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Biomes and Regions of Northern Eurasia
The Mountains of Central Asia and Kazakhstan
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The Formation and Morphology of the Mountains
The tectonic history of the Central Asian mountains is given in Zonenshain et al.
(1990). The contemporary tectonic pattern of the Central Asian mountains as well as their
seismicity originate from the continental collision between India and Eurasia (Figure
14.1).
Fig. 14.1 Lithosphere plates and microplates of Inner Asia. After
Zonenshain and Savostin (1981)
The initial collision occurred in the late Cretaceous, replacing simple subduction of
the Tethys oceanic lithosphere below the Eurasian Plate (Molnar and Tapponier, 1975). The
most intensive stage of collision manifested itself as the Alpine orogenic epoch which
began in the Miocene. The Alpine folding was extensive both in terms of duration and the
complexity of tectonic movements and, although it occurred everywhere, its manifestation
varied regionally. In the northern chains, the Alpine folding was relatively weak but its
intensity increased southwards, reaching its maximum in the Pamirs. The Pamirs and
Kopetdagh were formed as a result of the latest collision. By contrast, the Tien-Shan and
mountains of Kazakhstan are of an older age: they were formed by the convergence and
collision of the Siberian continent with the ancient massifs located south of the
continent; eroded, being transformed into a peneplain of the Kazakh Knolls type, and
rejuvenated in the Cenozoic. The formation of a peneplain and subsequent uplift had a
strong effect on the modern topography of the Tien-Shan, Dzhungarsky Alatau, Saur, and
Tarbagatay which is characterized by the occurrence of high elevation plateau-like and
inclined ancient denuded surfaces. The central (inner) Tien-Shan itself has an average
height of 3100 m and is encircled by the Terskey-Alatau, Kokshaal-Tau, and Fergana Ridges
with comparatively small relative elevations. Denuded surfaces often form high elevated
valleys covered by glacial and alluvial deposits termed in Turkic languages syrt.] Because
of their ubiquitous presence the central Tien-Shan is often referred to as the syrt
Tien-Shan. Typical of the Dzhungarsky Alatau, Saur, and Tarbagatay are plateaux which
occur at different heights, thereby giving the slopes a step-like appearance. Such
plateaux, which are ancient structures uplifted in the Neogene-Quaternary, occupy between
30 per cent and 40 per cent of the whole territory of these mountains.
The structure of the Pamirs results directly from the collision between India and
Eurasia and in this respect, the Pamirs are similar to the Himalayas. At present, in the
area of the Pamirs the Indian Plate moves at a rate of 4.4 cm a-1 relative to
Eurasia. While some of this movement is taken up by overthrusting in the Pemjab Himalayas,
the other half creates convergence between the Pamirs and Tien-Shan (Zonenshain et al,
1990). Geodetic measurements reveal a rate of convergence of 1.5-2.5 cm a-1
that makes it an area of extremely high seismic activity (Hamburger et al., 1992; 1993).
The Gissar-Alay deep fault, which extends along the southern slope of the Gissar Ridge and
further east along the valleys of the rivers Surkhob and Kyzylsu, mark a boundary between
the two structures and is an area of particularly devastating earthquakes. The territory
located south of the Gissar-Alay system is tectonically inhomogeneous and includes three
major zones: the Tajik depression which represents a deeply submerged Mesozoic-Cenozoic
sedimentary basin, the western Pamir (often considered together with the Zaalaysky Ridge),
and eastern Pamir which represents an active continental margin. Although both western and
eastern Pamir are characterized by great absolute heights, their topography is very
different. The fast and irregular upheaval and the continuing subsidence of the large
depressions (i.e., the Fergana valley and Tajik depression) predetermines a youthful
character of relief in the western Pamir which is characterized by large relative
elevations and narrow valleys with steep slopes. The highest summit in the FSU, the Peak
of Communism (also known as Garmo) (7482 m) and the largest alpine (Fedchenko) glacier are
located in the western Pamir on the junction of the Peter the First and Academy of
Sciences Ridges. The eastern Pamir2 has the character of a highly elevated plateau (Plate
16.1).
Plate 16.1 Lake Karakul in the eastern Pamir (photo: I. Merzlyakova)
The ancient relief has survived here in the form of vast flat valleys elevated to the
height of 3500-4500 m on which permafrost develops. Locally, these valleys are called
pamirs (meaning 'roof of the world'), the term which has given the region its name
(Svarichevskaya, 1965). Relative elevations are often comparatively small, about 1-1.5 km.
Within Turkmenistan lies the northern periphery of the Kopetdagh mountains which
continue into Iran. The mountains are regarded as a fold chain that originated on the
former passive margin due to the late Cenozoic motion of the Iranian block relative to
Eurasia (Zonenshain et al., 1990). The Kopetdagh is not a single ridge but a system of
mountainous chains (whose peaks do not exceed 3000 m) separated by the narrow valleys with
an west-east orientation.
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