Ongoing oroclinal bending in the Cascadia forearc and its relation to concave-outboard plate margin geometry
Ongoing oroclinal bending in the Cascadia forearc and its relation to concave-outboard plate margin geometry
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卡斯卡迪亚前弧持续的口斜弯曲及其与凹外侧板边缘几何形状的关系
作者：
Finley, Theron;Morell, Kristin;Leonard, Lucinda;Regalla, Christine;Johnston, Stephen T.;Zhang, Wenbo
凹内侧（凹向覆盖板）的几何形状，大多数收敛的边缘被认为是一个薄的球冠边缘的抑郁症的自然后果，而凹外侧边缘部分通常形成在俯冲板上的压头。在卡斯卡迪亚俯冲带，海沟中一个>500公里长的凹外侧弯曲的顶点目前没有显示出明显的压头俯冲，但确实与奥林匹克半岛周围拱形的上板岩石中面向外侧的凹陷的轴线重合。位于美国华盛顿州西北部。在这里，我们综合古地磁和结构数据与全球导航卫星系统数据的新的分析表明，在卡斯卡迪亚的上板块已被折叠从中新世到现在成一个造山带的轴向轨迹，平分奥林匹克半岛。适应弯曲的过程，我们认为包括（1）在造山翼上的挠曲滑动折叠和（2）缩短，隆起，并在奥林匹克山褶皱的核心内逃逸，有前弧的相对运动的结果向弧在造山带的核心，和持续的相反的旋转的上板的造山翼。我们建议，促进和维持沿走向变化的板块边界牵引力所产生的板界面的几何形状在深度和建议，这些过程可以有助于发展的凹外侧边缘，而不需要一个俯冲压头。
The concave-inboard (concave toward the overriding plate) geometry of most convergent margins is considered a natural consequence of the depression of the edge of a thin spherical cap, whereas concave-outboard margin segments commonly form around indenters on the subducting plate. At the Cascadia subduction zone, the apex of a >500-km-long concave-outboard bend in the trench presently shows no obvious subduction of an indenter, but does coincide with the axis of an outboard-facing concavity in upper-plate rocks arched around the Olympic Peninsula in northwestern Washington State, USA. Here we synthesize paleomagnetic and structural data together with new analyses of Global Navigation Satellite System data to show that the upper plate at Cascadia has been folded from the Miocene to the present into an orocline with an axial trace that bisects the Olympic Peninsula. The processes that accommodate bending, which we suggest include (1) folding by flexural slip on the orocline limbs and (2) shortening, uplift, and escape within the core of the fold at the Olympic Mountains, have the combined result of relative motion of the forearc towards the arc at the core of the orocline, and sustained opposing rotations of the upper plate on the orocline limbs. We propose that oroclinal bending is promoted and maintained by along-strike variations in plate-boundary tractions resulting from the geometry of the plate interface at depth and suggest that these processes can contribute to the development of concave-outboard margins without the need for a subducting indenter.
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