Permian to Cretaceous granites and felsic volcanics from SW Vietnam and S Cambodia: Implications for tectonic development of Indochina

Tod Waight,Lars H Nielsen,Tran Van Tri,Tonny B Thomsen,Dirk Frei,Ioannis Abatzis,Michael B.W Fyhn

doi:10.1016/j.jseaes.2021.104902

Abstract

Zircon ages and geochemistry are presented for igneous rocks from SW Vietnam and S Cambodia. Four main age groupings occur: Cretaceous (107–75 Ma), Early Jurassic (195 Ma), Late Triassic (230–222 Ma), and Permian (294–265 Ma). Cretaceous and Jurassic samples are amphibole-bearing biotite granodiorites to biotite granites and occur mainly east of the Kampot Fold Belt. Pre-Cretaceous samples occur within the Kampot Fold Belt and are dominantly felsic volcanics. The rocks are primarily high-K calc-alkaline, weakly peraluminous rhyolites or granites, with similar arc-like trace element patterns. Cretaceous granites are similar to Dalat Zone Granites and formed during Pacific subduction. Two Cretaceous granites have adakite-like signatures. The youngest Cretaceous granite has an A-type signature and may represent post-collision activity following the cessation of subduction. Jurassic granites are also linked to Pacific subduction. Two Triassic samples could be affiliated to similarly aged rocks in the Chanthaburi Terrane, or linked to the Loei Fold Belt and related to closure to the Sa Kaeo back arc. We cannot exclude that they are related to Pacific Plate subduction. Correlation of Permian volcanics to paleo-Tethys subduction and the Sukhothai-Chanthaburi arc is not clear as the Cambodian volcanics are older than Chanthaburi rocks, and there are stratigraphic contrasts between S Cambodia and Chanthaburi. Furthermore, such a correlation requires extension of the Sa Kaeo suture into S Cambodia and SW Vietnam at a high angle to regional structures. We propose that the Permian volcanics are also related to Paleo-Pacific subduction as shown in regional reconstructions of the region.

Highlights

Southeast Asia represents a complex collage of crustal blocks, vol canic arcs and suture zones progressively accreted during convergent tectonics associated with opening and closure of the Paleo, Meso, and Ceno-Tethys oceanic basins and subduction of the Paleo-Pacific in the late Paleozoic to Cenozoic (Metcalfe, 2013a, 2021; Hall, 2012) (Fig. 1)
We present U-Pb zircon ages and geochemical data for a comprehensive suite of plutonic and volcanic samples ranging in age from Early Permian to Late Cretaceous from the poorly studied re gions of SW Vietnam and S Cambodia with the aim of contributing to the characterization of this region, linking its geological evolution with the surrounding and better-characterized regions, and bridging the gaps in the literature
This study focuses on the region covered by the westernmost portions of the late Mesozoic Paleo-Pacific magmatic arc in the east in SW Vietnam, and westwards into the Kampot Fold Belt in southern Cambodia (Fyhn et al, 2010a) (Fig. 2)

Summary

Introduction

Southeast Asia represents a complex collage of crustal blocks, vol canic arcs and suture zones progressively accreted during convergent tectonics associated with opening and closure of the Paleo-, Meso-, and Ceno-Tethys oceanic basins and subduction of the Paleo-Pacific in the late Paleozoic to Cenozoic (Metcalfe, 2013a, 2021; Hall, 2012) (Fig. 1). This process continues today with the northwards collision of India into Asia and Australia into Southeast Asia (e.g., Hall, 1996; Morley, 2012).

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