Numerous late Paleoproterozoic to early Mesoproterozoic mafic magmatic rocks are exposed in the southwestern Yangtze Block, corresponding to early breakup of the Nuna supercontinent. Geochronological data reveal three episodes of mafic magmatism at ~1,740, 1,700, and 1,500 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 ~1,500 Ma mafic rocks possess OIB‐like Nb/Ta (16.7–19.1) and Zr/Hf (41.0–45.1) ratios, ε_Nd (t ) values (−0.8 to +0.1), and ε_Hf (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 in the Nuna configuration. Taking all synchronous mafic magmatism into account, a mantle plume beneath southern Siberia was considered to be initiated at ~1,750 Ma forming a broad region of mafic magmatism that extended into the Yangtze Block as well as beneath northern Laurentia and resulted in lithospheric extension. The Yangtze Block was possibly the nearest neighbor to northwestern Siberia at ~1,500 Ma and subsequently drifted from the Nuna supercontinent induced by the ~1,500 Ma Kuonamka mantle plume, heralding a period of limited magmatic activity and tectonic quiescence in the Yangtze Block that extended throughout the remainder of the Mesoproterozoic.

中文翻译：

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西南西南扬子地块的晚古元古代到中元古代镁铁质岩浆作用：地幔柱与努纳破裂有关？

在西南扬子地块中暴露出许多古元古代晚期至中元古代早期的镁铁质岩浆岩，这对应于努纳超大陆的早期破裂。地质年代学数据揭示了3次镁铁质岩浆作用事件，分别发生在1,740、1,700和1,500 Ma。这两个较早的世代具有类似MORB的Nb / Ta比和超软骨Nd-Hf同位素，表明它们很可能源自软流圈地幔的部分熔融。与此相反，〜1500马镁铁质岩石具有OIB状的Nb / TA（16.7-19.1）和Zr / HF（41.0-45.1）比，ε_钕（吨）的值（-0.8〜0.1），ε_的Hf（Ť）值（−3.3至+8.4），表明它们起源于地幔柱。扬子地块的这三个镁铁质岩浆活动脉冲具有地球化学特征（如TiO ₂含量，Nb / Y和La / Yb值），类似于西伯利亚和劳伦蒂亚的同时期镁铁质岩石，与碎屑锆石物源研究一致，该研究表明扬子地块与北劳伦蒂亚在努纳构造中存在空间联系。考虑到所有同步镁铁质岩浆作用，西伯利亚南部下方的地幔柱被认为是在大约1,750 Ma处形成的，形成了广泛的镁铁质岩浆作用区域，延伸到扬子块以及劳伦西亚北部，并导致岩石圈扩张。扬子地块可能是距西伯利亚西北部最近的邻国，距约1500 Ma，随后从约1500 Ma Kuonamka地幔柱诱发的努纳超大陆漂移，