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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Oxygen isotope evidence for short-lived high-temperature fluid flow in the lower oceanic crust at fast-spreading ridges
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Oxygen isotope evidence for short-lived high-temperature fluid flow in the lower oceanic crust at fast-spreading ridges

机译：氧同位素证据表明快速扩张的山脊下部洋壳中存在短暂的高温流体

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摘要

Millimeter-scale amphibole veins in the lower oceanic crust record fracture-controlled fluid flow at high-temperatures but the importance of this fluid flow for the thermal and chemical evolution of the lower oceanic crust is unclear. In the section of lower oceanic crust recovered at Hess Deep from ODP Hole 894G, which formed at the fast-spreading East Pacific Rise, these veins are randomly distributed with an average spacing of similar to 1 m. We unravel the history of fluid flow through one of these veins by combining in situ O-isotope analyses of wall-rock plagioclase with major element analyses, geothermometry and diffusion modeling. Thermometry indicates vein sealing by amphibole at similar to 720 degrees C over a narrow temperature interval (+/- 20 degrees C). In situ O-isotope analyses by ion microprobe, with a precision of <0.5 parts per thousand, reveal zoning of O-isotopes in plagioclase adjacent to the vein. The zoning profiles can be reproduced using a diffusion model if the duration of O-isotope exchange was <= 100 yr. A similar interval of fluid-rock exchange is suggested by modeling potassium depletion in plagioclase adjacent to the vein. If representative of fracture controlled fluid flow in the lower oceanic crust the limited duration of fluid flow, and its occurrence over a narrow temperature interval, suggest that high-temperature fluid flow in this porosity network does not transport significant heat. (C) 2007 Elsevier B.V. All rights reserved.
机译：下部洋壳的毫米级角闪石脉在高温下记录了裂缝控制的流体流动，但是这种流体对于下部洋壳的热和化学演化的重要性尚不清楚。在快速扩张的东太平洋上升区形成的ODP孔894G的Hess Deep下部低层地壳中，这些脉是随机分布的，平均间距约为1 m。通过结合壁岩斜长石的原位O同位素分析与主要元素分析，地热测定法和扩散建模，我们揭示了通过其中一条静脉流动的流体的历史。测温表明在狭窄的温度区间（+/- 20摄氏度）内，闪石在类似于720摄氏度的条件下进行静脉封闭。通过离子微探针进行的原位O同位素分析，其精确度小于千分之0.5，揭示了O同位素在与脉相邻的斜长石中的分区。如果O同位素交换的持续时间<= 100 yr，则可以使用扩散模型复制分区轮廓。通过对与静脉相邻的斜长石中的钾耗竭进行建模，可以提出相似的流体-岩石交换间隔。如果代表下部大洋地壳中受裂缝控制的流体流动，则流体流动的持续时间有限，并且其发生在狭窄的温度区间内，这表明该孔隙网络中的高温流体并未传递大量热量。 （C）2007 Elsevier B.V.保留所有权利。

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