Seismic structure and location of a CO2 source in the upper mantle of the western Eger (Ohře) Rift, central Europe
Seismic structure and location of a CO2 source in the upper mantle of the western Eger (Ohře) Rift, central Europe
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中欧埃格尔 (Ohře) 裂谷西部上地幔的地震结构和二氧化碳源位置
DOI：
10.1029/2004tc001672
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发表时间：
2005
期刊：
影响因子：
4.2
通讯作者：
V. Nehybka
中科院分区：
文献类型：
--
作者：
W. Geissler;H. Kämpf;R. Kind;K. Bräuer;K. Klinge;T. Plenefisch;J. Horalek;J. Zedník;V. Nehybka
P-SV转换提供了对西埃格尔(ohře)裂谷岩石圈的新见解，该裂谷是目前活跃的二氧化碳排放区、第四纪火山场和中欧地震群区。矿泉和莫夫岩中游离气相的气体和同位素(He和C)作图证实了以CO2为主的气体来自地壳下岩浆流体储集层。通过分析波西米亚地块西部几个地震台网的远震资料，研究了这些气体的源区。莫霍面转换有3到4.5%的S延迟。地壳厚度在27~38千米之间变化，波速比在1.63~1.81之间变化。在西部的艾格裂谷之下，存在着大约40公里宽的莫霍河隆起，高达27公里。局部观测到的微弱转换表明该地区存在复杂的莫霍面过渡带。局部的“6-S震相”可能起源于约50~60公里深度的不连续面，也可能是上地壳底部速度倒转的倍数。莫霍面隆起和“6 S相”的分布与地表CO_2脱气场和第四纪火山的位置相吻合。我们假设，在60-30公里深度范围内，以二氧化碳为主的流体/岩浆从孤立的熔体储集层中释放，在29-21公里深度范围内，二氧化碳从熔体中分离出来，二氧化碳通过地壳输送。地球物理标志可能指向研究区下方目前活动的岩浆底侵作用，支持天然气地球化学和同位素研究的结果。这是首次尝试将地震和天然气地球化学数据结合起来建立构造模型。我们的模型可以推广到世界其他大陆裂谷地区。
P‐SV conversions provide new insights into the lithosphere of the western Eger (Ohře) Rift, a presently active CO2 emanation area, Quaternary volcanic field, and earthquake swarm region in central Europe. Gas and isotope (He and C) mapping of free gas phases in mineral springs and mofettes proved the origin of CO2‐ dominated gases from a subcrustal magmatic fluid reservoir. Analyzing teleseismic data from several seismic networks in the western Bohemian Massif, the source region of these gases was investigated. Moho Ps conversions have 3 to 4.5 s delay. Crustal thicknesses vary between 27 and 38 km; vp/vs ratios vary between 1.63 and 1.81. Beneath the western Eger Rift an approximately 40 km wide Moho updoming up to 27 km exists. Locally observed weak conversions indicate a complex Moho transition zone in this area. A local “6 s phase” possibly originates at a discontinuity in approximately 50 to 60 km depth or may represent multiples from velocity inversions at the base of the upper crust. Moho updoming and the distribution of the “6 s phase” coincide with the CO2 degassing fields and the positions of Quaternary volcanoes at the surface. We hypothesize the release of CO2‐dominated fluid/magma from isolated melt reservoirs in the depth range of 60 to 30 km, separation of CO2 from the melt at 29 to 21 km depths, and CO2 transport through the crust. The geophysical indications may point to presently active magmatic underplating beneath the study area, supporting the results of gas geochemical and isotope investigations. This is the first attempt that combines seismic and gas geochemical data for a tectonic model. Our model may be transferable to other continental rift areas worldwide.