Caledonian granitoids in the Jinxiu area, Guangxi, South China: Implications for their tectonic setting

Jinxiu area is tectonically located between the Cathaysia and Yangtze blocks of South China. The area has three granitic plutons, Dajin, Boquan, and Lingzu plutons. Geochemically the plutons are high-K calc-alkaline, depleted in Ba, Sr, P, and Ti and rich in Pb, with decoupled Nb and Ta, and show non-island-arc magmatic affinity. Biotite monzogranite samples collected from the Dajin, Boquan, and Lingzu plutons yield zircon SHRIMP (206)pb,/U-238 ages of 419.0 +/- 5.0 Ma, 436.0 +/- 4.0 Ma, and 446.1 +/- 82 Ma, respectively, indicating that the plutons were emplaced during the Late Ordovician to Late Silurian of the Caledonian time. The granodiorite within the Lingzu biotite monzogranite pluton yields a zircon (206)pb/U-238 age of 174.5 +/- 1.9 Ma, indicating a superimposed Late Jurassic magmatic event. The monzogranites and their enclaves show epsilon(Nd(t)) values of -14.7 to -11.1 and -8.0 respectively and T-DM2 values of 2.1-2.4 Ga and 1.8 Ga, respectively, demonstrating that the magmas were derived from re-melted Paleoproterozoic continental crust. Based on geochronology and geochemistry of the granitic plutons, as well as regional stratigraphy and paleontology, it is concluded that any existence of oceanic crust and oceanic subduction was unlikely in the Jinxiu area and vicinity during the Paleozoic Caledonian Ordovician-Silurian time. (C) 2016 Elsevier B.V. All rights reserved.