Tectonic and Climatic Controls on Rapid Exhumation Along the Altiplano-Eastern Cordillera Boundary, Bolivia

加州大学洛杉矶分校（UCLA）的研究人员正在研究构造和气候在推动南美洲安第斯山脉中部快速侵蚀挖掘中的作用。在玻利维亚北部，安第斯山脉中部拥有整个安第斯山脉带最高的地形、最快的挖掘速度和最集中的同位素年龄数据（热年代学结果）。该地区还展示了地球上最引人注目的气候梯度之一，从北部极度潮湿的亚马逊流域到南部干旱的巴拉那流域。这项多学科研究的重点是4.5-6公里高的狭窄山脉的演变，该山脉定义了Altiplano高原和亚马逊流域系统之间的主要地理分界线。东科迪勒拉这一30至250公里范围的新生代隆升产生了深远的影响，可以说：(1)引发了4公里高的安第斯高原中部的生长，(2)在高原上形成了封闭的排水系统，(3)通过地形效应改变了区域气候，(4)在一个可能的稳态造山带中建立了侵蚀和构造之间的动态相互作用。以前的热年代学研究得出的同位素年龄产生了相互矛盾的解释，它们交替地在短暂的脉冲（不到几百万年）或长时间的变形、侵蚀和岩浆活动（几千万年）中引起加热或冷却。加州大学洛杉矶分校的研究人员正在分析玻利维亚北部两条短（约30公里长）横断面的地质结构、沉积和热历史，以了解狭窄山脉的侵蚀挖掘与变形和沉积盆地发展的关系。正在进行的山脉热年代学分析和邻近盆地的沉积学研究，正在确定山脉冷却历史中各个构造的功能，以及变形和盆地形成的时间。该项目包括与玻利维亚科学家合作，并有来自美国和玻利维亚的本科生和研究生参与实地和实验室研究。该项目由构造学计划和国际科学与工程办公室美洲组提供支持。

Researchers from the University of California Los Angeles (UCLA) are investigating the role of tectonics and climate in driving rapid erosional exhumation in the central Andes Mountains of South America. In northern Bolivia, the central Andes are host to some of the highest topography, most rapid rates of exhumation, and greatest concentration of isotopic age data (thermochronological results) in the entire Andean mountain belt. The region also displays one of the most dramatic climatic gradients on Earth, from the extremely humid conditions of the Amazon watershed in the north to the arid conditions of the Parana watershed in the south. The focus of this multidisciplinary study is the evolution of a 4.5-6-kilometer-high narrow mountain range that defines the main physiographic divide between the Altiplano plateau and Amazon drainage system. Cenozoic uplift of this 30 by 250 kilometer range in the Eastern Cordillera had far-reaching effects, arguably (1) triggering growth of the 4-kilometer-high central Andean plateau, (2) inducing closed drainage in the Altiplano, (3) modifying regional climate by orographic effects, and (4) setting up a dynamic interplay between erosion and tectonics in a possible steady-state orogen. Previous isotopic ages from thermochronological studies generate conflicting interpretations which alternately invoke heating or cooling during either brief pulses (less than several million years) or prolonged episodes (several tens of millions of years) of deformation, erosion, and magmatism. The UCLA researchers are analyzing geologic structures, sedimentation, and thermal histories along two short (~30-kilometer-long) transects in northern Bolivia in order to understand erosional exhumation of the narrow mountain range in relationship to deformation and sedimentary basin development. Ongoing thermochronological analyses of the range and sedimentological studies of an adjacent basin are determining the function of individual structures in the range's cooling history as well as the timing of deformation and basin genesis. The project includes collaboration with Bolivian scientists and involves undergraduate and graduate students from the United States and Bolivia in field and laboratory research.Support for the project is provide by the Tectonics Program and by the Americas Group of the Office of International Science and Engineering.