Mantle transition zone beneath a normal seafloor in the northwestern Pacific: Electrical conductivity, seismic thickness, and water content
Mantle transition zone beneath a normal seafloor in the northwestern Pacific: Electrical conductivity, seismic thickness, and water content
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DOI：
10.1016/j.epsl.2016.12.045
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发表时间：
2017-03
影响因子：
5.3
通讯作者：
T. Matsuno;D. Suetsugu;K. Baba;N. Tada;H. Shimizu;H. Shiobara;T. Isse;H. Sugioka;A. Ito;M. Obayashi;H. Utada
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文献类型：
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作者：
T. Matsuno;D. Suetsugu;K. Baba;N. Tada;H. Shimizu;H. Shiobara;T. Isse;H. Sugioka;A. Ito;M. Obayashi;H. Utada
我们进行了一项联合电磁（EM）和地震实验，以揭示西北太平洋130-145 Ma正常海底下的地幔结构，那里的海底相对平坦，下伏地幔预计是正常的（没有构造扰动）。在实验中，我们从2010年到2015年在两个阵列中部署了最先进的仪器。本文报道了利用电磁和地震资料研究地幔过渡带（MTZ）结构的结果。EM数据分析表明，两个阵列下面的电导率结构近似由北太平洋的平均1-D模型，并显示出可能的向下增加的导电性在MTZ的顶部。根据P波接收器函数分析，全球平均MTZ厚度的扰动估计分别为北方和南方阵列下方+20公里和+2公里，然后根据这两个阵列下方MTZ的温度分布估计。我们共同解释的电导率的配置文件，从而估计温度，参考的实验值的水对MTZ矿物（wadsleyite和ringwoodite）的电导率的影响从矿物物理。测定北方阵列下方的水含量的上限为0.4重量%或0.04重量%，根据矿物物理学的不同结果，南部阵列以下的地层被确定为略小。含水量的下限不受我们数据的限制。我们的研究结果表明，在西北太平洋的正常海底下的MTZ比俯冲带干燥，可能是一个贫水地区的李子布丁地幔模型。
We conducted a joint electromagnetic (EM) and seismic experiment to reveal the mantle structure beneath a normal seafloor at 130–145 Ma in the northwestern Pacific, where the seafloor is relatively flat and the underlying mantle is expected to be normal (free from tectonic perturbations). In the experiment, we deployed state-of-the-art instruments in two arrays from 2010–2015. Here, we report the result of analyses of the EM and seismic data for investigating the mantle transition zone (MTZ) structure. The EM data analysis revealed that an electrical conductivity structure below both arrays was approximated by an average 1-D model of the north Pacific, and showed a possible downward increase in conductivity at the top of the MTZ. From the P-wave receiver function analysis, perturbations in the MTZ thickness from a global average were estimated to be +20 km and +2 km below the northern and southern arrays, respectively, from which temperature profiles in the MTZ below these two arrays were then estimated. We jointly interpreted the profiles of electrical conductivity and thus estimated temperature, with reference to the experimental values of the effects of water on the electrical conductivities of MTZ minerals (wadsleyite and ringwoodite) from mineral physics. The upper bound of the water content below the northern array was determined to be 0.4 wt.% or 0.04 wt.%, depending on different results of mineral physics, and that below the southern array was determined to be slightly smaller. The lower bound of the water content was not constrained by our data. Our results indicate that the MTZ beneath the normal seafloor in the northwestern Pacific is drier than subduction zones, and may be a water-poor region in a plum-pudding mantle model.