库车坳陷第三系泥岩地球化学特征及其对构造背景和物源属性的指示

Geochemical characteristics of Tertiary mudstones in Kuqa depression and their implications to tectonic setting and provenance attribute

利用碎屑岩地球化学特征判断沉积盆地的构造背景和物源属性是盆地分析的重要手段,也是对利用粗碎屑沉积岩的组分统计判断盆地源区背景的有益补充和验证。对库车坳陷第三系36件泥岩样品的地球化学特征分析表明,主量元素中CaO的含量很高,对其他主量元素以及微量和稀土元素有稀释作用,一些可靠的物源分析指标主要指示了非碳酸盐沉积物的源区性质;REE分布模式与上地壳相似,轻稀土元素富集,Eu负异常,微量元素比值显示源岩以长英质岩石为主。通过K2O/Na2O-SiO2以及LaThSc和ThScZr/10判别图分析,认为源区的构造背景具有类似于岛弧的特征。这一结果与前人所做的砂岩组分的研究结果存在差异,说明板内造山带与其前陆盆地之间在沉积与构造耦合上具有特殊性。

The application of detrital geochemistry to determining tectonic setting and provenance attribute is an important means for basin analysis and also a helpful supplementary or verification method in using coarse detrital rocks to judge the background of provenance. Geochemical characteristics of 36 Tertiary mudstone samples from Kuqa depression show that the content of CaO is very high, which can somewhat dilute other major elements, trace elements and rare elements. Some reliable indicators for provenance analysis show the source rock nature of noncarbonate sediments. The REE distribution pattern is similar to that of the upper continental crust, characterized by enrichment of LREE and negative Eu anomalies. Some trace element ratios show that the source rocks are mainly felsic. According to K2O/Na2O-SiO2, La-Th - Sc and Th - Sc - Zr/10 discrimination diagrams, the tectonic setting of the provenance is similar to that of island arc. This result is different from the former research result on sandstones, suggesting that there exist specific characteristics between the orogenic inner plate and its foreland basin in sedimentary and tectonic coupling.