Shear Velocity Inversion Guided by Resistivity Structure From the PI-LAB Experiment for Integrated Estimates of Partial Melt in the Mantle
Shear Velocity Inversion Guided by Resistivity Structure From the PI-LAB Experiment for Integrated Estimates of Partial Melt in the Mantle
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DOI：
10.1029/2021jb022202
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发表时间：
2021-08-01
影响因子：
3.9
通讯作者：
Kendall, J. Michael
中科院分区：
文献类型：
--
作者：
Harmon, Nicholas;Wang, Shunguo;Kendall, J. Michael
岩石圈-软流圈系统是我们理解地幔对流和板块构造的基础。地震和电磁方法的不同灵敏度可以一起使用，以更好地约束系统的属性。在这里，我们重新检查剪切速度模型从瑞利波光大地电磁为基础的电阻率模型从被动成像的岩石圈软流圈边界（PI-LAB）实验赤道大西洋中脊附近，与生成一个结构一致的速度和电阻率模型的目标。模型的交叉图表明线性或接近线性的趋势，也与岩石物理预测一致。根据岩石物理关系，由电阻率模型生成了一个新的剪切速度模型。新的速度模型更好地拟合了相速度数据，提高了横波速度模型与电阻率模型的相关系数。该模型的大部分可以预测的热半空间冷却模型的期望，虽然有些地区需要更高的温度，挥发物，或部分熔化的组合。我们使用岩石物理预测来估计软流圈异常的熔体分数、熔体挥发分含量和温度结构。我们发现高达4%的熔体，最低的结晶度和剪切速度解释高达20%的水或20%CO2的熔体或类似的1%的近纯硫化物熔体，这取决于所使用的假设。在较宽深度范围内的间断异常和岩石圈底部的通道中，都需要熔融。软流层中的熔融是动态的，但在地质时间尺度上是持久的。
The lithosphere-asthenosphere system is fundamental to our understanding of mantle convection and plate tectonics. The different sensitivities of seismic and electromagnetic methods can be used together to better constrain the properties of the system. Here, we re-examine the shear velocity model from Rayleigh waves in light of the magnetotelluric based resistivity models from the Passive Imaging of the Lithosphere Asthenosphere Boundary (PI-LAB) experiment near the equatorial Mid-Atlantic Ridge, with the goal of generating a structurally consistent velocity and resistivity model for the region. Cross-plots of the models suggest a linear or near-linear trend that is also in agreement with petrophysical predictions. We generate a new shear velocity model from the resistivity models based on petrophysical relationships. The new velocity model fits the phase velocity data, and the correlation coefficient between the shear velocity and resistivity models is increased. Much of the model can be predicted by expectations for a thermal half-space cooling model, although some regions require a combination of higher temperatures, volatiles, or partial melt. We use the petrophysical predictions to estimate the melt fraction, melt volatile content, and temperature structure of the asthenospheric anomalies. We find up to 4% melt, with the lowest resistivities and shear velocities explained by up to 20% water or 20% CO2 in the melt or similar to 1% nearly pure sulfide melt, depending on the set of assumptions used. Melt is required in punctuated anomalies over broad depth ranges, and also in channels at the base of the lithosphere. Melt in the asthenosphere is dynamic, yet persistent on geologic timescales.