广西桂林石灰土元素迁移特征及影响因素——以会仙峰丛谷地石灰土为例

碳酸盐岩的化学风化是岩溶关键带各圈层相互作用的主要形式，风化壳中蕴含重要气候环境和物质循环信息。通过对广西桂林会仙峰丛谷地石灰土的化学风化强度及元素迁移特征的研究，并与滇黔湘和青藏高原的岩溶风化壳的对比分析，结果表明:（1）会仙石灰土化学蚀变指数（CIA）均值为92.14，与贵州兴义岩溶风化壳相当，反映炎热潮湿气候下的强烈化学风化；白云岩风化壳CIA与灰岩风化壳相当，CIA值主要受“不溶物”含量的影响；地形上，从上坡到下坡，从坡地到谷地，垂向剖面从浅部到深部，碳酸盐岩风化壳的CIA值呈减小趋势；（2）包括会仙石灰土在内的中国南方碳酸盐岩风化壳的CIA值与纬度成负相关，青藏高原地区和北方地区碳酸盐岩风化壳的CIA值与纬度不存在相关性，可能受晚第三纪以来印度板块俯冲推挤，青藏高原地区构造抬升和夷平面变形的影响；（3）与硅酸盐风化壳、黄土剖面不同，碳酸盐岩风化壳CIA和Na/K（摩尔比值）不存在相关性，但CIA和K/Al（摩尔比值）则存在显著负相关，可采用K/Al来表征碳酸盐岩剖面的风化程度，其主要是受可溶成分的快速淋失影响；会仙石灰土、贵州兴义风化壳较其他风化壳更接近Al端，化学风化程度更高；（4）会仙石灰土的化学成分与中国其他地区碳酸盐岩风化壳基本一致，剖面上分布均匀；与上陆壳相比，Na、K、Ca、Mg表现为亏损，其他元素为富集；和下伏碳酸盐岩的稳定元素Ti相比，除了Cr、Fe、P、Al富集或不变外，其他元素都发生明显的迁移淋失；会仙风化壳元素的迁移性由强到弱为:Ca ? Mg ? B ? Na ? N ? Cd ? Zn ? As ? K ? Pb ? Si ? Mn ? Al ? Cr ? Fe ? P，高含量Ca、Mg的快速溶失对其他元素的迁移性有重要影响。 

Characteristics of element migration and influencing factors of lime soil in Guilin,Guangxi:A case study of lime soil in Huixian peak-cluster valley

The chemical weathering of carbonate rocks is the main form of interaction between the layers in the karst key zone. The weathering crust contains important information about the climate， environment and material circulation. Based on the study of the chemical weathering intensity and element migration characteristics of the karst weathering crust in Guilin， Guangxi， and the comparison of karst weathering crusts of Yunnan， Guizhou and Hunan and the Qinghai-Tibet Plateau， the following conclusions are drawn， （1） The average value of the crust Chemical Alteration Index（CIA）of limestone in Huixian， Guangxi is 92.14， equivalent to the karst weathering crust in Xingyi， Guizhou， which reflects the intense chemical weathering in the hot and humid climate. The CIA of the dolomite weathering crust is equivalent to that of the limestone weathering crust， and is mainly affected by the "insoluble matter"； in terms of topography——from uphill to downhill， from slope to valley， from shallow to deep section——the CIA value of the weathering crust of carbonate rock shows a decreasing trend； （2） The CIA value in southern China， including the Huixian weathering crust in Guangxi，is negatively correlated with latitude. The carbonate weathering crusts in the Qinghai-Tibet Plateau and northern areas are paleoweathering ones， and their CIA values are not correlated with latitude， which may be affected by the subduction and pushing of the Indian plate since the late Tertiary， the uplift of the Qinghai-Tibet Plateau and the deformation of the planation plane； （3） Unlike silicate weathering crust and loess profile， there is no correlation between CIA and Na/K （molar ratio） of carbonate weathering crust，but there is a significant negative correlation between CIA and K/Al （molar ratio）. K/Al can be used to characterize the weathering degree of carbonate profiles， which is mainly affected by the rapid leaching of soluble components. The Chinese carbonate weathering crust has completed the dissolution and leaching of soluble components， and is in the stage of potassium feldspar weathering and clay mineral generation. The weathering crusts of Huixian in Guangxi and Xingyi in Guizhou are closer to the Al end than other weathering crusts，and the degree of chemical weathering is higher； （4） The chemical composition of the Huixian carbonate weathering crust in Guangxi is basically the same as that of the carbonate weathering crust in other parts of China， and an even distribution can be seen on the profile. Compared with UCC， Na， K， Ca and Mg are depleted， but other elements are enriched. Compared with the stable element Ti of the underlying carbonate rock， except that Cr， Fe， P and Al are enriched or unchanged，other elements have undergone significant migration and leaching. The migration order of the elements in the weathering crust of Huixian is，Ca ? Mg ? B ? Na ? N ? Cd ? Zn ? As ? K ? Pb ? Si ? Mn ? Al ? Cr ? Fe ? P. The rapid dissolution loss of high content of Ca and Mg is of an important influence on the mobility of other elements.