Volume 24, 1, 2005
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Volume 24, 1, 2005 |
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N.K. Bulin, A.S. Volsky
The regional prediction of oil and gas potential in the
junction area of the Central Asian and the East Asian riftogenic belt based on
deep geophysical criteria
The regional prediction of oil and gas potential in the junction area of the
Central Asian and the East Asian riftogenic belt is based on the analysis of
seismic sections of the crystalline earth’s crust (CEC) obtained by the method
of multi-wave deep seismic profiling (profiles: Tynda – Cape Nevelskoi and Tynda
– Amurzet) and by the method of differential deep seismic sounding along the
Zeya River – Bureya River trace. The prediction is based on the data on the
velocity characteristics (layer velocity of longitudinal waves Vp = 7.2-7.6 km/s
and shear waves Vs = 4.05-4.30 km/s) of waves in the basal layer of the lower
crust and the data on the thickness of this layer (h = 3-8 km), which lies
directly on the Moho boundary. Many specialists believe that the basal layer (or
reflectivity layer, according to western geophysicists) is one of the most
tectonically active layers of the upper lithosphere, which also affects the
development of mineragenic processes. These predictive features were previously
used for the regional prediction of oil and gas potential of the Russian
Platform. The minima locations on the isolines of the velocity Vs = 3.6 km/s and
Vs = 3.9 km/s and the lateral local waveguide of the velocity Vp ~ 6.5 km/s and
Vs = 3.5 km/s in the lower crust were also used for prediction for the first
time. The association of territories with areas of lower mean magnetization of
the upper magnetoactive crustal layer J < (0.2-0.5) A/m promising for
hydrocarbon accumulation empirically established in other regions of Russia were
used. On the basis of the above-mentioned deep geophysical features in the
studied area, four potential oil and gas fields were distinguished in the
following succession in descending order depending on the degree of prediction
reliability: Upper Zeya (I), Lower Zeya (IK), Uda-Selemdzha (II), and Middle
Zeya (IV). The predicted regions are about 300 km across strike.
T.K. Zlobin, R.G. Gureev, L.M.
Zlobina
Deep structure of southwestern Kamchatka from the data of the
earthquake converted wave method
The results of our interpretation of ECWM data from Kamchatka are considered.
These methods as distinct from the earlier applied approach allow us to take
into account the position of each conversion point in space. New specified ECWM
deep sections have been obtained. Relief charts have been constructed of major
seismic conversion boundaries related to the interface in the Cenozoic
volcanogenic-sedimentary layer (depths 0.1-1.9 km), base of the Upper Cretaceous
complex (5-10 km), roof of the granulite-basite (“basaltic”) layer (20-30 km),
Moho discontinuity (38-47 km), and planes in the upper mantle down to depths of
120 km. The position in space of deep boundaries and structures in the earth’s
crust and upper mantle and their relation to the surface tectonic structures
determined by geological methods have been assessed.
I.N.
Kotlyar, T.B. Rusakova
The geological-and-geochronological model of Cretaceous
continental volcanic formations in the Okhotsk-Chukotka magmatic province (north-eastern
part of Russia)
On the basis of geological-and-radiological data, the authors have developed the
geological-and-geochronological model of the formation of Cretaceous continental
assemblages. They distinguish 4 stages of volcanism, 3 of which are marked by
great activity. Their products are represented by calc-alkaline and
trachyryolite-trachybasaltic series of various tectonic implication: island-arc,
continental, intracontinental, and riftogenic. Their difference is also marked
by considerable temporal breaks and petrological features of rocks.
S.V. Zyabrev, M.V. Martynyuk, E.K.
Shevelyov
South-westerly portion of Kiselyovsko-Manominsky
accretionary complex, Sikhote-Alin: Stratigraphy, subduction-related accretion
and post-accretional displacements
The radiolarian biostratigraphic study of an accretionary complex in the south
of the Khabarovsk territory reveals its stratigraphic record and refines the
regional stratigraphy. On the basis of stratigraphy, the accretionary complex is
recognized as the south-westerly continuance of the Kiselyovsko-Manominsky
terrane, a mid-Cretaceous accretionary complex that is traced from the Lower
Amur region. The biostratigraphic data obtained place important temporal
constraints on the timing of subduction-related accretion and post-accretional
terranes’ displacement. The Kiselyovsko-Manominsky accretionary complex formed
in the mid-Aptian – earliest Albian, as bracketed by the ages of its youngest
deposits and the overlying strata. Subsequent juxtaposition against the
Zhuravlevsky terrane occurred along à sinistral strike-slip fault. This
large-scale along-strike displacement commenced in the Albian and terminated in
the Turonian. The average rate of the displacement is estimated at about 3 cm
per annum. We reconstruct a possible configuration of the mid-Cretaceous
convergent plate margin.
N.P. Mitrofanov
Geodynamics of the ore stage of formation of tin
deposits in the north-western part of the Pacific ore belt
Early Cretaceous collision and Cretaceous-Paleogene marginal-continental
subduction of the Andean type are the main geodynamic regimes at the ore stage
of formation of tin deposits in the north-western sector of the Pacific ore belt.
Collision processes are divided into frontal processes of the rigid and soft
types, and oblique collision processes. The rigid type corresponds to the
collision of the continental platform with the microcontinent, and the soft type
is related to the collision of the continental platform with island arcs. The
regime of the soft type causes intrusions in the continental rear of the
convergent boundaries. Oblique collision produces situations of the transform
continental margins (Asian type). Collision massifs of granodiorite and granite
of the longitudinal belts and series of intrusions of
diorite-granodiorite-granite diverging from them generate deposits of rare-metal-
and polymetallic-tin formations depending on substratum compositions. The
subductional gabbro-diorite-granodiorite-granite intrusions forming transverse
series in the rear of the marginal-continental volcano-plutonic belts generate
deposits of the polymetallic-tin formation. Conditions for large ore
concentrations are formed in the areas of superposition of collision and
subduction processes.
V.V.
Krapiventseva
Metal content of coals in Priamurye
Based on the data summarized on the spectral analysis of coals and to a lesser
degree, on their enclosing rocks of seven brown coal deposits of the Middle Amur
basin and the contiguous deposits, and also on two deposits and areas the
Bureinskiy basin, the maximal and average content of minor elements, including
rare earths and precious metals are considered.
It was established that commercial concentrations in the brown coals of the
Middle Amur basin have many elements primarily Ni, Ti, Y, Ga, and Zr.
Sr, Li and Nb display rare commercial concentrations; similarly Ag and Au in the
ash of the coals of the Ushumunskiy deposit.
The coals of the Bureinskiy basin are characterized by an array of minor
elements with commercially essential Be, Sr, Yb, Ti, Ga, Nb, and Zr
concentrations. Some elements, particularly those of the rare earths, were
determined only in single instances; hence it is not impossible that they are
present in coals from other deposits.
The summarized data allow a conclusion of the commercial metal content of coals
at some deposits (Ushumunskiy, Mukhenskiy, Rozengartovskiy, etc.).
Further detailed analysis is required of the regional geological regularities
that condition one or another metallogenic specialization of some deposits.
I.V. Buchko
The composition of the primary melt and mantle
substratum of the Veselkinsky peridotite-websterite-gabbroic massif of the
southern framing, North Asian craton (Amur region)
The composition of the primary melt of the Veselkinsky massif defined by
independent methods, particularly by mean weighting and modeling, corresponds to
subalkaline picritoid. Its crystallization took place at a pressure of about 10
kbar and initial temperature of 1320-1350°C. The crystal fractionation of the
subalkaline picritoid melt caused, on the one hand, the formation of dunites,
and on the other hand, the formation of a gabbro-monzonite association. The
primary mantle substratum was formed by equiponderant partial melting of spinel
peridotite at a pressure of 23 kbar, temperatures of 1796-1567°C, degree of
melting of about 60%, and water concentration of 2 %