Collaborative Research: Thrust Belt Response to Rapid Surface Uplift of the Altiplano: A Field Test of Cordilleran Cyclicity in Southern Bolivia

Cordilleran旋回性模型预测，致密大陆岩石圈的拆离应伴随着造山高原的快速隆升，从而导致前缘褶皱冲断带变形的快速推进。在安第斯高原中部，最近的同位素研究表明，玻利维亚南部高原在1600万年至1300万年前曾迅速抬升地表，这归因于深层致密物质的清除。Cordilleran旋回性模型预测，安第斯褶皱冲断带应该通过形变前沿的快速向东传播来响应这一快速隆升事件。然而，玻利维亚南部冲断带变形的时间和大小的准确记录是不可获得的，这使得这一关键预测没有得到检验。在这个项目中，我们正在进行一项实地研究，旨在记录安第斯褶皱冲断带对内陆高原迅速上升的反应(或缺乏反应)。该项目涉及玻利维亚南部冲断带东西走向横断面的地质测绘，这将为平衡横断面的建设提供支持。通过在横截面上按顺序恢复形变，我们正在创造过去约2000万年至3000万年来缩短的记录。这一记录将与分析地壳缩短期间沉积的沉积岩的场关系所产生的变形时间约束以及从低温冷却历史获得的多个逆冲片的侵蚀时间估计相结合。该项目的最终目标将是生成逆冲前缘和同期沉积中心的正向传播速率的时序记录。总而言之，这些记录将使我们能够评估造山作用对腹地表面快速抬升的响应，从而检验科迪勒旋回模型的关键预测。该项目正在培训研究生和本科生(包括一名在美国学习的玻利维亚研究生)。该研究所在STEM领域开展了一项研究，有助于扩大地球科学中代表性不足群体的代表性；它正在促进两个机构(内华达大学雷诺分校和德克萨斯大学奥斯汀分校)的美国研究人员之间的新合作；它正在促进美国和玻利维亚科学家之间宝贵的国际合作。该奖项由美国国家科学基金会国际科学与工程办公室共同资助。

The Cordilleran cyclicity model predicts that detachment of dense continental lithosphere should be accompanied by rapid uplift of an orogenic plateau and resulting rapid advance of deformation in the frontal fold-thrust belt. In the central Andean plateau, recent isotopic studies argue for rapid surface uplift of the southern Altiplano in Bolivia between 16 and 13 million years ago, which has been attributed to removal of dense material at depth. The Cordilleran cyclicity model predicts that the Andean fold-thrust belt should have responded to this rapid uplift event through rapid eastward propagation of the deformation front. However, accurate records of the timing and magnitude of deformation in the thrust belt in southern Bolivia are not available, which leaves this key prediction untested. In this project, we are performing a field-based study aimed at documenting the response (or lack thereof) of the Andean fold-thrust belt to the rapid rise of the hinterland plateau. The project involves geologic mapping along an east-west transect through the thrust belt in southern Bolivia, which will support construction of a balanced cross-section. By sequentially restoring deformation in the cross-section, we are generating a record of shortening over the last ~20-30 million years. This record will be integrated with deformation timing constraints from analysis of field relationships of sedimentary rocks deposited during crustal shortening, and timing estimates for erosion of multiple thrust sheets obtained from low-temperature cooling histories. The final goal of the project will be to generate a timing record of forward propagation rates of the thrust front and of contemporaneous depositional centers. Together, these records will allow us to evaluate the orogenic response to rapid hinterland surface uplift, and therefore to test a key prediction of the Cordilleran cyclicity model. This project is training graduate and undergraduate students (including a Bolivian graduate student studying in the U.S.) in a STEM field, and is contributing to the broadening of representation of underrepresented groups in the earth sciences; it is facilitating a new collaboration between U.S. investigators at two institutions (University of Nevada Reno and the University of Texas at Austin); and it is fostering a valuable international collaboration between U.S. and Bolivian scientists. This award is being co-funded by NSF's Office of International Science and Engineering.