J. Gregory McHone, GLSP, Wesleyan University, Middletown, CT 06459-0519
Mesozoic basins that preserve extrusive basalts of
the 200-Ma Central Atlantic Magmatic Province (CAMP) total about 300,000
km2. However, dikes and sills of CAMP
that fed the basin basalts also occur across 11 million km2
within four continents, centered upon but extending far outside of the
initial Pangaean rift zone. New maps show CAMP dikes, sills, and surface
lavas, with evidence that the province includes regions between Texas and
Venezuela along its western side. The N-S dimension of CAMP is greater
than 5,000 km, with several dikes greater than 500 km long, sills exceeding
100,000 km3, and lava flows larger
than 50,000 km2. In addition, basalts
of the East Coast margin igneous province (ECMIP) of North America, which
cause the East Coast Magnetic Anomaly, covered about 60,000 km2
with perhaps 1.3 million km3 of extrusive
lavas. If only half of the continental CAMP area was originally covered
by 200 m of lava, the total volume of CAMP and ECMIP extrusive basalt exceeded
2.4 million km3 and may be Earth's
largest subaerial flood basalt event. A similar amount remains frozen in
the uppermost crust. The distribution of chemical groups within the
province is pertinent to geodynamic and petrologic models for the origin
of this and other large flood basalt provinces. Radiometric and stratigraphic
ages indicate most of the magmatic activity was everywhere brief and close
to the Tr-J boundary, which is marked by a profound mass extinction. Huge
emissions of CAMP volcanic gases would have caused major world-wide environmental
problems. Proving a connection between CAMP volatiles and the mass extinction
will depend on how precisely new radiometric dates for the basalts bracket
the Tr-J boundary.