Abstract: Zircon U-Pb dating and geochemical data are reported for actinolitization amphibolites (metamorphic basic rocks) and intermediate-basic volcanic breccias of Nuodong-Anping plutons, southeastern Guangxi. The data show that the formation age of the Nuodong pluton is later than 123 Ma, and the Anping pluton record two important magmatic activities. One was in Yanshanian period (or later) with the youngest age of ~138 Ma, and the other was in Early Paleozoic (452-450 Ma). A large number of captured zircons ranging from Middle Archean-Paleoproterozoic (3076-1806 Ma), Mesoproterozoic-Neoproterozoic to Early Paleozoic in both plutons indicate the existence of the Middle Archean-Paleoproterozoic basement materials and the Mesoproterozoic, Neoproterozoic and Early Paleozoic magmatism. Geochemical data exhibit that the Nuodong pluton is characterized by a flat or slightly loss rare earth elements (REEs) distribution model, with relatively enriched in large-ion lithophile elements (LILEs) (Th, U and Pb) and depleted in high-field-strength elements (HFSEs) (Nb, Ta, Zr, Hf and Ti). The Anping pluton is also enriched in LILEs (Rb, Ba, Th, U and Pb) and depleted in HFSEs (Nb, Ta, P and Ti), but they show enrichment in light REEs and depletion in heavy REEs contents. The geochemical characteristics are similar to the Caledonian (metamorphic) basic rocks in the study area, indicating that the geochemical characteristics of rocks have limitations and multiple solutions in determining the tectonic setting.

Key words: (metamorphic) intermediate-basic rocks, zircon geochronology, geochemistry, the Nuodong and Anping plutons;
Southeastern Guangxi, South China Block