Constraining the Influence of Tectonics Versus Climate on Orogensis in the North Cascades (Washington and British Columbia)

限制构造与气候对北部喀斯喀特造山运动的影响（华盛顿和不列颠哥伦比亚省）

• 批准号: 0610072
• 负责人: Juliet Crider
• 金额: $ 6.26万
• 依托单位: Western Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2008-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0610072&HistoricalAwards=false
• 关键词: Constraining; Influence; Tectonics; Versus; Climate

Several lines of evidence suggest that the modern topography of the Pacific Northwest, encompassing mountain ranges from northern Washington to Alaska, formed within the last 8 to12 million years. However, plant fossils from the east side of the mountains suggest elevations were as much as two times their modern height approximately 45 million years ago. If the region was high before the inferred onset of mountain building, then many of the proxy signals for uplift could be the result of climate change rather than tectonically driven mountain uplift. Instead, increased erosion rates associated with changing climate could result in the unloading of the western edge of North America, potentially allowing narrow peaks to rebound isostatically. This hypothesis is difficult to evaluate because the initial topographic condition of the region before the inferred onset of recent mountain building is not known. The goal of this study is to define an initial state against which to gauge late Miocene changes in surface and peak elevation in the North Cascades through investigation of the paleotopography of the Okanogan Range, the eastern border of the North Cascades. The exhumation history and paleotopography of the Okanogan Range is determined using apatite and zircon (U-Th)/He low-temperature thermochronology, Eocene surface reconstruction, and thermal modeling of landscape evolution scenarios. Topographic relief serves as a proxy for the minimum elevation of peaks within the range. Paleotopography calculated via thermochronology will be compared to the relief preserved in erosional remnants of Eocene volcanic deposits scattered throughout the range. The refined elevation history of the Okanogan Range will then be used to evaluate the contribution of erosion and consequent flexural isostatic peak uplift to the production of high peaks in the Cascades.Evaluating the impact of erosion and flexural isostasy on high relief and high topography in the Pacific Northwest will help resolve an outstanding debate about the driving forces of mountain building in western North America over the past 20 million years. These results will allow evaluation of the idea that the onset of northern hemisphere glaciation might have resulted in increases in peak and ridge elevations in the western Coast Mountains, British Columbia, and western North Cascades, Washington state.

一些证据表明，太平洋西北部的现代地形，包括从北方华盛顿到阿拉斯加的山脉，形成于过去的800万到1200万年之间。然而，来自山脉东侧的植物化石表明，大约4500万年前，海拔高度是现代高度的两倍。如果该地区在推断的造山运动开始之前就很高，那么许多隆起的代理信号可能是气候变化的结果，而不是构造驱动的山脉隆起。相反，与气候变化相关的侵蚀率增加可能会导致北美西部边缘的卸载，从而可能导致狭窄的山峰均衡反弹。这一假设是难以评估的，因为该地区的初始地形条件之前，推断最近的造山运动是未知的。本研究的目标是确定一个初始状态，对测量晚中新世的变化，在北喀斯喀特山脉的表面和峰值海拔通过调查的古地形的奥卡诺根范围，北喀斯喀特山脉的东部边界。利用磷灰石和锆石（U-Th）/He低温热年代学、始新世地表重建和景观演化情景的热模拟，确定了奥卡诺根山脉的折返历史和古地形。地形起伏可作为该范围内山峰最小海拔的替代。通过热年代学计算的古地形将与散布在整个山脉中的始新世火山沉积物的侵蚀遗迹中保存的地形进行比较。奥卡诺根山脉的精确高程历史将用于评估侵蚀和随之而来的弯曲均衡峰值抬升对小瀑布中高峰形成的贡献。评估侵蚀和弯曲均衡峰值对太平洋西北部高起伏和高地形的影响将有助于解决关于过去2000万年北美西部造山运动驱动力的突出争论年这些结果将使人们能够评估这样的想法：北方半球冰川作用的开始可能导致不列颠哥伦比亚省西海岸山脉和华盛顿州西北喀斯喀特山脉的山峰和山脊海拔上升。