Abstract

Paleomagnetic studies have been carried out on tower Proterozoic (Aphebian) rocks of the Labrador Trough in central Quebec. The magnetizations are complex. Most magnetizations are secondary and none are demonstrably original, but their relative order can be estimated from their associated blocking temperatures. The oldest magnetizations (A) are thought to have been acquired at about 1800 Ma following deposition but not necessarily long afterwards. These magnetizations have blocking temperatures of about 600 °C and occur in the Seward Subgroup (mainly arkoses), the Menihek Formation (argillites), and the Retty Formation (peridotites). The Castignon carbonatitic complex also has A type magnetizations which are referred, tentatively, to a K–Ar date of 1875 ± 50 Ma, The next youngest magnetizations (B) have blocking temperatures commonly distributed between 300 and 500 °C and are considered to have been acquired at about 1600 Ma during uplift following the Hudsonian orogeny. B magnetizations are the commonest magnetizations and are found in the Seward, the Retty, and the Menihek. The youngest magnetizations (C) have low blocking temperatures predominantly less than 300 °C and were probably acquired long after the rocks were formed. The C magnetizations are found in the Seward Subgroup, the Willbob Formation (basalts), and the Wakuach Formation (gabbros). The age of the C magnetization appears to be about 1100 Ma, but its origin is not known. This chronology of magnetizations is consistent with the previously constructed path of apparent polar wandering for Laurentia.

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