| dc.creator |
Burnard, Pete |
|
| dc.creator |
Marty, Bernard |
|
| dc.creator |
Fischer, Tobias |
|
| dc.creator |
Hilton, David R. |
|
| dc.creator |
Mangasini, Frank |
|
| dc.creator |
Makene, C. |
|
| dc.date |
2016-07-11T11:10:41Z |
|
| dc.date |
2016-07-11T11:10:41Z |
|
| dc.date |
2006-11 |
|
| dc.date.accessioned |
2018-03-27T08:32:38Z |
|
| dc.date.available |
2018-03-27T08:32:38Z |
|
| dc.identifier |
Burnard, P., Marty, B., Fischer, T., Hilton, D., Mangasini, F. and Makene, C., 2006, December. Noble gases in carbonatite magmatism: Oldonyo Lengai. In AGU Fall Meeting Abstracts (Vol. 1, p. 0645). |
|
| dc.identifier |
http://hdl.handle.net/20.500.11810/3059 |
|
| dc.identifier.uri |
http://hdl.handle.net/20.500.11810/3059 |
|
| dc.description |
Full text can be accessed at
http://adsabs.harvard.edu/cgi-bin/nph-manage_account?man_cmd=login&man_url=http://adsabs.harvard.edu/abs/2006AGUFM.V23C0645B |
|
| dc.description |
Oldonyo Lengai,Tanzania, is the only volcano on Earth that is actively erupting carbonatitic lavas. In order to further constrain the origin of the Oldonyo Lengai magmas, an expedition to Oldonyo Lengai in July 2005 sampled to volcanic gases. Two fumaroles were sampled, one with a discharging temperature of 124 °C, the other more than 168 °C. The chemical composition of discharging gases is dominated by H2O (approx77 mol%) and CO2 (approx 22 mol%), SO2, H2S and HCl make up less than 1 mol%, combined. The inert gases (N2, He, He/Ne) show that these samples contain virtually no air. He/Ne ratios are between 2000 and 6500 and He/Ar ratios are up to 0.3 [Fischer et al, 2006, this volume]. The 3He/4He ratio of 6.7 - 6.8 Ra is consistent with an upper mantle origin of these gases. We have also measured Ne and Xe isotopic compositions of several aliquots of the sampled gases using a multicollector noble gas mass spectrometer (HELIX-MC). The additional precision afforded by multicollection allows us to identify noble gas isotopic anomalies at the sub 5 per mil level. Despite the excellent purity (low atmospheric content) of the gases, as evidenced by extremely high He/Ne ratios, the isotopic compositions of both Ne and Xe are very close to those of the atmosphere: a 2 per mil excess in 129Xe/130Xe ratio was observed (the remaining Xe isotope ratios being indistinguishable from air) and 20Ne/22Ne up to 10.3 was measured (50 per mil higher than air) in a split of the sample that has He/Ne = 6500. Although isotolically anomalous Ne was observed, it is not possible to determine if this is indeed mantle - derived Ne or if the 20Ne excesses result from kinetic fractionationed air entrained within the volcano's plumbing system: the composition of the three Ne isotopes (20Ne, 21Ne and 22Ne) are consistent with mass fractionation processes. Our results are most readily interpreted as atmospheric entrainment prior to sampling. However, further measurements of the remaining noble gases (principally the 4He/40Ar ratio) and results of on-going experiments on the solubility of noble gases in carbonatite melts will clarify this situation. |
|
| dc.language |
en |
|
| dc.subject |
Volcanic gases |
|
| dc.title |
Noble Gases in Carbonatite Magmatism: Oldonyo Lengai |
|
| dc.type |
Journal Article |
|