Development of Gneissic Banding and its Significance for Rheological Stratification of the Lithosphere

9725661 Sisson该项目将研究与阿拉斯加南部丘加奇山脉东部低压/高温变质带混合岩核的片麻岩带发育有关的变质和构造过程。片麻状条带的形成可能有两个过程：(1)长英质熔体的注入或(2)扩散传质的分凝。这些机制并不是相互排斥的，可以同时发生。这两种机制预示着中下地壳韧性区域的地壳流变性截然不同。这种流变性质的差异将影响岩石圈的大尺度力学。这项研究将试图通过观察从片麻状到片麻状组构的整个过渡带的结构和成分差异来区分片麻状条带形成的两种机制。PI将调查变质带宽度从15-25公里变化的几个地区。拟议的工作包括详细的野外工作，以阐明片麻岩过渡带的运动学，详细的结构和成分差异的岩石学研究，以及高分辨率计算机X射线层析成像。

9725661 Sisson This project will address the metamorphic and structural processes associated with the development of gneissic banding in the migmatitic core of a low-pressure/high-temperature metamorphic belt in the eastern Chugach Mountains, southern Alaska. Two processes which may be responsible for formation of the gneissic banding are: (1) injection of felsic melts or (2) segregation by diffusive mass-transfer. These mechanisms are not mutually exclusive and may occur simultaneously. These two mechanisms predict very different crustal rheologies for the ductile regions in the middle and lower crust. This difference in rheological properties will influence large scale mechanics of the lithosphere. This research will attempt to distinguish between the two mechanisms for development of gneissic banding by looking at textural and compositional differences throughout the transition zone from schistose to gneissic fabrics. The PI will investigate several regions where the width of the metamorphic belt changes from 15-25 km. The proposed work includes detailed flied work to elucidate kinematics of the gneissic transition zone, detailed petrographic studies of both textural and compositional difference, and high resolution computed x-ray tomography.