| DOI: | 10.1038/ngeo2605
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| 论文题名: | Emergence of blueschists on Earth linked to secular changes in oceanic crust composition |
| 作者: | Palin R.M.; White R.W.
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| 刊名: | Nature Geoscience
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| ISSN: | 17520894
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| 出版年: | 2016
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| 卷: | 9, 期:1 | | 起始页码: | 60
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| 结束页码: | 64
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| 语种: | 英语
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| Scopus关键词: | blueschist
; geothermal gradient
; Hadean
; low temperature
; magnesium
; mantle
; metamorphism
; oceanic crust
; oxide
; pressure gradient
; Proterozoic
; secular variation
; subduction
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| 英文摘要: | The oldest blueschists-metamorphic rocks formed during subduction-are of Neoproterozoic age, and 0.7-0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa â ∼'1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface. Here we show that the absence of blueschists in the ancient geological record can be attributed to the changing composition of oceanic crust throughout Earth history, which is a consequence of secular cooling of the mantle since the Archaean. Oceanic crust formed on the hot, early Earth would have been rich in magnesium oxide (MgO). We use phase equilibria calculations to show that blueschists do not form in high-MgO rocks under subduction-related geothermal gradients. Instead, the subduction of MgO-rich oceanic crust would have created greenschist-like rocks-metamorphic rocks formed today at low temperatures and pressures. These ancient metamorphic products can hold about 20% more water than younger metamorphosed oceanic crust, implying that the global hydrologic cycle was more efficient in the deep geological past than today. © 2015 Macmillan Publishers Limited. All rights reserved. |
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| 资源类型: | 期刊论文
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/106099
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| Appears in Collections: | 气候减缓与适应
科学计划与规划
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作者单位: | Institute of Geosciences, Johannes-Gutenberg University Mainz, Mainz, Germany
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| Recommended Citation: | |
Palin R.M.,White R.W.. Emergence of blueschists on Earth linked to secular changes in oceanic crust composition[J]. Nature Geoscience,2016-01-01,9(1)
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