Spatial Characteristics of Recycled and Primordial Reservoirs in the Deep Mantle
Spatial Characteristics of Recycled and Primordial Reservoirs in the Deep Mantle
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深部地幔再生与原始储层空间特征
DOI：
10.1029/2020gc009525
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Steinberger, B.
中科院分区：
文献类型：
--
作者：
Jackson, M. G.;Becker, T. W.;Steinberger, B.
地球化学域的空间分布承载再循环地壳和原始（高-3 He/4 He）水库，以及它们如何与地幔对流，知之甚少。位于核幔边界附近的两个大陆规模的地震异常-称为大型低剪切波速度区（LLSVP）-是潜在的地球化学储层宿主。有人认为，高3 He/4 He热点在空间上局限于LLSVP，采样再生大陆地壳的热点仅与其中一个LLSVP相关，再生大陆地壳与纬度无关。我们重新评估LLSVP和热点熔岩同位素签名之间的联系，使用改进的地幔流模型，包括羽导管平流。虽然大多数具有最高-3He/4He的热点确实可以追溯到LLSVP内部，但至少有一个高-3He/4He热点，黄石公园，位于LLSVP之外。这表明高3 He/4 He在地理上并不局限于LLSVP。相反，热点浮力通量与最大热点3 He/4 He之间的正相关性表明，这是羽流动力学（即，浮力），而不是地理位置，这决定了是否夹带了密集、深层和可能广泛分布的高3 He/4 He储层。我们还表明，地幔柱供给的EM热点（富集地幔，低-143 Nd/144 Nd），信号再生大陆地壳，在空间上与LLSVP都有联系，主要位于南半球。最后，我们确认热点采样HIMU（“高μ”或高238 U/204 Pb）域在空间上不限于LLSVP。这些研究结果澄清和推进我们对深地幔储层分布的理解，我们讨论了大陆和海洋地壳俯冲是如何与EM和HIMU的空间解耦相一致的。
The spatial distribution of the geochemical domains hosting recycled crust and primordial (high‐3He/4He) reservoirs, and how they are linked to mantle convection, are poorly understood. Two continent‐sized seismic anomalies located near the core‐mantle boundary—called the Large Low Shear Wave Velocity Provinces (LLSVPs)—are potential geochemical reservoir hosts. It has been suggested that high‐3He/4He hotspots are spatially confined to the LLSVPs, hotspots sampling recycled continental crust are associated with only one of the LLSVPs, and recycled continental crust shows no relationship with latitude. We reevaluate the links between LLSVPs and isotopic signatures of hotspot lavas using improved mantle flow models including plume conduit advection. While most hotspots with the highest‐3He/4He can indeed be traced to the LLSVP interiors, at least one high‐3He/4He hotspot, Yellowstone, is located outside of the LLSVPs. This suggests high‐3He/4He is not geographically confined to the LLSVPs. Instead, a positive correlation between hotspot buoyancy flux and maximum hotspot3He/4He suggests that it is plume dynamics (i.e., buoyancy), not geography, which determines whether a dense, deep, and possibly widespread high‐3He/4He reservoir is entrained. We also show that plume‐fed EM hotspots (enriched mantle, with low‐143Nd/144Nd), signaling recycled continental crust, are spatially linked to both LLSVPs, and located primarily in the southern hemisphere. Lastly, we confirm that hotspots sampling HIMU (“high‐μ,” or high238U/204Pb) domains are not spatially limited to the LLSVPs. These findings clarify and advance our understanding of deep mantle reservoir distributions, and we discuss how continental and oceanic crust subduction is consistent with the spatial decoupling of EM and HIMU.
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