Magnetotelluric investigations of the lithosphere beneath the central Rae craton, mainland Nunavut, Canada

Abstract

New magnetotelluric soundings at 64 locations throughout the central Rae craton on mainland Nunavut constrain 2-D resistivity models of the crust and lithospheric mantle beneath three regional transects. Responses determined from colocated broadband and long-period magnetotelluric recording instruments enabled resistivity imaging to depths of > 300 km. Strike analysis and distortion decomposition on all data reveal a regional trend of 45-53°, but locally the geoelectric strike angle varies laterally and with depth. The 2-D models reveal a resistive upper crust to depths of 15-35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries. Surface projections of the conductive layer coincide with areas of high grade, Archean metasedimentary rocks. Tectonic burial of these rocks and thickening of the crust occurred during the Paleoproterozoic Arrowsmith (2.3 Ga) and Trans-Hudson orogenies (1.85 Ga). Overall, the uppermost mantle of the Rae craton shows resistivity values that range from 3000 Ω m in the northeast (beneath Baffin Island and the Melville Peninsula) to~10,000 Ω m beneath the central Rae craton, to >50,000 Ω m in the south near the Hearne Domain. Near-vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of Hudsonian granites. A regional decrease in resistivities to values of~500 Ω m at depths of 180-220 km, increasing to 300 km near the southern margin of the Rae craton, is interpreted as the lithosphere-asthenosphere boundary.

Unraveling the Western Churchill Province Paleoproterozoic Gold Metallotect: Constraints from Re-Os Arsenopyrite and U-Pb Xenotime Geochronology and LA-ICP-MS Arsenopyrite Trace Element Chemistry at the BIF-Hosted Meliadine Gold District, Nunavut, Canada

“…4), which are considered part of the larger-scale fault network mentioned above ( Fig. 1; Jones et al, 2002;Spratt et al, 2014). The deformation history of the Meliadine gold district is divided into four separate increments (Carpenter and Duke, 2004): (D1) bedding-parallel folding and thrusting and possible initial juxtaposition of turbiditic and volcanic rocks packages; (D2) regional penetrative cleavage development (285/59; S2) and bedding-parallel folding and thrusting; (D3) asymmetric Z-folding associated with an axial planar, W-trending cleavage (270/67; S3); and (D4) kink banding and N-to NW-trending crenulation cleavage development.…”

“…Several of these faults, such as the Josephine River shear zone together with the Pyke fault, along which most of the Meliadine gold district gold deposits are located, correspond to the approximate surficial trace of lithospheric-scale geophysical features (Figs. 1, 3;Jones et al, 2002;Spratt et al, 2014).…”

“…Critically, several of these lithospheric-scale faults (Spratt et al, 2014) record pre-Trans-Hudson Orogeny hydrothermal and deformation histories along their strike length (Fig. 2;Sanborn-Barrie et al, 2001;Berman, 2010).…”

The electrical resistivity structure of lithosphere across the Dharwar craton nucleus and Coorg block of South Indian shield: Evidence of collision and modified and preserved lithosphere

“…The estimation of the LAB from depth variation of electrical resistivity provides critical knowledge of the architecture of the cratonic lithosphere. Hence, the nature and/or geometry of the electrical LAB (e‐LAB) is widely mapped and utilized to understand the past and/or present geodynamic and tectonic processes that molded the present‐day craton architecture and aid in diamond prospectivity of an area [e.g., Jones et al ., ; Muller et al ., ; Spratt et al ., ; Adetunji et al ., ]. The appropriate criterion to identify the e‐LAB could be to observe the upper mantle depth region where significant resistivity changes occur between the high‐resistivity electrical lithosphere (typically > 1000 Ωm) and conductive asthenosphere (10–100 Ωm) [ Jones et al ., ; Eaton et al ., ; Spratt et al ., ].…”

“…MT is therefore widely used to study the subsurface structures, crustal as well as upper mantle, associated with varied geological and tectonic settings, such as in ancient and active subduction/collision zones, volcanic and seismic regions, stable cratons, and rift zones [e.g., Unsworth et al ., ; Abdul Azeez and Harinarayana , ; Evans et al ., ; Zhao et al ., ; Abdul Azeez et al ., ; Thiel and Heinson , ; Padilha et al ., ]. Various MT studies have proved their efficacy in delineating the cratonic roots and upper mantle structures that could enlighten the evolution of cratons and their stability [e.g., Wei et al ., ; Jones et al ., ; Evans et al ., ; Khoza et al ., ; Thiel and Heinson , ; Adetunji et al ., ; Spratt et al ., ; Selway et al ., ]. The present study uses both broadband and long‐period (ranging up to 10,000 s) data to constrain the lithospheric electric structure along a profile that cuts across the known oldest part (nucleus) of the Dharwar craton, i.e., the Holenarsipur belt, and the Coorg block of India.…”