Abstract Widespread Mesozoic granitoids in the Cathaysia Block of South China are associated with intensive reworking of the lower crust as a result of magma underplating. This inference is based mainly on studies of mafic igneous rocks, whereas there is little evidence from lower-crustal rocks. Lower-crustal xenoliths in Mesozoic basalts in the Daoxian region within the Cathaysia Block might record information on the relationship between magma underplating and remelting of the pre-existing crust beneath the block. The xenoliths are mainly mafic granulites, with minor felsic granulites. The mafic granulites have low SiO2 contents (47.22–49.46 wt%) and high Mg# values (77.8–82.4), suggesting that their protoliths were derived from a mantle source. The felsic granulite xenoliths have high SiO2 (69.56–70.27 wt%) and low MgO (1.63–2.50 wt%) contents, and zircons in these xenoliths yield negative eHf(t) values (−6.1 to −12.6) and high δ18O values (6.8–7.6‰), consistent with a crustal source. Both mafic and felsic granulite xenoliths record magmatic (226–218 Ma) and metamorphic (218–193 Ma) events, suggesting a genetic link between mafic and felsic rocks in the lower crust. We propose that the magma underplating was responsible for the origin of the mafic granulites and partial melting of pre-existing lower crust, as recorded by the felsic xenoliths. The granulite xenoliths also contain abundant inherited zircons that formed during the Archean–Neoproterozoic (2584–659 Ma), early Paleozoic (peaking at ca. 425 Ma), and late Paleozoic (peaking at ca. 261 Ma). Zircons from the Daoxian granulite xenoliths have distinct Hf O isotopic compositions that record the multistage evolution of the lower crust beneath the Cathaysia Block. This evolution involved the accretion of juvenile crust during the late Archean (eHf(t) = +4.2 to +4.6) and late Paleozoic (eHf(t) = +1.3 to +5.3; δ18O = 5.8–6.2‰), crustal reworking during the Neoproterozoic (eHf(t) = −7.5 to −11.8; δ18O = 5.1–9.5‰) and early Paleozoic (eHf(t) = −0.5 to −2.2; δ18O = 7.3–7.5‰), and crustal accretion with significant reworking during the early Mesozoic (eHf(t) = −19.2 to +5.9; δ18O = 6.8–7.6‰). The U Pb ages and Hf O isotopic data of zircons from the Daoxian granulite xenoliths are consistent with the distribution of Phanerozoic igneous rocks in the Cathaysia Block. These data support the inference that Mesozoic magma underplating triggered the remelting of pre-existing crustal materials and produced extensive granitoid magmatism.

中文翻译：

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华夏地块下地壳重熔引起的显生宙岩浆底侵：来自华南道县麻粒岩包体的锆石U Pb年龄和Hf O同位素的证据

摘要 华南华夏地块广泛分布的中生代花岗岩与岩浆底侵引起的下地壳强烈改造有关。这一推论主要基于对镁铁质火成岩的研究，而几乎没有来自下地壳岩石的证据。华夏地块道县中生代玄武岩中下地壳捕虏体可能记录岩浆底侵与地块下原有地壳重熔关系的信息。捕虏体主要为镁铁质麻粒岩，少量长英质麻粒岩。镁铁质麻粒岩的 SiO2 含量低（47.22-49.46 wt%），Mg# 值高（77.8-82.4），表明它们的原岩来自地幔源。长英质麻粒岩捕虏体具有高 SiO2 (69.56–70.27 wt%) 和低 MgO (1.63–2.50 wt%) 含量，这些捕虏体中的锆石和锆石产生负 eHf(t) 值（-6.1 至 -12.6）和高 δ18O 值（6.8-7.6‰），与地壳来源一致。镁铁质和长英质麻粒岩捕虏体都记录了岩浆（226-218 Ma）和变质（218-193 Ma）事件，表明下地壳中的镁铁质和长英质岩石之间存在成因联系。我们认为，如长英质捕虏体所记录的那样，岩浆底侵是镁铁质麻粒岩的起源和预先存在的下地壳的部分熔融的原因。麻粒岩捕虏体还含有丰富的继承锆石，形成于太古代-新元古代（2584-659 Ma）、早古生代（在约 425 Ma 达到峰值）和晚古生代（在约 261 Ma 达到峰值）。来自道县麻粒岩包体的锆石具有独特的 Hf O同位素组成，记录了华夏地块下下地壳的多阶段演化。这种演化涉及太古宙晚期（eHf(t) = +4.2 ~ +4.6）和古生代晚期（eHf(t) = +1.3 ~ +5.3；δ18O = 5.8 ~ 6.2‰）的幼年地壳增生，以及新元古代 (eHf(t) = -7.5 至 -11.8; δ18O = 5.1–9.5‰) 和早古生代 (eHf(t) = -0.5 至 -2.2; δ18O = 7.3–7.5‰) 和具有显着再加工的地壳增生在中生代早期（eHf(t) = -19.2 到 +5.9；δ18O = 6.8–7.6‰）。道县麻粒岩包体中锆石的U Pb年龄和Hf O同位素数据与华夏地块显生宙火成岩的分布一致。