Explosive Ocean Island Volcanism Explained by High Magmatic Water Content Determined Through Nominally Anhydrous Minerals

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Harri Geiger, Franz Weis, Valentin R. Troll, Frances M. Deegan, Henrik Skogby, Juan Carlos Carracedo
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引用次数: 0

Abstract

Ocean island basalt (OIB) magmas are generally water poor and usually contain less than 1 wt.% of H2O. Explosive eruption styles are therefore rare. When explosive eruptions occur, they are thought to be driven by either volatile-enriched mantle sources or by gas segregation processes during magma differentiation. Here we report on crystal- and water-rich porphyritic basanites and ankaramites from El Hierro in the Canary Islands, Spain, that erupted inside the El Golfo giant landslide collapse embayment that formed at ≥39 ka. Using rock and mineral chemistry in combination with H2O contents of nominally anhydrous minerals (olivine and clinopyroxene), we show that despite their relatively primitive composition, the post-collapse ankaramites are not primary mantle melts. Instead, they record high crystal contents as well as unusually high water contents of up to 3.20 ± 0.64 wt.% H2O, and likely represent a normally inaccessible snapshot of dense crystal-rich magma compositions that reside in the sub-island underplating zone. We hypothesize that their eruption was facilitated by sudden decompression from crustal unloading, implying that the El Golfo landslide may have affected the deeper portions of the plumbing system and triggered the ascent of volatile-rich, crystal-laden magmas from the underplating zone. We propose that some “wet” and explosive ocean island eruptions might result from the ascent of deep-seated water-rich magmas in the aftermath of vertical unloading and associated decompression.

Abstract Image

由名义上无水矿物测定的高岩浆含水量解释爆炸性海洋岛屿火山作用
洋岛玄武岩(OIB)岩浆通常是缺水的,通常含有少于1 wt.%的水。因此,爆发性喷发非常罕见。当爆炸性喷发发生时,它们被认为是由富含挥发物的地幔源或岩浆分化过程中的气体分离过程驱动的。在这里,我们报道了来自西班牙加那利群岛El耶罗的富含晶体和水的斑状玄武岩和ankaramites,这些玄武岩喷发于形成于≥39 ka的El Golfo巨型滑坡崩塌坝内。结合岩石和矿物化学,结合名义上无水矿物(橄榄石和斜辉石)的H2O含量,我们表明,尽管它们的成分相对原始,但崩塌后的ankaramites不是原始的地幔熔体。相反,它们记录了高晶体含量和异常高的含水量,高达3.20±0.64 wt.% H2O,这可能代表了位于亚岛底板带的密集富含晶体的岩浆成分的通常难以接近的快照。我们假设它们的喷发是由于地壳卸载造成的突然减压而促成的,这意味着El Golfo滑坡可能影响了管道系统的深层部分,并引发了富含挥发物、富含晶体的岩浆从海底带上升。我们认为,一些“湿”和爆炸性的海洋岛屿喷发可能是由于在垂直卸载和相关减压之后,深层富水岩浆的上升造成的。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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