Data Series 202

USGS-NoGaDat – A Global Dataset of Noble Gas Concentrations and Their Isotopic Ratios in Volcanic Systems

By A.A. Abedini, S. Hurwitz, and W.C. Evans

2006

 

Introduction

Noble gases in rocks, minerals, and fluids provide unique insights to the degassing history of the Earth, the chemical heterogeneity of the mantle, and volcanic processes. The utility of noble gases towards the study of these topics is summarized in several books (Alexander and Ozima 1978; Ozima and Podosek 2002; Mamyrin and Tolstikhin 1984; Matsuda 1994) and review articles (Lupton 1983; Farley and Neroda 1998; Ozima 1994; McDougall and Honda 1998; Graham, 2002). Their value for Earth science problems arises from their lack of chemical reactivity, systematic variation in physical characteristics (e.g., solubility, diffusivity) with mass, and production by numerous radioactive decay schemes. The abundances of noble gases within Earth materials are modified only by radioactive decay and physical processes such as melting and vapor-phase transport. Measurable changes in the isotopic compositions of noble gases are closely related to the geochemical processes controlling the distribution of K, U and Th, the major heat-producing nuclides in the Earth.

In an ascending magma the noble gases will partition strongly into the first-formed vapor phase, usually nearly pure CO2. Because noble gas solubilities in silicate liquids decrease significantly with increasing atomic mass, the heavier gases will preferentially be enriched in the vapor phase. The strong partitioning of noble gases into the gas and vapor phase makes them especially useful as early indicators of magma ascent towards the ground surface. However, with the exception of He, the mantle component in geothermal gases is difficult to detect in the presence of admixed atmospheric gases. Therefore, helium isotopes are most often used in the study of magmatic degassing.

The extent to which ocean islands are derived from the deep mantle (mantle plumes), or from chemical heterogeneities embedded within the mantle convective flow has long been debated. Noble gases have unique properties that enable them to provide significant information regarding this debate and make them important geodynamic tracers. Whereas traditional models based on noble gas data hypothesized that MORB represents a broad sampling of the convecting upper mantle, the He-Ne isotope systematics of Ocean Island Basalts (OIBs) provide strong evidence of melting anomalies related to mantle upwelling from a thermal boundary layer in the deep mantle. In recent years alternatives to this model were developed around a different interpretation of mantle He isotope data.

 

Database Contents

The database (Version 1.0) is a MS-Excel file that contains close to 5,000 entries of published information on noble gas concentrations and isotopic ratios from volcanic systems in Mid-Ocean ridges, ocean islands, seamounts, and oceanic and continental arcs (location map). Where they were available we also included the isotopic ratios of strontium, neodymium, and carbon. The database is sub-divided both into material sampled (e.g., volcanic glass, different minerals, fumarole, spring), and into different tectonic settings (MOR, ocean islands, volcanic arcs). Included is also a reference list in MS-Word and pdf from which the data was derived. The database extends previous compilations by Ozima (1994), Farley and Neroda (1998), and Graham (2002). The extended database allows scientists to test competing hypotheses, and it provides a framework for analysis of noble gas data during periods of volcanic unrest.

There are six spreadsheets in the MS-Excel file:

Sample abbreviation in the database

The entries in the in the master spreadsheet appear in the following columns:

 

 

References

 

Plots of the data

Distribution of noble gas isotope ratios

 

The data base is intended to be updated periodically with new information. If relevant data are missing from the database we would appreciate any contribution. Please contact Atosa A. Abedini.


U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/ds202
Page Contact Information: Publications Team
Last modified: Wednesday, July 28 2006, 09:36:38 AM
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