Eastern Indian Ocean DSDP sites: Correlations between petrography, geochemistry and tectonic setting

The hydrothermal alteration of oceanic basalts by seawater

“…This constancy during alteration is of particular interest due to the recent use of these elements, together with titanium, for the identification of the original tectonic setting of basic volcanic rocks (Pearce and Cann, 1971;Frey et al, 1976). These workers have compared the trace element concentrations in rocks from known tectonic settings with those whose origin is unknown.…”

Leg 121 Background and Objectives

“…Relatively "evolved" lavas may characterize Ninetyeast Ridge. At Sites 214 and 216 the recovered lavas are ferrobasalts, and at Site 214 these are overlain by oceanic andesite (e.g., Frey et al, 1977;Ludden et al, 1980). When coupled with the northward age increase of the uppermost basement, the isotopic data favor formation of Ninetyeast Ridge as a hot-spot trace resulting from the northward movement of the Indian plate over a hot spot related to Kerguelen Island (Duncan, 1978;Mahoney et al, 1983).…”

“…The ridge is in local isostatic compensation (Bowin, 1973), which suggests that it formed on young, weak oceanic crust; this is in contrast to Hawaii, where the surrounding gravity anomalies and moat are evidence of volcanic loading on a relatively strong oceanic crust. Basement paleolatitudes are all near 50°S (Peirce, 1978), and the basalt geochemistry is similar to that of lavas from oceanic islands, particularly Kerguelen Island (Frey et al, 1977;Weis et al, 1987).…”

Isotope Geochemistry of Leg 115 Basalts and Inferences on the History of the Réunion Mantle Plume

“…Trace element geochemistry of samples from the Ninetyeast Ridge is uniform and similar to that of oceanic-island basalt (OIB), except at Deep Sea Drilling Project (DSDP) Site 253, where basalts have affinities to mid-ocean ridge basalts (MORB) (Frey et al, 1977). The e Nd values vary from 1.5 to 6.5, with no apparent systematic relationship to age (Mahoney et al, 1983).…”