Volatile f luxes during f lood basalt eruptions and potential effects on the global environment: A Deccan perspective

We examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases. Continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time, characteristically a fewmillion years.Within this period, a short-lived climactic phase that lasts about 1Ma typically emplaces a large proportion of the lava volume. This phase consists of a series of huge eruptions, each yielding 10–10 km of magma. Each eruption lasted on the order of a decade or more, and built an immense pāhoehoe-dominated lava flow field by eruptive activity along fissures tens to hundreds of km long. High fire-fountains, emanating from vents along the fissures, at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas. The combination of large eruption magnitudes, maintained high effusion rates during eruptions, and the repeated nature of the characteristic, large-scale eruptive activity occurs in Earth history only during periods of flood basalt volcanism. Based on recent analogs and determination of volatile contents of ancient flood basalt lavas, we estimate that individual eruptions were capable of releasing 10,000 Tg of SO2, resulting in atmospheric loadings of 1000 Tg a during a sustained decade-long eruptive event.We apply this model of flood basalt volcanism to estimate the potential mass of CO2 and SO2 released during formation of the ∼65 Ma Deccan province. The Deccan lava-pile contains the record of hundreds of enormous pāhoehoe flow-fields erupted within a period of about 1 Ma. Consequently, atmospheric perturbations associated with SO2 emissions from just one of these long-lasting eruptions were likely to have been severe, and constantly augmented over a decade or longer. By contrast, the amounts of CO2 released would have been small compared with the mass already present in the atmosphere, and thus muchmore limited in effect. Individual eruptions were followed by hiatuses of hundreds to thousands of years duringwhich the gas contributions to the atmosphere would be recycled. It is clear that the nature and potential atmospheric impact of a series of huge-volume, repeated, long-term degassing events requires further investigation in conjunction with appropriate climate models. © 2006 Elsevier B.V. All rights reserved.