HR: 1340h
AN: V33B-1395    [Abstracts]
TI: Geochemistry of Deccan Traps Dikes: Insights Into the Evolution of a Flood Basalt Feeder System
AU: * Mahoney, J J
EM: jmahoney@hawaii.edu
AF: SOEST, Geology and Geophysics Dept., University of Hawaii, Honolulu, HI 96822, United States
AU: Vanderkluysen, L
AF: SOEST, Geology and Geophysics Dept., University of Hawaii, Honolulu, HI 96822, United States
AU: Hooper, P R
AF: Geology Dept., Washington State University, Pullman, WA 99162, United States
AU: Sheth, H C
AF: Earth Sciences Dept., Indian Institute of Technology, Mumbai, 400 076, India
AU: Ray, R
AF: Earth Sciences Dept., Indian Institute of Technology, Mumbai, 400 076, India
AB: Three large dike swarms are exposed in the 500,000 km² Deccan Traps of India: the dominantly N-S trending West Coast swarm, the ENE-WSW trending Narmada-Tapi swarm in the northern Deccan, and the Nasik-Pune swarm in the central western Deccan. Dikes of the Nasik-Pune swarm show no strongly preferred trend. This swarm is commonly postulated (e.g., Hooper, Nature, 349, 246, 1990) to be the principal locus of feeders for the lava pile, and the lack of a preferred trend taken as evidence that the flood volcanism was not accompanied by significant rifting-related lithospheric extension. Our combined major and trace element and Pb-Nd-Sr isotope data reveal that dikes with signatures matching those of the three major lava formations in the upper part of the lava pile (Poladpur, Ambenali, and Mahabaleshwar formations) are abundant in the coastal and Nasik-Pune swarms. As a group, these dikes have no preferred trend. Dikes with similarities to formations lower in the lava stratigraphy (i.e., the Igatpuri, Jawhar, and Bushe formations) are present but rare in these two swarms. However, many dikes with strong affinities to the lower and middle lava formations (e.g., Igatpuri, Jawhar, Bushe, and Thakurvadi formations) are present in the Narmada-Tapi swarm. These dikes have geometries indicative of N-S extension. We infer that rifting did not drive emplacement of the upper lava formations, but was occurring in the Narmada-Tapi region during the earlier phases of volcanism. Thus, N-S rifting cannot be ruled out as a trigger mechanism for the massive melting event. In contrast, our data provide no evidence that E-W extension along the coast triggered the event.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 9320 Asia
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting