碎屑沉积物地球化学:物源属性、构造环境和影响因素

碎屑沉积物记录着有关源岩性质和构造演化等诸多重要的信息,对于沉积盆地分析和理解区域构造演化都有重要的指示意义。近年来碎屑沉积物地球化学的研究有了很大进展,尤其是同位素年代学在沉积物地球化学中的应用,如造山带前陆盆地、山间盆地沉积物的同位素年代学的研究可以有效地反演造山带隆升-剥蚀作用与盆地沉降之间的联系,为地壳演化和造山带隆升等地质过程提供了重要的地球化学证据。文章结合近几年来的研究实例,综述了沉积物地球化学方法在物源示踪和源区构造背景判别研究的一些进展。考虑到碎屑沉积物地球化学组成是源岩、风化作用、沉积循环、成岩作用和分选作用等综合作用的结果,我们对其中的主要影响因素进行了分析,指出了当前广泛应用的物源和构造背景判别图解需要注意的一些问题。

CLASTIC SEDIMENT GEOCHEMISTRY: IMPLICATIONS FOR PROVENANCE AND TECTONIC SETTING AND ITS INFLUENTIAL FACTORS

Clastic sediments bears much information about the nature of source rocks and their tectonic evolution,which is significant for sedimentary basin analysis. Much progress has been made in clastic sedimentary geochemistry in recent years,especially due to the application of isotope chronology.Isotope chronology analysis of orogenic fore-land basin and intermountain basin can provide chronology information about sediment source rocks,which is helpful to understand the correlation between sedimentary basin and its adjacent mountains.Such information is important to reconstruct the history of mountain uplift and erosion,and provides new constraints on the provenance and tectonic setting of clastic sediments.The method has been used in many areas and good results have been achieved.Through examples,the paper reports the research advances in provenance tracing and tectonic setting discrimination of sedimentary rocks using sedimentary geochemistry.However,the geochemical composition of sedimentary rocks is a complex function of the nature of the source rocks,intensity and duration of weathering,sedimentary recycling,diagenesis,and sorting.These make it difficult to trace provenance precisely if merely depending on the elemental geochemical characters of clastic sediments.The paper also discusses these factors in detail and points out the limitations and problems of diagrams that are often used in provenance tracing and tectonic setting discriminating.So the combination of elemental geochemistry and isotope chronology may be a better way to constrain the provenance and tectonic setting analysis of clastic sediments.