Evidence for Ordovician subduction-related magmatism in the Truong Son terrane, SE Laos

implications for Gondwana evolution and porphyry Cu exploration potential in SE Asia

C. J. Gardner*, I. T. Graham, E. Belousova, G. W. Booth, A. Greig

*Corresponding author for this work

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The Truong Son Fold Belt (TSFB) is characterised by Late Carboniferous-Late Triassic metamorphic, volcanic and plutonic rocks, the product of accretion of the Indochina Terrane onto the South China Terrane and a range of composite subduction, collision and extensional events. This study discusses geochronological and geochemical data obtained from a dioritic intrusion and rhyolitic tuff mapped in the Donken area of SE Laos, and previously assigned to the Permian Antoum Granodiorite rock suite within the TSFB. Magmatic zircon U-Pb Q-ICP-MS dating undertaken in this study suggests ages of ca 470 ± 2 Ma for the diorite and ca 476 ± 1.5 Ma for a proximal rhyolitic tuff. Whole-rock geochemistry of both units suggests a subduction-related island arc environment, with calc-alkaline and tholeiitic affinities for the diorite and tuff respectively. The intrusion also exhibits an adakitic signature (high Sr, low Y and HREE contents) suggesting that Ordovician magmatism also occurred within the Indochina Terrane, associated with an enigmatic, early Gondwana subduction event. This intrusion appears part of a broader, bilateral Early Ordovician magmatism, newly linked to the south-east subduction of the Tamky-Phuoc Son Ocean underneath the Kontum terrane, and a north-west subduction beneath the Truong Son terrane. Significantly, sub-economic hydrothermal Cu mineralisation observed within the dioritic intrusion, hints at the presence of local Ordovician, porphyry-style base metal enrichment.
Original languageEnglish
Pages (from-to)139-156
Number of pages18
JournalGondwana Research
Volume44
DOIs
Publication statusPublished - 1 Apr 2017

Keywords

  • porphyry
  • adakite
  • Gondwana
  • zircon U-Pb geochronology
  • Ordovician
  • Truong Son Fold Belt

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