Isotopic Evidence Suggests North China Craton Formed Prior to NeoArchean

Archean-Paleoproterozoic crustal evolution in the eastern North China Craton: Zircon U-Th-Pb and Lu-Hf evidence from the Jiaobei terrane

Authors:

Wang et al

Abstract:

The Precambrian metamorphic basement of the North China Craton (NCC) records a complex evolutionary history during the Neoarchean and the Paleoproterozoic. The Jiaobei terrane provides one of the best regions to evaluate the early Precambrian crustal growth of the Eastern NCC. Here we report the results of U-Pb zircon geochronology and Hf isotopes of tonalite-trondhjemite-granodiorite (TTG) gneiss and associated mafic rocks from the Jiaobei terrane. SIMS dating of zircons from the TTG gneiss shows that the protolith was formed at 2912 ± 6 Ma and subjected to anatexis at 2488 ± 9 Ma. Zircons from the mafic rocks yield three age populations at 2484 ± 7 Ma, 1855 ± 5 Ma and 1836 ± 3 Ma. Based on the differences in morphology, internal texture, and the U-Th compositions between magmatic and metamorphic zircons in the mafic suite, we interpret the 2484 ± 7 Ma and 1836 ± 3 Ma ages obtained from two meta-mafic intrusions as the crystallization age of their magmatic precursors, and the 1855 ± 5 Ma from a garnet amphibolite as the metamorphic age. Magmatic zircons from TTG gneiss and meta-gabbro yield Hf model ages ranging from 3.2 to 2.8 Ga, suggesting an important period for crustal growth during Mesoarchean. The earlier mafic magmatic event (2.49 Ga) involved magma generation from a depleted mantle, whereas the later phase (1.84 Ga) was derived from differentiation of a parent magma that originated from the partial melting of the Mesoarchean lower curst. The newly grown metamorphic zircons in the garnet amphibolite show initial 176Hf/177Hf and TDMC values from 0.281211 to 0.281343 and from 3.11 to 3.42 Ga, indicating that the Mesoarchean and older crustal materials reworked at 1.86 Ga.

The data reported in this study, coupled with previous geochronological and Lu-Hf isotopic data from other localities of the eastern NCC on the widespread emplacement of the mafic magmas and the coeval high-grade metamorphism or melting events at 2.50-2.48 Ga suggest that these regions were already part of a coherent tectonic unit with a common crustal evolution history during the end of Neoarchean.