DOI: 10.1016/j.epsl.2017.10.039
Scopus记录号: 2-s2.0-85034079610
论文题名: The effect of prior hydrothermal alteration on the melting behaviour during rhyolite formation in Yellowstone, and its importance in the generation of low-δ18O magmas
作者: Troch J. ; Ellis B.S. ; Harris C. ; Ulmer P. ; Bachmann O.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 481 起始页码: 338
结束页码: 349
语种: 英语
英文关键词: assimilation
; bulk crustal melting
; hydrothermal alteration
; rhyolite
Scopus关键词: Clay alteration
; Granite
; Isotopes
; Reservoirs (water)
; Trace elements
; assimilation
; Hydrothermal alterations
; Increasing temperatures
; Isotopic mass balance model
; Major and trace elements
; Oxygen isotope exchange
; rhyolite
; Volumetric constraints
; Melting
; caldera
; core analysis
; crustal structure
; hydrothermal alteration
; igneous geochemistry
; lithology
; magma assimilation
; melting
; oxygen isotope
; rhyolite
; water content
; United States
; Wyoming
; Yellowstone Caldera
英文摘要: Constraining the contribution of crustal lithologies to silicic magmas has important implications for understanding the dynamics of these potentially highly explosive systems. Low-δ18O rhyolite lavas erupted after caldera-forming events in Yellowstone have been interpreted as the products of bulk crustal melting of previously deposited and hydrothermally altered rhyolitic material in the down-dropped caldera roof. For lack of compositional data, the “self-cannibalisation bulk melting”-theory relies on the assumption that hydrothermally altered materials are near-cotectic and hydrous (>3 wt% H2O) and will therefore readily melt at temperatures below 850 °C. In this study, we examine the drillcores Y2, Y9 and Y13 from a USGS drilling campaign in Yellowstone in order to characterise the hydrothermally altered material in terms of major and trace elements, oxygen isotopes and water contents. Rhyolite δ18O values can decrease from “normal” (+5.8 to +6.1‰) on the surface to as low as −5‰ at depths of 100–160 m and probably lower as a function of increasing temperature with depth. While material in the drillcores is variably altered and silicified, oxygen isotope exchange in these samples is not accompanied by systematic changes in major and trace element composition and is independent of uptake of water. More than 75% of the drillcore samples have <0.5 wt% H2O, making water the most limiting factor during melting. Modelled melting curves using rhyolite-MELTS suggest a maximum of 35% melt can be created at 850 °C, and that bulk melting would require extremely high temperatures >1100 °C. Therefore, large-scale bulk melting is unrealistic and low-δ18O rhyolite magmas more likely result from assimilation of <30% partially melted altered crust with low δ18O into a normal-δ18O rhyolite magma from the main reservoir. This mechanism is supported by isotopic mass-balance models as well as thermal and volumetric constraints, and may be similarly applicable to other low-δ18O settings worldwide. © 2017 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/110175
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, Zurich, 8092, Switzerland; Department of Geological Sciences, University of Cape Town, 13 University Avenue, Rondebosch, 7701, South Africa
Recommended Citation:
Troch J.,Ellis B.S.,Harris C.,et al. The effect of prior hydrothermal alteration on the melting behaviour during rhyolite formation in Yellowstone, and its importance in the generation of low-δ18O magmas[J]. Earth and Planetary Science Letters,2018-01-01,481