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Grand Canyon provenance for orthoquartzite clasts in the lower Miocene of coastal southern California

机译：在沿海南部加州下部内突的正交凝固碎屑的大峡谷出处

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Orthoquartzite detrital source regions in the Cordilleran interior yield clast populations with distinct spectra of paleomagnetic inclinations and detrital zircon ages that can be used to trace the provenance of gravels deposited along the western margin of the Cordilleran orogen. An inventory of characteristic remnant magnetizations (CRMs) from 700 sample cores from orthoquartzite source regions defines a low-inclination population of Neoproterozoic–Paleozoic age in the Mojave Desert–Death Valley region (and in correlative strata in Sonora, Mexico) and a moderate- to high-inclination population in the 1.1 Ga Shinumo Formation in eastern Grand Canyon. Detrital zircon ages can be used to distinguish Paleoproterozoic to mid-Mesoproterozoic (1.84–1.20 Ga) clasts derived from the central Arizona highlands region from clasts derived from younger sources that contain late Mesoproterozoic zircons (1.20–1.00 Ga). Characteristic paleomagnetic magnetizations were measured in 44 densely cemented orthoquartzite clasts, sampled from lower Miocene portions of the Sespe Formation in the Santa Monica and Santa Ana mountains and from a middle Eocene section in Simi Valley. Miocene Sespe clast inclinations define a bimodal population with modes near 15° and 45°. Eight samples from the steeper Miocene mode for which detrital zircon spectra were obtained all have spectra with peaks at 1.2, 1.4, and 1.7 Ga. One contains Paleozoic and Mesozoic peaks and is probably Jurassic. The remaining seven define a population of clasts with the distinctive combination of moderate to high inclination and a cosmopolitan age spectrum with abundant grains younger than 1.2 Ga. The moderate to high inclinations rule out a Mojave Desert–Death Valley or Sonoran region source population, and the cosmopolitan detrital zircon spectra rule out a central Arizona highlands source population. The Shinumo Formation, presently exposed only within a few hundred meters elevation of the bottom of eastern Grand Canyon, thus remains the only plausible, known source for the moderate- to high-inclination clast population. If so, then the Upper Granite Gorge of the eastern Grand Canyon had been eroded to within a few hundred meters of its current depth by early Miocene time (ca. 20 Ma). Such an unroofing event in the eastern Grand Canyon region is independently confirmed by (U-Th)/He thermochronology. Inclusion of the eastern Grand Canyon region in the Sespe drainage system is also independently supported by detrital zircon age spectra of Sespe sandstones. Collectively, these data define a mid-Tertiary, SW-flowing “Arizona River” drainage system between the rapidly eroding eastern Grand Canyon region and coastal California.
机译：康瑞斯内部的Orthoquartzite Dritital Source地区源区产量含有不同光谱的古磁倾斜和碎屑锆石，可用于追踪沿着西南部造山的西部边缘沉积的砾石的出处。来自＆gt的特征残余磁化（CRMS）的清单来自Orthoqoquartzite源区的700个样本核心在莫哈韦沙漠死亡谷地区（以及Sonora，Mexico）和A的相关地层中的低倾角群东大峡谷1.1 Ga Shinumo形成中的中度至高倾斜人口。碎屑锆石可用于将古普罗科奇（1.84-1.20 GA）植物区分为与含有晚期元素Zircons（1.20-1.00 GA）的植物中源于年轻来源的植物中央亚利桑那高地区域。在44次密集的骨水泥型泥浆中测量了特征古磁性磁化，从Santa Monica和Santa Ana山脉的SESPE形成的下部内部部分采样，以及Simi山谷中的中部eocene部分。中间世氏SESPE CLAST倾斜度定义双峰群，具有接近15°和45°的模式。从脱滴锆谱的衰减锆石光谱的八个样品均具有1.2,1.4和1.7Ga的峰值。一个含有古生代和中生代峰，可能是侏罗纪。其余的七个用中度至高倾斜和大量谷物的鲜明组合定义了具有比1.2乔的丰富的谷物的独特组合。中度至高倾斜排除了莫哈韦沙漠死亡谷或索诺兰地区的源头国际化甲板锆石光谱排除了亚利桑那州中央高地源人口。 Shinumo形成，目前仅在东部大峡谷底部的几百米高之内暴露，因此仍然是中等至高倾斜夹层人口的唯一可象征的知名来源。如果是这样，那么东部大峡谷的上花岗岩峡谷被早期的内科时间（约20 mA）侵蚀了当前深度的几百米。在东部大峡谷地区的这种无可灭情的活动是由（U-Th）/ He Thermochronology的独立证实。在SESPE Sandstones的Detrital Zircon年龄光谱，也可以独立地支持俄克斯人的苏克斯·桑松的替代锆石的含量。总的来说，这些数据在快速侵蚀东部大峡谷地区和沿海加利福尼亚之间定义了一个中等的SW流动的“亚利桑那河”排水系统。

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