Timing of magmatism and ultrahigh- to high-grade metamorphism in the Kannak Complex, Kon Tum Massif, Vietnam: Magmatic activity and its tectonic implications

Abstract

Detailed geochronological and petrological investigations of metamorphic and igneous rocks can significantly improve our understanding of the tectonic processes that occur in orogenic belts. The Kon Tum Massif, central Vietnam, includes various types of magmatic and metamorphic rocks, the latter including ultrahigh- to high-temperature units. The Late Permian–Early Triassic metamorphic rocks in the massif correspond to the metamorphic characteristics of a collision between the Indochina and South China blocks in terms of their metamorphic evolution and timescales of deformation. U–Pb geochronological analyses of zircon obtained from two samples of garnet granite in the massif yielded magmatic ages of 239.6 ± 3.9 Ma and 243.5 ± 3.4 Ma. This permitted the reevaluation of previous Th–U–Pb electron microprobe analyses of monazite from the garnet granite and garnet-orthopyroxene gneiss and previously published U–Pb dating. These data reveal the metamorphic and magmatic history of the western part of the massif. The metamorphic rocks show a thermal evolution from 260 Ma to 240 Ma. Magmatic activity started at 260 Ma and ceased at 240 Ma. Considering this in terms of the regional-scale igneous activities in the Kon Tum Massif, the base of the massif, already thickened by the collision, was situated above underplating plume-related magma. Such magmatic activity resulted in high- to ultrahigh-temperature metamorphism and crustal melting during the Late Permian to Early Triassic, between 260 and 240 Ma.