赣东–浙西下寒武统荷塘组稀土元素特征及其地质意义

REE composition and its geological implications of the Hetang Formation mudstones in the East Jiangxi and west Zhejiang,China

为揭示下扬子下寒武统黑色岩系的物源属性、构造背景及其沉积环境等特征,对赣东-浙西地区下寒武统荷塘组野外露头及钻井岩心进行了系统采样与稀土元素分析测试。结果显示,荷塘组样品稀土元素总量变化波动大(16.83×10^(-6)~321.22×10^(-6)),均值低(103.11×10^(-6)),轻稀土元素富集且分异明显,重稀土元素亏损但分异小,普遍存在Ce负异常和明显Eu正异常。研究表明:①荷塘组硅质泥页岩形成于缺氧还原的裂陷海盆环境,构造背景为被动大陆边缘,物源受陆源、海水和热液共同影响,横峰、上饶受热液和海水影响最大,受陆源碎屑影响最小,常山、江山与之相反;②沉积过程普遍有热液活动参与,在上饶存在热液活动中心,活动强度呈西强东弱特点,并发现低温热液活动有利于有机质的富集。

The provenance,tectonic setting and sedimentary environment of the Lower Cambrian black shale named Hetang Formation in the east Jiangxi and west Zhejiang of the Lower Yangtze platform are studied in this paper.Characteristics of rare earth elements(REEs)are revealed from 22 outcrop samples and 15 core samples of the Well ZJD-1.It suggests that the total amount of rare earth elements in the Hetang Formation of the study area vary substantially from 16.83 to 321.22×10^(-6),with a lowest mean value around 103.11×10^(-6).Light rare-earth elements are obviously enriched and differentiated,while the heavy rare-earth elements deficit and poorly differentiated.Commonly observed are negative Ce and positive Eu anomalies.Combined with previous researches,we reached the followings as conclusions.(1)The Hetang Formation was deposited in a rift basin with anoxic water along a passive continental margin tectonically.The provenance of the sediments was jointly controlled by the terrestrial source and the outputs from seawater and hydrothermal fluid.The region of Hengfeng and Shangrao is little affected by terrigenous debris,but substantially influenced by the materials from hydrothermal fluid and seawater,and the region of Changshan and Jiangshan is just the opposite.(2)The Hetang Formation is obviously affected by hydrothermal activities,and the low temperature hydrothermal activity is favorable for the deposition and enrichment of organic matters.The hydrothermal activity was centered at Shangrao,with decreasing influence from west to east.