Abstract We present the results of a study of an Eoarchean rock assemblage in the Dniester-Bouh Domain of the Ukrainian Shield. This comprises granulite-facies granitoids intercalated with mafic and ultramafic granulites. Zircon U-Pb geochronology indicates enderbite crystallisation at 3786 ± 32 Ma, followed by a subsequent event at ca. 3500 Ma. Several events can be tentatively identified that affected these rocks between ca. 3000 and 2700 Ma. The last zircon growth event took place in response to granulite facies metamorphism and included two separate episodes at ca. 2000 and ca. 1900 Ma. The oldest two zircon populations in enderbites have eHf values around 0, indicating their crystallisation from a protolith with a short crustal residence time. Zircons that crystallised during the 3000-2700 Ma event(s) vary in Hf isotope systematics from eHf ∼1 at ca. 3000 Ma to eHf ∼ -14 at c. 2700 Ma. Paleoproterozoic zircons reveal even more significant variations in eHf value from +6 to -22. Such variations are indicative of juvenile input and mixing with old non-radiogenic Hf. All Eoarchean rocks are depleted in incompatible trace elements and have negative Ta-Nb, P, and Ti anomalies. Compared to the typical TTG associations, enderbites record depletion in felsic components (SiO2, Na2O, K2O, Rb, Th), and enrichment in mafic ones (TiO2, MgO, CaO, V), allowing them to be defined as “mafic” or “depleted” TTG. Geochemical data indicate that mafic and ultramafic rocks of the Dniester-Bouh Domain formed by shallow high-degree melting of the mantle, with the absence of garnet in their source, and the presence of residual Ti-bearing minerals and/or amphibole. In contrast, enderbites were formed from a mixed garnet-bearing amphibolite – eclogite source, i.e. melting over a range of pressures/depths. Our preferred model for the formation of the Eoarchean rock association involves the shallow melting of mantle and formation of basalts and accompanying ultramafic cumulates at a spreading centre, with subsequent underthrusting of one segment of oceanic crust beneath the other, and partial melting of hydrated metamorphosed (eclogitized) mafic rocks in the underthrust plate, leading to the formation of the TTG melts.

中文翻译：

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乌克兰地盾 Dniester-Bouh 域中的始太古代岩石组合：一套 LILE 耗尽的末影和镁铁质麻粒岩

摘要 我们介绍了对乌克兰地盾 Dniester-Bouh 域中始太古代岩石组合的研究结果。这包括夹有镁铁质和超镁铁质麻粒岩的麻粒岩相花岗岩。锆石 U-Pb 年代学表明，在 3786 ± 32 Ma 处出现了末叮咬结晶，随后发生在约 3500 马。可以初步确定影响这些岩石的几个事件。3000 和 2700 毫安。最后一次锆石生长事件是响应麻粒岩相变质作用而发生的，包括在大约 20 年的两个独立事件。2000 年和大约 1900 马。末影石中最古老的两个锆石群的 eHf 值约为 0，表明它们是从具有较短地壳停留时间的原岩中结晶出来的。在 3000-2700 Ma 事件期间结晶的锆石在 Hf 同位素系统学中从 eHf ∼1 变化到大约 3000 Ma 至 eHf ∼ -14 at c。2700 马。古元古代锆石揭示了从 +6 到 -22 的 eHf 值甚至更显着的变化。这种变化表明幼年输入和与旧的非放射性 Hf 混合。所有的始太古代岩石都缺乏不相容的微量元素，并具有负的 Ta-Nb、P 和 Ti 异常。与典型的 TTG 组合相比，尾咬伤记录了长英质成分（SiO2、Na2O、K2O、Rb、Th）的消耗和镁铁质成分（TiO2、MgO、CaO、V）的富集，因此可以将它们定义为“镁铁质”或“耗尽”的TTG。地球化学数据表明，Dniester-Bouh 域的基性和超基性岩由地幔浅层高度熔融形成，源中没有石榴石，以及残留的含钛矿物和/或闪石的存在。相比之下，尾石是由混合含石榴石的角闪岩 - 榴辉岩来源形成的，即在一定压力/深度范围内熔化。我们首选的始太古代岩石组合形成模型包括地幔的浅层融化和玄武岩的形成以及伴随的超镁铁质在扩张中心的堆积，随后一部分洋壳在另一段下方被下冲，以及水合变质的部分熔融（下冲断层中的榴辉岩化）基性岩，导致 TTG 熔体的形成。