Rapid hydrothermal cooling above the axial melt lens at fast-spreading mid-ocean ridge.
Rapid hydrothermal cooling above the axial melt lens at fast-spreading mid-ocean ridge.
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DOI：
10.1038/srep06342
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发表时间：
2014-09-11
影响因子：
4.6
通讯作者：
Behrens H
中科院分区：
文献类型：
--
作者：
Zhang C;Koepke J;Kirchner C;Götze N;Behrens H
夹在下洋壳和快速扩张的洋中脊席状岩墙序列之间的轴向熔融透镜体被认为是洋壳增生的主要岩浆源。根据广泛讨论的“辉长岩冰川”模型，下洋壳的形成需要轴向熔体透镜的有效冷却，导致部分结晶和晶体-熔体泥沉降到下地壳。这些过程被认为是由周期性的岩浆补充和热液循环以上的熔体透镜控制。在这里，我们量化的冷却速率以上熔体透镜使用斜长石的化学分区角长石重结晶席状岩脉钻从东太平洋在综合大洋钻探计划孔1256 D。我们估计的冷却速率使用的正演模拟方法的基础上CaAl-NaSi的相互扩散斜长石。结果表明，由于岩浆饥饿期间熔体透镜上方热液循环的影响，在10-30年内从1000-1050° C的热叠加峰值冷却到600°C。估计的快速热液冷却解释了如何从熔体透镜中有效地提取热量是在快速扩展的洋中脊实现的。
Axial melt lenses sandwiched between the lower oceanic crust and the sheeted dike sequences at fast-spreading mid-ocean ridges are assumed to be the major magma source of oceanic crust accretion. According to the widely discussed “gabbro glacier” model, the formation of the lower oceanic crust requires efficient cooling of the axial melt lens, leading to partial crystallization and crystal-melt mush subsiding down to lower crust. These processes are believed to be controlled by periodical magma replenishment and hydrothermal circulation above the melt lens. Here we quantify the cooling rate above melt lens using chemical zoning of plagioclase from hornfelsic recrystallized sheeted dikes drilled from the East Pacific at the Integrated Ocean Drilling Program Hole 1256D. We estimate the cooling rate using a forward modelling approach based on CaAl-NaSi interdiffusion in plagioclase. The results show that cooling from the peak thermal overprint at 1000–1050°C to 600°C are yielded within about 10–30 years as a result of hydrothermal circulation above melt lens during magma starvation. The estimated rapid hydrothermal cooling explains how the effective heat extraction from melt lens is achieved at fast-spreading mid-ocean ridges.
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