Collaborative Research: Storage Duration of Giant Plagioclase Basalts, Deccan Traps, India

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Intellectual Merit. The bulk of the voluminous Deccan (India) flood basalts erupted at the K/T boundary, a major stratigraphic boundary associated with a major faunal extinction (e.g., the dinosaurs). Hence, there is a great deal of interest in understanding how long the Deccan eruption lasted and what impact it had on biotic evolution. Conventional dating techniques (40Ar/39Ar, K/Ar methods) have an uncertainty of +/- 0.5 m.y., and thus we do not know whether the whole eruption lasted a few years, 100 kyr, or 500 kyr! Preliminary calculations based on crystal growth rate data suggest that the most voluminous lava package from the Western Ghats region could have been erupted in as little as 50 kyr, corresponding to a phenomenal eruption rate. The present project is a pilot study aimed at evaluating a technique (time-dependent relaxation of diffusion profiles of elements across compositional zones in giant plagioclase phenocrysts) that may eventually provide an independent method for quantifying the duration of activities of individual Deccan magma chambers. Compositional profiles across large complexly zoned plagioclase crystals will also be utilized to evaluate their potential as 'micro-stratigraphic' correlations between crystals carried in successive lava flows to investigate magma chamber models - that is, do successive lavas erupt from long-lived dynamic reservoirs that underwent multiple episodes of magma emplacement, recharge, recharge, and extrusion. This work will entail detailed petrographic and crystal-size distribution studies coupled with high precision trace element (Mg, Fe, Sr) and 87Sr/86Sr profiles across compositional zones in individual phenocrysts using microdrill and Laser-ablation ICP-MS at work at Washington State University and electron microprobe analysis at Florida International University (FIU).Broader impacts. An appealing aspect of the proposed study is its potential to deliver time-resolution that is not attainable with current isotopic and paleomagnetic methods. FIU is a minority institution. The project will involve the education and training of a doctoral student (Melroy Borges) and likely will involve one part-time undergraduate (Kevin Chau). The proposed work will promote collaborations between investigators at several institutions in the US and India.