Formation age and petrogenesis of the Xinxing pluton in western Guangdong: Constraint on the closure of the East Paleo-Tethys Ocean

The tectonic framework on the southern margin of South China Block (SCB) between Permian and Triassic Periods has long been a controversial subject. The regional geological survey and research show that the Xinxing pluton in western Guangdong was emplaced in Late Triassic (240-224 Ma) rather than Jurassic, whose main lithology is medium-fine and fine-grained porphyritic monzonitic granite. The Xinxing granite is characterized by high potassium calc-alkaline and peraluminous-strongly peraluminous series, which is enriched in LREE, Rb, U, and depleted in HREE, Nb, Ta, Zr, Hf, Ti. It exhibits relatively low ε_Nd(t) (-11.5- -10.5) and ε_Hf(t) (-2.9- -10.3) values, showing the crustal source affinity. Therefore it is suggested that the start of the Indosinian tectonic-magmatic event in Western Gongdong probably took place in ~250 Ma. These new geochemical and geochronological evidence have furthermore restricted the timing of tectonic activities on the southern margin of SCB between later Permian (Darongshan pluton) and later Triassic (Xinxing pluton). Hence, the closure time of East Paleo-Tethys Ocean would be about 250 Ma, and the continental-continental collision between Indo-China Block and SCB continued till 240-224 Ma.