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

摘要

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.