Abstract

It is widely accepted that the lithospheric mantle under the North China craton (NCC) has undergone comprehensive refertilization due to input from surrounding subducted slabs. However, the possible contribution from the Paleo-Asian oceanic slab to the north is poorly constrained, largely because of the lack of convincing evidence for the existence of this slab under the NCC. We report here carbonatite intruding Neogene alkali basalts in the Hannuoba region, close to the northern margin of the NCC. Trace element patterns with positive Sr and U anomalies, negative high field strength elements (Nb, Ta, Zr, Hf, and Ti) and Ce anomalies, high 87Sr/86Sr ratios (0.70522-0.70796), and high δ18OSMOW (standard mean ocean water) values (22.2‰–23‰) indicate that this carbonatite had a limestone precursor. However, the presence of coarse-grained mantle-derived clinopyroxene, orthopyroxene, and olivine, and chemical features of the carbonates suggest that the carbonate melts were derived from the mantle. The carbonates have high 143Nd/144Nd ratios (0.51282-0.51298) and show negative correlation between CaO and Ni contents, resulting from reaction between carbonate melt and peridotite. Considering the regional tectonic setting, the carbonatite probably formed by melting of subducted sedimentary carbonate rocks that formed part of the Paleo-Asian oceanic slab, and thus could provide the first direct evidence for the presence of the Paleo-Asian oceanic slab beneath the NCC.

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