长江流域岩体锆石U-Pb年龄与Hf同位素特征及沉积物源示踪意义

U-Pb AGES AND Hf ISOTOPIC COMPOSITION OF CRYSTALLINE ZIRCONS FROM IGNEOUS ROCKS OF THE CHANGJIANG DRAINAGE BASIN AND THEIR IMPLICATIONS FOR PROVENANCE

物源精细示踪是当前单矿物颗粒微区分析技术运用的重要领域。长江流域因面积巨大、源岩构成与分布非常复杂，充分掌握流域内岩体锆石U—Pb年龄等微区分析信息成为精细物源示踪的关键。在系统搜集与分析近十年来发表的长江流域内岩体锆石U—Pb年龄和Hf同位素组成的数据资料，结合区域地质各类岩体岩性、年龄和面积调查的新成果，认为只有少量锆石可直接根据特定年龄峰值进行物源判别，如〈50、250～270和〉3000Ma的3组锆石分别源自长江上游的昌都地块与金沙江缝合带、扬子地块北缘的峨眉山玄武岩省和三峡地区的崆岭群；联用锆石U—Pb年龄与cHf（t）值可进一步提高物源判别精度；但需注意再旋回的沉积锆石对沉积物源判别的影响。

High-resolution provenance study has been an important target for application of single-grain mi- croanalysis technique. It is vital to carry out high-resoulation provenance study in the Changjiang drainage to set up detail crystalline-zircon microanalysis database including U-Pb age because of its vast catchment area, complex composition and distribution of parent rocks. The data of crystalline-zircon U-Pb age and Hf isotope in the catchment were therefore systematically collected from the recent decadal publications, and analyzed together with the update geologic investigation results of parent rock lithology, age and out- cropped areas. It was indicated that only a few zircon grains can be traced to their separate sources directly by their typical ages, including those of ~50 Ma, 250~270 Ma and ~3 000 Ma, which are discriminated to the sources of the Changdu Block or the Jinshajiang Suture zone in the upper reach of the catchment, the Emeishan Basalt province in the Western Yangtze Block, and the Kongling Complex in the Three Gorges region, respectively. The effectiveness of provenance discrimination can be much highly improved through combined ananlyses of zircon U-Pb age and eHf（t） value. It is worthy noting that input of recycled detrital zircons will make the source discrimation more complicated.