RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 10, ES1006, doi:10.2205/2007ES000223, 2008

Introduction

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Figure 1
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Figure 2
[2]  The Tien Shan is a Paleozoic folded area. The southern Tien Shan is composed of rocks of the Paleozoic Alay-Tarim continent (Figures 1 and 2) that is separated by the Turkestan oceanic basin suture from Paleozoic rocks of the so-called Kyrgyz or Kazakh-Kyrgyz microcontinent [Burtman, 1997, 2006a, 2006b]. In the Late Paleozoic, oceanic crust rocks of the Turkestan basin and sediments that accumulated at its margins were overthrusted onto the Alay-Tarim continent and nowadays form nappe ensembles in the southern Tien Shan. These nappes are the greatest Paleozoic nappes known in Asia.

[3]  By the early 1960s thrust faults that separated different facies of synchronous sediments were described in the Alay and Turkestan ranges, southern Tien Shan, on limbs of large synclines [Porshnyakov, 1960, 1962]. Studies of thrust faults in that and other southern Tien Shan regions suggest that they represent fragments of a multilayered Late Paleozoic nappe ensemble that covered a vast territory [Burtman, 1968, 1970; Burtman and Klishevich, 1971]. Nappes from different southern Tien Shan regions were described in books by Biske [1996], Biske et al. [1982, 1985], Burtman [1973, 1976, 2006a], Mukhin et al. [1991], and in many papers. Russian book by Burtman [2006a] and this paper discuss the nappe distribution throughout the southern Tien Shan.

Methods.
[4]  Nappe ensembles consist of several or numerous allochthonous thrust sheets separated by overthrust faults. They are described in successive units overlying each other in the composite geologic section. The structural units differ in composition of sediments that accumulated in various geotectonic environments, namely, on shelf, continental slope, in accretionary prism, and others. A unit is composed of rocks of an initial mono- or polyfacies zone.

[5]  Geologic sections of the area include ten or more allochthonous thrust sheets. In multilayered tectonic ensembles the sheets formed by rocks of similar composition and genesis are repeated several times in the geologic section.

[6]  In the proposed model of southern Tien Shan nappes we distinguish primary and secondary overthrust faults. Primary overthrust faults separate tectonic sheets composed of rocks that were formed in different, mainly adjacent tectonic environments, for instance, on shelf and continental slope. Primary overthrust faults represent unit boundaries. Secondary overthrust faults twin the sets of tectonic sheets in the geologic section. They complicate the nappe ensemble structure and internal structure of the units. Tectonic sheets composed of rocks of the same origin and age are referred to a single unit independently of their position in geologic sections that are commonly deformed by secondary overthrust faults. The reconstructed position of units, which they occupied prior to overthrusting, appears as a natural succession of facies zones on continental margins and in oceanic basins.

[7]  Rocks of the structural units comprise tectonic sheets, windows, and sheet fragments of different origin: tectonic slices, klippes, tectonic mélange blocks, and olistoplaques and olistoliths in olistostromes. Position of these fragments is commonly a debated topic. On describing a complicated nappe structure in the Tien Shan the generalized term "oreade'' is convenient for designation of unit parts and fragments independently of their position and mode of setting apart (oreades are nymphs of mountains and rocks in ancient Greek myths).

[8]  It is appropriate to begin the discussion of southern Tien Shan nappes from the western Tien Shan where they are better studied.


RJES

Citation: Burtman, V. S. (2008), Nappes of the southern Tien Shan, Russ. J. Earth Sci., 10, ES1006, doi:10.2205/2007ES000223.

Copyright 2008 by the Russian Journal of Earth Sciences

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