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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Asthenospheric flow and lithospheric evolution near the Mendocino Triple Junction
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Asthenospheric flow and lithospheric evolution near the Mendocino Triple Junction

机译：门多西诺三结附近的软流圈流动和岩石圈演化

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The migration of the Mendocino Triple Junction in northern California creates a complicated lithosphere-asthenosphere boundary system at shallow depths (< 60. km), following the progressive transition from Cascadia subduction to San Andreas transform motion. It provides a natural laboratory to examine lithospheric evolution associated with slab removal in an active tectonic setting. However, pathways of the asthenospheric sources that fill the slab-free region created by the triple junction migration remain unclear. Previous active source profiles and body-wave tomography are limited to either crustal or a deeper upper mantle scale, respectively. In this study, we present a three-dimensional shear velocity model from joint inversion of ambient noise (8-30. s) and ballistic Rayleigh wave dispersion curves (22-100. s), as well as Ps receiver functions, using 111 stations from the Flexible Array Mendocino Experiment, USArray Transportable Array and the regional Berkeley Digital Seismic Network. In the crust, we have observed the low-Vs Franciscan Complex in the Coast Ranges and the relatively high-Vs Great Valley ophiolite abutting the low-Vs Sierran basement. The low-Vs uppermost mantle imaged near the sudden steepening of the subducted oceanic slab extends seismic evidence for forearc mantle serpentinization further south along the Cascadia margin. In addition to the asthenosphere beneath the Gorda plate, the joint inversion Vs model further identifies three other young asthenospheres resulting from different partial melting mechanisms. Northward motion of the triple junction causes asthenospheric flow both from under the Gorda plate and from the cooling former mantle wedge left under the Great Valley and Sierra Nevada, imaged from the joint inversion as a relatively deep (> 75. km) low-Vs anomaly. These two mantle flows appear to begin mixing ~. 100. km south of the southern edge of the Gorda plate in the slab window region. We speculate that the latter provides the wedge-type geochemical signature seen in the Coast Range volcanic rocks, reconciling slab window models and volcanic geochemistry. This 'staggered' upwelling model proposed here also explains the ~. 3. Myr delay in onset of volcanism after triple junction migration.
机译：从卡斯卡迪亚俯冲向圣安地列斯变换运动的逐步过渡之后，北加州门多西诺三结的迁移在浅深度（<60公里）处形成了一个复杂的岩石圈-软流圈边界系统。它提供了一个天然的实验室，以研究在活跃的构造环境中岩石与板块清除相关的演化。然而，充满由三重结合迁移产生的无平板区域的软流圈源的途径仍不清楚。以前的活动源剖面和体波层析成像分别限于地壳或更深的上地幔尺度。在这项研究中，我们使用111个站，从环境噪声（8-30。s）和弹道瑞利波频散曲线（22-100。s）的联合反演以及Ps接收器函数提出了三维剪切速度模型来自灵活阵列Mendocino实验，USArray可移动阵列和地区性的伯克利数字地震网络。在地壳中，我们观察到了海岸范围内的低伏特方济各联合体和低伏特西勒然地下室附近的高伏特大山谷蛇绿岩。在俯冲的海洋平板突然陡峭附近成像的低Vs最上层地幔，为沿卡斯卡迪亚边缘向南的前陆地幔蛇形化扩展了地震证据。除了Gorda板下的软流圈，联合反演Vs模型还确定了由不同的部分熔融机制产生的另外三个年轻的软流圈。三重结的北向运动会导致流变层的气流从戈尔达板下方和大谷和内华达山脉下方遗留的冷却前地幔楔中流失，这从联合倒影中可以看出是相对较深（> 75. km）的低Vs异常。 。这两个地幔流似乎开始混合〜。平板窗口区域中的Gorda板南缘以南100. km。我们推测，后者提供了在海岸山脉火山岩中看到的楔型地球化学特征，协调了平板窗口模型和火山地球化学。这里提出的这种“交错”上升流模型也解释了〜。 3.三联结迁移后，Myr延迟了火山爆发。

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