ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    华北克拉通南缘熊耳山地区太华群TTG片麻岩成因及地质意义

    Petrogenesis and Geological Significance of the Taihua Group TTG Gneisses in the Xiong'ershan Area, Southern Margin of the North China Craton

    • 摘要: 华北克拉通经历太古宙—古元古代漫长且复杂的地质演化历史,形成该稳定克拉通的岩浆作用和变质作用过程一直是学者们关注的焦点。笔者以华北克拉通南缘熊耳山地区太华群TTG(英云闪长岩–奥长花岗岩–花岗闪长岩)片麻岩为研究对象,基于详细的野外地质调查、室内镜下研究、岩石地球化学、锆石U-Pb定年和Hf同位素分析,揭示该地区古元古代岩浆作用机制及其构造指示意义。锆石U-Pb定年结果显示,熊耳山地区太华群TTG片麻岩的岩浆结晶年龄约为 2300 Ma,而变质年龄为 19841940Ma。太华群TTG片麻岩具有变化范围较大的SiO 2(59.35%~70.78%)、Al 2O 3(12.41%~17.93%)和较高的CaO(1.40%~5.52%)和MgO(0.95%~2.56%)含量,富集轻稀土元素亏损重稀土元素,并表现出轻、重稀土元素强烈分异的特点,成分上类似于高铝型TTG 片麻岩。样品富集Rb、Ba、Sr等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,与岛弧花岗岩的特征相似。此外,岩浆锆石具有相对较高的 ( 176Hf/ 177Hf) i值( 0.2812820.281332),εHf(t)值(−2.98~0.20)和二阶段模式年龄( 28442994 Ma),指示其岩浆源区为中太古代古老地壳的熔融。综合研究认为,熊耳山地区的TTG片麻岩形成于华北克拉通东、西部陆块之间的古元古代俯冲过程,其 19841940 Ma的变质年龄记录沿中部造山带的碰撞拼合过程,进一步约束了东、西部陆块的碰撞时限。

       

      Abstract: The North China Craton underwent a prolonged and complex geological evolution during the Archean to Paleoproterozoic, with the magmatic and metamorphic processes remain as the research questions. This study focuses on the TTG (tonalite-trondhjemite-granodiorite) gneisses of the Taihua Group in the Xiong’ershan area along the southern margin of the North China Craton. The integrated field investigations, petrographic analysis under the microscope, geochemistry, zircon U-Pb dating and Hf isotopic studies are conducted to elucidate the Paleoproterozoic magmatic mechanisms and the tectonic evolution of this region. Zircon U-Pb dating constrains the magmatic crystallization age of the Taihua Group TTG gneisses in the Xiong’ershan area to approximately 2300 Ma, while the metamorphic ages range from 1984 Ma to 1940 Ma. The Taihua Group TTG gneisses exhibit a wide compositional range, with SiO 2 (59.35%~70.78%), Al 2O 3 (12.41%~17.93%), and relatively high CaO (1.40%~5.52%) and MgO (0.95%~2.56%) contents. It is enriched in light rare earth elements (LREE) and depleted in heavy rare earth elements (HREE), displaying strong fractionation between LREE and HREE. In composition, it resembles high-Al TTG gneisses. The samples are enriched in large-ion lithophile elements (LILEs) such as Rb, Ba, and Sr, but depleted in high-field-strength elements (HFSEs) like Nb, Ta, and Ti, which are similar to the features of island arc granites. Additionally, magmatic zircons display relatively high ( 176Hf/ 177Hf)ᵢ ratios ( 0.2812820.281332), εHf(t) values (−2.98 ~ +0.20), and two-stage model ages ( 28442994 Ma), indicating that the magmatic source originated from the partial melting of Mesoarchean ancient crust. These findings suggest that the TTG gneisses in the Xiong’ershan area formed during the Paleoproterozoic subduction process between the eastern and western blocks of the North China Craton. The metamorphic age of 19841940 Ma records the collisional process along the Trans-North China Orogeny. This further constrains the timing of collision between the eastern and western continental blocks.

       

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