Chemical composition of basement rocks from ODP Leg 121, Ninetyeast Ridge

• Main Authors: Weis, D, Frey, Frederick A, Saunders, A, Gibson, Ian L
• Format: Dataset
• Language: English
• Published: PANGAEA 1991
• Subjects: 121-756D; 121-757C; 121-758A; DRILL; Drilling/drill rig; Indian Ocean; Joides Resolution; Leg121; Ocean Drilling Program; ODP; South Indian Ridge; South Indian Ocean; Kerguelen; Heard Island; Indian; Southeast Indian Ridge; Long Ridge
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.711816; https://doi.org/10.1594/PANGAEA.711816

Data and observation from Drifting Program Leg 121 and plate-tectonic reconstructions indicate that the Ninetyeast Ridge (Indian Ocean) was derived from the interaction of a deep-seated Dupal hotspot and a nearby spreading-ridge axis. The 5000-km-long ridge, from lat 34°S to lat 10°N, was drilled at three sites during Leg 121. About 178 m of basalt, >38 to >80 Ma, were recovered from a total penetration of ~310 m. Shipboard petrographic and geochemical studies showed that each site has distinctive characteristics. Most of the cored lavas have a tholeiitic basalt composition. Incompatible-element abundanes and ratios show systematic trends, consistent with an origin for the Ninetyeast Ridge lavas by mixing between a depleted component-Indian Ocean mid-ocean ridge basalt-and an enriched component-oceanic-island basalt similar to that observed in the youngest alkalic basalts from the Kerguelen archipelago. Preliminary shore-based trace element abundance and isotopic data are compatible with this hypothesis, although Pb isotopes indicate the involvement of another component. The long-lasting and more or less continuous activity of the Kerguelen-Heard plume (ca. 115 Ma), now located under Heard Island, south of the Southeast Indian Ridge, provides evidence that the source of the Dupal anomaly is deep seated.