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

这个项目将研究在南极洲西部玛丽·伯德土地的福特山脉的福斯迪克山脉中发现的混合岩穹顶。这一区域提供了独特的三维曝光，可能会为穹顶的形成提供新的见解，这是造山的基本过程。这些穹顶来自沉积原岩和深成原岩，这些原岩在分米到千米的尺度上复杂地交错在一起。斜方辉石的地质压力测量和独居石U-Pb测年的初步结果表明，在105 Ma，地壳深度约25公里处发生了峰期变质作用，99 Ma时，福斯迪克穹隆侵位到地壳16-17公里处，或可能低至8.5公里处，发生了减压作用。在上升过程中保持了近等温条件，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，这是一种可行的解释，因为穹顶位于白垩纪中期，当时冈瓦那原太平洋边缘的分叉构造正在迅速形成。然而，福斯迪克山脉复杂的内部结构尚未被考虑，可能与其他解释更一致，如收缩环境中的向上挤压或横流附着带中的横向流动。这项建议是为了进行详细的结构分析，结合地质温压测量和地质年代学，以确定产生福斯迪克穹顶内部建筑的流动行为和结构风格。这一结果将加深我们对片麻岩穹隆在造山过程中物质和热传递作用的总体理解，并将表征冈瓦那活动边缘从发散构造向汇聚构造快速过渡时期中地壳的行为。就更广泛的影响而言，这项工作将培养本科生和研究生，并让他们作为合作者参与课程材料的开发。它还将培养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.