Conductivity structure of the lithosphere‐asthenosphere boundary beneath the eastern North American margin

Abstract

Tectonic plate motion and mantle dynamics processes are heavily influenced by the characteristics of the lithosphere-asthenosphere boundary (LAB), yet this boundary remains enigmatic regarding its properties and geometry. The processes involved in rifting at passive margins result in substantial alteration of the lithosphere through the transition from continental to oceanic lithologies. Here we employ marine magnetotelluric (MT) data acquired along a 135 km long profile, offshore Martha's Vineyard, New England, USA, to image the electrical conductivity structure beneath the New England continental margin for the first time. We invert the data using two different MT 2-D inversion algorithms and present a series of models that are obtained using three different parameterizations: fully unconstrained, unconstrained with an imposed LAB discontinuity and a priori constrained lithosphere resistivity. This suite of models infers variability in the depth of the LAB, with an average depth of 115 km at the eastern North America passive margin. Models robustly detect a 350 Xm lithospheric anomalous conductivity zone (LACZ) that extends vertically through the entire lithosphere. Our preferred conductivity model is consistent with regional P-to-S receiver function data, shear-wave velocity, gravity anomalies, and prominent geological features. We propose that the LACZ is indicative of paleolithospheric thinning, either resulting from kimberlite intrusions associated with rifting and the New England Great Meteor hot spot track, or from shear-driven localized deformation related to rifting.

Aquifer systems extending far offshore on the U.S. Atlantic margin

“…Analysis of the Martha’s Vineyard MT profile for deep crustal and mantle structure using the full data bandwidth is presented in ref. 38 .…”

Crustal Heating and Lithospheric Alteration and Erosion Associated With Asthenospheric Upwelling Beneath Southern New England (USA)

“…Note the ring of strong Δ V S 's around the outline of the NAA, especially on its seaward side (see section ). Attias et al's () lithospheric anomalous conductive zone (LACZ, blue line) is also shown.…”

“…Both effects would tend to increase the amplitude of S-to-P converted waves. Attias et al (2017) reports a 50-km-wide lithospheric anomalous conductive zone on the continental shelf south of Cape Cod, Massachusetts (Figure 4c), with electrical conductivities that are about 10 times higher than normal in the 40-to 100-km depth range. It is just south of one of the regions with negative velocity gradients and may represent a seaward extension that is out of range of the seismic imaging (which is based on stations on land).…”

Formation and geophysical character of transitional crust at the passive continental margin around Walvis Ridge, Namibia

“…Only limited electromagnetic surveys have been performed to image the electrical resistivity structure of passive margins. Authors have identified varying structures, such as a conductive lithospheric anomaly imaging mantle upwellings (Attias et al, 2017); upper-crustal conductors imaging subbasalt sediment basins (Hoversten et al, 2015), or graphite and massive sulfide mineralization (Corseri et al, 2017;Heinson et al, 2005); and high lower-crustal resistivities depicting magmatic underplating (Jegen et al, 2016). The underlying reason for the different characteristics is linked to the "plates vs. plumes" hypothesis, which discusses the triggers of continental breakup in terms of mantle convection, mantle plumes, melt generation, and plate tectonics (Anderson, 2001;Foulger, 2010;Morgan, 1971;Wilson, 1963).…”