We have measured ³He/⁴He ratios and He and Ne concentrations on a suite of 24 basalt glasses from the neovolcanic zone of the Juan de Fuca Ridge (JdFR) from 44.6°N near the Blanco Transform up to 48.0°N on the Endeavour Segment. The helium isotope ratios exhibit a clear geographic variation,...
The basement of the Tonga intraoceanic forearc comprises Eocene arc volcanic crust formed during the earliest phases of subduction. Volcanic rocks recovered from the forearc include boninites and arc tholeiites, apparently erupted into and upon older mid-oceanic ridge tholeiites. Rock assemblages suggest that the forearc basement is a likely analog...
We report new major element, trace element, isotope ratio, and geochronological data on the Galapagos
Archipelago. Magmas erupted from the large western volcanos are generally moderately fractionated tholeiites of
uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic
basanitoids. While these volcanoes do not...
Cobb hotspot, currently located beneath Axial seamount on the Juan de Fuca ridge, has the temporal
but not the isotopic characteristics usually attributed to a mantle plume. The earlier volcanic products of
the hotspot, from eight volcanoes in the Cobb-Eickelberg seamount (CES) chain, show a westward age
progression away from...
The Marquesas archipelago is a short. NW-SE trending cluster of islands and seamounts that formed as a result of volcanic activity over a weak hotspot. This volcanic chain lies at the northern margin of a broad region of warm and compositionally diverse mantle that melts to build several other subparallel...
Determination of reliable crystallization ages by
K-Ar methods for young (<1 Ma), fresh basalts from the
seafloor has been frustrated by several effects. The small
amounts of radiogenic ⁴⁰Ar developed over these timescales in
such low-K rocks are difficult to resolve from predominantly
atmospheric ⁴⁰Ar. An additional concern is that...