M. G. Leonov

Underthrusting of Tarim beneath the Tien Shan and deep structure of their junction zone: Main results of seismic experiment along MANAS Profile Kashgar-Song-Köl

The results of reflection CMP seismic profiling of the Central Tien Shan in the meridional tract 75–76° E from Lake Song-Köl 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 near-horizontal delamination with vertical and inclined zones of compositional and structural differentiation was constructed from processing of initial data of reflection CMP seismic profiling, earthquake converted-wave method (ECWM), and seismic tomography. The most important is the large zone of underthrusting of the Tarim Massif beneath the Tien Shan.

Within-plate zones of concentrated deformation: Tectonic structure and evolution

A specific category of extremely complex linear within-plate structural zones is described. The state of their art, structure and evolution, abundance in various regions, and geodynamic settings are discussed, and formation models are considered.

Pull-apart formation mechanism of Cenozoic basins in the Tien Shan and their transpressional evolution: Structural and experimental evidence

The geodynamic settings of the evolution of Cenozoic basins in the North and Middle Tien Shan and their Paleozoic framework have been estimated from a kinematic analysis and detailed structural geological mapping of key sites. Two stages of their development in different geomechanical settings are distinguished. It is suggested that in the late Oligocene, Miocene, and early Pliocene, the pull-apart basins developed under the setting of simple left-lateral shear or transtension. Presumably in the late Pliocene and Quaternary, this setting gave way to right-lateral transpression; extension in the basins was changed by compression with the formation of local fold-thrust structural elements. The reconstruction of geomechanical sections was tested by analog tectonophysical simulation. The natural and experimental structural assemblies and patterns reveal satisfactory convergence.

Granitic protrusions in the structure of intraplate reactivation, southern Mongolia

The paper describes tectonic assemblies determining structure and kinematics of the plate evolution in the eastern segment of the Gobi Altay and Gobi Tien Shan intraplate reactivation zones in southern Mongolia. These zones are characterized by deformations corresponding to a 3D brittle-ductile shear flow. The structural and compositional reworking is most strikingly expressed in certain varieties of granites, which form specific geostructures called crystalline protrusions. The internal structure of protrusive bodies is distinguished by fragmentation differing in scale, intense brecciation, cataclasis, and structural-mineral reworking of rocks. Taken together, these phenomena facilitate the tectonic mobility of rock masses under low-temperature and hypabyssal conditions and maintain 3D tectonic flow in basement rocks. The tectonic style of the region and its evolution are predetermined by the 3D flow of granitoids in the crystalline basement, which is related to the joint action of various mechanisms discussed in this paper.

Lateral protrusions in the structure of the Earth’s lithosphere

The factual material and modeling results concerning the geology of specific structural elements defined as lateral protrusions, or flowing layers, are considered. The formation of such structural elements is a fundamental phenomenon that controls many features of the structural evolution and geodynamics of platform basement and foldbelts. A lateral protrusion, or flowing layer, is a spatially constrained, nearly horizontal geological body with attributes of 3D tectonic flow (rheid deformation) and lateral transport of rock masses. Flowing layers are large lateral protrusions that play important role in the structure of the continental and oceanic lithosphere. They embody the internal mobility of huge rock bodies and confirm the possibility of their lateral redistribution at different depths of the continental lithosphere. The lateral displacement of rocks within such assemblies may occur in the regime of cold deformation, heating, metamorphism, and ductile flow of rocks under subsolidus conditions or in the process of their partial melting.

The posthumous tectonics and mechanism of exhumation of granitic plutons: The case of the Transbaikal region and the Tien Shan

The study of granitic plutons of the Baikal Highland and the Tien Shan has made it possible to establish new features of their posthumous (after incorporation into the consolidated Earth’s crust) structural reworking and to understand the implications of the cataclastic flow for the exhumation of the crystalline basement in the studied regions. It is shown that granitic plutons undergo appreciable structural transformation at the stages of tectonic reactivation that is significantly separated in time from the moment of formation of plutons as geological bodies. The 3D cataclastic deformation is the main mode of structural reworking of granitic plutons, while the cataclastic flow is the main form of their mobility. Newly recognized slice structures characterize the volumetric deformation of granites.

Nature of electric conductive layers of the upper crust and infrastructure of granites of the Central Tien Shan

We studied the infrastructure of granite massifs of the Central Tien Shan and its correlation with the electric conductive layer of the upper crust, which made possible to reveal new peculiarities of the structure of the granite layer in the region and to clarify the nature of low resistivity layers.

Alpine tectonics of granites in basement of Ysyk-Köl Basin, northern Tien Shan

The Ysyk-Köl Basin filled with Lower Jurassic–Quaternary sedimentary rocks is the largest intermontane negative structural unit of the northern Tien Shan. The basement of this basin is composed of Precambrian–Paleozoic rocks, largely of Ordovician and Silurian granitoids exposed in mountain ranges of the basin framework and as separate anticlinal domes situated in areas occupied by the Mesozoic–Cenozoic sedimentary cover. The postmagmatic tectonic internalstructure of the Chonkurchak (Chunkurchak), Kyzyl-Choku, Kyzyl-Bulak, and Prishib massifs emplaced in the basement, as well as their relationships to the sedimentary cover, are described in the paper. The study was carried out using the morphostructural method, detailed geological mapping, structural kinematic analysis, and petrographic examination of rocks. The internalstructure of Paleozoic granites in the basement and indications of their 3D tectonic flow are characterized. It is shown that granites underwent 3D deformation after their emplacement in the consolidated crust, and this process had a substantial influence on tectonic processes at the plate and orogenic stages of regional evolution.

Tectonic structure and evolution of the Hissar–Alay Mountain Domain and the Pamirs

The paper presents a comparative description of two large mountain systems in the intracontinental Eurasian Orogen: the Hissar (Gissar)–Alay Mountain Domain (MD) and the Pamirs (or Pamir). It has been established that the Hissar–Alay MD and the Pamirs substantially differ in morphostructure, geometry, tectonic style, the set of kinematic parageneses, sequence of events, and the manifestation of magmatism, metamorphism, and recent orogeny. These regions belong to different segments of the Earth’s crust. In other words, they represent two distinct historical–structural–geological provinces belonging to different mobile belts of Asia: the Hissar–Alay MD is incorporated into the structure of the Central Asian (Ural–Mongolia) Belt in contrast to the Pamirs, which is a constituent of the Alpine–Himalayan Belt. The Hissar (Gissar)–Alay MD and the Pamirs formed independently and did not reveal significant geodynamic interaction.

New data on the deep structure of the South Kochkor zone of concentrated deformation

Based on a complex study of the upper crust structure in the southern margin of Kochkor basin (Northern Tien Shan), including study of the structure of the Cenozoic sedimentary cover, the deep geoelectrical structure, the structural unconformities, and occurrences of recent deformations in the basement rocks, new geological–geophysical cross sections are constructed. The cross sections show both fault structures that penetrate the cover from the basement and flat interplate detachments with related fold-overthrust structures. The comparison of the cross sections has established the absence of common planes of fault extensions along the entire margin of the hollow, except for the zone where the margin and the hollow adjoin, which can be caused by the zones of dynamic influence of secondary faults, the zones of fracturing, and the zones of cataclasis of blockwise disintegrated granite massifs.