Abstract To constrain the accretion history of the South China Block (SCB), a geochronological and geochemical study was carried out for the Changba Complex within the Mianlue zone in the northwestern margin of the SCB. Zircon U-Pb dating reveals that the metagabbros and metatonalites were formed at ca. 985–950 Ma, while the bt-amp gneisses have a younger protolith age of ca. 830 Ma. The metagabbro and metatonalite are low- to medium-K tholeiitic series and are significantly enriched in LILEs (Rb, Ba, Th, U, K) and slightly enriched in LREEs, but depleted in HFSEs such as Nb, Ta and Ti. In addition, they have highly positive zircon eHf(t) values (+11.3~ +16.9) and whole-rock eNd(t) values (+3.9~ +5.5) and eHf(t) values (+11.0 ~ +11.8). These geochemical features resemble to those of the magmatic rocks in juvenile oceanic arcs. Zircon δ18O value ranges from 3.0 to 6.2‰ for metagabbro and 4.6 to 5.34‰ for metatonalite, which are slightly lower than the mantle values. Hydrothermally altered gabbros in the lower oceanic crust often have lower δ18O values than mantle and can be primary components of arc lower crust. Therefore the Changba tonalite is interpreted to have been formed by partial melting of the hydrothermally altered gabbroic lower crust. The ca. 830 Ma gneisses are enriched in LREEs and incompatible elements and depleted in HFSEs, similar to the trace element pattern of the average bulk continental crust. They have enriched Sr-Nd-Hf isotopic compositions (0.7055 ~ 0.7060, −5.1 ~ −6.3, and −8.5 ~ −8.8, respectively), which is distinct from the juvenile arc crust. Besides, variable zircon eHf(t) values of −40.6 to 0 and slightly low to elevated zircon δ18O values of 4.2 to 6.6‰, suggesting derivation from reworking of a heterogeneous crustal source. In this regard, the Changba complex records the accretion of juvenile island arc and subsequent reworking of both juvenile and ancient crustal materials, which highlights the crustal growth and geodynamical evolution of the northern margin of the South China Block during the Neoproterozoic in response to the assembly of Rodinia.

中文翻译：

---

新元古代华南地块西北缘的增生史——来自绵略带长坝杂岩的记录

摘要 为确定华南地块（SCB）的增生历史，对华南地块西北缘勉略带长坝杂岩进行了年代学和地球化学研究。锆石 U-Pb 测年表明变辉长岩和变质岩形成于约。985-950 Ma，而 bt-amp 片麻岩的原岩年龄较年轻，大约为 985-950 Ma。830 马。变辉长岩和变辉石属于低至中 K 拉斑岩系列，并且显着富集 LILEs（Rb、Ba、Th、U、K）和轻微富集轻稀土，但贫乏 Nb、Ta 和 Ti 等 HFSE。此外，它们具有高度正的锆石 eHf(t) 值 (+11.3~ +16.9) 和全岩 eNd(t) 值 (+3.9~ +5.5) 和 eHf(t) 值 (+11.0 ~ +11.8)。这些地球化学特征类似于幼年洋弧中的岩浆岩。锆石δ18O值范围为变辉长岩的3.0～6.2‰，偏透岩的4.6～5.34‰，略低于地幔值。下大洋地壳中的热液蚀变辉长岩通常具有比地幔低的 δ18O 值，并且可以是弧下地壳的主要成分。因此，长坝灰长岩被认为是由热液蚀变辉长岩下地壳部分熔融形成的。约。830 Ma片麻岩富含轻稀土元素和不相容元素，贫乏HFSEs，类似于大陆地壳平均的微量元素模式。它们富集了Sr-Nd-Hf同位素组成（分别为0.7055～0.7060、-5.1～-6.3和-8.5～-8.8），与幼年弧壳不同。此外，可变锆石 eHf(t) 值为 -40。6 至 0 和略低至升高的锆石 δ18O 值 4.2 至 6.6‰，表明来自非均质地壳源的再加工。在这方面，长坝杂岩记录了幼年岛弧的增生和随后的幼年和古地壳物质的再加工，突出了新元古代华南地块北缘响应组装的地壳生长和地球动力学演化。罗迪尼亚。