The Pivoting Motion of Africa in the Late Cretaceous and Early Cenozoic

Abstract:

Indo-Atlantic plate kinematics during the Late Cretaceous and early Cenozoic were characterized by two distinctive events: a period of unusually rapid motion of India starting around 70 Ma and lasting until roughly 50 Ma, and a large slowdown of Africa also starting around 70 Ma and also lasting roughly 20 Ma. The synchroneity of India’s fastest motion (66 to 63 Ma) with the maximum outpouring of Deccan flood basalts has been noted by many, leading some to conclude that the speedup was caused by the arrival of the Reunion plume head at the Earth’s surface. The slowdown of Africa starting at 70 Ma has not received as much attention, but the near synchroneity of this event with India’s speedup is striking and suggests that it too may have been driven by the Reunion plume head. Establishing the connection between the changes in motion of India and Africa remains an outstanding problem. Cande and Stegman (2011) showed that an analysis of Africa’s motion in which the stage poles constraining the relative motion of North America-Africa, South America-Africa and Antarctica-Africa are treated as velocity vectors reveal important aspects of Africa’s motion that had not previously been noticed. Specifically they showed that Africa had a distinctive pivoting motion that started at the same time that India started to speed up. Here I use recently revised Antarctic-Africa stage poles to re-examine the pivoting motion of Africa. These rotations show that there were two distinctive events in Africa’s motion. There was an initial, large slowdown (decrease in the rate of counterclockwise rotation) of Africa about a pivot point in the North Atlantic around 71 Ma, about the time India starts to speed up. This initial slowing was followed by a second event in which the change in motion was a gradual but prolonged increase in the rate of Africa’s clockwise rotation about a pivot point in the South Atlantic that lasted from 68 Ma until 53 Ma, the period of the most rapid motion of India. The same two events are seen in the absolute motion of Africa. The initial slowing at 71 Ma may be an early response to the Reunion plume head. The distinctive character of Africa’s pivoting motion during the second stage suggests that it may be related to a ridge push driving force.