Petrology and zircon U–Pb geochronology of pelitic gneisses and granitoids from the Dai Loc Complex in the Truong Son Belt, Vietnam: Implication for the Silurian magmatic-metamorphic event

Abstract

The Dai Loc Complex, located in the southern Truong Son Belt, is separated from the northern Kontum Massif by the early Paleozoic Tam Ky–Phuoc Son suture zone. This study presents new zircon U–Pb ages and petrographic observations of the migmatitic pelitic gneisses and mylonitized granite intrusions from the Dai Loc Complex in order to constrain the Early Paleozoic thermal history of the eastern Indochina Block. The identification of metamorphic zircon with sillimanite inclusions, euhedral cordierite, and garnet in the migmatitic pelitic gneisses indicates high temperature metamorphic conditions at ca. 430–440 Ma. The metamorphism was followed by an isobaric cooling stage defined by the replacing of cordierite by kyanite–staurolite–quartz symplectite. The Dai Loc granite likely intruded the metapelites at ca. 430 Ma and was subsequently mylonitized. The thermal event in the Dai Loc Complex may be correlated with Ordovician–Silurian low pressure/high temperature metamorphism caused by subduction related arc magmatism in the Kannack and Ngoc Linh Complexes of the Kontum Massif. However, the frequency distribution of detrital zircon ages suggests the metasedimentary rocks from Dai Loc Complex have a unique provenance that was distinct from those of the neighboring A Vuong Formation and South China Block.