Magnetotelluric investigation of the Appalachians, Newfoundland, Canada

McNeice, Gary Wayne (1998) Magnetotelluric investigation of the Appalachians, Newfoundland, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

Data from 77 magnetotelluric (MT) soundings across the Appalachian orogen in Newfoundland, Canada, are, analysed to determine the conductivity structure of major tectonic boundaries of the orogen and the regional conductivity structure. An extended Groom-Bailey tensor decomposition analysis is developed and employed to remove galvanic distortion effects produced by the complex near surface geology of Newfoundland. In the proposed decomposition analysis a global minimum is sought to determine the most appropriate strike direction and telluric distortion parameters for a range of frequencies and a set of sites. The recovered 2D responses are representative of regional-scale structures and 2D inversion algorithms can be employed to recover the regional conductivity structure. -- The regional conductivity structure of the orogen suggests that the Baie Verte Line, Red Indian Line and Dover fault - Hermitage flexure represent significant crustal tectonic boundaries. The conductivity structure changes both across and along strike in Newfoundland. The magnetotelluric data do not support a near two-dimensional model of three lower crustal blocks but indicate a more complex three-dimensional geometry in southern Newfoundland. -- The Baie Verte Line is imaged as an upper-middle crustal boundary separating the deformed and duplicated passive margin of Laurentia (Humber zone) and resistive arc terrain of the Notre Dame subzone. The Red Indian Line marks the boundary between the Notre Dame and Exploits subzones of the Dunnage zone and is roughly coincident with a change in lower crustal conductivity. The Dover fault is imaged as a near vertical boundary between upper-middle crusts of contrasting electrical properties, extending to a depth of at least 20 km. -- The sharp change in upper-middle crustal conductivity observed in the magnetotelluric data suggest that orogen parallel motions were important in the development of many of the major boundaries of the orogen. The data support a three part division of the lower crust.

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