TOWARD A HIGH-RESOLUTION AGE MODEL FOR THE DECCAN TRAPS BY U-PB ZIRCON GEOCHRONOLOGY (Invited Presentation)
Because basalt typically does not crystallize zircon, we have focused our sampling efforts on paleosol horizons between basalt flows (locally termed “redboles”) that sometimes contain small amounts of zircon-bearing volcanic ash. Of >150 such samples collected over three field excursions, ~25 redboles spanning >90% of Deccan Traps stratigraphy have yielded zircon. We combine age data with stratigraphic constraints and zircon geochemistry to inform best estimates for each sample’s eruption date, with uncertainties typically <±50 kyr (2σ). These data are used to test existing regional stratigraphic correlations and build an age model for the Deccan eruptions.
Our results are consistent with recently published U-Pb and 40Ar/39Ar geochronological data that demonstrate the majority of Deccan Traps basalt erupted in ~700 kyr, beginning near the C30n/C29r magnetic reversal, ~250 kyr before the main extinction event. We find that while our data can be used to resolve the tempo and duration of magmatic activity from individual stratigraphic sections, uncertainties in stratigraphic correlation present a challenge to quantifying eruption rates. Therefore, despite the extensive number of excellent geologic studies thus far undertaken in the Deccan Traps, additional mapping, stratigraphy, geochemistry, and geochronology may be required before calculating robust volumetric eruptions rates is tenable. Such data are essential to test models that address the effect of Deccan eruptions on the biosphere and carbon cycle on 100 kyr timescales, and to test proposed linkages between the Deccan Traps, the end-Cretaceous extinction, and Chicxulub impact.