Выпуск 300
Автор(ы):Cloetingh S., Jan-Diederik van Wees, Ziegler P.A.
Издание:Journal Tectonophysics, 1998 г., 27 стр.
Mechanical controls on collision-related compressional intraplate deformation

Intraplate compressional features, such as inverted extensional basins, upthrust basement blocks and whole lithospheric folds, play an important role in the structural framework of many cratons. Although compressional intraplate deformation can occur in a number of dynamic settings, stresses related to collisional plate coupling appear to be responsible for the development of the most important compressional intraplate structures. These can occur at distances of up to 1600 km from a collision front, both in the fore-arc (foreland) and back-arc (hinterland) positions with respect to the subduction system controlling the evolution of the corresponding orogen. Back-arc compression associated with island arcs and Andean-type orogens occurs during periods of increased convergence rates between the subducting and overriding plates. For the build-up of intraplate compressional stresses in fore-arc and foreland domains, four collision-related scenarios are envisaged: (1) during the initiation of a subduction zone along a passive margin or within an oceanic basin; (2) during subduction impediment caused by the arrival of more buoyant crust, such as an oceanic plateau or a microcontinent at a subduction zone; (3) during the initial collision of an orogenic wedge with a passive margin, depending on the lithospheric and crustal configuration of the latter, the presence or absence of a thick passive margin sedimentary prism, and convergence rates and directions; (4) during post-collisional over-thickening and uplift of an orogenic wedge. The build-up of collision-related compressional intraplate stresses is indicative for mechanical coupling between an orogenic wedge and its fore- and=or hinterland. Crustal-scale intraplate deformation reflects mechanical coupling at crustal levels whereas lithosphere-scale deformation indicates mechanical coupling at the level of the mantle-lithosphere, probably in response to collisional lithospheric over-thickening of the orogen, slab detachment and the development of a mantle back-stop. The intensity of collisional coupling between an orogen and its fore- and hinterland is temporally and spatially variable. This can be a function of oblique collision. However, the build-up of high pore fluid pressures in subducted sediments may also account for mechanical decoupling of an orogen and its fore- and=or hinterland. Processes governing mechanical coupling=decoupling of orogens and fore- and hinterlands are still poorly understood and require further research. Localization of collision-related compressional intraplate deformations is controlled by spatial and temporal strength variations of the lithosphere in which the thermal regime, the crustal thickness, the pattern of pre-existing crustal and mantle discontinuities, as well as sedimentary loads and their thermal blanketing effect play an important role. The stratigraphic record of collision-related intraplate compressional deformation can contribute to dating of orogenic activity affecting the respective plate margin.

МеткиCollision, Compression, Intraplate, Lithosphere, Rheology, Rifting, Коллизия, Литосфера, Рифтогенез
Выпуск 52
Автор(ы):Buslov M.M.
Издание:Russian Geology and Geophysics, 2011 г., 20 стр.
Tectonics and geodynamics of the Central Asian Foldbelt: the role of Late Paleozoic large-amplitude strike-slip faults

The following structural elements have been recognized to constitute the tectonic demarcation of Central Asian Foldbelt: (1) The Kazakhstan–Baikal composite continent, its basement formed in Vendian–Cambrian as a result of Paleoasian oceanic crust, along with Precambrian microcontinents and Gondwana-type terranes, subduction beneath the southeastern margin of the Siberian continent (western margin in present-day coordinates). The subduction and subsequent collision of microcontinents and terranes with the Kazakhstan–Tuva–Mongolia island arc led to crustal consolidation and formation of the composite-continent basement. In Late Cambrian and Early Ordovician, this continent was separated from Siberia by the Ob’–Zaisan ocean basin. (2) The Vendian and Paleozoic Siberian continental margin complexes comprising the Vendian–Cambrian Kuznetsk–Altai island arc and the rock complexes of Ordovician–Early Devonian passive margin and Devonian to Early Carboniferous active margin. Fragments of Vendian–Early Cambrian oceanic crust represented by ophiolite and paleo-oceanic mounds dominate in the accretionary wedges of island arc. The Gondwana-type continental blocks are absent in western Siberian continental margin complexes and supposedly formed at the convergent boundary of a different ocean, probably, Paleopacific. (3) The Middle–Late Paleozoic Charysh–Terekta–Ulagan–Sayan suture-shear zone separating the continental margin complexes of Siberia and Kazakhstan–Baikal. It is composed of fragments of Cambrian and Early Ordovician oceanic crust of the Ob’–Zaisan basin, Ordovician blueschists and Cambrian–Ordovician turbidites, and Middle Paleozoic metamorphic rocks of shear zones. In the suture zone, the Kazakhstan–Baikal continental masses moved westward along the southeastern margin of Siberia. In Late Devonian and Early Carboniferous, the continents amalgamated to form the North Asian continent. (4) The Late Paleozoic strike-slip faults forming an orogenic collage of terranes, which resulted from Late Devonian to Early Carboniferous collision between Kazakhstan–Baikal and Siberian continents and Late Carboniferous to Permian and Late Permian to Early Triassic collisions between East European Craton and North Asian continent. As a result, the Vendian to Middle Paleozoic accretion-collisional continental margins of Siberia and the entire Kazakhstan–Baikal composite continent became fragmented by large-amplitude (up to a few thousand kilometers) strike-slip faults and conjugate thrusts into several strike-slip terranes, which mixed with each other and thus disrupted the original geodynamic, tectonic, and paleogeographic demarcation.

МеткиAccretion, Central Asian Foldbelt, Collision, Island arcs, Late Paleozoic displacements, Microcontinents, Terranes, Аккреция, Коллизия, Микроконтинент, Террейн, Центральная Азия
Автор(ы):Buslov M.M., Dmitrieva N.V., J. De Grave, Travin A.V., Zhimulev F.I.
Издание:Russian Geology and Geophysics, 2011 г., 15 стр.
Early–Middle Ordovician nappe tectonics of the junction between the Kokchetav HP-UHP metamorphic belt and the Stepnyak paleoisland arc

The North Kokchetav tectonic zone is located between the Kokchetav HP-UHP metamorphic belt and the Stepnyak zone of Ordovician island arc and oceanic complexes. The Kokchetav zone is a collage of nappes (thrust sheets) that consist of basement gneiss and sedimentary rocks of the Kokchetav microcontinent, granite gneiss, mica schists with eclogite blocks, the Shchuch’e ophiolite, Middle Proterozoic felsic volcanics, and Arenigian siliceous-terrigenous sediments with olistostromes. The latter are of gravity-sliding origin and their clastic material includes quartz-muscovite and quartz-garnet-muscovite schists, gneiss, dolomite, and amphibolite. The sheet boundaries are marked by mylonite and Early Ordovician mica schists (40Ar/39Ar ages of syntectonic muscovite are 489–469 Ma). The North Kokchetav collage of compositionally diverse thrust sheets can be interpreted as a collisional zone. According to geological evidence, tectonic activity in the zone lasted as late as the Middle Ordovician. Syncollisional thrusting in the North Kokchetav zone was coeval with the latest dynamic metamorphic event in the history of the Kokchetav belt. All events of retrograde metamorphism and exhumation of HP and UHP rocks in the belt have Cambrian ages, i.e., the rocks had been exhumed prior to the Early–Middle Ordovician collisions and the related orogeny.

ТематикаРегиональная геология
Метки40Ar/39Ar dating, Collision, Early Paleozoids of Kazakhstan, Exhumation, High-pressure rocks, Kokchetav metamorphic belt, North Kokchetav tectonic zone, Olistostrome, Thrust sheet, Кокчетавский метаморфический пояс, Коллизия, Олистостромы
Том 47, Выпуск 4
Автор(ы):Buslov M.M., Dobretsov N.L., Travin A.V., Zayachkovsky A.A., Zhimulev F.I.
Издание:Russian Geology and Geophysics, 2006 г., 17 стр., УДК: 551.24:552.48 (574)
Vendian-early ordovican geodynamic evolution and model for exhumation of ultrahigh- and high-pressure rocks from the Kokchetav subduction-collision zone (northern Kazakhstan)

The Kokchetav subduction-collision zone (KSCZ) hosting ultrahigh- and high-pressure (UHP-HP) rocks underwent the multistage Vendian-Early Ordovician geodynamic evolution. The subduction of the Paleoasian oceanic lithosphere bearing blocks of continental crust and the collision of the Kokchetav microcontinent with the Vendian-Cambrian island-arc system ultimately led to the formation and exhumation of UHP-HP rocks. In the Vendian-Early Cambrian the margin of the Kokchetav microcontinent deeply subsided into the subduction zone (150–200 km), which led to UHP-HP metamorphism (the maximum at about 535 Ma) and to partial melting of its rocks. In next stage (535–528 Ma), the generated acidic melts including blocks of UHP-HP rocks quickly, at a rate of 1 m/year, ascended to depths of 90 km for 1 Myr. During subsequent 5 Myr, the UHP-HP rocks ascending at a rate of 0.6–1 cm/year reached the base of the accretionary prism (depths of 60–30 km). Then, in the period from 528 to 500 Ma, the UHP-HP rocks ascended along the faulting structures of the lower crust as a result of jamming the subduction zone by the Kokchetav microcontinent. During the period from 500 to 480 Ma, the UHP-HP rocks became part of the upper crust. This process led to the KSCZ, which comprises terranes of the Vendian-Early Arenigian subduction zone occurring at different depths, separated by zones of garnet-mica and mica schists, blastomylonites and mylonites. In the same period there was a jump of subduction zone, which led to the formation of the Ordovician Stepnyak island arc. As a result of the Late Arenigian-Early Caradocian microcontinent-island arc collisions (480–460 Ma), the KSCZ overrided upon the fore-arc trough of the Stepnyak island arc to form a thick accretion-collision orogen, which having experienced anatectic melting was intruded by collisional granites of the Zerenda complex 460–440 Ma in age.

МеткиCollision, Diamond-coesite gneisses, Eclogites, Exhumation, Kokchetav microcontinent, Olistostromes, Over-thrusts, Subduction, Tectonic nappes, Кокчетав, Кокчетавский массив, Коллизия, Олистостромы, Эклогиты
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