Zircon U–Pb geochronology from a Paleoproterozoic mafic dyke in the Jiapigou terrane (North China Craton): inferences about formation and evolution of the early crust

The formation and evolution of the ancient crust have long been popular issues in the field of Earth sciences. At present, crustal rocks with ages older than 3.8 Ga are in the form of residual blocks and preserved only in the Wopmay orogenic belt in northern Canada, the new Labrador region in western Greenland, Mount Sones in Antarctica, and the Anshan area in China. A > 3.8 Ga remnant in the North China Craton is found in the Baijiafen felsic gneiss in the Anshan banded-iron formation (BIF) mining area. Most reported > 3.8 Ga zircons are captured detrital zircons. However, they can provide important clues for exploring the early continental crust by the mineral microprobe method. In the Jiapigou terrane, many data show that the ages of geological bodies that underwent Archean regional metamorphism are 2.53–2.59 Ga and 2.68–2.7 Ga. We accidentally found a 3.8-Ga captured zircon in a mafic dyke, which intruded the metamorphic rock series. By means of LA-ICP-MS zircon geochronology dating, we totally obtained three age groups. The 3.8-Ga captured zircon with magmatic features, including semi-automorphic column structures, oscillatory zoning and core-rim textures, and a Th/U value of 1.01 (> 0.3), which indicates that the Jiapigou terrane may have experienced early Archean magmatism. The 2.55-Ga captured zircons with magmatic features reveal that the early crust was destroyed by 2.5-Ga magmatic tectonic events. The 1.9-Ga magmatic zircons reveal that the emplacement process of basic magma clearly involved assimilation of the upper crust or Neoarchean granitic gneiss. Thanks to our results it was possible to add some more geochronological constraints to the evolution of the early crust outcropping in the Jiapigou terrane.