Volume 26, 2, 2007
|
|
Volume 26, 2, 2007 |
|
Yu.F. Malyshev, V.Ya. Podgorny,
B.F. Shevchenko, N.P. Romanovsky, V.B. Kaplun, P.Yu. Gornov
Deep structure of the bounding zone structures of the Amur lithospheric plate
The deep structure of the bounding zone structures of the Amur plate has been
studied. Seismogravity (density) and geoelectrical sections of the lithosphere
have been constructed which cross the geologically and seismically distinguished
plate boundaries, and the three-dimensional model of the Amur plate lithosphere
has also been produced. The model has a structure close to the ring one with a
relatively subsided for 50 km and a more inner part, and uplifted framing. The
framing of the lithospheric structure is represented by the orogenic belts (Mongol-Okhotsk,
Selenga-Stanovoy, Transbaikal, and Sikhote-Alin) and margins of the Siberian and
North China platforms. The plate boundaries are characterized by models of
mantle diapirism with mainly a two-sided oblique dip of the bounding zone
structures of the framing belts.
A.A. Shchetnikov
Morphotectogenesis of lacustrine basins of the Baikal rift zone
The mechanisms of formation and the peculiarities of development of tectonically
governed lacustrine basins of the Baikal rift zone are examined. They are
represented in great quantity and morphogenetic variety. Their regional
classification is suggested, and representatives of all varieties of lacustrine
basins are characterized.
R.A.
Kemkina
Fahlores of the Prasolovka volcanogenic Au-Ag deposit (Kunashir Island, Russian
Far East)
Based on the electron microprobe analyses data, the complex and variable
chemical composition of fahlores from the Prasolovka ore deposit has been
established. The fahlores are characterized by significant variations of the
chemical elements composing them and by a quantitative ratio of the latter.
Based on the differences of the fahlore chemical composition, three mineral
kinds and eleven intra-kind and inter-kind varieties are distinguished. The
results of the comparison of the fahlore chemical composition and the
confinement of the fahlores to certain mineral associations in different ore
types allow the conclusion that during ore formation the generation of
essentially arsenic fahlores was replaced by an antimony-rich generation, then
by a tellurium-bearing antimony-rich generation, and still then, by a
tellurium-rich one. The revealed evolution of the ore-forming solutions from the
early to the late stages testifies of different physical-chemical conditions of
formation of various mineral ore types at the Prasolovka deposit.
L.F. Simanenko
Forms of occurrence of admixtures in galena of the Partizansky base-metal skarn
deposit (Primorye)
This article concerns compositional peculiarities and mode of occurrence of
galena from the Partizansky base-metal skarn deposit as exemplified by two
orebodies – the Second Contact orebody and the Bol’nichny lode. The base-metal
skarn ore at the Partizansky deposit was formed during two stages: base-metal
skarn and silver-sulfosalt. The great bulk of galena was deposited at the first
stage and occurs within the productive galena-sphalerite assemblage. In the
Second Contact orebody, galena of the productive assemblage is well
distinguished by its impurity composition depending on the depth of the
assemblage occurrence. Galena from the root zone of the orebodies (the level of
-135 m) is characterized by stable high concentrations of both isomorphic and
nonisomorphic admixtures of silver and bismuth. In the middle horizons of the
orebody, galena is practically free of admixtures structurally bound in solid
solutions and has some microscopic inclusions of Ag-bearing minerals (basically,
Ag-tetrahedrite). In the uppermost horizon (the level of + 285 m), inclusions of
various silver minerals related to the late silver-sulfosalt stage of
mineralization are abundant in galena. In the Bol’nichny lode at a great
interval of its occurrence, galena is characterized by higher concentrations of
isomorphic silver and bismuth, and it also contains abundant inclusions of
native bismuth.
A.Yu. Antonov
Geochemistry and petrology of Mesozoic-Cenozoic magmatic formations of the Aldan
shield southern framing. The problems of geodynamics
The paper gives a brief summary of the results of long-term geological,
geochemical and petrological investigations of the Mesozoic-Cenozoic magmatic
formations of the Stanovoy Range aimed at identification of the main causes of
their origin and evolution. The analysis of the materials shows that the
compositionally widely varying magmatic formations of the Stanovoy Range formed
in the different facies of depth (from abyssal to surficial). Compositionally,
most salic formations among them change insignificantly, but mafic formations
vary strongly, primarily in the south-eastern part of the region. Incidentally,
both the subalkaline and low-alkaline magmatic formations are just about equally
manifested in the south-eastern part of the Stanovoy Range; subalkaline
varieties predominate in its central part, and only the shoshonite-latite series
is known on the north-west. This zoning is fundamentally different from “island
arc” zoning, because in the latter case each zone shows equitype volcanic rocks
with respect to alkalinity. The effusive and intrusive assemblages of almost the
same alkalinity and SiO2-abundant (as well as shliren enclaves in the regional
granitoids) formed from the same magmas of corresponding composition. Besides,
both mafic and most salic magmas formed there as a result of independent melts,
but intermediate magmas formed mainly due to mixing of contrasting magmas, that
is, basic and salic magmas.
The available material on the regional magmatism is best interpreted in the
context of the mantle diapirism model. Thus, in Mesozoic time mantle diapirs
uplifted rather slowly; incidentally, in the Jurassic-Cretaceous (J3-K1) period
they uplifted over the entire Stanovoy Range territory generating alkaline and
subalkaline basalts. However, in the Early-Later Cretaceous (K1-K2) period, in
the central and eastern parts they were forming low-alkaline basalts. However,
in the Cenozoic period the diapir rose rather quickly only in a small eastern
part of the region and formed alkaline basalts. Unlike Cenozoic diapirs,
Mesozoic diapirs and mafic magmas influenced actively the Earth’s crust
formations, bringing them to their fluid transformation and then, to fusion from
them of huge volumes of salic magmas of corresponding composition that
consequently interacted and mixed with mafic magmas and formed corresponding
material zoning. At the same time, a maximum of the formation of crust magmas
falls on the axial areas of the diaphirs rise, where the energetic effect is
maximal. Autochthonous gneiss-granitoids (different from intrusive formations)
formed more often at a distance from this axis.
O.P. Smekalin,
A.V. Chipizubov, V.S. Imaev, V.M. Besstrashnov, A.I. Melnikov
Paleoseismogeological investigations of the Kichera fault zone ( the northern
Pribaikalye)
The Kichera fault forms the north-western margin of the Angara-Kichera
accumulative depression in the Baikal rift modern structure. A seismotectonic
scarp up to 60 m high has been formed by fault motions during Late Pleistocene–Holocene
time. The analysis of the development of erosive-accumulative and seismic
genesis landforms is evidence of irregularity of the scarp growth in time. We
excavated two trenches that crossed the scarp with the purpose of studying the
direction of the seismic process in the Kichera fault zone. The Holocene stage
of seismotectonic activation in the fault zone with the preceding period of
relative calm was established based on the character of deformations in the
trench sections and from the earlier results of morphological studies. According
to our preliminary estimations, the activity of the stage that started at the
end of the Late Pleistocene and has been not completed by the present time was
accompanied at least by three large paleoearthquakes with vertical displacement
of 3 m per the most resent event.
A.V. Konovalov,
A.I. Ivashchenko, Kim Jung Woon, A.S. Sychev
The structure and features of seismic
regime of the Takoe earthquake focus zone, September 1, 2001 (MW 5.2)
The Takoe earthquake (MW 5.2) which occurred on September 1, 2001 in
the en echelon junction zone of two segments of the Aprelovsky fault was
accompanied with a swarm of earthquakes that were successfully registered by the
local system of digital seismic stations located in the southern part of
Sakhalin Island. A system of up-to-date methods used in the process allowed a
redistribution of foci parameters for the earthquake swarm and substantial
detailing of their spatial distribution and of relations with the
structural-geological features of the complex system of interacting faults. New
evidence was obtained regarding the relation between the foci mechanism and the
present-day geodynamic setting in Southern Sakhalin.
B.V.Levin, Kim Jung Woon,
I.N.Tikhonov
The August 17(18), 2006, Gornozavodsk earthquake on Southern Sakhalin
Some anomalous seismological and geophysical phenomena before the 17(18), 2006,
Gornozavodsk earthquake (MW = 5.6) in the south-western part of
Sakhalin Island are revealed and analyzed. A large volume of digital seismic
station data was processed to investigate the dynamics of aftershock process
development during one day after the main event. Various effects of this
earthquake are described.