| 西刚果夭折裂谷带内拉伸纪A型花岗岩的时代及地质意义 |
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| 引用本文：董洪凯,张洪瑞,潘志龙,罗迪柯,邢伟伟,贾鹏飞,魏广辉,王硕,杨宁.2026.西刚果夭折裂谷带内拉伸纪A型花岗岩的时代及地质意义[J].地球学报,47(3):580-596. |
| DOI：10.3975/cagsb.2025.070322 |
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| 基金项目:本文由安哥拉国家地质调查计划项目(编号: PLANAGEO)资助。 |
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| 中文摘要:为了解西刚果夭折裂谷形成背景, 利用锆石U-Pb定年、岩石地球化学对安哥拉西北部的Quindegi花岗岩进行了研究。测得Quindegi花岗岩的结晶年龄为(904±7) Ma、(905±6) Ma, 时代为新元古代拉伸纪。多数样品具富硅(SiO2=64.35%~74.77%)、低铝(Al2O3=12.52%~14.78%)、富钾(K2O=4.09%~5.67%)、TFeO含量高(1.87%~6.04%)的特点, 岩浆源区具有高初始温度的特征(TZr=783~891 ℃, 平均为847 ℃), 10 000Ga/Al平均值为2.61, 属A型花岗岩, 源于Gangila玄武质岩浆的分离结晶与同化混染。Quindegi花岗岩整体富集轻稀土元素La、Ce及高场强元素Zr、Hf, 亏损U、Ta、Nb、P、Ti等高场强元素及大离子亲石元素Sr。Nb等高场强元素的亏损可能与外来热源的参与下混入大量壳源物质有关。通过岩石地球化学、锆石年代学分析, 结合区域地质背景, 显示Quindegi花岗岩形成于大陆裂谷环境, 属Bahia-Gangila大火成岩省的一部分, 为多期次脉冲式岩浆活动的产物。西刚果裂谷为马卡乌巴斯洋形成过程中深入陆内的一条夭折裂谷, 在地幔柱驱动背景下形成。地幔柱活动提供的巨量物源补给和高温热源为Quindegi花岗岩沿西刚果夭折裂谷上侵就位创造了条件。 |
| 中文关键词:Quindegi花岗岩 新元古代拉伸纪 A型花岗岩 西刚果夭折裂谷 地幔柱 |
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| Chronology and Geological Implications of Tonian A-type Granites in the West Congo Aborted Rift |
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| Abstract:To investigate the tectonic setting of the West Congo aborted rift, zircon U-Pb geochronological and petrogeochemical analyses were performed on Quindegi granites in northwestern Angola. These granites yielded crystallization ages of (904±7) Ma and (905±6) Ma, corresponding to Neoproterozoic Tonian. The Quindegi granites are classified as A-type granites, originating from the fractional crystallization and assimilation of Gangila basaltic magmas. These granites are characterized by high silicon content (SiO2=64.35%–74.77%), low aluminum (Al2O3=12.52%–14.78%), rich potassium (K2O=4.09%–5.67%), and elevated TFeO (1.87%–6.04%). Their magmatic source is inferred to be high-temperature (TZr=783–891 ℃, avg. 847 °C), with a high 10 000Ga/Al ratio (avg. 2.61) further supporting A-type affinity. Geochemically, the granites are enriched in light rare earth elements (LREE: La, Ce) and high-field-strength elements (HFSE: Zr, Hf), with marked depletion in HFSE (U, Ta, Nb, P, Ti) and large-ion lithophile elements (LILE: Sr). The pronounced depletion of HFSE, such as Nb, likely reflects crustal contamination related to thermal perturbations from external heat sources. Petrogeochemistry, zircon geochronological analysis, and the regional geological background indicated that the Quindegi granites were emplaced in a continental rift setting. They are part of the Bahia-Gangila Large Igneous Province and represent products of multiple-pulse magmatic activities. The West Congo Rift was an aborted intracontinental rift formed during the evolution of the Macaúbas Ocean driven by mantle plume activity. The abundant material supply and high-temperature heat input from the mantle plume created favorable conditions for the intrusion and emplacement of the Quindegi granite along the West Congo aborted rift. |
| keywords:Quindegi granites Neoproterozoic Tonian A-type granite West Congo aborted rift mantle plume |
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