Collaborative Research: Uplift of the Washington Cascades and Climatic Evolution of Eastern Washington

华盛顿瀑布是北美最大的气候雨影区之一，其西侧部分地区年平均降水量高于4 m/yr，而东侧则低于0.15 m/yr。我们利用喀斯喀特结晶岩本身的低温磷灰石(U-Th)/He热时测定方法，以及在该山脉干燥的东侧不同年龄的古土壤中粘土和碳酸盐中自生矿物的稳定同位素变化，研究了该地区造山与气候的时间关系。此外，通过GIS和He测年工作的结合，我们正在研究喀斯喀特地形起伏的形成与更新世至近代冰川作用之间的关系，并评估相对较近的侵蚀力对造山发掘的作用。我们的初步工作表明，He年龄记录比喀斯喀特地区其他辐射测量系统记录的年龄要年轻得多，这表明出土时间相对较晚（最早为中新世晚期），这与华盛顿东部的古生物学证据一致，因为在此之前缺乏严重的气候对比。

MontgomeryReiners00874130087318The Washington Cascades cast one of the largest climatic rain shadows in North America, with mean annual precipitation in some areas on the west side higher than 4 m/yr, and on the east side lower than 0.15 m/yr. We are studying the temporal relationships between mountain-building and climate in this regional setting by using a combined approach of low-temperature apatite (U-Th)/He thermochronometry in the Cascades crystalline rocks themselves, and stable isotope variations in authigenic minerals in clays and carbonates in paleosols of different ages on the dry, east side of the range. In addition, through combined GIS and He dating work, we are examining the relationship between creation of Cascades topographic relief and Pleistocene-to-recent glaciation in the range, and evaluating the role of relatively recent erosional forces on orogenic exhumation. Our preliminary work indicates that He ages record much younger ages than other radiometric systems in the Cascades, suggesting a relatively recent (late Miocene at the earliest) period of exhumation, which is consistent with paleontological evidence from eastern Washington for the lack of a severe climate contrast until this time.