When did the Altiplano Form? A Coupled Thermochronometer and Numerical Model Test

了解与山地带高原形成相关的时间、速率和变形对于量化高原、板块构造和气候之间的关系是至关重要的。高原发展的计算机模型将地壳温度和强度的变化作为高原形成的主要机制。强度变化是重要的，因为随着构造过程缩短和加厚地壳，下地壳减弱并横向流动，优先支持狭窄山脉带上的高原形成。然而，由于缺乏对高原形成运动学历史的了解，这些计算机模型的测试受到了阻碍。该项目利用岩石冷却历史、场约束构造分析和计算机模型来描绘玻利维亚褶皱和冲断带的构造演化，以推断安第斯高原的形成过程和地表隆起年代学。沿着玻利维亚褶皱和冲断带的两个断面收集和分析Aatite裂变径迹(AFT)和锆石(U-Th)/He(Ze)年龄，以确定岩石冷却历史。AFT和ZHE数据被用来确定沿每个采样样带的隆升时间和速率。耦合的二维热、构造和侵蚀计算机模型正被用来通过预测冷却年龄并将其与AFT和ZHE数据进行比较来量化玻利维亚褶皱和冲断带的历史。耦合的计算机模型通过几个步骤帮助解释数据：(1)用2DMove软件描述逆冲带的构造历史，恢复的构造剖面和沿两个剖面的地质图，(2)构造模型然后驱动热模型中的平流热传递和侵蚀模型中的地表抬升，(3)对于模拟的每一次跨越褶皱和冲断带的构造和侵蚀历史，使用磷灰石裂变径迹退火法和锆石扩散算法计算暴露在地表的温度计时年龄。将模型预测和观测年龄与统计方法进行比较，以确定安第斯高原形成和地表隆起的允许构造和侵蚀历史范围。数据和计算机模型正在整合，以量化每个采样断面上每个逆冲断层上的运动时间、速率和持续时间。结合每个断面上所有断层的变形和剥蚀历史，将为(1)安第斯高原形成的时间和历史，以及(2)与温度和强度有关的高原形成的计算机模型提供约束。

Understanding the timing, rates, and deformation associated with mountain belt plateau formation is central to quantifying relationships between plateaus, plate tectonics, and climate. Computer models of plateau development invoke variations in crustal temperatures and strength as the main mechanism of plateau formation. Strength variations are important because as tectonic processes shorten and thicken the crust the lower crust weakens and flows laterally, preferentially supporting plateau formation over a narrow mountain belt. However, tests of these computer models are hampered by a lack of knowledge about the kinematic history of plateau formation. This project is using rock cooling histories, field-constrained structural analysis, and computer models to delineate the tectonic evolution of the Bolivian fold and thrust belt to infer the formation process and surface uplift chronology of the Andean Plateau.Apatite fission track (AFT) and zircon (U-Th)/He (ZHe) ages are being collected and analyzed along two transects in the Bolivian fold and thrust belt to determine rock cooling histories. The AFT and ZHe data are being used to define the timing and rates of uplift along each sampling transect. Coupled two dimensional thermal, tectonic, and erosion computer models are being used to quantify the history of the Bolivian fold and thrust belt by predicting cooling ages and comparing them with the AFT and ZHe data. The coupled computer models aid in the interpretation of data through several steps: (1) the tectonic history of the thrust belt is prescribed using the 2DMove software, restored structural cross-sections, and geologic maps along both profiles, (2) the tectonic model then drives advective heat transfer in the thermal model and surface uplift in the erosion model, (3) for each tectonic and erosion history simulated across the fold and thrust belt the thermochronometer ages exposed at the surface are computed using apatite fission track annealing and zircon He diffusion algorithms. Model predicted and observed ages are compared with statistical methods to identify the range of permissible tectonic and erosion histories for Andean Plateau formation and surface uplift. The data and computer models are being integrated to quantify the timing, rate, and duration of motion on each thrust fault across each sampling transect. Combining the deformation and erosion history of all the faults across each transect will provide constraints on (1) the timing and history of Andean Plateau formation, and (2) temperature and strength dependent computer models of plateau formation.