New geochronology and geochemistry of felsic dykes in Kontum massif, central Vietnam: implications for Permian-Triassic tectonics in the Indochina block

Felsic dykes (FDs) are widely dispersed in the Kontum massif (KM), particularly along the near-meridional and northeast-southwest directions. The observed length of the FDs ranges from a few dozen metres to over 1,000 metres, and they are 0.5 to 15 m wide. They also penetrate into Hai Van host granite (243 Ma). The FDs mainly consist of aplites, rhyolitic dykes, and dacitic dykes. The rock-forming minerals include phenocrysts of plagioclase, K-feldspar, quartz, and biotite as well as groundmass of plagioclase, K-feldspar, quartz biotite, sericite, and ore. Zircons separate from the FDs, exhibit euhedral shapes and high-luminescence under CL imaging, evident zoning structure, and a Th/U ratio greater than 0.1, indicating magmatic origin. The U-Pb zircon age analysis yielded an average ²⁰⁶Pb/²³⁸U age of 241–239 Ma, corresponding to the Middle Triassic period. The FDs have negative ε_Hf(t) values ranging from −10.2 to −7.3 (mean value = -8.9 ± 2.6, MSWD = 0.029) and T_DM2 model ages ranging from 1731 to 1918 Ma. This indicates that the FDs in the KM were formed by mixing mantle materials with Meso-Paleoproterozoic crustal materials. Their formation may be connected to the Indochina and South China blocks’ post-collision extensional process, which facilitated the ascent and emplacement of FDs.