华北克拉通乌拉山地区古元古代早期—新太古代晚期石榴石花岗岩的成因及地质意义
作者:
作者单位:

1.中国地质大学(北京)地球科学和资源学院;2.吉林大学地球科学学院;3.中国地质科学院地质研究所北京离子探针中心

基金项目:

(编号 42372236)、中国地质调查局项目(编号 DD20221645)资助成果。


Early Paleoproterozoic-late Neoarchean garnet granites from the Wulashan area, North China Craton: Genesis and geological significance
Author:
Affiliation:

1.School of Earth Sciences and Resources, China University of Geosciences, Beijing;2.College of Earth Sciences, Jilin University;3.Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences

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    摘要:

    乌拉山位于华北克拉通西部孔兹岩带中段,以榴云片麻岩为主的表壳岩十分发育。榴云片麻岩遭受强烈变质变形和深熔作用改造,形成石榴石花岗岩。本文对石榴石花岗岩开展了野外地质、地球化学和锆石SHRIMP U-Pb年代学研究。榴云片麻岩、深熔榴云片麻岩和石榴石花岗岩之间多呈过渡渐变,石榴石花岗岩具有原地-半原地性质。4个石榴石花岗岩样品变质-深熔锆石年龄为2442~2463 Ma,考虑到古元古代晚期强烈构造热事件改造,认为把石榴石花岗岩形成时代暂定为2.45~2.5 Ga之间或更接近2.5 Ga较为合理。这支持了榴云片麻岩形成于新太古代晚期的认识。石榴石花岗岩的元素组成变化很大,SiO2=66.41 %~73.79 %,TFeO+MgO=0.22 %~5.59 %,=Na2O=2.96 %~5.27 %,K2O=1.54 %~5.27 %,TREE、(La/Yb)n和Eu/Eu*分别为83.45×10-6~262.44×10-6、11.2~182.6和1.15~3.62。全岩εNd(t)和tDM2(Nd)分别为 -0.18~1.65和2.60~2.77 Ga,变质-深熔锆石εHf(t)和tDM2(Hf)分别为-0.86~4.54和2.69~3.04 Ga。石榴石花岗岩元素组成大的变化在很大程度上反映了它们的物源区组成和形成过程中石榴石结晶分异程度不同。物源区岩石为新太古代晚期成熟度不同的变质碎屑沉积岩(主要为榴云片麻岩)。石榴石花岗岩的形成标志着古元古代早期-新太古代晚期构造体制从挤压向伸展转换、变质基底初步稳定化的过程。

    Abstract:

    Wulashan is located in the middle section of the Khondalite Belt, western North China Craton, with well-developed supracrustal rocks mainly composed of garnet-biotite gneiss. They underwent strong metamorphism, deformation and anateixs, resulting in the formation of garnet granite. This study conducted field geological, geochemical, and zircon SHRIMP U-Pb geochronological studies on the garnet granite. There are often transitional relationships between garnet-biotite gneiss, anatectic garnet-biotite gneiss and garnet granite, with the garnet granite exhibiting in situ to semi in situ properties. Four garnet granite samples have the metamorphic-anatectic zircon ages of 2442~2463 Ma. Considering the strong overprinting of late Paleoproterozoic tectonothermal event, it is reasonable to tentatively set the formation age of garnet granite between 2.45 and 2.5 Ga or closer to 2.5 Ga. This supports the conclusion that garnet-biotite gneiss formed in the late Neoarchean. The garnet granite shows large variations in elemental composition, with SiO2, TFeO, MgO, Na2O, and K2O contents of 66.41 %~73.79 %, 0.15 %~4.02 %, 0.07 %~1.57 %, 2.96 %~5.27 %, and 1.54 %~5.27 %, respectively. TREE, (La/Yb)n, and Eu/Eu* are 83.45×10-6~262.44×10-6, 11.2~182.6 and 1.15~3.62, respectively. They have whole rock εNd(t) of -0.18 to 1.65 and tDM2(Nd) of 2.60 to 2.77 Ga, while metamorphic-anatectic zircons have εHf(Hf) of -0.86 to 4.54 and tDM2(Hf) of 2.69~3.04 Ga. The significant variation of garnet granite in elemental composition largely reflect the differences in the composition of their source regions and the garnet differentiation degree during their formation process. The source rocks are late Neoarchean meta-clastic sedimentary rocks with different maturity (mainly garnet-biotite gneiss). The formation of the garnet granite marks a transition of the tectonic regime from compression to extension in the early Paleoproterozoic to the late Neoarchean, as well as the initial stabilization of the metamorphic basement.

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  • 收稿日期:2025-04-19
  • 最后修改日期:2025-04-19
  • 录用日期:2025-04-26