In this study, the LA-ICP-MS zircon U–Pb dating of the Shimo-ondori diorites in the Shimanto accretionary complex of SW Japan provides ~130 Ma, representing the timing of their crystallization ages. Combined with the geological occurrence, that age clearly indicates that the diorites occur as blocks, not as intrusive rocks as suggested by previous studies. Moreover, the ages of the Shimo-ondori diorites are suggesstive that they could be influential for the estimate of the early-Cretaceous tectonic evolution for the eastern Asian margin. Their whole-rock chemical compositions show high MgO, Ni and Cr contents, and low total FeO/MgO ratios, indicating that they were crystallized from high magnesian andesite (HMA) magmas. Moreover, their TiO₂ and REE compositions suggest that they were formed by the same processes as the sanukites. And, the zircon Hf isotopic ratios (ε_Hf [~130 Ma] = +9.9 − +17.5), which is close to or slightly lower than that of the ~130 Ma depleted mantle, suggest that the wedge-mantle materials were predominantly involved in the formation of the dioritic magmas. Their geochronological and geochemical similarities of the Shimo-ondori diorites with the early Cretaceous adakites and HMAs in the eastern Asian margin suggest that they might have been formed possibly by the same slab rollback of the Izanagi plate at the early Cretaceous. After the crystallization of the Shimo-ondori diorites, they were delivered and deposited as blocks in a trench site with the surrounding sedimentary rocks of the Shimanto accretionary complex.

中文翻译：

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日本西南四国Shimo-ondori闪长岩成因和侵位的地球化学和年代学约束

在这项研究中，日本西南部 Shimanto 增生复合体中 Shimo-ondori 闪长岩的 LA-ICP-MS 锆石 U-Pb 定年提供了~130 Ma，代表了它们的结晶年龄时间。结合地质事件，该年龄清楚地表明闪长岩以块状形式出现，而不是像先前研究表明的那样侵入岩。此外，Shimo-ondori 闪长岩的年龄表明它们可能对估计东亚边缘早白垩世构造演化有影响。它们的全岩化学成分显示出高 MgO、Ni 和 Cr 含量，以及低总 FeO/MgO 比，表明它们是从高镁安山岩 (HMA) 岩浆中结晶出来的。此外，它们的 TiO ₂和 REE 成分表明它们是通过与 sanukites 相同的过程形成的。而且，锆石 Hf 同位素比（ε _Hf [~130 Ma] = +9.9 − +17.5）接近或略低于~130 Ma 贫化地幔，表明楔形地幔物质主要参与其中在闪长岩浆的形成过程中。它们的年代学和地球化学上的 Shimo-ondori 闪长岩与早白垩世埃达克岩和东亚边缘的 HMA 的相似性表明它们可能是由早白垩世伊邪那岐板块的同一板块回滚形成的。Shimo-ondori 闪长岩结晶后，它们作为块体被输送并沉积在四万十增生复合体周围沉积岩的海沟遗址中。