山东昌乐新生代玄武岩地球化学特征及地质意义

Geochemical Characteristics and Significance of Cenozoic Changle Basalt in Shandong Province

摘要:

临朐昌乐火山岩盆地位于华北陆块东缘，以发育新生代玄武岩为特征。对临朐群尧山组玄武岩地球化学进行研究表明：SiO2含量为44.14%～45.69%， Al2O3含量为14.12%～14.76%，Na2O含量为4.12%～4.98%，K2O含量为0.95%～3.22%，A/CNK值在0.56～0.64之间，属超基性—基性岩类碱性玄武岩，具贫铝、富碱特征。大离子亲石元素Ba、K轻度富集， Rb元素显示相对亏损特征，高场强元素Nb、Ta表现为富集峰， Zr、Hf相对亏损，Ti富集，具地幔柱相关的碱性玄武岩特征；轻稀土总量（∑LREE）为188.84×10-6～283.41×10-6之间，重稀土总量（∑HREE）为18.76×10-6～24.14×10-6之间，δEu值为0.96～1.09，暗示岩浆源区没有斜长石残留。地球化学特征表明尧山组玄武岩形成于板内环境，其形成温度为1187.88～1215.70℃，形成压力大于等于3GPa，形成深度大于100km。

Abstract:

Linqu-Changle volcanic basin is located in the eastern margin of the North China Block, and is characterized by the development of Cenozoic basalts. As showed by geochemistry of the basalt in Yaoshan formation, the content of SiO2 is 44.14%~45.69%, the content of Al2O3 is 14.12%~14.76%, the content of Na2O is 4.12%~4.98%, the content of K2O is 0.95%~3.22%, and the A/CNK value is 0.56~0.64. It is an alkaline basalt—ultrabasic basic basic rocks with the characteristics of aluminum deficiency and alkali enrichment. Large ion lithophile elements Ba and K are slightly enriched, Rb elements show the characteristics of relative loss, high field strength elements Nb and Ta show the enrichment peak, Zr and Hf are relatively depleted, Ti is enriched, and has the characteristics of alkaline basalt related to mantle plume.Total amount of light rare earth（∑LREE) is 188.84×10-6～283.41×10-6. The total amount of heavy rare earths（∑HREE) is 18.76×10-6～24.14×-6. The δEu value is 0.96~1.09, which suggests that there is no plagioclase residue in the magma source area. The geochemical characteristics show that the basalt of Yaoshan formation was formed in the intraplate environment. The formation temperature of 1187.88~1215.70 ℃, the formation pressure is more than or equal to 3GPa, and the formation depth is more than 100km.