The effect of mantle plume heads on the motion between the African and Antarctic plates in the Late Cretaceous and Early Cenozoic

Indo-Atlantic plate kinematics during the Late Cretaceous and Early Cenozoic were dominated by a period of roughly 25 million years during which the motions of India and Africa appear to have been coupled: a rapid speedup of India's absolute motion starting around 68 Ma was accompanied by a dramatic slowdown of Africa's absolute motion and the subsequent slowdown of India between 52 and 45 Ma was accompanied by a speedup of Africa. Cande and Stegman (2011) proposed that the coupled nature of these plate motions was caused by the arrival of the Reunion plume head at the Earth's surface: the speedup of India (slowdown of Africa) was due to the onset of the plume head, while the slowdown of India (speedup of Africa) was due to the waning of the plume head. This hypothesis is controversial since the slowdown of India has long been attributed to the initial collision of India with Eurasia and it is not clear how mantle plume heads affect plate motions. In order to better understand the cause of the coupled motions of India and Africa we have re-examined the motion of Africa relative to Antarctica as constrained by magnetic anomalies and fracture zones on the Southwest Indian Ridge (SWIR). The bends of the SWIR fracture zones contain a particularly important record of plate motion changes: a gradual ccw bend starting at Chron 32 is followed by a sharp cw bend at Chron 24. We present here a set of 13 revised rotations for the SWIR for the time interval from Chron 34 to Chron 18. These rotations quantify in more detail than in previous studies the changes recorded by the SWIR fracture zones. The onset of the ccw change in spreading direction and start of a rapid decrease in spreading rate on the SWIR occurs around Chron 32 (71 Ma). From Chron 32 to Chron 24 the motion between Africa and Antarctica is characterized by a continuous and apparently smooth migration of the Africa-Antarctic stage pole. The most dramatic change in motion along the SWIR is the sudden cw bend of the fracture zones (and shift in the Africa-Antarctic stage pole) around Chron 24 (53 Ma). Although both India and Africa appear to respond to the Reunion plume head around 71 Ma, it is notable that the time of India's most rapid speedup (starting around Chron 31, at 68 Ma) appears to lag the time of Africa's most rapid slowdown (Chron 32) by two or three million years, a relationship which may be an important clue as to how the Reunion plume head affects the motions of India and Africa. The sudden change in spreading direction between Africa and Antarctica as recorded on the SWIR at Chron 24 (53 Ma) is also puzzling. This change in motion is roughly synchronous with major tectonic events throughout the Atlantic region, which suggests that it was caused by the arrival of the Iceland plume head, whose onset is related to the rifting of Norway and Greenland just before Chron 24. The major Eocene slowing of India and speedup of Africa start soon after this event, around 52 Ma, suggesting that this phase of the coupled motion may also have been triggered by the arrival of the Iceland plume head. Cande, S.C. and D. R. Stegman. Indian and African plate motions driven by the push force of the Reunion plume head, Nature, v. 475, 47-52, 2011.