Paleozoic geodynamics and architecture of the southern part of the Mongolian Altai Zone

Published: 19 August 2022| Version 1 | DOI: 10.17632/x3kgmywvj6.1
Contributor:
Turbold Sukhbaatar

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I am a corresponding author of a paper named "Paleozoic Geodynamics and Architecture of the Southern Part of the Mongolian Altai Zone" that have recently accepted at the Tectonics in AGU and stored our data on behalf of the co-authors on the Mendeley Data Repository. The data set (Tables A1-A9) belongs to it is paper and is included original data of the whole-rock geochemistry (Tables A1 and A2), zircon-U-Pb isotopic data (Tables A3-A7), and zircon-Hf isotopic data (Tables A8 and A9). Paleozoic geodynamics and architecture of the southern part of the Mongolian Altai Zone T. Sukhbaatar, O. Lexa, K. Schulmann, C. Aguilar, P. Štípská, J. Wong, Y. Jiang, J. Míková and D. Zhao Abstract The Mongolian Altai Zone of the Central Asian Orogenic Belt has been traditionally interpreted as a mosaic of Paleozoic magmatic arcs, back-arcs, and Precambrian continental terranes. In order to define its architecture and its tectonic evolution, three domains previously interpreted as terranes were investigated. The findings show that the Northern and Central domains are formed by a metamorphic sequence characterized by Barrovian S1 fabric transposed by recumbent folds and dominant sub-horizontal amphibolite facies S2 schistosity. The latter is associated with the intrusions of late Devonian syntectonic granite sheets and anatexis in the south. The Southern domain is formed by early Permian migmatites and anatectic granites separated from the metamorphic envelope by amphibolite to green-schist facies D3 shear zone cross-cutting S2 fabrics. All domains have been reworked by E-W upright folds associated with axial-planar greenschist facies cleavage, reflecting the final mid-Permian to Triassic D4 shortening. Lithological, geochemical, and U-Pb zircon analyses of metasediments of all domains indicate that they are formed by Ordovician mature quartzite derived from Precambrian basement intruded by Cambrian–Ordovician continental arc and Silurian immature graywacke which originated through erosion of an oceanic arc. Altogether, the whole sequence represents a fore-arc basin in front of a migrating arc affected by thickening and late Devonian extension. The Southern domain is interpreted as an early Permian core complex amplified by mid-Permian to Triassic compression. The apparent “terrane” architecture of the Mongol Altai Zone originated due to Devonian and Permian heterogeneous reworking of a giant Ordovician to Silurian fore-arc.

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1. Whole-Rock Analyses The powders produced using an agate mill were analyzed at both the Activation Laboratories Ltd. (Actlabs) and the Bureau Veritas Mineral Laboratories in, Vancouver (Canada). In the Actlabs, 3 sedimentary and 1 magmatic sample were analyzed, using the 4Lithoresearch procedure (http://www.actlabs.com), and the. major-element concentrations were obtained by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and trace-element concentrations by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), following lithium metaborate/tetraborate fusion and weak nitric acid dissolution. For the remaining samples, 4 sedimentary and 5 magmatic rocks, the whole-rock analyses were done using the X-ray fluorescence (XFR) (major and minor elements, code XF700) and the lithium borate fusion inductively coupled plasma - Emission Spectrometer/Mass Spectrometer (ICP-ES/MS) (Ultra Trace, code MA250) in the Bureau Veritas Mineral Laboratories (https://www.bvna.com/sites/g/files/zypfnx386/files/media/document/Bureau-Veritas-CAD-Fee-Schedule-2022.pdf). 2. Uranium-Lead Dating The U-Pb isotopic analyses were performed by Laser Ablation – Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) at the Czech Geological Survey in Prague (Czech Republic). The LA-ICPMS is an Analyte Excite 193 nm excimer Laser Ablation system (LA; Proton Machines), equipped with a two-volume HelEx ablation cell, in tandem with an Agilent 7900x ICPMS (Agilent Technologies Inc., Santa Clara, USA). Samples were ablated in He atmosphere (0.8 l min–1) at a pulse repetition rate of 5 Hz using a spot size of 25 μm and laser fluence of 7.59 J cm–2. 3. Lutetium-Hafnium Dating The Zircon Hf isotope analyses were carried out in two different laboratories in several analytical sequences: a Nu Plasma HR MC-ICP-MS coupled with a Resonetics RESOlution M-50 laser ablation system (LLC, USA) conducted at the Department of Earth Sciences of the University of Hong Kong and a Nu Plasma II MC-ICP-MS (Wrexham, Wales, UK) equipped with a RESOlution LR laser-ablation system (Canberra, Australian) conducted at Nanjing FocuMS Technology Co. Ltd. A spot size of 50–55 μm was used for each analysis sited at the same position as the previous U–Pb spot with highly concordant ages (95%–105% concordance), respectively. Standard zircons (including GJ-1, 91500, Plešovice, Mud Tank and Penglai) were treated as quality control every fifteen unknown samples. The 193 nm ArF excimer laser, homogenized by a set of beam delivery systems, was focused on zircon surface with fluence of 4.5J/cm2. Each acquisition incorporated 20 s background (gas blank), followed by spot at 9 Hz repetition rate for 40 s. Helium(370ml/min) was applied as carrier gas to efficiently transport aerosol out of the ablation cell, and was mixed with argon (~0.97 L/min) via T-connector before entering ICP torch.

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Whole-Rock Analysis, Uranium-Lead Dating, Lutetium-Hafnium Dating

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