胶北地体新太古代晚期石英闪长质片麻岩成因及其动力学意义
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1.中国地质调查局发展研究中心;2.中国地质大学(北京)

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中国地质调查局地质调查项目(DD20240100708)、国家自然科学基金面上项目(42272231)、深地国家科技重大专项子课题(2024ZD1001902)、部省合作项目(2024ZRBSHZ123)


Petrogenesis and geodynamic significance of late Neoarchean quartz dioritic gneisses in the Jiaobei terrane, North China Craton
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1.Development and Research Center, China Geological Survey, Beijing;2.China University of Geosciences, Beijing, Beijing;3.China University of Geosciences, Beijing

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    摘要:

    早期地球大陆地壳的起源机制是早前寒武纪地质学研究的热点问题。大陆地壳的成分被认为是中性的,因此解析中性岩浆岩的岩石成因及其壳幔作用过程是理解陆壳形成及其动力学体制的关键。本研究选择华北克拉通东缘胶北地体内出露的新太古代晚期石英闪长质片麻岩为研究对象,开展锆石U-Th-Pb-Lu-Hf同位素和全岩主微量元素测试分析,依据时空分布规律、地球化学特征和壳幔作用过程综合探讨中性岩浆的起源机制。研究结果表明,胶北地体新太古代晚期石英闪长质片麻岩主要出露于栖霞东北、马家窑、黄燕底、十里庄、大柴北部等地,形成时代为2563~2500 Ma。依据岩石结晶年龄的不同,石英闪长质片麻岩被分为>2.55 Ga和<2.55 Ga两组。>2.55 Ga石英闪长质片麻岩样品中暗色矿物主要以角闪石为主,锆石Lu-Hf同位素相对亏损。它们具有较低的SiO2含量(大部分为54.59%~59.27%)、Mg#值(37.59~50.51)和Sr+Ba总量(357 ×10-6~1166 ×10-6),属于低钾-中钾系列岩石,同时表现出中等的稀土分馏程度((La/Yb)N=3.92~7.12)。相比而言,<2.55 Ga石英闪长质片麻岩中暗色矿物主要以黑云母为主,并表现出弱亏损的锆石Lu-Hf同位素特征。样品具有较高的SiO2含量(55.48%~63.54%)、Mg#(45.43~63.24)和Sr+Ba总量(866 ×10-6~3480 ×10-6),属于中钾-高钾系列岩石,且具有强烈分馏的稀土配分模式((La/Yb)N=10.84~65.67),化学成分类似太古宙赞岐岩类岩石。岩石成因研究表明,>2.55 Ga石英闪长质片麻岩起源于受到玄武质地壳熔体为主较弱交代改造的亏损地幔的部分熔融,<2.55 Ga石英闪长质片麻岩由沉积物熔体为主强烈交代的弱亏损地幔的部分熔融形成。它们记录了表壳物质再循环及地幔交代等壳幔作用过程,反映新太古代晚期重要的地壳生长事件,并可能形成于洋壳俯冲动力学过程。

    Abstract:

    The origin of early continental crust is a hot issue in early Precambrian research. Since the intermediate average composition of the continental crust, unraveling the petrogenesis of intermediate rocks and the processes of crust-mantle interaction is key to understand the formation of continental crust and related geodynamic regimes. In this study, the late Neoarchean quartz dioritic gneisses exposed in the Jiaobei terrane of North China Craton were selected as the research object, and the zircon U-Th-Pb-Lu-Hf isotopes and whole-rock major and trace elements were analyzed. Based on these data, comprehensive studies of the spatial and temporal distribution, geochemical characteristics, and crust-mantle interaction were conducted to decipher the origin mechanism of these intermediate magmas. The results show that the late Neoarchean quartz dioritic gneisses of Jiaobei terrane are mainly exposed in the northeastern part of Qixia, Majiayao, Huangyandi, Shilizhuang, and northern Dachai, with crystallization ages of 2563~2500 Ma. These quartz dioritic gneisses are further divided into >2.55 Ga and <2.55 Ga groups. The >2.55 Ga quartz dioritic gneisses show hornblende as the major mafic minerals, with depleted zircon εHf(t2) values. They have relatively low SiO2 (mostly of 54.59%~59.27%), Mg# (37.59~50.51), and Sr+Ba (357 ×10-6~1166 ×10-6), belonging to the low- to medium-K series. Meanwhile, they show moderately fractionated chondrite-normalized rare earth elements (REE) patterns with low (La/Yb)N (3.92~7.12). In comparison, the <2.55 Ga quartz dioritic gneisses contain less volume of mafic minerals that are dominated by biotite, with less depleted zircon εHf(t2) values. These samples exhibit relatively high SiO2 contents (55.48%~63.54%), Mg# (45.43~63.24), and Sr+Ba (866 ×10-6~3480 ×10-6), belonging to the medium- to high-K series. In addition, they have strongly fractionated chondrite-normalized REE patterns with high (La/Yb)N (10.84~65.67), which are chemically analogous to those of Archean sanukitoids. Detailed petrogenetic studies reveal that the >2.55 Ga quartz dioritic gneisses were derived from the partial melting of the depleted mantle weakly modified by the metasomatism of basaltic crustal melts. In contrast, the <2.55 Ga quartz dioritic gneisses were formed by the partial melting of a less depleted mantle that was strongly metasomatized by sediment melts. Taken together, the late Neoarchean quartz dioritic gneisses in the Jiaobei terrane record crust-mantle interactions involving the recycling of crust-derived materials and mantle metasomatism, which could mark an important episode of crustal growth that was likely evolved under a plate subduction setting during the late Neoarchean.

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  • 收稿日期:2025-06-25
  • 最后修改日期:2025-08-23
  • 录用日期:2025-08-24
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