Figure 3
(a) Sr–Nd isotopic compositions of the fresh MD carbonatites and their calcite separates. Other CARD-hosted carbonatites (e.g., Bayan Obo24 and Laiwu6) and associated Cenozoic-Mesozoic igneous rocks in China13,38 are shown for comparison with carbonatites from southwest China, East Africa (EACL)27, North America26, Brazil22 and India29. The dotted line outlines the global marine sediment field32. The MD samples yield an Sr-Nd isotopic array shifted toward marine sediment. The DM (depleted mantle), HIMU (high-μ mantle), EMI (enriched mantle I) and EMII (enriched mantle II) fields are distinct mantle end-members39. (b) 207Pb/204Pb vs. 206Pb/204Pb correlation diagram for the fresh MD carbonatites and calcite separates. Carbonatites from East Africa31 and Cenozoic potassic rocks from southwest China13 are shown for comparison. (c) δ13C vs. δ18O correlation diagram for the calcite separates and fresh carbonatites. Previously collected calcite data were re-examined by extensive microscope observations and plotted for comparison with the fresh carbonatites. All the plotted data fall into the fields of mantle-derived primary carbonatites35. Fresh samples from the Dalucao and Lizhang districts feature two distinct coherent trends with weak positive correlations between δ18OVSMOW and δ13CVPDB values. All data from Tables S2–4.
