The Jurassic evolution of the Africa-Iberia conjugate margin and its implications on the evolution of the Atlantic-Tethys triple junction

摘要

The Central Atlantic, North Atlantic and Maghrebian Tethys formed a triple junction during the Mesozoic break-up of Pangea. Plate reconstructions of this triple junction have concentrated on the Atlantic branches, for which there are abundant geophysical data over their conjugate margins and associated oceanic domains. This is not the case for the Maghrebian Tethys, where both the Mesozoic Iberian and African margins and the intervening ocean are mostly overthrust by the Betic-Rif-Tell orogenic systems. The resulting lack of constraints on the evolution of the Africa-Iberia system has led most authors to treat the evolution of this system as a secondary problem in the more global Atlantic and Tethys systems. In this paper the evolution of the basins of Iberia and Northwest Africa is discussed and geological constraints are used to propose a new Late Triassic fit of Iberia with North America and Africa. This Late Triassic fit and its implications for Jurassic evolution are compared with the evolution of the sedimentary basins of the Atlantic-Tethys triple junction, and in particular those of the Africa Iberia margins. The geological evidence and the resulting plate reconstructions are consistent with a Jurassic evolution of the Africa-Iberia system that is dominated by three major events: 1) the Early to Middle Jurassic transition, in which oblique rifting gives way to transtensional rifting; 2) the Middle to Late Jurassic transition, marking the termination of most rifting in the system and interpreted to coincide with exhumation of subcontinental mantle and formation of oceanic crust in a setting dominated by transcurrence between Africa and Iberia; and 3) the Late Jurassic to Early Cretaceous transition, in which the rate of relative motion between and Iberia and Africa decreased significantly as rifting in the North Atlantic gained momentum.