Rare gas systematics on Lucky Strike basalts (37°N, North Atlantic): Evidence for efficient homogenization in a long-lived magma chamber system?

Abstract

We present rare gas data in fresh glasses from the Lucky Strike segment located on the Mid Atlantic Ridge (∼37.3N), close to the Azores plateau. We analyzed the helium and neon isotopes in 28 samples by melting as well as He-Ne-Ar-Kr-Xe isotopes in 9 samples by crushing. Samples were collected during the Graviluck06, MOMAR08, and Bathyluck09 cruises over a ridge length of ∼13 km (mean sample spacing of ∼500 m), and at depths ranging from 1550 m to 2174 m. The helium isotopic ratio varies between 84,410 and 88,235 (R/Ra between 8.19 and 8.56). The samples having the "most" primitive helium isotopic ratio are the enriched samples (e.g. high K 2 O/TiO 2) although the difference to the depleted samples is small. It appears that all of our samples derive from the same and well-homogenized magma chamber. Neon isotopes clearly show the influence of the Azores hotspot, which is not seen with helium because of lower 3 He/ 22 Ne in the plume source compared to the MORB source. Copyright 2011 by the American Geophysical Union.