Mid-to-Deep-crustal Electromagnetic Investigation of the Tepic–Zacoalco Rift (DEMITZ) – Exploring Magmatic Systems and Electrical Anisotropy in Western Mexico

该提案建议大规模大地电磁（MT）调查的导电性分布在岩浆系统的构造过程的背景下，例如在墨西哥西部的Tepic-Zacoalco裂谷。深部地壳和上地幔的电导率异常使我们可以得出岩浆房和上地幔之间存在联系的结论。更深处的共同来源。此外，我们预计，可能的各向异性导电性的空间分布的分析将暗示岩浆相关的断裂系统及其与地堑结构的相互作用。在上地幔内，各向异性可能是与附近俯冲有关的地球动力学过程的特征，该提议是根据提议者工作组内Philip Hering最近的一篇论文提出的，证实了Ceboruco火山内的两个电导率异常和10公里深处的一个各向异性层。这座火山位于特皮克-扎科阿尔科裂谷（Tepic-Zacoalco Rift）内。因此，应在火山周围150 km x 100 km的大区域内安装48个MT宽带系统和12个长周期站点。数据将由论文中开发的法兰克福软件包FFMT进行处理。它使用一个特征值标准计算强大的MT传递函数（TF），如阻抗张量，CART（复视电阻率张量）和tipper矢量，频率范围为0.0001-1000 Hz的同时记录MT系统。研究表明，在长周期范围内，相张量椭圆的空间一致性模式可以代表电导率的各向异性特性。对附近圣佩德罗火山的MT数据进行的初步研究再现了这种模式。由于CART和自卸车不受静位移现象的影响，站点之间的距离与目标深度相适应，从而允许上述站点数量的区域覆盖。建模包括两个步骤：首先，使用ModEM反演传递函数，ModEM是一种广泛使用的反演代码，用于计算各向同性3D电导率异常。第二，模型。通过使用各向异性体和Comsol Multiphysics® FE软件计算TF，逐步改进数据拟合。特别地，我们将研究电导率的大尺度非均匀性和/或各向异性对所观察到的相位差的影响。构造-地球动力学背景，考虑到其他地球科学调查的结果。该项目将大大有助于全面描述俯冲作用引发的岩浆过程以及随后的构造和地球动力学过程。

The proposal suggests a large scale magnetotelluric (MT) investigation of the conductivity distribution within magmatic systems in the context of tectonic processes, exemplarily for the Tepic-Zacoalco Rift in Western Mexico. Deep crustal and upper mantle conductivity anomalies allow conclusions about the linkage between magma chambers resp. a common source at greater depth. Furthermore, we expect that the analysis of the spatial distribution of possible anisotropic conductivity will hint at magma related fracture systems and their interaction with the graben structure. Within the upper mantle, anisotropy may characterize geodynamic processes related to subduction nearby.The proposal, based on a recent dissertation by Philip Hering within the working group of the proponent, verified two conductivity anomalies within the Ceboruco Volcano and an anisotropic layer at 10 km depth. The volcano is located, among other volcanoes, within the Tepic-Zacoalco Rift. Thus 48 MT broadband systems and 12 long period sites shall be installed within a 150km x 100km large area around the volcano. The data will be processed by the Frankfurt software package FFMT developed within the dissertation. It uses an Eigenvalue criterion for calculating robust MT transfer functions (TF), such as impedance tensors, CARTs (complex apparent resistivity tensor) and tipper vectors, for the frequency range 0.0001-1000 Hz from simultaneously recording MT systems. The dissertation shows that for the long period range the spatially consistent pattern of the phase tensor ellipses may represent anisotropic properties of the conductivity. The pattern was reproduced by a preliminary study for MT data from the San Pedro volcano nearby. As CARTs and tippers are not influenced by static-shift phenomena, the distance between sites is adapted to the target depth, allowing regional coverage by the number of sites mentioned above.Modeling comprises two steps: At first, the transfer functions are inverted using ModEM, a widely used inversion code for the computation of isotropic 3D conductivity anomalies. Secondly, the model resp. the data fit is improved stepwise by the implementation of anisotropic bodies and the calculation of the TFs by Comsol Multiphysics® FE software. In particular, we will investigate the influence of large scale heterogeneities and/or anisotropy of the electrical conductivity on the observed phase differences.Finally, the conductivity model will be interpreted within the petrophysical resp. the tectonic-geodynamic context, considering the findings of other geoscientific investigations. The project will contribute substantially to the overall description of magmatic processes triggered by subduction and subsequent tectonic and geodynamic processes.