Uplift History of the Cordillera Occidental, Southern Peru, from Canyon Geomorphology

麻省理工学院(MIT)的研究人员正在研究秘鲁南部西部科迪勒拉山脉的隆起史，这标志着安第斯山脉中部阿尔蒂普诺高原的西部边界。他们的方法是研究两个主要河流水系(科尔卡河和科塔瓦西河)横穿被认为是西半球最深的两个峡谷的切割的时空历史，每个峡谷的总起伏超过3200米。尽管河流切割并不能完全代表岩石的抬升，但主要河流系统在构造活动期间的行为是相对于海平面的地表抬升的敏感指标。无论是否满足稳态条件，这都是正确的。这些流域的地质和地理状况提供了四种独立的方法来估计河流切割的历史和模式。这种情况提供了一个非同寻常的机会，可以制作科尔卡河和科塔瓦西河水系切割历史的详细图像，麻省理工学院的研究人员正在利用这些图像来推断高原西缘的隆起演化，并检验这四种方法在标准应用中的隐含假设。麻省理工学院的研究人员结合使用以下四种方法来破译河流切割的历史和模式：1)切割花岗岩的热年代学研究；2)基于保存下来的火山流残留物重建古代陆地表面；3)使用基岩层阶地测量河流切割的时间综合速率；以及4)重建在冲积充填梯田和火山填充物残留物中记录的山谷沉积和随后的重新挖掘历史。从这些研究中收集到的关于科尔卡河和科塔瓦西河水系切割历史的信息，对于评估目前的安第斯山脉生长和抬升模型以及更好地为未来的模型提供信息是必不可少的。

Massachusetts Institute of Technology (MIT) researchers are studying the uplift history of the Cordillera Occidental of southern Peru, which marks the western boundary of the Altiplano plateau in the central Andes. Their approach is to study the spatial and temporal history of incision of two major river systems (the Colca and Cotahuasi river systems) that transect the range through what are regarded as the two deepest canyons in the Western Hemisphere, each with a total relief in excess of 3200 meters. Although river incision is an imperfect proxy for rock uplift, the behavior of major river systems during tectonic activity is a sensitive indicator of surface uplift relative to sea level. This is true regardless of whether or not steady-state conditions have been met. The geology and geography of these drainages provide four independent ways to estimate the history and pattern of river incision. This circumstance provides an extraordinary opportunity to develop a detailed image of the incision history of the Colca and Cotahuasi river systems, which the MIT researchers are using to deduce the uplift evolution of the western edge of the Altiplano, and to test the implicit assumptions in standard applications of each of the four methods. The MIT researchers are using a combination of the following four methods to decipher the history and pattern of river incision: 1) thermochronologic studies of incised granitic plutons; 2) reconstructions of ancient land surfaces based on preserved remnants of volcanic flows; 3) measurements of the time-integrated rate of river incision using bedrock strath terraces; and 4) reconstructions of the history of valley aggradation and subsequent re-excavation recorded in alluvial fill terraces and remnants of volcanic infills. The information being gleaned from these studies about the incision histories of the Colca and Cotahuasi river systems is essential for evaluating current models of the growth and uplift of the Andes, and for better informing future models.