Abstract The late Mesoproterozoic geodynamic setting of the Yangtze Block, South China remains largely unknown due to the scarce geological records of this age. This study presents a new dataset consisting of petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf isotopes of newly identified late Mesoproterozoic diabases in the southwestern Yangtze Block. Two diabase samples give zircon U-Pb ages of 1138 ± 4 Ma and 1141 ± 4 Ma. The diabases are tholeiitic in composition and have consistent high TiO2 contents (2.18 – 2.93 wt.%) but low Mg# values (41 – 47). They are slightly enriched in LREEs with (La/Yb)N ratios of 2.87 – 3.99 and show E-MORB-like trace element patterns with positive Nb-Ta anomalies. The diabase samples exhibit positive zircon eHf(t) values from +9.4 to +13.7 and whole-rock eNd(t) values from +3.4 to +4.0. These results suggest that they may have undergone negligible crustal contamination during the magma evolution and were most likely generated from partial melting of a depleted asthenosphere mantle source. The diabases possess consistent Nb/Yb (4.87 – 5.91) and Th/Yb (0.031 – 0.59) ratios, ruling out the possibility of interaction with subduction-related materials. They have high Ti/V (38 – 46) and Zr/Y (3.36 – 5.23) ratios, typical of within-plate basalts. Considering the contemporary A-type granites and alkaline basalts in the same region, intense continental rifting most likely occurred in the southwestern Yangtze Block during the late Mesoproterozoic. Widespread intraplate magmatism of 1.2 – 1.1 Ga in the Yangtze Block indicates that it may not have been involved in the Rodinia assembly at the time.

中文翻译：

---

华南西南扬子地块1.14 Ga基性侵入体：晚中元古代板内岩浆作用记录

摘要 由于该时代的地质记录稀少，华​​南扬子地块晚中元古代地球动力学环境在很大程度上仍不为人所知。本研究提供了一个新的数据集，包括扬子地块西南部新发现的晚中元古代辉绿岩的岩石学、全岩地球化学、锆石 U-Pb 年代学和 Hf 同位素。两个辉绿岩样品的锆石 U-Pb 年龄分别为 1138 ± 4 Ma 和 1141 ± 4 Ma。辉绿岩在成分上是拉斑性的，并且具有一致的高 TiO2 含量（2.18 – 2.93 wt.%），但 Mg# 值较低（41 – 47）。它们在轻稀土中略微富集，(La/Yb)N 比率为 2.87 – 3.99，并显示出类似 E-MORB 的微量元素模式，具有正 Nb-Ta 异常。辉绿岩样品显示出 +9.4 至 +13.7 的正锆石 eHf(t) 值和 +3.4 至 +4.0 的全岩 eNd(t) 值。这些结果表明，它们在岩浆演化过程中可能经历了可以忽略不计的地壳污染，并且很可能是由枯竭的软流圈地幔源的部分熔融产生的。辉绿岩具有一致的 Nb/Yb (4.87 – 5.91) 和 Th/Yb (0.031 – 0.59) 比率，排除了与俯冲相关材料相互作用的可能性。它们具有高 Ti/V (38 – 46) 和 Zr/Y (3.36 – 5.23) 比率，是板内玄武岩的典型特征。考虑到同一地区同时期的A型花岗岩和碱性玄武岩，在中元古代晚期，扬子地块西南部最有可能发生强烈的大陆裂谷。扬子地块广泛分布的 1.2-1.1 Ga 的板内岩浆活动表明它当时可能没有参与罗迪尼亚组合。