Viti Levu, Fiji, provides one of the best exposed Phanerozoic analogues for the formation of juvenile continental crust in an intra-oceanic setting. Tonalites and trondhjemites are present in several large (75 – 150 km²) adjacent, mid-Cenozoic plutons. We report major and trace element data including rare-earth element (REE) and high-precision high field strength element (HFSE) compositions, new Hf-Nd-Sr-Pb isotope data, and zircon U/Pb-ages, O-Hf isotopes, and trace elements, from five different plutons. The Eocene Yavuna pluton and the Miocene Colo plutons are mainly composed of tonalites and trondhjemites and represent the exposed middle crust of the former Vitiaz island arc. The plutons can be divided into three suites. One suite is light REE (LREE) depleted with some trace element ratios lower than average normal mid-ocean ridge basalts (N-MORB). A second suite has flat REE patterns similar to local island-arc basalts. Both suites occur near the coast of Viti Levu, include a wide compositional spectrum from gabbro to tonalite, and can be produced mostly by fractional crystallization of mafic precursor melts. The third suite is characterized by LREE-enrichments with higher La_N/Yb_N (2.3 – 4.9), higher Zr/Y (4.3 – 7.1), and lower Nb/Ta (9.6 – 12.4). They occur closer to the center of the island and are bimodal trondhjemite-gabbro intrusions. These characteristics are consistent with formation mostly by partial melting of mafic crust. Trace element modeling shows that the trace element ratios of the third suite can be produced by 10 – 20 % melting of the mafic crust in the presence of residual amphibole, resulting in the retention of the medium rare earth elements (MREE) and diagnostic trace element ratios including low Nb/Ta and high Zr/Y. Geochemical similarities of the LREE-enriched suite to typical “low”-pressure Archean tonalites-trondhjemites-granodiorites (TTGs) imply a common petrogenetic origin and similar mechanisms for the generation of juvenile Archean and modern differentiated crust by partial melting of mafic crust with residual amphibole. In modern oceanic arcs, genetically unrelated felsic plutonic as well as volcanic rocks co-exist, and in this regard, the Fijian plutons accompany major tectonic disruptions to arc processes. [336 words]

斐济的 Viti Levu 为海洋内环境中幼年大陆地壳的形成提供了最佳暴露的显生宙类似物之一。Tonalites 和 trondhjemites 存在于几个大型（75 – 150 km ²) 相邻的中新生代岩体。我们报告主要和微量元素数据，包括稀土元素 (REE) 和高精度高场强元素 (HFSE) 成分、新的 Hf-Nd-Sr-Pb 同位素数据以及锆石 U/Pb-age、O-Hf同位素和微量元素，来自五种不同的岩体。始新世 Yavuna 岩体和中新世 Colo 岩体主要由 Tonalites 和 trondhjemites 组成，代表了前 Vitiaz 岛弧的出露中地壳。岩体可分为三个套间。一组是轻稀土 (LREE)，其中一些微量元素比率低于平均正常洋中脊玄武岩 (N-MORB)。第二套房具有类似于当地岛弧玄武岩的平坦 REE 模式。两个套房都出现在维提岛海岸附近，包括从辉长岩到辉长岩的广泛成分，并且可以主要通过镁铁质前体熔体的分步结晶来生产。第三套房的特点是 LREE 富集具有较高的 La_N /Yb _N(2.3 – 4.9)、较高的 Zr/Y (4.3 – 7.1) 和较低的 Nb/Ta (9.6 – 12.4)。它们发生在更靠近岛屿中心的地方，是双峰长长闪长岩-辉长岩侵入体。这些特征与主要由基性地壳部分熔融形成的特征一致。微量元素模型表明，在残留闪石存在的情况下，镁铁质地壳熔化 10-20% 可以产生第三组的微量元素比例，从而保留中稀土元素 (MREE) 和诊断微量元素比率包括低 Nb/Ta 和高 Zr/Y。富含 LREE 的套件与典型的“低压”太古宙方长岩-长闪长岩-花岗闪长岩 (TTG) 的地球化学相似性暗示了一个共同的成岩成因和类似的机制，通过部分熔融含残余物的基性地壳形成幼年太古代和现代分化地壳闪石。在现代大洋弧中，与成因无关的长英质深成岩和火山岩共存，在这方面，斐济岩体伴随着弧过程的主要构造破坏。[336 字]