Detrital sanidine 40Ar/39Ar dating confirms <2 Ma age of Crooked Ridge paleoriver and subsequent deep denudation of the southwestern Colorado Plateau
Detrital sanidine 40Ar/39Ar dating confirms <2 Ma age of Crooked Ridge paleoriver and subsequent deep denudation of the southwestern Colorado Plateau
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碎屑砂质40Ar/39Ar定年证实了弯曲岭古河流的<2 Ma年龄和随后科罗拉多高原西南部的深度剥蚀
DOI：
10.1130/ges02319.1
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发表时间：
2021-01
期刊：
影响因子：
2.5
通讯作者：
M. Heizler;K. Karlstrom;M. Albonico;R. Hereford;L. Beard;S. Cather;L. Crossey;K. Sundell
中科院分区：
文献类型：
--
作者：
M. Heizler;K. Karlstrom;M. Albonico;R. Hereford;L. Beard;S. Cather;L. Crossey;K. Sundell
亚利桑那州东北部（美国西南部）的弯曲山脊和怀特梅萨以倒置地形的形式，在科罗拉多河、圣胡安河和小科罗拉多河之间现有的排水分水岭附近保留了一条 57 公里长的废弃冲积系统。这条古河的路径向西南流向大峡谷东部，因其在雕刻大峡谷方面的潜在重要性而产生了具有争议性的替代模型。约 50 米厚的白色台地冲积层是该古河流系统唯一有数据记录的记录。我们提出了新的 40Ar/39Ar 烷胺定年法，证实了大约。 White Mesa 冲积层的最大沉积年龄为 2 Ma，由 2.06 至 1.76 Ma 的大众数 (n = 42) 支持。更古老的颗粒模式显示丰富的 37-23 Ma 颗粒主要来自圣胡安山脉，白台地冲积层中罕见的火山和基底卵石也记录了这一点。下面插入了年龄为 1.07 ± 0.05 Ma 的凝灰岩，因此为 White Mesa 冲积层提供了一个更年轻的年龄范围。 Black Mesa 上新测年的残余矿床含有类似的 37-23 Ma 颗粒和奇异卵石，以及 9.052 ± 0.003 Ma 的大众数 (n = 71)。这些沉积物可能是没有任何更新世颗粒的白色台地冲积层的一部分，但来自亚利桑那州加纳多附近的 Bidahochi 组上部的新碎屑碎屑数据具有相似的最大沉积年龄，为 11.0–6.1 Ma，并显示类似的 40–20 Ma 来自圣胡安山脉的碎屑。因此，我们暂时将 <9 Ma Black Mesa 矿床解释为 11-6 Ma Bidahochi 冲积系统的残余物，该系统源自现已受到侵蚀的圣胡安山脉西南边缘。该冲积边缘可能是 40-20 Ma 碎屑碎屑和外来碎屑重新加工成渐新世 Chuska 砂岩、中新世 Bidahochi 组并最终形成 <2 Ma White Mesa 冲积层的可能来源。怀特台地冲积层<2Ma年龄不支持弯曲山脊古河起源于晚渐新世至中新世圣胡安河并最终横穿凯巴布隆起的模型。相反，我们将弯曲岭古河流解释为小科罗拉多河的 1.9-1.1 Ma 支流，类似于现代的莫恩科皮华盛顿。我们拒绝基于测绘、地层和地貌限制的“旧古河谷中的年轻沉积物”假设。圣胡安河和科罗拉多河支流的深度挖掘和砍头导致弯曲山脊古支流在 1.9 Ma 和 1.1 Ma 之间被废弃。热年代学数据也没有为早期（渐新世-中新世）科罗拉多-圣胡安古河流系统的假说提供任何证据，并且造成很大的困难，该系统沿着弯曲山脊路径流动并穿过凯巴布隆起。
Crooked Ridge and White Mesa in northeastern Arizona (southwestern United States) preserve, as inverted topography, a 57-km-long abandoned alluvial system near the present drainage divide between the Colorado, San Juan, and Little Colorado Rivers. The pathway of this paleoriver, flowing southwest toward eastern Grand Canyon, has led to provocative alternative models for its potential importance in carving Grand Canyon. The ∼50-m-thick White Mesa alluvium is the only datable record of this paleoriver system. We present new 40Ar/39Ar sanidine dating that confirms a ca. 2 Ma maximum depositional age for White Mesa alluvium, supported by a large mode (n = 42) of dates from 2.06 to 1.76 Ma. Older grain modes show abundant 37–23 Ma grains mostly derived ultimately from the San Juan Mountains, as is also documented by rare volcanic and basement pebbles in the White Mesa alluvium. A tuff with an age of 1.07 ± 0.05 Ma is inset below, and hence provides a younger age bracket for the White Mesa alluvium. Newly dated remnant deposits on Black Mesa contain similar 37–23 Ma grains and exotic pebbles, plus a large mode (n = 71) of 9.052 ± 0.003 Ma sanidine. These deposits could be part of the White Mesa alluvium without any Pleistocene grains, but new detrital sanidine data from the upper Bidahochi Formation near Ganado, Arizona, have similar maximum depositional ages of 11.0–6.1 Ma and show similar 40–20 Ma San Juan Mountains–derived sanidine. Thus, we tentatively interpret the <9 Ma Black Mesa deposit to be a remnant of an 11–6 Ma Bidahochi alluvial system derived from the now-eroded southwestern fringe of the San Juan Mountains. This alluvial fringe is the probable source for reworking of 40–20 Ma detrital sanidine and exotic clasts into Oligocene Chuska Sandstone, Miocene Bidahochi Formation, and ultimately into the <2 Ma White Mesa alluvium. The <2 Ma age of the White Mesa alluvium does not support models that the Crooked Ridge paleoriver originated as a late Oligocene to Miocene San Juan River that ultimately carved across the Kaibab uplift. Instead, we interpret the Crooked Ridge paleoriver as a 1.9–1.1 Ma tributary to the Little Colorado River, analogous to modern-day Moenkopi Wash. We reject the “young sediment in old paleovalley” hypothesis based on mapping, stratigraphic, and geomorphic constraints. Deep exhumation and beheading by tributaries of the San Juan and Colorado Rivers caused the Crooked Ridge paleotributary to be abandoned between 1.9 and 1.1 Ma. Thermochronologic data also provide no evidence for, and pose substantial difficulties with, the hypothesis for an earlier (Oligocene–Miocene) Colorado–San Juan paleoriver system that flowed along the Crooked Ridge pathway and carved across the Kaibab uplift.