Geomagnetic induction studies in eastern Newfoundland

Pal, Badal Kanti (1983) Geomagnetic induction studies in eastern Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

An electromagnetic induction study has been carried out in the period range 40 seconds to 1 second at eight stations in eastern Newfoundland. The results show that conductivity anomalies in the Gander-Avalon zone are mainly associated with geological boundaries and faults. -- Because of the dominance of coast effect in the area, the signature of the inland induction anomaly in the observed data is separated from the superimposed coast effect by applying a difference arrow analysis technique. Difference arrows are obtained by taking a vector subtraction of the analogue model coast effect induction arrows from the observed induction arrows, based on assumption that the mutual inductance between the conducting ocean and any lithospheric conductor is small and can be neglected to a first order approximation. The most important feature apparent from this study is a zone of high conductivity under the Gander-Avalon boundary. -- Two dimensional numerical modelling is used to test models that are compatible with existing geological and geophysical results. A fossil oceanic lithospheric slab remnant from past subduction associated with the closure of the proto-Atlantic ocean is modelled on 25 x 30 grid. Two models, an east-dipping subduction model and an obduction model are shown to be quantitatively consistent with the observations. On the basis of these observations, we are unable to distinguish between these two models. The model of east-dipping subduction places the slab at a depth of 5 km and dipping eastward under the Gander Avalon boundary. The obduction model places the slab at the same depth as the previous model. However, it is extended laterally 28 km into the Avalon zone compared to 22 km as inferred from the previous model. A conductivity of 0.04 s/m which is the typical conductivity of hydrous minerals is determined as the conductivity of the slab.

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