Volume 24, 4, 2005
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Volume 24, 4, 2005 |
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G.V. Roganov, G.L. Kirillova,
V.V. Kiriyanova, N.D. Litvinenko
Sedimentological peculiarities and biota of the J/K transional
deposits in the epicontinental basins of Russian Priamurie
This paper deals with the transitional Jurassic to Cretaceous deposits of the
continental basins in Priamurie that were formed after the collision between the
Siberian and North China cratons. The collision processes of this region
progressed from west to east, like as closing scissors. The emplacement of the
191 Ma post-collisional granites suggest a late Early Jurassic collision in
Upper Priamurie, while the development of the Early/Middle Jurassic accretionary
turbidite complex indicates the late Middle Jurassic collision in West
Priokhotie. This event is represented as the change from a shallow
coastal-marine environment with crinoids to a regime of extensive alluvial
plains, often characterized by bog-coal. The environmental change is supported
by the change in biota.
The chronostratigraphic succession of the continental deposits of Priamurie is
based mostly on floral associations (spore/pollen assemblages) in alternating
marine and non-marine beds enabling to clarify the chronostratigraphic
succession of floral associations and illustrate the possibility of their
application for disjunction and correlation of the continental beds in Priamurie.
It has been further established that environmental change from coastal-marine to
continental took place in the residual post-collisional sublatitudinal basins in
the Upper Amur and Dep basins during the late Middle Jurassic and in the Uda and
Torom basins during the Berriasian-Valanginian.
Further south, in the rift basins of Bureya and Partizansk, the similar change
started in the late Kimmeridgian and Hauterivian times, respectively.
Thought frequent during the Middle Jurassic-Neocomian interval, most substantial
changes of the ecosystem occurred at the J/K boundary.
Yu.D. Markov, A.V. Mozherovsky,
V.S. Pushkar, N.G. Vashchenkova, V.P. Nechaev
Sedimentation features and stratigraphical correlation of
nonconsolidated deposits of the Clarion transform fault zone (north-eastern part
of the Pacific Ocean
Based on materials of underwater studies, new data on the lithology and
stratigraphy of Cenozoic sediments of the Clarion transform fault zone (Pacific
Ocean) are offered. It was established that on different blocks (uplifted and
subsided) of the tectonic structure under the same name occur different age
deposits (Eocene to Quaternary). Nonconsolidated sediments have been deposited
in the pelagic conditions since the Eocene (probably, since the Early Cretaceous)
till now. Their mineralogical composition and content of different ore
components are given.
M. N. Luneva
Temporal variations of wave
parameters of small local earthquakes with similar hypocentral location in
southeastern Kamchatka
Seismic wave parameter measurements of local earthquakes of similar locations
(clusters) are used to determine stress-strain state changes with time. The
local small seismic events recorded at the PET IRIS station (Petropavlovsk-Kamchatsky
City) for the period of 1993-2002 were analyzed. Waveforms of the crust event
cluster show comparatively good similarity with cross-correlation coefficients
higher than 0.8 with the exception of the event happened during the aftershock
period of the Kronotsky Earthquake (M7.8, 05.12.97). At the same time, temporal
changes of relative amplitudes of converted and multiple waves are detected.
Waveform instability is more typical of the event clusters of 90-110 km depths.
The most significant variations are observed for the fast azimuths, split shear
wave time delays and amplitude ratio between direct P and fast S waves. A
tendency of cyclic variation in fast azimuths and shear wave splitting time
delays with time is observed.
M.Yu. Nosyrev
Velocity anomalies in the Earth?s crust of Priamurye, and distribution
of gold ore mineralization
The anomalies of the velocity ratio of P waves in the Earth?s crust and S waves
in the Amur Region and western part of the Khabarovsk Territory are considered.
Spatial relationships have been established between the gold ore districts and
individual deposits, and the areas of anomalous velocity characteristics in the
Earth?s crust. It has been inferred that the anomaly data register blocks of the
Earth?s crust with a high degree of tectonic disturbance; these blocks could
serve as channels of heat and mass transfer at the stage of ore formation.
L.V. Eirish, A.P. Sorokin
The primary sources of gold placers in the Russian Far East, and the degree
of their erosion
The level of the erosional truncation of the gold placer sources distinguishes
three groups of gold-bearing districts: ore, ore-placer, and placer districts.
The first are insignificantly eroded, and the placers are poorly developed
there. The second group is characterized by medium-scale erosion, and it
contains rich and large placers. In the third group of districts the ore
deposits are deeply eroded. Their placers are numerous and often large, and they
formed mainly at the expense of rewashing of Neogene-Quaternary deposits of
depressions and high terraces.
The maximal placer-forming potential is peculiar to gold ore deposits of the
low-sulfide gold-quartz formation located in the dioritoid (gabbroid,
monzonitoid) stocks and in the vein-streaky zones of fold black shale complexes.
The minimal significance in gold placer formation is attributed to deposits of
the subvolcanic type.
Placer formation is forced by ore metamorphism (gold increases in size and
becomes ennobled), post-ore fracturing, and physical-and-chemical crust
formation.
A.S. Karetnikov
The problem of age definition of the Kondyor massif
Direct geological observations access the age of the Kondyor massif (geographic
coordinates 57°36'N and 134°37'E) as only post-Archean. This paper offers the
analysis of geochronological data on the massif obtained for ultrabasites and
associated magmatites using different isotopic systems. Besides, the age defined
on the basis of paleomagnetic characteristics of dunites ? one of the two (dunites
and clinopyroxenites) most ancient varieties of the massif ultrabasic rocks,
enabled the author to draw an inference that the age of the massif is Late
Riphean. However, datings obtained for ultrabasites from isotopic systems
suggesting either their Paleozoic or Mesozoic age do not give evidence of the
rock age (in the final analysis, age of the massif) but rather of the moments of
time of progress of two stages of postcrystallization activation that were
recognized for Kondyor. They are supported by determinations from the results of
paleomagnetic investigations of dunites.
G.F. Ufimtsev
Morphotectonics of the south-western frontal slope of the high
Himalayas
The contemporary Himalayan orogeny is a complex combination of thrust-and-nappe tectonics and fold deformations, which are apparently accompanied with gravitational shifts, and also with a specific process of the south-westward motion of the gently sloping monoclinal plates; due to this process a system of high-mountain cuesta-like horsts-Himals formed within the allochthon of the Main Central Thrust, which are bounded from the south-west by steep frontal walls ? 3 km high. Given its great significance, the process of the south-westward extension and upward protrusion of the massifs-Himals occurs due to movements along the stratigraphic and interformational boundaries, and thus it does not disturb the essentially formed geologic structure. However, it favors the reduction of horizontal dimensions of the upper lithospheric slabs in the conditions of lateral contraction and the transfer of great masses of matter into the sphere of activity of exogenic processes.