ГЕОЛОГО-ГЕОФИЗИЧЕСКИЙ ТРАНСЕКТ СРЕДИННОГО ТЯНЬ-ШАНЯ ЧЕРЕЗ НАРЫНСКУЮ И АТБАШИНСКУЮ ВПАДИНЫ

Przhiyalgovskii E.S., Morozov Y.A., Leonov M.G., Rybin A.K., Lavrushina E.V.

The article presents data on the structure of transition zones from areas of relative downwarping (intramountain depressions) to anticlinor uplifts dividing them. The geological and geophysical data obtained by the authors in recent years in different areas of the Northern Tien Shan are considering and discussing to compare the structure and tectonic evolution of key objects. A comparative analysis of the depression / uplift tectonic zones in different regions indicates a fundamental similarity in their structure. These areas of gradient vertical movements are zones of concentrated deformation. We described ensembles of structures formed at the same time in the sedimentary cover and in the basement rocks. Similar structural features are due to the common tectonic evolution of basins and ridges as parts of a unified activation structure of the Paleozoic folded belt. Over a long period of time, from the Oligocene to the Pliocene inclusive, the depressions of the Northern Tien Shan had developed under conditions of sedimentary subsidence, probably by the type of pool-apart structures in a latitudinally oriented region of plastic shear deformation. The relatively quiet tectonic setting of this stage is reflected in the lithological features of the sedimentary complexes. The next stage, which began about 3 Ma b.p., was marked not only by the emergence of a high-altitude relief and the accumulation of molasses, but also by a change of tectonic regime to transpression. The generally flexible bending of the foundation surface in the steep sides of the depressions, to some extent complicated by uplifts, was accompanied by the formation of extensive detachments and thrust-folded structural ensembles in the sedimentary cover of the depressions. Contrary to popular point of view volumes of disintegrated basement rocks demonstrate significant plasticity. The lateral pressure of the side ledges inside the sedimentary cover was transmitted for many kilometers towards the depression’s center. At the same time, contrary to traditional ideas, the volumes of disintegrated rocks of the basement demonstrate significant plasticity, while the lateral pressure of the side ledges was transmitted for many kilometers into the depressions inside the sedimentary cover.

Leonov M.G., Morozov Y.A., Przhiyalgovskii E.S., Rybin A.K., Bakeev R.A., Lavrushina E.V., Stefanov Y.P.

The article provides geological data on the morphostructural differentiation of sedimentary basins and the results of tectonophysical and digital modeling reflecting the shape and possible mechanisms of this process. It is shown that morphostructural differentiation is the fundamental property of sedimentary basins, associated with interaction of rock masses in the basement–sedimentary cover system. The specific features of rock mass deformation in the basement and cover of sedimentary basins, as well as the kinematic conditions characterizing the morphostructural differentiation of sedimentary basins, are considered.

Przhiyalgovskii E.S., Lavrushina E.V., Batalev V.Y., Bataleva E.A., Leonov M.G., Rybin A.K.

Abstract The basement surface and sediments of the Kochkor basin have been studied by structural geological and geophysical methods. The work included high-resolution mapping of the southern basin margin, with a focus on Cenozoic basin stratigraphy, structural unconformities, basement/sediment contacts, and latest deformation (folds, fractures, and faults). Magnetotelluric (MT) soundings provided insights into basin and basement structure, especially important in the poorly exposed eastern flank of the basin margin. The sections across the southern margin of the basin based on geological and geophysical data reveal deformation in both the basement and the sediments. Deformation in sediments shows up as folding, conformal peneplain surfaces, large faults, low-angle detachment faults, and related thrust-fold belts. Thrusting in sediments is inferred to result from cataclastic flow and mass redistribution in disintegrated basement granites. With this mechanism, the total amount of thrusting in the central part of the basin can exceed the convergence of the basin sides.

Rybin A.K., Bataleva E.A., Morozov Y.A., Leonov M.G., Batalev V.Y., Matyukov V.E., Zabinyakova O.B., Nelin V.O.

New magnetotelluric data were obtained for the Karabuk profile crossing the Naryn basin–Baibichetoo Ridge–Atbashi basin geodynamic system (Central Tien-Shan). The complex geological–geophysical cross section along the profile provides a good agreement between the surface tectonic structures and the deep geoelectric model. The electric conductivity anomalies revealed as subvertical conductors striking along the flanks of basins may be explained by the zones of dynamic influence of faults and cataclasis of granite.

Przhiyalgovskii E.S., Lavrushina E.V.

A structural–geological study has been performed on the northern slope of the Kyrgyz Ala-Too Range. Deformations of the peneplaned Paleozoic basement surface, structures of granite disintegration, and morphostructural manifestation of Late Cenozoic tectonic movements have been investigated. Based on the location of pre-Paleocene peneplain remnants with the retained weathering mantle partly overlapped by Paleocene–Miocene sedimentary complexes, we have reconstructed the morphology of the folded surface of the Chunkurchak Trough separated from the Chu Basin at the early Miocene. The dome–fold forms, the morphology and arrangement of which are controlled by disintegration of the basement, have been described for the basement surface. It has been established that granites are broken by systems of steeply dipping, fanshaped, and gently dipping faults and fractures. Variously oriented insignificant offsets along slickensides, as well as displacements deduced from the geometry of fracture intersections, are a result of volumetric cataclastic flow of rocks. The tectonic mobility of disintegrated granites, which are abundant in the Paleozoic–Precambrian basement, explains the complexity and scale of tectonic processes initiated by Cenozoic activation. In paleotectonic reconstructions, which take into consideration tectonic flow and the redistribution of basement masses, the estimates of Cenozoic relative rapprochement of the Chu Basin and the Kyrgyz Ala-Too Range decrease substantially to 4–6 km.

Brandes C., Tanner D.C.

Folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts, accretionary wedges, fold-and-thrust belts, and intra-plate settings in either strike-slip, compressional, or extensional regimes. Due to their widespread occurrence, knowledge about the development of these structures is important to a broad spectrum of geoscience sub-disciplines, such as structural geology, seismology, geomorphology, petroleum geology, and Quaternary geology. Fault-related folding has been analyzed intensively over the last 140 years. For the sake of this review, we divide the folds according to the way the faults and the folds form; that is into detachment, fault-bend, and fault-propagation folds. All fault-related folds are caused by changes in fault parameters. The simplest method to produce folds is to transport material along faults that have stepped, flat–ramp–flat geometries (fault-bend fold). Alternatively the slip can decrease along the length of the fault, and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy, either a detachment fold or a fault-propagation fold is formed, respectively. Detachment folding was first investigated in the early 20th Century, whereas the full significance of fault-propagation folds was recognized quite late in the 1980s. Seminal work on fault-related folding was carried out in the 1930s, but quantitative kinematic models have only been available in the last 30 years. These models are extremely valuable, because they allow a comprehensive understanding of the evolution of fault-related folds and lead to more accurate predictions of the sub-surface structure. From the mid-1990s onwards, numerical simulations have been used to identify how fault parameters (such as dip and fault-bend angle, propagation-to-slip ratio, and shape of the trishear zone) influence the geometry of the related folding. This is directly applicable to the analysis of the shape of anticlines produced. However, this does not mean that fold geometry is uniquely related to fault geometry; on the contrary, different kinematic approaches can lead to a similar fold shape.

Goode J.K., Burbank D.W., Ormukov C.

In response to the Indo-Asian collision, deformation of the Tien Shan initiated at ∼25 Ma along the northwestern margin of the Tarim Basin. 300 km north, the Kyrgyz Range began deforming ∼15 Ma later. Although multiple intervening structures across the Tien Shan are currently active, the sequencing of initial deformation across the orogen's entire width remains poorly known. To determine whether deformation migrated sequentially northward or developed less predictably, we documented deformation patterns within the Naryn Basin in south-central Kyrgyzstan. Detailed mapping and a published balanced cross section across the Naryn Basin suggest that deep-seated, relatively steeply dipping thrust faults have disrupted the basin during late Cenozoic deformation. Dating of deformed fluvial terraces with ages between ∼10 and 250 ka constrains the rate of deformation across relatively young structures in the Tien Shan interior. Based on geodetic surveys of dated terraces, local rates of relative rock uplift span from 0.3 to 3.5 mm/yr. Folding rates and patterns are temporally persistent at a given site. Moreover, they mimic modern geodetic rates measured from interferometric synthetic aperture radar. Extrapolating these rates into the past suggests that structures within the interior of the Naryn Basin formed in the last 1 Myr, whereas the ranges surrounding the basin initiated at least 1-4 Myr earlier. Hence, within the Naryn Basin itself, deformation has migrated from margins to interior. Similarly, these new chronologies indicate that at least some deformation in the interior of the Tien Shan initiated millions of years later than along either orogenic margin. ©2014. American Geophysical Union. All Rights Reserved.

Morozov Y.A., Leonov M.G., Alekseev D.V.

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.

Delvaux D., Cloetingh S., Beekman F., Sokoutis D., Burov E., Buslov M.M., Abdrakhmatov K.E.

Central Asia is a classical example for continental lithospheric folding. In particular, the Altay–Sayan belt in South-Siberia and the Kyrgyz Tien Shan display a special mode of lithospheric deformation, involving decoupled lithospheric mantle folding and upper crustal folding and faulting. Both areas have a heterogenous crust with a long history of accretion–collision, subsequently reactivated as a far-field effect of the Indian–Eurasian collision. Thanks to the youthfulness of the tectonic deformation in this region (peak deformation in late Pliocene–early Pleistocene), the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures. A review of the paleostress data and tectono-stratigraphic evolution of the Kurai-Chuya basin in Siberian Altai, Zaisan basin in Kazakh South Altai and Issyk-Kul basin in Kyrgyz Tien Shan suggests that they were initiated in an extensional context and inverted by a combination of fault-controlled deformation and flexural folding. In these basins, fault-controlled deformation alone appears largely insufficient to explain their architecture. Lithospheric buckling inducing surface tilting, uplift and subsidence also played an important role. They form typical basins in a folding lithosphere (FLB). Their characteristic basin fill and symmetry, inner structure, folding wavelength and amplitude, thermal regime, time frame are examined in relation to basement structure, stress field, strain rate, timing of deformation, and compared to existing modelling results.

Glorie S., De Grave J., Buslov M.M., Zhimulev F.I., Stockli D.F., Batalev V.Y., Izmer A., Van den haute P., Vanhaecke F., Elburg M.A.

[1] Multimethod chronology was applied on intrusives bordering the Kyrgyz South Tien Shan suture (STSs) to decipher the timing of (1) formation and amalgamation of the suturing units and (2) intracontinental deformation that built the bordering mountain ranges. Zircon U/Pb data indicate similarities between the Tien Shan and Tarim Precambrian crust. Caledonian (∼440–410 Ma) and Hercynian (∼310–280 Ma) zircon U/Pb ages were found at the edge of the STSs, related to subduction and closure of the Turkestan Ocean and the formation of the suture itself. Permian-Triassic (∼280–210 Ma) titanite fission track and zircon (U-Th)/He data record the first signs of exhumation when the STSs evolved into a shear zone and the adjacent Tarim basin started to subside. Low-temperature thermochronological (apatite fission track, zircon and apatite (U-Th)/He) analyses reveal three distinct cooling phases, becoming younger toward the STSs center: (1) Jurassic-Cretaceous cooling ages provide evidence that a Mesozoic South Tien Shan orogen formed as a response to the Cimmerian orogeny; (2) Early Paleogene (∼60–45 Ma) data indicate a renewed pulse of STSs reactivation during the Early Cenozoic; (3) Neogene ages constrain the onset of the modern Tien Shan mountain building to the Late Oligocene (∼30–25 Ma), which intensified during the Miocene (∼10–8 Ma) and Pliocene (∼3–2 Ma). The Cenozoic signals may reflect renewed responses to collisions at the southern Eurasian border (i.e., the Kohistan-Dras and India-Eurasia collisions). This progressive rejuvenation of the STSs demonstrates that deformation has not migrated steadily into the forelands, but was focused on pre-existing basement structures.

Goode J.K., Burbank D.W., Bookhagen B.

[1] In Central Asia's Tien Shan, deformation is distributed across the wide orogen, a characteristic of intracontinental mountain building. Active faults are commonly found within intramontane basins that separate its constituent ranges. In order to explore the controls on this intramontane basin deformation, we study the Naryn Basin of south-central Kyrgyzstan. A series of five balanced cross-sections reveals a transition in patterns of faulting from faults confined to basin margins to faults focused within the basin center. The 20-km-wide eastern Naryn Basin displays deformation attributed to low-angle splays of the northern, basin-bounding fault. In the 40-km-wide western Naryn Basin, the pattern of deformation linked to the northern range remains, but is accompanied by steeper faults that dip both south and north without being directly linked to the basin-bounding fault. We compare these cross-sections to synthetic aperture radar interferometry (InSAR) measurements of surface deformation. Profiles of InSAR-derived surface deformation rates across the Naryn Basin reveal that in the west, deformation is distributed across the broad basin interior, whereas in the east, rapid uplift is concentrated at the margin of the narrower basin. From the geodetic and structural data, we infer that in the western Naryn Basin, deformation has migrated away from the northern basin margin and into the interior. Deformation of the eastern basin interior, however, remains linked to the basin-bounding fault. A simple mechanical model demonstrates that basin width may control basin deformation whereby basin-interior faulting in the narrow, eastern Naryn Basin is inhibited by the overburden of adjacent ranges.

Burtman V.S.

Geological and biogeographical data on the paleooceanic basins of the Tien Shan and High Asia are summarized. The oceanic crustal rocks in the Tien Shan, Pamir, and Tibet belong to the Tethian and Turkestan-Paleoasian systems of paleooceanic basins. The tectonic evolution of these systems in the Phanerozoic was not coeval and unidirectional. The sialic blocks of the future Tien Shan, Pamir, and Tibet were incorporated into the Eurasian continent during several stages. In the Late Ordovician and Silurian several microcontinents were preliminarily combined into the Kazakh-Kyrgyz continent as a composite aggregation. The territories of the Tien Shan and Tarim became a part of Eurasia after the closure of the Turkestan, Ural, and Paleotethian oceans in the Late Carboniferous and Early Permian. The territories of the Pamir, Karakorum, Kunlun, and most of Tibet attached to the Eurasian continent in the Triassic. The Lhasa and Kohistan blocks were incorporated into Eurasia in the Cretaceous, whereas Hindustan was docked to Eurasia in the Paleogene.

Makarov V.I., Alekseev D.V., Batalev V.Y., Bataleva E.A., Belyaev I.V., Bragin V.D., Dergunov N.T., Efimova N.N., Leonov M.G., Munirova L.M., Pavlenkin A.D., Roecker S., Roslov Y.V., Rybin A.K., Shchelochkov G.G.

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.

Berdichevsky M.N., Dmitriev V.I.

Buslov M.M., Kokh D.A., De Grave J.

Abstract Apatite fission-track (AFT) thermochronological modeling as a diagnostic tool for periods of stability (peneplanation) and tectonic activity (orogeny) has been broadly used in tectonic studies of Central Asia in recent years. We discuss more than 100 AFT ages of samples from the Kyrgyz Tien Shan and Altai and compare them with AFT data from northern Kazakhstan. Geological, geomorphological, and AFT data indicate intense activity in the Late Cenozoic Eurasian continental interior. The impact from the India-Eurasia collision on the northern Tien Shan, Altai, and northern Kazakhstan regions showed up at 11, 5, and 3 Ma, respectively, as a result of stress propagation into the continent, with the ensuing reactivation and mountain growth. We hypothesize that a distant effect of the Late Cenozoic India-Eurasia collision was to rejuvenate Paleozoic fault zones and to deform the Mesozoic sedimentary cover north of the collision front as far as the West Siberian Plate. The reactivation facilitated formation of tectonic oil and gas traps. The activity in northern Central Asia under the effect of the Indian indentation into Eurasia appears to continue and may evolve to include uplift of southern West Siberian plate with uplift.