Synthesizing Seemingly Contradictory Seismic and Magnetotelluric Observations in the Southeastern United States to Image Physical Properties of the Lithosphere
Synthesizing Seemingly Contradictory Seismic and Magnetotelluric Observations in the Southeastern United States to Image Physical Properties of the Lithosphere
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DOI：
10.1029/2019gc008279
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发表时间：
2019-06
期刊：
影响因子：
3.7
通讯作者：
B. Murphy;G. Egbert
中科院分区：
文献类型：
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作者：
B. Murphy;G. Egbert
虽然地震速度和电导率都对温度敏感，但岩石圈的热性质几乎完全来自地震数据，因为电导率往往受到小的高导电相的强烈影响，不能作为温度的可靠指标。然而，在某些情况下，电学观测可以对地幔温度提供强有力的限制。在美国东南部（SEUS），大地电磁（MT）数据要求高电阻率值（>300 Ωm），深度至少为200 km。由于干地幔矿物传导定律为观测到的电阻率值提供了温度上限，因此唯一的解释是岩石圈温度（<1330 °C）持续到200 km。然而，地震层析成像显示，在这个地区的速度一般略慢，相对于参考模型，这一观察导致了相对较薄（<150公里），侵蚀热岩石圈SEUS下面的看法。我们表明，MT和地震（层析成像，衰减，接收器功能）的结果是一致的厚（~200公里），相干热岩石圈在这一地区。降低的地震速度（相对于参考模型）可以通过考虑有限粒度（滞弹性）的影响来解释。当包括滞弹性效应时，作为温度函数的计算速度总体上较慢，即使在1 mm至1 cm的合理粒度下;这允许地幔温度比通常推断的温度更低。我们认为，在地球动力学的情况下，目前的热岩石圈在SEUS形成与大西洋中部岩浆省，并随后存活完整的~200马。
Although seismic velocity and electrical conductivity are both sensitive to temperature, thermal lithosphere properties are derived almost exclusively from seismic data because conductivity is often too strongly affected by minor highly conductive phases to be a reliable indicator of temperature. However, in certain circumstances, electrical observations can provide strong constraints on mantle temperatures. In the southeastern United States (SEUS), magnetotelluric (MT) data require high resistivity values (>300 Ωm) to at least 200‐km depth. As dry mantle mineral conduction laws provide an upper bound on temperature for an observed resistivity value, the only interpretation is that lithospheric temperatures (<1330 °C) persist to 200 km. However, seismic tomography shows that velocities in this region are generally slightly slow with respect to references models; this observation has led to a view of relatively thin (<150 km), eroded thermal lithosphere beneath the SEUS. We show that MT and seismic (tomography, attenuation, receiver function) results are consistent with thick (~200 km), coherent thermal lithosphere in this region. Reduced seismic velocities (relative to reference models) can be explained by considering the effect of finite grain size (anelasticity). Calculated velocity as a function of temperature is overall slower when including anelastic effects, even at reasonable grain sizes of 1 mm to 1 cm; this permits mantle temperatures that are colder than would typically be inferred. We argue for a geodynamic scenario in which the present thermal lithosphere in the SEUS formed in association with the Central Atlantic Magmatic Province and has subsequently survived intact for ~200 Ma.