Discovery of Late Ordovician Subvolcanic Rocks in South China:Existence of Subduction-Related Dacite from Early Paleozoic?
Yi Liwen
Ma Changqian
Wang Lianxun
Lai Zhongxin
Li Xiangyu
Yang Yanan
Wu Fei
Hu Yanru
Abstract：Though Early Paleozoic granites are widely distributed in South China,contemporary volcanic and subvolcanic rocks are rare.This study analyzed dacites from Hekou and Shangdong in Northern Guangdong Province,using detailed LA-ICPMS zircon U-Pb geochronology and Sr-Nd-Hf isotopic geochemistry.The results show that the dacite was formed in 448.7 ± 1.7 Ma,and associated with Late Ordovician volcanism.These rocks are generally porphyritic with prophyroclastic or embayed quartz.The matrixes are normally cryptocrystalline.These features fit well with typical subvolcanic rocks.Geochemically,the dacite is high-K calc-alkaline series.They are enriched in LREE,depleted with Ta,Nb and are extremely low in Cr,Ni con-tents.Isotopic data show that they have I Sr =0.709 0-0.714 0,εNd (t)=-8.9 to -9.3,εHf (t)=-8.06 to -3.80,consist-ent with the isotopic compositions of the Caledonian granitoids in South China.The model ages of two stages based on zircon Hf isotopes range from 1.67 Ga to 1.93 Ga,consistent with the whole rock Nd dating (1.91 - 1.94 Ga),implying that the dacite might have originated from the Paleoproterozoic crustal materials.This new finding of Hekou and Shangdong Ordovician dacite confirms the existence of Early Paleozoic subduction magmatism in this area.
Keywords：South Chinadacitezircon U-Pb geochronologyisotopesCaledoniangeochemistry
Publication Date：2014-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：17( 637-653 )