Electromagnetic images of the Trans-Hudson orogen: the North American Central Plains anomaly revealed

Abstract

Magnetotelluric studies of the Trans-Hudson orogen over the last two decades, prompted by the discovery of a significant conductivity anomaly beneath the North American Central Plains (NACP), from over 300 sites yield an extensive database for interrogation and enable three-dimensional information to be obtained about the geometry of the orogen from southern North Dakota to northern Saskatchewan. The NACP anomaly is remarkable in its continuity along strike, testimony to along-strike similarity of orogenic processes. Where bedrock is exposed, the anomaly can be associated with sulphides that were metamorphosed during subduction and compression and penetratively emplaced deep within the crust of the internides of the orogen to the boundary of the Hearne margin. A new result from this compilation is the discovery of an anomaly within the upper mantle beginning at depths of ~80–100 km. This lithospheric mantle conductor has electrical properties similar to those for the central Slave craton mantle conductor, which lies directly beneath the major diamond-producing Lac de Gras kimberlite field. While the Saskatchewan mantle conductor does not directly underlie the Fort à la Corne kimberlite, which is associated with the Sask craton, the spatial correspondence is close.

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

“…5 is likely linked to shear deformation of the DST in the middle and lower crust and related processes. High conductivities in active tectonic zones have often been associated with fluids and hydrous minerals (Boerner et al 1998;Unsworth & Bedrosian 2004;Jones et al 2005;Ritter et al 2005;Wannamaker 2005;Becken et al 2011;Meqbel et al 2014). For instance, Becken et al (2011) interpreted a subvertical conductive anomaly extending through the entire crust northwest of Parkfield in California as a migration path for deep (partly mantle derived) fluids into the San Andreas Fault system.…”

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

“…Aside from the chemical composition, other available alternative causes for high conductivity anomalies can be considered, such as water in nominally anhydrous minerals (Wang et al, 2006;Yang, 2011;Karato, 2009, 2014a), interconnected saline (or aqueous) fluids (Hashim et al, 2013;Shimojuku et al, 2014;Sinmyo and Keppler, 2017;Guo et al, 2015;Li et al, 2018), partial melting (Wei et al, 2001;Maumus et al, 2005;Gaillard et al, 2008;Ferri et al, 2013;Laumonier et al, 2015Laumonier et al, , 2017Ghosh and Karki, 2017), interconnected secondary high conductivity phases (e.g., FeS, Fe 3 O 4 ; Jones et al, 2005;Bagdassarov et al, 2009;Padilha et al, 2015), dehydration of hydrous minerals (Wang et al, 2012(Wang et al, , 2017Manthilake et al, 2015Manthilake et al, , 2016Hu et al, 2017;Sun et al, 2017a, b;Chen et al, 2018) and graphite films on mineral grain boundaries (Freund, 2003;Pous et al, 2004;Chen et al, 2017). In consideration of the similar formation conduction and geotectonic environments, the Himalaya-Tibetan orogenic system was compared with the Dabie-Sulu UHPM belt and explained high electrical conductivity anomalies.…”

Electrical-resistivity imaging of the central Trans-Hudson orogen

“…As noted by , the NACP conductor lies within westward dipping reflectivity and tracing of the reflections updip to the surface indicates that the conductor lies within the rocks of the La Ronge domain. More detailed interpretations of the NACP conductor are given in and Jones et al (1997aJones et al ( , 2005. The NACP conductor is interpreted to be bounded above by the Birch Rapid straight zone and below by the Guncoat thrust, with its western extent limited by the Needle Falls shear zone.…”

“…Finally, the westernmost sites in the present study cross the NACP conductor and allow detailed examination of the tectonic setting of the conductor. The paper by Jones et al (2005) in this volume considers the NACP conductor in greater detail.…”