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

来自加州大学洛杉矶分校(UCLA)的研究人员正在调查构造和气候在推动南美洲中部安第斯山脉快速侵蚀挖掘遗骸中的作用。在玻利维亚北部，安第斯山脉中部是整个安第斯山脉地带一些地势最高、挖掘速度最快、同位素年龄数据(热年代学结果)最集中的地方。该地区还表现出地球上最显著的气候梯度之一，从北部亚马逊分水岭的极端潮湿条件到南部巴拉那分水岭的干旱条件。这项多学科研究的重点是一条4.5-6公里高的狭窄山脉的演变，该山脉界定了阿尔蒂普罗高原和亚马逊水系之间的主要地理分水岭。新生代在东科迪勒拉的这一30-250公里范围内的隆升具有深远的影响，可以说(1)触发了4公里高的安第斯高原中部的增长，(2)导致了高原的封闭排水，(3)通过地形效应改变了区域气候，以及(4)在可能的稳定造山带中建立了侵蚀和构造之间的动态相互作用。以前来自热年代学研究的同位素年龄产生了相互矛盾的解释，在短暂的脉冲(不到几百万年)或较长的变形、侵蚀和岩浆作用的时期(几千万年)交替地提到加热或冷却。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个短(约30公里长)断面的地质结构、沉积和热史，以了解这一狭窄山脉的侵蚀折返与变形和沉积盆地发育的关系。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个别构造在山脉冷却历史中的作用，以及变形和盆地成因的时间。该项目包括与玻利维亚科学家的合作，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。该项目由构造计划和国际科学与工程办公室美洲小组提供支持。

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.