Trace elements in volcanic rocks from Yangba Formation, Bikou Group, Qinling area, China——Implications for tectonics  

作　　者：DING Zhenju~(1,2) and LIU Congqiang~1 1. Open Laboratory of Ore Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China 2. China University of Geosciences, Wuhan 430074, China 

出　　处：《Chinese Science Bulletin》1999年第S2期44-46,共3页

摘　　要：YANGBA Formation of Bikou Group is located in south Qinling, a famous orogenic belt separating Chinesecontinent into two parts: North China plate and Yangzi plate. The Yangba Formation comprises the maficand felsic volcanic rocks formed in an ancient seafloor environment during the Proterozoic era. The suitesof mafic and felsic volcanic rocks are petrochemically divided into tholeiite and calc-alkaline dacite, respectively, showing characteristics of bimodal volcanic rock mainly by lithology and major element content, and a lack of typical intermediate rocks. These signatures indicate that the volcanic rocks of YangbaFormation were generated in rift tectonics setting. The tholeiites of Yangba Formation are similar in trace element content to mid-ridge basalt, displaying a slight depletion to enrichment in light rare earth elements (LREE’s) (La/Yb_n = 0.6-1.4), slightfractionation between LREE (La/Sm_n =0.55-1.14) and HREE (Gd/Lu_n = 1.09-1.50), and relative flat patterns in whole. The decoupling of Eu to its neighboring elements in two samples likely indicates an effect of fractional crystallization in magma evolution. The La-La/Sm, Ni-La, Ni-Th, Ni-Ta,and Ni-Hf diagrams all support a conclusion that the mafic rocks are generated by partial melting pro-

关 键 词：TRACE element VOLCANIC rock TECTONICS SETTING Bikou Group. 

分 类 号：P588.14[天文地球—岩石学]