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

科罗拉多河上的大峡谷洞穴，以前被认为发生在6.0到1.2 Ma之间，实际上是相对年轻的，正在进行中，并以不同的速度沿着大峡谷发生。来自东部大峡谷中-晚第四纪河流阶地的信息表明，对冰川/间冰期气候变化的强烈侧流和主流响应叠加在0.2-0.6毫米/年的总体切割速率上。这表明，目前大峡谷东部高达一半的地貌是在第四纪时期产生的。相比之下，来自西部大峡谷的新数据显示，同一时期的切割率最高可低一个数量级。这种差异被解释为是由于托罗韦普-飓风断裂系统向西向下的第四纪滑动调节了该地区地壳块体的切割。最近在这个断裂系统上发现的大约0.25毫米/年的滑动速率大约等于在断裂带内和紧邻其下的较大的上游速率(东部大峡谷)和较小的下游速率之间的差值。一幅新的画面正在浮现，它是一个更年轻的分段的大峡谷，其中包含了科罗拉多高原剥蚀历史的敏感记录。该项目利用详细的地貌和构造野外研究，结合冲积阶地内钙华的U系列测年和玄武岩的Ar-Ar测年，对这一假设进行了重点检验。这些数据有助于更好地了解大峡谷的年龄，以及驱动和调节这一地区和其他高原地区切割的力量。这项工作还产生了广泛的教育和推广影响；我们正在与大峡谷国家公园的解说部密切合作，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，我们继续在多所大学合作的背景下培训一批研究生和本科生，该合作涉及美国西南部构造和景观演变的许多方面。

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.