HR: 0800h
AN: V21B-0608    [Abstracts]
TI: Geochemistry of Basaltic Dikes From the Northwestern Deccan Volcanic Province: Chemostratigraphic Implications
AU: * Bondre, N R
EM: bondren1@muohio.edu
AF: Department of Geology, Miami University, 114 Shideler Hall, Oxford, OH 45056 United States
AB: Basaltic dikes occurring in the northwestern part of the Deccan Volcanic Province (DVP) remain poorly studied; yet, their position within the province is important since this region has been postulated to be the source for most of the Deccan lavas. In the Sangamner region of the northwestern DVP, more than 30 dikes and at least 1 sill intrude the Thakurvadi Formation, which is part of the oldest Kalsubai subgroup. This study focuses on the geochemistry of these intrusives and seeks to understand their relationship to the flows that they intrude, and to other flows in the DVP. The ultimate objective is to attempt to place the instrusive suite into a chemostratigraphic context in order to address broader issues such as the location of potential feeders and the evolution of the magmatic plumbing system. Most dikes trend NE-SW or E-W, and range in thickness from 5-18 m. 25 dikes and a sill were analyzed for major and selected trace elements in order to relate them to existing DVP chemostratigraphy, as well as to identify chemical groups within the dikes. High MgO ($>$ 8%) and low MgO ($<$ 7%) groups are readily distinguished. Within this context, further subgroups are identified based primarily on concentrations and ratios of elements such as Fe, Ti, Nb, Y, and Zr. A combination of geochemical characteristics was used to assign the intrusives to particular subgroups within the established DVP chemostratigraphy and to individual formations in some cases. The high MgO group (including the picritic sill) is assigned to either the Thakurvadi or the Bushe formations. Most dikes belonging to the low MgO group are assigned to either of the Poladpur, Bhimashankar, or Khandala formations. Three dikes belonging to this group have chemical characters similar to the Giant Plagioclase Basalts, which separate each of the older formations (although they lack the typical plagioclase mega-phenocrysts). These data highlight the compositional diversity of the intrusives in this region. They suggest that while some dikes could have been feeders to the flows that they intrude, most dikes probably fed younger formations or were simply late stage intrusions of magmas representing the younger formations. The dikes are presently under investigation for radiogenic isotopes and REE in order to better constrain their stratigraphic affiliation as well as to understand their petrogenesis.
DE: 1099 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting