Recycling of Paleo-Asian Ocean carbonates and its influence on the lithospheric composition of the North China Craton

The deep carbon cycle, which plays a critical role in mantle evolution and Earth habitability, is closely linked to the recycling of carbonate-bearing rocks through subduction. Marine carbonates are subducted to different depths during the closure of oceanic basins, thus carry important signatures of the disappeared oceanic basins. Petrological and geochemical features of the Hannuoba carbonatites in the northern North China Craton indicate that they were formed by melting of limestone subducted to mantle depths. Here, we show that detrital zircons carried by these carbonatites have a broad spectrum of U-Pb ages from Precambrian to Phanerozoic. Precambrian age peaks are at ∼2.5 Ga, 2.1–2.3 Ga, 1.8–2.0 Ga, ∼1.65 Ga, 1.3–1.4 Ga,∼1.1 Ga, 0.91–0.94 Ga, 0.74–0.81 Ga, and 0.62–0.63 Ga, respectively. The recorded age peaks are different from those in the northern North China Craton and thus preclude an origin of crustal contamination. Nevertheless, the Precambrian age spectra are compatible with those of the Xingmeng Orogen in the southeastern Central Asian Orogenic Belt. Furthermore, the significantly positive ε_Hf(t) values of 7.7–13.5 for the 300–373 Ma zircons are similar to those in the Xingmeng Orogen but different from those in the northern North China Craton. All these features suggest that the limestone precursor for the Hannuoba carbonatites was originated from the Paleo-Asian Ocean, and its deposition time was not earlier than 300 Ma. This indicates that the Paleo-Asian Ocean still existed in the late Carboniferous to early Permian. The widespread distribution of metamorphic carbonates in the Central Asian Orogenic Belt indicates that there may have been widespread sedimentary carbonates in the Paleo-Asian Ocean. A large amount of sedimentary carbonates was probably carried into mantle during subduction of the Paleo-Asian oceanic slab, which significantly modified the chemical and physical properties of the lithospheric mantle.