DOI: 10.1016/j.earscirev.2020.103299
论文题名: Low-δ18O silicic magmas on Earth: A review
作者: Troch J. ; Ellis B.S. ; Harris C. ; Bachmann O. ; Bindeman I.N.
刊名: Earth Science Reviews
ISSN: 00128252
出版年: 2020
卷: 208 语种: 英语
中文关键词: Assimilation
; Caldera
; Crustal melting
; Granite
; Hydrothermal alteration
; Magmas
; Oxygen isotopes
; Rhyolite
英文关键词: data assimilation
; Earth science
; hydrothermal alteration
; igneous geochemistry
; isotopic composition
; magma chamber
; oxygen isotope
; tectonic setting
; trace element
英文摘要: Silicic magmas play an important role in the formation of continental crust and are responsible for some of the most hazardous volcanic eruptions on the planet. Low-δ18O silicic magmas (δ18O < 5.5 ‰) have been a petrological conundrum as they require significant incorporation of rocks that were hydrothermally altered by meteoric water at high water/rock ratios in the shallow, permeable, and relatively cold upper crust (<400 °C), a region thought to be unfavorable for the production of large melt volumes. Their genesis is therefore crucial in understanding how silicic magma reservoirs interact with the upper crust, and how they can remain active and produce extensive amounts of silicic magma over timescales of millions of years. In this paper, we compare low-δ18O silicic magmas from different tectonic settings, in order to identify general mechanisms for the production of low-δ18O silicic magmas on Earth. Low-δ18O magmas can be linked to either assimilation of pre-existing hydrothermally altered crust, or (more commonly) to assimilation of syn-magmatically altered rocks. Assimilation of syn-magmatically altered rocks may occur in a variety of volcanic settings, but is most likely in shallow, large-scale, long-lived caldera-forming systems that host extensive high-temperature hydrothermal systems and produce hot (>800 °C) and dry silicic magmas. The relative scarcity of low-δ18O silicic magmas on Earth compared to normal- and high-δ18O magmas implies that coincidence of these factors is rare, and is most likely encountered in hotspot and rift settings characterized by bimodal basaltic-rhyolitic volcanism. Low-δ18O silicic magmas are usually generated by bulk assimilation of rocks that were hydrothermally altered at high temperatures (>300 °C) by isotopically light meteoric water, prevalent at mid to high latitudes and altitudes and/or linked to global glaciation episodes in Earth's history. We estimate that <30-40 % assimilation can explain most of the oxygen isotope compositions of low-δ18O magmas, consistent with estimates from thermal models. At conditions optimal for oxygen isotope exchange towards lower δ18O values, alteration is not associated with hydration, and hydrothermally altered low-δ18O rocks do not melt more readily than average crust. Assimilation of co-genetic hydrothermally altered rocks rarely leaves identifiable traces in the major and trace element record of low-δ18O silicic magmas, and may often be obscured by assimilation of high-δ18O crustal rocks. These findings provide a framework for the assessment of low-δ18O silicic magmas on Earth, and the parameters that play a role in their genesis. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/166279
Appears in Collections: 气候变化与战略
There are no files associated with this item.
作者单位: Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook Street, Providence, RI 02912, United States; Institute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, Zurich, 8092, Switzerland; Department of Geological Sciences, University of Cape Town, 13 University Avenue, Rondebosch, 7700, South Africa; Department of Earth Sciences, University of Oregon, 1272 University of Oregon, Eugene, OR 97403, United States; Fersman Mineralogical Museum, Leninskiy Prospekt, Moscow, 115162, Russian Federation
Recommended Citation:
Troch J.,Ellis B.S.,Harris C.,et al. Low-δ18O silicic magmas on Earth: A review[J]. Earth Science Reviews,2020-01-01,208