Other
Scientific paper
Aug 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011e%26psl.308...52g&link_type=abstract
Earth and Planetary Science Letters, Volume 308, Issue 1, p. 52-64.
Other
Sylhet Traps, Kerguelen Plume, Nd–Sr–Pb, Trace-Major Element Geochemistry, Rajmahal Basalts
Scientific paper
The 117 Ma Sylhet Traps, exposed on the southern edge of the Shillong Plateau in northeastern India, are separated from the Rajmahal Traps ~ 550 km to the west by the Gangetic-Brahmaputra alluvium of the Bengal basin. On the basis of their similar age, Sylhet and Rajmahal Traps are correlated. We report Nd-Sr-Pb-isotopic and multiple trace element data for 18 discrete and consecutive lava flows from two sections of the Sylhet Traps. Thirteen of the analyzed lavas are from the Cherrapunji-Shella (CH) Bazaar section and five from the Mawsynram-Balot (MB) section. In major, trace elements and Nd-Sr-Pb isotopes, most of these lavas show similarity with Rajmahal Traps, Bunbury basalts and lavas from Naturaliste and parts of the Kerguelen Plateaus, allowing reconstruction of a ~ 800 km Kerguelen plume-head in the Bengal basin aligned with the Ninetyeast Ridge.The combined geochemical data and their correlation with the Rajmahal Traps, Bunbury basalts, and some Kerguelen Plateau lavas, imply a relatively less depleted plume source for CH basalts. We assess the average composition of this source at 117 Ma to be: ɛNd(I) = 2, 87Sr/86Sr(I) = 0.7046, with relatively flat rare earth element patterns, similar to the basalts from the Ocean Drilling Sites 1138, 1141 and 1142 on the Kerguelen Plateau. The Nd-Sr-isotopic data for the Sylhet basalts are modeled with two end members, an 18% partial melt from a chondritic garnet peridotite source, and a granulitic contaminant of the Eastern Ghats Belt. Most of the Sylhet lavas are close to the proposed plume end-member. The contaminated Sylhet basalts reflect as much as 20% of the granulite component caused by the incorporation of lower-continental crust in the Kerguelen plume-derived melt.Combined Nd-Sr-Pb-isotopic evidence, and, in particular, Ce/Pb vs. ɛNd(I) mixing-models among different reservoirs indicate more primitive CH lavas to be mixture of bulk-chondritic Earth and E-MORB, without apparent mixing with N-MORB, continental crust, or non-chondritic bulk Earth. However, Sr-Pb-isotopic ratios of these lavas fall in the estimated ranges of non-chondritic bulk Earth. The least contaminated Kerguelen plume component may be common to other large igneous provinces.
Basu Asish R.
Ghatak Arundhuti
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