RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES6002, doi:10.2205/2005ES000187, 2005

The Modern Structure and Formation Types of the South Tien Shan Region

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Figure 2
[4]  The southern segment of the South Tien Shan orogenic belt is a nappe-type fold belt of a divergent structure, which includes structural elements of different tectonic styles and different rocks [Leonov, 1996] which can be classified into at least three major types of structural and formation assemblages (Figure 2). The first type is represented by the zones of antivergent structure showing the anticlinal style of folding, the axial planes of the folds flattening from the middle of the fold to its limbs, the gentle overthrusts in the marginal parts of the zone, and with well developed axial cleavage. Classified as this type are the Zeravshan-Turkestan and Turkestan-Alai zones composed of thick Lower Paleozoic and Silurian terrigenous-argillaceous-carbonate sedimentary rocks, often showing a typical flysch appearance. With the exception of orogenic granitoids, volcanic and metamorphic rocks are almost absent in these zones.

[5]  The second type of the structural and formation assemblages, mapped in the Zeravshan-Gissar, Yagnob-Sugut, and Kan-Milisuy structural zones, is distinguished by the general synform structure, overthrusts and tectonic nappes, recumbent folds, flow texture and schistosity, as well as greenschist metamorphism. The synform zones are composed of Ordovician-Lower Carboniferous terrigenous, siliceous terrigenous, and siliceous-terrigenous-carbonate deposits. The siliceous terrigenous rocks often give way to the accumulation of basic volcanic rocks (tholeite basalts and the like). Also typical of these synform zones are the associations of basic volcanics and reef limestones. Associated with the synform zones are the outcrops of ultrabasic rocks and ophiolite melange. The synform zones are represented by two varieties: parauthochthonous and allochthonous ones represented by similar rock sequences, the allochthonous rocks being the tectonically detached rock masses of the para-autochthone type.

[6]  The third type is represented by narrow suture zones (Karakul-Zidda, Zeravshan, Naratau-Kurganak, Kulgedzha, to name but a few) with subvertical or steep fan-like arrangement of rock layers and structural elements. These zones show concentric dislocations and local dynamic metamorphism. No volcanic activity is recorded. Two types of suture zones have been identified. One of them is composed of relatively deep-sea carbonate and siliceous rocks (Devonian-Carboniferous), replaced upward by Late Paleozoic flysch and tectonic-gravitational mixtite bodies. The second type of the suture zones is distinguished by their terrigenous and terrigenous-carbonate deposits (Ordovician-Devonian), Carboniferous carbonate reef deposits, and Late Paleozoic molassoid block-conglomerate deposits. Associated with the suture zones are Mz-Kz basins filled with Jurassic-Eocene platform deposits and Neogene-Quaternary molasse rocks.

[7]  The cross sections of the nappe-fold structural feature show the alternation of the zones of these different types. The zones of the two former (synclinorium and anticlinorium) types contact one another along the systems of head-on overthrusts, or are separated by narrow subvertical zones of the third type. Both the interior parts of the zones and their contacts show nappes and overthrusts, though no huge surface overthrusts, accompanied by the large-magnitude overlaps of the rocks of some zones over the other, are characteristic of the South Tien Shan Belt. The exception is the northern margin of the region (the piedmont of the Alai Range and the Nuratau Mts. yet even in these regions the nappe magnitudes are not greater that 10-20 km, the overthrusting showing a head-on direction.


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Citation: Leonov, M. G. (2005), The Post-Oceanic Geodynamics of the South Tien Shan Region, Russ. J. Earth Sci., 7, ES6002, doi:10.2205/2005ES000187.

Copyright 2005 by the Russian Journal of Earth Sciences

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