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Geochronology and petrogenesis of the Early Palaeozoic Fuxi magnesian granodiorite in southern Zhuguangshan, South China Block and its geodynamic significance
Geological Journal ( IF 1.4 ) Pub Date : 2022-08-08 , DOI: 10.1002/gj.4557
Yushuai Yu 1, 2, 3 , Yun Zhou 1, 2 , Pingyun Dai 1, 2 , A'sui Liu 1, 2 , Qidi Yang 1, 2 , Bo Bao 1, 2 , Xiaozhan Xie 4 , Chunshuang Wang 5
Affiliation  

This study provides relevant data on the granodiorite in southern Zhuguangshan, South China Block (SCB), including mineralogical information, zircon U–Pb ages, zircon Hf isotope data, whole-rock geochemical data, and Sr–Nd–Pb isotopic data. These data indicate that the granodiorite in southern Zhuguangshan crystallized at approximately 448.7 Ma. The hornblende and micas of the granodiorites are magnesio-hornblende and Mg-rich biotite, respectively. The granodiorite samples are characterized by relatively high SiO2 contents of 61.72–66.19 wt.%, K2O contents of 3.77–5.18 wt.%, Na2O contents of 2.42–3.16 wt.%, low FeOT contents of 3.93–5.79 wt.%, and relatively high MgO contents of 1.78–2.55 wt.%, with Mg# values (molar Mg/[Mg + Fe] × 100) of 43–50. The contents of rare earth elements (REEs) in the granodiorite specimens are 166–283 ppm, and the REEs show both a chondrite-normalized REE pattern that inclines rightward and slightly negative Eu anomalies (0.62–0.90). The Fuxi granodiorite is rich in large-ion lithophile elements (LILEs; Rb, Th, U, and K) but is depleted in high-field-strength elements (HFSEs; Nb, Ta, and Ti). All the samples have similar Sr–Nd–Pb and zircon Hf isotopic compositions and have a (87Sr/86Sr)i ratio of 0.707319–0.710888, a (143Nd/144Nd)i ratio of 0.511705–0.511760, a (206Pb/204Pb)t ratio of 17.918–18.459, a (207Pb/204Pb)t ratio of 15.711–15.813, and a (208Pb/204Pb)t ratio of 37.953–38.563. The εNd(t) and εHf(t) values range from −7.12 to −5.88 and from −9.81 to −4.45, respectively, with corresponding two-stage Nd model ages of 1.66–1.76 Ga and two-stage Hf model ages of 1.55–1.78 Ga. These findings indicate that the granodiorite is magnesian andesite and that the magmas are derived from a mixture of crustal and mantle materials. Based on these findings in combination with previous research results, it can be concluded that the mantle beneath the Cathaysia Block was moderately depleted during the Early Palaeozoic and that Early Palaeozoic magmatism may be related to Early Palaeozoic oceanic crust subduction.

中文翻译:

华南地块珠光山南部早古生代伏羲镁质花岗闪长岩的年代学、岩石成因及其地球动力学意义

本研究提供了华南区块(SCB)珠光山南部花岗闪长岩的相关数据,包括矿物学信息、锆石U-Pb年龄、锆石Hf同位素数据、全岩地球化学数据和Sr-Nd-Pb同位素数据。这些数据表明,珠光山南部的花岗闪长岩在大约 448.7 Ma 结晶。花岗闪长岩的角闪石和云母分别为镁角闪石和富镁黑云母。花岗闪长岩样品的特点是 SiO 2含量较高,为 61.72-66.19 wt.%,K 2 O 含量为 3.77-5.18 wt.%,Na 2 O 含量为 2.42-3.16 wt.%,FeO T含量较低,为 3.93- 5.79 wt.%, 相对较高的 MgO 含量为 1.78-2.55 wt.%, Mg #值(摩尔 Mg/[Mg + Fe] × 100)为 43–50。花岗闪长岩样品中稀土元素(REEs)含量为166-283 ppm,稀土元素呈现出向右倾斜的球粒陨石归一化REE模式和略微负的Eu异常(0.62-0.90)。伏羲花岗闪长岩富含大离子亲石元素(LILEs;Rb、Th、U 和 K),但缺乏高场强元素(HFSEs;Nb、Ta 和 Ti)。所有样品的 Sr–Nd–Pb 和锆石 Hf 同位素组成相似,( 87 Sr/ 86 Sr) i比值为 0.707319–0.710888, ( 143 Nd/ 144 Nd) i比值为 0.511705–0.511760, ( 206铅/ 204铅)比率为 17.918-18.459,(207 Pb/ 204 Pb)t比率为 15.711-15.813,(208 Pb/ 204 Pb)t比率为 37.953-38.563。ε Nd (t) 和 ε Hf(t) 值范围分别为 -7.12 至 -5.88 和 -9.81 至 -4.45,相应的两阶段 Nd 模型年龄为 1.66-1.76 Ga 和两阶段 Hf 模型年龄为 1.55-1.78 Ga。这些发现表明花岗闪长岩是镁质安山岩,岩浆来源于地壳和地幔物质的混合物。结合前人的研究结果,可以得出华夏地块下地幔在早古生代中度耗竭的结论,早古生代岩浆作用可能与早古生代洋壳俯冲有关。
更新日期:2022-08-08
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