A long-standing question is how felsic continental crust is differentiated from its mafic parent mantle magmas. One currently proposed fundamental mechanism is lithospheric foundering and loss of dense material into the mantle. A type locality is the young extinct arc forming the Sierra Nevada, California. Here, we image a distinct anisotropic shear layer below the crust-mantle boundary using receiver functions. The sense of shear is consistent with west- to southwestward removal of lithosphere. The shear signal is strongest in the southern Sierra, where lithospheric foundering was proposed to have concluded several million years ago, and is deeper and less pronounced in the central Sierra, where ongoing lithospheric foundering is corroborated by a band of unusually deep (40+ km) seismicity along the western foothills. Our observations provide progressive snapshots of a lithospheric foundering process spanning several million years and hundreds of kilometers, illuminating a fundamental differentiation process by which continents are built.

中文翻译：

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在已灭绝的大陆弧下成像的岩石圈沉没


一个长期存在的问题是长英质大陆地壳与其镁铁质母体地幔岩浆有何区别。目前提出的一个基本机制是岩石圈沉没和致密物质流失到地幔中。一个类型地点是形成加利福尼亚州内华达山脉的年轻灭绝弧。在这里，我们使用接收器函数对地壳-地幔边界下方明显的各向异性剪切层进行成像。切变感与岩石圈从西向西到西南的移除一致。切变信号在南部 Sierra 最强，那里的岩石圈凿陷被认为在数百万年前就已经结束，而在 Sierra 中部更深且不那么明显，那里正在进行的岩石圈凿岩被沿西部山麓的异常深 （40+ km） 地震带证实。我们的观测提供了跨越数百万年和数百公里的岩石圈凿成过程的渐进快照，阐明了大陆形成的基本分化过程。