Geochemical Characteristics and Provenance Indication of the Zhujiang Formation in Well HZ21 at the Huizhou Depression

Key words: 
• Pearl River Mouth Basin

Abstract: It has been found that the components of MnO, Na2O, P2O5 and TiO2  in the clastic rock of the Zhujiang Formation in well HZ21 at the Huizhou Depression, Pearl River Mouth Basin are similar to those in PAAS through a comprehensive analysis on the major elements, trace elements and rare earth elements. Comepared with PAAS, a fact that the clastic rock of the Zhujiang Formation is richer in SiO2 while poorer in Al2O3, Fe2O3, K2O and MgO. Referring to the mudstone, the content of Ba is slightly lower than the supracrustal abundance, but it is far higher than lowercrustal abundance; the content of Cr is slightly higher than the supracrustal abundance, but it is far lower than lowercrustal abundance; the content of Th is higher than the supracrustal abundance, and it is far greater than lowercrustal abundance. As regards to the sandstone, the content of Ba is similar to the supracrustal abundance, but it is far higher than lowercrustal abundance; the content of Th is slightly lower than the supracrustal abundance in NSQ1 and NSQ2 while it is far greater than supracrustal abundance in NSQ3 and NSQ4. The REE distribution pattern is similar to that of the upper continental crust, characterized by enrichment of LREE, uniform of HREE and negative Eu anomalies. Eu anomalous value of NSQ1 and NSQ2 is higher than the Eu anomalous value of PASS and it has the opposite situation in NSQ3 and NSQ4. The ratios of major elment and the diagrams of nonmigration trace elments show that the source rocks are mainly felsic, and the principal source of detritus in NSQ1 and NSQ2 are derived from the sedimentary rock and calcareous mudstone, and the principal source of detritus in NSQ3 and NSQ4 are derived from compositon of the granite, alkali basalt, sedimentary rock and calcareous mudstone. According to SiO2 K2O/Na2O, La ThSc discrimination diagrams and the anomalies of Ce, it can be inferred that the tectonic setting of the provenance is similar to that of passive continental margin. The value of Al2O3/Na2O and chemical index of alteration (CIA) suggest that it was warmwet climate in the area, but the degree of dampheat was relatively higher in NSQ1 and NSQ2, and that is one of the reason why the intensity of weathering was relatively strong. But, it has an opposite situation in NSQ3 and NSQ4: the warmwet degree was relatively lower and the intensity of weathering was relatively weak.