赣南版石-蔡坊火山岩年代学、地球化学和锆石Hf同位素特征及其地质意义

Geochronology, Geochemistry and Zircon Hf Isotope for Banshi and Caifang Volcanic Rocks from Southern Jiangxi Province and their Geological Implications

赣南版石和蔡坊盆地流纹质火山岩LA-ICP-MS锆石U-Pb定年结果分别为129.2±2.3 Ma和138.0±2.4 Ma。综合报道的同时期火山岩年龄,可以确定武夷山西缘发育的早白垩世火山岩形成时限大约在145~130 Ma。版石和蔡坊火山岩SiO_2>70%,属于高硅流纹质岩石,具有较低的Fe_2O_3~t/MgO比值(平均值<10),富集大离子亲石元素和轻稀土元素,亏损中-重稀土元素,具显著的Eu负异常(δEu=0.06~0.20),类似于湿冷氧化性流纹岩,可能由来自交代岩石圈地幔的富钾岩浆结晶分异形成。湿冷氧化性的版石和蔡坊流纹质火山岩在武夷山西缘出现,并没有扩展到华南内陆,很可能表明古太平洋俯冲对华南地幔的影响范围主要位于武夷山西缘及其以东地区。

LA-ICP-MS zircon U-Pb dating of the Banshi and Caifang rhyolitic rocks from the southern Jiangxi province yielded ages of 129.2±2.3 Ma and 138.0±2.4 Ma, respectively. Combined with reported ages of volcanic rocks in the vicinity, the Early Cretaceous volcanism in the western flank of the Wuyi Mountains can be restricted at ca. 145-130 Ma The Banshi and Caifang rhyolitic rocks are characterized by high SiO2 contents （〉70%）, and belong to high silica rhyolitic rocks. These rocks have tow Fe203t/MgO ratios （average less than 10）, enriched in large-ion lithophile elements （LILE） and light rare earth elements （LREE）, depleted in medium rare earth elements （MREE） and heavy rare earth element （HREE）, and have significant Eu negative anomalies, these geochemical features suggest that they are similar to cold-wet-oxidized rhyolite, therefore, the rocks probably formed by fractionated crystallization of a K-enriched magma formed by partial melting of metasomatized sub-continental lithosphere. The occurrence of the cold-wet-oxidized rhyolitic rocks at the western flank of the Wuyi Mountains and absent in the South China interior imply that the influence of the South China mantle by the Paleo-Pacific subduction was restricted to the coastal area east of the western Wuyi Mountains.