Petrogenesis of microgranitoid enclaves and their host granites: The example of Late Cretaceous Guyong pluton in Tengchong Block, SW China

Abstract

Granitoids and their hosted microgranitoid enclaves (MEs) can provide crucial information in understanding the evolution of granitoids and continental crustal growth.The Guyong pluton in central Tengchong Block is mainly composed of monzogranites and abundant coeval MEs (76 Ma). This study reports their petrological, geochemical, and Sr-Nd, zircon U-Pb, and Lu-Hf-O isotopic features to shed light on their petrogenesis and the evolution of the Neo-Tethys. The Guyong MEs have low SiO 2 (56.88-69.61 wt%) and high MgO (1.04-3.91 wt%) contents. They have typical igneous textures and are characterized by similar mineral assemblages, chondritenormalized rare earth element diagrams, and Sr-Nd and zircon Hf-O isotopic compositions (ε Hf (t) of À9.0 to À2.3, δ 18 O of 6.57-8.07) with their host monzogranites, indicating that they are cognate. The acicular apatite and fine-grained texture and geochemical characteristics suggest that the MEs were generated in a rapid cooling and crystallization process at the margin of magma conduit. The Guyong monzogranites have high SiO 2 contents (70.79-74.24 wt%) and low MgO contents (0.24-0.78 wt%). They are calc-alkalic and weakly peraluminous and show characteristics of I-type granites. The geochemical and isotopic compositions of the Guyong monzogranites and MEs suggest that they were produced by partial melting of the metasedimentary and meta-igneous rocks from the Proterozoic Gaoligong metamorphic complex. The Late Cretaceous magmatism in the central Tengchong Block is correlated with the northward subduction of the Neo-Tethys.