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Spätpaläozoische Geodynamik des Zentralasiatischen Orogens in der südlichen Mongolei

English title Late Paleozoic Geodynamics of the Cenral Asian Orogenic Belt in southern Mongolia
Applicant Winkler Wilfried
Number 134739
Funding scheme Project funding
Research institution Geologisches Institut ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geology
Start/End 01.04.2011 - 30.09.2012
Approved amount 146'272.00
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All Disciplines (3)

Discipline
Geology
Geochronology
Geochemistry

Keywords (6)

Central Asian Orogenic Belt; southern Mongolia; geodynamics; detrital zircons; ICP-MS laser ablation dating; Hf-isotopes

Lay Summary (English)

Lead
Lay summary

Mongolia is a key area of the Central Asian Orogenic Belt (CAOB) because on its territory the complete Neoproterozoic - Paleozoic history of the Paleo-Asian Ocean is preserved in a great variety of tectono-stratigraphic units (terranes). The northern belt (north of the Main Mongolian Lineament, MML) was formed by successive subduction and accretion of oceanic basement, volcanic arcs, and continental blocks against the Siberian craton during Late Proterozoic and Early Paleozoic. Subsequently, the CAOB was completed by the collision of various terranes (intra-oceanic and continental arcs, microcontinents) at the end of the Paleozoic correlating with the closure of the Paleo-Asian Ocean. The present project focuses on the Late Paleozoic history of the Paleo-Asian Ocean south of the MML. In order to develop an accurate model for the southern Mongolian mountain belt, we investigate the clastic sedimentary formations that are comprised within the various terranes south of the MML. We assume that the conglomerates and sandstones closely record with their facies and detrital content, their stratigraphic age, and the bedding relationships, the contemporaneous tectonic processes of basin formation and inversion. The analysis of detrital zircon grains plays a crucial role in our reconstructions.

Standard methods of provenance analysis (e.g. modal framework grain and heavy mineral analyses) are useful but show limited resolution because of high diagenetic overprint and the lack of age informations. Therefore, they will be complemented by geochronological and geochemical analyses of the ubiquitous detrital 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 in detrital zircons). 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 can be achieved.


Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
The Mongol-Okhotsk Belt in Mongolia - an appraisal of the geodynamic development by the study of sandstone provenance und detrital zircons
Bussien D. Gombojav N. Winkler W. von Quadt A. (2011), The Mongol-Okhotsk Belt in Mongolia - an appraisal of the geodynamic development by the study of sandstone provenance und detrital zircons, in Tectonophysics, 510, 132-150.

Collaboration

Group / person Country
Types of collaboration
Mongolian University of Science and Technology Mongolia (Asia)
- in-depth/constructive exchanges on approaches, methods or results

Associated projects

Number Title Start Funding scheme
156244 Neoproterozoic-Cambrian geodynamic history of the Anti-Atlas (Morocco) and implications for the European Alpine basement 01.10.2014 Project funding
121712 Geodynamics of the Mongol-Okhotsk belt in NE Mongolia 01.01.2009 Project funding
121712 Geodynamics of the Mongol-Okhotsk belt in NE Mongolia 01.01.2009 Project funding

Abstract

Mongolia is a key area of the Central Asian Orogenic Belt (CAOB) because on its territory the complete Neoproterozoic - Paleozoic history of the Paleo-Asian ocean is preserved in a great variety of tectono-stratigraphic units (called terranes). The northern belt (north of the Main Mongolian Lineament, MML) was formed by successive subduction and accretion of oceanic basement, volcanic arcs, and continental blocks against the Siberian craton during Late Proterozoic and Early Paleozoic. This early tectonic collage was unconformably cut by the opening of the Mongol-Okhotsk ocean presumably as backarc basin due to continued northward (in actual coordinates) subduction of the Paleo-Asian ocean. Previous project work in the Mongol-Okhotsk Belt (MOB) using data from associated sandstone formations (see details below) revealed the subsequent subduction of the ocean basin as paralleled by continental arc development on both margins. The final collision of the margins occurred in the Triassic - Early Jurassic. The present project focuses on the Late Paleozoic history of the Paleo-Asian ocean south of the MML, which is contemparaneous with the development of the MOB. We want to reconstruct in time and space the processes working during the consumption of the two oceans.In order to develop an accurate model for the Late Paleozoic southern Mongolian mountain belt, we investigate the clastic sedimentary formations that are comprised within the various terranes south of the MML. The conglomerate and sandstones closely record with their facies and detrital content, their stratigraphic age, and the bedding relationships, the contemporaneous tectonic processes of basin formation and inversion. The analysis of detrital zircon grains will play a crucial role in our reconstructions. We combine (1) genetic facies analysis (sedimentary environment), (2) sedimentary source rock analysis (sandstone framework grains, heavy minerals), (3) single detrital zircon grain U/Pb laser ablation ICP-MS dating reflecting the age of source rocks and eventual multiple recycling, (4) trace element analysis of detrital zircons (essentially using P, Y, Th, U, Nb, Ta, REE and Hf concentrations) indicating the magmatic environment in which the zircons crystallized, and (5) 176Hf/177Hf isotope ratios 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.
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