Carbonatite and highly peralkaline nephelinite melts from Oldoinyo Lengai Volcano, Tanzania: The role of natrite-normative fluid degassing

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dc.contributor.authorBerkesi, Martaen
dc.contributor.authorBali, Enikoen
dc.contributor.authorBodnar, Robert J.en
dc.contributor.authorSzabo, Abelen
dc.contributor.authorGuzmics, Tiboren
dc.contributor.departmentGeosciencesen
dc.date.accessioned2020-12-14T15:46:03Zen
dc.date.available2020-12-14T15:46:03Zen
dc.date.issued2020-09en
dc.description.abstractOldoinyo Lengai, located in the Gregory Rift in Tanzania, is a world-famous volcano owing to its uniqueness in producing natrocarbonatite melts and because of its extremely high CO2 flux. The volcano is constructed of highly peralkaline [PI = molar (Na2O + K2O)/Al2O3 > 2-3] nephelinite and phonolites, both of which likely coexisted with carbonate melt and a CO2-rich fluid before eruption. Results of a detailed melt inclusion study of the Oldoinyo Lengai nephelinite provide insights into the important role of degassing of CO2-rich vapor in the formation of natrocarbonatite and highly peralkaline nephelinites. Nepheline phenocrysts trapped primary melt inclusions at 750-800 degrees C, representing an evolved state of the magmas beneath Oldoinyo Lengai. Raman spectroscopy, heating-quenching experiments, low current EDS and EPMA analyses of quenched melt inclusions suggest that at this temperature, a dominantly natritess-normative, F-rich (7-14 wt%) carbonate melt and an extremely peralkaline (PI = 3.2-7.9), iron-rich nephelinite melt coexisted following degassing of a CO2+H2O-vapor. We furthermore hypothesize that the degassing led to re-equilibration between the melt and liquid phases that remained and involved 1/mixing between the residual (after degassing) alkali carbonate liquid and an F-rich carbonate melt and 2/enrichment of the coexisting nephelinite melt in alkalis. We suggest that in the geological past similar processes were responsible for generating highly peralkaline silicate melts in continental rift tectonic settings worldwide. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of International Association for Gondwana Research.en
dc.description.notesThis study was financially supported by project NRDIO (National Research, Development, and Innovation Office of Hungary) K-119535 (to M. Berkesi and T. Guzmics) and by the Betta Uzletlanc Ltd. to Guzmics. In addition, M. Berkesi acknowledges to the ELTE Institutional Excellence Program (1783-3/2018/FEKUTSRAT) supported by the Hungarian Ministry of Human Capacities. We thank Toshiaki Tsunogae for his editorial handling, and Alan Cooper and an anonymous reviewer for their constructive comments that helped to improve the manuscript.en
dc.description.sponsorshipproject NRDIO (National Research, Development, and Innovation Office of Hungary) [K-119535]; Betta Uzletlanc Ltd.; Hungarian Ministry of Human Capacities [1783-3/2018/FEKUTSRAT]en
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1016/j.gr.2020.03.013en
dc.identifier.eissn1878-0571en
dc.identifier.issn1342-937Xen
dc.identifier.urihttp://hdl.handle.net/10919/101111en
dc.identifier.volume85en
dc.language.isoenen
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en
dc.titleCarbonatite and highly peralkaline nephelinite melts from Oldoinyo Lengai Volcano, Tanzania: The role of natrite-normative fluid degassingen
dc.title.serialGondwana Researchen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten
dc.type.dcmitypeStillImageen

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