Underthrusting of Tarim beneath the Tien Shan and ... - Springer Link

ISSN 00168521, Geotectonics, 2010, Vol. 44, No. 2, pp. 102–126. © Pleiades Publishing, Inc., 2010. Original Russian Text © V.I. Makarov, D.V. Alekseev, V.Yu. Batalev, E.A. Bataleva, I.V. Belyaev, V.D. Bragin, N.T. Dergunov, N.N. Efimova, M.G. Leonov, L.M. Munirova, A.D. Pavlenkin, S. Roecker, Yu.V. Roslov, A.K. Rybin, G.G. Shchelochkov, 2010, published in Geotektonika, 2010, Vol. 44, No. 2, pp. 23–42.

Underthrusting of Tarim beneath the Tien Shan and Deep Structure of Their Junction Zone: Main Results of Seismic Experiment along MANAS Profile Kashgar–SongKöl V. I. Makarova, D. V. Alekseevb, V. Yu. Batalevc, E. A. Batalevac, I. V. Belyaevd, V. D. Braginc, N. T. Dergunovd, N. N. Efimovad, M. G. Leonovb, L. M. Munirovae, A. D. Pavlenkinf, S. Roeckerg, Yu. V. Roslovd, A. K. Rybinc, and G. G. Shchelochkovc a

Sergeev Institute of Environmental Geosciences, Russian Academy of Sciences, 13 Ulansky per., bldg. 2, Moscow, 101000 Russia email: [email protected] b Geological Institute (GIN), Russian Academy of Sciences, 7 Pyzhevskii per., Moscow, 119017 Russia cScientific Station, Russian Academy of Sciences, Bishkek49, 720049 Kyrgyzstan d FGUNPP Sevmorgeo, Ministry of Natural Resources of the Russian Federation, 36 ul. Rozenshteina, St. Petersburg, 198095 Russia e Pulkovo Seismic Station, Geophysical Survey, Russian Academy of Science, 65 Pulkovskoe sh., St. Petersburg, Russia f AllRussia Research Institute of Geology and Mineral Resources of the World Ocean, 1 Angliiskii pr., St. Petersburg, 190121 Russia g Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York, 121803590, USA Received May 18, 2009

Abstract—The results of reflection CMP seismic profiling of the Central Tien Shan in the meridional tract 75–76° E from Lake SongKöl in Kyrgyzstan to the town of Kashgar in China are considered. The seismic section demonstrating complex heterogeneous structure of the Earth’s crust and reflecting its nearhorizontal delamination with vertical and inclined zones of compositional and structural differentiation was constructed from processing of initial data of reflection CMP seismic profiling, earthquake convertedwave method (ECWM), and seismic tomography. The most important is the large zone of underthrusting of the Tarim Mas sif beneath the Tien Shan. DOI: 10.1134/S0016852110020020

INTRODUCTION In the current concept of the structure and evolu tion of the lithosphere and the Earth’s crust of Eurasia, much importance is attached to the collision of litho spheric plates. In this regard, crucial are the questions concerning the distance by which deformation propa gates from collision sutures to the interior of continen tal massifs; the mechanisms that provide such long range action; and the real structural elements created at different levels of the lithosphere. The vast region of High Asia, including the mountain systems of the Himalayas, Kunlun, Karakorum, Hindu Kush, Pam irs, Tien Shan, and Altai; the Tibet Plateau; and the intermontane Afghan–Tajik, Tarim, and Junggar basins are rather representative in this respect. The grandiose mountainbuilding deformations of the Earth’s crust in this region are deemed to be related to the Cenozoic collision of the Indian (IndoAustra lian) and Eurasian lithospheric plates. This idea was once stated by E. Argand [4] (Fig. 1). During the last

three decades, the basic paper by Molnar and Tappo nier [56] is the most widely quoted, supplemented by the paper by Cobbold and Davy [49]. Considerable data have been gathered and many possible interpretations of the deep structure have been published on the basis of various facts, approaches, and methods. The DDS data, regional seismology, gravity, and magnetic and thermal fields are sources of information on the deep structure. In the second half of the 20th century, deep research related to geological surveying and exploration have focused on the Pamir–Tien Shan region and have been conducted mainly in the Pamirs, Western Tien Shan, and northern zones of the Central Tien Shan (commonly called the Northern Tien Shan). The unique data along Toktogul–Osh–Srinagar and Kokand–Ishkashim geotraverses obtained in 1974– 1978 in the framework of the International Pamir– Himalayan project [16] should be noted. In addition to the above monograph prepared by Uzbek researchers, important data on the deep structure of Central Asia

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Fig. 1. Transverse section of the lithosphere in the region of converging Eurasia (2) and Gondwana (1) across the Central Asian segment, after [4]. Black is the sima and white is the sial of the continental blocks. The arrows indicate the direction of movements of each object relative to the other.

have been published by many other researchers [16, 17, 33 etc.]. Many geological and geophysical fea tures have been established (heterogeneous multilayer structure of the Earth’s crust in the Pamir–Tien Shan region in section and the block structure in plan view; its lateral and vertical heterogeneity in composition, structure, and velocity; the occurrence of three struc tural stages differing significantly in velocity charac teristics; the discontinuous and often arbitrary charac ter of the boundaries between the crustal layers and blocks; the variability of the velocity characteristics and thickness of the layers and their pinchout; the variable (from sharp to diffuse) character of the boundaries between the layers; and some other fea tures and patterns. The averaged Vp values and the thickness of the aforementioned crustal stages were estimated as follows: 5.8–6.4 km/s and 13–20 km; 6.4–6.8 km/s and 9–14 km; 6.8–7.4 km/s and 15–20 km. The refractor velocity of the M surface varies from 7.6 to 8.3 km/s with predominant values of 8.1–8.2 km/s [16]. This evidence characterizes the region of Pamir– Tien Shan collision (Penjab Syntaxis and Western Tien Shan), which differs principally from the region of conjugation of the Central and Eastern (Chinese) Tien Shan with the Tarim Platform Massif in the east. The latter territory remains poorly explored. On the basis of general concepts and geological data concerning largely the Late Cenozoic orogenic structure, the reverse–thrust junction of the Tien Shan with the Tarim accompanied by leftlateral strikeslip faulting has been suggested [19, 20, 49, 55]. The strikeslip component was inferred from the general structural relationships, including the enechelon arrangement of large and minor structural elements. Further, also on the basis of indirect evidence, it was specified that the Tarim Platform was underthrust beneath the Tien Shan rather than overthrust. The deep crustal structure in the south of the Central Tien Shan was deduced only by analogy with the Northern Tien Shan assum ing quasisymmetric divergent structure of the orogen [20, 24, 33]. GEOTECTONICS

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In the last 15–20 years, significant progress has resulted in an increasing number of scientific publica tions in the study of geology, deep structure, and geo dynamics of this key region. The substantial contribu tion of geophysical and seismological research should be noted in this respect. The works of Chinese special ists related to the discovery, exploration, and develop ment of the Tarim petroleum province are very effi cient [42], as well as their investigations carried out in Tibet in the framework of national projects and in cooperation with foreign scientists (see, for example, [58]). Seismological and seismotomographic studies of the lithosphere in the Northern and Central Tien Shan and adjacent territories performed in the last decade by Vinnik [6, 7, 62, 63], Roecker [54, 57, 63], and Shatsilov [26, 27, 37, 38] together with their col leagues should be pointed out as well. The joint efforts of Russian, American, Kyrgyz, and Chinese institutions under the international pro gram “Geodynamics of the Tien Shan” has resulted in implementation of joint and coordinated works aimed at active seismic sounding along the profile MANAS (Middle AsiaN Active Seismic profiling). The seismic line extends from Lake SongKöl in Kyrgyzstan to the town of Kashar in China through a corridor of merid ians 75–76.5° E and encompasses a latitudinal interval 39–42° N (Fig. 2). Its objective was to study the deep structure of the Earth’s crust and the uppermost man tle of the todate poorly explored southern part of the Central Tien Shan and its junction with the Tarim Platform. The Scientific Station of the Russian Acad emy of Sciences (RAS) in Bishkek, Kyrgyzstan; the Universtity of South Carolina; University of Califor nia at Riverside; and Rensselaer Polytechnic Institute in Troy, United States; FGUNPP Sevmorgeo, Minis try of Natural Resources of the Russian Federation; AllRussia Research Institute of Geology and Mineral Resources of the World Ocean; Institute of Environ mental Geosciences and Geological Institute, RAS; and Agency for Geology and Mineral Resources of Kyrgyzstan participated in the organization and con duction of these works in the Kyrgyz part of the Tien

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Shan. The works were supported by the Agency for Science and Innovation of the Russian Federation, Russian Foundation for Basic Research, and National Science Foundation (NSF) of the United States. The works in the Chinese segment of the profile were per formed by the Institute of Geology of the Chinese Academy of Geological Sciences and SINOPEC Exploration Company with the support of the Geolog ical Survey of the People’s Republic of China (project “Deep Structures in Junction Zones of Basins and Mountains”), NSF USA, National Natural Science Foundation of China, Ministry of Science and Tech nology of PRC, Open Fund of Geodetection Labora tory, Ministry of Education of PRC, and Chinese Uni versity of Geosciences. The initial data on the reflec tion CMP seismic profiling were accessible for participants of the project for further processing and interpretation along the entire seismic line. In this paper, we present the main results obtained throughout the profile by Russian specialists with the participation of American colleagues. The paper fills a gap in the proceedings of the fourth international sym posium on the geodynamics of intracontinental oro gens and geoenvironmental problems held in Bishkek, June 15–20, 2008, where these results were presented for the first time; the results were published in part a year later [40]. The first results of processing of the ini tial data on the Chinese segment of the profile were published in the proceedings of the symposium men tioned above [52]. BASIC FEATURES OF THE EARTH’S CRUST STRUCTURE ESTABLISHED BY PREVIOUS RESEARCH The information on the wellknown crustal ele ments presented below may be used for verification of the compositional, structural, and geodynamic inter pretation of the data obtained in the course of seismic experiments. These are the results of long and com prehensive systematic investigations integrated in many maps, publications, and openfile reports. Geological basement (ancient structural units). In terms of the previously accepted lithotectonic region alization of the Tien Shan, the profile transects fold regions of the Middle and Southern Tien Shan and attains the boundary of the Tarim Platform (often called the plate or massif) (Fig. 3). The first region includes the Late Caledonian, Middle and Late Her cynian fold zones, and the second region comprises the Early, Middle, and Late Hercynian zones. The older Precambrian and Caledonian complexes occur to the north, beyond the limits of this transect. The crystalline basement of the Tarim Platform is Sinian in age. The major boundaries between these regions have been identified as deep faults. The Nikolaev Tectonic Line extends via the district of Lake SongKöl; the At Bashy–Inylchek Fault is traced along the northern foothills of the AtBashy Range; and the South Tien

Shan dislocation system comprises the Maydantag, Muzduk, and other faults in the junction zone of the Tarim Platform and the Tien Shan. Subsequent studies based on the platetectonic concept have introduced substantial structural, his toric, and geodynamic corrections into the knowledge on the nature of the abovementioned zones. The lithotectonic grain of the region under consideration is now interpreted as a collage of tectonic nappes, which are relics of continental massifs differing in age, oceans, and transitional zones (see, for example, the section written by A.B. Bakirov and R.A. Maksumova in monograph [33] or papers [2, 3, 64]). From this standpoint, the Middle Tien Shan is considered to be a block of the Kazakh continent with Precambrian crust and Devonian and Carboniferous shelf facies, whereas the Southern Tien Shan is a large packet of tectonic sheets formed in the course of the Late Car boniferous subduction of the Turkestan paleoocean beneath the Kazakh continent and thrust over the Tarim margin at the end of Carboniferous and in the Early Permian. Allochthonous blocks of various types (ophiolites, metamorphic rocks, cherty–terrigenous and cherty–volcanic bathyal complexes, carbonate oceanic and shelf plateaus, etc.) are recognized therein. They make up extended bodies which under went boudinage and deformation into folds of several generations. In the south and the north, the fold– thrust belt of the Southern Tien Shan is rimmed by a foredeep and backarc trough formed as a result of early collision in the Late Carboniferous and Early Per mian. In the backarc trough, folding occurred at the mature stage of collision, beginning from the Asselian Age. The Tarim Platform is a Precambrian continental massif with Middle–Upper Paleozoic carbonate shelf and inner regions where Precambrian basement is overlain by thin Lower and Middle Paleozoic sedi mentary cover. Topography and recent tectonic structure. The Earth’s surface in the tract of the transect is character ized by highmountain topography typical of the arid belt of Central Asia. Eight mountain ranges extending in the latitudinal and eastnortheastern direction, the crests of which exceed 3500–4700 m in height, alter nate with basins variable in width and situated at a height of 1600–3500 m (Fig. 4). Their strike, discon tinuity, height, extent, width, steepness, asymmetry, junction of one another, depth, and erosion dissection are rather variable, depending to a great degree on the neotectonic deformation and crustal structure [19]. After the formation of a continental massif in the Mesozoic and Early Cenozoic, the geodynamic con ditions of this and the adjacent territories changed drastically. The Paleozoic and older lithotectonic complexes experienced deep denudation and plana tion with formation of peneplane as early as in Triassic. A reactivation of tectonic movements took place only in the Late Triassic–Early Jurassic. The development of shallow continental basins at the margins of the GEOTECTONICS

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Fig. 2. Location of MANAS transect. (1) Location of shotpoints along the transect; (2) rectified profile line; numerals indicate the distance from the southern end of the profile, km; (3) lake and river; (4) state border of Kyrgyzstan; (5) gap in profile; (6) location of stationary broadband recording systems. Letters denote those continuous segments of the profile for which reflec tion CMP sections are constructed.

future mountains was related to this event. Localiza tion of the basins shows that some features of the future neotectonic differentiation of the Tien Shan were outlined at this time, long before the collision of the Indian and Eurasian lithospheric plates [19, 21]. Further, up to the late Oligocene, the platform regime remained here and in the vast adjacent territories of Central Asia. The importance of this circumstance must be emphasized. This implies that a rather significant change in the state and structure of deepseated layers should have occurred over this longterm interval of structural evolution of the lithosphere. The regional GEOTECTONICS

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planation of the Paleozoic topography probably gave rise to a certain transformation of all deep lithospheric layers, including leveling of their interfaces and changes in thickness. It may be suggested that the crust of the Late Paleozoic mountains, like their present day counterparts, was thicker and more differentiated in comparison with the crust of the platform territo ries. In the epoch of Mesozoic–Early Cenozoic pla nation, its thickness probably was close to that of the epiPaleozoic Kazakh Shield situated to the north (35–40 km), i.e., was 20–25 km thinner than the crust of the presentday orogen and thinner than the Paleo zoic crust. If this was indeed the case, than the ques

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Fig. 3. Tectonic regionalization and structure of preCretaceous basement. (1–3) Northern Tien Shan: (1) Precambrian and Lower Paleozoic, (2) red sandstone and conglomerate of the Lower (upper part)–Upper (lower part) Carboniferous, (3) Famen nian and lower Tournaisian red beds and upper Tournaisian–Bashkirian turbidites; (4, 5) Middle Tien Shan: (4) Precambrian and Lower Paleozoic, (5) Givetian and Frasnian red beds and Famennian–lower Bashkirian carbonate rocks; (6–13) Southern Tien Shan: (6, 7) metamorphic rocks of (6) medium and high pressures and (7) low pressure, (8) Devonian–Lower Carboniferous cherts and basalts, (9, 10) carbonate rocks of isolated Silurian and Devonian seamounts, (11) Silurian, Devonian, and Carbonif erous pelagic cherts and shales, (12) Devonian and Carboniferous turbidites and cherts of continental slope and rise of the Tarim continent, (13) ophiolites; (14, 15) Tarim massif: (14) Middle and Upper Paleozoic mainly carbonate rocks of continental shelf, (15) inner regions of the massif; (16) Late Carboniferous subductionrelated volcanics in the Middle Tien Shan; (17) Upper Car boniferous and Permian terrigenous rocks (background color reflects character of basement); (18) Jurassic rocks of the Fergana– Yarkend Trough; (19) Late Paleozoic intrusions; (20) faults. Faults (numerals in circles): 1, Talas–Fergana; 2, Nikolaev Line; 3, AtBashy–Inylchek; 4, Maydantag (Kipchak); 5, Muzduk. Dark blue line denotes MANAS seismic line.

tion arises as to the contribution of Paleozoic and neo tectonic structural elements and processes to the presentday deep structure of the lithosphere beneath the Tien Shan and many other presentday mountain regions. This question must be kept in mind when the seismic crustal section is interpreted. The positive and negative warps of the ancient basement called basement folds [4, 11, 12, 19, 28, 31, 32, 36, 39] form the basis of the neotectonic structure of the studied region and the Tien Shan as a whole. These folds are largely linear and distinguished by a small curvature. The longitudinal reverse and thrust faults (often with a strikeslip component), oblique strikeslip faults, and much less abundant transverse normal faults and extension zones are conjugated with the folds. This structural assembly definitely indicates its development under conditions of nearmeridional lateral compression. It should be noted that the causeandeffect rela tionship between basement folds and faults remains a matter of debate. The once popular idea of the block nature of the uplifts and basins in the Tien Shan and their correspondence to the differentiated vertical motions of crustal blocks is unsupported by factual data and is now discarded. Two viewpoints are dis cussed: (1) Faults are secondary with respect to basement folds and complicate them at the late stages of struc tural evolution [4, 19, 31, 32, 36, 39]. (2) Folding expressed in topography and involving the ancient basement is a result of largescale thrusting (faultbend folding, faultrelated and thrustrelated folding, detachment folding [1, 43–47, 59, 61, 65]). Four neotectonic structural elements of the second order pertaining to the Central Tien Shan (except the mountain belt as a whole) are recognized in the sec 1

tion under consideration: (1) MoldoToo –Terskey AlaToo system of uplifts in the north (Fig. 4, D); (2) Naryn–AtBashy, or Naryn system of intermont ane troughs (Fig. 4, E); (3) AtBashy–KakshaalToo system of uplifts (Fig. 4, F); and (4) Pishan, or Kalpin tag piedmont step in the south as a system of linear 1 The

modern English spelling of Kyrgyz geographic names (see Map of Kyrgyz Republic, Bishkek, 1997) is used in this transla tion (translator’s note). GEOTECTONICS

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horstanticlinal asymmetric uplifts (ridges) separated by relatively shallow basins (Fig. 5). Each of the above mentioned systems is characterized by internal differen tiation and consists of alternating extended uplifts and troughs (structural forms of the third order) [19–22]. Here we come up against the problem of the struc tural essence and nature of zones and systems of troughs and uplifts in the Tien Shan and their bound aries. Are they limited by lateral folding of the delam inated Earth’s crust? Most likely, this is not the case. As was shown in [13–15, 20–22], the contribution of deep processes (structural and compositional transfor mation, variation in density, and flow of crustal and mantle materials at different levels) are significant in addition to the dislocation forms related to meridional compression and shortening of the crust as a result of collision and northward flow of subcrustal masses. Precisely these processes are assumed to be responsi ble for the formation of the largest and deepest Fer gana, Naryn–AtBashy, YsykKöl intermontane basins and the Shu, Ili, Kashgar, and Afghan–Tajik foredeeps. To a certain extent, similar ideas are devel oped by Artyushkov [5, 35]. According to his calcula tions, the mountainbuilding differentiated uplifts of the Earth’s crust are related to the replacement of the lithospheric mantle with asthenospheric material due to the infiltration of active fluids from the underlying mantle. Such infiltration results decreased viscosity and strength of the lithosphere. Substantial impor tance is attached to phase transition in the lower crust. Let us take into consideration geodynamic concepts developed by Bakirov [33], Vinnik [6, 57], Grachev [9], Mikolaichuk [25, 55], Pogrebnoi and Sabitova [29], Roecker [57], Sobel and Arnaud [60], Shatsilov et al. [26, 27], Yudakhin [17, 41], and other research ers of Central Asia who refer the recent mountain building and orogenic structures to the decompaction of the subcrustal lithosphere, mantle plumes, and other rheological differences, compositional transfor mations, and redistribution (flow) of materials in the upper mantle and the asthenosphere. The anomalies related to heat and mass transfer in the course of recent tectonomagmatic reactivation should be kept in mind too. The sharply nonisothermic conditions at the crust– mantle interface [33] should be noted as well. The MoldoToo–Terskey AlaToo system of uplifts is crossed by the MANAS profile in its southern por

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Fig. 4. Major neotectonic and orographic elements of the Central Tien Shan, modified after Makarov [19]. (1) Zone of uplifts; (2) zone of basins; (3) the large anticlines of sedimentary cover; (4) boundaries of the systems of uplifts and basins; (5) MANAS seismic profile (without Chinese segment); (6) state border of Kyrgyzstan. Structural and orographic elements (letters and numerals in figure). Systems of foredeeps and intermontane basins: A, Shu–Ili (North Tien Shan); C, YsykKöl; E, Naryn; systems of uplifts: B, Talas–Kungo; D, MoldoToo–Terskey AlaToo; E, AtBashy–KakshaalToo; local uplifts and zones of uplifts: 31, KavakToo–Sook; 33a, MoldoToo–JetimToo; 33b, Bauralbas; 35, AkChatash–Bauk; 37, AkShyyrak; 41a, BaybicheToo– KaraToo; 41b, JamanToo; 47, AtBashy; 49, Torugart; 53, Kakshaal; local basins and zones of basins: 17, Kochkor; 18, Ysyk Köl; 32, SongKöl; 34, Dudumol; 34b, Karatal; 36, Toguztorau; 38, Naryn; 42, Arpa; 43, AtBashy; 48, ChatyrKöl–West Ak Say, 51, Balyktyjon. GEOTECTONICS

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tion that comprises the SongKöl intramontane basin (Fig. 4, 32) framed by asymmetric uplifts of the KavakToo–Sook chain of mountain ranges in the north (Fig. 4, 31) beyond the transect and Bauralbas Range in the south (Fig. 4, 33b). The intramontane Karatal Basin (up to 5–7 km) situated further to the south (Fig. 4, 34b) is located still higher, and in con trast to the SongKhol Basin, is deeply dissected and less distinct in morphology. The uplifts of the Ak Chatash and Bauk ranges (Fig. 4, 35) occupy a mar ginal position in this system at the boundary with the Naryn Basin (Fig. 4, 38). The fact merits special atten tion that the most important Nikolaev Tectonic Line of the Tien Shan, which is regarded as one of the cru cial deep structural elements of this region and whose implications are emphasized in many structural, pale otectonic, and geophysical schemes, is not expressed in the neotectonic structure at all or at least does not stand out against the background of ordinary internal structural elements of the MoldoToo–Terskey Ala Too system of uplifts. The Naryn–AtBashy, or Naryn Basin consists of a series of large and minor basins separated by intrabasi nal uplifts [19, 22]. The North Naryn zone of neotec tonic reverse–strikeslip dislocations separates the basin and the abovementioned system of uplifts. The seismic profile crosses this zone at the southern foot hills of the Bauk Mountains. In contrast to the Nikolaev Line, the boundary zone is a very expressive neotectonic structural element. No definite data on its deep roots, which could shed light on the relationship between basement folds and tectonic nappes, were available earlier. The North AtBashy Fault that bounds the inter montane Naryn–AtBashy Basin in the south is another such boundary in the given section of the Tien Shan. This fault is a western chain of the extended regional AtBashy–Inylchek Fault Zone (Fig. 3, 3), which is marked by rocks of ophiolite complex; its old age and deep nature is supported by numerous data reported in the literature. Precisely this ancient boundary zone is inherited by the neotectonic struc ture; however, no specific data on its behavior at depth have been reported. In the northern, Naryn Basin proper, the surface of the folded basement close to the profile is subsided to a depth of 2–3 km below sea level [8, 19]. The recent orogenic complex makes up several extended and wide anticlines trending in the latitudinal direction as a con tinuation of asymmetric horstanticlinal basement juts of the AkShyyrak Range situated in the west (Fig. 4, 37), as well as of the Alamyshik, Karacha, and KaraToo juts grown into the Naryn Basin in the east and the south (Fig. 4, 41a). The BaybicheToo crossed by the profile is the western link of this series of asymmetric (south verging) horstanticlines (Fig. 4, 41a), which sepa rated the Naryn and AtBashy basins in the Pliocene and Quaternary; before that, it was a single sedimenta tion basin [19]. GEOTECTONICS

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Fig. 5. Satellite image of junction zone of uplift of the Maydantag Range and the Tarim massif. In the north—the snowcovered field of the highmountain part of the uplift with the clearly expressed NEtrending rectilinear reverse–strikeslip Maydantag Fault Zone to the south. The mottled tract in the center is a system of linear ranges and basins of the Chultag (Kalpintag) Piedmont Step. In the south—the sandshale plain with oases of the Kashgar River valley (black). The solid heavy straight line denotes the southern segment of the MANAS seismic profile Song Köl–Kashgar.

The neotectonic structural unit located to the south of the AtBashy Basin is similar to a certain extent with the Naryn Basin, but its depth and other important features remain only conjectural. In the seismic section, it was important to reveal the unknown position of the upper basement surface. An opportunity appeared to verify the suggestion of the buried eastern continuation of the Paleozoic Jaman Too jut (Fig. 4, 41b). The northern, highly uplifted and deeply dissected part of the basin, including the Oynakjar Range, where the thick Neogene sequence is exposed, could be related to this continuation. Another attractive object was the junction zone of this uplifted portion of the basin and the Quaternary aggradation plain situated to the south and directly adjoining the AtBashy Uplift. Some young reverse–

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strikeslip faults, including seismic dislocations [1, 19, 33], are known in this zone, so that its morphology and depth is an important issue. The AtBashy–Kakshaal system of uplifts. The seismic profile encompasses the western part of this highest and a very wide (more than 100 km) system. The large AtBashy Range (Fig. 4, 47) is bounded by faults on both sides. The northern boundary fault was mentioned above. The reverse–strikeslip South At Bashy Fault is deemed to be a less significant reacti vated ancient fault that controls the junction zone of the sharply asymmetric AtBashy Uplift and the asymmetric ChatyrKöl–West AkSay Basin. How ever, are these faults actually so distinct in both the ancient and neotectonic structural grains? The ChatyrKöl–West AkSay Basin (Fig. 4, 48) occupies a transitional position in its height, width, and thickness of the Cenozoic fill between the inter and intramontane basins. Its deep structure was previ ously unknown and was reconstructed only on the basis of indirect data [19, 33]. In the south, it is bounded by relatively short horstanticlinal jut of the Torugart Range (Fig. 4, 49). This jut and its eastern continuation in the uplifts of the KakshaalToo sepa rate the ChatyrKöl–West AkSay Basin from the very shallow Balyktyjon Basin (Fig. 4, 51). This basin, whose Paleozoic basement occurs at a height of no less than 3000 m, is the eastern structural extension of the deeper Tuoyun Basin, where the bottom of the recent orogenic complex occurs at a height of 2000–2500 m. The Tuoyun Basin is situated in the extreme northwest of Xinjiang and distinguished by widespread Mesozoic and Lower Cenozoic sedimentary rocks intercalated by basaltic flows [19, 25, 34, 55, 60]. The southern slope of the Balyktyjon Basin grades in the gentle (4–5°) slope of the extreme southwestern link of the enechelon arranged chain of the Kakshaal 2

Too uplifts extending far to the east (Fig. 4, 53). In the section under consideration, this link consists of four relatively narrow (~10 km) zones of NEtrending tight linear uplifts bounded by rectilinear reverse–strike slip faults clearly expressed in the topography and steeply lower down toward the Tarim Platform (Fig. 5). The southern marginal Maydantag Zone with heights above 3000 m is separated by the Kashgar system of overthrust (underthrust) dislocations from the Pishan, or Kalpintag, Piedmont Step at a height of 1500–3000 m. This step is an uplifted and intensely deformed part of the Kashgar Foredeep broken by a series of Neogene– Quaternary imbricate thrust faults as a part of the Kashgar Basin Thrust, or the South Tien Shan Thrust System [43, 45–47, 51, 65]. According to the available geological and geophysical data and their interpreta tion, these thrust faults merge into a nearhorizontal detachment at a depth of ~3 km at the base of Cam 2 These

uplifts are shown in Fig. 4 only in the territory of Kyr gyzstan, largely on the northern slope of the KakshaalToo.

brian strata [65]. In the immediate proximity of the con sidered seismic line, the surface of the general detach ment was detected at a depth of ~6 km [59, 60]. The dis tinctly expressed frontal tectonic scarp of the Kalpintag Range separates the Pishan Step from the Quaternary alluvial plain of the Kashgar–Yarkend Depression pertaining to the slightly deformed part of the Tarim Plate. Thus, the southernmost (Chinese) segment of the seismic profile crosses the zones of Paleozoic accretion and recent high uplifts of the Kak shaalToo and Maydantag and Pishan Piedmont Step, and practically does not involve the undeformed part of the Tarim Platform. SEISMIC MEASUREMENTS ALONG THE GEOTRAVERSE AND PREPARATION OF SEISMIC SECTION Initial data. The seismic section is based on multi wave seismic measurements using explosive sources in the systems of multifold coverage using reflection commonmidpoint method. Because of the mountain topography and existing road network, the seismic line is characterized by substantial curvature, which ham pers processing. In addition, the line was interrupted when passing the Naryn River and at the nearcrest parts of the AtBashy Range and the southern slope of the KakshaalToo. Thus, the profile is subdivided into three segments (Fig. 2). In central segment B–D (Fig. 2), 188 gathers have been obtained between the Naryn River and the crest of KakshaalToo; 21 gathers in northern segment E between the Naryn River and Lake SongKöl; and 467 gathers in southern segment A on the southern slope of the Tien Shan and the adjacent part of Tarim. The total length of the profile is 340 km. The length of the seismic record was 90 s in segment B–E and 120 s with discreteness of 4 ms in segment A. The number of traces in one gather varied from 240 to 1000. The average distances between the shotpoints and geophone points were 1 km and 100 m, respec tively. The recording was implemented using autono mous highsensitive TEXAN 125A geophones (REFTEK, USA). The accuracy of the geophones was controlled by B. Greschke, L. Carothers, and S. Harder from the PASSCAL Corporation (USA). The profiling technique corresponded to the standard variant with specification of shooting parameters necessary because of variable geological features. In addition, broadband recording systems mounted along the seis mic line provided seismic measurements using ECWM. Additional information on the technology of the seismic experiment is given in [40]. Processing of reflection CMP data. Reflected waves were processed with the FOCUS 5.4 program packet, starting from input of seismic records, descrip tion and control of the profile geometry, analysis of the wave pattern, estimation of the gather quality within profile, and elaboration of a processing graph. After removal of the constant amplitude constituent, two GEOTECTONICS

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refracted waves with apparent velocities of 4500 and 7000 m/s are traced in the first arrivals in the gathers of a common source point (CSP). The traveltime curves of refracted waves in the first arrivals are curvilinear in most gathers owing to sharp variations in the topogra phy and curvilinear profile (nonlinear offset). Reflected waves are commonly not seen in CSP gathers; some CSP gathers allows fragmentary recog nition of two reflected waves on times of 6–7 s. After Gilbert transformation and representation of gathers in instantaneous amplitudes, the visible signal fre quency decreases and tracing of reflected waves improves. The third stage included processing of gath ers, velocity analysis, and summation. The standard processing of gathers, including deconvolution and fil tering, was combined with special processing and rep resentation of gathers in instantaneous amplitudes. The summary time section obtained according to this graph was transformed into the section of instanta neous amplitudes. Tomographic processing of the seismic profiling data. The recovery of the velocity parameters of the medium with the method of seismic tomography allowed us to create a velocity model of the upper part of the section and to fulfill residual static correction in processing of CMP data. The FIRSTOMO program packet for seismic tomography and the XTOMO sys tem of tomographic processing were used. The initial data were prepared for this purpose with the DPU XTOMO program. The traveltime curves of the first waves selected in the CSP gathers processed by the FOCUS program packet were used in tomographic processing. After processing, the gathers were again examined carefully to estimate the correctness of tak ing the time of the first arrivals. The first arrival picking was carried out by the DPU XTOMO program. About 200000 pairs of sourceto geophone arrivals were taken in total (22000 arrival pairs in the central segment; 7200 in the northern seg ment; and 151000 in the southern segment). The modeling of the raypaths showed that a significant part of rays occur out of seismic line, testifying to the incor rectness of the 2D approach. Therefore, it was decided to perform 3D tomographic processing using the FIR STOMO packet. To optimize computational resources and to increase detailing of investigation, the studied region was divided into separate sites with overlapping. The coordinates were also transformed for the sake of optimization computational resources. After seismo tomographic processing of all sites, a vertical section of the obtained velocity cube was performed along the line of geophone location. The upper time of velocity model resulted from the seismotomographic process ing was the basis for calculation of static corrections used in the processing of reflection CMP data. The combined seismotomographic section for the upper +5 to –5 km and time section for 0 to –80 km are pre sented in Fig. 6. To minimize the geometric distortions of the tectonic zones, the sections were rectified by GEOTECTONICS

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transferring nearly parallel intervals of the curvilinear profile and omitting the transverse segments extending along the strike of the structural elements (Fig. 2). The most extended transverse segment F corresponds to the West AkSay Basin. The gap between the central and northern segments was closed by their juxtaposi tion, which is possible from the structural conditions. Density section. To create a deep section, a gravity (density) model was computed along the seismic line (Fig. 7). The model is based on the data of deep seis mic exploration and correlation between the elastic wave velocity and rock density, taking into account the isostatic equilibrium of disturbing dense masses in the lithosphere. The modeling consisted of two stages. (1) The joint spectral analysis of the gravity anom alies and topography over an area of 1000 × 1000 km, where the seismic profile is localized. The analysis was carried out for the study of the isostatic compensation style and the estimation of the main geomechanical parameters of the lithosphere necessary for optimiza tion of the discrepancies between the seismic data and gravity measurements. Such discrepancies commonly established along the seismic–gravimetric profiles assigned for investigation of the deep structure are quite acceptable, taking into account the statistical character of the relationships between the elastic wave velocity and rock density. Two possible styles of isos tatic compensation were considered: (1) regional isos tasy as elastic sagging of the lithospheric plate under loading of mountain edifices, and (2) local isostasy according to the Airy model, when deepseated com pensating masses formed by configuration of deep boundaries and lateral inhomogeneities of the crust correspond to all orographic elements. After determi nation of the compensation style and choice of a local model of anomalous excess mass equilibrium in the lithosphere, the construction of an eventual seismo gravitational model becomes possible. (2) Seismogravitational modeling contemplates the joint usage of gravity and wave fields in searching for a physical and geological model that satisfies all observed data. The seismic data determine the bound ary conditions of modeling, which are used for estab lishing the characteristic density on the basis of empir ical relationships between density and elastic wave velocity. The modeling was performed in a 2.5D set ting using a GMSYS Oasis Montaj module (GEOSOFT). The elements of the seismic velocity model which were set initially comprised the bound aries and densities determined directly from the elastic wave velocity. It was assumed that the physical param eters of the selected model body (geocomplex) are constant. Further fitting with the observed field was performed by variation in the geometry of the bound aries, addition of new boundaries (if necessary) and/or change in density within acceptable deviations of the velocity–density relationship (0.13 g/cm3 for any velocity value). A more complex real pattern of physi cal parameters makes the model boundaries arbitrary;

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their possible variations caused by change of parame ters within the bodies may reach 15–20%. Errors of the 2.5Dapproximation of the real 3D geological space may attain 15% for the chosen distribution structure of the geocomplexes. In this connection, it was unnecessary to strive for complete correspon dence of the model field to the observed one; the resid ual discrepancies were no greater than 2 mGal and mainly caused by real heterogeneities of the deep structure, which were not reflected in the seismic data and thus not taken into account in the model. The characteristic elastic wave velocities estab lished from seismic data for different layers of the con solidated crust were converted into densities using empirical relationships that take into account the pressure at various depths [48]. To estimate the density of sedimentary formations from the data on the seis mic wave velocities, the Gardner equation [50] was used. The model parameters for units of the lower crust were based on the most stable characteristics known from the global summaries and the specific data of previous interpretations. The a priori density distribution was accepted from the results of tomo graphic processing, according to which the elastic wave velocity in the sedimentary rocks attains 4.5–5.0 km/s and 5–6 km/s at the surface of the fold basement. The starting densities were as follows (g/cm3): 2.6 for the basement, 2.7 for the upper crust, 2.75 for the middle crust, 2.85 for the lower crust, and 3.3 for the upper most mantle. In particular blocks, the density below the M surface may be as high as 3.45 g/cm3. As followed from the a priori model constructed beforehand, the mean square deviation of the model field from the initial gravity anomalies reached 35 mGal. To eliminate this deviation, some minimal changes have been introduced into the initial model, which take into account the isostatic compensation style determined at the first stage of analysis. The crust thickness beneath Tarim was reduced by 6 km (occurrence of crust–mantle mixture is probable above the M surface). Near the 100th kilometer (Fig. 7), the crust thickness was increased by 3 km. The density of the lower crust was increased at the end of the profile, where a lens of mantle–crust mixture may be expected. The fulfilled correction decreased the discrep ancy between the initial and model fields to 2.5 mGal. Processing of data on the wave forms of remote earthquakes with ECWM. In addition to the data of active seismic reflection CMP profiling, data on the wave forms of remote earthquakes collected by 22 sta tionary recording systems mounted along the seismic line (Fig. 2) were processed. At each system, signals were recorded by Streckeisen STS2 3Dcomponent wideband geophones with 40Hz frequency of discret ization. The function of the converted wave received from remote earthquakes was calculated using the standard technique [62]. The earthquakes with M ≥ 6.0 occurred at a distance of 30 to 95° from the recording system at a source depth more than 33 km were selected for calculation. For 12 recording systems in

the Kyrgyz portion of the seismic line from TEKE to DEBE (Fig. 2), 110 events were processed in addition to 32 events for 10 systems in the territory of China. To construct the function of the converted wave received, the first arrival of the longitudinal Pwave was selected and the interval of ±100 s from this arrival was ana lyzed. The noise level before the Pwave arrival was used as a damping parameter for stabilization of the spectra ratio. The horizontal components of the gath ers were turned along the radial and transverse direc tions determined by the position of the system and earthquake epicenter. Using the spectra ratios, the radial and transverse receiver functions were con structed. In construction of the velocity section, it is suggested that the Vp/Vs ratio is 1.72–1.73. Because the recording systems were operating for two years, it was possible to construct receiver functions in various back azimuths and to calculate the transverse receiver functions. A velocity model with the closest observed and synthetic receiver function was fitted iteratively. The dip angle and strike azimuth of the boundaries beneath the recording systems were estimated on the basis of the receiver function distribution on the back azimuths and transverse functions. The velocity sec tion of the Earth’s crust and mantle constructed in this way down to a depth of –80 km along the MANAS seismic line is shown in Fig. 8. COMPOSITIONAL, STRUCTURAL, AND GEODYNAMIC INTERPRETATION OF THE SEISMIC SOUNDING DATA The seismic cross section of the Central Tien Shan obtained as a result of comprehensive processing of the data on the MANAS transect comprises two parts dif ferent in thickness, which are characterized by differ ent parameters with different resolution. The upper (shallow) part corresponds to rather wellstudied recent and ancient geological formations; their struc ture is known and briefly described above. The struc ture of this part of the section arbitrarily called geo logic is characterized by a distribution of Pwave velocities, whose values vary from 1.6 to 6.3 km/s, gen erally decreasing downward. Such a tomographic sec tion was created down to the zero mark in the Song Köl–Kakshaal segment and somewhat deeper (to –5 km) in the southern (Chinese) part of the profile. The structure of the lower part of the section down to a depth of –80 km is displayed in various reflective and refractive abilities of the medium, localization of reflectors and diffractors, and their abundance in wave fields expressed in the seismic turbidity of the medium. The analysis of the reflection CMP seismic sections in terms of the degree of their turbidity is an untraditional approach to compositional and struc tural differentiation of the lithosphere. Let us draw attention to the reference Bc boundary in the uppermost part of the section, which corre sponds to the fold–thrust basement (deformed preo GEOTECTONICS

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4 3 2 1 0 –5 –10 –15 –20 –25 –30 –35 –40 –45 –50 –55 –60 –65 –70 –75 –80

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10

20

30

40

50

60

70

80

90

V, m/s

100 110 120 130 140 150

190 200 210 220

230 240 250 270

280 290

Fig. 6. The combined seismotomographic section (upper +4 to –5 km) and reflection CMP section (0 to –80 km) along the rectified Manas seismic line. The distances in km (for the upper 4 km in m) are shown along the horizontal and vertical axes. The colored velocity (V, m/s) scale of the longitudinal seismic waves is shown in the left upper corner.

0

1800 2300 2800 3300 3800 4300 4800 5300 5800

4 3 2 1 0 –5 −10 –15 −20 −25 −30 −35 –40 −45 −50 −55 −60 −65 −70 −75 −80

UNDERTHRUSTING OF TARIM BENEATH THE TIEN SHAN AND DEEP STRUCTURE 113

Gravity anomaly, mGal

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60

40

20

–250 –260 –270 –280 –290 –300 0

0

D = 2.3

D = 3.3

D = 2.75

D = 2.45 D = 2.55

D = 2.9

100

D = 2.6

D = 2.65

200

D = 2.85

Distance, km

D = 3.5

D = 2.95

D = 2.7

D = 3.3

D = 2.9

D = 2.3

D = 3.22

300

Fig. 7. Density model of the lithosphere along the MANAS seismic line. The crustal and mantle layers differing in density are shown by color; the numerals are density values D, g/cm3. The distances in km are shown along the horizontal and vertical axes. The graphs above the section indicate measured (dots) and calculated (solid curve) gravity along the profile, mGal.

Depth, km

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ATSH

40

50

KKTM

60

70

TEQL 80

90

6.8

8

6.8

KOKA 7.8

5.8

GOLB DAMB 6.8

KULA 7.8

5.8

DEU4

KOKD

KARD

KAKK

240 250 260 270 280

7.8

UCHS

KYZY

KORU

DEBE

100 110 120 130 140 150 160 170 180 190 200 210 220 230

5.8

5.8

2.8

3.2

3.6

4.0

4.4

4.8

5.2

5.6

6.0

6.4

6.8

7.2

7.6

8.0

Fig. 8. ECWM velocity section (longitudinal waves) along the MANAS seismic line. The location of the stationary recording systems along the seismic line is shown above (see Fig. 2). The thin contour lines correspond to Vp, km/s; the black solid heavy lines are boundaries with Vp = 7.4 km/s (to the left) and 7.0 km/s (in the central and right parts); the gray solid heavy lines are fault zones. The distances in km are shown along the horizontal and vertical axes.

–80

AQKE

7.8

8 6.

5 .8

7.

–70

–60

–50

–40

–30

–20

–10

0

TRKX AHQI TLKC ORTO 6.8

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0

0

10 20

50

60

70

80

AkSay Basin

AtBashy Range

Oynakjar Range

AtBashy Basin

Baybiche Range Naryn Basin

3

Lake SongKöl

Bauralbas and Bauk ranges

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Fig. 9. Structural interpretation of reflection CMP section along the MANAS seismic line. The solid heavy lines denote the main compositional and structural interfaces described in the text; the thin solid lines are the boundaries of the internal homogeneities; the thin dashed lines are faults in the upper crust. The gray solid heavy lines denote the major deep fault zones: the South TienShan Fault System to the left and the Maydantag Fault beneath the KakshaalToo and AkSay Basin to the right.

V, m/s

–80

–80

1800 2300 2800 3300 3800 4300 4800 5300 5800

–70

–70 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280

–60

–50

–60

–30

C –10 1 C2 –20

0 C02

–40 M –50

30 40

C02

Kakshaal Range

–40

C02 –20 C1 –30

M

Maydantag Range

1

Kalpintag Fault

1

Muzduk Fault

2

C01 –10

Bс

Pishan Piedmont Step

Maydantag Fault

2

3

km 4

Tarim Plate

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rogenic peneplane) and characterizes rather definitely the neotectonic constituent of its deformation (Fig. 9). The wellknown shallowseated geological structure allows us to accept the boundary with Vp ~3.5 km/s as this marker. This and the higher boundaries demon strate the structural differentiation of the Naryn Basin and its subdivision into two sufficiently large troughs, where the Paleozoic basement is subsided to a depth of –2 to –3 km. The differentiated and contrasting northern boundary of the Naryn Basin with the devel opment of reverse–strikeslip dislocations is not man ifested clearly in the geologic layer below the roof of the consolidated basement but may be suggested at deeper levels of the consolidated crust and waveguide (see below). The area adjoining the intramontane SongKöl Basin is difficult to interpret because of the minor shotpoint density and possible marginal effects. Note only that lowvelocity layers plunge here to a great depth commensurable to that beneath the Naryn Basin and differing from the other basins situated to the south. It is known, however, that the Paleozoic basement of the SongKöl Basin lies very highly, almost at ground level. Thus if the velocity of the Pale ozoic rocks actually is low, it may be suggested that this is related (in one way or another) to the basin localiza tion in the ancient suture zone of the Nikolaev Line, where the density of rocks is decreased or the temper ature of the rocks in the subsurface rises. The poor knowledge on thermal field of this and the more southern areas [33] does not allow us to judge about this phenomenon more definitely. At the same time, magnetotelluric sounding and modeling of the geo electrical section of the lithosphere based on the phe nomenon showed that an insertion with anomalously low resistance occurs in this zone as an offset of the regional lowresistance zone at a depth of 20–35 km [33, Chapter II. 4]. The seismic section is irrelevant in this respect. The AtBashy Basin turned out to be much shal lower than it was expected previously [19]. The Paleo zoic basement occurs here at a depth of no greater than +2500 m, and this basin should be regarded as a marginal one with respect to the formerly (at the early orogenic stage) existing single AtBashy–Naryn sedi mentary basin. The young folding and faulting in the basement are insignificant here. The anticlinal nature of the intrabasinal uplift of the Oynakjar Range is evi dent. This range is composed of rocks belonging to the recent orogenic complex. Its southverging asymme try and the conjugate young reverse–strikeslip Oynakjar Fault are described in [1, 19, 33]. Our data indicate that this fault is traced as an active dislocation to the surface of the consolidated basement, whereas the North AtBashy Fault Zone, much more contrast ing and striking in topography of neotectonic and Paleozoic structures, is not clearly expressed in the upper part of the seismic section. GEOTECTONICS

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The Paleozoic basement of the West AkSay Basin is established in the tomographic section at a depth of ≥2300 m as a rather simple syncline. Its internal differ entiation is insignificant. The rather contrasting South AtBashy Fault bounds this basin in the north as an almost vertical reverse–strikeslip fault traceable deeply into the crust. The aforementioned KakshaalToo system of uplifts, steps of piedmont ridges, and the Tarim Plate are manifested in the tomographic section rather dis tinctly. It should be noted that highvelocity deep bound aries in the geologic part of the section wittingly related to the Paleozoic formations, e.g., the boundary with Vp ~ 4.4 km/s, mimic the topography of the roof of the Paleozoic and do not correspond to the ancient structural boundaries within the sequence of Paleozoic formations. They are crosscutting relative to the latter boundaries, which are rather steep. For example, the abovementioned boundary on the northern slope of the KakshaalToo is conformable to the lowangle neotectonic Balyktyjon Syncline, being sharply dis cordant relative to the Paleozoic structural elements. This is confirmed by the ECWM velocity section, where this syncline is depicted up to the contour line with Vp = 4.8 km/s, i.e., to a depth of –3 to –4 km (Fig. 9). The same is established along almost the entire transect. Thus, the upper crustal velocity boundaries, at least the uppermost ones, are coordi nated with the deformed surface of the preorogenic peneplane, indicating that the velocity parameters at the top of the section are mainly of the lithostatic nature. They were probably formed during the Meso zoic and Early Cenozoic stage of quasiplatform evolu tion, when the previously existing topography (geom etry) of the boundaries and the layer’s thickness in the deep part of the section were cardinally rearranged. Thus, the structure of this part of the seismic section is postPaleozoic, mainly neotectonic, if not completely but to a significant extent. The older compositional and structural inhomogeneities are reflected therein only in fragmentary form. We accept the C02 boundary, which is rather persis tent and clearly visible throughout the profile, as an interface between the shallow and deep parts of the section. This boundary separates the shallowseated formations with high turbidity from the relatively homogeneous (transparent) underlying C02–C1 layer. This interface corresponds to the roof of the consoli dated basement, which is detected at a depth of –2 to –6 km beneath the Tien Shan, descending in the north, in the junction zone of the MoldoToo–Ters key AlaToo system of uplifts and the Naryn Basin and beneath the southern zones of the Kakshaal system of uplifts (Maydantag Range, Pishan Step). The ECWM section demonstrates a similar pat tern: a discontinuous layer with Vp = 5.8–6.2 km/s is traced therein from the AkSay Basin to the Naryn River at a depth of about 5 km (Fig. 9). A small body

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with relatively high velocity beneath the KULA recording system attracts attention within this layer. This body is noted in the tomographic reflection CMP section as a highvelocity (Vp = 5.3–5.8 km/s) jut up to 2 km high (Figs. 6, 9). Probably, this is a buried ancient core of the aforementioned Quaternary Oynakjar Uplift on the northern slope of the AtBashy Basin. This body is separated from the lower crust by a lowvelocity layer and may be regarded as an upper crustal element. At the same time, in the ECWM lower crustal section, this body is underlain by the crest of a vast uplift and by a columnlike highvelocity (Vp = 8 km/s) jut of the upper mantle. The opposite situation takes place to the north, beneath the adjacent BaybicheToo (KYZY recording system), where all crustal and upper mantle layers are characterized by lowered Vp, mark ing a rather narrowly localized, probably weakened zone, steeply dipping to the north in the lower crust (Fig. 8). In the northern marginal part of Tarim, the C02 boundary is sunk to a depth of –16 to –20 km, plung ing beneath the abovementioned zones of the Tien Shan for a distance more than 50 km. Such interpreta tion of the position of C02 boundary at the northern margin of the Tarim Platform is based on the following arguments. In the considered segment of the Kashgar Foredeep, the surface of the fold–thrust basement of the Tien Shan (Vp ~3.5 km/s) occurs near the zero mark in the seismic section. The surface of the Pre cambrian crystalline basement was previously deter mined here at a depth of 8–10 km [51]. In the reflec tion CMP section, an interface corresponding to Vp = 5.8–6.0 km/s is noted at this level and may be regarded as a roof of the Precambrian basement of the platform or consolidated basement (C01). If this interpretation is valid, the overlying layer with Vp = 3.5–5.8 km/s corresponds to the petroliferous complex of Paleozoic, Mesozoic, and Lower Cenozoic sedimentary rocks in the Kashgar Trough and to the Paleozoic fold–thrust complex of sedimentary and volcanic rocks in the Southern Tien Shan. In this case, the underlying layer, ~7.0–7.5 km thick, may be regarded as the Precam brian basement of the Tarim Platform. In its image in the seismic section, this layer is classified among the turbidity layers, but at the same time is distinguished by a rather thin nearhorizontal delamination clearly expressed beneath the trough and somewhat worse beneath the Pishan Step. The nature of this delamina tion remains unclear. We suggest that it may be related to intense tectonic movements and detachments that accompanied underthrusting of Tarim beneath the Tien Shan. At a depth of about –17 km, this layer is underlain by a rather persistent and homogeneous sequence, which is similar in its pattern to the C02–C1 layer of consolidated basement of the Tien Shan, and we iden tify it in this way. In addition, the velocity Swave sec tion of the Tien Shan [7, 63] demonstrates a clearly expressed highgradient zone between the rocks with

Vs = 3.7–3.9 km/s and Vs = 3.4–3.5 km/s at the same depth (the level of Vs = 3.5–3.6 km/s). The same boundary is distinctly manifested in the velocity struc ture of the lithosphere in the Tien Shan for Pwaves [30]. Such coordination of the data obtained indepen dently and with different methods looks nonrandom and sufficiently convincing. Thus, the seismic profiling shows the real structure of the Earth’s crust in the junction zone of the Tarim Platform and the Tien Shan and confirms that the sec tion at the level of the upper crustal and deeper layers is doubled here with far (more than 50 km) under thrusting of the Tarim Platform beneath the Tien Shan along a gently dipping (~30°) regional detachment. In the field of reflected and scattered waves, this detach ment is distinctly traced to the bottom of the Earth’s crust beneath the entire KakshaalToo system of uplifts and apparently may be regarded as the major element of the South Tien Shan system of thrust dislo cations. The detachment is characterized by flatramp geometry and ensures inter and intraformational dis placements along the nearhorizontal segments of the master and auxiliary fault planes. In particular, such displacements may be suggested along the boundaries of the abovementioned Precambrian crystalline base ment (C02–C01) of the Tarim Platform and within this complex, which stands out by its delaminated pattern. As concerns the time of underthrusting, its high activity during recent mountain building is not in doubt and is confirmed by the syn and postsedimen tation dislocations of the recent orogenic complex and correlative landforms, as well as by high seismicity. Nevertheless, this crustal dislocation probably origi nated during the Late Paleozoic accretion of the Mid dle and Upper Paleozoic formations on the continen tal slope of the Tarim (KakshhalToo) and Upper Paleozoic formations of the Tarim Basin. The thickness and character of the boundaries of the C02–C1 layer vary along the profile. In the extreme south, beneath the open portion of the Tarim Plat form, its thickness is 7.0–9.5 km and gradually decreases to 4–6 km under the Tien Shan nappe (beneath the Pishan Step and uplifts of the Maydantag Range). In the hanging wall of the Maydantag Range– Pishan Step segment, the layer thickness and its inter nal pattern are retained except for slight thickening and possible detachment near the thrust fault. Further to the north, beginning from the drainage divide of the KakshaalToo, the C02–C1 layer differs in structure and internal pattern. Beneath the Kakshaal Too system of uplifts, it is distinguished by high homo geneity (seismic transparency), which is disturbed by turbidity wedges beneath the Balyktyjon and AkSay basins. These wedges are traced, varying in thickness, to the north up to the center of the Naryn Basin and further beneath the northern slope of the latter, the Bauralbas and Bauk ranges, and Lake SongKöl, com pletely replacing the transparent zone. The thickness of the layer in this region of the Tien Shan is 6–11 km. GEOTECTONICS

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Thus, the C02–C1 layer is reliably traced over the entire extent of the geotraverse characterized by verti cal and lateral variations of the internal structure (reflector and diffractor pattern) and outer bound aries, which are contrasting continuous lines in one place, discontinuous lines in another place, and more or less diffuse contours in the third place. Such varia tion may result from technological effects or composi tional and structural heterogeneities of the geologic medium. Comparison with the wellknown structure of the upper 4–5 km of the section indicates that nei ther older nor younger geological inhomogeneities are reflected in the C02–C1 layer. The Tarim, Maydantag, and Kakshaal segments are the only exceptions; they are different lithotectonic zones separated by the thrust faults of the Kashgar Basin, including the Muzduk Fault and the reverse–strikeslip Maydantag Fault (see below), respectively. The compositional and structural inhomogeneities of the shallow part of the section in these segments, however, are expressed vaguely. In the case of this layer, which is a consoli dated base of the upper crustal section, one should suggest that its structural features manifested in the field of reflected and scattered waves are of the super imposed geophysical, mainly lithostatic nature rather than having any geologic sense. The middle crustal C1–C2 layer traditionally recog nized in the reflection MCP seismic section is distin guished by a high degree of turbidity. In the previous interpretations of the deep structure of the Tien Shan, it was identified as a lowviscosity layer, or waveguide. This layer appreciably differs beneath the Tarim Plat form and the Tien Shan. In the first segment, it under lies (with a rather sharp interface) the consolidated upper crust within a depth range of –25 to –30 km and gently slopes toward the Tien Shan, gradually thinning northward from 5.0 to 3.5 km. In the zone of under thrusting, the layer dips more steeply and is traced to a depth of ~65 km down to the lower edge of the Earth’s crust. Over this entire region, the lower boundary of the layer is almost conformable to the upper boundary but is expressed less contrastingly. As a matter of fact, this layer is not separated from the lower crustal layer, and the crust here is actually twolayered. Beneath the TienShan, the C1–C2 layer occurs far higher at a depth of –10 to –18 km. Insignificantly ris ing southward in this depth range, it is traced in the ECWM section as a discontinuous lowvelocity (up to Vp = 5.0–6.0 km/s) zone. In the northern segment of the profile, beneath uplifts of the MoldoToo–Terskey AlaToo system and its junction zone with the Naryn Basin, the C1–C2 layer is similar to that described above but differs substantially over the rest of the terri tory. Here it is distinguished by small and variable thickness (1.5–2.5 km) and varies in depth. This is especially characteristic of the AkSay–Kakshaal seg ment. The generally distinct (contrasting) lower and upper boundaries of this layer become somewhat dis sected and embayed beneath the AkSay Basin and the GEOTECTONICS

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KakshaalToo uplifts. The offsets of this layer extend into the adjacent, intensely reflecting layers. This structure of the C1–C2 layer and the echeloned char acter of its conjugation with the adjacent layers allow us to suggest that tectonic delamination, destruction, and decompaction of the Earth’s crust with disloca tions along gently dipping detachments played an important role in the separation and structure of this layer. The delamination, detachments, and offsets are consistent with the crustal dislocations in the Tien Shan caused by underthrusting of the Tarim massif. The lower crustal layer bounded by the C2 and M surfaces is also characterized by differentiated struc ture of reflectors and diffractors. In the Tarim seg ment, about 140 km in extent, it is relatively thin (17– 20 km) and distinguished by a uniform pattern; the distinct but not contrasting delamination is discernible against the background of this pattern. In the Kashgar Underthrust Zone, this delamination becomes con formable to the latter and dips northward. The vertical banding of the pattern characteristic of the whole section at the lower crustal and deeper levels remains an enigma. In the segment under consider ation, the banding is displayed as not numerous but striking narrow insertions with anomalous (off struc ture) appearance and may be explained by technolog ical causes. At the same time, the width and density of such insertions increase toward the Tien Shan, and this feature may reflect the real compositional, struc tural, and rheological attributes of the medium. In addition, the vertical bands spread from the Chinese part of the profile, which differs in the conditions of obtaining of the initial data and thus rules out links with methodical and technological causes. The bands change the structure and shape with depth and do not penetrated in the upper crust, and thus cannot be referred to defects of processing. The lower crustal layer beneath the Tien Shan is distinguished by greater thickness, attaining a maxi mum (42–45 km) beneath the AkSay Basin and the northern slopes of the KakshaalToo, whereas a mini mum (≤25 km) is reached beneath the Naryn Basin. Another characteristic feature of the C2–M layer is its complex structure manifested in diverse and peculiar patterns of reflectors and diffractors dominated by nearvertical bands of various depths (3–5 to 27 km) distinguished more or less contrastingly by turbidity and internal variations of pattern. The inclined, and to a lesser extent, nearhorizontal boundaries and thin layers, not so persistent and contrasting, develop against this background. Beneath the AtBashy, Kak shaal, and Maydantag mountain ranges of the South ern Tien Shan, the boundaries and layers dip to the north conformably with the South Tien Shan (Kash gar) regional zone of Tarim underthrusting beneath the Tien Shan. The arcuate boundary as a deep continuation of the WSW–ENEtrending Maydantag Fault—the reverse– strikeslip fault strikingly expressed in the topography

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and structure of the Paleozoic formations (Fig. 9)— attracts attention. Almost vertical in the shallow zone, this boundary flattens with depth and plunges northward at an angle of ~30°. In the depth interval of 10 to 45 km, the boundary is marked by a highgradient zone of decreasing density and offset of density units (Fig. 7), as well as by a decrease in the seismic wave velocity (Fig. 8). The extrapolation of this inclined boundary to the upper crustal units based on density section (Fig. 7) and shown in Fig. 10 leads it to the Maydantag and Muzduk faults that separate the Tien Shan and the Pishan Piedmont Step. This allows us to suggest that this boundary divides crustal blocks of fundamentally different structure: the Tarim massif with mainly shallowwater shelf facies in the south and the accretionary complex of the Southern Tien Shan in the north. In this case, the amplitude of underthrusting of the Tarim massif beneath the Southern Tien Shan mainly related to Paleozoic tectogenesis is no less than 100 km. It should be noted that the reflection CMP seismic section and the density section (Fig. 7) are characterized by quite different resolution. The first one (Figs. 6, 9) does not support the above extrapolation and indicates that the Muzduk Fault Zone most likely is a branch of the Kalpintag Fault or, more probably, of the Kashgar Underthrusting Zone as a whole, which is no less deep and characterized by high activity at the stage of recent mountain building. The ECWM velocity section displays a similar pat tern (Fig. 8). The Maydantag Fault localized near the AHQI and TRKX recording systems is expressed in a rather narrow lowvelocity zone of Vp, which is dis tinctly traced to a depth of about –30 km and accom panied by a narrow highvelocity zone in the hanging (northern wall). At a greater depth, the fault zone gradually flattens and may be distinctly traced to the lower crust (to the level of Vp = 7.2–7.4 km/s) and probably deeper to the layer with Vp = 7.6–7.8 km/s (Fig. 8) somewhere beneath the ChatyrKöl–West AkSay Basin at a depth of 55–60 km. It should be noted that the crust–mantle transition in this section is characterized by an elevated Vp gradi ent in the range of 7.0–7.8 km/s and by a rather com plex structure. The boundary at the base of the crust with Vp = 7.4 km/s complicated by nearhorizontal tectonic detachments, at least in some segments, may be accepted as the most persistent and distinct struc tural interface. Such a lower boundary of the crust, probably with participation of the upper mantle mate rial, is suggested in the segment from the Kakshaal Too to the AtBashy Range. As a result, the boundary with Vp = 7.4 km/s rises up to –45 km.1 A similar but 1 This

rise and that noted further are consistent with the previ ously established general rise of the crust bottom and reduction of its thickness beneath the AtBashy–Naryn basins. At the same time, this section allows doubling of a part of the section at the base of the lower crust due to the underthrusting of Tarim beneath the Tien Shan.

smaller tectonic detachment at the base of the crust takes place beneath the Baybiche Range and the southern Naryn Basin near the KYZY recording sys tem and to the north of it. As a result, the same bound ary rises still higher to the level of about –40 km (Fig. 8). A similar detachment is inferred at the southern end of the section beneath the Pishan Piedmont Step. It can not be ruled out that the tectonic scarp of the Kalpin tag Range clearly expressed in topography and sepa rating this step from the Quaternary Kashgar–Yarkend Depression is genetically related to this detachment, as is supported by the reflection CMP section (Fig. 9). In general, crustscale tectonic slices progressively weakening northward are established. The reflectors with counter (southward) slope are not characteristic of the considered segment of the reflection CMP section. They are not numerous and detected only in the thinned portion of the lower crustal layer beneath the AtBashy Basin and the Bay biche Range, outlining another, obviously asymmetric limb of a synform, whose axis falls on the junction of the AtBashy Range and the basin of the same name (AtBashy–Inylchek Fault). It is appropriate to men tion here the asymmetry of the general pattern of the lower crustal layer together with the underlying por tion of the upper mantle. Beneath the AtBashy Range and to the north of it, the medium is characterized by a generally higher intensity of seismic wave reflection and higher brightness of the pattern. To the south, beneath the AkSay Basin, KakshaalToo, and May dantag, the least bright (dark, turbid) pattern domi nates, resembling the pattern of the most decom pacted and delaminated middle crustal layer (waveguide). Precisely in this southern segment, the inclined boundaries and the layers with contrasting density (?) are conformable to the abovementioned dislocations and compositional and rheological heter ogeneities related to the underthrusting of Tarim beneath the Tien Shan. This gives grounds to deem that vertical banding of the section may be related to the natural composi tional, structural, and rheological differentiation of the medium. The consistency of the largest and the most turbid (darkest) columns with the AkSay and Naryn basins and the AtBashy–Inylchek Fault Zone is indirect evidence for such an interpretation. If this is the case, the mentioned neotectonic basins and sepa rating uplifts are reflected in the structure of the lower crust and the upper mantle in agreement with the above suggestion that these heterogeneities are a result not only of the lateral folding of the Earth’s crust but also of the autonomous flow of matter at different lev els of the crust and the upper mantle. The bottom of the Earth’s crust (M boundary) does not reveal any spectacular features in the reflection CMP section, where it is expressed in a lowcontrast ing boundary against the background of a rather homogeneous medium of the lower crust and the uppermost mantle. In general, this medium is charac GEOTECTONICS

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–60

–50

–40

–30

–20

–10

0

Basement of Tarim (AR–PR1)

KZ

Late Cenozoic Underthrusting Zone in the Tarim Block

MOHO

Late Paleozoic Underthrusting Zone of Tarim beneath Kazakhstan

C2P1

Allochthonous terranes in accretionary complex of the Southern Tien Shan (PZ)

Sedimentary rocks of continental slope and rise of Tarim (PZ)

50 km

Basement of the Kazakh continent AR(?), PR, and PZ)

KZ

Naryn Basin

Fig. 10. An alternate geological interpretation of the density model of the seismic section of the Earth’s crust along the MANAS profile, after D.V. Alekseev.

km

S

Tarim Basin

Sedimentary rocks of shelf and inner regions of Tarim (PR2–PZ)

–60

–50

–40

–30

–20

–10

0

N km

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H, m

5000

0

0

100

Depth, km

200

300

400

500

600 –300

–200

–100

0

100

200

S

–2

0

300 N

2

Fig. 11. Variable deviations of longitudinal wave velocity (dVp/Vp) from the average basic model determined from inversion of the difference of the wave traveltime from remote earthquakes in the section of the Earth’s crust and upper mantle in the Central Tien Shan along 76° E, after [54]. The scale of the deviations, %, is shown below the section. The triangles above the section show the location of the broadband recording systems along the MANAS seismic line. The depth, km bsl, is shown along the vertical axis; the distance, km (m for the upper 4 km), from the point with coordinates 41.5° N and 76.0° E in km is shown along the horizontal line below the section. The topography of the Earth’s surface (H, m asl) along the section is shown above.

terized by a homogeneous pattern, so that the M boundary is determined from the position of the man tle–crust interface obtained previously with other methods. In the outer, open part of the Tarim Block, it is located at a depth of –47 to –50 km and smoothly plunges northward in the tectonically buried part. In the zone of crustal superposition of the TienShan and Tarim beneath the KakshaalToo, the M boundary is sunk to a depth of –60 to –65 km. Thus, the crust thickness here reaches 70 km. Further to the north, the lower crustal edge rises to the level of –40 km, con firming the minimal thickness of the Earth’s crust beneath the Naryn Basin previously established by

independent methods. No other appreciable changes in the topography of the M surface are noted. Only the greatest neotectonic units are definitely manifested in this section at the level of the crust–mantle interface: (1) the South Tien Shan system of foredeeps in the form of the rather differentiated Kashgar Basin; (2) the South Tien Shan system of uplifts, which com prises the Kakshaal and AtBashy highmountain ranges separated by a series of highly uplifted and shal low intramontane basins; and (3) the complexly built intermontane AtBashy–Naryn Basin. In the ECWM velocity section (Fig. 8), the mantle– crust interface and the structure of its zone are mani GEOTECTONICS

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fested in a somewhat different style. Some features of this zone were mentioned above. The available data show that the resolution of the ECWM concerning the lower crust and the upper mantle is higher in compar ison with the reflection CMP seismic profiling. The results of seismic profiling testify to the exclu sively crustal (mainly upper crustal) origin of the neo tectonic basement folds, the zones formed by them, and the conjugate faults. This circumstance poses a basically important but currently almost unresolved question about the causes of the vertical and lateral differentiation of the Earth’s crust of the mountain belt and the mechanisms of tectonic (deformational) delamination of the lithosphere under seemingly uni form geodynamic conditions of lateral folding of the lithosphere. One such mechanism is related to the multilayer consecutive displacement of one lithos pheric or asthenospheric layer relative to another, which gives rise to tangential stress at their interfaces and to the formation of drag structural elements [10, 18]. We actually see such elements at the base of the crust. They do not, however, explain everything, and we return to the necessity of referring to the autono mous deep transformation and flow of matter at differ ent levels of the lithosphere [13–15, 20, 21]. As concerns the older structural elements of vari ous ages and dimensions, they are not expressed dis tinctly in the seismic section at the bottom of the crust. Moreover, we do not see them in either the velocity (tomographic) structure of the shallow part of the sec tion or in the structure of the consolidated basement and deeper crustal layers. The only exceptions are the abovementioned large dislocations in the junction zone of the Tien Shan and Tarim, which are mani fested in the field of reflection waves down to the crust bottom and coordinated with some elements of the density section. They may be interpreted as Paleozoic crustal slices of the Middle and Southern Tien Shan and the northern margin of Tarim (Fig. 10). In general case, it is suggested that the fragments of older crusts underwent more or less significant trans formations at certain stages of tectonomagmatic evo lution. These processes were most intense in the deep zones, where compositional, structural, and rheologi cal alterations were combined with spatial redistribu tion (flow) of matter, which provided isostatic and other variations in the height and thickness of the Earth’s crust and its particular layers. As an argument, we repeat the reasoning concern ing the variations in the thickness and structure of the lithosphere and the Earth’s crust of the Tien Shan in the Late Paleozoic and Early Mesozoic, when the for mation of the continental crust completed over the entire territory that has passed into the quasiplatform regime of evolution. It is evident that exogenic destruction, lowering, and planation (peneplanation) of the crust surface along with reduction of the total thickness of the crust and its particular layers could have been possible only along with the corresponding GEOTECTONICS

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change in the lithosphere structure and transforma tion and flow of the matter focused on rheologically weakened waveguides and layers. Similar processes that provoked vigorous mountain building were active in the Late Cenozoic as well. Thus, the transformation of the primary fold– thrust and other structural elements known from the shallow part of the section led to averaging and smoothing of their properties under the effect of regional metamorphism related to the lithostatic pres sure, on the one hand, and fluid and thermal deep flows inferred by many researchers. As a result, the secondary regional structures, mainly layered and often unconformable to the older, primary structures, including upper crustal ones, were superimposed on the primary structure and their fragments. The super imposed and apparently the latest layered structure is fixed by seismic profiling. In light of the aforesaid, the vertical transit banding of the seismic section, at least the largest columns of the most turbid (dark) media beneath the AkSay and Naryn basins and the At Bashy–Inylchek Suture Zone, are in fact of natural origin and display regions (channels) of intense fluid and heat flows. It may be suggested that these regions ensure vertical transport and redistribution of matter in different crustal layers, including its inflow beneath systems of uplifts with thickened crust and outflow from under the intermontane basins and foredeeps resulting in thinning of the crust. CONCLUSIONS (1) The seismic profiling of the Earth’s crust in the junction zone of the Tarim Plate and the Central Tien Shan and the related research have made it possible to display a rather detailed deep crustal structure of this region for the first time. The main point is a lowangle underthrusting of the Tarim Platform beneath the Tien Shan for a distance of 50–100 km. These dislocations extend to at least the Naryn Basin and involve almost the entire crust and the uppermost lithospheric man tle. The dislocations are consistent and to a large extent inherit the Middle and Late Paleozoic accre tionary structural elements of the allochthonous ter ranes in the Southern Tien Shan, together with forma tions of the continental slope and the northern shelf of the Tarim, undoubtedly remaining active during recent mountain building and confirming its colli sional character. These conclusions are in agreement with the structure of the lithosphere established by seismotomographic investigations down to a depth of ~600 km [53, 54] and indicate that the dislocations in the junction zone of the Tarim Platform Massif and the Tien Shan have mantle, perhaps asthenospheric, roots (Fig. 11). (2) The upper crustal layer with lithotectonic com plexes accessible to direct observation in its shallow part (and therefore arbitrarily called geologic) extends to the first regional waveguide at a depth of 0 to –17 km.

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The underlying delaminated basement is character ized only by physical parameters (density, viscosity, temperature, and electric conductivity). The compo sitional, structural, and historic links of the deep base ment with the geologic layer remains unclear and most likely reflects only a residual evolutional pattern dom inated by rheological properties, geodynamic condi tions, and the process of recent mountain building. (3) The geologic layer is a collage of the relics of preMesozoic continents, terranes, and oceans differ ent in age and amalgamated into the solid continental crust, probably extending to its bottom with retention of the initial structure, which is transformed by super imposed regional metamorphism and tectonic flow. The processes related to recent mountain building are dominant, averaging, and smoothing. The delamina tion and lateral inhomogeneities revealed in the reflec tion CMP and ECWM sections characterize superim posed epiPaleozoic regional transformation under the effect of lithostatic pressure and tectonic stresses, mantlederived fluid, and heat flows. The structure of the deep (geophysical) layers is mainly related to recent mountain building. The older lithotectonic complexes and foldthrust structural units make up a background or noise inherent to the used research methods. (4) Seismic sounding showed a relatively small thickness of the middlecrustal C1–C2 layer of lowered viscosity and the substantial role of tectonic disloca tions in its formation and internal structure, including nearhorizontal detachments that compensate com positional, structural, and rheological geodynamic disharmony of the upper and the lower crustal layers. (5) The lateral heterogeneity of the deep crustal layers and vertical banding of the section may be of natural origin, which requires additional study.

3.

4. 5. 6. 7.

8. 9.

10.

11. 12. 13.

ACKNOWLEDGMENTS This study was supported by the Agency for Science and Innovations of the Russian Federation, the Rus sian Foundation for Basic Research, and the National Science Foundation of the United States. We thank the institutions and persons who promoted directly or indirectly the seismic investigations along the MANAS profile, processing of the initial data, and publication of this paper and are especially grateful to Yu.G. Leonov for constant support of this research. We thank the reviewers for their helpful comments. REFERENCES 1. K. E. Abdrakhmatov, S. Tompson, and R. Weldon, Active Tectonics of the Tien Shan (Ilim, Bishkek, 2007) [in Russian]. 2. D. V. Alekseev, V. A. Aristov, and K. E. Degtyarev, “Age and Tectonic Setting of Volcanic and Cherty Sequences in the Ophiolite Complex of AtBashy Range, the Southern Tien Shan,” Dokl. Akad. Nauk 413 (6), 781–

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784 (2007) [Dokl. Earth Sci. 413a (3), 380–383 (2007)]. D. V. Alekseev, K. E. Degtyarev, A. V. Mikolaichuk, et al., “Tectonic Regimes and Evolution Stages of the Southern Margin of the Kazakh Paleocontinent in the Central Tien Shan,” in Proceedings of the 41st Tectonic Conference on General and Regional Problems of Tecton ics and Geodynamics (GEOS, Moscow, 2008), Vol. 1, pp. 12–17 [in Russian]. E. Argand, La Tectonique de l’Asie (Congres Geologique International, C.R. de la Session en Belgique, 1922, Liege 1924; ONTI NKTP, Moscow, 1935). E. V. Artyushkov, Physical Tectonics (Nauka, Moscow, 1993) [in Russian]. L. P. Vinnik, “Seismic Properties of Mantle Plumes,” Vestnik OGGGGN RAN, No. 3(5), 194–202 (1998). L. P. Vinnik, I. M. Aleshin, M. K. Kaban, et al., “Crust and Mantle of the Tien Shan from Data of the Receiver Function Tomography,” Fiz. Zemli 42 (8), 14–26 (2006) [Izv. Physics Solid Earth 42 (8), 639–651 (2006)]. Geological Map of the Kirgiz SSR on a Scale of 1 : 500000 (Ministry of Geology of the USSR, Moscow, 1982) [in Russian]. A. F. Grachev, “Early Cenozoic Magmatism and Geo dynamics of North Tien Shan,” Fiz. Zemli 35 (10), 26–51 (1999) [Izv. Physics Solid Earth 35 (10), 815–839 (1999)]. A. V. Zubovich, V. I. Makarov, S. I. Kuzikov, et al., “Intracontinental Mountain Building in Central Asia as Inferred from Satellite Geodetic Data,” Geotekton ika 41 (1), 16–29 (2007) [Geotectonics 41 (1), 13–25 (2007)]. N. P. Kostenko, Development of Folds and Faults in Oro genic Topography (Nedra, Moscow, 1972) [in Russian]. N. P. Kostenko, V. I. Makarov, and L. I. Solov’eva, “Neotectonics,” in Geology of the USSR, Vol. 25, Book 2 (Nedra, Moscow, 1972), pp. 249–266 [in Russian]. M. G. Leonov, “Internal Mobility of Basement and Tectogenesis of Reactivated Platforms,” Geotektonika 27 (5), 16–33 (1993). M. G. Leonov, “Phanerozoic Geodynamic Regimes of the Southern Tien Shan,” Geotektonika 30 (3), 36–53 (1996) [Geotectonics 30 (3), 200–216 (1996)]. M. G. Leonov, “The Alpine Stage in Geodynamic Evo lution of the Southern Tien Shan: A Case of the Gis sar–Alay System,” in Recent Geodynamics of the Regions of Intracontinental Collisional Mountain Build ing, Central Asia, Chapter V. 2 (Nauchnyi Mir, Moscow, 2005), pp. 327–348 [in Russian]. Lithosphere of the Pamirs and Tien Shan (Fan, Tash kent, 1982) [in Russian]. Lithosphere of the Tien Shan (Nauka, Moscow, 1986) [in Russian]. L. I. Lobkovsky, A. M. Nikishin, and V. E. Khain, Cur rent Issues of Geotectonics and Geodynamics (Nauchnyi Mir, Moscow, 2004) [in Russian]. V. I. Makarov, Neotectonic Structure of the Central Tien Shan (Nauka, Moscow, 1977) [in Russian]. V. I. Makarov, Doctoral Dissertation in Geology and Mineralogy (Moscow, 1990). GEOTECTONICS

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