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首页> 外文期刊>Geochemistry, geophysics, geosystems >Constraints on Cooling of the Lower Ocean Crust From Epidote Veins in the Wadi Gideah Section, Oman Ophiolite
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Constraints on Cooling of the Lower Ocean Crust From Epidote Veins in the Wadi Gideah Section, Oman Ophiolite

机译：关于旱地静脉静脉静脉静脉切片，阿曼奥海尔矿石冷却较低海洋地壳的限制

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摘要

Timing, depth, and extent of high-temperature hydrothermal alteration in the ocean crust is key to understanding how lower oceanic crust is cooled after accretion. Epidote veins were collected in spatially recurring zones of intense alteration of the lower crustal Wadi Gideah section and the root zone of sheeted dykes at Wadi Amadhi. ~(87)Sr/~(86)Sr ratios feature a narrow range from 0.70429 to 0.70512, while O isotope compositions vary between -0.7‰ and +4.9‰ in δ~(18)O_(SMOW). These compositions indicate water-rock ratios between 1 and 5 and formation temperatures in the range of 300 to 450 °C. Fluid inclusion entrapment temperatures for a subset of samples linearly increase from 338 °C to 465 °C in lowermost 3 km of crust of the Wadi Gideah section and record 340 °C for the Wadi Amadhi basal sheeted dike sample. Salinities are uniform throughout and scatter closely around seawater values (3.2 ± 0.2 wt%). A model in which cooling down to 2 km(i.e., the depth of the melt lens) is followed by slow off-axis hydrothermal cooling of the lower crust to 1 Myr predicts a thermal gradient for the lower crust that matches this observed trend for ages between 1 and 2.5 Myr. We suggest that the epidote veins formed in off-axial hydrothermal systems that reach the base of the crust within 50- to 100-km off axis. This deep circulation provides an efficient mechanism for mining heat that escapes the crust in the young flanks of mid-ocean ridges.
机译：海底高温水热改变的时序，深度和程度是了解在增生后如何冷却了较低的海洋地壳。在Wadi Amadhi的下面地壳WADI GideAH部分和片状染料根带的空间重复变化的空间复制区域中收集了静脉。 〜（87）SR /〜（86）SR比率具有0.70429至0.70512的窄范围，而OisoTope组合物在-0.7‰和+ 4.9‰之间变化δ〜（18）O_（污点）。这些组合物表示在300至450℃的300至450℃的1至5之间的水岩比。对于瓦迪GideAH截面的较低3千米，将样品的流体包裹物滞留温度从338℃下线性增加至3千米的3千米。盐度整体均匀，围绕海水值密切散射（3.2±0.2wt％）。一种模型，其中冷却至2 km（即熔体透镜的深度），然后是下壳的慢轴下水热冷却，1 myr预测符合这一观察到的趋势的下层地壳的热梯度在1到2.5 myr之间。我们建议在脱轴水热系统中形成的静脉，该系统在50至100厘米的轴线内到达外壳的底部。这种深度循环为采矿热量提供了一种有效的机制，可在海洋山脊的年轻侧翼逸出地壳。

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