McHONE, J. Gregory, Wesleyan University, Middletown, CT 06459-0519, jmchone@wesleyan.edu
Mesozoic basins that preserve extrusive basalts of the 200 Ma Central Atlantic Magmatic Province (CAMP) may total about 300,000 km2. However, dikes and sills of CAMP that fed the basin basalts are spread across an area greater than 10 million km2 within four continents. 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 surface basalt exceeded 2.3 million km3 and may be the largest known subaerial flood basalt event.
    Averages of volatile contents of eastern North American CAMP tholeiitic dikes and sills, in weight %, are: CO2 = 0.066; S = 0.046; F = 0.032; and Cl = 0.064. Atmospheric emissions of volatiles from extrusive basalts can be reasonably estimated as half of the volatile content of their comagmatic intrusive sources, mainly as gaseous plumes from lava curtains at the erupting fissures. Volcanic emissions of these gases therefore ranged between 1.13E+12 and 2.33E+12 metric tons, enough for major world-wide environmental problems. Climatic effects could include both immediate cooling from S converted to sulfuric acid haze, and a longer period of greenhouse effects from the CO2. The substantial F and Cl were short-term poisons with undocumented effects. Radiometric and stratigraphic ages indicate most of the magmatic activity was brief, widespread, and close to the Tr-J boundary, which is marked by a profound mass extinction. A causal connection between these great lava flows and the mass extinction has not been demonstrated within Mesozoic basins, so it may depend upon how precisely radiometric dates for CAMP basalts in other regions bracket the Tr-J boundary, and on other geochemical and fossil evidence.

Submitted in November for the 2000 NEGSA meeting.