Zircon-based proxies for source-rock prediction in provenance analysis: A case study using Upper Devonian sandstones, northern South China Block

• Published in: Sedimentary geology 2023-04, Vol.447, p.106366, Article 106366
• Main Authors: Shi, Guanzhong, Wauschkuhn, Bastian, Ratschbacher, Lothar, Shen, Chuanbo, Fu, Hongyang, Frölich, Sonja
• Format: Article
• Language: English
• Subjects: Detrital zircon geochronology; Provenance analysis; Qinling orogen; Source-rock prediction; Zircon radiation damage
• ISSN: 0037-0738; 1879-0968
• DOI: 10.1016/j.sedgeo.2023.106366

Detrital zircon geochronology is a common tool of provenance analysis. It is based on the comparison of zircon-age spectra with those of potential source rocks. Several factors, for example zircon fertility and detritus transport paths, may bias the age spectra of detrital zircon, possibly causing misleading interpretations. However, additional proxies, such as trace elements and lattice damage, can reflect the source-rock types and thus supplement the provenance interpretation. Herein, we use Upper Devonian sandstones of the northern South China Block for a case study. We classify zircons into S-, I-, annealed-, and unannealed-types and link them to potential source rocks. S-type refers to zircons crystallized from re-melted supra-crustal rocks (e.g., S-type granite), and I-type to those crystallized from the melts of intra-crustal or mantle rocks; these types can be distinguished by their trace elements (P, Eu, REE + Y). Unannealed-type zircons stem from rapidly-cooled igneous (e.g., volcanic and volumetrically-small plutonic) and high-grade metamorphic rocks, and annealed-type zircons from slowly-cooled plutonic and metamorphic rocks. The unannealed- and annealed-types can be discriminated by the degree of radiation damage caused by α-decay of uranium and thorium. We define five zircon U-Pb age groups for the Upper Devonian sandstones: 420–460 Ma (peak ∼436 Ma), 480–620 Ma, 700–840 Ma (peak ∼820 Ma), 0.89–1.2 Ga (peak ∼955 Ma), and 1.6–2.5 Ga. The 420–460 Ma and 0.89–1.2 Ga zircon groups contain a significant number of S-type zircons. Most of the 480–620 Ma zircons are of the I-type, and ∼70 % of them are of the unannealed-type. The 0.89–1.2 Ga group contains ∼23 % S-type and ∼20 % unannealed-type zircons. The potential source rocks include Silurian and Neoproterozoic rift-related bimodal volcanic rocks of the South Qinling Belt, Ediacaran to Ordovician sedimentary rock in the South China Block that contain zircons reworked from the peripheral accretionary arcs of east Gondwana, the metamorphic and plutonic rocks of the Sibao orogen of the South China Block, and the Qinling complex of the North Qinling Belt. An improved prediction of source rocks—as shown herein—can be helpful in provenance analysis, source-to-sink reconstruction, and tectonic-setting discrimination.