Volume 24, 3, 2005
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Volume 24, 3, 2005 |
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V.Ya. Podgorny, Yu.F. Malyshev
The density section of the lithosphere of the Aldan-Stanovoy
shield
The density section of the lithosphere of the Aldan-Stanovoy shield has been
studied based on the seismic line Dzhalinda-Ulu along the Aldan-Stanovoy-Yakutia
highway which takes into account new data on the deep structure of the shield.
The method of layer-by-layer density modeling was applied which makes it
possible to see the lateral density changes in the layers. Density models for
the one-layer, two-layer and multilayer lithosphere have been constructed.
Extensive development of strike-slip faults, thrusts and zones of density
inversion along the whole section of the earth’s crust has been established, and
the active cover-basement contact of the Lena-Maya plate and a peculiar show of
faults have been identified. The deep structure of the shield in the central
part of the profile is represented by a zone of decreased density and extension
down to a depth of over 160 km attended by the rise of the cover and
asthenosphere. Its peripheral part is made up of inclined zones of compression
dipping south in the southern part of the profile; and they are north-dipping in
the northern part. The structure covers the whole Aldan-Stanovoy shield
crosswise and is possibly related to not only active rifting but also to the
penetration of the long-lived Siberian superplume.
Yu.A. Martynov, A.Yu. Martynov,
A.A. Chashchin, A.V. Rybin
Basalts of Tyatya Volcano: petrology and genesis (Kunashir
Island, Kuril island arc)
The main effusives of the ancient and present cones of Tyatya Volcano differ in
the content of CaO, Al2O3, Sr, K2O and most incoherent elements. Geochemical
evidence and also results of numerical modeling suggest that basalts of the
initial stage of formation of the volcano were the result of the relatively high
degree of melting of mantle source and subsequent deep fractionation in its rise
to the surface accompanied with plagioclase accumulation. Considering that the
lavas of the ancient cone of Tyatya Volcano are in many respects petrologically
close to basic volcanics of the Miocene stage of Kunashir Island formation, the
results of the relevant investigations can have implications for understanding
the features of the evolution of volcanism in the Kuril island arc on the whole.
A.M.
Korotky, N.I. Belyanina, T.A. Grebennikova, L.P. Karaulova, E.D. Ivanova, L.M.
Mokhova, E.I. Tsar’ko
Late Quaternary marine deposits in the coastal zone of Peter
the Great Bay (Japan Sea)
The phases of the Japan Sea level rise are fixed in the deposits of three marine
terraces (height 6–8, 8–10 and 12–15 m) at the beginning of the Late Pleistocene.
The maximum rise exceeding the contemporary rise by 8–10 m is compared with the
first phase of Riss- transgression (stage 5ĺ). Traces of three oscillations of
the Japan Sea level with the maximum rise up to +6 m are fixed in the marine
terrace section (6–8 m). The wide distribution of estuary-lagoon and coastal
deposits with moderate-cold and cold pollen and diatomic assemblages above the
modern sea level contradicts the standard theoretical presupposition about the
coincidence of transgressive peaks with the warm phases of Pleistocene climate.
Significant regressions in the time of climatic cooling occur only in the event
that there are continental glaciations due to withdrawal of water from the World
Ocean. Traces of large glaciations for the Riss- climatic phases of cooling have
not been yet identified. Similar relationships of the marine facies
characterized by cold pollen assemblages have been recognized for the Riss-
marine terraces on the coast of Sakhalin.
Yu.D. Zakharov, A.M. Popov, G.I. Buriy,
O.P. Smyshlyaeva
The problem of the Lower – Middle Triassic boundary within the Shimeuza sequence
of the Petrovka River basin (South Primorye)
The new finds of ammonoids showed that the Shimeuza sequence in
the Petrovka low reaches is represented by the Upper Olenekian and Lower and
Middle Anisian (Triassic). It is suggested that the Lower and Middle Triassic
section of the Petrovka River basin differs from other Triassic basic sections
of South Primorye in the erosion of the Upper Olenekian Subcolumbites
multiformis zone at the Olenekian-Anisian boundary. The new ammonoid taxa are
described.
L.P. Eikhvald
The first finds of Middle Paleozoic conodonts in Western Priokhotye
The results of biostratigraphic
study of the sections of the Lantarskaya and Uluikanskaya suites in a stratotype
territory are presented. For the first time, conodonts have been distinguished
and monographically described, and correlation has been made with conodont zones
of the Standard Stratigraphic Chart.
Ye.N. Diman
Mesotransformations as the cause of geological restructuring
Consideration is given to the problems of mesotransformations in geology. A new
hypothesis was offered that both nanocrack swarms and a small temperature
gradient are the cause of mesotransformations in rocks (Diman, 2004).The
movement of mesotransformations occurs by fictitious conventional propagation of
the nanocrack into the domain of high temperature. Mesotransformations precede
and further many geological events, namely strip-like violation of rock strength,
earthquakes, formation of dikes and pipes, including diamond pipes and dikes,
and longitudinal and transverse dislocation of crystal layers. The
mesotransformations rate reaches several hundreds of meters per second.
The minimum temperatures for substances are determined at which
mesotransformations can begin without outward influence. An inference is made
that mesotransformations are widely distributed in the rocks of the earth’s
crust.
This paper also offers a structure of the mesotransformations zone, and
differences in mesotransformations are considered for both metals and silicate
rocks (as exemplified by granite). Sufficient features are adduced for the
mesotransformations as the product of the transverse motion of nanocracks.