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

科迪勒兰旋回模型预测，密集大陆岩石圈的剥离应伴随着造山带的快速隆升，并导致前缘褶皱-冲断带的快速变形推进。在安第斯高原中部，最近的同位素研究认为，在1600万至1300万年前，玻利维亚南部高原的表面迅速隆起，这被归因于深层致密物质的移除。科迪勒兰旋回模型预测，安第斯褶皱冲断带应通过变形锋的快速东扩来响应这一快速隆升事件。然而，玻利维亚南部冲断带的变形时间和程度的准确记录是不可用的，这使得这一关键预测未经检验。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快速上升的反应（或缺乏反应）。该项目涉及沿着玻利维亚南部冲断带的东西样带进行地质测绘，这将支持平衡剖面的建设。通过在剖面上依次恢复变形，我们得到了过去2000万至3000万年的缩短记录。该记录将与地壳缩短期间沉积的沉积岩的场关系分析的变形时间约束以及从低温冷却历史中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冲断前缘和同时期沉积中心正向传播速率的时间记录。总之，这些记录将使我们能够评估对腹地表面快速隆起的造山反应，从而验证对科迪勒拉旋回模型的关键预测。该项目旨在培养STEM领域的研究生和本科生（包括一名在美国学习的玻利维亚研究生），并为扩大地球科学领域代表性不足的群体的代表性做出贡献；它正在促进两所机构（内华达大学里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有价值的国际合作。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.