Detrital zircon U-Pb geochronology of the Qinling Group in Wulichuan-Zhaigen area, West Henan

The Qinling Group is the main component of the Qinling microcontinent, and the accurate determination of its age is of great significance for the study of the tectonic evolution of the Qinling orogenic belt. This paper presents zircon LA-MC-ICPMS U-Pb geochronologic data of the albite two-mica schist from Yanlinggou Formation and the sillimanite two-mica monzo-gneiss from Guozhuang Formation of Qinling Group in Wulichuan-Zhaigen area. The dating results of the magmatic core of detrital zircons from albite two-mica schist show 5 age groups mainly, i.e., 545-551 Ma, 754-778 Ma, 900-1000 Ma, 1340-1830 Ma and 2300-2500 Ma, in which the 900-1000 Ma group exhibits most obvious peaks of detrital zircons, and an inconsistent line of the upper intersection point of (2478 ±25) Ma can be fitted to a part of data points. The sillimanite two-mica monzo-gneiss ages are mainly concentrated in 1400-1800 Ma, with only four data points being in the range of 1134-1243 Ma, and the youngest magmatic core of detrital zircons is (1103 ±6) Ma. According to the data, the authors hold that the age of Yanlinggou Formation was younger than 900 Ma, and older than 438 Ma pluton of Wuduoshan. Guozhuang Formation is mainly formed during late Mesoproterozoic, younger than 1122 Ma, and older than 962 Ma Neoproterozoic granitic rocks. The sedimentary material of Yanlinggou Formation complex was mainly from Neoproterozoic granitic rocks and Proterozoic continental crust, with a little from Guozhuang Formation. Most sources of Guozhuang Formation were from the late Paleoproterozoic to Mesoproterozoic granitic continental crust. Yanlinggou Formation and Guozhuang Formation were formed in different periods, and there was a discontinuity between them. Their sedimentary materials were also different, and even a small amount of material of Yanlinggou Formation was postredeposition material from Guozhuang Formation. The two formations are different tectonic sheets. Therefore, the Yanlinggou Formation should be separated from the Qinling Group.