Late Paleo-to early Mesoproterozoic mafic magmatism in the SW Yangtze Block: Mantle plumes associated with Nuna breakup?

Numerous late Paleoproterozoic to early Mesoproterozoic mafic magmatic rocks are exposed in the southwestern Yangtze Block of South China, corresponding to the early breakup of the Nuna supercontinent. The geochronological data reveal three episodes of mafic magmatism at ~1740 Ma, 1700 Ma and 1500 Ma. The two older generations have MORB-like Nb/Ta ratios and superchondritic Nd-Hf isotopes, indicating that they were likely derived from partial melting of asthenospheric mantle. In contrast, the ~1500 Ma mafic rocks possess OIB-like Nb/Ta (16.7-19.1) and Zr/Hf (41.0-45.1) ratios, εNd (t) values (-0.8 to +0.1) and εHf (t) values (-3.3 to +8.4), suggesting that they originated from a mantle plume. These three pulses of mafic magmatic activity in the Yangtze Block have geochemical features (such as TiO2 contents, Nb/Y and La/Yb values), similar to coeval mafic rocks in Siberia and Laurentia, consistent with detrital zircon provenance studies which show a spatial linkage of the Yangtze Block with northern Laurentia and southern Siberia in the Nuna configuration. Taking all synchronous mafic magmatism into account, a mantle plume beneath southern Siberia initiated at ~1750 Ma forming a broad region of mafic magmatism that extended into the Yangtze Block and resulted in lithospheric extension. The Yangtze Block was possibly the nearest neighbor to western part of the Siberian Craton at ~1500 Ma. It subsequently drifted from the Nuna supercontinent induced by the ~1500 Ma Kuonamka mantle plume, heralding a period of limited magmatic activity and tectonic quiescence that extended throughout the remainder of the Mesoproterozoic.