Evidence for a compositional boundary within the lithospheric mantle beneath the Kalahari craton from S receiver functions
Evidence for a compositional boundary within the lithospheric mantle beneath the Kalahari craton from S receiver functions
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DOI：
10.1016/j.epsl.2008.05.026
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发表时间：
2008-08
影响因子：
5.3
通讯作者：
B. Savage;P. Silver
中科院分区：
文献类型：
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作者：
B. Savage;P. Silver
从南部非洲地震实验的S和P接收器功能进行了分析，岩石圈不连续的卡拉哈里克拉通。除莫霍面外，最显著的特征是在约150 km深度处地震速度不连续地降低约4.5%。不连续面的宽度似乎约为10公里。被称为K-不连续面，这一特征仅限于阵列的北方，从津巴布韦克拉通向南延伸到TML（Thabazimbi-Murchison线性构造），从博茨瓦纳向西延伸到东部的卡拉哈里克拉通边缘。它跨越几个太古代缝合线，因此不太可能与太古代构造有关。然而，它似乎与随后的岩浆事件有关。最强烈的异常与最强烈的卡鲁火山作用相一致，并延伸到布什维尔德侵入体的北方边缘。从地幔捕虏体和捕虏晶来看，整个岩石圈似乎经历了玄武岩熔体和交代流体的长期浸润。我们建议，K-不连续性反映了这种熔体/交代渗透的影响，随着时间的推移，侵入和再受精的岩石圈。基于金伯利岩管道，表现出明显的迹象，熔体交代作用和可能的卡鲁影响，所观察到的地震速度的减少是合理的符合所观察到的主要元素和挥发性富集在150公里深的金伯利岩。如果这种解释是正确的，那么最清楚地反映这种扰动的高温金伯利岩结核可能代表了岩石圈下部的一般状态，而不仅仅是反映金伯利岩喷发附近的局部地幔特性。
S and P receiver functions from the Southern African Seismic Experiment are analyzed for lithospheric discontinuities beneath the Kalahari craton. Besides the Moho, the most prominent feature is a discontinuous reduction in seismic velocity of about 4.5% at approximately 150 km depth. The discontinuity appears to have a width of about 10 km. Termed the K-discontinuity, this feature is restricted to the northern half of the array, extending from the Zimbabwe craton south to the TML (Thabazimbi–Murchison lineament), and in the west from Botswana to the edge of the Kalahari craton in the east. It spans several Archean sutures and is thus unlikely related to Archean tectonics. It does, however, appear to be related to subsequent magmatic episodes. The strongest anomaly is coincident with the most intense Karoo volcanism, and it extends to the northern edge of the Bushveld intrusion. From mantle xenoliths and xenocrysts, the entire lithosphere in this region appears to have experienced a long-term infiltration of basaltic melt and metasomatic fluids. We propose that the K-discontinuity reflects the influence of this melt/metasomatic infiltration, which has, over time, intruded and refertilized the lithosphere. Based on kimberlites pipes that show obvious signs of melt metasomatism and likely Karoo influence, the observed reduction in seismic velocity is plausibly consistent with the observed major-element and volatile enrichment at 150 km depth in such kimberlites. If this interpretation is correct, then the high-temperature kimberlite nodules that most clearly reflect this perturbation likely represent the general state of the lower lithosphere, rather than only reflecting local mantle properties in the immediate vicinity of the kimberlite eruption.