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Late-Triassic high-Mg andesite from the Zhangguangcai Range (NE China): Hydrous melting of depleted mantle wedge in active continental margin
Geological Journal ( IF 1.4 ) Pub Date : 2022-08-01 , DOI: 10.1002/gj.4552 Guoshun Zheng 1 , Jiangfeng Qin 1 , Shaocong Lai 1 , Xiaoping Long 1 , Yinjuan Ju 1 , Zezhong Zhang 1 , Hongbing Zhang 1
Geological Journal ( IF 1.4 ) Pub Date : 2022-08-01 , DOI: 10.1002/gj.4552 Guoshun Zheng 1 , Jiangfeng Qin 1 , Shaocong Lai 1 , Xiaoping Long 1 , Yinjuan Ju 1 , Zezhong Zhang 1 , Hongbing Zhang 1
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The Zhangguangcai Range is located in the junction zone of the Palaeo-Asian and Palaeo-Pacific tectonic regimes; Mesozoic igneous rocks in this area are considered to have been formed in an active continental margin, which is related to the western subduction of the Palaeo-Pacific Plate beneath the Eurasian continent. However, the nature of the mantle wedge and related melting mechanism remains unclear. This paper reports zircon U–Pb data, whole-rock geochemistry, and zircon Lu–Hf isotope for a Late-Triassic high-Mg andesite in the southern part of the Zhangguangcai Range. Zircons from the andesite yield a concordant 206Pb/238U age of 218.6 ± 3.3 Ma, which is contemporary with the diorite in the study area. The Lengshan high-Mg andesite is characterized by moderate SiO2 (57.30–60.15 wt.%), high Mg# (61–67), Al2O3 (15.05–17.35 wt.%), (La/Yb)N (16.9–22.4), and variable Na2O/K2O (1.06–1.59). Its insignificant Eu negative anomalies (Eu/Eu* = 0.88–0.99) and high Sr/Y (68.4–96.4) may prove the existence of garnet or amphibole in the residual melt, where feldspar is more or less absent. The andesite is enriched in Rb, Ba and depleted in Nb, Ta, Ti, and other high-field-strength elements, with Nb/Ta ratios of 14.6–17.2, U/Th ratios of 0.28–0.31. In combination with its depleted zircon Lu–Hf isotopic compositions (e.g., εHf(t) = −0.48 to +13.1), it is proposed that the high-Mg andesite formed by hydrous melting of the mantle wedge, which was metasomatized by slab-derived adakitic melts. The subsequent assimilation of ancient crust results in the formation of some zircons with negative Eu*/Eu anomalies (0.05–0.1) and εHf(t) values (−13.8 to −18.5), which is approved by the relative evolved whole-rock Sr–Nd isotopic compositions.
中文翻译：
张广才山脉晚三叠世高镁安山岩：活动大陆边缘贫化地幔楔的含水熔融
张广才山脉位于古亚洲和古太平洋构造体系的交界地带；该区中生代火成岩被认为形成于活动大陆边缘，与古太平洋板块向欧亚大陆下方的西部俯冲有关。然而，地幔楔的性质和相关的熔融机制仍不清楚。本文报道了张广才山脉南部晚三叠世高镁安山岩的锆石 U-Pb 数据、全岩地球化学和锆石 Lu-Hf 同位素。安山岩锆石的206 Pb/ 238 U 年龄一致，为 218.6 ± 3.3 Ma，与研究区闪长岩同时期。冷山高镁安山岩以中等SiO 2为特征(57.30–60.15 wt.%)、高 Mg# (61–67)、Al 2 O 3 (15.05–17.35 wt.%)、(La/Yb) N (16.9–22.4) 和可变 Na 2 O/K 2 O (1.06–1.59)。其微不足道的 Eu 负异常（Eu/Eu* = 0.88-0.99）和高 Sr/Y（68.4-96.4）可能证明残余熔体中存在石榴石或闪石，其中或多或少不存在长石。安山岩富Rb、Ba，贫Nb、Ta、Ti等高场强元素，Nb/Ta比为14.6～17.2，U/Th比为0.28～0.31。结合其贫锆石 Lu-Hf 同位素组成（例如，ε Hf ( t) = -0.48 到 +13.1)，推测高镁安山岩是由地幔楔的含水熔融形成的，它被板片衍生的埃达克质熔体交代。随后古地壳的同化导致形成了一些具有负Eu*/Eu异常（0.05-0.1）和ε Hf（t）值（-13.8至-18.5）的锆石，这是相对演化的全岩所认可的。 Sr-Nd 同位素组成。
更新日期：2022-08-01
中文翻译：
张广才山脉晚三叠世高镁安山岩：活动大陆边缘贫化地幔楔的含水熔融
张广才山脉位于古亚洲和古太平洋构造体系的交界地带；该区中生代火成岩被认为形成于活动大陆边缘，与古太平洋板块向欧亚大陆下方的西部俯冲有关。然而，地幔楔的性质和相关的熔融机制仍不清楚。本文报道了张广才山脉南部晚三叠世高镁安山岩的锆石 U-Pb 数据、全岩地球化学和锆石 Lu-Hf 同位素。安山岩锆石的206 Pb/ 238 U 年龄一致，为 218.6 ± 3.3 Ma，与研究区闪长岩同时期。冷山高镁安山岩以中等SiO 2为特征(57.30–60.15 wt.%)、高 Mg# (61–67)、Al 2 O 3 (15.05–17.35 wt.%)、(La/Yb) N (16.9–22.4) 和可变 Na 2 O/K 2 O (1.06–1.59)。其微不足道的 Eu 负异常（Eu/Eu* = 0.88-0.99）和高 Sr/Y（68.4-96.4）可能证明残余熔体中存在石榴石或闪石，其中或多或少不存在长石。安山岩富Rb、Ba，贫Nb、Ta、Ti等高场强元素，Nb/Ta比为14.6～17.2，U/Th比为0.28～0.31。结合其贫锆石 Lu-Hf 同位素组成（例如，ε Hf ( t) = -0.48 到 +13.1)，推测高镁安山岩是由地幔楔的含水熔融形成的，它被板片衍生的埃达克质熔体交代。随后古地壳的同化导致形成了一些具有负Eu*/Eu异常（0.05-0.1）和ε Hf（t）值（-13.8至-18.5）的锆石，这是相对演化的全岩所认可的。 Sr-Nd 同位素组成。
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