Thirty-nine 1D shear wave velocity profiles, obtained by jointly inverting receiver functions and Rayleigh wave group velocities, are used to investigate the crustal structure of the Bushveld Complex in northern South Africa. Data from teleseismic earthquakes recorded on broadband seismic stations between 1997 and 1999 and 2015–2020 were used to compute P-wave receiver functions. Rayleigh wave group velocities between 5 and 30 s period were obtained from an ambient noise tomography and combined with group velocities between 30 and 60 s period from a published continental-scale surface wave tomography model. Moho depths of 45–47.5 km are found under the center of the complex compared to 40 km thick crust, on average, surrounding the complex, indicating ∼5–7 of crustal thickening. The bottom ∼10 km or more of the lower crust across much of the Bushveld Complex has a Vs ≥ 4.0 km/s, consistent with a mafic composition, whereas in most areas around the margins of the complex the thickness of the mafic lower crust is much less than 10 km. In the upper crust higher velocity structure (Vs > 3.6 km/s) above 15 km depth underlain by lower velocity structure is seen in many locations, suggesting the presence of mafic/ultramafic layering. These results favor the continuous-sheet model for the structure of the Bushveld Complex because the ensemble of 1D models is characterized by three diagnostic features consistent with that model: (1) thicker crust under the center of the complex than away from the complex; (2) a greater thickness of high-velocity (i.e., mafic) layering in the lower crust under the complex compared to away from the complex; (3) high-velocity (i.e., mafic/ultramafic) layering in the upper crust beneath much of the complex. The lack of upper crustal mafic/ultramafic layering beneath some parts of the complex is consistent with the post-emplacement tectonic and magmatic history of the complex.

中文翻译：

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来自一维横波速度模型的南非 Bushveld 杂岩体的地壳结构：全复杂地壳改造的证据


通过联合反转接收器函数和瑞利波群速度获得的 39 个一维横波速度剖面用于研究南非北部布什维尔德杂岩体的地壳结构。1997 年至 1999 年和 2015-2020 年期间宽带地震站记录的远程地震数据用于计算 P 波接收器函数。从环境噪声断层扫描中获得 5 到 30 s 周期的瑞利波群速度，并与来自已发表的大陆尺度表面波断层扫描模型的 30 到 60 s 周期之间的群速度相结合。在复合体中心下发现的莫霍深度为 45-47.5 公里，而复合体周围的平均地壳厚度为 40 公里，表明地壳增厚约为 5-7 公里。在布什维尔德杂岩体的大部分地区，下部地壳底部 ∼10 公里或更深处的 Vs ≥ 4.0 公里/秒，与镁铁质成分一致，而在杂岩体边缘周围的大多数地区，镁铁质下部地壳的厚度远小于 10 公里。在上地壳中，在许多地方可以看到超过 15 km 深度的较高速度结构（Vs > 3.6 km/s），下方是较低速度结构，表明存在镁铁质/超镁铁质分层。这些结果有利于布什维尔德杂岩结构的连续片模型，因为一维模型的集成具有与该模型一致的三个诊断特征：（1） 杂岩中心下的地壳比远离杂岩的地壳更厚;（2） 与远离杂岩相比，在杂岩体下方的下部地壳中，高速（即镁铁质）分层的厚度更大;（3） 大部分复合物下方上部地壳中的高速（即镁铁质/超镁铁质）分层。 在该杂岩体的某些部分下方缺乏上地壳镁铁质/超镁铁质层，这与该杂岩体的后放置构造和岩浆历史一致。