Publication Date:
2009-05-09
Description:
Carbonatite lavas are highly unusual in that they contain almost no SiO(2) and are 〉50 per cent carbonate minerals. Although carbonatite magmatism has occurred throughout Earth's history, Oldoinyo Lengai, in Tanzania, is the only currently active volcano producing these exotic rocks. Here we show that volcanic gases captured during an eruptive episode at Oldoinyo Lengai are indistinguishable from those emitted along mid-ocean ridges, despite the fact that Oldoinyo Lengai carbonatites occur in a setting far removed from oceanic spreading centres. In contrast to lithophile trace elements, which are highly fractionated by the immiscible phase separation that produces these carbonatites, volatiles (CO(2), He, N(2) and Ar) are little affected by this process. Our results demonstrate that a globally homogenous reservoir exists in the upper mantle and supplies volatiles to both mid-ocean ridges and continental rifts. This argues against an unusually C-rich mantle being responsible for the genesis of Na-rich carbonatite and its nephelinite source magma at Oldoinyo Lengai. Rather, these carbonatites are formed in the shallow crust by immiscibility from silicate magmas (nephelinite), and are stable under eruption conditions as a result of their high Na contents.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fischer, T P -- Burnard, P -- Marty, B -- Hilton, D R -- Furi, E -- Palhol, F -- Sharp, Z D -- Mangasini, F -- England -- Nature. 2009 May 7;459(7243):77-80. doi: 10.1038/nature07977.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, MSC03 2040, 1 University of New Mexico, New Mexico 87131-0001, USA. fischer@unm.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19424154" target="_blank"〉PubMed〈/a〉
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
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Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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