Abstract This contribution is dedicated to the second author Prof. Dr. Alfred Kroner. Alfred was working on this manuscript till Saturday the 18th of May 2019, just four days before he passed unexpected and to early away. Tonalite, Trondhjemite, Granodiorite (TTG) rocks in Viti Levu, Fiji islands formed through hydrous melting of gabbroic oceanic crust at low-pressure amphibolite-facies conditions caused by flat subduction of an oceanic plateau from Yavuna creek during late Eocene time. Followed by magmatic underplating through mid Miocene time, were a Qtz-diorite unit was formed out of the gabbro under granulite-facies conditions. The investigated TTǴs occur as stocks and veins within the older gabbroic unit of the Yavuna Pluton. Zircon ages show the parental gabbro to be ∼47.5 Ma in age, whereas the TTǴs, which can be subdivided into a tonalite and a Qtz-diorite suite, are ∼37.1 Ma and ∼16.5 Ma, old respectively. The average δ18O value of ∼4.8 in zircon selected from the parental gabbro and the tonalite suggest a very homogenous mantle source. However, about 50% of the analyzed zircons from the gabbroic and tonalitic rock samples showing lower δ18O values, and these are interpreted as reflecting interaction of hydrothermally altered seafloor with the deep depleted mantle source. eHf in zircon values of ∼13 in the analyzed TTǴs are interpreted as reflecting typical juvenile continental crust. PerpleX whole-rock calculations suggest that the tonalite formed by melting of the gabbro through decompression under water-saturated amphibolite-facies conditions at a temperature of ∼770 °C and a pressure of ∼3.8 kbar, whereas the Qtz-diorite formed at a temperature of up to ∼900 °C at very shallow depth close to the Earth’s surface. Our investigation provides new evidence for episodic growth of continental crust

中文翻译：

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冷雪崩、“超级俯冲”、地幔翻转，随后大洋高原的浮力俯冲和始新世斐济群岛维提岛的 TTǴs 形成

摘要 此贡献献给第二作者教授阿尔弗雷德·克罗纳 (Alfred Kroner)。阿尔弗雷德一直在研究这份手稿，直到 2019 年 5 月 18 日星期六，就在他意外去世前四天，并提前离开。斐济群岛 Viti Levu 的 Tonalite、Trondhjemite、花岗闪长岩 (TTG) 岩石在始新世晚期由 Yavuna 溪的大洋高原平坦俯冲引起的低压角闪岩相条件下通过辉长岩大洋地壳的含水熔融形成。随后是中新世中期的岩浆底侵，在麻粒岩相条件下从辉长岩中形成了一个 Qtz-闪长岩单元。所研究的 TTǴ 以亚武纳岩体较老的辉长岩单元内的股和脉形式出现。锆石年龄显示父母辉长岩的年龄约为 47.5 Ma，而 TTǴs，可细分为辉长岩和Qtz闪长岩组，分别为~37.1 Ma和~16.5 Ma，年龄分别为~37.1 Ma和~16.5 Ma。选自母辉长岩和辉长岩的锆石的平均 δ18O 值约为 4.8，表明地幔来源非常均匀。然而，大约 50% 的辉长岩和斜长岩样品的锆石显示出较低的 δ18O 值，这些被解释为反映了热液蚀变海底与深部枯竭地幔源的相互作用。在分析的 TTǴs 中，锆石中的 eHf 值约为 13，被解释为反映了典型的幼年大陆地壳。PerpleX 全岩计算表明，辉长岩在水饱和角闪岩相条件下，在约 770 °C 的温度和约 3.8 kbar 的压力下通过减压熔化形成的辉长岩，而 Qtz-闪长岩是在接近地球表面的非常浅的深度，在高达 ~900 °C 的温度下形成的。我们的研究为大陆地壳的偶发生长提供了新的证据