Abstract The late Paleozoic–early Mesozoic tectonic nature of the eastern Central Asian Orogenic Belt (CAOB) has been subject to debate, and the late Paleozoic–early Mesozoic magmatism in the Bureya Massif provides an opportunity to address this issue. We report new zircon U Pb ages, Hf isotope data, and whole-rock major and trace element data for late Paleozoic–early Mesozoic igneous rocks from the south of the Bureya Massif. These data provide insight into the petrogenesis of the igneous rocks, and constrain the late Paleozoic–early Mesozoic tectonic nature of the eastern CAOB. Zircon U Pb ages indicate that the late Permian (ca. 255 Ma) and Middle–Late Triassic (ca. 216 Ma) magmatic events are identified in the south of the Bureya Massif. The late Permian igneous rocks consist mainly of bimodal rock suites, which include quartz monzodiorites, gneissic monzogranites, and A-type gneissic syenogranites. The Middle–Late Triassic igneous rocks are dominated by porphyritic syenogranites, and A-type granite porphyries, syenogranites, and gneissic macroporphyritic quartz syenites. The quartz monzodiorites have low SiO2 contents (53.9–56.1 wt%), high Mg# (56–57), and Cr (160–175 ppm), Co (25.2–27.8 ppm), and Ni (61.2–72.3 ppm) contents, and are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE; e.g., K, Rb, Sr, and Ba). These characteristics, along with enriched zircon Hf compositions [eHf(t) = −8.31 to −0.44], suggest that their primary magma was derived from the partial melting of lithospheric mantle that had been metasomatized by fluids released from a fossil subducted slab. The granitoids have high SiO2, and low MgO contents, and are enriched in LILE, depleted in high field strength elements (HFSE), and yield eHf(t) values of −11.5 to +2.87 and two-stage model ages (TDM2) ages of 1968–1024 Ma. These characteristics suggest that they were derived from the partial melting of Paleoproterozoic–Mesoproterozoic accreted crustal material; however, these granitoids have distinct, heterogeneous geochemical compositions, precluding simple fractional crystallization of a single parental melt, and strongly suggesting that they were originated from distinct petrogenetic processes. The late Permian–Triassic bimodal igneous rock suites and A-type granites imply an extensional environment in the eastern CAOB.

中文翻译：

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中亚造山带东部晚二叠世-三叠世构造性质：来自布里亚地块火成岩年代学和地球化学的约束

摘要 中亚造山带东部（CAOB）的晚古生代-早中生代构造性质一直存在争议，而布里亚地块的晚古生代-早中生代岩浆作用为解决这一问题提供了机会。我们报告了来自布里亚地块南部的晚古生代-早中生代火成岩的新锆石 U Pb 年龄、Hf 同位素数据以及全岩主要和微量元素数据。这些数据提供了对火成岩岩石成因的深入了解，并限制了 CAOB 东部晚古生代 - 早中生代的构造性质。锆石 U Pb 年龄表明在布列亚地块南部确定了晚二叠世（约 255 Ma）和中-晚三叠世（约 216 Ma）岩浆事件。晚二叠世火成岩主要由双峰岩组组成，其中包括石英二长闪长岩、片麻岩二长花岗岩和A型片麻岩正长花岗岩。中晚三叠世火成岩以斑状正长花岗岩、A型花岗斑岩、正长花岗岩和片麻质大斑状石英正长岩为主。石英二闪长岩具有低 SiO2 含量 (53.9–56.1 wt%)、高 Mg# (56–57) 和 Cr (160–175 ppm)、Co (25.2–27.8 ppm) 和 Ni (61.2–72.3 ppm) 含量，并富含轻稀土元素 (LREE) 和大离子亲石元素 (LILE；例如，K、Rb、Sr 和 Ba)。这些特征以及丰富的锆石 Hf 成分 [eHf(t) = -8.31 至 -0.44] 表明，它们的原生岩浆来自岩石圈地幔的部分熔融，该地幔已被化石俯冲板片释放的流体交代。花岗岩中 SiO2 高，MgO 含量低，富含 LILE，耗尽了高场强元素 (HFSE)，产生了 -11.5 到 +2.87 的 eHf(t) 值和 1968-1024 Ma 的两阶段模型年龄 (TDM2) 年龄。这些特征表明它们来源于古元古代—中元古代增生地壳物质的部分熔融；然而，这些花岗岩类具有独特的、异质的地球化学成分，排除了单一母体熔体的简单分步结晶，并强烈表明它们源自不同的成岩过程。晚二叠世-三叠纪双峰火成岩套件和 A 型花岗岩意味着 CAOB 东部的伸展环境。这些特征表明它们来源于古元古代—中元古代增生地壳物质的部分熔融；然而，这些花岗岩类具有独特的、异质的地球化学成分，排除了单一母体熔体的简单分步结晶，并强烈表明它们源自不同的成岩过程。晚二叠世-三叠纪双峰火成岩套件和 A 型花岗岩意味着 CAOB 东部的伸展环境。这些特征表明它们来源于古元古代-中元古代增生地壳物质的部分熔融；然而，这些花岗岩类具有独特的、异质的地球化学成分，排除了单一母体熔体的简单分步结晶，并强烈表明它们源自不同的成岩过程。晚二叠世-三叠纪双峰火成岩套件和 A 型花岗岩意味着 CAOB 东部的伸展环境。