Evolution of the Indochina block from its formation to amalgamation with Asia: Constraints from protoliths in the Kontum Massif, Vietnam

Abstract

This study reported the U-Pb ages and Hf isotopes of the zircons of Triassic and Silurian metamorphic rocks in the Kontum Massif, central Vietnam to understand the origin and evolution of the Indochina Block. The detrital zircon signature of the Triassic metasedimentary rocks corresponds to the Neoproterozoic sequence in the Indochina Block and that of the Silurian rocks corresponds to the Paleo- to Mesoproterozoic sequence in the southwestern margin of the Yangtze Block. From Triassic metaigneous rocks, we obtained three meaningful inherited ages; ~1450 Ma, 500 Ma, and 450 Ma. The Triassic metasedimentary rocks occur in close association with the Triassic felsic gneiss and mafic granulite (former eclogite) with magmatic inherited zircon ~1450 Ma and intermediate gneiss with ~500 Ma protolith age. The Hf isotopes suggest the ~1450 Ma age as the earlier or primary stage of the formation of the Indochina Block and the ~500 Ma age as the timing of its reworking, before the block subducted beneath the South China Block to form Triassic eclogite relicts. The Ordovician magmatic ages (~450 Ma) from metaigneous rocks in the Kontum Massif, combined with their volcanic arc whole-rock chemistry, Ordovician–Silurian low-pressure/high-temperature isobaric heating metamorphism, and the detrital zircon signature strongly suggest an Ordovician–Silurian continental arc in the present southwestern margin of the South China Block prior to the Triassic continental collision.