| Popis: |
The Paleo-Asian Ocean controlled the tectonic evolution of Northeast Asia and formed the Karamaili Orogenic Belt in the eastern Junggar basin. However, the chronological constrain of the evolution of the paleo-Karamaili Ocean remains unclear. In this study, we focused on the sandstones of the Lower Jurassic Badaowan and Sangonghe Formations in the Dongdaohaizi Depression, Junggar basin near the Karamaili orogenic belt. After detailed observations and descriptions of the macroscopic features of the sandstone, we obtained information on petrology and geochronology. The Dickinson diagrams indicate that the provenance area had the characteristics of a transitional and recycling provenance, which is a collisional orogenic belt with a background of oceanic-continental subduction. The detrital zircon ages of the Lower Jurassic sediments in the Dongdaohaizi Depression can be divided into three peaks: ~300 Ma, ~420 Ma, and ~510 Ma for Badaowan Formation and ~310 Ma, ~410 Ma, and ~500 Ma for Sangonghe Formation. The youngest detrital zircon age is 241 ± 2 Ma, representing an Early Permian depositional age. Combined with previous studies, the sediments in the study area represent a provenance from the Karamaili Ocean. During the Early Jurassic, the consistent subduction of the residual East Junggar Ocean induced continuous uplift in the Karamaili region, resulting in an increasing exposure of deep-seated rocks to provide sedimentary material. According to the tectonic background of the Junggar region, the results indicate that the Karamaili Ocean, as part of the Paleo-Asian Ocean, experienced three evolutionary stages: Cambrian-Early Silurian (460–540 Ma), Late Silurian-Early Carboniferous (360–440 Ma), and Late Carboniferous–Triassic (240–340 Ma). |
