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

该项目将研究阿拉斯加南部Chugach山脉东部低压/高温变质带混染岩心中与片麻岩带发育相关的变质和构造过程。可能导致片麻岩带形成的两个过程是：(1)长硅熔体的注入或(2)扩散传质引起的偏析。这些机制不是相互排斥的，可以同时发生。这两种机制预测了中、下地壳韧性区的地壳流变学非常不同。这种流变特性的差异将影响岩石圈的大尺度力学。本研究将通过观察从片麻织物到片麻岩织物的整个过渡带的纹理和成分差异，试图区分片麻岩带发育的两种机制。PI将调查变质带宽度在15-25公里之间变化的几个地区。建议的工作包括详细的飞行工作，以阐明片麻岩过渡带的运动学，详细的岩石学研究，包括结构和成分的差异，以及高分辨率的计算机x射线断层扫描。

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.