LA-ICP-MS U–Pb ages of detrital zircons from Middle Jurassic sedimentary rocks in southwestern Fujian: Sedimentary provenance and its geological significance

Abstract

In order to determine the tectonic regime change of the early Mesozoic in the South China Block, this study analyzed sedimentary rocks in the Middle Jurassic of southwestern Fujian by modal analysis of sandstones, elemental geochemical analysis of mudstones, and detrital zircons U–Pb dating. The results show that the detrital zircons in Southwestern Fujian mainly consist of Paleoproterozoic to early Mesozoic zircons in the Middle Jurassic. Within the Dongkeng profile of the Zhangping Formation, DK5 sample (lower part) showed a major age peak at ca. 1,848 Ma and two secondary age peaks at ca. 235 and 180 Ma, while DK15 sample (middle part) showed a major age peak at ca. 1,876 Ma and two secondary age peaks at ca. 233 and 190 Ma; the age compositions of these two samples’ were similar. Modal analysis of sandstones indicated that sediments of Zhangping Formation might source from arc orogen and recycled orogen, and element geochemical analysis showed that source rocks of Zhangping Formation might be sedimentary rocks and granites. The Indosinian zircons were mainly derived from the Wuyi region, and the Yanshanian zircons were mainly derived from the Nanling region. The major age group changes from ca. 230 to 220 Ma of the Late Triassic – Early Jurassic to ca. 190 to 180 Ma of the Middle Jurassic in Southwestern Fujian, and main sources changed from Indosinian magmatic rocks in the Late Triassic – Early Jurassic to early Yanshanian magmatic rocks in the Middle Jurassic.

Keywords

• indosinian movement
• middle jurassic
• provenance
• southern china block
• southwestern fujian
• zircon u–pb ages