DETRITAL ZIRCON ANALYSIS OF CENOZOIC RIFT-DRIFT TRANSITIONS IN THE HSUEHSHAN TROUGH, TAIWAN

Understanding the sedimentary provenance of infill records within evolving sedimentary basins is essential for unraveling geological processes. In rifting settings, the syn-rift period is marked by sedimentation from local sources due to active normal faulting. However, during the post-rift stage, thermal subsidence allows for sediment influx from distant sources, resulting in a polymodal detrital zircon age spectrum that indicates diverse provenance. Unfortunately, previous studies in Taiwan have overlooked basin evolution, focusing solely on variations in drainage systems.

To investigate the source-to-sink history of the Hsuehshan Trough from the Late Oligocene to Early Miocene, we compiled data from previous studies and conducted detrital zircon U-Pb dating on samples from the Wuchihshan to Shihti Formations in the well-studied Waimushan Profile using LA-ICP-MS. Our analysis reveals shifts in sedimentary provenance, aided by comparisons with the well-explored Songliao Basin, employing the bivariate discrimination model and the multidimensional scaling.

This study combines nine samples and 1,071 effective U-Pb detrital zircon dating data points. The lower Wuchihshan Formation exhibits a relatively simple age spectrum, reflecting a syn-rift signal, while the upper Wuchihshan and Mushan Formations depict a transitional stage. Notably, the Mushan Formation contains latest Paleogene detrital zircons, which may correlate with igneous activity in the northern Hsuehshan Trough, and displays a distinct Cenozoic peak. The subsequent Taliao and Shihti Formations demonstrate a polymodal age distribution, indicating diverse provenance. Additionally, the presence of Eocene zircons in the Mushan Formation may suggests the influence of breakup processes on sediment sourcing.

Overall, these findings underscore the dominance of basin development processes in shaping sedimentary provenance. While our results align with previous studies, we propose an older boundary between the syn-rift and transitional stages.