Major and trace element variations in basalts from Leg 115

Abstract

Basalts recovered from Sites 706 (34 Ma), 707 (64 Ma), 713 (49 Ma), and 715 (57 Ma) along the Deccan-Reunion hot spot lineament are all tholeiitic, with differentiation indexes varying from 16 to 31 and magnesium ratios from 31 to 64. They are predominantly porphyritic, and phenocryst assemblages at Sites 706, 707, and 713 dominated by plagioclase, with subordinate augite and minor olivine. Site 715 lavas, which include the most mafic varieties found on Leg 115, are almost exclusively olivine-phyric. In terms of compatible major and trace elements, Sites 706, 707, and 713 comprise mildly differentiated suites with variation controlled by limited shallow-level fractionation of plagioclase + augite ± olivine. Incompatible-element abundances and ratios suggest, however, that two separate magma types with variably developed Mid-Ocean Ridge basalt (MORB) and oceanic-island basalt (OIB) characteristics may be present at these sites. Site 715 basalts, in contrast, show OIB affinities, approximating the Reunion compositions. -from Author