direction, organisms, and velocities of continental plate movements during the last » 1700 m.y. are collected and analyzed. The following regularities were revealed: 1) long-term intervals of the steady field state with very rare reversals, spaced by 160-200 m.y. (a fractal dimension of about 0.9-1.0); 2) nearly chaotic field state, characterized by frequent reversals (a fractal dimension of 0.5-0.6); 3) in the first regime, the latitude dependence of variations in both intensity and direction are typical of dipole field, whereas in the second regime this dependence is different; 4) generally, the geomagnetic field exhibits no periodicity in its intensity, direction, and reversals throughout the Neogea: (a) in 95% cases, the "periods" consisted of only one or two oscillations, (b) oscillations of all geomagnetic elements with similar periods are commonly asynchronous, and (c) the "periods" often decrease or increase smoothly in time. The comparison of geomagnetic field pattern, on the one hand, and changes in the organic world and continental plate velocities, on the other hand, shows that either processes near the Earth's core and surface are synchronous (» 0± 10 my) or processes of the second group lag behind those of the first group (by 40± 20 my). The first case implies the presence of an "external" mechanism, the changes of the second group are due to an "internal" mechanism". The value of this lag corresponds to a velocity of 4-10 cm/yr (this is the velocity of energy transfer from the mantle bottom to the Earth's surface). This value is in accordance with mean velocities of continental plate movements. However, there is no causal relation between the aforementioned processes.

The evidence of an active paleosubduction zones absolute motions were obtained as a result of paleomagnetic investigations of the Eastern Kamchatka Upper Cretaceous-Lower Paleocene (Kumroch Ridge) and Paleocene-Eocene (Kamchatsky Mys Peninsula) volcanics.

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E-mails:

Belokon: stmaster@dvgu.marine.su

Bronshtein: bred@itig.khabarovsk.su

Hurgaliev: Danis.Nourgaliev@ksu.ru

Molostovskii: stmaster@schit.saratov.su

Hramov: khramov@oloy.spb.su

Shapiro: seva@maglab.mplik.ru

Scherbakov: valera@borok.unigar.ac.ru