Late Cretaceous to Early Tertiary Apparent Polar Wander Path for South America from Bahia Seamounts Magnetic Anomalies

We analyze magnetic data collected during 1988 and 1989 cruises in the South Atlantic run jointly by the Naval Research Laboratory (NRL) and the Diretoria de Hidrographia e Navigacao (DHN). The cruises surveyed the Bahia Seamount group that lies off the Brazil coast between latitudes 11°S and 12°S and longitudes 31°W and 35°W (Figure 1). The seamounts are on oceanic crust formed during the Cretaceous Normal Superchron, and were found to be typically small, deep. and conical. We find paleomagnetic poles for 6 seamounts by inverting magnetic anomaly data using the seminorm minimization method. We find one paleomagnetic pole for 7 seamounts that share a volcanic platform using a least-squares inversion that models seamounts with rocks of opposing polarity. We could not find poles for other seamounts owing to reversals in magnetic polarity along the seamount group and the large number of seamounts sharing volcanic platforms. We construct a South American Tertiary apparent polar wander (APW) path using our seamount poles. One of the seamounts was radiometrically dated. We estimate ages for the other seamounts by comparing their paleomagnetic poles with Late Cretaceous South American poles, and with North American Tertiary poles. Our APW path begins with a Late Cretaceous pole at 76.4 °N, 178.4 °E, then moves toward the spin axis in a slight zigzag, through a Paleocene pole at 84.2°N. 194.3°E. and an Early Eocene pole at 85.7°N, 123.9°E. We estimate that the South American paleomagnetic pole reached the spin axis in the Middle Eocene.