HR: 14:10h
AN: V43D-02    [Abstracts]
TI: Style, Magnitude, and Rate of Deccan Lava Super-eruptions at K-T Boundary Times
AU: * Self, S
EM: stephen.self@open.ac.uk
AF: Department of Earth Sciences, The Open University , Milton Keynes, MK7 6AA United Kingdom
AU: Jay, A E
EM: a.e.jay@open.ac.uk
AF: Department of Earth Sciences, The Open University , Milton Keynes, MK7 6AA United Kingdom
AU: Widdowson, M
EM: m.widdowson@open.ac.uk
AF: Department of Earth Sciences, The Open University , Milton Keynes, MK7 6AA United Kingdom
AU: Kelley, S P
EM: s.p.kelley@open.ac.uk
AF: Department of Earth Sciences, The Open University , Milton Keynes, MK7 6AA United Kingdom
AB: A study of 100s of individual lava flow units exposed in sections through the upper part of the main Deccan basaltic lava pile includes flow fields that were being erupted across the K-T boundary, about 65 Ma ago. Pahoehoe flow fields (the products of one eruption), each commonly 50 m, and exceptionally 80 m, thick, dominate the pile in the central Western Ghats region. The main landscape-builders are inflated sheet lobes between 15-30 m (occasionally 50 m) thick, with subordinate smaller inflated lobes and units down to the size of toes. These are typical tholeiitic pahoehoe sheet lobes, similar to those found in many other flood basalt provinces. Defining flow fields by several criteria permits an estimate of how many eruptions built up this portion of the Deccan pile, which is 30-40 in number. Based on the extent of the formations, some of the lava fields may be the longest yet described on Earth (1000 km). All formations studied have the same style lava flows, and, thus, fissure-fed, pahoehoe-flow-forming effusive volcanism dominated. Evidence from inter-flow horizons suggests extensive explosive activity also accompanied some eruptions (cf. Icelandic eruptions such as Eldgja AD 934). The 1,200-m-thick lava pile can be assigned to Deccan Group formations in the Wai Sub-group (WSG) by compositional fingerprinting, to the paleomagnetic timescale by polarity and declination measurements, and, by cross-correlation, to the radiometric time scale. During eruptions that built up the WSG lavas, which encompass the K-T boundary and the slightly younger paleomagnetic chron 29R-N boundary, the widespread nature of the formations attests that enormous volumes of lava were produced during each eruption. Volumes of eruptive units (flow fields) exceeded 2,000, and probably 5,000, cubic km of lava, and this was likely repeated in most eruptive events, each lasting many years. The age span of the WSG series of lava eruptions was so short that it falls within the errors of radiometric age dates on the flows; if it was about 300,000 years the average eruption frequency was one every 10,000 years, or slightly less. How this series of huge-volume, prolonged lava-forming eruptions affected the global environment remains to be determined.
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms and flow emplacement
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005