黄山景观流域稀土元素地球化学特征及其控制因素

发布时间：2019-05-30 05:53

【摘要】：稀土元素在环境中的分布和分异机制,是其作为地球化学示踪剂研究的重要基础和前提。目前国内外学者对稀土元素的研究大多集中于大江、大河和一些特定地质区域,主要是对土壤、水体等特定对象的稀土元素研究,而对于混合地质条件下的整个流域稀土的来源、分布、迁移和分异的系统性研究相对欠缺。黄山景观流域是典型的混合硅酸盐岩地区,流域源头为燕山期花岗岩,中下游流经浅变质沉积-火山岩和微量分布的碳酸盐岩地层,是一个以硅酸盐岩为主的流域。流域土壤主要发育于酸性花岗岩,呈酸性和微酸性。黄山景观流域是一个研究复杂岩性背景下稀土元素分布分异规律的理想场所。本文以黄山景观流域作为研究区域,利用微量元素地球化学研究手段,根据流域流经岩性空间上的分布,选择源头到下游代表性区域的土壤剖面、河水、雨水、地下水、悬浮物及沉积物进行了样品采集,分析了这些样品的主微量元素化学组成,尤其对稀土元素在流域循环过程中的规律进行了研究,以期解释复杂岩性背景下稀土元素的来源、分布及分异等规律,探讨其地球化学特征与物质来源,亦为黄山景区保护提供基础数据。得出如下主要结论:(1)选择源头到下游的三个风化剖面,通过对土壤风化剖面中主成分分布及化学风化系数分析,得出黄山景观流域土壤剖面均经历了风化淋溶过程和脱硅富铁铝作用。化学蚀变系数(CIA)值相差较大,花岗岩的芙蓉岭风化剖面(FRL)经历了中等强度的风化,而混合沉积岩性的太平湖风化剖面(TPH)的化学风化强度则十分强烈,风化剖面中化学风化强度与轻重稀土分异(LREE/HREE)大小成正比。土壤风化剖面中稀土总量(∑REE)关系为:芙蓉岭剖面密坑剖面太平湖剖面,主要与成土母质有关。三个土壤风化剖面中稀土元素页岩标准化的Ce,均在淋溶层表现出一定的正异常,越往下层则表现为负异常,与土壤表层酸性较强有关。下游地区土壤剖面中的页岩标准化的Eu异常不明显,可以归因于岩石的差异性风化。(2)对黄山景观流域径流中溶解态稀土元素进行了研究,以探讨其地球化学特征与物质来源。结果表明,其主要来源为岩石化学风化,其次为大气输入。黄山景观流域中溶解态稀土总量(∑REE)关系为:源头中下游,与源头到下游土壤风化剖面中稀土总量一致,表明与所处地质有关,表现出典型的岩性控制特征。通过定量计算估算出丰水期雨水对河水中REE的贡献大约为25%,枯水期为17%,说明大气沉降对流域水体稀土元素有着一定的贡献。整个流域水源区主要表现为HREE相对与LREE富集,中下游地区则表现为LREE相对于HREE富集,与源头火成岩(花岗岩)到中下游沉积岩中稀土富集情况一致,表现为岩石风化的控制作用。溶解态稀土元素分布模式中Ce表现出明显的负异常,主要归因于对源岩如花岗岩的继承,与氧化还原条件的影响有着重要的关系。而Eu源头和中下游地区的不一致性,下游的Eu正异常归因于花岗岩中斜长石/钾长石等矿物的优先风化释放。黄山景观流域源头水中Y/Ho比值比中下游水体中Y/Ho比值小,这种空间上的分异,主要为流经岩性不同所致,季节性分异则受到了水/粒相互作用的影响。(3)悬浮物和沉积物的稀土元素总量在空间上表现为源头地区稀土总量明显低于中下游,与溶解态和土壤风化剖面中稀土总量相反,经分析与岩石风化(源头中下游)差异导致释放稀土离子与河水中离子形成络合物或沉淀有关。而悬浮物和沉积物中LREE相对于HREE富集,与该地区所处地层黄山花岗岩--砂岩、页岩等岩石中轻稀土富集一致,表明该流域悬浮物和沉积物中LREE富集主要受岩石风化的控制作用。悬浮物和沉积物中Ce表现出明显的正异常,主要归因于Ce的氧化还原性。沉积物中Eu大部分表现为正异常,可能受富含Eu的钾长石或斜长石的化学风化所影响。此外,通过对比河流颗粒态和土壤剖面中δEu-(La/Yb)N关系图,进行物源分析发现黄山景观流域土壤风化剖面和河流溶解态中稀土分布受岩石风化的控制作用,而沉积物中稀土分布则与水体理化性质、氧化还原条件和岩石差异性风化等其他因素有关。
[Abstract]:The distribution and differentiation mechanism of rare earth elements in the environment is an important basis and premise for the study of geochemical tracer. At present, the research of rare earth elements at home and abroad is mostly concentrated on the major rivers, great rivers and some specific geological areas, mainly on the rare earth elements of specific objects such as soil and water, and for the source and distribution of the rare earth in the whole river basin under the mixed geological conditions, The systematic study of migration and differentiation is relatively short. The Huangshan landscape basin is a typical mixed silicate rock area, the source of the basin is the Yanshanian granite, the middle and lower reaches of the basin flow through the shallow metamorphic sedimentary-volcanic rock and the micro-distributed carbonate formation, which is a basin dominated by the silicate rock. The soil of the basin is mainly developed in the acid granites and is acidic and slightly acidic. The Huangshan landscape basin is an ideal place to study the distribution of rare-earth elements in complex lithological background. Taking the Huangshan landscape as a research area, this paper uses the method of trace element geochemistry to study the soil profile, river water, rain water, ground water, suspended matter and sediment from the source to the downstream representative area according to the distribution of the river basin through the lithological space, and the sample collection is carried out on the river water, the rain water, the ground water, the suspended matter and the sediment, The chemical composition of the main trace elements of these samples was analyzed, especially the law of the rare earth elements in the process of basin circulation, in order to explain the source, distribution and differentiation of the rare earth elements in the complex lithological background, and to study the geochemical characteristics and material sources. It also provides basic data for Huangshan scenic spot protection. The main conclusions are as follows: (1) The three weathering profiles from the source to the downstream are selected. Through the analysis of the main component distribution and the chemical weathering coefficient in the soil weathering profile, it is concluded that the soil profile of the Huangshan landscape basin is subjected to the weathering leaching process and the desiliconization of the iron-rich aluminum. The chemical alteration coefficient (CIA) has a large phase difference, and the weathered section (FRL) of the granite is moderately weathered, and the weathering intensity of the weathered section (TPH) of the mixed sedimentary rock is very strong. The weathering intensity in the weathering section is directly proportional to the size of the heavy rare earth differential (LREE/ HREE). The relation of the total amount of rare earth (HREE) in the soil weathering profile is: the profile of the Taiping Lake in the close-pit section of the Furong section, which is mainly related to the formation of the soil. In the three soil weathering profiles, Ce, which is standardized by the rare-earth elements in the weathering profile, shows a certain positive anomaly in the leaching layer, and the lower the lower layer shows a negative anomaly, which is strongly related to the acidity of the surface of the soil. The Eu anomaly of the shale in the soil profile in the downstream area is not obvious and can be attributed to the differential weathering of the rock. (2) The dissolved-state rare-earth element in the runoff of Huangshan landscape basin was studied to study its geochemical characteristics and material source. The results show that the main source is the weathering of the rock, followed by the atmospheric input. The total amount of dissolved rare earth (EREE) in the Huangshan landscape basin is as follows: in the middle and lower reaches of the source, the total amount of the rare earth in the weathering profile of the source to the downstream soil is consistent, indicating that it is related to the geological conditions and shows the typical characteristics of the lithological control. By means of quantitative calculation, the contribution of rain water to the REE in the river is about 25%, and the dry period is 17%, which indicates that the atmospheric settlement has a certain contribution to the rare earth elements in the water body of the basin. The water source region of the whole basin is mainly characterized by the REE enrichment of the REE and the enrichment of the LREE in the middle and lower reaches of the basin, which is consistent with the enrichment of the rare earth in the source igneous rock (granite) to the middle and lower reaches of the middle and lower reaches, and is characterized by the control effect of the weathering of the rock. Ce in the dissolved-state rare-earth element distribution mode shows a significant negative anomaly, mainly due to the inheritance of source rock, such as granite, and the influence of oxidation-reduction conditions. And the Eu anomaly in the lower reaches of Eu is due to the preferential weathering and release of the minerals such as plagioclase/ potassium feldspar in the granite. The ratio of Y/ Ho in the source water of the Huangshan landscape basin is smaller than that in the middle and lower reaches of the middle and lower reaches, and the spatial difference is mainly caused by the different lithology, and the seasonal differentiation is affected by the water/ particle interaction. and (3) the total amount of the rare earth elements in the suspended matters and the sediments is obviously lower than the total amount of the rare earth in the source area in the space, and the total amount of the rare earth in the dissolved state and the soil weathering profile is opposite to the total amount of the rare earth in the dissolved state and The difference between the analysis and the weathering of the rock (in the middle and lower reaches of the source) results in the release of the rare earth ions in relation to the formation of complex or precipitation of the ions in the river water. The REE enrichment of the LREE in the suspended matter and the sediment is consistent with the enrichment of the REE in the rock, such as the Huangshan granite--sandstone and the shale in the region, which indicates that the enrichment of the LREE in the suspended matter and the sediment of the basin is mainly controlled by the weathering of the rock. Ce in the suspended matter and the sediment showed a significant positive anomaly, mainly due to the oxidation and reduction of Ce. The majority of Eu in the sediments are positive and may be affected by the chemical weathering of the Eu-rich potassium feldspar or plagioclase. In addition, that distribution of the rare earth in the soil weathering profile and the dissolved state of the river is controlled by the weathering of the rock, and the distribution of the rare earth in the sediment and the physical and chemical properties of the water body are found by comparing the relation graph of the Eu-(La/ Yb) N in the river particle state and the soil profile. The oxidation and reduction conditions are related to other factors such as the weathering of the rock.
【学位授予单位】：安徽工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P595

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