中文摘要：

根据大量年代学、地球化学和岩石学等方面的研究，前人对碧溪岭榴辉岩的形成及变质历史有了较明确的认识，但这些研究对超高压变质前后过程中元素和同位素的变化涉及较少。通过分步淋洗方法对碧溪岭榴辉岩中石榴石的Pb同位素研究发现，不同淋洗步骤的Pb同位素组成明显不同，但对不同的石榴石样品以及同一样品用不同的淋洗流程，得到的淋洗规律以及Pb同位素组成变化范围基本一致。不同淋洗步骤的Pb同位素组成构成等时线，给出表面年龄为30亿年左右，与前人报道的碧溪岭地区榴辉岩原岩形成及超高压变质的年龄数据有明显差异。结合前人研究可以判断，这些年龄不具有明确的地质意义，属于假等时线。但分步淋洗结果能反映碧溪岭榴辉岩中Pb同位素的来源可能由地幔组分和上地壳组分混合而成，地幔组分的Pb反映了碧溪岭榴辉岩的原岩是地幔成因的，上地壳组分的Pb表明在榴辉岩快速折返过程中，受到具有上地壳Pb同位素组成的含水流体交代。

英文摘要：

After many studies on geochronology, geochemistry and petrology of the eclogite from Bixiling have been done, its formation and metamorphic history are well known now. However, little work about elements and isotopes changes during the UHP metamorphism was conducted. The garnet Pb isotopes from Bxiling eclogites were studied by the stepwise-leaching technique in this paper. The Pb isotopic compositions obtained by different individual steps are various; However, the evolution trends of Pb isotopic compositions of different garnets and different progresses are almost consistent. The Pb-Pb ＂isochron＂ ages are about 3 billion years ,which are different from the ages of protolith formation and UHP metamorphism obtained by precursors. Although the ages perhaps have no geologic significance, the results of stepwise-leaching may reflect that Pb isotopic compositions of the eclogite from Bixiling are mixture of materials from mantle and upper crust. In brief, the protolith of the eclogite was originated from mantle materials, and during rapid exhumation after the Triassic collison, the eclogites were matesomatized by the hydrous fluid with the upper crust Pb isotopic compositions.