Collaborative Research: Tectonic Geomorphology of Grand Canyon--Testing a Hypothesis for Differential Incision Due to Quaternary Slip on the Hurricane-Torweap Fault System

0107117 Karlstrom 0107065 Pederson科罗拉多河旁大峡谷的挖掘，以前认为发生在6.0和1.2 Ma之间，实际上是相对年轻的，正在进行的，沿着大峡谷的长度以可变的速率发生。 来自大峡谷东部中晚期第四纪河流阶地的信息表明，对冰期/间冰期气候变化的强烈侧流和主流响应已叠加在0.2至0.6 mm/年的整体切割率上。 这表明大峡谷东部现今的地形有一半是在第四纪形成的。 相比之下，西部大峡谷的新数据表明，在同一时期，切割率低了一个数量级。 这种差异被解释为是由于西下第四纪滑动的托罗韦普飓风断层系统调制该地区的地壳块体的切口。 最近认识到，该断层系统的滑动速率约为0.25 mm/年，约等于较大的上游速率（大峡谷东部）和较小的下游速率之间的差异，在断层带内和下方。 一幅新的画面正在浮现，一个年轻的、分段的大峡谷，它包含了科罗拉多高原剥蚀历史的敏感记录。该项目是对这一假设的重点检验，采用详细的地貌和结构实地研究，结合冲积阶地内的铀系测年和玄武岩的Ar-Ar测年。 这些数据提供了对大峡谷的年龄以及驱动和调节这个和其他高原地区切割的力量的更好的理解。 这项工作也有广泛的教育和推广影响;我们正在与大峡谷国家公园的解释部门密切合作，设计“时间之路”，向每年来公园的500万游客传达地质知识。 此外，我们继续培养研究生和本科生的主机在多所大学的合作，处理与美国西南部的构造和景观演变的许多方面的背景下。

0107117Karlstrom0107065PedersonExcavation of Grand Canyon by the Colorado River, previously thought to have happened between 6.0 and 1.2 Ma, is actually relatively young, ongoing, and happening at variable rates along the length of the Grand Canyon. Information from middle-late Quaternary stream terraces in eastern Grand Canyon indicates that strong side-stream and mainstream responses to glacial/interglacial climate changes have been superimposed on an overall incision rate of 0.2 to 0.6 mm/yr. This suggests that up to half of the present-day relief in eastern Grand Canyon has been generated in the Quaternary Period. In contrast, new data from western Grand Canyon indicate up to an order of magnitude lower incision rate over the same time period. This discrepancy is interpreted to be due to west down Quaternary slip on the Toroweap-Hurricane fault system modulating the incision of crustal blocks in the region. Recently recognized slip rates of ~0.25 mm/yr on this fault system are approximately equal to the difference between greater upstream rates (eastern Grand Canyon) and smaller downstream rates obtained within and immediately below the fault zone. A new picture is emerging of a younger, segmented Grand Canyon, which contains a sensitive record of the denudational history of the Colorado Plateau. This project is a focused test of this hypothesis using detailed geomorphic and structural field studies combined with U-Series dating of travertine within alluvial terraces and Ar-Ar dating of basalts. These data provide an improved understanding of the age of the Grand Canyon and the forces that drive and modulate the incision of this and other high plateau regions. This work also has a broad educational and outreach impact; we are working closely with the Interpretive Division of Grand Canyon National Park to design the "Trail of Time" to communicate geologic understanding to the 5 million visitors that come to the Park annually. Additionally, we continue to train a host of graduate and undergraduate students in the context of a multi-university collaboration that deals with numerous aspects of the tectonic and landscape evolution of the southwestern U.S.A.