Paleomagnetism of Late Archean metavolcanics and metasediments, Abitibi orogen, Canada: volcanics of the Blake River Group and sediments and volcanics of the Timiskaming Group

Abstract

A paleomagnetic study (159 samples, 30 sites) was done on calc-alkaline volcanics of the Blake River Group, dated at 2703 ± 2 Ma and occupying the central portion of a major synclinorium in the Abitibi Greenstone Belt. Magnetically stable single- and multi-vectorial components of magnetization were resolved in demagnetization; however, there was poor consistency of directions linearly decaying to the origin in vector analysis on the site, sample, and subsample levels (e.g., D = 190.0°, I = −29.2°, k = 1.5, α95 = 25.0°, n = 21 specimens from N = 21 samples). Preliminary results from a conglomerate test performed on the Chaput–Hughes Member of the overlying Timiskaming Group suggest that a pre-depositional remanence was retained and that there was not a widespread regional metamorphic event after the sediments were deposited. Cobbles derived from alkali volcanics of the Timiskaming Group and Kinojevis (tholeiites) and Blake River volcanics display dispersed directions of magnetization between cobbles. Preliminary magnetization data from the matrix of the conglomerate are well grouped, and correction for regional structure results in a direction similar to the characteristic one of Matachewan dikes. Paleomagnetic data from a downfaulted block of Timiskaming volcanics cut by Matachewan diabase dike may be interpreted to suggest that the fault block has been rotated clockwise (80°+) and subsequently tilted to the west (80°).