An alternative early opening scenario for the Central Atlantic Ocean

The overall kinematic history of the Central Atlantic Ocean is reasonably well documented. Although published plate kinematic models are able to reproduce most of the broad scale features of the formation of the continental margins and the tectonic history, the initial breakup of Pangaea and the early evolution of the Central Atlantic Ocean are still debated. Here, we propose an alternative scenario for the early opening of the Central Atlantic Ocean. The new model is based on 1) recently published results which demonstrate that the opening of the Central Atlantic Ocean started as early as the Late Sinemurian (190 Ma) - i.e. about 15 myr earlier than most previous models and only 10 myr after of the Central Atlantic Magmatic Province (CAMP) event, 2) the identification of the African conjugate of the Blake Spur Magnetic Anomaly (BSMA) based on all available magnetic data and on the similarity in shape of its counterpart as well as on seismic data, 3) an analysis of the most recent geophysical data (including seismic lines, an interpretation of the newly compiled magnetic data and satellite derived gravimetry), and 4) an analysis of important tectonic events observed in the geology of Morocco, related to the opening of the Central Atlantic Ocean. The early opening history for the Central Atlantic Ocean can be described by three distinct phases spanning the time interval from the Late Sinemurian (190 Ma) to Chron M0 (125 Ma). During the initial breakup and the first 25 myr, from 190 Ma to the base Callovian (BSMA, 165 Ma), oceanic crust was formed during a significant oblique motion which differs drastically from previous studies and with a spreading rate which was significantly slower. In contrast to previous studies, which consider an eastern ridge jump at Blake Spur time (165 Ma), the newly identified African conjugate of BSMA suggests a plate reorganization phase both in the relative plate motion direction (from NNW-SSE to NW-SE) and in spreading rate. This hypothesis is strengthening by the observation of a significant change in basement topography at Blake Spur time. From Chron M22 (150 Ma) onwards, the spreading rate slowed down and remained fairly constant until Chron M0 (125 Ma). Finally, kinematic reconstructions show a significant and widespread spreading asymmetry, from the initial breakup to at least Chron M0. This spreading asymmetry is consistent along the entire ridge which seems to favor an interpretation related to an asymmetric thermal structure of the mantle underlying the separating plates rather than a succession of ridge jumps.