Ophiolites of the Central Asian Orogenic Belt: Geochemical and petrological characterization and tectonic settings

We present a compilation of published data (field, petrography, ages and geochemistry) from 73 ophiolitic complexes of the Central Asian Orogenic Belt. The ophiolitic complexes, ranging in age from Neoproterozoic to Triassic, have been geochemically classified as subduction-related and subduction-unrelated categories applying recent, well-established discrimination diagrams. The subduction-unrelated category is further subdivided into Mid-Ocean Ridge type (MOR), a common rift-drift stage and Plume type, and the subduction-related category is subdivided into Backarc (BA), Forearc (FA), Backarc to Forearc (BA-FA) and Volcanic Arc (VA) types. The four subduction-related types define highly different geochemical features, with the BA and FA types defining end members showing subduction influence of 10%–100% and 90%–100% subduction influence, respectively, and the two other types (BA-FA and VA) define values between the two end members. The subduction-related category comprises 79% of the examined ophiolites, of which the BA type ophiolites is by far the dominant group, followed by the BA-FA type, and with FA and VA types as subordinate groups. The Neoproterozoic and Ordovician complexes exhibit the highest, whereas those of Silurian age exhibit the lowest subduction-influence. Of the remaining 21% subduction-unrelated ophiolites, the MOR type dominates. Both the subduction-related and subduction-unrelated types, in particular the latter, are commonly associated with alkaline basalts taken to represent ocean island magmatism. Harzburgite, dunite, gabbro and basalt are the common lithologies in all ophiolite types, whereas the BA-FA, FA and VA types generally contain intermediate to felsic rocks, and in the FA type boninites occur. The subduction-related ophiolites types generally show low metamorphic grade, whereas greenschist, amphibolite and blueschist grades occur in the subduction-unrelated and BA types. The highly different subduction contribution (from 0 to 100% in the MOR and FA, respectively), attest to variable dips of the subducting slab, as well as variable flux of subduction-related elements into the mantle above subducting slabs, from where the ophiolite magmas got their geochemical fingerprints. As most MOR ophiolites get subducted to the deep mantle, the subduction-related ophiolites have become a dominant ophiolitic type on Earth's surface through all times supporting the idea about the early start of Plate Tectonics.publishedVersio

Developing flexibility of female variety dance students

The use of the developed complex of static exercises of a stretching nature using expanders made it possible to increase the flexibility indicators of female students engaged in variety dances. The complex of static exercises of a stretching nature using band and ring expanders included 4 blocks of static exercises for the development of mobility of the shoulder girdle, spinal column, hip and ankle joints. All exercises were performed slowly and with certain retention for a while, which contributed to the safe execution of the complex

Orogen architecture and crustal growth from accretion to collision (IGCP#662): Scientific Activities 2018-2019

The scientific board of the International Geoscience Programme (IGCP), jointly sponsored by IUGS and UNESCO, approved for funding in March 2018 the IGCP-662 project (2018-2023) entitled “Orogenic architecture and crustal growth from accretion to collision”. Four meetings and field excursion, as well as training courses, have been successfully held respectively in 2018 and 2019. The first workshop was held during 21th - 22nd September 2018 in Beijing, China, with a 5-day (15th - 19th September) preworkshop field trip and one-day (23 September 2018) post-conference training course on “Using isotopes in zircon and sulfides to understanding crust-mantle evolution”. The second workshop and field trip of the IGCP-662 project were held in Mongolia from July 4th - 10th, 2019. Besides, the IGCP-662 project joined as co-sponsor the organization of an international symposium “The Geology of Eurasia” held at the Helmholtz-Centre Potsdam - German Research Centre for Geosciences (GFZ) during 26th June - 1st July 2019.This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited

The Russian-Kazakh Altai orogen: An overview and main debatable issues

The paper reviews previous and recently obtained geological, stratigraphic and geochronological data on the Russian-Kazakh Altai orogen, which is located in the western Central Asian Orogenic Belt (CAOB), between the Kazakhstan and Siberian continental blocks. The Russian-Kazakh Altai is a typical Pacific-type orogen, which represents a collage of oceanic, accretionary, fore-arc, island-arc and continental margin terranes of different ages separated by strike-slip faults and thrusts. Evidence for this comes from key indicative rock associations, such as boninite- and turbidite (graywacke)-bearing volcanogenic-sedimentary units, accreted pelagic chert, oceanic islands and plateaus, MORB-OIB-protolith blueschists. The three major tectonic domains of the Russian-Kazakh Altai are: (1) Altai-Mongolian terrane (AMT); (2) subduction-accretionary (Rudny Altai, Gorny Altai) and collisional (Kalba-Narym) terranes; (3) Kurai, Charysh-Terekta, North-East, Irtysh and Char suture-shear zones (SSZ). The evolution of this orogen proceeded in five major stages: (i) late Neoproterozoic–early Paleozoic subduction-accretion in the Paleo-Asian Ocean; (ii) Ordovician–Silurian passive margin; (iii) Devonian–Carboniferous active margin and collision of AMT with the Siberian continent; (iv) late Paleozoic closure of the PAO and coeval collisional magmatism; (v) Mesozoic post-collisional deformation and anarogenic magmatism, which created the modern structural collage of the Russian-Kazakh Altai orogen. The major still unsolved problem of Altai geology is origin of the Altai-Mongolian terrane (continental versus active margin), age of Altai basement, proportion of juvenile and recycled crust and origin of the middle Paleozoic units of the Gorny Altai and Rudny Altai terranes

Ophiolites of the Central Asian Orogenic Belt: Geochemical and petrological characterization and tectonic settings

We present a compilation of published data (field, petrography, ages and geochemistry) from 73 ophiolitic complexes of the Central Asian Orogenic Belt. The ophiolitic complexes, ranging in age from Neoproterozoic to Triassic, have been geochemically classified as subduction-related and subduction-unrelated categories applying recent, well-established discrimination diagrams. The subduction-unrelated category is further subdivided into Mid-Ocean Ridge type (MOR), a common rift-drift stage and Plume type, and the subduction-related category is subdivided into Backarc (BA), Forearc (FA), Backarc to Forearc (BA-FA) and Volcanic Arc (VA) types. The four subduction-related types define highly different geochemical features, with the BA and FA types defining end members showing subduction influence of 10%–100% and 90%–100% subduction influence, respectively, and the two other types (BA-FA and VA) define values between the two end members. The subduction-related category comprises 79% of the examined ophiolites, of which the BA type ophiolites is by far the dominant group, followed by the BA-FA type, and with FA and VA types as subordinate groups. The Neoproterozoic and Ordovician complexes exhibit the highest, whereas those of Silurian age exhibit the lowest subduction-influence. Of the remaining 21% subduction-unrelated ophiolites, the MOR type dominates. Both the subduction-related and subduction-unrelated types, in particular the latter, are commonly associated with alkaline basalts taken to represent ocean island magmatism. Harzburgite, dunite, gabbro and basalt are the common lithologies in all ophiolite types, whereas the BA-FA, FA and VA types generally contain intermediate to felsic rocks, and in the FA type boninites occur. The subduction-related ophiolites types generally show low metamorphic grade, whereas greenschist, amphibolite and blueschist grades occur in the subduction-unrelated and BA types. The highly different subduction contribution (from 0 to 100% in the MOR and FA, respectively), attest to variable dips of the subducting slab, as well as variable flux of subduction-related elements into the mantle above subducting slabs, from where the ophiolite magmas got their geochemical fingerprints. As most MOR ophiolites get subducted to the deep mantle, the subduction-related ophiolites have become a dominant ophiolitic type on Earth's surface through all times supporting the idea about the early start of Plate Tectonics

Mud volcano origin of the Mottled Zone, South Levant

The Mottled Zone (MZ) or Hatrurim Formation, which occurs near the Levantine Transform in the South Levant, has been studied during the last 150 years but its origin remains debatable. Mottled Zone Complex/Complexes (MZC/MZCs) consist of brecciated carbonate and low-temperature calcium-hydrosilicate rocks, which include unusual high- and ultra-high-temperature low-pressure (HT-LP) metamorphic mineral assemblages. The MZ has been regarded as a product of combustion of bituminous chalks of the Ghareb Fm. of Cretaceous (Maastrichtian) age. In this paper we present detailed geographic, geomorphologic, structural and geological data from the MZCs of the South Levant, which show that the MZCs cannot be stratigraphically correlated with the Ghareb Fm., because MZC late Oligocene–late Pleistocene deposits occur within or unconformably, i.e., with stratigraphic hiatus, overlap both the late Cretaceous and, in places, Neogene stratigraphic units. We propose an alternative model for the formation of MZCs by tectonically induced mud volcanism during late Oligocene–late Pleistocene time. This model explains (i) the presence of dikes and tube-like bodies, which consist of brecciated exotic clastic material derived from stratigraphically and hypsometrically lower horizons; (ii) mineral assemblages of sanidinite facies metamorphism; (iii) multi-stage character of HT-LP pyrometamorphism; and (iv) multi-stage low-temperature hydrothermal alteration. High temperatures (up to 1500 °C) mineral assemblages resulted from combustion of hydrocarbon gases of mud volcanoes. Mud volcanism was spatially and structurally related to neotectonic folds and deformation zones formed in response to opening of the Red Sea rift and propagation of the Levantine Transform Fault. Our model may significantly change the prospects for oil-and-gas deposits in the region

Triggers and sources of volatile-bearing plumes in the mantle transition zone

The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ) in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbonated sediments and basalts and serpentinite of oceanic slabs, which can be subducted down to the deep mantle. Tectonic erosion of continental crust supplies crustal material enriched in uranium and thorium into the mantle, which can serve source of heat in the MTZ. The heating in the MTZ induces melting of subducted slabs and continental crust and mantle upwelling, to produce OIB-type mafic and felsic melts, respectively

Geochemical characterization of ophiolites in the Alpine-Himalayan Orogenic Belt: Magmatically and tectonically diverse evolution of the Mesozoic Neotethyan oceanic crust

Ophiolites are important archives of oceanic crust development and preservation in the rock record, and the Alpine-Himalayan Orogenic Belt (AHOB) is one of the most comprehensive ophiolite depositories in earth’s history. We have compiled published data on the field occurrences and geochemistry from 137 AHOB ophiolites, ranging in age from Triassic through Cretaceous, in order to characterize the nature of the Mesozoic Neotethyan oceanic crust. We have used in this synthesis our recent ophiolite classification approach and applied the most effective geochemical discrimination diagrams to categorize the Neotethyan ophiolites within the AHOB. The subduction-related, Backarc (BA), Forearc (FA), Backarc to Forearc (BA-FA) and Volcanic Arc (VA) ophiolites exhibit different geochemical features, with the BA and FA types defining the end-members with low-high and high subduction influence, respectively. The subduction-related ophiolites constitute 76% of the ophiolite record in the AHOB, with the BA type ophiolites being the most dominant group (43%), followed by the BA-FA (19%) and with FA and VA types as subordinate groups (8% and 6%, respectively). The subduction-unrelated ophiolites, making up 24% of the AHOB ophiolite archive, include Mid-Ocean Ridge (MOR), Continental Margin, and Plume type ophiolites. The MOR type comprises 19% of this total and is the dominant type in the western part of the AHOB. Both major ophiolite categories are commonly associated with tholeiitic to alkaline ocean island basalt (OIB) associations, which represent the remnants of plume-proximal magmatism in different Neotethyan seaways. Subduction-unrelated ophiolites in the westernmost end of the Neotethyan realm were derived from downgoing oceanic plates, and were involved in high-pressure, subduction zone metamorphism prior to their exhumation along the suture zones. Subduction-related ophiolites, derived from the upper plates at Neotethyan convergent margins, escaped such high-pressure metamorphism and extreme fragmentation during their emplacement. Therefore, their complete Penrose ophiolite stratigraphy with greenschist facies metamorphic overprint is commonly well preserved in the collision zones of the AHOB. Different subduction contributions (from zero to 100% in the MOR and FA, respectively) may attest to variable slab dip angles and fluctuations in slab-induced elements and sediments into the mantle melt source of ophiolite–forming magmas

Detrital zircon provenance of early Palaeozoic sediments at the southwestern margin of the Siberian craton: insights from U-Pb geochronology

Abstract not availableS. Glorie, J. De Grave, M.M. Buslov, F.I. Zhimulev, I.Yu. Safonov