Abstract Paleo- to early Mesoproterozoic rocks in the Yangtze Block are extremely sparse and are predominately exposed along the southwestern margin. Their petrogenesis and tectonic significance remain unclear, resulting in a limited understanding of the tectonic evolution of the southwestern Yangtze Block during this period. Therefore, we report here detailed geochronological and geochemical analyses of newly discovered Paleo- to early Mesoproterozoic mafic intrusive rocks in the Huili-Dongchuan area, southwestern Yangtze Block and interpret their petrogenesis and tectonic significance. Secondary ion mass spectroscopy (SIMS) zircon and baddeleyite U-Pb dating yielded crystallization ages of ca. 1716–1714 Ma for gabbros and diabases (referred to as the 1.72–1.71 Ga group), ca. 1705–1700 Ma for gabbros and a diabase-porphyrite (the 1.70 Ga group), and ca. 1519–1504 Ma for a gabbro and a diabase (the 1.52–1.50 Ga group), which effectively constrain the minimum depositional age of the Tong'an and Dongchuan groups that they intrude to 1.72 Ga. The three groups (or episodes) of intrusive rocks differ from each other in their chemical compositions and isotopic characteristics, most likely because of varying degrees of melting in a convective upper mantle (probably the asthenosphere), which had been metasomatized by melts with enriched components input by a plume from the lower mantle. Modeling calculations suggest that fractional crystallization (FC) and assimilation and fractional crystallization (AFC) were the most important processes involved in modifying the chemical compositions of these rocks. These magmatic activities are interpreted to have been related to mantle plumes and continental rifting that occurred in the Huili-Dongchuan area near the southwestern margin of the Yangtze Block.

中文翻译：

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华南扬子地块西南部古至中元古代岩浆和构造演化：来自约 会理-东川地区1.7～1.5 Ga基性岩

摘要 扬子地块古至早中元古代岩石极为稀疏，以西南缘出露为主。它们的岩石成因和构造意义尚不清楚，导致对这一时期扬子地块西南部的构造演化认识有限。因此，我们在此报告了扬子地块西南部会里-东川地区新发现的古至早中元古代基性侵入岩的详细年代学和地球化学分析，并解释了它们的成因和构造意义。二次离子质谱 (SIMS) 锆石和斜锆石 U-Pb 测年得出的结晶年龄约为 辉长岩和辉绿岩的 1716-1714 Ma（称为 1.72-1.71 Ga 组），约。辉长岩和辉绿岩-斑岩（1.70 Ga 组）为 1705–1700 Ma，和约。1519-1504 Ma 为辉长岩和辉绿岩（1.52-1.50 Ga 组），有效地将其侵入的同安和东川组的最小沉积年龄限制在 1.72 Ga。三组（或集）侵入岩石的化学成分和同位素特征彼此不同，很可能是因为对流上地幔（可能是软流圈）中的熔融程度不同，上地幔已被下地幔羽流输入的富含成分的熔体交代。建模计算表明，分级结晶 (FC) 和同化和分级结晶 (AFC) 是改变这些岩石化学成分的最重要过程。