Detailed structural analysis of the formations of the Maksyutov eclogite–glaucophane–schist complex in the Southern Urals has been carried out. U–Pb (LA-ICP-MS) isotopic dates of detrital zircons ...from quartzites of the Yumaguzino and Karamala groups (tectonostratigraphic units) making up the complex were obtained. The data show that both groups are similar in age but differ in the facies formations that comprise the proximal (Yumaguzino Group) and distal (Karamala Group) regions of the Paleozoic margin of the Baltica paleocontinent. The alternation of these groups in the Maksyutov Complex is explained by their tectonic juxtaposition during the formation of the scaly-thrust structure of this complex. Formations of the Maksyutov Complex subsided in the subduction zone beneath the Magnitogorsk island arc and were subjected to fold deformations during the subsequent exhumation. Four deformation stages have been established during the structural evolution of the complex. The first stage is associated with the development of the southwest-vergent folds and sheath folds F
1
and corresponds to the eduction of the formations of the Maksyutov metamorphic complex from the subduction zone of the Magnitogorsk island arc in the southwestern direction (in modern coordinates) in the middle of the Famennian–Late Devonian. The second stage manifests itself in the development of the southeast-vergent folds F
2
, which are most common in the Maksyutov Complex. This stage is associated with an oblique sinistral collision of the Magnitogorsk island arc with the Baltica margin in the Late Devonian. At the third deformation stage, the west-vergent folds F
3
were formed, caused by movements during the Late Paleozoic continental collision in the Main Ural Fault Zone. Postcollisional shear movements at the fourth deformation stage, marked by the development of folds F
4
with steeply dipping hinges, completed the main stage of the structural evolution of the region.
Lenses of eclogites (the Tulepsai complex) that formed at the peak of metamorphism at
P
= 15 kbar and
T
= 700–750°C and experienced decompression at 12 kbar (granulite-facies metamorphism) are ...located among the amphibolite sequences in the Eastern Mugodzhar Zone. The insignificant difference between the age of zircon cores, which, we believe, formed under the conditions of the eclogite-facies metamorphism (374 ± 4 Ma) at depths of 50–60 km (?) and the age of their rims (372 ± 6 Ma) formed during the isothermal decrease in pressure up to 12 kbar (25–35 km?) may indicate a rapid uplift of eclogites from considerable depths. Rutile extracted from eclogites yields a U–Pb age at 360 ± 2 Ma and reflects a later stage of rock transformation at 630–690 ± 40°C. The Maksyutov eclogite–glaucophane–schist and Tulepsai complexes are structural analogs of similar age and compose the lower allochthons on different branches of the Magnitogorsk synform. The complexes were formed in a similar geodynamic setting at the arc–continent collision.
The U–Pb age of accessory zircon of the magmatic protolith for various metamorphic rocks of the UHP Maksyutovo complex is determined by the U–Th–Pb SIMS (SHRIMP II) method. The protolith age is most ...confidently estimated for metabasite shales in two samples (648 ± 3 and 566 ± 3 Ma). The age of zircon from shales, the chemical composition of which corresponds to andesidacites, is 549 ± 4 Ma. The age of the protolith from garnet–omphacite metabasite rocks is 501 ± 5 Ma. Individual crystals of magmatic zircon 893 ± 6 Ma in age, representing a xenogenic population, are separated from eclogites. The age value of 561 ± 10 Ma is taken for the protolith of eclogites, according to the data of the previous researchers. Magmatic complexes with an age close to the age range obtained for the protolith (549–648 Ma) are known in the Uraltau zone and represent fragments of the volcanic–plutonic belt of the active continental margin. The integrated age of metamorphism in the Maksyutovo complex from two samples of this area is 380 ± 3 Ma.
The first U–Pb (LA–ICP–MS) isotope dating of detrital zircons from quartzites of two strata of the Maksyutov metamorphic complex (Southern Urals) was performed. Zircon grains from the Galeevo ...quartzites are well rounded. The concordant zircon ages fall into the ranges of 529–594, 956–2144, and 2709–2781 Ma; the main age peaks are 544, 551, and 1491 Ma. Zircon grains from the Yumaguzino quartzites are idiomorphic and weakly rounded. The concordant zircon ages fall into the ranges of 497–640 and 957–1027 Ma, forming distinct age peaks of 514, 548, and 605 Ma. The U–Pb ages obtained and their comparison with similar data on the other sequences of the Southern Urals and the Caspian Sea Region indicate the Ordovician age of the protolith of the studied quartzites of the Maksyutov complex.
The study is focused on mesostructural folded parageneses of the Taldyk antiform (a.k.a. Taldyk block) located in the East Mugodzhar zone. The sequence of their formation is established; the ...structural evolution of the study area is investigated, and four stages of deformation are identified. The NW-trending folds F1 with SE-vergence formed during the first stage of deformation, DI. The geodynamics and timeline of this stage remain unclear. The W-E-trending folds F2 with E-vergence are related to tectonic movements that took place at stage DII. In the western limb of the antiform, stage DII is evidenced by folds overturned towards the south-east. In the eastern limb, folds plunge to the east and northeast. These fold structures are probably related to the Devonian subduction-obduction processes. At stage DIII, thrusting of the Taldyk antiform over the West Mugodzhar zone and folding F3 with W-vergence is related to the Ural continental collision in the Late Paleozoic, which completed the geodynamic evolution of the Ural paleo-ocean. At stage DIV, postcollisional shearing is evidenced by folds F4 with steeply dipping hinges, which completed the structural evolution of the study area.
Metagabbroid garnet amphibolite formed after high-pressure granulite with an estimated
P–T
peak of 12–16 kbar at 700–790°C occurs at the sole of the Kempirsai ophiolite allochthon (Southern Urals). ...Garnet amphibolite includes high-Fe varieties with the assemblages of garnet and relics of pyroxene, as well as high-alumina rocks composed of garnet, pyroxene, corundum, and sapphirine. The Ediacaran and Early–Middle Palaeozoic sequences underlying the allochthon were metamorphosed under the conditions of amphibolite facies. Our studies were aimed at estimation of the peak metamorphic age of garnet amphibolite. The mean
206
Pb/
238
U (SIMS, SHRIMP II) age obtained for the zircons from garnet amphibolite is 392 ± 4 Ma. The estimated age characterizes the timing of metamorphism related to mantle magmatism accompanying obduction.
New U–Pb SIMS zircon datings from granitoid plutons and dikes of Western Chukotka, together with data obtained earlier, confirm that postcollisional granitoid magmatism and dike intrusion occurred in ...the Aptian–Albian (117–105 Ma ago) and marked a change in the tectonic regime during tectonic evolution of Chukotka Mesozoides from collision to extension. These events might be related to the opening of the Amerasian Basin, which had begun in the Jurassic, and to the formation (in the Aptian–Albian time) of the Makarov and Podvodnikov oceanic basins, as well as the Anakhurgen, Nutesyn, and Kameshkov basins in the continental framework of the Eastern Arctic. The synchronicity of the tectonic extension and spreading events in the Canada Basin, on the one hand, and collisional events, deformations, and reorganization of structural style and sedimentary environment in the South Anyui suture, on the other hand, is noted. This may be regarded as confirmation of the rotation hypothesis of formation of the Amerasian Basin.
The U–Pb (LA-ICP-MS) dating of detrital zircons from the Upper Cretaceous Derevyannye Gory Formation in the Novaya Sibir Island revealed that tuffites and tuffaceous sandstones contain zircons widely ...ranging in age from Archean to Upper Cretaceous. The weighted average age of the youngest zircon population is 88 ± 1.0 Ma, which constrains the lower age limit for sedimentation of the Derevyannye Gory Formation to the Coniacian. The clastic material was transported from the southwest and south to the north and northeast. The main source areas for the Upper Cretaceous sedimentary basin in the Novaya Sibir Island were the Upper Jurassic–Neocomian terrigenous sequences of the New Siberian–Chukotka fold area, lithotectonic complexes of the South Anyui suture, as well as the northern part of the Verkhoyansk–Kolyma fold area, and post-orogenic Aptian–Albian volcanic and plutonic rocks from the Lyakhov Islands and Svyatoi Nos Cape. Triassic terrigenous rocks of the northern Verkhoyansk region could serve as additional sources of clastics. It is also possible that the clastic material was partially supplied from the western Anjou Islands as a result of erosion of the Aptian–Lower Albian volcaniclastic–siliciclastic rocks. The Late Cretaceous zircon population is related to the Late Cretaceous explosive acid volcanism in the eastern Arctic region.
The structural evolution of the Late Precambrian and Early to Middle Paleozoic complexes is considered for the southern part of the Uraltau Zone and its extension in the Ebeta Antiform, as well as ...for the northeastern and northwestern frameworks of the ophiolitic Khabarny Allochthon, where the Late Precambrian and Paleozoic complexes of the continental margin in combination with ophiolites are drawn together in packets of tectonic nappes. The formation of the regional structure took place during several stages in various geodynamic settings. Five deformation stages have been recognized in the regional structural evolution from new data on mesostructural parageneses, which consist of folds that developed within outcrops and their relationships in rocks differing in age. The first stage is related to the Late Precambrian Timanian, or Cadomian Orogeny, and four subsequent deformation stages characterize Paleozoic tectonic evolution of the region. The geodynamic nature of the second stage remains unknown; the third stage is related to overthrusting of ophiolites in the Early Devonian; the fourth stage of deformations marks Late Paleozoic continental collision. The fifth stage of postcollisional strike-slip deformations completes the regional structural evolution.
—
Detailed lithological, stratigraphic, and structural studies of the fold-thrust structures were conducted on New Siberia Island. We have established that the jointly deformed complexes of the Upper ...Cretaceous–Middle Neopleistocene are overlapped by undeformed sediments of the Upper Neopleistocene. This fact confirms the completion of the deformation process at the end of the Middle Neopleistocene. An additional argument excluding the ancient age of dislocations is the result of the fission track dating for apatites. The resulting track ages of apatites significantly exceeded the age of deformed rocks, which was reliably established by the other methods. In deformed complexes, unlithified permafrost rocks predominate. Folded structures are characterized by joint deformation of sedimentary rocks, formation ice and ice-ground, inconsistency of fold orientation and different direction of structural evolution in the northern and southern parts of the island New Siberia. Considering the correspondence of the established age of dislocations to the age of the largest Pleistocene glaciation, all these facts allow us to state that the fold-and-thrust deformations of the island New Siberia are glaciodislocations.
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