Geochemistry of Pelites at Chengmen Area: Implications for Sediments Resource and Tectonic Environment

Abstract

The pelite samples were collected from drillholes from the Chengmen area of the Fuzhou Basin of Fujian, China to reveal the sediments resource and tectonic environment of these pelites via an analysis of its lithology and geochemistry. The rare earth element distribution pattern of the pelites exhibited a high degree of fractionation between light and heavy rare earth elements, moderate negative Eu anomalies, and positive Ce anomalies, which are consistent with the rare earth element distribution pattern of Minjiang sediments and Fujian soils. Moreover, the variations in trace elements are also generally consistent, indicating a common provenance. The extremely high chemical index of alteration (CIA) and index of chemical variability (ICV) values of the pelites suggest that the source area experienced intense weathering, indicating a subtropical hot and humid climate environment in the source area and the Fuzhou Basin at that time. The source rock attribute discrimination diagrams show that the main source of pelites is felsic igneous rocks. The ratios of REDOX parameters show that during the sedimentary period, the water body in the study area was predominantly in an oxidizing environment. Furthermore, the tectonic background diagrams reveal that the source area underwent geological tectonic evolution processes of active and passive continental margins, marking the transition from the continental margin above the subduction of the ancient Pacific plate to the continental margin extension after subduction cessation.

Figure 1

(A) Simplified geological map of the South China (modified from Dai et al. reproduced with permission from Elsevier, and copyright forever), (B) Main (Hidden) fracture of Fuzhou Basin (modified from Zhu et al. reproduced with permission from Earthquake Research in China, and copyright forever) and (C) the lithology column of the hole at Chengmen area.

Figure 2

(a) Chondrite REE pattern diagram for underlying formation in Chengmen area, compared with UCC, FJS, and MJS; (b) trace element spider diagram of Chengmen area.

Figure 3

Source area discriminant graph ((a) base map after Hayashi et al. reproduced with permission from Elsevier and copyright forever, and (b) base map after Allègre and Michard reproduced with permission from Springer Nature and copyright forever).

Figure 4

A–CN–K diagram of pelites in the Chengmen area (base map after Nesbitt et al. reproduced with permission from Elsevier and copyright forever; base map after Fedo et al. reproduced with permission from Copyright Clearance Center, Inc., and copyright forever; base map after Fu et al. reproduced with permission from Acta Sedimentologica Sinica, and copyright forever).

Figure 5

Tectonic Setting Discrimination Chart (a–c) ((a, b) base Map after Bhatia et al. reproduced with permission from Springer Nature, and copyright forever; (c) base Map after Roser and Korsch reproduced with permission from Copyright Clearance Center, Inc., and copyright for 5 years; A: oceanic island arc; B: continental island arc; C: active continental margin; D: passive margin).