摘要
清湖二长岩风化壳发育良好,垂向剖面可分为表土层、全风化层、半风化层,各层位稀土含量有较大差别。风化壳主要成份为高岭石、埃洛石,次要成份有钾长石、钛铁矿、赤铁矿、含钡锶的稀土质点及石英、云母等。风化壳中稀土源于原(母)岩中褐帘石、角闪石、斜长石、榍石等风化分解时释出的稀土。稀土元素在风化过程中活动性强,随原岩的风化分解其中绝大部分从母岩中释出进入风化壳中;岩体不同部分风化壳中稀土含量有差别;在风化壳垂向剖面上轻、重稀土分馏作用明显,在上部(表土层)富轻稀土,下部(半风化层)富重稀土,中部(全风化层)轻、重稀土选择性富集不明显;单个稀土元素在风化壳中迁移能力有差别,特别是铈,它主要以CeO_2形式富集在表土层,向中下部迁移能力很弱;重稀土向风化壳下部迁移能力比轻稀土强。这些稀土元素的地球化学行为在风化壳样的稀土元素球粒陨石标准化曲线上都有所反映。
The weathering crust of Qinghu monzonite has grown perfectly, and in vertical section it could be divided into three layers: surface soil layer, complete weathering layer and partly weathering layer, and there is different rare earth element (REE) abundance in different layer.
The main compositions of the weathering crust are kaolinite and halloysite, then potash feldspar, ilmenite, hematite, montmorillonite, bearing barrium and storntium, quartz and mica, etc. The REE in the weathering crust came from the decomposition of the REE mineral orthite and REE - bearing mineral amphibole , plagioclase and titanite in the mother rock.
In the process of weathering, the geochemical activity of the REE is very strong. As the mother rock resolved, the REE was given off from the rock, and came from into the weathering crust. The weathering crust REE abundance of the mother rock body is different from one place to another. In vertical section the fractionation of LREE (light REE) and HREE (heavy REE) is clear: in upper layer (surface soil layer) there is enrichment of LREE, in middle layer (complete weathering layer) there is not enrichment of LREE and HREE, and in the lower layer (partly weathering layer) there is enrichment of HREE. The capability of immigration of every single REE element is not the same, ratherly the cerium, it mainly enriched in the surface soil layer in the form of cerium dioxide (CeO2) ,and its capacity of immigration to middle or lower layer is very poor. Besides , HREE had strong capacity than LREE to immigrate down to the lower layer of the weathering crust,All these geochemical behaviours of REE have been shown on the leaching- and total - content chondrite nomalized patterns of weathering crust sample.
