Friday seminars of Institute of Earth Sciences and Nordic Volcanological Center 24. November at 12:30 - Sunna Harðardóttir


Sunna Harðardóttir, PhD Candidate, Department of Earth Science, University of California-Santa Barbara

"Isotope variability in global ocean island basalts: a highly biased dataset focused on high buoyancy-flux hotspots"

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List of Friday seminars of Institute of Earth Sciences and Nordic Volcanological Center



A comprehensive geochemical ocean island basalt (OIB) database for 48 oceanic hotspots that includes previously published isotope data for 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 187Os/188Os, 3He/4He, and δ18O as well as supporting information about major and trace element chemistry of the lavas, sample locality, analytical methods, and data references will be presented. The database is used to systematically investigate isotope variability in global OIB, and the relationships between different radiogenic isotopes, and their relationships with major and trace elements. A key finding is that EM lavas are found in only low MgO lavas, while HIMU and high 3He/4He lavas (> 20 RA) are found in a wide range of MgO. Additionally, our analyses demonstrate that compositional and isotope distributions of the global OIB dataset are highly biased because isotope measurements are unevenly sampled across different hotspot localities and many hotspots—which are mainly low buoyancy flux hotspots—are missing key isotope data. For example, 35% (143Nd/144Nd, 206,207,208Pb/204Pb, and 3He/4He analyses) to 45% (176Hf/177Hf) of all radiogenic isotope data in the global OIB dataset are from Hawaii and Iceland alone, leaving other oceanic hotspots woefully undersampled. Similarly, alkalic (53%) and tholeiitic (47%) OIB exist in similar proportions in the database but, if Hawaii and Iceland—the two best geochemically characterized hotspots in the global OIB database which happen to be predominantly tholeiitic—are excluded, then 74% of OIB are alkalic. In short, the high buoyancy flux, hotter plumes have been overcharacterized at the expense of the lower buoyancy flux, cooler plumes.

All are welcome.