Basalts of the northeastern Deccan Traps, India: Isotopic and elemental geochemistry and relation to southwestern Deccan stratigraphy

The northeastern Deccan Traps include flows with strong isotopic and elemen tal affinities to lavas in the southwest as far as 900 km away. However, ma ny of the northeastern flows show a negative correlation of Pb-206/Pb-204 W ith epsilon(Nd)(t) and positive correlation of Pb-206/Pb-204 with (Sr-87/Sr -86)(t), distinct from any of the isotopic fields for the southwestern form ations; this array (from epsilon(Nd)(t) = +5, (Sr-87/Sr-86)(t) = 0.7041, Pb -206/Pb-204 = 17.9 to epsilon(Nd)(t) = 0, (Sr-87/Sr-86)(t) = 0.7068, Pb-206 /Pb-204 = 20.5) overlaps the Ambenali Formation (Fm.) field and runs toward that of the "common signature" [Peng et al., 1994] that appears to have be en an important magma type in several of the lower formations of the southw est. This array appears to represent mixing between an Ambenali-type and(1) a common-signature end-member or (2) an end-member with even higher Pb-206 /Pb-204 and Sr-87/Sr-86 and lower epsilon(Nd) than the common signature; su ch mixing has been postulated, but not documented previously, for the Decca n. Lavas isotopically and chemically indistinguishable from the Ambenali Fm . form the tops of sections near Jabalpur and Chikaldara. Beneath them are flows that chemically resemble the Poladpur Fm. (which sits immediately bel ow the Ambenali in the southwest) and several lavas similar to the Khandala Fm. (beneath the Poladpur and intervening Bushe Fm, in the southwest). Giv en the general stratigraphic correspondence with the southwestern sequence, many of these northeastern flows may be petrogenetically related to the re spective southwestern formations. Lavas with broadly Poladpur- and Khandala -like elemental compositions are also abundant in a thick section south of Mhow; several other Mhow-area flows resemble the distinctive Bushe Fm. Howe ver, nearly all of the Poladpur- and Khandala-like northeastern Deccan lava s analyzed have higher Pb-206/Pb-204 than any southwestern Poladpur or Khan dala Fm. basalts. If they indeed are related petrogenetically to these form ations, many of the northeastern magmas interacted less with low-Pb-206/Pb- 204 continental material and thus must have erupted from different feeder s ystems.