Synchronous magmatic cycles during the fragmentation of Gondwana: radiometric ages from the Levant and other provinces

Reliable and acceptable radiometric ages (mainly Ar-40/Ar-39) of igneous wh ole rocks from the Levant, representing non-orogenic igneous provinces, tog ether with six igneous provinces of Gondwana, reveal 17 synchronous global magmatic events, including flood basalts. Their starting ages in the course of the last 205 million years (in Ma) are: 202, 190, 184, 169, 160, 145, 1 38, 125, 112, 97, 83, 69, 56, 44, 32, 17 and 5. The chronology of these eve nts in Gondwana igneous provinces points to short-term magmatic cycles, con sisting of magmatic events plus intermagmatic intervals, with an average du ration of ca 13 m.y. The suggested synchronous events, which conform to geo logical periods and stage boundaries, probably reflect cycles of high-rate upper mantle upwellings that played a major role in the periodic ascent of melts across the lithosphere. The common geodynamic evolution of Gondwana i gneous provinces was extension of the continental lithosphere, thinning, up lifting, breakup, massive igneous activity, spreading and drifting. All the se provinces were affected by upwelling of lower mantle thermal anomalies. The chronology of magmatic events in each igneous province, which extended over thousands of kilometers and includes the plume provinces, suggests tha t the life-span (magmatic period) of these provinces averages 58 m.y., and in many cases, the first-term magmatic cycles are longer (11-17 m.y.) and m ore intensive. The periodic magmatism, which followed the breakup and dispersal of Gondwan a, suggests an evolutionary scenario for the development of oceanic spreadi ng centers by the ascent of one or more (coexisting) large plume heads acro ss the upper mantle. (C) 2000 Elsevier Science B.V. All rights reserved.