Zircon Constraints on the Eruptive Sequence and Magma Evolution of Rhyolites at South Sister Volcano, Oregon

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Annika E. Dechert, Nathan L. Andersen, Josef Dufek, Christine E. Jilly
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引用次数: 0

Abstract

We present 230Th-238U crystallization ages and trace element compositions for zircons spanning the late Pleistocene to Holocene rhyolite eruptive record at South Sister volcano in the central Oregon Cascade Range. Most zircon ages are between 100 and 20 ka, with very few in secular equilibrium (>350 ka). The weighted mean of zircon ages for the two oldest South Sister rhyolites, 31.5 ± 2.1 and 39.1 ± 2.4 ka, are significantly younger than the associated 40Ar/39Ar ages, 47.4 ± 9.7 and 51.4 ± 9.7 ka. We propose that these 40Ar/39Ar dates, performed on plagioclase separates, are compromised by a subtle amount of excess Ar and therefore the younger weighted mean zircon ages yield more reliable eruption ages. These results imply that the interval of rhyolite eruption at South Sister during the late Pleistocene was both shorter and more productive than previously thought and that eruption at South Sister initiated after Middle Sister. Compositionally, zircons from the Pleistocene rhyolites are broadly similar and show down-temperature zircon and plagioclase crystallization trends. However, we argue that destabilized amphibole and titanite in a common mush also exert leverage on the Pleistocene zircon trace element compositions. Divergence in the Eu/Eu* ratio between the Pleistocene and Holocene lavas implies chemically distinct magma reservoirs originating from the Pleistocene rhyolite eruptive sequence and the Holocene eruptive sequence. This work suggests a higher flux of rhyolite volcanism than previously thought and characterizes magmatic storage distinctions between the Pleistocene and Holocene rhyolites, aiding in the assessment of future eruptive hazards at South Sister volcano.

Abstract Image

俄勒冈州南姊妹火山流纹岩喷发序列和岩浆演化的锆石制约因素
我们展示了俄勒冈州喀斯喀特山脉中部南姐妹火山晚更新世至全新世流纹岩喷发记录中锆石的 230Th-238U 结晶年龄和微量元素组成。大多数锆石的年龄在 100 到 20 ka 之间,只有极少数处于世俗平衡(350 ka)状态。两个最古老的南姊妹流纹岩的锆石年龄加权平均值(31.5 ± 2.1 ka)和(39.1 ± 2.4 ka)明显比相关的 40Ar/39Ar 年龄(47.4 ± 9.7 ka)和(51.4 ± 9.7 ka)年轻。我们认为,这些 40Ar/39Ar 年龄是在斜长石分离物上测定的,受到了微量过量氩的影响,因此较年轻的加权平均锆石年龄得出了更可靠的喷发年龄。这些结果表明,南姊妹火山在晚更新世的流纹岩喷发时间比之前认为的更短,产量更高,南姊妹火山的喷发始于中姊妹火山之后。从成分上看,更新世流纹岩的锆石大致相似,并呈现出降温锆石和斜长石结晶趋势。然而,我们认为,在一个共同的泥浆中,脱稳的闪石和榍石也对更新世锆石微量元素成分产生了影响。更新世和全新世熔岩的 Eu/Eu* 比率不同,这意味着源自更新世流纹岩喷发序列和全新世喷发序列的岩浆库在化学性质上截然不同。这项研究表明,流纹岩火山活动的通量比以前认为的要高,并描述了更新世和全新世流纹岩之间岩浆储藏的区别,有助于评估南姊妹火山未来的喷发危害。
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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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