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Geodynamics of the Mongol-Okhotsk belt in NE Mongolia

English title Geodynamics of the Mongol-Okhotsk belt in NE Mongolia
Applicant Winkler Wilfried
Number 121712
Funding scheme Project funding
Research institution Geologisches Institut ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geology
Start/End 01.01.2009 - 31.03.2011
Approved amount 186'142.00
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Keywords (13)

Mongolia; Mongol-Okhotsk belt; collisional belt; geodynamics; terranes; pre-and post-collisional sediments; Central Asian Orogenic Belt; Siberia; provenance analysis; detrital zircons; laser ablation-ICP-MS U/Pb dating; trace elements; Hf isotopes

Lay Summary (English)

Lead
Lay summary
With their detrital composition, sandstone accumulations in basins provide an immediate record of the rocks coevally exposed on the earth surface at particular geological times. Therefore, they corroborate large-scale tectonic movements which drive rock uplift, exhumation and erosion. The quantification of the detrital grains for the description of the rocks exposed in the sediment source areas is called provenance analysis. This method is aimed at identifying characteristic metamorphic, plutonic, volcanic basement rocks and sedimentary cover, and to conclude on the plate tectonic situation of the basins and connected source areas.Standard methods of provenance analysis (e.g. thin sections and heavy minerals) are useful but show limited resolution and therefore, will be complemented by geochronological and geochemical analyses of the ubiquitous zircon grains. Zircon have an extremely long geological memory because very resistant, the grains survive weathering and transport as well as high temperature metamorphism and anatexis. The application of in-situ laser-ablation microprobe-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on detrital zircons reveals their igneous and/or metamorphic U-Pb age, and the chemical composition and crystallization environment of the magma from which they precipitated (essentially using P, Y, Th, U, Nb, Ta, REE and Hf concentrations). 176Hf/177Hf isotope ratios, in addition, are measured to depict their mantle origin or recycled character due to crustal anatexis. As the different measurements can be performed on the same grain, the straight correlation of geological age and geochemical signatures is achieved.The Mongol-Okhotsk Belt extends from Central Mongolia across southeastern Siberia towards the Uda Sea in the northwestern Pacific. The belt formed in a late stage of Jurassic collision within the composite Central Asian Orogenic Belt by the final consumption of the Mongol-Okhotsk ocean. The timing and mode of ocean formation, subduction and the collision of the framing margins is controversial. From structural and sedimentary relationships with the units of the Early Paleozoic domain in northern Mongolia, we hypothesize that the Mongol-Okhotsk ocean opened during Silurian-Devonian by backarc-spreading due to subduction of the Paleotethys under the Siberian, Early Paleozoic margin. Our data set acquired during a first project period is promising by indicating that the fringing margins depict different times of subduction-related volcanism and different source areas in the Devonian and Permian, and in the Carboniferous and Triassic, respectively. Reworking of Early Paleozoic and minor Proterozoic material is evident on the southern margin (in modern coordinates). However, for better constraining our ideas, coeval sediment formations of the Late Paleozoic (Paleotethys) domain in southern Mongolia also will be tested and compared. The obtained data will be synthesized into a geodynamic model of the belt, which will be situated in the larger plate tectonics frame of the Central Asian Orogenic Belt.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
134739 Spätpaläozoische Geodynamik des Zentralasiatischen Orogens in der südlichen Mongolei 01.04.2011 Project funding
134739 Spätpaläozoische Geodynamik des Zentralasiatischen Orogens in der südlichen Mongolei 01.04.2011 Project funding
113645 Geodynamics of the Mongol-Okhotsk belt in NE Mongolia 01.10.2006 Project funding

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