Studies of Plateau Uplift Using 4He/3He Apatite Thermochronometry and 13C-18O Carbonate Paleothermometry

利用4He/3He磷灰石测温法和13C-18O碳酸盐古测温法研究高原隆升

• 批准号: 0810324
• 负责人: Brian Wernicke
• 金额: $ 21.12万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0810324&HistoricalAwards=false
• 关键词: Studies; Plateau; Uplift; Using; 4He

The Colorado Plateau was a subsiding platform from Cambrian to Cretaceous time (for about 500 million years) while about 4000 meters of sedimentation maintained its elevation near sea level. At some time after 80 million years ago, net uplift of the topographic surface resulted in a plateau with its current mean elevation of 1900 meters, with little internal strain of the upper part of the crust. The focus of this project is to provide new constraints on how and when the lithosphere acquired so much buoyancy, and the relationship between topographic uplift, rock uplift and erosional unroofing. Recent innovations in He thermochronometry and carbon-oxygen clumped isotope thermometry are being used to investigate both the unroofing and surface uplift histories of the southwestern portion of the plateau. Constraints are placed on the timing and rate of low-temperature cooling events down to temperatures significantly lower than those accessible by conventional whole crystal (U-Th)/He apatite ages (approximately 70 degrees C for typical cooling rates). These data are used to test the hypothesis that a major component of time-transgressive (from the northwest to the southeast) unroofing and uplift along the southwestern plateau margin occurred between 60 to 35 million years ago. Paleoelevation constraints obtained from clumped carbon-oxygen carbonate paleothermometry will test the hypothesis that the plateau interior lay at much lower elevations through much of the Cenozoic before major surface uplift since about 6 million years ago.The geologic evolution of the Grand Canyon region has been a focal point for educating the general public about the geological sciences, and science in general, for over a century. The region is also among the best natural laboratories in the world for addressing the relationship between uplift of the continental crust and the erosional forces acting upon it. This project uses new techniques rooted in the chemistry and physics of the earth?s naturally occurring isotopes of helium, carbon and oxygen to address two fundamental questions that might occur to anyone who has ever peered into the Grand Canyon: When and why did the high plateau, whose surface is made of limestone deposited in a shallow ocean, rise to its current height of about 2000 meters above sea level? And when did the carving of the Grand Canyon take place - at the same time uplift occurred, or at a much later time? Results from the earlier phase of this study suggest that the canyon was initially cut in the Early Tertiary of Cretaceous times, by a river that flowed from the southeast to the northwest, opposite the modern direction of flow. Further, data suggest that in the Upper Granite Gorge region, the canyon had formed in strata much younger than those exposed today, and in a pulse of erosion about 20 million years ago this canyon lowered itself through the rock column to a point very close to its modern position. Another preliminary result is that approximately half of the modern elevation of the plateau interior was attained only after 6 million years ago.

科罗拉多高原从寒武纪到白垩纪（约5亿年）是一个下沉的平台，而大约4000米的沉积保持其海拔接近海平面。在8000万年前的某个时候，地形表面的净隆起导致了一个高原，其目前的平均海拔为1900米，地壳上部几乎没有内部应变。这个项目的重点是提供新的限制如何以及何时岩石圈获得这么多的浮力，地形隆起，岩石隆起和侵蚀去顶之间的关系。最近的创新，他thermochronometry和碳-氧聚集同位素测温正在被用来调查的去顶和高原西南部的表面隆起的历史。限制被放置在低温冷却事件的时间和速率上，温度显著低于常规的全晶体（U-Th）/He磷灰石年龄（典型的冷却速率约为70摄氏度）。这些数据被用来测试的假设，一个主要组成部分的时间海侵（从西北到东南）去顶和隆升沿着西南高原边缘发生在60至3500万年前。从块状碳-氧碳酸盐古温度测定法获得的古海拔限制将检验这一假设，即高原内部在大约600万年前的主要地表隆起之前，在新生代的大部分时间里处于低得多的海拔。大峡谷地区的地质演化一直是世纪以来教育公众了解地质科学和一般科学的焦点。该区域也是世界上研究大陆地壳隆起与作用于其上的侵蚀力之间关系的最佳自然实验室之一。这是一个自然存在的氦、碳和氧的同位素，以解决任何一个曾经窥视过大峡谷的人可能会想到的两个基本问题：高原是何时以及为什么上升到目前海拔约2000米的高度，高原的表面是由沉积在浅海中的石灰岩组成的？大峡谷的雕刻是什么时候发生的--是在隆起发生的同时，还是在更晚的时间？这项研究的早期结果表明，峡谷最初是在白垩纪第三纪早期被一条从东南流向西北的河流切割的，与现代的流向相反。此外，数据表明，在花岗岩峡谷上部地区，峡谷形成于比今天暴露的地层年轻得多的地层中，在大约2000万年前的侵蚀脉冲中，这个峡谷通过岩石柱降低到非常接近其现代位置的位置。另一个初步结果是，高原内部现代海拔的大约一半是在600万年前才达到的。