Detrital zircon geochronology and provenance of Cenozoic deposits in the Qaidam basin, northern Tibetan plateau: An overview with new data, implications and perspectives

Abstract

An increasing number of detrital zircon U–Pb geochronological data have been reported to trace sediment provenance for the Cenozoic Qaidam basin, which is crucial to understanding crustal deformation, paleoclimate change and basin development in northern Tibetan Plateau and to assessing geodynamic models of plateau growth. However, the existing provenance interpretations are highly diverse and how the northern Tibet has evolved remains controversial. This contribution presents new detrital zircon dating results from Cenozoic outcrop and borehole samples and compiles published data from the whole Qaidam basin, adjacent small Cenozoic basins and the surrounding mountains. Our new synthesis indicates that, Paleoproterozoic signals (1800–2000 Ma and 2350–2500 Ma), rather than the Permian–Triassic ages, can be applied effectively to distinguish the Qilian, Altun and Eastern Kunlun-sourced detrital zircons. The Cenozoic Qaidam basin exhibits spatiotemporally variable detrital zircon age populations. Most sandstones from the western and southern basin are characterized by Phanerozoic bimodal age spectra (i.e., 400–480 Ma and 220–280 Ma) with minor Precambrian signals, indicating major contributions from the neighboring Altun and Eastern Kunlun ranges. By contrast, almost all the northern and eastern basin sandstones display prominent early Paleozoic detrital zircon ages; but Paleoproterozoic, Neoproterozoic (750–950 Ma) and Permian–Triassic signals only appear as dominant age clusters in some samples. Different temporal variation trends are observed from the investigated sections in this region, revealing variable zircon supply from different micro-terranes in the Qilian Mountains. This implies that using detrital zircon provenance data from a single section or from a local area of the Qaidam basin to address regional tectonic and climatic issues of the northern Tibetan Plateau unlikely provide useful results. We propose that the Cenozoic Qaidam basin deposits were derived from localized, adjacent source regions, rather than cross-basinal, distant mountains. Our conclusions support models with synchronous deformation throughout most of northern Tibet in the Cenozoic. The observed spatiotemporal variations in detrital zircon populations are not only attributed to tectonic deformation-induced source changes, but can also be due to heterogeneity of the source terranes (e.g., durability and zircon fertility) and variable factors (e.g., hydrodynamic sorting, recycling and sedimentary microenvironment) in transport-deposition processes. This study also highlights the importance of involving detrital zircon textural and sedimentological parameters to zircon provenance interpretations. An integrated provenance analysis combining other detritus components is helpful to comprehensively characterize source-to-sink systems for sedimentary basins.