The Western Block of the North China Craton consists of the Yinshan Block in the north and the Ordos Block in the south which were amalgamated along the east-west trending Khondalite Belt at ∼1.95 Ga. The Western Block then collided with the Eastern Block to form the coherent basement of the North China Craton along the north-south trending Trans-North China Orogen at ∼1.85 Ga. The Huaian Complex, a high-grade terrrane located at the conjunction of the Khondalite Belt and Trans-North China Orogen, records metamorphic events associated with both collisions. The complex consists of lithologies from both the Khondalite Belt and Trans-North China Orogen, of which the former consist of graphite-garnet-sillimanite gneiss, garnet quartzite, felsic paragneiss, calc-silicate rock and marble, together called the Khondalite series. Zircons in the graphite-garnet-sillimanite gneiss can be divided into three types: (1) spherical grains without internal structures, (2) grains with a core-and-rim structure; and (3) grains with a dark core surrounded by double rims. Except for the dark core in type 3, all other types of zircon domains are structureless and highly luminescent, with very low Th/U ratios, typical of a metamorphic origin. Analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 ± 26 and 1947 ± 22 Ma, similar to previously determined metamorphic ages from the Khondalite Belt and thus interpreted as the time of collision between the Yinshan and Ordos Blocks. Analyses on type 1 zircons, rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 ± 15 and 1857 ± 16 Ma, interpreted as the time of collision between the Eastern and Western Blocks. Thus, zircons in the graphite-garnet-sillimanite gneiss of the Huaian Complex record both of the Paleoproterozoic collisional events in the North China Craton.
- North China Craton