暖温带花岗岩风化壳中黑云母微量元素的富集与流失变化——以山东半岛院格庄花岗岩体风化壳为例

Enrichment and Loss of Trace Elements in Biotite in Weathering Crust of Granite in Warm Temperate Zone—A Case Study of the Weathering Crust of the Yuangezhuang Pluton, Shandong Peninsula

摘要: 黑云母属于花岗岩中次要的矿物之一，是易风化矿物。本文以院格庄花岗岩风化壳中的黑云母作为研究对象，分析其在风化壳中的微量元素富集与流失的变化，目的是想了解黑云母对暖温带花岗岩母岩风化的响应，了解特定矿物对地表化学过程的专属影响，结果表明：此风化壳中黑云母富含元素Ba、Zn、Rb、Zr、Li、V、Cr、Sr、Nb、Ni，贫Cd、Mo、Tl、Ge、Ta、Be、W、U、Hf等元素。风化壳中黑云母微量元素流失率Ba > Rb > Li > Co > Cs > V > Ge > Ni > Cr > Nb > Sc，富集率Sr > Pb > Th > Be > Cd > Ga。大离子元素Ba、Rb、Cs流失率较高，亲铁元素Co、V、Ni、Cr、Sc、Ge的流失率次之；Sr富集率远高于其他元素，亲铜元素Pb、Cu、Cd的富集率在风化程度最强时达到最大值，元素的迁移/富集率在次表层达到最大值，在顶层和下层变化趋势不同；黑云母Rb/Sr、Li/Sc、Rb/Cs、Ba/Sr这些微量元素比值在风化壳中随风化进程加深呈稳定减小趋势，可作为有效的黑云母风化程度判别指数；稀土元素含量在表层强烈富集，含量较高，主要以Ce族元素为主，但轻稀土富集内部分异状况较大，Ce和Eu元素均有盈亏变化，整体表现为轻微亏损状态。

Abstract: Biotite is one of the minor minerals in granite and easy to weather. This article takes biotite in the weathering crust of Yuangezhuang pluton as the research object, and analyzes the changes of the enrichment and loss of trace elements in the weathering crust. The purpose is to understand the response of biotite to the weathering of warm-temperate granite host rock and the exclusive influence of specific minerals on the earth’s surface chemical process. The results showed that the biotite in this weathered crust is rich in elements Ba, Zn, Rb, Zr, Li, V, Cr, Sr, Nb, Ni, and is poor in Cd, Mo, Tl, Ge, Ta, Be, W, U, Hf and other elements. The loss rate of biotite trace elements in theweathered crust is Ba > Rb > Li > Co > Cs > V > Ge > Ni > Cr > Nb > Sc, and the enrichment rate Sr > Pb > Th > Be > Cd > Ga. The loss rate of large ion elements Ba, Rb, Cs is higher and the loss rate of iron-philic elements Co, V, Ni, Cr, Sc, Ge is secondary; Sr enrichment rate is much higher than other elements; concentration rate of Pb、Cu、Cd chalcophile element reaches maximum when weathering is strongest. The element migration/enrichment rate reaches the maximum in the subsurface layer, and the change trend is different at the top and lower layers; The ratio of trace elements of Rb/Sr, Li/Sc, Rb/Cs, Ba/Sr showed a steady decreasing trend with the deepening of the weathering process in weathering crust, which can be used as an effective index for determining the degree of weathering of biotite. The content of rare earth elements is strongly enriched in the surface layer, and the content is high. The Ce group elements are the main elements, but the light rare earth enrichment has a large difference in some parts. Both Ce and Eu elements have profit and loss changes, and the overall performance is slightly deficient.