V41C-3084
High-Precision 40Ar/39Ar dating of the Deccan Traps
Thursday, 17 December 2015
Poster Hall (Moscone South)
Courtney Jean Sprain1,2, Paul R. Renne1,2, Mark A Richards3, Stephen Self4, Loÿc Vanderkluysen5, Kanchan Pande6, Leah E Morgan7 and Michael A Cosca8, (1)Berkeley Geochronology Center, Berkeley, CA, United States, (2)University of California Berkeley, Earth and Planetary Science, Berkeley, CA, United States, (3)University of California Berkeley, Berkeley, CA, United States, (4)Organization Not Listed, Washington, DC, United States, (5)Drexel University, Biodiversity, Earth & Environmental Science, Philadelphia, PA, United States, (6)Indian Institute of Technology Bombay, Mumbai, India, (7)University of Glasgow, Glasgow, United Kingdom, (8)USGS, Denver, CO, United States
Abstract:
The Deccan Traps (DT) have been strongly implicated over the past thirty years as a potential cause of the mass extinctions at the Cretaceous-Paleogene boundary (KPB). While a broad coincidence between the DT eruptions and the KPB is increasingly clear, variables such as tempo, volume of eruptions, and amount of associated climate-modifying volatiles, are too poorly constrained to properly assess causality. In order to appropriately test whether the DT played a role in the mass extinctions a high-precision geochronologic framework defining the timing and tempo of volcanic eruptions is needed. Recent high-precision U/Pb dating of zircons from inferred paleosols (red boles) and melt segregation horizons is the only available geochronology of the DT that is sufficiently precise to resolve age differences of less than 100 ka (Schoene et al., 2015). While this technique can achieve high-precision dates for individual zircon crystals, protracted age distributions may not include the actual eruption age. Moreover, the applicability of U/Pb dating in the DT is limited as suitable material is only sporadically present and therefore the technique is unlikely to achieve the resolution necessary to assess the tempo of DT eruptions. To mediate these limitations, we present new high-precision 40Ar/39Ar ages for plagioclase separated from the lava flows sampled from each of ten chemostratigraphically-defined formations within the Western Ghats. Multiple (N = 1-4) plateau ages from each sample and detailed neutron fluence monitoring during irradiation yield ages with precision commonly better than 100 ka (1 sigma). Results provide the first precise location of the KPB within the DT eruption sequence, which approximately coincides with major changes in eruption frequency, flow-field volumes, extent of crustal contamination, and degree of fractionation. Collectively, these results suggest that a state shift occurred in the DT magma system within ~50 ka of the Chicxulub impact, consistent with transient effects of seismic energy associated with the impact. Further, our new data invalidate the concept of three discrete eruption pulses in the Western Ghats (Chenet et al., 2007, 2009; Keller et al., 2008) and rather indicate only a sharp increase in mean volumetric eruption rates near the KPB.
