Secular evolution of continental crust of the North China Craton constrained by U-Pb and Lu-Hf-O/Sm-Nd isotopic analyses of detrital zircon and monazite in river sediments

Abstract

Robust detrital minerals from large rivers that sample large-scale continental areas represent important archives of continental crust evolution though time. Compared to the single proxy approach, integrating multiple isotope systems of multiple detrital minerals helps to gain a more comprehensive understanding of crustal growth and evolution. This novel method has so far only been applied to single-sample studies of large rivers and has not yet been utilized for reconstructing continental growth on a cratonic scale. Here, we analyze the U-Pb age, trace element and Lu-Hf-O/Sm-Nd isotopic systematics of detrital zircon (DZ) and monazite (DMnz) from multiple river sediments, with their corresponding drainage basins covering most of the North China Craton (NCC). The results show that the Precambrian DZ have U-Pb age clusters coincident with known episodes of felsic magmatism within the NCC basement. These zircons have variable δ¹⁸O values reflecting extensive incorporation of supracrustal materials into their parent magmas. The DZ sourced from Phanerozoic orogens show mantle-like to high δ¹⁸O values and highly negative to positive ε_Hf(t) values, reflecting the accretion of juvenile crust as well as reworking of ancient continental material. In contrast, DMnz are mostly sourced from high-grade metamorphic rocks and peraluminous granites formed in orogens. The Sm-Nd isotopic compositions of the Paleoproterozoic DMnz reflect a contribution from widespread granulite-amphibolite facies metamorphic rocks of lower crustal origin, recording a major juvenile crust extraction event at ca. 2.5–2.4 Ga that is absent in the DZ record. The integrated DZ-Hf and DMnz-Nd datasets indicate ca. 65–70 % of the existing continental crust was separated from the mantle before ca. 2.4–2.3 Ga with a sharp decrease in growth rate since then, likely linked to the preservation potential of continental masses before and after cratonization of the NCC.