Seismic evidence for orthopyroxene enrichment in the continental lithosphere
Seismic evidence for orthopyroxene enrichment in the continental lithosphere
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大陆岩石圈斜方辉石富集的地震证据
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
G. Zandt
中科院分区：
文献类型：
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作者：
L. Wagner;M. Anderson;J. Jackson;S. Beck;G. Zandt
我们评估了预测地震速度（Vp，压缩波；Vs，剪切波；和 Vp/Vs）的能力，以识别上地幔中相对于正常熔体贫乏橄榄岩成分富含斜方辉石的区域。在包括科罗拉多高原和卡普瓦尔克拉通在内的许多地点的地幔捕虏体中都发现了正方辉石富集。我们发现Vp/Vs比对斜方辉石浓度非常敏感，但对耗尽水平不敏感。我们将这些预测的速度和 Vp/Vs 比率与智利-阿根廷中部平板上方发现的高 Vs、低 Vp/Vs 异常进行比较。在误差范围内，一些富含斜方辉石的捕虏体的预测速度与智利-阿根廷上地幔观测到的速度相匹配。由于智利-阿根廷中部平板上方的异常不符合已知的地体边界，而是与下行的胡安·费尔南德斯山脊轨迹一致，因此我们认为该地区的斜方辉石富集可能与平板过程有关，这对我们了解美国西部和其他地方的岩石圈二氧化硅富集具有影响。
We assess the ability of predicted seismic velocities (Vp, compressional wave; Vs, shear wave; and Vp/Vs) to identify regions in the upper mantle that are enriched in orthopyroxene relative to normal melt-depleted peridotite compositions. Orthopyroxene enrichment has been found in mantle xenoliths from a number of locations, including the Colorado Plateau and the Kaapvaal craton. We find that the Vp/Vs ratio is very sensitive to orthopyroxene concentration, but it is not sensitive to depletion level. We compare these predicted velocities and Vp/Vs ratios to the high Vs, low Vp/Vs anomaly found above the central Chile–Argentina flat slab. Within error, the predicted velocities of some of the orthopyroxene-enriched xenoliths match the observed velocities from the Chile-Argentina upper mantle. Because the anomaly above the central Chile–Argentina flat slab does not conform to known terrane boundaries but does align with the downgoing Juan Fernandez ridge track, we suggest that the orthopyroxene enrichment in this area may be related to flat slab processes, which would have implications for our understanding of lithospheric silica enrichment in the western U.S. and elsewhere.