An in situ zircon Hf isotopic, U-Pb age and trace element study of banded granulite xenolith from Hannuoba basalt: Tracking the early evolution of the lower crust in the North China craton

Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied. The results show that the banded granulite is a sample derived from the early lower crust of the North China craton. It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes, however, is contained in the granulite. These processes include the addition of mantle material, crustal remelting, metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842 ±40 Ma, except few ages of 3097-2824 Ma and 2489-2447 Ma. The zircons with ages older than 2447 Ma have high ε_Hf (up to ±18.3) and high Hf model age (2.5-2.6 Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most fur of the zircons with early Proterozoic U-Pb age vary around zero, but two have high ε_Hf up to ±9.2-±10.2, indicating mantle contribution during the collision and assembly between the Eastern and Western blocks in the early Proterozoic that resulted in the amalgamation of the North China craton.