Provenance and tectonic setting of Paleogene sandstone in the center of the northern Qaidam Basin, China

Abstract

The average thickness of Paleogene sandstones reaches about 3000 m or even 4000 m at the northern margin of the Qaidam Basin. However, the provenance of these sandstones has been uncertain; thus, more comprehensive research is needed. Integrated research was conducted on the provenance based on petrological characteristics, heavy mineral analysis, and U–Pb dating in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction-accretionary or fold-thrust belt; The results of heavy mineral analysis show that the heavy mineral combinations in the Lenghu seventh area and Mabei area are consistent, mainly composed of zircon, garnet, magnetite, and leucosphenite. Moreover, GZi [garnet/garnet + zircon] and RZi [leucosphenite/(leucosphenite + zircon)] have good correlation with ZTR (the ZRT index refers to the proportions of three kinds of transparent heavy minerals in clastic rocks: zircon, rutile, and tourmaline). The zircon U–Pb results for the Paleogene sandstone in the northern Mabei area are consistent with the results of U–Pb dating in the middle of the South Qilian Mountains, which yielded the same results as river sand in the modern Yuka River. Based on three types of data, it is confirmed that the two areas, Lenghu seventh and Mabei, had the same sediment sources in the Paleogene, mainly from the middle of the South Qilian Mountains. The source rocks are mainly neutral - basic magmatic rocks and metamorphic rocks and the structure background is dominated by the magmatic island arc and the collision-thrust suture zone at the active continental margin.