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DeepEarthshape链接的一部分，通过钻探和地球物理，地球化学和微生物方法的组合来调查风化或临界区（CZ）。CZ是地壳的最上部，岩石和土壤通过空气/气体，水和/或生物有机体的影响经历机械或化学分解。其厚度取决于侵蚀和风化过程之间的平衡，从而加深风化和新鲜基岩之间的界面。CZ的现有地球化学特征表明，它比预期的要深得多（可能> 30米）。因此，在开挖的土坑中几乎没有研究风化锋。虽然在浅深度（1- 2米）观察到可观数量的微生物生物量和DNA计数可能与风化有关，但我们对整个CZ及其过程的了解仍然有限。例如，我们不知道风化的深度，推进风化的过程或特定的肇事者。由于CZ的属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，属于不同的气候带，具有不同的植被，降水和侵蚀。然而，智利漫长的海岸是研究气候依赖性的主要地点，同时也是一个类似的地质复合体-沿海科迪勒拉。因此，通过比较从这四个研究地点获得的结果，我们最终想要测试CZ的假设，例如，通过年轻的有机质推动的深层风化层中的生物地球化学反馈或微生物活动，风化前沿在深度与最近的气候驱动过程和表面侵蚀的可能联系。浅层水文物理学正在成为CZ调查的一个重要组成部分，以测试水文地貌和风化锋模型。在这里，我们提出了联合地球物理实验，使用P-和S-波地震和浅层电磁（Radiomagnetotelluric）测量沿着~ 500米长的配置文件在所有四个研究地点。这些地球物理实验的主要目标是：a）对CZ的深度及其变化进行成像; B）将地震和EM方法观察到的物理特性变化与在同一地点钻探的岩心中发现的物理特性变化相关联; c）评估钻孔结果在更大的空间尺度上是否具有代表性; d）将CZ的地球物理图像与水文地貌模型预测的图像进行比较; e）确定地下水位的深度及其如何与为大气降水提供通道的裂缝相联系; f）将地震速度与电导率联系起来，以获得可靠的孔隙度估计值; g）对不同的地球物理、地球化学和微生物观测得出一致的地质解释。