Upper Mantle Melt Distribution From Petrologically Constrained Magnetotellurics
Upper Mantle Melt Distribution From Petrologically Constrained Magnetotellurics
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DOI：
10.1029/2019gc008227
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发表时间：
2019-07
期刊：
影响因子：
3.7
通讯作者：
K. Selway;J. O’Donnell;S. Özaydın
中科院分区：
文献类型：
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作者：
K. Selway;J. O’Donnell;S. Özaydın
三个参数：温度、氢含量和部分熔融的存在是对流上地幔流变学的主要控制因素。因此，它们决定了控制板块构造和大陆演化的动力学。由于氢压低橄榄岩固相线温度，这些参数是密切相关的岩石学。我们已经开发了一个遗传算法代码，以统计评估的可能性，上地幔的一部分包含部分熔融。该代码使用大地电磁观测和岩石学约束的组成和固相线温度，并允许在地热和电导率结构的不确定性。我们已经将这套程序应用于（1）一个稳定大陆（上级Ocean）;（2）一个热点（Tristan da库尼亚）;（3）一个稳定的古老的大洋岩石圈（西北太平洋）;（4）一个年轻的大洋岩石圈（邻近东太平洋隆起）下面的对流上地幔。结果表明，对流作用下上地幔熔体的体积是不均匀的。最高的熔化比例在热点下方，而在其他区域几乎不需要熔化。所有地区的对流上地幔含水量都很低（橄榄石中的含水量一般<50 ppm），因此水不太可能在岩石圈和对流地幔之间造成大的或尖锐的粘度对比。不同的实验橄榄石氢电导率模型的结果显着不同，突出了调和这些实验约束的重要性。
Three parameters: temperature, hydrogen content, and the presence of partial melt, are the dominant controls on the rheology of the convecting upper mantle. As such, they determine the dynamics that control plate tectonics and continental evolution. Since hydrogen depresses the peridotite solidus temperature, these parameters are strongly linked petrologically. We have developed a genetic algorithm code to statistically assess the likelihood that a section of upper mantle contains partial melt. This code uses magnetotelluric observations and petrological constraints on composition and solidus temperatures and allows for uncertainties in the geotherm and the electrical conductivity structure. We have applied this code to the convecting upper mantle beneath (1) a stable continent (the Superior Craton); (2) a hot spot (Tristan da Cunha); (3) stable, old oceanic lithosphere (the northwest Pacific Ocean); and (4) young oceanic lithosphere (adjacent to the East Pacific Rise). Results show that the volume of melt in the convecting upper mantle is heterogeneous. The highest melt proportions are beneath the hot spot while little to no melt is required in the other regions. All regions show low water contents (generally <50 wt ppm in olivine) in the shallow convecting upper mantle, making it unlikely that water causes a large or sharp viscosity contrast between the lithosphere and the convecting mantle. Results differ significantly for different experimental olivine hydrogen conductivity models, highlighting the importance of reconciling these experimental constraints.