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Title: Discovery of a Late Devonian magmatic arc in the southern Lancangjiang zone, western Yunnan: Geochemical and zircon U-Pb geochronological constraints on the evolution of Tethyan ocean basins in SW China
Contributor(s): Nie, Xiaomei (author); Feng, Qinglai (author); Metcalfe, Ian  (author); Baxter, Alan  (author); Liu, Guichun (author)
Publication Date: 2016
DOI: 10.1016/j.jseaes.2015.12.026
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Abstract: The Tibetan Plateau and western Yunnan are known to have formed by the amalgamation of Gondwana-derived continental blocks and arc terranes as a result of Tethyan subduction followed by continental collisions during the Paleozoic, Mesozoic and Cenozoic. The Devonian and the southern Lancangjiang zone, western Yunnan is a critical period and key region for studying the transformation between the "Proto-Tethyan" and Paleo-Tethyan oceanic systems. New geochemical data and LA-ICPMS U-Pb zircon ages of the Late Devonian volcanogenic sediments from the southern Lancangjiang zone in western Yunnan, SW China, are presented. The studied sedimentary rocks of the Nanguang Formation are volcaniclastic rocks with high volcanic lithic content (55-65%, mostly andesite, dacite, with some rhyolite and tuffs). Whole rock geochemistry, zircon trace elements and detrital modal analyses indicate derivation from a subduction-related magmatic arc. Three tuff samples yield Late Devonian weighted mean 206Pb/238U ages of 378 ± 4 Ma, 366 ± 5 Ma and 382 ± 8 Ma, suggesting a Late Devonian depositional age. 104 zircon U-Pb analyses on 104 zircon grains from two sandstone samples present extremely tight age clusters, mostly ranging from 380 Ma to 360 Ma. This indicates a single Late Devonian igneous source. A short transport distance and a high rate of denudation and deposition within an arc-related basin are considered likely for the tuffs and volcaniclastic rocks in this study. This implies the presence of an as yet unidentified Late Devonian magmatic arc in the southern Lancangjiang zone. The cryptic Late Devonian arc is likely to represent either a continuation of Late Ordovician-Late Silurian "Proto-Tethyan" subduction or the initial stage of the Paleo-Tethyan Lincang Arc and indicates that subduction of the Changning-Menglian ocean beneath the Simao/Indochina Block occurred in the Late Devonian.
Publication Type: Journal Article
Source of Publication: Journal of Asian Earth Sciences, v.118, p. 32-50
Publisher: Pergamon Press
Place of Publication: United Kingdom
ISSN: 1878-5786
Field of Research (FoR) 2008: 040313 Tectonics
040303 Geochronology
040202 Inorganic Geochemistry
Field of Research (FoR) 2020: undefined
370502 Geochronology
370302 Inorganic geochemistry
Socio-Economic Objective (SEO) 2008: 840199 Mineral Exploration not elsewhere classified
Socio-Economic Objective (SEO) 2020: undefined
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
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