Synthetic images of dynamically predicted plumes and comparison with a global tomographic model
Synthetic images of dynamically predicted plumes and comparison with a global tomographic model
复制标题
动态预测羽流的合成图像以及与全局断层扫描模型的比较
DOI：
10.1016/j.epsl.2011.09.012
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发表时间：
2011
影响因子：
5.3
通讯作者：
H. Smith
中科院分区：
文献类型：
--
作者：
E. Styles;S. Goes;P. V. Keken;J. Ritsema;H. Smith
地幔柱的地震探测可以解决热点的起源和地幔柱在地幔对流中的作用的争论。在本文中，我们测试的假设，即整个地幔柱存在的主要热点之下，通过定量比较物理上合理的地幔柱模型与地震图像以下三个步骤。我们（1）通过求解轴对称球壳中类地参数的控制方程来模拟一组代表性的热羽流，（2）使用自洽热动力学关系将热结构转换为剪切速度异常，以及（3）使用S40 RTS层析滤波器将理论羽流投影为地震图像，以解释有限的地震分辨率。在300 ~ 660 km深度范围内，超温为375 K的模拟地幔柱出现4-8%的负剪切波异常，中下地幔出现2.0-3.5%的负剪切波异常。由于S40 RTS的分辨率不均匀，如果上地幔的尾窄于150- 250 km或下地幔的尾窄于400- 700 km，则不容易探测到这种强度的羽流。在S40 RTS中，我们研究的40个热点中有一半以上覆盖着延伸穿过大部分下地幔的低速异常。这些异常超过0.6%，在下地幔，热柱强度兼容。它们的宽度大多在800- 1200公里之间，这是合理的热羽流结构的高端，而在S40 RTS中要解决的低端。在上地幔，剪切速度在90%以上的热点之下是低的。对于包括冰岛、东非热点、夏威夷、萨摩亚/塔希提岛和科布/鲍伊对在内的大约10个地区，S40 RTS低速异常延伸穿过过渡带，意味着在~ 1000 km宽的区域内有200- 300 K的高温。这比热羽流尾部的预期要广泛得多。这种异常可能是兼容的深层次的羽流，但只有当羽流流量是强烈的变化，由于，例如，与相变和/或化学夹带的相互作用。
Seismic detection of a mantle plume may resolve the debate about the origin of hotspots and the role of plumes in mantle convection. In this paper, we test the hypothesis that whole-mantle plumes exist below major hotspots, by quantitatively comparing physically plausible plume models with seismic images following three steps. We (1) simulate a set of representative thermal plumes by solving the governing equations for Earth-like parameters in an axisymmetric spherical shell, (2) convert the thermal structure into shear-velocity anomalies using self-consistent thermo-dynamic relationships, and (3) project the theoretical plumes as seismic images using the S40RTS tomographic filter to account for finite seismic resolution. Simulated plumes with excess potential temperatures of 375K map into negative shear-wave anomalies of up to 4–8% between 300 and 660km depth, and 2.0–3.5% in the mid-lower mantle. Given the heterogeneous resolution of S40RTS, plumes of this strength are not easily detectable if tails are narrower than 150–250km in the upper-mantle or 400–700km in the lower mantle. In S40RTS, more than half of the forty hotspots we studied overlie low-velocity anomalies that extend through most of the lower mantle. These anomalies exceed 0.6% in the lower mantle, compatible with thermal plume strengths. They have widths mostly with the range 800–1200km, which is at the high end of plausible thermal plume structures, and at the low end to be resolved in S40RTS. In the upper mantle, the shear velocity is low beneath more than ninety percent of the hotspots. For about ten, including Iceland, the East African hotspots, Hawaii, and the Samoa/Tahiti and Cobb/Bowie pairs, S40RTS low-velocity anomalies extending through the transition zone imply 200–300K excess temperatures over a ~1000km wide region. This is substantially broader than expected for thermal plume tails. Such anomalies may be compatible with deep-seated plumes, but only if plume flux is strongly variable due to, for example, interaction with phase transitions and/or chemical entrainment.