Evaluation of radiometric ages for the Central Atlantic magmatic province: timing, duration, and possible migration of magmatic centers
Ajoy K. Baksi, Dept. of Geology & Geophysics, Louisiana State Univ., Baton Rouge, LA 70803, USA (abaksi@geol.lsu.edu).



Recent reports have suggested that the Central Atlantic magmatic province (CAMP), covering sections of North America, Africa and South America, was formed within a relatively short period of time around 200 Ma. To examine this more closely, all relevant 40Ar/39Ar ages are corrected for interlaboratory differences, mini or marginal plateau values are rejected as accurate estimates of crystalhzation age, and results examined closely for the presence of excess argon in some samples and alteration effects in others. Twenty-three accurate ages span ~230 to 175 Ma, with a strong concentration around 200 Ma. Examination of the latter set, suggests that magmatism in North America and contiguous parts of Africa in Pangaea, occurred at 200 Ma, whereas that in South America occurred at 198 Ma. The age difference appears to be statistically significant, and suggests a younging of ages moving north to south. From a temporal viewpoint, the postulated genetic link between CAMP and the Triassic-Jurassic boundary extinction event appears valid. The extinction event may have occurred first on land and then at sea over a million years or so, bridging 200 Ma, and the magmatism related to CAMP covers essentially the same temporal regime.