Gneiss Dome architecture: Investigation of Form and Process in the Fosdick Mountains, W. Antarctica

该项目将研究在南极洲玛丽伯德地西部福特山脉的福斯迪克山脉中发现的混合岩圆顶。该区域提供了独特的三维曝光，可以为穹顶形成提供新的见解，这是造山的基本过程。这些圆顶源自沉积和深成原岩，这些原岩在分米到千米尺度上复杂地交错折叠。地压测量和深熔岩 U-Pb 独居石测年的初步结果表明，峰值变质作用在 105 Ma 处地壳深度约 25 km 处发生，随后随着 Fosdick 圆顶在 99 Ma 时在地壳中移动至 16-17 km，或可能低至 8.5 km，发生减压。在上升过程中保持接近等温的条件，有利于通过黑云母脱水熔融产生大量熔体。这个圆顶被解释为伸展折返的产物。从区域角度来看，这是一个可行的解释，因为圆顶是在白垩纪中期，沿着冈瓦纳原太平洋边缘迅速发生分异构造运动时形成的。然而，福斯迪克山脉复杂的内部结构尚未得到考虑，并且可能更符合其他解释，例如收缩环境中的向上挤压或横向附着区域内的横向流动。该提案用于详细的结构分析，结合地温气压测量和地质年代学，以确定产生福斯迪克圆顶内部建筑的流动行为和结构风格。这些结果将提高我们对片麻岩穹丘在造山过程中传递物质和热量的作用的总体理解，并将描述沿冈瓦纳活动边缘从发散构造向聚合构造快速转变期间中地壳的行为特征。就更广泛的影响而言，这项工作将培训本科生和研究生，并让他们作为合作者参与课程材料的开发。它还将促进研究生和本科生之间的指导关系。

This project will study migmatite domes found in the Fosdick Mountains of the Ford Ranges, western Marie Byrd Land, Antarctica. This area offers unique, three-dimensional exposures that may offer new insight into dome formation, which is a fundamental process of mountain building. These domes are derived from sedimentary and plutonic protoliths that are complexly interfolded at decimeter to kilometer scales. Preliminary findings from geobarometry and U-Pb monazite dating of anatexite suggest that peak metamorphism was underway at 105 Ma at crustal depths of ~25 km, followed by decompression as the Fosdick dome was emplaced to 16-17 km, or possibly as low as 8.5 km, in the crust by 99 Ma. Near-isothermal conditions were maintained during ascent, favorable for producing substantial volumes of melt through biotite-dehydration melting. This dome has been interpreted as a product of extensional exhumation. This is a viable interpretation from the regional standpoint, because the dome was emplaced in mid-Cretaceous time during the rapid onset of divergent tectonics along the proto- Pacific margin of Gondwana. However, the complex internal structures of the Fosdick Mountains have yet to be considered and may be more consistent with alternative intepretations such as upward extrusion within a contractional setting or lateral flow within a transcurrent attachment zone. This proposal is for detailed structural analysis, paired with geothermobarometry and geochronology, to determine the flow behavior and structural style that produced the internal architecture of the Fosdick dome. The results will improve our general understanding of the role of gneiss domes in transferring material and heat during mountain-building, and will characterize the behavior of the middle crust during a time of rapid transition from divergent to convergent tectonics along the active margin of Gondwana. In terms of broader impacts, this work will train undergraduate and graduate students, and involve them as collaborators in the development of curricular materials. It will also foster mentoring relationships between graduate and undergraduate students.