The secret life of a Paleoarchean granitic dome: The cryptic internal structure... Nicolas Roberts

The secret life of a Paleoarchean granitic dome: The cryptic internal structure of the Mt Edgar dome (East Pilbara Terrane) and the hints it provides about the formation of early continental crust
Nicolas Roberts
-Hamilton College
Many of Earth’s earliest continents have a dome-and-keel map pattern, characterized by a variable deformed supracrustal sequence (‘greenstones’) that has been intruded by large, multicomponent granitic-gneiss domes. Although these domes comprise a majority of the mapped surface in many Archean terranes, their greenstone counterparts have received much more attention from structural geologists, because granitic dome rocks have only a barely perceptible fabric in the field. In this talk, I will present work that seeks to understand in much greater detail the internal 3D structure - and ultimately flow patterns - of the Paleoarchean Mt Edgar dome in the East Pilbara Terrane, one of the archetypal dome-and-keel terranes. The approach uses Anisotropy of Magnetic Susceptibility (AMS), microstructural analysis, and Electron Backscatter Diffraction (EBSD) to map out dome structures and begin to interpret the kinematics of dome flow during emplacement. These flow patterns have important implications for early crustal processes, and suggest that the Mt Edgar dome experienced both vertical and horizontal constrictional flow. I will discuss what the structure might mean for the development of the East Pilbara terrane as well as the ultimate question of whether Plate Tectonics may have been active at this period.