Paleoproterozoic basement of the Xing'an Block in the eastern Central Asian Orogenic Belt: Evidence from the geochemistry and zircon U-Pb geochronology of granitic gneisses

The Precambrian evolution of the Central Asian Orogenic Belt (CAOB) in NE China remains enigmatic. The Xinghuadukou Complex, located in the Xing'an Block of NE China, contains important records of the Precambrian geological evolution of the eastern CAOB. In this study, we present petrographic observations, zircon U-Pb ages, and major and trace element data of Precambrian granitic gneisses from the Xinghuadukou Complex. The granitic gneisses are characterized by high SiO2 (69.62-80.66 wt%) and K2O (2.15-3.80 wt%), enrichments in Rb, Th, Ba, and Pb, depletions in Nb, Ta, Sr, Ti, and P, and negative Eu anomalies. These geochemical signatures suggest that the granitic gneisses were derived from high-K, calc-alkaline, I-type granites, which were formed in a volcanic arc setting from magmas involving partial melting of thickened crust and extensive fractional crystallization. A total of 133 zircons in six granitic gneiss samples yielded weighted mean ,Pb- 207/Pb-206 ages of 1865 +/- 10, 1847 +/- 13, 1858 +/- 12, 1852 +/- 9, 1872 +/- 9, and 1859 +/- 13 Ma, respectively. All the zircons combined define a weighted-mean Pb-207/Pb-206 age of 1861 +/- 4 Ma, indicating a Paleoproterozoic basement in the Xing'an Block. In combination with data from previous studies, we suggest that the Xing'an Block was a microcontinent, likely part of the Columbia supercontinent.