碎屑磷灰石对沉积物源判别的指示

Sedimentary Provenance Analysis Using Detrital Apatite: A Review

基于单颗粒碎屑磷灰石原位分析的物源分析是沉积地质学研究的一种重要手段。磷灰石中Sr,Y和稀土等微量元素含量由Si O2含量和所在熔体中的分配系数控制,微量元素的含量在不同岩石的磷灰石中差异较大,可作为指示其母岩类型的重要指标。磷灰石在物源分析中的应用可归纳为以下3个方面:(1)元素地球化学,特征元素包括Sr、Y、稀土元素(REE)等;(2)同位素地球化学,包括Sr-Nd同位素、Lu-Hf同位素等;(3)单颗粒多法定年,即同颗粒磷灰石进行(U-Th)/He、裂变径迹和U-Pb定年分析。综合上述3个方面可获得磷灰石的母岩类型、形成条件和后期演化、源区抬升剥蚀史、沉积区沉降史等信息。尽管碎屑磷灰石的热年代学目前在沉积物源研究中运用广泛,但基于碎屑磷灰石元素及同位素地球化学(包括磷灰石U-Pb同位素定年)的沉积物源判别仍处于起步阶段,在沉积地质学、盆地分析、构造地质学等研究领域具有广阔的应用前景。

In situ analysis of detrital apatite is a significant approach to sedimentary provenance analysis, which is an important aspect in sedimentary geology study. Several trace elements such as Sr, Y and Rare Earth Elements (REEs) concentrate in apatites, and the distribution of these elements depends on the content of SiO2 and the distribution coefficient of the melt, thus the trace element abundances is obviously different in different rocks. These features can be used to indicate parent-rocks of detrital apatites in sedimentary rocks. The approaches and proxies of detrital apatite to sedimentary provenance analysis can be summarized as follows. ①elemental geochemistry, such as Sr, Y, REEs, the approaches including chondrite-normalised REE distribution patterns of apatites, Classification and Regression Tree (CART) and discriminant plots of REE parameters; ②isotopic geochemistry, including Sr-Nd and Lu-Hf isotopes; ③Multi-dating, including low-temperature thermochronology such as (U-Th)/He (AHe)and Fission Track (AFT) dating, and high-temperature thermochronology such as U-Pb dating. Based on an integrated analysis using these methods, we can get various and comprehensive geological information such as the rock type, formation conditions and evolution of source rocks, the history of uplift and exhumation of source areas and even the subsidence history of sedimentary basins. Although the low-temperature thermochronology of detrital apatite is widely used in sedimentary provenance analysis, the elemental and isotopic geochemistry, as well as the U-Pb dating, remains to be developed. These approaches are supposed to have wide application prospects in several research areas such as tectonics, sedimentary geology basin analysis and even paleoclimatology.