HELIUM, ARGON, AND XENON IN CRUSHED AND MELTED MORB

Abstract

Helium, argon, and xenon were measured in vesicles of MORB from a variety of locations and in sequential crushing steps in two locations. Melting extractions, compared to these data, indicate that most of the trapped radiogenic gases are contained in the glass matrix and that vesicle/glass equilibrium has not been reached. 4He40Ar∗ ratios (where the asterisk indicates the radiogenic component) are clearly a function of eruption depth, a fact that I interpret in terms of the Klein/Langmuir model. Within individual samples, they correlate with 36Ar40Ar∗, indicating that some of the helium is included in the atmospheric-like contamination that is inherited in a diffusion process immediately prior to eruption. The previously documented 129Xe anomaly is not seen in these samples, suggesting that it may not be ubiquitous in MORB.