Volatile-Rich Magmas Distributed Through the Upper Crust in the Main Ethiopian Rift
Volatile-Rich Magmas Distributed Through the Upper Crust in the Main Ethiopian Rift
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DOI：
10.1029/2019gc008904
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发表时间：
2020-06-01
影响因子：
3.5
通讯作者：
Edmonds, Marie
中科院分区：
文献类型：
--
作者：
Iddon, Fiona;Edmonds, Marie
了解东非裂谷的岩浆储存和分异，巩固了我们对大陆裂谷环境中火山活动的理解。在这里，我们提出了地球化学的熔融包裹体爆发在主埃塞俄比亚裂谷过渡玄武岩，粗面岩，过碱性流纹岩，分离结晶。玄武岩储存在轴上和轴外的饱和在一个exsolved挥发相在上地壳高达18公里。从岩浆中释放出来的大部分CO2可能是通过扩散脱气而损失的。观测到的CO2通量要求每年在裂谷下方侵入多达0.14 km（3）的玄武岩。轴上过碱性流纹沉积较浅，深度约为4-8 km。在戴利缺口，岩浆饱和在硫化物和出溶的挥发性相，这促使岩浆上升到地壳较浅的水平。在这里，岩浆经历进一步延长的分离结晶和脱气，导致形成大量的出溶挥发相，这可能会积累在一个富气帽。出溶的挥发相富含硫和卤素：预计在MER爆炸性过碱性喷发期间，它们进入大气的预计负荷将大大高于其他环境中的金属发光对应物。高比例的出溶挥发物在存储的岩浆增强其可压缩性，必须考虑解释地面位移时，认为是由岩浆侵入在深度，否则，侵入量将被低估。在岩浆储层的顶部区域可能存在出溶挥发物的口袋，这可能是使用地球物理技术解决的。
Understanding magma storage and differentiation in the East African Rift underpins our understanding of volcanism in continental rift settings. Here, we present the geochemistry of melt inclusions erupted in Main Ethiopian Rift transitional basalts, trachytes, and peralkaline rhyolites, produced by fractional crystallization. Basalts stored on- and off-axis are saturated in an exsolved volatile phase at up to 18 km in the upper crust. Much of the CO2 outgassed from the magmas is likely lost through diffuse degassing. Observed CO2 fluxes require the intrusion of up to 0.14 km(3) of basalt beneath the rift each year. On-axis peralkaline rhyolites are stored shallowly, at similar to 4-8 km depth. In the Daly Gap, magmas saturate in sulfide and an exsolved volatile phase, which promotes magma rise to shallower levels in the crust. Here, magmas undergo further protracted fractional crystallization and degassing, leading to the formation of a substantial exsolved volatile phase, which may accumulate in a gas-rich cap. The exsolved volatile phase is rich in sulfur and halogens: their projected loadings into the atmosphere during explosive peralkaline eruptions in the MER are predicted to be substantially higher than their metaluminous counterparts in other settings. The high fraction of exsolved volatiles in the stored magmas enhances their compressibility and must be considered when interpreting ground displacements thought to be caused by magma intrusion at depth; otherwise, intruding volumes will be underestimated. Pockets of exsolved volatiles may be present at the roof zones of magma reservoirs, which may be resolvable using geophysical techniques.