The Earth's lowermost mantle is characterized by two large low shear velocity provinces (LLSVPs). The regions outside the LLSVPs have been suggested to be strongly influenced by subducted slabs and, therefore, much colder than the LLSVPs. However, localized low‐velocity seismic anomalies have been detected in the subduction‐influenced regions, whose origin remains unclear. Here, three‐dimensional geodynamic calculations are performed, and they show that linear, ridge‐like hot thermal anomalies, or thermal ridges, form in the relatively cold, downwelling regions of the lowermost mantle. Like the formation of Richter rolls due to sublithosphere small‐scale convection (SSC), the thermal ridges form as a result of SSC from the basal thermal boundary layer and they extend in directions parallel to the surrounding mantle flow. The formation of thermal ridges in subduction regions of the lowermost mantle is very sensitive to the thermal structures of the subducted materials, and thermal heterogeneities brought to the bottom of the mantle by subducting slabs greatly promote the formation of thermal ridges. The formation of thermal ridges is also facilitated by the increase of core‐mantle boundary heat flux and vigor of lowermost mantle convection. The thermal ridges may explain the low‐velocity seismic anomalies outside of the LLSVPs in the lowermost mantle. The results suggest that the relatively cold, subduction‐influenced regions of the Earth's lowermost mantle may contain localized hot anomalies.

中文翻译：

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地球最低地幔冷俯冲影响区热异常的形成

地球的最低地幔具有两个大的低剪切速度省（LLSVP）。有人认为，低层低纬度卫星以外的区域受俯冲板的强烈影响，因此比低层低纬度卫星要冷得多。但是，在俯冲影响的地区发现了局部低速地震异常，其起源尚不清楚。在这里，进行了三维地球动力学计算，结果表明，线性，脊状热异常或热脊形成在最低地幔的相对较冷的井下区域。就像由于岩石圈下小尺度对流（SSC）形成里希特辊一样，热脊是基底热边界层的SSC形成的结果，它们沿与周围地幔流平行的方向延伸。最下层地幔俯冲区的热脊的形成对俯冲物质的热结构非常敏感，俯冲板带到地幔底部的热非均质性极大地促进了热脊的形成。地幔边界热通量的增加和最低地幔对流的活力也促进了热脊的形成。热脊可能解释了最下地幔中的LLSVPs以外的低速地震异常。结果表明，地球最底层的地幔相对较冷，受俯冲影响的区域可能包含局部的热异常。俯冲板带到地幔底部的热非均质性极大地促进了热脊的形成。地幔边界热通量的增加和最低地幔对流的活力也促进了热脊的形成。热脊可能解释了最下地幔中的LLSVPs以外的低速地震异常。结果表明，地球最底层的地幔相对较冷，受俯冲影响的区域可能包含局部的热异常。俯冲板带到地幔底部的热非均质性极大地促进了热脊的形成。地幔边界热通量的增加和最低地幔对流的活力也促进了热脊的形成。热脊可能解释了最下地幔中的LLSVPs以外的低速地震异常。结果表明，地球最底层的地幔相对较冷，受俯冲影响的区域可能包含局部的热异常。热脊可能解释了最下地幔中的LLSVPs以外的低速地震异常。结果表明，地球最底层的地幔相对较冷，受俯冲影响的区域可能包含局部的热异常。热脊可能解释了最下地幔中的LLSVP以外的低速地震异常。结果表明，地球最底层的地幔相对较冷，受俯冲影响的区域可能包含局部的热异常。