Global receiver function observations of the X-discontinuity reveal recycled basalt beneath hotspots
Global receiver function observations of the X-discontinuity reveal recycled basalt beneath hotspots
复制标题
X 不连续性的全局接收函数观测揭示了热点下方的再生玄武岩
DOI：
10.1016/j.epsl.2021.116813
复制
发表时间：
2021
影响因子：
5.3
通讯作者：
S. Cottaar
中科院分区：
文献类型：
--
作者：
S. Pugh;J. Jenkins;Alistair Boyce;S. Cottaar
热区下方化学不均质的分布对岩浆活动和地幔对流的来源具有重要的制约作用。上地幔中的化学不均一性产生了可以用地震探测到的不连续。一种这样的不连续现象--X-不连续现象(230-350公里深度)--在全球范围内间歇性地被观测到，有多种可能的原因机制。然而，为了更好地了解X不连续的原因及其与地幔隆起的关系，我们需要全球短波观测，以前没有通过具有宽阔上地幔菲涅尔区的反射相来分辨。利用具有短波横向敏感性(∼100千米)的高频P波接收函数(RF)，可以定位由地震可观测到的阻抗对比引起的不连续。利用P-to-S转换的30-90∘远震震相，我们在全球28个热点和6个克拉通的深度域和时间慢度域中叠加了RF。这揭示了在244-344公里深度的热点下有15个强健的X-不连续观测。另有10个潜在观测出现在热点之下，6个零观测出现在克拉通之下。在预计热点下地幔温度升高的情况下，两种原因机制仍然可能存在。柯石英-辉石相变发生在榴辉岩中和/或碳酸盐硅酸盐熔体在一定条件下形成。无论哪种机制提供地震可观测的阻抗对比，上地幔必须局部富含玄武岩。评估X-不连续的全球分布揭示了与大的低速省的相关性，这表明地幔热柱可能携带了来自最低地幔的再循环玄武岩。
The distribution of chemical heterogeneity beneath hotspots provides important constraints on the source of magmatism and mantle convection. Chemical heterogeneities in the upper mantle produce discontinuities that can be interrogated seismically. One such discontinuity, the X-discontinuity (230-350 km depth), is observed intermittently across the globe, with multiple possible causal mechanisms. However, to better understand the cause of the X-discontinuity and its relationship to mantle upwellings, we require global short wavelength observations, previously unresolved by reflected phases with broad upper mantle Fresnel zones. Discontinuities resulting from seismically observable impedance contrasts can be targeted using high frequency P wave receiver functions (RFs) possessing short wavelength lateral sensitivity (∼100 km) to structures almost directly beneath the station. Thus, below well-instrumented hotspots we can investigate the properties of the X-discontinuity and constrain the causal mechanisms in these locations.Using P-to-s converted teleseismic phases between 30-90∘, we stack RFs in the depth and time-slowness domains at 28 hotspots and 6 cratons globally. This reveals 15 robust X-discontinuity observations beneath hotspots between 244-344 km depth. A further 10 potential observations are present beneath hotspots, and 6 null observations beneath cratons. Two causal mechanisms remain possible at the elevated mantle temperatures expected beneath hotspots. The coesite-stishovite phase transition occurs in eclogite and/or carbonated silicate melt may form under certain conditions. For either mechanism to provide seismically observable impedance contrasts, the upper mantle must be locally enriched in basalt. Assessing the X-discontinuity global distribution reveals a correlation with the Large Low Velocity Provinces, suggesting that mantle plumes may entrain recycled basalt from the lowermost mantle.
DOI：
10.1029/2019gc008437
发表时间：
2019
期刊：
Geosystems
影响因子：
--
作者：
Williams, C. D.;Mukhopadhyay, S.;Rudolph, M. L.;Romanowicz, B.
通讯作者：
Romanowicz, B.
加拉帕戈斯群岛下方岩石圈结构和融化开始的接收函数成像
影响因子：
5.3
作者：
Rychert C
通讯作者：
Rychert C