Abstract

One hundred and five specimens were collected from 40 different sites in northwest-striking metabasalts and metagabbros of Lower Proterozoic (Aphebian) age in the northeastern part of the Labrador Trough (longitude: 69 °W, latitude: 57 °N). The radiogenic age determinations of surrounding rocks of the same age yielded 1860 m.y. A petrological and chemical description of the rocks is included. The chemical results for total Fe, MgO, and Na2O + K2O combined, drawn on a ternary diagram show that the metabasalts and metagabbros fall in the tholeiite field. Magnetite (with some occasional 5% ulvospinel) is the most frequent magnetic memory carrier; pyrrhotite is less commonly found. In order to obtain some pertinent information relative to the stability of the NRM component, step-wise alternating field demagnetization was conducted on 40% of the specimens and the others were demagnetized at a specific AF intensity. In 35% of the specimens, the AF demagnetization process induced an anhysteretic magnetization component above 250 Oe. A secondary isothermal remanent magnetization of lesser stability was often detected in the 50–150 Oe range. Tilting of the formations sometimes increased and sometimes decreased the dispersion of the NRM vectors. After tilting the lithological units that were AF demagnetized, the mean paleomagnetic pole position is 152 °E, 20° S (dm = 14°,dp = 07°, K = 34), with at least one reversal.

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