Highly Oxidising Conditions in Volatile-Rich El Hierro Magmas: Implications for Ocean Island Magmatism
Highly Oxidising Conditions in Volatile-Rich El Hierro Magmas: Implications for Ocean Island Magmatism
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富含挥发性物质的耶罗岩浆中的高度氧化条件：对大洋岛岩浆作用的影响
DOI：
10.1093/petrology/egac011
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发表时间：
2022
影响因子：
3.9
通讯作者：
Taracsák Z
中科院分区：
文献类型：
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作者：
Taracsák Z
最近的研究调查岩浆挥发分含量表明，广泛富集的碳，硫和卤素的洋岛玄武岩（OIB）。在西加那利群岛的耶罗，具有异常高的CO2和S含量的岩浆在整个全新世一直在喷发。高达5200 ppm的高硫含量需要一个氧化地幔源，但初始岩浆氧逸度（fO 2）的估计是稀疏的。在这里，我们提出的估计ofO 2和岩浆温度的厄尔尼诺耶罗连同全球地幔潜在温度数据集，以评估氧化还原和温度条件的熔体演化的早期阶段，挥发分丰富的OIBs。利用熔融包裹体（MI）与其橄榄石宿主之间的钒分配计算的氧逸度>FMQ + 2.9（高于铁橄榄石-磁铁矿-石英缓冲层2.9 log 10单位），表明El Hierro岩浆高度氧化。MI和基质玻璃硫形态数据记录FMQ-1至FMQ + 2之间的fO 2;这些值强烈依赖于S2−至S6+跃迁相对于FMQ缓冲区的位置。尽管如此，玻璃硫形态数据记录较低的氧逸度比V分配数据，表明MI能够保持Fe 3 +/Fe 3Fe和S6+/Fe 3S平衡与周围的熔体在其演变过程中。耶罗岩浆的高fO 2与加那利群岛的平均地幔位温估计值1443 ± 66°C（1σ，n= 17）相关联，略高于邻近洋中脊段的平均位温估计值（1427 ± 33°C，1σ，n= 474），尽管这两个值都在误差范围内。我们发现，98%的加那利岛的岩石成分不适合使用目前可用的方法计算地幔位温。这是由于加那利群岛下存在大量辉石岩和富含挥发分的橄榄岩地幔域造成的。各种岩石学模型的更广泛的成分校准是必要的，以精确地确定富含挥发分的碱性玄武岩的地幔位温。我们对耶罗岩浆的高氧逸度估计反映了西加那利群岛下地幔源的肥沃，易熔和挥发性富集的性质。
Recent studies investigating magmatic volatile contents indicate widespread enrichment of carbon, sulfur, and halogens in ocean island basalts (OIBs). At El Hierro in the Western Canary Islands, magmas with exceptionally high CO2and S contents have been erupting throughout the Holocene. High S content of up to 5200 ppm requires an oxidised mantle source, but estimates of initial magmatic oxygen fugacity (fO2) are sparse. Here, we present estimates offO2and magmatic temperature for El Hierro together with a global mantle potential temperature dataset to evaluate redox and temperature conditions in the early stages of melt evolution for volatile-rich OIBs. Oxygen fugacities calculated using vanadium partitioning between melt inclusions (MIs) and their olivine hosts are >FMQ + 2.9 (2.9 log10units above the fayalite-magnetite-quartz buffer), indicating that El Hierro magmas are highly oxidised. MI and matrix glass sulfur speciation data recordfO2between FMQ-1 to FMQ + 2; these values strongly depend on the position of the S2−to S6+transition relative to the FMQ buffer. Nonetheless, glass sulfur speciation data record lower oxygen fugacity than V partitioning data, indicating MIs were able to maintain Fe3+/ΣFe and S6+/ΣS equilibrium with the surrounding melt during their evolution. The highfO2of El Hierro magmas is coupled with an average mantle potential temperature estimate of 1443 ± 66°C (1σ,n= 17) for the broader Canary Islands, which is slightly higher than the average potential temperature estimated for adjacent mid-ocean ridge segments (1427 ± 33°C, 1σ,n= 474), albeit the two values are well within error. We find that ~98% of Canary Island rock compositions are not suitable for calculation of mantle potential temperatures using currently available methods. This is caused by the presence of substantial pyroxenite and volatile-enriched peridotite mantle domains under the Canary Islands. A wider compositional calibration of various petrological models is necessary to precisely determine mantle potential temperatures for volatile-rich alkali basalts. Our high oxygen fugacity estimates for El Hierro magmas reflect the fertile, fusible, and volatile-enriched nature of the mantle source beneath the Western Canary Islands.