Hot and Heterogenous High‐ 3 He/ 4 He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island
Hot and Heterogenous High‐ 3 He/ 4 He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island
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热且异质的高 3 He/4 He 成分：来自原始冰岛巴芬岛熔岩熔岩的新限制
DOI：
10.1029/2019gc008654
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Byerly, Benjamin L.
中科院分区：
文献类型：
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作者：
Willhite, Lori N.;Jackson, Matthew G.;Blichert‐Toft, Janne;Bindeman, Ilya;Kurz, Mark D.;Halldórsson, Sæmundur A.;Harðardóttir, Sunna;Gazel, Esteban;Price, Allison A.;Byerly, Benjamin L.
冰岛热点在新生代的大部分时间内爆发了具有最高幔源3 He/4 He的玄武岩浆，从早新生代巴芬岛-西格陵兰泛滥玄武岩区（49.8RA）到冰岛西北部的中新世熔岩（40.2至47.5RA），再到冰岛新火山区的更新世熔岩（34.3RA）。巴芬岛熔岩通过前寒武纪大陆基底，并可能同化变量。我们使用地球化学指标敏感的大陆地壳同化（Nb/Th，Ce/Pb，MgO），以确定最少的地壳污染熔岩。被确定为“地壳污染程度最低”的四个熔岩具有较高的MgO（>15重量%），Nb/Th和Ce/Pb比值为15.6 ± 2.6，Ce/Pb为24.3 ± 4.3，属于地幔范围。这些熔岩的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高达39.9RA，类地幔δ 18 O为5.03-5.21‰。地壳污染程度最低的熔岩的放射性同位素组成比冰岛的高3 He/4 He熔岩更地球化学贫化，这种转变不能用巴芬套中的大陆地壳同化来解释。因此，我们认为存在两个地球化学上不同的高-3 He/4 He组分在冰岛羽。此外，来自巴芬岛-西格陵兰的地壳污染最少的原生熔体具有比Siqueiros洋中脊玄武岩（1300至1410 ° C）更高的地幔潜在温度（1510至1630 ° C），这证明了早期冰岛羽状熔岩的热浮力羽状起源。这些观测结果支持了地球化学不均匀的高3 He/4 He区域是致密的，位于地幔深部，并且仅由最热的地幔柱采样的论点。
The Icelandic hotspot has erupted basaltic magma with the highest mantle‐derived3He/4He over a period spanning much of the Cenozoic, from the early‐Cenozoic Baffin Island‐West Greenland flood basalt province (49.8RA), to mid‐Miocene lavas in northwest Iceland (40.2 to 47.5RA), to Pleistocene lavas in Iceland's neovolcanic zone (34.3RA). 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 have87Sr/86Sr = 0.703008–0.703021,143Nd/144Nd = 0.513094–0.513128,176Hf/177Hf = 0.283265–0.283284,206Pb/204Pb = 17.7560–17.9375,3He/4He up to 39.9RA, and mantle‐like δ18O of 5.03–5.21‰. The radiogenic isotopic compositions of the least crustally contaminated lavas are more geochemically depleted than Iceland high‐3He/4He lavas, a shift that cannot be explained by continental crust assimilation in the Baffin suite. Thus, we argue for the presence oftwogeochemically distinct high‐3He/4He 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‐3He/4He domain is dense, located in the deep mantle, and sampled by only the hottest plumes.