HR: 0800h
AN: V51B-0545    [Abstracts]
TI: 40Ar/39Ar Geochronology of the Sylhet Traps, Eastern India, and their relationship to the Kerguelen Plume related magmatism
AU: * Ray, J S
EM: jsray@prl.ernet.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380009 India
AU: Pande, K
EM: kanchanpande@iitb.ac.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380009 India
AB: It is now an accepted view that the Rajmahal-Bengal flood basalts of eastern India belong to the Kerguelen plume generated Large Igneous Province (LIP) that encompasses the Bunbury-Naturaliste Plateau basalts of western Australia, volcanism on the southern and central Kerguelen Plateau, Elan Blank, and Broken Ridge in the Indian Ocean (e.g., Kent et al., J. Petrol., 43, 2002). The lesser-known Sylhet Traps (25.5$^{o}$ N, 91.8$^{o}$ E), exposed ${\sim}$400 km east of the Rajmahal Traps, are assumed to be a part of the ${\sim}$118 Ma old Rajmahal-Bengal flood basalt province (e.g., Bakshi, Chem. Geol., 121, 1995). However, absence of physical continuity between these volcanic activities, and more importantly lack of precise age data always created difficulty in correlations. In an attempt to test the hypothesis of their cogenesis we dated the Sylhet Traps using $^{40}$Ar/$^{39}$Ar incremental-heating technique. Two whole rock samples yielded good plateau ages: 115.9{$\pm$}4.1 (2{$\sigma$}) Ma, and 115.5{$\pm$}5.4 (2{$\sigma$}) Ma, calibrated against an age of 523.2{$\pm$}0.9 Ma for the Minnesota Hornblende (MMhb-1; Spell and McDougall, Chem. Geol., 198, 2003). The concordant plateau, isochron and inverse isochron ages, the atmospheric value for the trapped $^{40}$Ar/$^{36}$Ar component, and good MSWD values for the isochrons suggest that 115.8{$\pm$}3.2 Ma (the weighted mean of both the ages) can be considered as the age of crystallization. This age for the Sylhet Traps clearly falls within the range of ages reported for various groups of lavas in the Rajmahal-Bengal province (118-115), and is consistent with the idea that magmatism in this part of India continued well beyond the major pulse at ${\sim}$118 Ma (e.g., Kent et al., J. Petrol., 43, 2002). It also supports the proposal based on geochronology and geochemistry that the Kerguelen hotspot was located close to the eastern Indian margin during its peak activity (e.g., Kumar et al., Geophys. Res. Lett., 30, 2003).
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 1749 Volcanology, geochemistry, and petrology
DE: 1035 Geochronology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting