Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Abstract

S U M M A R YWe report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSB where the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of the world. A very pronounced feature of our 2-D inversion model is a deep, subvertical conductive zone beneath the DSB. The conductor extends through the entire crust and is sandwiched between highly resistive structures associated with Precambrian rocks of the basin flanks. The high electrical conductivity could be attributed to fluids released by dehydration of the uppermost mantle beneath the DSB, possibly in combination with fluids released by mid-to low-grade metamorphism in the lower crust and generation of hydrous minerals in the middle crust through retrograde metamorphism. Similar high conductivity zones associated with fluids have been reported from other large fault systems. The presence of fluids and hydrous minerals in the middle and lower crust could explain the required low friction coefficient of the DST along the eastern boundary of the DSB and the high subsidence rate of basin sediments. 3-D inversion models confirm the existence of a subvertical high conductivity structure underneath the DSB but its expression is far less pronounced. Instead, the 3-D inversion model suggests a deepening of the conductive DSB sediments off-profile towards the south, reaching a maximum depth of approximately 12 km, which is consistent with other geophysical observations. At shallower levels, the 3-D inversion model reveals salt diapirism as an upwelling of highly resistive structures, localized underneath the Al-Lisan Peninsula. The 3-D model furthermore contains an E-W elongated conductive structure to the northeast of the DSB. More MT data with better spatial coverage are required, however, to fully constrain the robustness of the above-mentioned off-profile features.

Electrical Structure of the Lithosphere From Rio de la Plata Craton to Paraná Basin: Amalgamation of Cratonic and Refertilized Lithospheres in SW Gondwanaland

“…The main motivation for carrying on 3‐D electrical modeling of the subsurface is that the 2‐D/3‐D parameterization from the Groom‐Bailey decomposition failed in some cases, mainly at the central and southern parts of the study area, which can lead to incorrect results if the data are modeled using 2‐D inversion scheme. Despite that our data coverage is nonideal for 3‐D modeling, several authors (Bologna et al, ; Kapinos et al, ; Meqbel et al, ; Patro & Egbert, ; Siripunvaraporn et al, ; Tietze & Ritter, ) have shown that application of 3‐D inversion MT profile data can provide realistic images of the resistivity distribution beneath the data.…”

Quality over quantity: on workflow and model space exploration of 3D inversion of MT data

“…When the RMS decrease per iteration is less than a certain value (default 1.0e−3), then is decreased by a user input divisor (default 10), and this process is repeated until the exit value is reached. This process ensures that the orthogonality of the search direction vector is maintained and allows the algorithm to escape from a local minimum (Meqbel et al 2016). An initial damping parameter of 1, 10, 100 and 1000 was tested (with exit value and divisor kept as default), with the results outlined in Figs.…”

“…Additionally, where transects are collected, it is now becoming more commonplace to invert using a 3D inversion code to allow for three-dimensionality of data (e.g. Robertson et al (2016); Meqbel et al (2016)).…”

Electrical conductivity of a locked fault: investigation of the Ganos segment of the North Anatolian Fault using three-dimensional magnetotellurics

“…Magnetotellurics (MT) is capable of providing satisfying results to reveal the shallow and deep electrical properties of active and fossil fault zones (Unsworth et al 1997;Bedrosian et al 2002Bedrosian et al , 2004Becken et al 2008Becken et al , 2011Wannamaker et al 2009;Meqbel et al 2016). The MT method is a geophysical tool that uses naturally occurring electromagnetic fields to decipher the electrical properties of the subsurface (Vozoff 1972;Kaufman and Keller 1981;Jiracek 1995).…”