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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Relationship between recent heat flow and seismic properties: Some notes from crustal research in Germany
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Relationship between recent heat flow and seismic properties: Some notes from crustal research in Germany

机译：最近的热流与地震特性之间的关系：德国地壳研究的一些笔记

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摘要

Deep seismic reflection profiling has been used extensively during the last 25 years in order to unravel crustal structure and evolution, complemented by deep drilling in crystalline rocks. Examples are presented from the Variscan/Hercynian crust in Germany showing moderate-to-high surface heat flow densities which can be studied for relationships with seismic reflections and velocities. Four main seismic features are identified which emphasise that heat transfer through the crust is a strong-three-dimensional problem similar to that of sedimentary basins: (1) The top and thickness of the highly reflective lower crust as a specific dominant crustal entity correlate with high surface heat flow. The creation of lower crustal reflections is commonly attributed to a post-collisional extensional regime. The rheological character of top and bottom (crust-mantle boundary) of the lower crust indicates decoupling horizons at these levels. (2) Upper crustal reflectivity is frequently attributed to fault and fracture zones. These may delineate pathways for heat transport through fluid circulation due to higher (crack) porosity and possibly higher permeability. (3) Seismic anisotropy of large crustal volumes has been confirmed as a common feature and is particularly strong in gneisses due to their strain-related preferred orientation of the texture. Gneisses are also known for their anisotropy of heat conductivity having the same magnitude and preferred orientation. (4) Seismic in-situ velocities are always lower than laboratory-derived or composition-derived velocities. In consequence, crustal composition models inverted from seismic velocity models tend to be biased towards felsic composition. The reason for this is most likely the porosity of crystalline rocks including some hydrothermal activity which may also explain the occurrence of low-velocity zones often observed in the middle crust. Modelling of crustal temperatures, heat transfer and heat production should account for these phenomena.
机译：在过去的25年中，为了揭示地壳的结构和演化，并在结晶岩中进行深钻探，深层地震反射剖面法得到了广泛的应用。来自德国瓦里斯坎/赫尔辛基地壳的例子显示了中等到较高的表面热流密度，可以研究其与地震反射和速度的关系。确定了四个主要地震特征，这些特征强调通过地壳的热传递是一个强三维问题，类似于沉积盆地的问题：（1）作为特定的主要地壳实体的高反射率下地壳的顶部和厚度与高表面热流。下部地壳反射的产生通常归因于碰撞后的扩张机制。下地壳的顶部和底部（地壳-地幔边界）的流变特性表明在这些水平上地层是解耦的。 （2）上地壳反射率通常归因于断层和断裂带。由于较高的（裂纹）孔隙率和可能较高的渗透率，这些可以描绘出通过流体循环进行热传递的路径。 （3）大地壳体积的地震各向异性已被确认为一个共同特征，由于其应变相关的质地优先取向，在片麻岩中尤为强烈。片麻岩也因其具有相同大小和优选取向的热导率各向异性而闻名。 （4）地震原位速度总是低于实验室衍生速度或成分衍生速度。结果，从地震速度模型反演的地壳成分模型倾向于偏向长英质成分。造成这种现象的原因很可能是包括某些热液活动在内的晶体岩石的孔隙度，这也可以解释在中地壳中经常观察到的低速带的发生。地壳温度，传热和热量产生的模型应该解释这些现象。

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