Hot Upper Mantle Beneath the Tristan da Cunha Hotspot From Probabilistic Rayleigh-Wave Inversion and Petrological Modeling
Hot Upper Mantle Beneath the Tristan da Cunha Hotspot From Probabilistic Rayleigh-Wave Inversion and Petrological Modeling
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DOI：
10.1002/2017gc007347
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发表时间：
2018-05-01
影响因子：
3.5
通讯作者：
Baba, Kiyoshi
中科院分区：
文献类型：
--
作者：
Bonadio, Raffaele;Geissler, Wolfram H.;Baba, Kiyoshi
了解特里斯坦-库尼亚地区神秘的板内火山活动需要了解岩石圈和软流圈的温度，我们测量了瑞利波的相位-速度曲线，利用特里斯坦周围海底地震仪阵列的瑞利波地震图的互相关，约束了区域平均剪切速度结构，并推断了热点下面的岩石圈和软流圈的温度。海底数据集带来了一些挑战，需要采用不同于陆基台站阵列的数据处理和测量方法。推导出一个强大的，相速度曲线的特里斯坦地区，我们反演横波速度剖面使用概率（马尔可夫链蒙特卡罗）的方法。该模型显示出明显的低速异常从70至至少120公里的深度。低速区的VS为4.1-4.2 km/s，不像夏威夷报告的那样低（约为4.0 km/s），这可能表明热异常不太明显，也可能表明部分熔融较少。岩石学建模表明，地震和测深数据与中等温度的地幔（地幔潜在温度为1，410 - 1，430摄氏度，与全球平均水平相比高出约50-120摄氏度）和小于1%的熔融分数一致。纯粹的地震反演和岩石学建模都表明岩石圈厚度为65-70公里，与接收器功能的最新估计一致。特里斯坦下方存在高于平均温度的软流层，这与来自地幔深部的热上涌（羽流）相一致。然而，我们确定的超额温度比其他一些主要热点，特别是夏威夷报告的要小。简明语言摘要当海洋构造板块移动到下伏地幔中的极热区域（热点）时，就产生了像夏威夷这样的火山海洋岛屿链。热点的起源被归因于地幔柱，即从地球的核幔边界（2，800公里深）发生的壮观的热隆起。羽流的存在及其在火山活动特定地点之下的出现是一个激烈辩论的问题。查明是否存在热上升流的一种方法是确定热点位置构造板块下方地幔深处的温度。然而，这些深度约为100公里，那里的温度无法直接测量。在这项研究中，我们使用了部署在特里斯坦-达库尼亚（南大西洋的一个突出热点）周围的海底地震仪阵列的新地震数据，并确定了它下面的地震速度。我们能够利用这种依赖关系来推断特里斯坦周围构造板块内部和下方的温度。气温高得令人不安。这与热地幔柱从下面到达特里斯坦并导致该位置不寻常的长期火山活动相一致。
Understanding the enigmatic intraplate volcanism in the Tristan da Cunha region requires knowledge of the temperature of the lithosphere and asthenosphere beneath it. We measured phase-velocity curves of Rayleigh waves using cross-correlation of teleseismic seismograms from an array of ocean-bottom seismometers around Tristan, constrained a region-average, shear-velocity structure, and inferred the temperature of the lithosphere and asthenosphere beneath the hotspot. The ocean-bottom data set presented some challenges, which required data-processing and measurement approaches different from those tuned for land-based arrays of stations. Having derived a robust, phase-velocity curve for the Tristan area, we inverted it for a shear wave velocity profile using a probabilistic (Markov chain Monte Carlo) approach. The model shows a pronounced low-velocity anomaly from 70 to at least 120 km depth. VS in the low velocity zone is 4.1-4.2 km/s, not as low as reported for Hawaii (approximate to 4.0 km/s), which probably indicates a less pronounced thermal anomaly and, possibly, less partial melting. Petrological modeling shows that the seismic and bathymetry data are consistent with a moderately hot mantle (mantle potential temperature of 1,410-1,430 degrees C, an excess of about 50-120 degrees C compared to the global average) and a melt fraction smaller than 1%. Both purely seismic inversions and petrological modeling indicate a lithospheric thickness of 65-70 km, consistent with recent estimates from receiver functions. The presence of warmer-than-average asthenosphere beneath Tristan is consistent with a hot upwelling (plume) from the deep mantle. However, the excess temperature we determine is smaller than that reported for some other major hotspots, in particular Hawaii.Plain Language Summary The chains of volcanic ocean islands such as Hawaii are created when oceanic tectonic plates move over anomalously hot regions (hotspots) in the underlying mantle. The origin of hotspots has been attributed to mantle plumes, spectacular hot upwellings from the Earth's core-mantle boundary (2,800 km depth). The existence of the plumes and their occurrence beneath particular locations of volcanism are a matter of a heated debate. One way to find out whether a hot upwelling may be present is to determine the temperature in the mantle at depths just beneath the tectonic plate in the location of a hotspot. These depths are around 100 km, however, and temperature there cannot be measured directly. In this study, we used new seismic data from an array of ocean-bottom seismometers deployed around Tristan da Cunha, a prominent hotspot in the South Atlantic Ocean, and determined seismic velocities beneath it. Seismic velocities depend on the temperature of the mantle rock. We were able to use this dependence to infer the temperature within and below the tectonic plate around Tristan. The temperature is anomalously high. This is consistent with a hot mantle plume reaching Tristan from below and causing the unusual, long-lived volcanism at this location.