Thermal and Compositional Structure of Antarctica from Probabilistic Joint Inversion of Seismic, Gravity, and Topography Data and Petrological Modelling

摘要南极冰盖下地幔的物理状态在南极冰盖与固体地球的相互作用中起着关键作用，对冰川系统的演化具有重要影响。一般来说，地幔温度剖面是通过分析地幔的岩石样本来确定压力-温度条件，或者将地震速度异常转换为温度异常来确定的。然而，地幔岩只在南极洲的极少数地方被发现，地震异常不仅反映了热异常，而且反映了成分的变化。在这个项目中，研究人员将(1)使用最新的对温度和成分敏感的地球物理数据集（高分辨率地震速度模型、地形、卫星重力）；(2)将这些数据集的敏感性结合起来，检索最可靠的热和成分结构模型；(3)将结果转化为温度片和地幔铁成分的二维图；(4)将结果与其他大陆的结果进行比较，以更好地了解南极的地质历史；(5)利用新的热模型以及已建立的岩石关系来估计地幔粘度。技术摘要：南极洲岩石圈的热化学结构是了解该大陆地质演化及其与周围冈瓦纳大陆关系的基础。此外，热结构控制着固体地球对冰川卸载的响应，这对冰盖模式和南极西部冰盖的未来具有重要意义。然而，仅从稀疏的岩石学/地球化学分析中获得准确的温度和成分图像是具有挑战性的，并且大多数以前在地球物理上解决这一问题的尝试都仅依赖于地震或重力数据。在这里，我们建议使用概率联合反演（高分辨率区域地震数据、卫星重力数据、地形）和岩石学建模方法来确定地幔的三维热化学结构。反演将使用马尔可夫链贝叶斯蒙特卡罗方法进行，提供不确定性的定量估计。绘制三维热化学结构（热量和成分）将提供水平（50-100公里分辨率）和垂直（从地表到380公里）变化的全面视图。这个新模型将给我们从地表向下380千米的温度变化以及岩石圈地幔和亚岩石圈地幔的枯竭程度。这个新模型还将与最近的冈瓦纳200迈地体模型进行比较，以建立一个新的克拉通地幔热化学演化模型。新的热化学结构可用于更好地了解冰盖下的地热通量，并改进冰川均衡调整和冰盖模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical abstractThe physical state of the mantle beneath the Antarctic Ice Sheet plays a key role in the interaction between the Antarctic ice cover and the solid earth, strongly influencing the glacial system's evolution. Generally, mantle temperature profiles are determined by analyzing rock samples from the mantle to determine pressure-temperature conditions, and/or by conversion of seismic velocity anomalies to temperature anomalies. However, mantle rocks have been found only in a very few places in Antarctica, and seismic anomalies reflect not only thermal anomalies but also compositional variations. In this project, the investigators will (1) use the most recent geophysical datasets sensitive to temperature and composition (high-resolution seismic velocity model, topography, satellite gravity), (2) Combine the sensitivity of these datasets in a to retrieve the most reliable model of thermal and compositional structure, (3) translate the results into 2-dimensional maps of temperature slices and the composition of iron in the mantle,(4) compare the results with results from other continents to better understand Antarctic geological history, and (5) use the new thermal model along with established rock relationships to estimate mantle viscosity. Technical abstract The thermochemical structure of the lithosphere beneath Antarctica is fundamental for understanding the geological evolution of the continent and its relationship to surrounding Gondwana continents. In addition, the thermal structure controls the solid earth response to glacial unloading, with important implications for ice sheet models and the future of the West Antarctic Ice Sheet. However, it is challenging to get an accurate picture of temperature and composition from only sparse petrological/geochemical analysis, and most previous attempts to solve this problem geophysically have relied on seismic or gravity data alone. Here, we propose to use a probabilistic joint inversion (high resolution regional seismic data, satellite gravity data, topography) and petrological modelling approach to determine the 3D thermochemical structure of the mantle. The inversion will be carried out using a Markov-chain Bayesian Monte Carlo methodology, providing quantitative estimates of uncertainties. Mapping the 3-dimensional thermochemical structure (thermal and composition) will provide a comprehensive view of the horizontal (50-100 km resolution) and vertical (from the surface down to 380 km) variations. This new model will give us the temperature variation from the surface down to 380 km and the degree of depletion of the lithospheric mantle and the sub-lithospheric mantle. This new model will also be compared to recent models of Gondwana terranes 200 Myrs to build a new model of the thermochemical evolution of the cratonic mantle. The new thermal and chemical structures can be used to better understand the geothermal heat flux beneath the ice sheet as well as improve glacial isostatic adjustment and ice sheet models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.