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川西昌台地区上三叠统勉戈组中酸性火山岩之上主要为一套灰黑色至黑色沉积岩石组合,包括板岩、页岩和泥岩等。这套岩石组合可分为两类:底部为存在热水活动参与形成的沉积岩,厚度较薄;底部之上为无热水活动参与形成的沉积岩,厚度较大。本文取样上述两类岩石测得的稀土元素特征基本相似,无明显区别:两类样品稀土含量普遍偏高,与球粒陨石标准化的的配分曲线呈右倾型,LREE富集,基本无Ce正/负异常,具有明显的Eu负异常。有热水活动参与的沉积岩样品与太平洋SER地区现代海底典型热水沉积物的稀土元素特征明显不一致;与该区域内呷村矿区的典型热水沉积岩重晶石和硅质岩的稀土元素特征也不一致。但与秦岭志留系部分热水沉积岩样品和湘黔寒武系牛蹄塘组底部碳质伊利石页岩样品的稀土特征一致,呈现正常碎屑岩的稀土元素特征。综合分析认为,川西勉戈组碎屑页岩出现Eu负异常特征的主要原因是所测样品中的热液组分含量较少甚至无。
Above the middle-acidic volcanic rocks of the Upper Triassic Miangge Formation in the Changtai area of western Sichuan are mainly composed of a combination of gray-black to black sedimentary rocks, including slate, shale and mudstone. The rock assemblage can be divided into two types: the bottom is sedimentary rocks formed by the participation of hot water activities, and the thickness of the sedimentary rocks is relatively thin; the sedimentary rocks formed by no hot water activities on the bottom are thicker. The characteristics of rare earth elements measured by these two types of rock samples are basically similar, with no obvious difference: the rare earth contents of two types of samples are generally high, and the normalized distribution curves with chondrite are right-tilted and LREE enriched with no Ce / Negative anomaly with obvious Eu anomaly. The samples of sedimentary rocks involved in hot water activities are obviously different from those of the typical hydrothermal sediments in the SER region of the Pacific Ocean. They are also different from those of the typical hydrothermal sedimentary rocks of barren and chert . However, the characteristics of REE of the normal clastic rocks are consistent with those of some samples of the hydrothermal sedimentary rocks of the Silurian in the Qinling Mountains and the carbonaceous illite shale samples from the bottom of the Cambrian Niutitang Formation in the Hunan-Guizhou Province. The comprehensive analysis shows that the main reason for the Eu negative anomalies in the detrital shale in the western Sichuan Miange Formation is that there are few or no hydrothermal components in the samples tested.