SIMILARITY OF MAGNETIC ANOMALY PATTERNS OVER SOUTHWESTERN ALBERTA AND NORTHWESTERN MONTANA AND OVER NORTHERN VICTORIA LAND AND THE ADJACENT ROSS SEA, ANTARCTICA

An aeromagnetic anomaly map of northern Victoria Land and the adjacent Ross Sea, Antarctica, published by Ferraccioli et al. (Tectonophysics, 478:43, 2009), appears similar to standard magnetic anomaly maps of S Alberta and NW Montana. A new magnetic anomaly map of S Alberta and NW Montana was prepared at the same scale as the map of Ferraccioli et al. (2009) to better compare the sizes of the anomalies in the two maps and their complementary patterns. The new map was produced using residual total magnetic field data obtained from the North American Magnetic Anomaly Map grid (NAMAG, 2002) and mapped at 1-km resolution to a Lambert conformal conic projection. Five major magnetic anomaly features identified in Ross (Can. J. Earth Sci., 39:413, 2002) as characterizing basement domains in S Alberta and NW Montana are visible in the new map and have counterparts in the map of Ferraccioli et al. (2009). These features are, in order from S Alberta to N Montana, (1) a blocky magnetic high at the western end of the Proterozoic Thorsby domain, (2) an elongate magnetic high at the western end of the Proterozoic Rimbey domain, (3) an elongate magnetic high at the western end of the Archean Matzhiwin domain, (4) the wide-field N-S trending magnetic anomalies over the Archean Medicine Hat block (MHB), and (5) the distinctive magnetic anomaly pattern over the Proterozoic Great Falls tectonic zone (GFTZ). The sizes, shapes, orientations and relative positions of these five magnetic anomaly features in the two maps are comparable. For example, the N-S trending magnetic anomalies over the MHB, which Lemieux et al. (Can. J. Earth Sci., 37:1473, 2000) correlate with dipping seismic reflection surfaces in the upper crust, trend more toward the west over the northern end of the MHB. This same pattern is mimicked in the map of Ferraccioli et al. (2009). The distinctive comb-like pattern that is displayed by the magnetic anomalies over the GFTZ, which in this study is inferred to be a reflection of superimposed folding, is also displayed in the map of Ferraccioli et al. (2009).

Lone geophysical observations that suggest the fragmental breakup of an ancient continent require tangible supporting evidence. A plan to drill beneath the Ross Sea to extract cores of sedimentary and basement rocks (Coulman High Project) should produce clues to their provenance.