Breakup of Pangea and the Cretaceous Revolution. Issue 2 (7th February 2023) - Le Pichon, Xavier
Abstract: A 250 Ma, Pangea had just reached an equatorial position of dynamic equilibrium, after a 60° northward migration due to True Polar Wandering. It then began oscillating about itself for the next 150 Myr. The resulting extensional stresses triggered three successive phases of breakup, controlled by the mechanical resistance of a crescent of thick lithosphere, surrounding the Tethyan realm, which had adjusted the supercontinent to its hemispheric shape. The fracturing of the crescent was produced in three successive generations, each new generation corresponding to Coulomb fractures, conjugates of the preceding set. Flood basalts were associated with these deep fractures within the thick lithosphere crescent. We consider unlikely that this highly ordered pattern of fracturing was determined by the locations of the impacts of successive plumes. Between 260 and 180 Ma, thermal isolation was maximal and the asthenosphere of Pangea was about 150°C warmer than below Panthalassa. From 180 to 100 Ma, the breakup elongated Pangea by about 3, 000 km in a north‐northwest–south‐southeast direction, producing gaps in the subduction girdle. Lateral mixing began, leading to a continuous rise in global sea level and progressive return to a globally homogeneous upper mantle with sea‐level at its maximum 100 Ma. This Cretaceous Revolution marked the end of the Pangea tectonics, radically different from our present plate tectonics. Neither post‐Cretaceous plate kinematic inferences, nor mantle dynamic and associated planetary cooling inferences are extendable to Pangea times. Key Points: 250–100 Ma, oscillations of Pangea about itself triggered three successive phases of breakup The disruption of the subduction girdle of Pangea allowed lateral mixing and return to a globally homogeneous upper mantle The Cretaceous Revolution marked the passage 100 Ma from Pangea style tectonics to plate tectonics as we know it today