Cenozoic Evolution of the Iceland Hotspot Reveals a Temporal Shift in the Composition of the Primordial Component
Abstract
The Iceland hotspot has been active over most of the Cenozoic, beginning with eruption of the Baffin Island-West Greenland flood basalt province at 62 Ma and presently erupting in the Neovolcanic Zones of Iceland. An outstanding feature of the Icelandic hotspot is that it has erupted lavas with elevated 3He/4He over its entire history. High-3He/4He ratios reflect the preservation of ancient, relatively un-degassed, domains in Earth's interior: 3He/4He of up to 49.8 Ra (ratio to atmosphere) are found in the Baffin Island-West Greenland flood basalt province, while 3He/4He up to 43 Ra (or possibly 47.5 Ra) are found in the mid-Miocene lavas of northwest Iceland and up to 34.3 Ra in the Pleistocene Neovolcanic Zone lavas. However, the high 3He/4He lavas from mainland Iceland remain inadequately characterized. We present new Sr-Nd-Pb-Hf-He-O isotopic data on a suite of lavas from northwest Iceland (with 3He/4He ratios ranging up to 43 Ra) and a suite of Pleistocene lavas from the South Iceland Volcanic Zone (with 3He/4He ranging up to 25 Ra). A key observation is that, after filtering Baffin Island lavas for continental crustal contamination, the least contaminated lavas have more geochemically depleted 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf, and less radiogenic Pb isotopic compositions, than lavas with elevated 3He/4He from northwest Iceland and the South Iceland Volcanic Zone. This observation is consistent with the highest 3He/4He Icelandic hotspot lavas from Baffin Island hosting a smaller amount of recycled materials than lavas from northwest Iceland, because recycled crustal materials lower 3He/4He and contribute geochemically enriched Sr-Nd-Pb isotopic compositions and radiogenic Pb. Additionally, we find that, in 3He/4He versus Sr, Nd, Hf, and Pb isotopic space, the extrapolated arrays formed by the least contaminated Baffin Island lavas do not converge on the same high-3He/4He endmember as the extrapolated arrays from northwest Iceland and the South Iceland Volcanic Zone. This argues against a common high-3He/4He component in the Iceland plume, which may be the result of progressive addition of recycled crustal materials to the high-3He/4He mantle component.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V23H0202J
- Keywords:
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- 1011 Thermodynamics;
- GEOCHEMISTRY;
- 1042 Mineral and crystal chemistry;
- GEOCHEMISTRY;
- 8124 Earth's interior: composition and state;
- TECTONOPHYSICS;
- 8178 Tectonics and magmatism;
- TECTONOPHYSICS