中国南方二叠-三叠系界线及其附近粘土层稀土元素地球化学研究

RARE EARTH GEOCHEMISTRY OF CLAYS AT AND NEAR THE PERMIAN-TRIASSIC BOUNDARY IN SOUTH CHINA

本文对广泛发育于中国南方,连续的二叠-三叠系海相界线及其附近粘土层(蒙脱石—伊利石粘土岩)进行了稀土元素地豫化学的研究。查明了REE分布特征;REE沿粘土层垂向上的变化,比较了界线粘土与非界线粘土在REE分布上的差异。讨论了界线粘土的成因,根据稀土模式所作的综合分析,提出了由中酸性山火山岩和代表冲击溅射产物的上部地壳物质组合的混合新模式。

In this paper, we discuss the INAA results of REE in clays at and near some Permian/Triassic boun- daries of South China. We find that the REE patterns of boundary clays differ from those of non-boundary clays. One difference is that the boundary clays seem more enriched in LREE, have steeper slope of LREE and HREE. and have smaller Eu negative anomaly than the non-boundary clays. Another difference lies in the Ce anomaly, The boundary clays show small Ce negative anomaly, but no Ce anomaly in the non-boundary clays.As a comparison, we also determine the REE of the Triassic acidicintermediate volcanic rocks in South China, and the PC/C, D/C and K/T boundary clays.From those REE patterns and some other experimental facts, we put forward a proposal that the P/T boundary clay may be a mixed product consisting of the acidic-intermediate volcanic ash and the upper crust representing spattering component. And the calculated fraction of the former and latter is 3/7.The mixing model of forming P/T boundary clay in South China can better explain the experimental facts from two aspects, i.e. the volcanic activity and impact event. A possible scenario is that at the end of the Permian, an extraterrestrial impact triggered severe activity of volcanos in South China. Or these two interactions simultaneously occurred at that time.