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Hot and Heterogenous High‐ 3 He/ 4 He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island
The Icelandic hotspot has erupted basaltic magma with the highest mantle‐derived 3 He/ 4 He over a period spanning much of the Cenozoic, from the early‐Cenozoic Baffin Island‐West Greenland flood basalt province (49.8 R A ), to mid‐Miocene lavas in northwest Iceland (40.2 to 47.5 R A ), to Pleistoce...
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Published in: | Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2019-12, Vol.20 (12), p.5939-5967 |
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Main Authors: | , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
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Summary: | The Icelandic hotspot has erupted basaltic magma with the highest mantle‐derived
3
He/
4
He over a period spanning much of the Cenozoic, from the early‐Cenozoic Baffin Island‐West Greenland flood basalt province (49.8
R
A
), to mid‐Miocene lavas in northwest Iceland (40.2 to 47.5
R
A
), to Pleistocene lavas in Iceland's neovolcanic zone (34.3
R
A
). The Baffin Island lavas transited through and potentially assimilated variable amounts of Precambrian continental basement. We use geochemical indicators sensitive to continental crust assimilation (Nb/Th, Ce/Pb, MgO) to identify the least crustally contaminated lavas. Four lavas, identified as “least crustally contaminated,” have high MgO (>15 wt.%), and Nb/Th and Ce/Pb that fall within the mantle range (Nb/Th = 15.6 ± 2.6, Ce/Pb = 24.3 ± 4.3). These lavas have
87
Sr/
86
Sr = 0.703008–0.703021,
143
Nd/
144
Nd = 0.513094–0.513128,
176
Hf/
177
Hf = 0.283265–0.283284,
206
Pb/
204
Pb = 17.7560–17.9375,
3
He/
4
He up to 39.9
R
A
, and mantle‐like δ
18
O of 5.03–5.21‰. The radiogenic isotopic compositions of the least crustally contaminated lavas are more geochemically depleted than Iceland high‐
3
He/
4
He lavas, a shift that cannot be explained by continental crust assimilation in the Baffin suite. Thus, we argue for the presence of
two
geochemically distinct high‐
3
He/
4
He components within the Iceland plume. Additionally, the least crustally contaminated primary melts from Baffin Island‐West Greenland have higher mantle potential temperatures (1510 to 1630 °C) than Siqueiros mid‐ocean ridge basalts (1300 to 1410 °C), which attests to a hot, buoyant plume origin for early Iceland plume lavas. These observations support the contention that the geochemically heterogeneous high‐
3
He/
4
He domain is dense, located in the deep mantle, and sampled by only the hottest plumes.
Baffin Island‐West Greenland high‐
3
He/
4
He lavas are more geochemically depleted than any other high‐
3
He/
4
He lavas globally
The isotopic composition of the high‐
3
He/
4
He mantle source in the Iceland plume has evolved through time
Baffin Island and West Greenland primary melts record hotter temperatures than high‐MgO MORB, consistent with a deep, dense plume source |
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ISSN: | 1525-2027 1525-2027 |
DOI: | 10.1029/2019GC008654 |