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Mountains of the Sikhote Alin and East Manchurian mountainous regions occupy
Seventy-five percent of Primorye. The rest of the territory is essentially
flatland, including the Razdolnoye-Khanka Plain and some intermontane depressions.
Structurally, the Razdolnoye-Khanka plain represents an intemontane depression
that separates the said mountain regions, the intermontane depressions
being concentrated along the boundaries of zones and subzones of
mountain regions. Several morphogenetic types of relief form the Sikhote
Alin mountain region.
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The Sikhote Alin chain with peaks
of parates the Japan and Okhotsk Sea
basins.
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The time of Sikhote Alin’s active formation and build up of relief heights is associated with the introduction of magmas a volcanic eruptions in Late Cretaceous and Early Paleogene. That is when the system of magmatogenic domal structures formed. |
In Cenozoic, the relief’s heights
continued to grow and the territory to rise to form against this background
in relatively narrow transversal linear zones as the Verkhneussuri, Zerkalnin,
Maximov, Verkhnebikin and other Cenozoic depressions.
The Zeva-Dagdy, Adinsk, Edinkin, Samarga
and smaller volcanic volcanic plateaus of Pliocene and Pliocene-Quarternary
time cross the ridge in sublatitudinal directions to pass from its western
zone to its eastern zone.
A system of medium-low altitude (up to 1,500
m high) and low-altitude (up to 1,000 m high) massifs and their groups,
which formed in introduction of Upper Cretaceous granitoids and in local
volcanic eruptions, extends parallel and to the west of Sikhote Alin.
The Cenozoic stage of geomorphogenesis showed in destruction of the marginal
sections of the massifs, to which narrow valleys of rivers flowing to the
northwest, southwest and west are assigned.
The Sikhote Alin chain and mountain massifs
are divided by intramontane settling of the relief, drained by such average
and big rivers as the Bikin (upper reaches), Kolumbe, Bolshaya Ussurka
(middle and upper reaches) and others. Here, magmatic activity was weak
to cause appreciable increase in relief altitudes. In sites, where magmatic
activity was more intensive, sections of river valleys are of antecedent
nature.
The low Vostochnyi Sinii, Kholodnyi and
several smaller ranges extend alongside low and medium mountain massifs,
being separated from them by intramontane depressions of undoubtedly Cenozoic
age. These are primarily the Srednebikinskaya, Marevskaya and several smaller
depressions. Again, these also include the already known small blankets
of Pliocene basalts. The forming of Vostochny Sinii range is associated
with volcanic activity of Late Cretaceous-Early Paleocene with subsequent
block deformations in Cenozoic. The Kholodnyi range formed
in introduction of minor single Upper Cretaceous intrusions and intensive
block movements in Cenozoic. Extending along the western boundary of the
range zone described above is a system of intramontane Cenozoic depressions,
the largest of which are Arsenievskaya, Khvischanskaya, Malinovskaya and
Orekhovskaya.
Sinii range is the westernmost element of
the Sikhote Alin Mountain region. This low, occasionally low altitude (300-500
m) structure formed for a long time, but especially in Neocene-Quarternary
time under compression and ejection of this narrow (5-15 km) block, restricted
by ejection, showing in the relief as benches and abrupt folding of the
geomorpholgical surface. Low-altitude sites in the range were subjected
to ascending movements of lesser intensity and are to some extent relicts
of Pre-Upper Cretaceous relief.
Uplands and plateau-like surfaces are characteristic
of the basins of Alchan and Bikin (lower reaches) Rivers. They alternate
with narrow faults, relicts of relief development in Cretaceous. Isolated
small extrusive, volcanic and volcanoplutonic domes, whose altitudes grow
as one moves northward, hover over flat and plateau-like surfaces.
The Strelnikovsky low-mountain range extends
along the northwestern boundary of Primorye. With regard to conditions
in which it formed, it is reminiscent of Sinii, Vostochnyi Sinii and Kholodnyi
ranges.
The Nizhnebikin and Alchan intramontane
depressions formed in Cenozoic. Today, they are involved in a weak elevation,
their surfaces breaking up intensely. Relicts of basalt plateaus evidence
this.
The southern section of Sikhote Alin Mountain
region is represented by the low Przhevalsk and Livadia ranges and by the
southern tip of the Sikhote Alin and Makarov ranges. The same zone incorporates
the Shkotovo basalt plateau of Pliocene age. The ranges are separated relief
depressions, occupied by river valleys of high order of magnitude. Pliocene-Quarternary
low-altitude swell-like elevations are situated on boundaries with Cenozoic
depressions.
So, the mountain country of Sikhote Alin
consists of a series of anticline-block faulting ranges divided by intramontane
depressions, mostly of Cenozoic age. Transversal zoning is associated with
Cenozoic disjunctive structures, but their laying site was predetermined
by earlier events. A combination of diagonal and orthogonal disjunctive
zones created Sikhote Alin’s vesicular structure. Fault zones form the
section boundaries, and their massive central zones have maximal altitudes.
These very elements determine the overall stability of the mountain region,
and that of its elements and blocks.
The East Manchurian mountain region passes
into Primorye only with its eastern ridges. These are the low-altitude
Pogranichnyi and Chernye Gory block ranges and the Borisov basalt plateau.
The ranges are of Late Neocene-Quarternary age, this being evidenced a
whole series of events, and the most important of which are relicts of
the Cenozoic depression bonnet that occupies the highest relief sections.
The Borisov plateau represents a dome (radius 40-50 km) with flattened
central one (up to 5), sloping (10-20) intermediate zone and flat (fewer
than 5) marginal zone. The mountain chains articulate with adjacent depressions
along benches and abrupt slope folding, and an intermontane plain smoothly
changes the plateau.
The Razdolnoye-Khanka intermontane depression
is a plain that extends from the lower reaches of Tumangan River to the
estuary of Bolshaya Ussurka River. The Nizhnebikin depression is located
over its extension. The flatland section of the intermontane depression
occupies the lower geomorphological stage. These are baths of Amur Bay,
Lake Khanka and Posiet Bay with its inlets, bogged spaces in their coastal
sections. Here, younger ones bury Paleocene, Neocene, Lower- and Middle-Quarternary
deposits.
The surface of the intermediate geomorphologic
stage is ridgy and occasionally complicated by individual mounds or groups
of mounds. These are usually uplifts, residual rocks that separate Cenozoic
depressions, grabens and graben synclines formed by loose and weakly cemented
Paleocene and Neocene sedimentary and sedimentary-volcanogenic rocks with
brown coal beds of workable thickness.
The relief of the upper geomorphologic stage
of the intermontane depression is composed of mounds and rare ridges, small
hills and little mountains. Relicts of Cenozoic depressions are represented
by graben-synclines, moulds and flat declivities with thin hood, chiefly
composed of Neocene rocks. The Khorol low-hill ridge separates the Khanka
group of depressions from the Razdolnoye depression. There is also a low-mountain
bridge between the Slavianka and Khasan group of depressions.
Ruins of Cenozoic volcano-tectonic structures,
most of them under sea level, still show along the western coast of Amur
Bay and Possiet Bay. Centers of volcanic activity are known to exist along
the entire intermontane depression, which formed in the regional Ussuri
plutonic fault. It is active today, too, this being evidenced by earthquake
centers. The Baranov volcano, prepared by Razdolnaya River, is an example.
In Quarternary, the lower geomorphologic
stage submerged and is apparently submerging today. The upper geomorphologic
stage is rising and is quite active in places. The intermediate stage plays
the role of a hinge, its movements being low amplitude and randomly directed.
Along the coastline of Peter the Great Bay and the Sea of Japan in the
east of Primorye, a narrow strip of low-altitude and hilly relief stretches,
its formation being closely associated with the Japan Sea depression. Tectonically,
this zone is now more active than the Sikhote Alin Mountain region.
Primorye’s relief is perpetually changing.
In some places quite actively, in others less actively. Here, we have briefly
characterized only its macro- and certain mesoforms, whose destruction
by exogenous processes (from above) depends on numerous factors, including
the climate, which did not play a special part in the formation of the
forms described above. Groupings of relief microforms and their types and
forms, formation rates and life are essentially varied, but nonetheless
closely related with macro- and mesoforms.
The Sikhote Alin, East Manchurian and Razdolnaya-Khanka
macroforms form the basic relief background. Mesoforms (zones and geomorphologic
stages) are its structural framework called cells. Microforms are the pattern
with which nature has “decorated” mesoforms. Macroforms may be observed
from space, mesoforms from bird’s eyeview or in panorama forms. Some microforms
may even be covered with your palm. Relief microforms may be handmade and,
if done sensibly, would serve mankind; and if not, would take “revenge”.
S. TASCHI, Candidate of Science (Geology and
Mineralogy), Leading Research Fellow, Laboratory of Geomorphology,
Pacific Institute of Geography,
Far East Branch, Russian Academy of Science.