The thermo-chemical and physical structure beneath the North American continent from Bayesian inversion of surface-wave phase velocities
The thermo-chemical and physical structure beneath the North American continent from Bayesian inversion of surface-wave phase velocities
复制标题
通过表面波相速度贝叶斯反演了解北美大陆下方的热化学和物理结构
DOI：
10.1029/2011jb008380
复制
发表时间：
2011
影响因子：
--
通讯作者：
F. Deschamps
中科院分区：
文献类型：
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作者：
Amir Khan;A. Zunino;F. Deschamps
[1] 我们联合反演北美大陆下方约 1000 公里深度的地幔热化学和各向异性物理结构的径向模型的局部基模和高阶表面波相速度。热化学态反演依赖于自洽热力学方法，通过该方法将相平衡和物理性质（纵波、横波速度和密度）计算为成分（在 Na2O-CaO-FeO-MgO-Al2O3-SiO2 模型系统中）、压力和温度的函数。我们采用基于采样的策略来解决非线性逆问题，依靠马尔可夫链蒙特卡罗方法对模型空间中的后验分布进行采样。获得了一系列在不确定性范围内拟合观测结果的模型，从中可以估计任何统计数据。为了进一步细化采样模型，我们计算这些数据集合的大地水准面异常，并与观测值进行比较，举例说明通过使用附加数据进行后验过滤。我们的热化学图显示，相对于活跃的较年轻地区（西缘和海洋），北美东部地区构造稳定，化学成分贫乏（高 Mg#）且温度较低（>200°C）。在过渡带，热化学结构与上地幔的热化学结构脱钩，克拉通区域下方出现相对较热的热异常，并可能延伸至下地幔。在下地幔中，没有观察到一致的大规模热化学异质性，尽管我们的结果确实表明上地幔和下地幔的成分不同。关于各向异性结构，我们发现了许多明显的各向异性层遍布地幔的证据，包括过渡带和最上层的下地幔。
[1] We jointly invert local fundamental-mode and higher-order surface-wave phase-velocities for radial models of the thermo-chemical and anisotropic physical structure of the Earth's mantle to ∼1000 km depth beneath the North American continent. Inversion for thermo-chemical state relies on a self-consistent thermodynamic method whereby phase equilibria and physical properties (P-, S-wave velocity and density) are computed as functions of composition (in the Na2O-CaO-FeO-MgO-Al2O3-SiO2 model system), pressure and temperature. We employ a sampling-based strategy to solve the non-linear inverse problem relying on a Markov Chain Monte Carlo method to sample the posterior distribution in the model space. A range of models fitting the observations within uncertainties are obtained from which any statistics can be estimated. To further refine sampled models we compute geoid anomalies for a collection of these and compare with observations, exemplifying a posteriori filtering through the use of additional data. Our thermo-chemical maps reveal the tectonically stable older eastern parts of North America to be chemically depleted (high Mg#) and colder (>200°C) relative to the active younger regions (western margin and oceans). In the transition zone the thermo-chemical structure decouples from that of the upper mantle, with a relatively hot thermal anomaly appearing beneath the cratonic area that likely extends into the lower mantle. In the lower mantle no consistent large-scale thermo-chemical heterogeneities are observed, although our results do suggest distinct upper and lower mantle compositions. Concerning anisotropy structure, we find evidence for a number of distinct anisotropic layers pervading the mantle, including transition zone and upper-most lower mantle.