Provenance, depositional setting, and crustal evolution of the Cathaysia Block, South China: Insights from detrital zircon U–Pb geochronology and geochemistry of clastic rocks

Abstract

We report the results of a combined study of detrital zircon U–Pb geochronology and bulk‐rock elemental geochemistry on late Neoproterozoic to Cambrian clastic sedimentary rocks from South Jiangxi within Cathaysia. These clastic rocks are characterized by moderate chemical index of alteration (CIA) values of 73 and high Th/U ratios (>3.8), indicating moderate weathering of the source area. The relatively high index of compositional variability (ICV = 0.62–1.30) values indicates a source compositionally dominated by immature material that lacks alumina‐rich minerals. Bulk‐rock major and trace element systematics on discrimination diagrams are consistent with the source provenance being felsic‐intermediate igneous rocks of ancient continental crust origin. The geochemistry is also consistent with the clastic sedimentary rocks being deposited in a setting at or in the vicinity of passive continental margins. Detrital zircon U–Pb ages of the clastic rocks record five major age populations: 2,614–2,376 Ma (peak at ca. 2,482 Ma), 1,953–1,353 Ma, 1,000–900 Ma (peak at ca. 958 Ma), 850–730 Ma (peaks at ca. 845 and 763 Ma), and 685–571 Ma (peak at ca. 635 Ma). The age data provide a record of igneous activity in the source provenance: the 2,482 Ma peak is consistent with the global Neoarchean continental crust growth; the 1,953–1,353 Ma population correlates with the period of assembly and breakup of the Columbia supercontinent; the prominent peak at ca. 958 Ma corresponds to a common thermal–tectonic event associated with the assembly of Rodinia, and the 850–730 Ma population is consistent with the breakup of the Rodinia supercontinent. The ca. 850 Ma age is indicative of initial stage of Rodinia breakup in South China. Our data also reveal a 670–530 Ma population that correlates well with the Pan‐African event associated with the formation of the Gondwana supercontinent, although no direct geological evidence for this event has been found within the SCB. Moreover, complex zircon morphology and comparisons of detrital zircon U–Pb age spectra in a global context suggest the late Neoproterozoic–Cambrian sedimentary rocks in the Cathaysia Block must have sourced from an exotic source with magmatic activities of late Archean, Grenvillian, and Pan‐African ages, which do not outcrop in the Cathaysia Block or adjacent regions and need to be further explored.