Seismic structure of the upper mantle and problems of geodynamics
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Інститут геофізики ім. С.I. Субботіна НАН України
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| Cite this: | Seismic structure of the upper mantle and problems of geodynamics / N. Pavlenkova, G. Pavlenkova // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 129-130. — Бібліогр.: 6 назв. — англ. |
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irk-123456789-1021362016-06-11T03:02:35Z Seismic structure of the upper mantle and problems of geodynamics Pavlenkova, N. Pavlenkova, G. 2010 Article Seismic structure of the upper mantle and problems of geodynamics / N. Pavlenkova, G. Pavlenkova // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 129-130. — Бібліогр.: 6 назв. — англ. 0203-3100 http://dspace.nbuv.gov.ua/handle/123456789/102136 en Геофизический журнал Інститут геофізики ім. С.I. Субботіна НАН України |
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Pavlenkova, N. Pavlenkova, G. |
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Pavlenkova, N. Pavlenkova, G. Seismic structure of the upper mantle and problems of geodynamics Геофизический журнал |
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Pavlenkova, N. Pavlenkova, G. |
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Seismic structure of the upper mantle and problems of geodynamics |
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Seismic structure of the upper mantle and problems of geodynamics |
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Seismic structure of the upper mantle and problems of geodynamics |
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Seismic structure of the upper mantle and problems of geodynamics |
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Seismic structure of the upper mantle and problems of geodynamics |
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seismic structure of the upper mantle and problems of geodynamics |
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Інститут геофізики ім. С.I. Субботіна НАН України |
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2010 |
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Seismic structure of the upper mantle and problems of geodynamics / N. Pavlenkova, G. Pavlenkova // Геофизический журнал. — 2010. — Т. 32, № 4. — С. 129-130. — Бібліогр.: 6 назв. — англ. |
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Геофизический журнал |
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AT pavlenkovan seismicstructureoftheuppermantleandproblemsofgeodynamics AT pavlenkovag seismicstructureoftheuppermantleandproblemsofgeodynamics |
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2025-07-07T11:53:51Z |
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Seismic structure of the upper mantle and
problems of geodynamics
N. Pavlenkova, G. Pavlenkova, 2010
Institute of Physics of the Earth, RAS, Moscow, Russia
ninapav@ifz.ru
During the last decades of the XX century seve-
rall long-range seismic profiles were carried out by
Russian institutions in oceans and in the continents.
The longest profiles are the Angola-Brazil geotraverse
in the Southern Atlantic with the investigation depth
of 100 km [Pavlenkova et al., 1993] and a system
of profiles with large chemical and Peaceful Nucle-
ar Explosions (PNE) in the Northern Eurasia with
the wave penetrating depth of 700 km [Fuchs,
1997; Pavlenkova G., Pavlenkova N., 2006]. The
studies show that the revealed structural
peculiarities of the oceanic and continental upper
mantle are difficult to describe in a simple
lithosphere-asthenosphere system.
The Angola-Brazil geotraverse shows that the
oceanic basin lithosphere is of 60—70 km thick-
ness and it is underlined by the low velocity layer
(the asthenosphere). However beneath the mid-oce-
anic ridge instead of the asthenosphere uplift, two
local low velocity zones (asthenolites) are revealed
at depth of 20 and 50 km. The seismic velocities
between these zones are too high (up to 8.5 km/s)
for such high heat flow area, they may be explained
only by the anisotropy effects.
In the cratonic regions of the Northern Eurasia
the thermal lithosphere was proposed from the heat
flow data at depth of 200—250 km. The seismic data
have not revealed any decrease of the velocities at
these depths. On the contrary the low velocity lay-
ers are often observed inside the lithosphere at depth
of 80—100 km. Two basic boundaries were traced
over the study area: N boundary at the low velocity
layer bottom, and L boundary at a depth of 180—
240 km. All the boundaries are not simple disconti-
nuities, they are thin layering zones with the alter-
nation of high and low velocities in inner layers.
The N and L boundaries divide the upper mantle
in three layers of different plasticity. It follows from
regular change of the upper mantle horizontal hete-
rogeneity. The most heterogeneity is observed in
the uppermost mantle: the velocities change from
the average 8.0—8.1 km/s beneath the high heat
flow areas (the West Siberian Plate) to 8.3—
8.4 km/s in some blocks of the Siberian Craton
and of the Urals. At the depth of 100—120 km the
local high velocity blocks disappear and low ve-
locity layers are often observed. These structural
features propose that the depth of 100—120 km
is a bottom of a brittle part of the lithosphere.
Another visible change of the matter plasticity is
observed at depths of 200—250 km where the
mantle structural pattern is changed too: the ve-
locities decrease beneath the L boundary uplifts,
which makes the isostatic equilibrium of the up-
per mantle. At these depths the Q-factor is also
decreased [Egorkin, Kun, 1978].
The other large explosion experiments and the world
seismological studies show that these boundaries may
have a global significance. The geophysical and geo-
logical data reveals some additional characteristics of
these complicate mantle boundaries. They are the
higher electrical conductivity zone favoring the exi-
stence of fluids at a depth interval of 100—150 km.
The most part of the xenoliths comes from the depths
around 100, 150 and 200 km and the xenoliths from
the Siberian Craton kimberlites taken from the depths
of these seismic boundaries have indications of film
melting [Solov’eva et al., 1989]. In different tectonic
regions, inside the continents and in the continental
margins, the most earthquakes are located at depths
of around 100 and 200 km.
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The correlation the xcenolits origin depth and the earthquake clusters with the regional mantle boun-
daries could no be an accidental correlation and it shows that the depths of the regional boundaries
are critical depths where some regular transforma-tions of the matter are happened.
One possible explanation of these upper mantle properties involves the deep fluids. The concentra-
tion of fluids at certain PT-levels changes mechani-cal properties of the matter, they initiate partial
melting and metasomatism of the mantle material which results in the velocity changes. The practi-
cally infinite energy sources for earth-quakes are the explosive chain reaction of the decomposition,
triggered by decompression within the fault zone [Gilat, Vol, 2005]. The matter flow along these weak
zones results in origin of the seismic boundaries with the velocity anisotropy.
The determined upper mantle weak zones can have a great effect on all dynamic processes. Together with
deep faults they form a channel system for the mantle fluids and matter transportation. The weak zones play
an important role in the horizontal displacement of the lithosphere blocks and in formation of tectonic struc-
tures. During tectonic activation the weak layers can be transformed in the asthenolites by partial melting
and provoke the plume tectonics.
Egorkin A. V., Kun V. V. P-wave attenuation in the up-
per mantle of the Earth // Izvestiya. Phys. Solid Earth.
— 1978. — 4. — P. 25—36.
Fuchs K. U��er mantle heterogeneities from active and
�assive seismology, NATO ASI Series (1.Disarma-
ment Technologies — Vol. 17) // Contribution ¹336,
International Lithos�here �rogram. — Dordrecht:
Kluwer Acad. �ubl., 1997. — 366 �.
References
Gilat A., Vol A. Primordial hydrogen-helium degas-
sing, an overlooked major energy source for inter-
nal terrestrial processes // HAIT J. Science and Eng.
— 2005. — 2, ��1—2. — P. 125—167.
Pavlenkova G. A., Pavlenkova N. I. Upper Mantle Struc-
ture of the Northern Eurasia from Peaceful Nuclear
Explosion Data // Tectonophysics. — 2006. — 416.
— �. 33—52.
Pavlenkova N. I., Pogrebitsky Yu. E., Romanjuk T. V.
Seismic-density model of the crust and upper man-
tle of the South Athlantic along Angola-Brasil geo-
traverse // Phys. Sol. Earth. — 1993. — ��10. —
P. 27—38.
Solov'eva L. V., Vladimirov B. M., Kiselev A. I., Zavija-
lov L. L. Two stages of mantle metasamatites of
deep xenoliths from Yakutia kimberlites and their
relation to lithosphere processes // Precambrian
metasamotites and their ore deposits. — Moscow:
Nauka, 1989. — P. 3—17 (in Russian).
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