Evidence of Subduction-Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions
Evidence of Subduction-Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions
复制标题
DOI：
10.1029/2018gl078378
复制
发表时间：
2018-09-16
影响因子：
5.2
通讯作者：
Goes, Saskia
中科院分区：
文献类型：
--
作者：
Maguire, Ross;Ritsema, Jeroen;Goes, Saskia
法拉隆板块的俯冲改变了美国地幔过渡带(MTZ)的温度和组成。基于相变性质随温度和成分变化的实验约束，我们利用美国阵列波形数据和理论地震剖面，通过在矿物学相变时映射P-S转换来研究MTZ结构。在研究区域内，MTZ的宽度变化约35公里，对应的温度变化超过300K。MTZ是美国东部最冷、最厚的区域，高剪切速度异常在那里得到层析解析。我们在520公里和730公里处探测到了间歇性的P-S转换。在美国东南部730公里深度的转换是一致的，并与大约50%的玄武岩富集度一致，这可能是由于大洋高原的一部分(即赫斯共轭)侵位所致。简而言之，地球在大约400公里到800公里深度之间的地幔过渡带的特征是矿物学相变，这取决于压力、温度和成分。通过矿物相变传播的地震波可以改变极化：纵波(P波)可以变成横波(S波)。在这项研究中，我们使用美国地震仪网络(即美国阵列)的地震记录来分析P到S转换波。根据对P-S转换到达时间和幅度的估计，我们绘制了矿物相变的深度和强度以及过渡带的温度和成分。我们的地震观测证实了北美大陆西缘法拉隆板块俯冲的地质史模型。美国东部的地幔过渡带是最冷的，在墨西哥湾地区的过渡带底部仍然存在以前的大洋高原的碎片。
The subduction of the Farallon Plate has altered the temperature and composition of the mantle transition zone (MTZ) beneath the United States. We investigate MTZ structure by mapping P-to-S conversions at mineralogical phase changes using USArray waveform data and theoretical seismic profiles based on experimental constraints of phase transition properties as a function of temperature and composition. The width of the MTZ varies by about 35km over the study region, corresponding to a temperature variation of more than 300 K. The MTZ is coldest and thickest beneath the eastern United States where high shear velocity anomalies are tomographically resolved. We detect intermittent P-to-S conversions at depths of 520km and 730km. The conversions at 730-km depth are coherent beneath the southeastern United States and are consistent with basalt enrichment of about 50%, possibly due to the emplacement of a fragment of an oceanic plateau (i.e., the Hess conjugate).Plain Language Summary The Earth's mantle transition zone between depths of about 400km and 800km is characterized by mineralogical phase transitions that depend on pressure, temperature, and composition. Seismic waves that propagate through mineral phase transitions can change polarization: a compressional wave (P wave) can change into a transverse wave (S wave). In this study, we analyze P-to-S converted waves using recordings of earthquakes from a network of seismographs in the United States (i.e., the USArray). From estimates of the arrival times and amplitudes of P-to-S conversions, we map the depths and strength of mineral phase transitions and the temperature and composition of the transition zone. Our seismic observations confirm models of the geologic history of Farallon Plate subduction along the western margin of the North American continent. The mantle transition zone is coolest beneath the eastern United States, and fragments of former oceanic plateaus are still present at the base of the transition zone beneath the Gulf of Mexico region.