Timing of Tectonothermal Events in Archean Basement of the North China Craton

The North China Craton (NCC) has a long-term formation and evolution history up to 3.8 Ga rock records, with 4.0-4.1 Ga zircons. This paper summarizes the Archean tectonothermal events of the Craton, mainly focusing on the timing of the events. The oldest metamorphic zircon ages are 3.71-3.75 Ga and 4.0 Ga identified for detrital or xenocrystic zircons from Paleozoic meta-volcano-sedimentary rock in western segment of the North Qinling Belt near the southern margin of the NCC. Paleoarchean (~3.3 Ga) tectonothermal event widely occurs in the Anshan area, resulting in formation of banded trondhjemite gneisses. Early Neoarchean-late Mesoarchean metamorphic zircon ages can be subdivided into two groups: 2.65-2.85 Ga and ~2.6 Ga. 2.65-2.85 Ga metamorphic zircon ages have been obtained in western Shandong, eastern Shandong and Lushan. It is difficult to determine the exact age of tectonothermal event because of strong overprinting of the late Neoarchean. However, late Mesoarchean to early Neoarchean tectonothermal event must have occurred in the NCC. Compared with the 2.65-2.85 Ga tectonothermal events, the ~2.6 Ga event was more clearly developed in the NCC, such as in eastern Shandong and Lushan, besides being widely identified in western Shandong. 2.6 Ga is a convenient time to set as the early Neoarchean-late Neoarchean boundary. The most important Archean tectonothermal events occurred at the late Neoarchean (2.49-2.53 Ga), which have been identified in every Archean basement area of the NCC. In general, its northern domain recorded higher-grade metamorpism than its southern domain probably due to the former exposuring deeper crustal level. In the NCC, metamorphic intensity and scope became stronger and larger with time going on, peaking at the end of the Noearchean, consistent with the Archean continental crust becoming larger in thickness and scale with time. In some areas where the late Paleoproterozoic tectonothermal event was well developed, some metamorphic zircons recorded the earlest Paleoproterozic and even younger ages (2.40-2.47 Ga). This may not mean the existence of these events, but is a result of strong overprinting of the late Paleoproterozoic events. © 2020, Editorial Department of Earth Science. All right reserved.