西湖凹陷平湖斜坡带平湖组微量元素和稀土元素地球化学特征及其地质意义

Geochemical Characteristics of Trace Elements and Rare Earth Elements of Pinghu Formation in Pinghu Slope Belt of Xihu Sag and Their Geological Significance

对采自平湖斜坡带平湖组的55块泥岩样品进行ICP-MS实验,分析其微量元素和稀土元素,结果表明:1)平湖斜坡带平湖组存在明显的轻、重稀土元素的分异现象,总体呈现LREE相对富集、HREE相对亏损、Eu正异常及Ce微弱负异常的特征;2)微量元素及稀土元素参数指示研究区平湖组处于弱氧化-弱还原的沉积环境,以淡水沉积环境为主,局部存在海侵作用的影响;3)平湖组存在一定程度的气候变化,表现为平湖组上段、中段下部以及下段处于温暖潮湿的气候,平湖组中段上部处于干热的气候,总体有逐渐变温暖潮湿的趋势;4)研究区平湖组泥岩稀土主要来源于陆源碎屑矿物,源岩主要为碱性玄武岩和沉积岩,整体处于大陆岛弧的构造背景下。

The trace elements and rare earth elements in 55 mudstone samples collected from Pinghu Formation in Pinghu slope belt of Xihu sag are analyzed by ICP-MS experiment.The result shows that:1)There is obvious differentiation of LREE and HREE in the Pinghu Formation of Pinghu slope zone,which is characterized by LREE relative enrichment,HREE relative depletion,Eu positive anomaly and Ce weak negative anomaly.2)The parameters of trace elements and rare earth elements indicate that the Pinghu Formation in the study area is in a weak oxidation-weak reduction sedimentary environment,which is dominated by fresh water sedimentary environment,with local transgression.3)There is a certain degree of climate change in the Pinghu Formation,which indicates that the upper member,the lower part of the middle member and the lower member of the Pinghu Formation are in warm and humid climate,while the upper part of the middle member is in dry and hot climate,and the climate of the Pinghu Formation has a trend of gradually becoming warm and humid.4)REE in the Pinghu Formation mudstone of the study area mainly comes from terrigenous clastic minerals.The source rocks are mainly alkaline basalt and sedimentary rocks,and the tectonic background is continental island arc.