Petrography and Geochemistry of Cenozoic Sandstones in the Dunhua Basin, Northeast China: Implications for Provenance, Source Weathering, and Tectonic Setting

Abstract

Petrographic, mineralogical, and geochemical analyses were conducted on Cenozoic sandstones from the Dunhua Basin, which located in Dunhua-mishan fault zone of northeast China, to investigate the provenance of the sediments, as well as the weathering intensity and tectonic setting of the source region. Petrographic data indicate that average quartz-feldspar-lithic (Q-F-L) proportions in the sandstones are Q = 68%, F = 16%, and L = 16%, the lithic fraction mainly contains volcanic clasts. The chemical index of alteration (CIA) varies from 59 to 69 (average 63), while the index of chemical variability (ICV) ranges from 0.68 to 0.91 (average 0.77), and the average Th/U ratio is 3.2. Chondrite-normalized REE distributions show LREEs enriched relative to HREEs, and a prominent negative Eu anomaly. These data indicating that the sandstones are compositionally immature and a weak degree of weathering in the source region. The petrographic and mineralogical characteristics, combine with Zr/Sc–Th/Sc, Hf–La/Th and Co/Th–La/Sc discrimination diagrams reveal that these sandstones are derived from the surrounding felsic volcanic and intrusive rocks of Late Triassic-Early Jurassic, which exposed to the southeast or northwest of the basin. Multidimensional tectonic discrimination diagrams, including geochemical data and Dickinson triangular charts, indicate that the sandstones were derived from recycled orogenic in an active continental margin setting.