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中南大学学报(英文版)

Journal of Central South University

Vol. 26    No. 12    December 2019

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Petrogenesis of Middle Triassic andesite in Sayaburi area,Laos: Constraints from whole-rock geochemistry, zircon U-Pb geochronology, and Sr-Nd isotopes
OUYANG Yuan(欧阳渊)1, 2, LIU Hong(刘洪)2, NIE Fei(聂飞)2, CONG Feng(丛峰)2, ZHANG Jian-long(张建农)2, ZHANG Jing-hua(张景华)2, HUANG Han-xiao(黄瀚霄)2, LIU Shu-sheng(刘书生)2, LEI Chuan-yang(雷传扬)3

1. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China;
2. Chengdu Center, China Geological Survey, Chengdu 610081, China;
3. Sichuan Geological Survey, Chengdu 610081, China

Abstract:Despite the presence of a large area of andesite in the Sayaburi Province of Laos, it has received very little attention. Based on a combination of detailed field investigations, geochronology and geochemical analysis, this study aims to explore the geochemical, Sr-Nd isotopic, and source rock characteristics, as well as the genesis and tectonic setting of the andesite in this region. In the Sayaburi Province, the andesite zircon U-Pb age is (241.2±1.2) Ma. The andesite rock is classified in the metaluminous-weak peraluminous calc-alkaline series. The light rare-earth elements (LREEs) are enriched and characterized by clear fractionation, whereas heavy rare-earth elements (HREEs) are relatively depleted and have no signs of fractionation. The average δEu is 0.96 with weak-or-no Eu anomalies. It is enriched in large ion lithophile elements such as Rb and K, while depleted in high field-strength elements such as Nb, Ta, P and Ti. For andesites in the Sayaburi Province, the (87Rb/86Sr)t value ranges in 0.702849-0.704687, the εNd(t) value is between 3.53 and 4.77, the tDM(t) value ranges in 633-835 Ma, and the tDM2(t) ranges in 625–724 Ma. The results based on the synthesis of petrology, geochemistry, and regional tectonic background studies show that 1) the andesitic magma source in the study area is an enriched mantle, which is modified by subduction zone fluids; 2) the geotectonic background environment of the andesite in Sayaburi area is the continental island arc environment and related to the tectonic evolution of Jinghong–Nan–Uttaradit back-arc basin, which reflects that the magmatic source is enriched with a mantle wedge component modified by a subduction zone fluid (or melt).

 

Key words: Laos; Sayaburi area; zircon U-Pb geochronology; geochemistry

中南大学学报(自然科学版)
  ISSN 1672-7207
CN 43-1426/N
ZDXZAC
中南大学学报(英文版)
  ISSN 2095-2899
CN 43-1516/TB
JCSTFT
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