DeepEarthShape - Geophysical Imaging: Imaging weathering fronts in deep regolithwith seismic and electromagnetic methods [GIDES]

DeepEarthShape - 地球物理成像：使用地震和电磁方法对深层风化层中的风化锋面进行成像 [GIDES]

• 批准号: 408246628
• 负责人: Professorin Dr. Charlotte Krawczyk
• 金额: --
• 依托单位: Sektion 2.2: Geophysikalische Abbildung des Untergrunds
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/408246628?language=en
• 关键词: DeepEarthShape; Geophysical; Imaging; weathering; fronts

This project is part of the interdisciplinary DeepEarthshape linkage to investigate the weathering or critical zone (CZ) with drilling and a combination of geophysical, geochemical and microbiological approaches. The CZ is the uppermost part of the Earth’s crust where rocks and soils experience breakdown either mechanically or chemically through the impact of air/gases, water and/or biological organisms. Its thickness depends on the balance between erosion and weathering processes that deepen the interface between weathered and fresh bedrock. Existing geochemical characterisation of the CZ has shown that it is much deeper than expected (possibly >30m). As a result, the weathering front has hardly been studied in the excavated soil pits. Although at shallow depths (1-2m) appreciable amounts of microbial biomass and DNA counts were observed that might be related to weathering, our insight into the entire CZ and its processes is still limited. We do not know for instance the depth of weathering, the process advancing it or the particular perpetrators. Since properties and characteristics of the CZ seem to be linked to climate, a set of four study sites is proposed within the framework of the DFG SPP 1803 belonging to different climate zones with different vegetation, precipitation and erosion. However, the long-stretched coast of Chile represents a prime location to examine climatic dependencies while staying in a similar geological complex - the Coastal Cordillera. Therefore by comparing the obtained results from these four study sites we finally want to test hypotheses for the CZ, like a possible linkage of the advance of the weathering front at depth with recent climate-driven processes and erosion at the surface through a biogeochemical feedback or microbial activity in the deep regolith fueled by young organic matter that advances weathering. Shallow geophysics is now emerging as an essential component of CZ investigations to test hydro-geomorphological and weathering front models. Here, we propose combined geophysical experiments using P- and S-wave seismics and shallow electromagnetic (Radiomagnetotelluric) measurements along ~500m long profiles at all four study sites. The major objectives to be addressed by these geophysical experiments are a) imaging the depth of the CZ and its variations; b) correlating changes in physical properties seen by seismic and EM methods with those found in cores drilled at the same site; c) assessing if borehole results are representative on a larger spatial scale; d) comparing geophysical images of the CZ with those predicted by hydro-geomorphological models; e) determining the depth of the water table and how it is linked to fractures providing pathways for meteoric water; f) linking seismic velocities with electrical conductivities to obtain reliable estimates of porosity and g) to derive a consistent geological interpretation of different geophysical, geochemical and microbiological observations.

该项目是跨学科的深地上链接的一部分，可以通过钻孔以及地球物理，地球化学和微生物学方法的结合来研究风化或临界区（CZ）。 CZ是地壳的最高部分，岩石和土壤通过空气/气体，水和/或生物组织的影响在机械上或化学上经历崩溃。它的厚度取决于侵蚀和风化过程之间的平衡，从而加深了风化和新鲜基岩之间的界面。 CZ的现有地球化学表征表明，它比预期的要深得多（可能> 30m）。结果，在挖掘的土壤坑中几乎没有研究风化的阵线。尽管观察到可能与风化有关的浅深度（1-2M）可欣赏的微生物生物量和DNA计数，但我们对整个CZ及其过程的见解仍然受到限制。我们不知道例如风化的深度，推进它或特定肇事者的过程。由于CZ的特性和特征似乎与气候有关，因此在DFG SPP 1803的框架内提出了一组四个研究地点，属于不同气候区，具有不同的植被，精度和侵蚀。然而，智利长裂的海岸代表了在类似的地质综合体中 - 沿海山核桃岛（Coastal Cordillera）的同时检查杂物依赖性的主要位置。因此，通过比较这四个研究地点获得的结果，我们最终希望测试CZ的假设，例如，在深度的前进阵线的发展与最新的气候驱动过程和表面的近期侵蚀通过生物地球化学反馈或幼小有机物燃烧的深层腐殖石中的微生物活性。现在，浅层地球物理学已成为CZ研究的重要组成部分，以测试水力地球化学和风化的前模型。在这里，我们提出了使用P-和S波地震学以及浅层电磁（放射性电磁（放射性磁性）测量沿所有四个研究地点沿〜500m长的轮廓的结合地球物理实验。这些地球物理实验要解决的主要目标是a）成像CZ的深度及其变化； b）将地震和EM方法看到的物理特性的变化与在同一位置钻取的核心中发现的变化相关联； c）评估钻孔结果是否在较大的空间尺度上代表； d）将CZ的地球物理图像与水力地球化学模型预测的图像进行比较； e）确定地下水位的深度及其与裂缝如何相关的裂缝，以提供陨石水的途径； f）将地震速度与电导率联系起来，以获得可靠的孔隙率和g）来得出对不同地球物理，地球化学和微生物观测值的一致地质解释。