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Volume 17, ¹ 6, 1998 |
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Magmatism, Geodynamics and Minerageny
S.V.Vysotskiy, G.I.Govorov, I.V.Kemkin, V.I. Sapin. The
boninite-ophiolite assemblage of east Sakhalin Island: geology and some features of
petrogenesis 3
I.A.Tararin, D.U.Li, J.G.Jong. Ophiolite covers of Karaginsky Island
(East Kamchatka), and the peculiarities of metamorphism at their base
16
V.Y. Fridovsky. Structures of Early Collision Gold Ore Deposits of the
Verkhoyansk Fold-and-Thrust Belt 26
Stratigraphy and Sedimentology
B.I.Pavlyutkin.The age of the Suifun suite (South Primorye)
37
E.L.Shkolnik, Ye.A.Zhegallo. Phosphate sandstones and siltstones of the
Nutovskaya suite, North of Sakhalin 46
D.I.Agapitov, L.I.Mitrofanova. Stratigraphy of Paleogene deposits of the
Khatyrsky basin (Chukotka) 53
Mineralogy and Geochemistry
L.G.Filimonova. Accessory Ca-amphiboles the Far Eastern rhyolite and its
role in petrogenesis of S-type magma 61
V.V.Velinsky, A.L.Pavlov. Physical-and-chemical modeling of the processes
of ultrabasite serpentinization and serpentinite dehydration by use of fluid
68
A.Yu.Antonov. Geochemistry of Late Mezozoic volcanic formations of the
Aldan shield southern boundary (Stanovoi range) 79
Geophysics
A.V.Vikulin, A.G.Ivanchin. The rotational model of the seismic process
94
M.N.Luneva. Wave propagation througth a fractured medium: theory and
experiment 103
Yu.F.Manilov. Evaluation of the effect of density heterogeneities in the
upper part of the crust by deep gravimetrical studies (as exemplified by deep seismic
sounding profiles of Priamurie) 110
V.I.Isaev, N.A.Volkova. Evaluation of oil and gas potential of the
Cretaceous deposits of the Central Sakhalin fault zone from mathematical modeling results
115
Index of papers published in the journal in 1998 119
S.V.Vysotskiy, G.I.Govorov, I.V.Kemkin, V.I. Sapin
The boninite-ophiolite assemblage of East Sakhalin Island: geology and some
features of petrogenesis
A boninite assemblage consisting of Late Jurassic - Early Cretaceous lavas and
layered intrusions has been found in the accretionary prism of East Sakhalin. The geology,
mineralogy and geochemistry of the rocks show that they were comagmatic and formed in
specific conditions. A high degree of reduction of primary spinel in the intrusive rocks
and the change of redox conditions during crystallization of boninite magma suggest that
the boninite assemblage formed under the influence of a reduced (hydrogen) fluid. The
layered intrusions of Sakhalin resulted from differentiation of boninite melt influenced
by this fluid.
I.A.Tararin, D.U.Li, J.G.Jong
Ophiolite covers of Karaginsky Island (East Kamchatka), and the peculiarities of
metamorphism at their base
The ophiolite assemblages of Karaginsky Island composing serpentinitized peridotites,
serpentinite melange, a layered complex of basic and ultrabasic rocks, a complex of
parallel dikes, globular lavas of basalts and apobasite metamorphic rocks form relatively
large allochthonous sheets in the watershed area of the island and smaller fragments among
the Paleogene deposits of its eastern part. The structure of the ophiolite complex as well
as of the island as a whole is thrust-imbricated conditioned by accretion processes, which
compensated spreading in the axial zone of the Commander basin of the Bering Sea in the
Middle Oligocene – Middle Miocene. The composition of harzburgite minerals prevailing
among the ophiolite sheets is evidence of their formation at the expense of the strongly
depleted mantle source of a back-arc basin. The metamorphic rocks occurring at the base of
the ophiolite sheets or as blocks amongst the serpentinite melange are represented by
apobasite crystalline and green schists, corresponding to tholeiitic composition of
spreading zones and island arcs. Metamorphism of the initial deposits involved several
stages. Relics of the earliest oceanic green-schist metamorphism, accompanied by irregular
spilitization, are retained in the cores of zonal amphibolite crystals of metamorphic
rocks. Superimposed metamorphism is caused by the thermal effect of the heated ophiolite
masses of the young oceanic crust, originated in the conditions of a back-arc basin of the
pre-Upper Cretaceous island-arc system and tectonically matched with the island-arc
deposits of this system under extension regime changed by compression regime. This
metamorphism, responsible for the origin of optical and chemical zoning of metamorphic
minerals, is dated as 70±2 Ma by K-Ar method and differs in the high gradients of
metamorphic parameters, non-completeness and irregularity of metamorphic reactions; its
parameters get quickly lower at a distance from the amphibolite – green-schist ophiolite
sheets. It is presumed that such matchings of metamorphic processes of different
geodynamic environments are not only possible in the accretionary prisms of island-arc
systems, but also in the intraoceanic structures of the ocean floor.
V.Yu. Fridovsky
Structures of early collision gold ore deposits of the Verkhoyansk fold-and-thrust
belt
Early collision gold ore deposits were formed in Late Jurassic-Neocomian at the beginning
of collision of the Kolyma-Omolon superterrain and the Okhotsk terrain with the eastern
margin of the Siberian continent. They form an extended belt in the western Verkhoyansk
sector and western zone of the southern Verkhoyansk synclinorium of the Verkhoyansk
fold-and-thrust belt. The connection of gold-quartz mineralization with tectonic
metamorphic transformations of terrigenous rocks is emphasized. The major ore controlling
structures are shown to be shear zones along which early thrust movements took place.
Later superimposed deformations of ore controlling structures are found correlating with
regional geodynamic events. The geological structures of the Dyandinsk-Okhonosoisk and
Yursk-Brindakit ore clusters are characterized. These have a discrete lenticular-banding
structure with alternating intensely and poorly deformed plates, which form the structure
of a scaly fan with a listric mixture type. The main deformation mechanism is plastic
flow. The relation of the morphological features of ore bodies to different types of shear
zones is traced. The revealed features of the structural control of mineralization of the
minutely studied regions are also characteristic for other structures of the Verkhoyansk
belt of early collision gold ore deposits.
B.I.Pavlyutkin
The age of the Suifun suite (South Primorye)
The problems of interpretation of paleobotanical data on the age of the Suifun suite
(according to the official point of view, it is Pliocene) are discussed. The analysis done
by the author of the results of the study of plant remains from the Suifun suite type
section in its stratotype area (Pavlovsky brown coal basin) does not give grounds to
consider the leaf flora, found recently in it, to be more ancient (up to Late Miocene).
Its age and the age of the suite itself is on the contrary younger: it corresponds to
Eopleistocene with the lower layer deviation into Pliocene. This is indicated by not only
flora composition, but also by the results of paleomagnetic measurements and direct
geological evidence, as well as by the correlation with the contiguous regions.
E.L.Shkolnik, Ye.A.Zhegallo
Phosphate sandstones and siltstones of the Nutovskaya suite, North of Sakhalin
Using a scanning electron microscope (SEM) we have studied for the first time the youngest
in Russia phosphate occurrences in the Pliocene Nutovskaya suite, Sakhalin Island,
represented by phosphate sandstones and more rare siltstones. They make up interbeds of
different thickness (ten centimetres to several metres) and length (the first tens to
hundreds of meters) in loose sands and clays of the suite. They show a rather high degree
of lithification and extremely high contents of P2O5 soluble with citric acid (up to
80-90%) and with citrate (up to 35%). When studying phosphate sands under the SEM we have
revealed that their phosphate cement is composed for the most part of a phosphatized mass
of cocco-like microorganisms of the first microns in diameter and less often, of other
kinds of microorganisms and relics. Phosphate siltstones contain abundant phosphatized
diatoms, their fragments, and other organic remains including microorganisms. Our
investigations support the opinion that phosphatization happens only in the beds enriched
in organic remains independently of the systematic type of organisms, and that
phosphatization has early nature, up to total lithification of the sedimentary mass. The
unique development of microorganism mass in the form of the filling cement of sand clastic
particles with the absence of any significant amount of other organic remains allow
various explanations: from their autotrophic nature to their development on the oil
leaking from the underlying oil-bearing Okabykaiskaya suite. However, the complex of
organisms in phosphate siltstones is similar to some of the known phosphate occurrences,
like those of modern oozes on the shelf of Namibia.
D.I.Agapitov, L.I.Mitrofanova
Stratigraphy of Paleogene deposits of the Khatyrsky basin (Chukotka)
The terrestrial part of the Khatyrsky basin is characterized by a high degree of facies
variability of Cenozoic sedimentary deposits which impedes correlation of discrete
Paleogene and Neogene sections. On the basis of detailed paleontological study of the core
from the drilled holes and correlation of the defined stratigraphic units with the
sections of the exposed areas, a more precise correlation scheme is suggested that
involves all facial zones. The paper examines the stratigraphy of Paleogene deposits,
which are ubiquitous in this region and penetrated by 14 holes on 8 sites. The Paleogene
assemblages in the Khatyrsky basin are represented by rocks of all the three divisions of
Paleocene, Eocene and Oligocene.
L.G.Filimonova
Accessory Ca-amphiboles of the Far Eastern rhyolite, and their role in
petrogenesis of S-type magma.
Inclusions of Ca-amphiboles and microaggregates of the dark-coloured minerals
were discovered in the subvolcanic facies of biotite rhyolite, belonging to S-type
orogenic magma. The chemical compositions and properties of these minerals testify that
they could not crystallize from the acid melt. Edenites and edenite hornblendes could
crystallize at 3, 4 - 5,1 kbar from subalkali magmas in the magma chambers, located within
the lower crust at a depth of 12 -18 km. Pargasites and pargasite hornblendes could belong
to hornblende peridotites.
V.V.Velinsky, A.L.Pavlova
Physical-and-chemical modeling of the processes of ultrabasite serpentinization
and serpentinite dehydration by use of fluid
Computer modeling was done on the basis of the “Selector” program allowing for the
effect on the processes of dunite and harzburgite serpentinization and dehydration of the
obtained serpentinites of fluid, represented by H2O, CH4, CO2, CO, and H2. It was shown
that a gaseous mixture of such composition lowered the temperature of ultrabasite
serpentinization and the beginning of serpentinite olivinization. The character of rock
alternation in the P-T coordinates was determined, and it is concluded that Alpine-type
ultrabasites in the lithospheric conditions has metamorphogenic nature. The derived data
are in good agreement with the experimental results and geological-petrographical
observations.
A.Yu.Antonov
Geochemistry of Late Mezozoic volcanic formations of the Aldan shield southern
boundary (Stanovoi range)
The study of the compositions of all J3-K1 general volcanic rock varieties (> 250
samples) from the Stanovoi range revealed the following: - The composition of medium- and
high SiO2-saturated volcanics within of individual parts of the region is quite similar to
the corresponding plutonic formations. This indicates their formation from the same
magmas. - The majority of the high SiO2-saturated volcanics of the Stanovoi range has a
similar composition, but there is a tendency to an increase in Mg-concentrations, total
alkalinity and potassium alkalinity in the more mafic volcanics, forming from south-east
to north-west along the region's strike. Besides, an increase in alkalinity in the series
of regional magmatic rocks from low- to high SiO2-saturated becomes lesser to its absence
in the series of the most alkaline rocks.This contradicts the presumed formation of these
magmatic series as a result of crystallization differentiation of mafic magmas and allows
us to suppose that their origin was conditioned by the mixing of mafic and high
SiO2-saturated magmas.
- In spite of petrochemical similarity in terms of thei rare element composition, the
Mesozoic Stanovoi volcanics differ in the most degree (high concentrations of Ba, Sr, F,
Li, Be, Sn, Pb, Nb, Ta, Zr, Hf, and low B) from the corresponding, as to alkalinity and
SiO2-saturation, volcanic formations of island arcs, and to a lesser degree, from the
active continental boundaries. Besides, the Mezozoic Stanovoi basalts are most similar to
Mesozoic and Cenozoic basalts, respectively, of the East Zabaikalie and Stanovoi range
intracontinental rifting zones, Their initial magmas, most probably, were melted out from
the least depleted substratum.
- On the basis of the obtained geochemical data it may be supposed that it were the
rifting processes that conditioned Stanovoi range magmatism both in Mesozoic and Cenozoic
time. In the course of these processes, within the upper mantle were melted out basaltic
magmas, most likely, of alkaline composition. Ascending to the Earth's crust level these
magmas caused melting out of great volumes of salic granitoid magmas, and then they mixed
with the latter. Besides, repeated magmatic activity in the region (especially in its
south-eastern part) lead to depletion of the magma-generating substratum and, accordingly,
to melting out of basitic magmas of still lesser alkalinity, etc. This stipulated
corresponding lateral zoning in the magmatic rocks composition.
A.V.Vikulin, A.G.Ivanchin
The rotational model of the seismic process
The paper shows that the author’s rotational model for the source of the largest
earthquake can be applied to the description of the Pacific seismic process. The
analytical expression for the energy of focal block interaction has been obtained. An
explanation is presented for the spectra of velocities of seismicity migration. It is also
shown that the known dislocation models for the source of a tectonic earthquake are an
extreme situation for the rotational model when the interaction of the blocks-sources can
be neglected. The employment of the rotational model for the purpose of studying tectonic
movement is also suggested.
M.N.Luneva
Wave propagation througth a fractured medium: theory and experiment
The analysis of elastic wave propagation through isotropic media with parallel
fractures under static stress in a range from 1 MPa to 24 MPa and for various material
saturating the fractures has been performed. The study was based on the comparison of the
experimental ultrasonic data published with the theory of wave propagation in the medium
composed of thin isotropic layers with non-rigid contact between them. Plots of phase
velocity, ray velocity, slowness vectors and polarization vectors of three body waves were
constructed as functions of the azimuthal angle for various static stress of the medium.
The normal and tangential impedances , which define the resistance of layers to
displacements relative to each other, were estimated as a function of acting pressure. It
was shown that the maximum value of ratio corresponds to the maximum anisotropy degree of
medium and compliance of layers to slip displacements, and the case testifies that the
medium properties are close to isotropy. For an oil saturated medium, a viscosity
coefficient and wave attenuation were estimated.
Yu.F.Manilov
Evaluation of the effect of density heterogeneities in the upper part of the crust
by deep gravimetrical studies (as exemplified by deep seismic sounding profiles of
Priamurie)
The effect of subsurface petrodensity heterogeneities is evaluated when studying deep
structure. A nomogram was plotted to determine the minimum boundary heterogeneity
parameters starting from which the above heterogeneities are to be taken into account when
carrying out different-scale deep investigations. The necessity of mapping deep interfaces
with reference to the subsurface heterogeneities is illustrated by the Zeya R. - Bureya R.
seismogravitational profile. The dependence Dgîñò =f(Hìî) obtained on the Zeya R. -
Bureya R. profile allows us to estimate the depths to the Moho boundary on the adjacent
profile Svobodny - Komsomolsk and to compare the data obtained with those of deep seismic
sounding.
V.I.Isaev, N.A.Volkova
Evaluation of oil and gas potential of the Cretaceous deposits of the Central
Sakhalin fault zone from mathematical modeling results
On the basis of seismogravimetry data and mathematical modeling of the heat transfer
process in the conditions of sedimentation were produced sections, maps of density and
maximum paleotemperatures distribution in the Cretaceous deposits of Sakhalin South.
Forecast evaluation of oil and gas potential was provided for the Cretaceous sedimentary
complex of the Susunaisky basin in the zone of the Central Sakhalin fault.