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

该项目将研究在南极玛丽伯德地西部福特山脉的福斯迪克山脉发现的混合岩圆顶。这个区域提供了独特的三维暴露，可能为圆顶形成提供新的见解，这是一个基本的造山过程。这些圆顶是由沉积和深成原岩形成的，它们在分米到千米的尺度上复杂地相互交错。从地球气压测量和无水沸石的U-Pb单氮石定年的初步发现表明，变质作用的高峰发生在105 Ma，地壳深度为~25 km，随后在99 Ma时，随着Fosdick穹丘被放置到地壳的16-17 km，或可能低至8.5 km，出现了减压。在上升过程中保持近等温条件，有利于通过黑云母脱水融化产生大量的熔体。这个圆顶被解释为伸展挖掘的产物。从区域的角度来看，这是一种可行的解释，因为穹顶是在白垩纪中期，在冈瓦纳原太平洋边缘的分裂构造迅速开始的时候形成的。然而，福斯迪克山脉复杂的内部构造尚未得到考虑，可能与其他解释更为一致，例如在收缩环境中向上挤压或在横向附着带中横向流动。这一建议是为了进行详细的结构分析，结合地温计和地质年代学，以确定形成Fosdick圆顶内部结构的流动行为和结构风格。这些结果将提高我们对片麻岩圆顶在造山过程中传递物质和热量的作用的一般认识，并将描述冈瓦纳活动边缘从发散构造到收敛构造快速过渡时期中地壳的行为。就更广泛的影响而言，这项工作将训练本科生和研究生，并使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师徒关系。

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.