摘要
华南早古生代花岗岩广泛分布,但同时代的(次)火山岩却很罕见.本次研究采用LA-ICPMS锆石U-Pb定年方法,结合微区原位Hf同位素分析,对南岭广东韶关地区的河口、上洞英安岩进行了系统研究.结果表明英安岩形成于448.7±1.7Ma,为晚奥陶世岩浆活动产物.岩石为斑状结构,常见石英碎斑或港湾状石英斑晶,基质为隐晶质,具有典型浅成岩石特征.地球化学资料表明,这些岩石属于高钾钙碱性英安岩.英安岩微量元素显示了轻稀土富集、高场强元素(Ta、Nb)亏损和极低的Cr、Ni含量等明显火山弧岩浆特征.同位素数据显示河口、上洞英安岩全岩ISr=0.709 0~0.714 0,εNd(t)=-8.9^-9.3,锆石εHf(t)变化范围为-8.06^-3.80,与华南加里东期主要花岗岩类同位素特征一致,具有壳源属性.二阶段Hf模式年龄范围为1.67~1.93Ga,与Nd模式年龄结果1.91~1.94Ga相近;表明河口、上洞英安岩来源于古元古代结晶基底地壳物质.河口、上洞奥陶纪英安岩的发现,进一步证明该区早古生代存在俯冲岩浆活动,为研究华南早古生代地质事件提供了新的证据.
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 contents. Isotopic data show that they have Isr=0. 709 0-0. 714 0, εNd（t）=-8. 9 to -9. 3, εHf（t）=-8. 06 to -3. 80, consistent 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.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2014年第6期637-653,共17页
Earth Science-Journal of China University of Geosciences
基金
广东核工业地质局南岭贵东花岗岩体构造变形与铀矿成矿关系研究
