U-Pb Ages of Zircons in Western Qinling Shan, China, and Their Tectonic Implications

Abstract

The Western Qinling Shan is the westward extension of the Eastern Qinling Shan, which connects the North China craton, the Qilian and Qaidam, and the Songpan-Ganzi block on the north, on the west, and on the south, respectively. Clastic sedimentary rocks of Precambrian to Triassic age from this region are studied in this article. Detrital zircons were extracted from the sedimentary rocks for U-Pb dating through LA-ICPMS. Nd depleted mantle model ages resemble those of the Yangtze craton, with a statistical population of 1.55–1.98 Ga, peaking approximately at 1.81 Ga, in contrast to Paleoproterozoic and Archean population of the North China craton. Devonian detrital zircon U-Pb ages of 930 to 730 Ma indicate their affinity to the Yangtze craton, which was the intensive crustal growth stage in the provenance region. The majority of the Permo-Triassic clastic sedimentary rocks are characterized by ages older than 1600 Ma. Detrital zircon U-Pb ages and Sm-Nd isotopic compositions indicate that the basement rocks, on the southern margin of the North China craton, became an important component of the Permo-Triassic clastic sedimentary rocks. The Yangtze craton conjoined the North China craton during the Triassic time period. Up to 50% of the Permo-Triassic clastic sedimentary rocks of the west Qinling segment contain material from the basement rocks on the southern margin of the North China craton.