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ABSTRACT
Magmatic rocks distributed along the western part of the Po Ko fault, which documented tectono-thermal evolution of the Indochina block, when and how they formed are less constrained. Our new geochronological and geochemical data reveal that they were generated at 488–457 Ma and display a variety of SiO2 concentrations (SiO2 = 50.7–72.8 wt%). They also generally show slightly negative Eu anomalies (Eu/Eu* = 0.65–0.98) and enrich in LILEs (e.g. Rb and K) but deplete in HFSEs (e.g. Nb and Ta), consistent with arc-related signatures. Combined with their relatively high Mg# values (Mg# = 56–40) and initial87Sr/86Sr ratios (0.7085–0.7167) but negative εNd(t) values (−2.5 to −3.7), we consider those magmatic rocks originated from an enriched mantle source (e.g. EMII), which was metasomatized in the past. In comparing our data with tectono-thermal events in the southern Truong Son belt, we infer that there existed an ocean (a branch of the proto-Tethys Ocean) between the Truong Son belt and the Kontum massif during Late Cambrian, which subsequently underwent southeast subduction beneath the Kontum mass if initiated at ~488 Ma and terminated at ~457 Ma.
Acknowledgments
This study was financially supported by the National Foundation for Sciences and Technology Development of Vietnam (NAFOSTED) for the project 105.01-2018.320. We are deeply grateful to Mr Pham Binh for thin section preparation and guiding fieldwork. Last but not least many thanks to Ms Pham Dung for guiding zircon separation.
Disclosure statement
No potential conflict of interest was reported by the authors.
Supplementary material
Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2024.2366972.