A Reappraisal of the Paleomagnetism of the Lewisian Foreland, NW Scotland: the occurrence of primary magnetizations and their implication for a Baltica-Lewisian fit at 2.0 Ga.

摘要

The Lewisian foreland is predominantly comprised of late Archean tonalitic-trondhjemitic gneisses which are intruded by the Paleoproterozoic Scourie dyke swarm. Previous paleomagnetic investigations of these dykes have concluded the most ancient magnetizations to have been acquired during Laxfordian events (∼1.7 Ga) thereby significantly post-dating time of Scourie dyke emplacement. However, this thesis presents evidence of relict primary magnetizations. These magnetizations are asserted to a particular section of the study area that hosts a suite of well preserved Scourie dykes that are accurately dated at 1992 Ma. It is suggested that by ∼ 1.9 Ga crustal temperatures were sufficiently low enough to permit acquisition of a primary magnetic remanence during dyke crystallization. These magnetizations yield a paleomagnetic pole at 33.8°N, 263.9°E (N=4 sites A95=15.7). The proposed 1990 Ma paleomagnetic pole has significant implications on the paleoposition of the Lewisian foreland as a strong correlation may be presented between the proposed 1990 Ma paleomagnetic pole and other similar aged poles from the Fennonscandian shield, Scandinavia.