Abstract Recent studies have revealed that following collision between the Western Sulawesi and Sula Spur microcontinents during the early to middle Miocene, the Western Sulawesi microcontinent subsequently underwent extension. However, the geodynamic process that resulted in extension is unknown. The petrogenesis of late Miocene to Pliocene granitoids in the region provides insights to the mechanism of extension. To achieve this goal, we studied the Palopo granodioritic intrusion, a well-exposed representative pluton that crops out along the Palu–Koro Fault. Zircon U–Pb dating indicates a 4.8–4.7 ± 0.1 Ma crystallization age for the pluton. Compared with arc igneous rocks, the pluton has high Sr contents and low Y and Yb contents, with relatively high Sr/Y and LaN/YbN ratios. These geochemical signatures are similar to those of typical adakites. The samples exhibit high MgO (1.60–2.54 wt%), Cr (46–65 ppm), and Ni (14.1–19.0 ppm) contents relative to adakitic rocks derived from thickened lower crust. In addition, negative eHf(t) (−9.7 to −5.5) and eNd(t) (−8.5 to −11.1) values, together with relatively low 143Nd/144Nd and high initial 87Sr/86Sr ratios, reflect an origin through recycling of ancient crustal materials, which is clearly different from adakites derived from melting of a subducting slab. The most plausible mechanism for generation of the late Miocene–Pliocene adakitic granodiorites in the Western Sulawesi microcontinent is partial melting of delaminated lower crust that interacted with the mantle. We propose that the late Miocene to Pliocene crustal extension in the Western Sulawesi microcontinent was triggered by delamination of pre-existing thickened lithosphere.

中文翻译：

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印度尼西亚西苏拉威西岛~5 Ma Palopo花岗闪长岩侵入体揭示的晚中新世至上新世地壳伸展和岩石圈分层

摘要 近年来的研究表明，西苏拉威西岛微大陆与中新世早中期发生碰撞后，西苏拉威西岛微大陆发生扩张。然而，导致伸​​展的地球动力学过程是未知的。该地区晚中新世至上新世花岗岩的岩石成因提供了对延伸机制的见解。为实现这一目标，我们研究了 Palopo 花岗闪长岩侵入体，这是一种暴露良好的代表性岩体，沿帕卢-科罗断层出露。锆石 U-Pb 测年表明岩体的结晶年龄为 4.8-4.7 ± 0.1 Ma。与弧形火成岩相比，岩体的 Sr 含量高，Y、Yb 含量低，Sr/Y 和 LaN/YbN 比值相对较高。这些地球化学特征类似于典型的埃达克岩。与源自增厚的下地壳的埃达克质岩石相比，样品表现出高 MgO (1.60–2.54 wt%)、Cr (46–65 ppm) 和 Ni (14.1–19.0 ppm) 含量。此外，负 eHf(t)（-9.7 至 -5.5）和 eNd(t)（-8.5 至 -11.1）值，以及相对较低的 143Nd/144Nd 和较高的初始 87Sr/86Sr 比率，反映了通过回收利用古代地壳材料，明显不同于俯冲板片熔化产生的埃达克岩。西苏拉威西微大陆中晚中新世-上新世埃达克闪长岩的最合理机制是与地幔相互作用的分层下地壳的部分熔融。我们认为，西苏拉威西微大陆的晚中新世至上新世地壳伸展是由预先存在的增厚岩石圈的分层引发的。