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

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
Publication Date
2016
Author(s)
Nie, Xiaomei
Feng, Qinglai
Metcalfe, Ian
( author )
OrcID: https://orcid.org/0000-0003-3538-1686
Email: imetcal2@une.edu.au
UNE Id une-id:imetcal2
Baxter, Alan
( author )
OrcID: https://orcid.org/0000-0002-1278-6536
Email: abaxter9@une.edu.au
UNE Id une-id:abaxter9
Liu, Guichun
Type of document
Journal Article
Language
en
Entity Type
Publication
Publisher
Elsevier Ltd
Place of publication
United Kingdom
DOI
10.1016/j.jseaes.2015.12.026
UNE publication id
une:18638
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.
Link
Citation
Journal of Asian Earth Sciences, v.118, p. 32-50
ISSN
1878-5786
1367-9120
Start page
32
End page
50

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