Late Paleoproterozoic tectonothermal events in the North China Craton as revealed by rutile U-Pb dating of the Sushui Complex

The Sushui Complex is an important component of the Precambrian basement in the southern North China Craton (NCC), and it mainly formed in the time interval from the Neoarchean to Paleoproterozoic. Although it is confirmed that the Paleoproterozoic is a key period for the final amalgamation of the NCC, and the granulite facies metamorphism can be recognized in the Sushui Complex. However, limited studies suggest that the Sushui Complex has undergone Paleoproterozoic metamorphism. Thus, a significant controversy exists regarding whether the Sushui Complex has been involved and reworked by the final assembly of the NCC. Rutile, one of the most important titanium minerals, occurs in a variety of medium- to high-grade metamorphic rocks, which have a lower closure temperature (500–630 °C) than zircon (>850 °C), thus rutile can record a wealth of useful and additional information about subsequent magmatic and metamorphic events, which makes it a complementary mineral to zircon to reveal the complete geologicalal history. In this contribution, we carried out the LA-ICP-MS U-Pb dating on zircon and rutile grains that collected from the Sushui Complex. Zircons from two trondhjemitic gneiss samples yield crystallization ages of 2520 and 2509 Ma. Rutile grains from the samples give the metamorphic ages of 1937, 1840, and 1811 Ma, respectively. The mica schist sample records the two populations of rutile U-Pb ages of 1924 and 1832 Ma. Zircon U-Pb dating reveal that the monzogranite sample was emplaced at 2300 Ma, and rutiles in the sample yield variable ages ranging from 2079 to 1715 Ma with a main peak age of 1820 Ma. The rutile U-Pb ages of the Sushui Complex reveal two distinct stages of metamorphism. The period of 1937–1924 Ma corresponds to the timing that is close to the peak metamorphism; whereas the subsequent period of 1840–1811 Ma indicates the cooling age associated with the exhumation of the basement in the Zhongtiao Mountains. Available studies reveal that the Sushui Complex has experienced Paleoproterozoic metamorphism during the final assembly of the NCC. In addition, our study provides an excellent example of how rutile U-Pb dating is a valuable geochronological tool for revealing late tectonothermal events of the Precambrian metamorphic terranes.