Uplift and Exhumation of the Transantarctic Mountains and Relation to Rifting in West Antarctica

该奖项由极地项目办公室的南极地质和地球物理项目提供，支持应用数值模拟来限制横贯南极山脉的隆起和挖掘历史的研究。横贯南极山脉（TAM）是一个异常高（4500米）和相对宽（200公里）的裂谷翼隆起，划定了东南极洲和西南极洲之间的边界。南极东部冰盖的动态和气候受到山脉的影响，了解山脉的隆升历史对理解这些过程至关重要。该项目将在热力学模型的基础上约束横贯南极山脉的隆起和剥蚀历史，该模型忠实于热年代学、地质和地球物理数据。该研究将由博士后研究员Audrey Huerta主要负责，与Dennis Harry， 1名本科生和1名研究生合作。从白垩纪到新生代的快速冷却的热年代学证据表明，TAM内部有不同的隆升和挖掘时期。然而，如果不了解TAM在隆升之前和隆升期间的热结构和地形的演变，就很难对隆升历史进行更详细的解释。对不断演变的区域构造环境的理解可以最好地限制山脉的这些方面。TAM靠近南极西部裂谷系统（WARS），表明TAM的隆升与WARS内部的伸展之间存在联系。该项目将整合两种技术：岩石圈尺度的地球动力学模拟和地壳尺度的热模拟。TAM的岩石圈尺度的变形和热演化将通过一个有限元模型来模拟，该模型旨在跟踪南极岩石圈对长期伸展环境的热和变形响应。先前的研究人员将TAM的高海拔和宽宽度与深颈缩联系起来，在深颈缩中，地幔变薄与地壳伸展的位置相抵消。在本研究中，将使用三维动力学模型来跟踪TAM在颈缩处于深部、地壳内伸展与地幔内伸展相抵消的背景下的隆升和热演化。应用于模型边缘的速度边界条件将随时间变化，以模拟WARS的张拉和张拉演化。由于模型是动态的，热结构、强度和应变场随着这些初始条件和边界条件的变化而自然演化。动力学模型是唯一适合于理解岩石圈变形和热演化的模型，而运动学模型则最适合于解决地壳隆升的详细热历史和挖掘历史。因此，将设计一个二维运动学-热模型来模拟TAM的隆起历史以及由此产生的侵蚀、地形和热演化。隆升将被建模为一组离散的断层平面上的正断层运动，其隆升速率随时间变化。侵蚀将被模拟为一个扩散过程，其中侵蚀速率可以随时间变化（模拟气候变化），并在空间上作为梯度和离分水岭距离的线性函数而变化。将计算合成时间-温度（t-T）历史，以便将模式结果与热年代学数据进行比较。

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports research to apply numerical modeling to constrain the uplift and exhumation history of the Transantarctic Mountains. The Transantarctic Mountains (TAM) are an anomalously high (4500 m) and relatively broad (up to 200 km) rift-flank uplift demarcating the boundary between East and West Antarctica. Dynamics of the East Antarctic ice-sheet and the climate are affected by the mountain range, and an understanding of the uplift history of the mountain range is critical to understanding these processes. This project will constrain the uplift and denudation history of the Transantarctic Mountains based on thermo-mechanical modeling held faithful to thermochronological, geological, and geophysical data. The research will be the primary responsibility of post-doctoral researcher Audrey Huerta, working in collaboration with Dennis Harry, 1 undergraduate student, and 1 graduate student.Thermochronologic evidence of episodic Cretaceous through Cenozoic rapid cooling within the TAM indicates distinct periods of uplift and exhumation. However, a more detailed interpretation of the uplift history is difficult without an understanding of the evolving thermal structure and topography of the TAM prior to and during uplift. These aspects of the mountain range can best be constrained by an understanding of the evolving regional tectonic setting. Proximity of the TAM to the West Antarctic Rift System (WARS) suggests a link between uplift of the TAM and extension within the WARS.The project will integrate two techniques: lithospheric-scale geodynamic modeling and crustal-scale thermal modeling. The lithospheric-scale deformational and thermal evolution of TAM will be modeled by a finite element model designed to track the thermal and deformational response of the Antarctic lithosphere to a protracted extensional environment. Previous investigators have linked the high elevation and broad width of the TAM to a deep level of necking in which mantle thinning is offset from the location of crustal extension. In this study, a three-dimensional dynamic model will be used to track the uplift and thermal evolution of the TAM in a setting in which necking is at a deep level, and in which extension within the crust and extension within the mantle are offset. Velocity boundary conditions applied to the edges of the model will vary through time to simulate the extensional and transtensional evolution of the WARS. Because the model is dynamic, the thermal structure, strength, and strain field, evolve naturally in response to these initial and boundary conditions.Dynamic models are uniquely suited to understanding lithospheric deformational and thermal evolution, however kinematic models are best suited for addressing the detailed thermal and exhumation history of crustal uplifts. Thus, a 2-dimensional kinematic-thermal model will be designed to simulate the uplift history of the TAM and the resulting erosional, topographic, and thermal evolution. Uplift will be modeled as normal-fault movement on a set of discrete fault planes with uplift rate varying through time. Erosion will be modeled as a diffusive process in which erosion rates can be varied through time (simulating climate changes), and vary spatially as a linear function of gradient and distance from the drainage divide. Synthetic time-temperature (t-T) histories will be calculated to compare model results to thermochronologic data.