江汉盆地周缘主要河流沉积物碎屑磷灰石的微量元素特征及其物源判别指标分析

江汉盆地堆积的沉积物记录了长江演化的地质信息,一直是长江演化研究的热点,但目前的物源示踪方法存在诸多争议,因此寻找新的物源示踪指标是研究的重点.磷灰石是河流沉积物中常见的副矿物,其微量元素主要受原岩组成的影响而有良好的稳定性,在不同构造单元差异明显,是开展河流物源示踪研究的理想指示矿物.基于此,本文利用激光剥蚀电感耦合等离子质谱(LA-ICP-MS)对江汉盆地周缘主要地表河流沉积物进行碎屑磷灰石原位微量元素分析,并结合Kolmogorov-Smirnov统计方法的多维判别(MDS)图解寻找区分长江上游与中游物源的新指标,并检验了特征元素指标在物源判别中的有效性.结果表明碎屑磷灰石的Sr/Y比值及Nd-Sm、Sm-Eu、Eu-Gd、La/Yb-La/Sm的微量元素双变量图解能有效区分长江上游和中游(汉江、湘江、沅江)的物源,可作为区分长江上游与中游物源的重要特征指标.综合研究认为:河流沉积物碎屑磷灰石的微量元素比值和稀土元素分布特征在贯通大河的物源示踪研究中具有重大潜力.

Detrital Apatite Trace Element Characteristics of Main Rivers around Jianghan Basin and An Analysis of Their Provenance Discriminant Indicators

Sediments deposited in the Jianghan Basin record important information about the formation and evolution of the Yangtze River, and hence the provenance tracer of detrital materials in the basin has always been a hot topic, but the timing of the cutting through the Yangtze River is still inconclusive. Apatite is a common accessory mineral in fluvial sediments, and trace elements of apatite are mainly affected by their source rocks and significant differences in the trace elements of apatite existent in different regions, so it can be used as a good indicator of source minerals. On such a basis, the authors used the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in combination with the multi-dimensional identification (MDS) of statistical method to systematically analyze new indicator so as to distinguish the provenance of the upper and middle reaches of the Yangtze River; the MDS diagram also verifies the rationality of the characteristic elements indicators. The results indicate that the Sr/Y ratio of detrital apatite can be used to distinguish the provenance of Hanjiang River, Yuanjiang River, Xiangjiang River and main stream of the Yangtze River in the study area. The bivariate diagrams of trace elements of Nd-Sm, Sm-Eu, Eu-Gd and La/Yb-La/Sm can effectively distinguish the provenance of the upper and middle reaches of the Yangtze River. On the whole, the trace element ratio diagram and distribution characteristics of REE have great potential in the study of provenance tracer in large rivers.