Ordovician continental arc magmatism in the Tam Ky-Phuoc Son Suture Zone, Central Indochina Block, Southeast Asia

The Indochina Block is considered as a part of the Indian and Australian margins of Gondwana, and the Tam Ky-Phuoc Son Suture Zone (TPSZ) lies in its central region as the boundary between the Truong Son Belt and Kon Tum Massif (KTM). However, the early Palaeozoic tectonic nature and timing of magmatism within the TPSZ are still controversial. To tackle the issue, we present herein the zircon U–Pb ages with their trace-element compositions of five dioritic–granitic granitoids in the TPSZ. U–Pb age dating of magmatic zircons from them suggests emplacement ages of ca. 447–450 Ma. Whole-rock geochemistry of the samples shows low TiO₂ contents (0.36–1.18 wt%) and Mg# (42.04–53.07). They display enrichment in light rare earth elements ([La/Yb]_N = 4.10–15.19), pronounced negative Nb, Ta and Ti anomalies relative to the chondrite-normalized rare earth element patterns and primitive mantle-normalized trace-element distribution diagrams. The whole-rock geochemical characteristics together with zircon trace-element compositions from the same samples revealed their petrogenesis of a continental arc tectonic setting. Combining the results from this study together with available data from the TPSZ and its neighbouring units, we suggest accretionary orogenesis was responsible for generation of the Ordovician magmatic arc in the KTM, which will provide better understanding of the Early Palaeozoic evolution of the eastern Indochina Block.