Understanding geophysical imprints of suture zones: Development of 2D constraint inversion for electrical anisotropy

在2004 - 2006年期间，沿着650公里长的大陆尺度样带进行了几次高分辨率大地电磁（MT）实验，成像了南非活动带和相关缝合带上下地壳的各种结构细节。各向同性二维反演可以解释主要的区域特征：(i)出乎意料的导电纳马夸-纳塔尔活动带（NNMB）向高电阻Kaapvaal克拉通的过渡，该克拉通位于比预期远70公里的西南方向；（ii） NNMB基底的亚垂直高导电性带，可能是大型地壳尺度剪切带的图像；（iii）广泛的浅层亚水平高导电性层，与卡鲁盆地突出的黑色页岩层相关。（iv） NNMB基底在10 - 25 km深度的一个以前未知的导电型构造，以及(v)角褶皱带（CFB）的导电深盆地（vi）夹在电阻性强褶皱山脉之间。沿剖面的一些受限区域在MT阻抗张量中表现出三维（3D）效应，可能是由电各向异性引起的。模拟和量化缝合带的电各向异性是我以前申请的主要目标之一，也是博士项目的一部分。不幸的是，这位博士生病得很重，这个职位直到2008年10月才有空缺。这位新博士生目前正在研究各向异性反演。根据这一建议，我们打算(i)模拟目前尚未解释的MT数据中电性各向异性的影响，（ii）量化电性各向异性以获得相关断层系统的结构细节，（iii）通过将各向异性带的区域信息和结构细节结合在一起，获得保存在岩石圈中的冈瓦纳沉积过程复杂演化的更完整图像。

Between 2004 - 2006 several high resolution magnetotelluric (MT) experiments along a 650 km long continental scale transect imaged various structural details in the upper and lower crust of South African mobile belts and associated suture zones. With isotropic 2D inversion the main regional features can be explained: (i) the transition of the unexpectedly conductive Namaqua-Natal Mobile Belt (NNMB) into the highly resistive Kaapvaal Craton, which is located 70 km farther southwest than expected, (ii) a sub-vertical zone of high electrical conductivity in the NNMB basement, likely an image of a large crustal scale shear zone, (iii) an extensive shallow sub-horizontal high conductivity layer which correlates with a prominent black shale horizon in the Karoo Basin, (iv) a previously unknown conductive synformal structure in the NNMB basement in 10 - 25 km depth , and (v) the conductive deep basins of the Cape Fold Belt (CFB), which (vi) are sandwiched between the resistive, intensely folded mountain ranges. Some confined areas along the profile exhibit three-dimensional (3D) effects in the MT impedance tensor, likely caused by electrical anisotropy. Modelling and quantifying electrical anisotropy in suture zones has been one of the major goals of my previous application and was part of a PhD project. Unfortunately, the PhD student got severely ill and the position could only be filled again in October 2008. The new PhD student is currently working towards anisotropic inversion. With this proposal we intend to (i) model the effects of electrical anisotropy in the MT data which are currently not explained, (ii) quantify the electrical anisotropy to derive structural details of the associated fault systems and (iii) derive a more complete image of the complicated evolution of Gondwana’s accretion processes preserved in the lithosphere, by putting together the regional information and structural details of anisotropic zones.