湘黔地区牛蹄塘组黑色岩系稀土特征──兼论海相热水沉积岩稀土模式

REE CHARACTERISTICS oF BLACK ROCK SERIES OF THE LOWER CAMBRIAN NIUTITANG FORMATION IN HUNAN-GUIZHOU PROVINCES,CHINA,WITH A DISCUSSION ON THE REE PATTERNS IN MARINE HYDROTHERMAL SEDIMENTS

本文在海相热水沉积物具海水型稀土模式形成机理研究基础上，提出海相化学沉积物一般具有海水型稀土模式，而海相火山喷发成因热水沉积物的稀土元素将主要反映火山物质来源区特征的新认识。湘黔下寒武统牛蹄塘组黑色岩系稀土总量在富金属碳质伊利石页岩层出现峰值，向上在薄层状和厚层状碳质伊利石页岩，向下在磷块岩和硅质岩中均有减少。该岩系稀土模式与海水相同，同时，在La／Yb－Ce／La、La／Yb－REE图解上显示与玄武岩类相关，综合其他资料，本文认为牛蹄塘组系汲取有武陵期和雪峰期岩浆岩成分的热水与正常海水混合沉积产物。

Reported in previous literature were seawater-type REE patterns in marine hydrothermal sedi-ments. On the basis of the forming mechanism of the REE patterns, it is suggested that chemically deposited marine sediments generally show the REE patterns mentioned above, where as the REE patterns in hydrothermal sediments associated with marine volcanic eruption would mainly reflect the characters of source regions.The ∑REE content of the black rock series of the Niutitang Formation reaches its peak value in metal-rich shales, and reduces upward and downward, which may be connected with an abnor-mal seawater sedimentary process. The REE patterns in the black rock series are of seawater type. In La/Yb-Ce/La and La/Yb-REE diagrams some connect1on is observed between the black rock series and basalt. Combined with other evidence, it is suggested that the black rock series re-sulted from mixing of hot seawater sediments from preexisting basic-ultrabasic and acidic igneous rocks and normal seawater sediments.