| 龙门山逆冲带假玄武玻璃在其形成及后期抬升过程中的化学变化 |
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| 引用本文：王焕,李海兵,司家亮,张蕾.2019.龙门山逆冲带假玄武玻璃在其形成及后期抬升过程中的化学变化[J].地球学报,40(1):199-211. |
| DOI：10.3975/cagsb.2018.111401 |
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| 基金项目:国家自然科学基金项目(编号: 41602226; 41830217);中国地质科学院基本科研业务费项目(编号: J1619; YYWF201601) |
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| 中文摘要:假玄武玻璃作为地震断层摩擦熔融的产物记录了断层带内地震破裂的相关信息, 是认识断层带形成过程及其活动历史的重要物质组成。钻探获取的地下深部的断层岩样品, 免受地表物理化学风化, 相对较为新鲜, 能够提供更接近其形成时的相关信息。本文以龙门山映秀—北川断裂带南段彭灌杂岩中发育多期假玄武玻璃为研究对象, 应用扫描电镜、微区X射线荧光光谱(μXRF)岩心扫描仪以及布鲁克M4 TORNADO高性能微区X射线荧光光谱仪等仪器对虹口八角庙地表和汶川地震断裂带科学钻探(WFSD)岩心中发育的假玄武玻璃的化学组成进行对比研究。显微结构特征表明这些假玄武玻璃为地震断层快速滑动摩擦熔融的产物。化学元素对比分析结果显示, 熔融物形成于高温还原环境下, 其化学性质以高Fe、Ti、K值, 低Si值为特征, 并具高磁化率值的物理性质。地表假玄武玻璃经受表生流体作用, 化学性质发生明显变化, 以低K、Ti值和出现含Ca元素的新生矿物为特征。同时岩心中来自较深断层带的多期假玄武玻璃的成分差异也表明, 大气水和地表水已沿断层带侵入到了585 m以下或更深部位。因此在应用假玄武玻璃对地震断层瞬时滑动环境进行判断时需谨慎, 应考虑其后期化学成分变化等造成的各种影响。 |
| 中文关键词:假玄武玻璃 地球化学 µXRF 汶川地震断裂带科学钻探 龙门山 |
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| Geochemical Variations of the Pseudotachylytes during Their Formation and Subsequent Uplift Processes, in the Longmen Shan Thrust Belt |
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| Abstract:Pseudotachylytes, as the product of the frictional melting during seismic slip, convey important information about the earthquake rupture in the fault zone, and provide crucial material for learning fault zone formation processes and their faulting activity history. As fault rocks drilled from the deep fault zone exempt the supergenetic physical-chemical weathering, their chemical properties should be much similar to those during their formation. In this paper, multiple generations of pseudotachylytes in southern Yingxiu–Beichuan fault were studied. Their chemical properties were analyzed using SEM, μXRF core scanner and M4 TORNADO. Microstructures show that the pseudotachylytes are of melt-origin. Results of geochemical analysis indicate that the melts were formed in a high temperature reductive environment, characterized by high Fe, Ti, K, low Si with high magnetic susceptibility. The chemical properties of the surface pseudotachylytes were significantly changed due to the supergenetic weathering processes. Different elemental features of the multiple generations of pseudotachylytes in the WFSD drilling cores also indicate that the meteoric water (atmospheric water and surface water) had injected into 585 m or greater depth along the fault zone. Therefore, the geochemical variations should be taken into consideration when pseudotachylyte is used to judge the instantaneous sliding environment of seismic slip. |
| keywords:pseudotachylyte geochemical µXRF WFSD Longmen Shan |
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