Syn-tectonic melt-rock interaction and complex geochronology, Entia Dome: nature and experiments
Across all scales, fluid-rock interactions facilitate metamorphism, increase chemical mobility, disturb geochronological systems and change the rheological properties of rocks. In regions affected by fluid activity, determining the nature of fluid-rock interaction, i.e., fluid type (aqueous fluid or silicate melt), scale of fluid migration and the proceeding reactions, is required to better understand the region's geological history. The Entia Dome in central Australia is well-studied, but lack of a comprehensive understanding of fluid-rock interaction has limited previous interpretations. This thesis uses microstructures to implicate silicate melt as the key fluid present during dome formation. Syn-tectonic melt migration, reaction and metasomatism in major shear zones modified the chemistry of precursor rocks. Melt-rock interaction at the mineral scale modified zircons via coupled dissolution-precipitation and disturbed their U-Pb ages. Although, new apatite U-Pb dates (~312 Ma) confirm the Carboniferous age of doming. This study finds tectonic extrusion of melt-weakened lower crust is critical in forming the extensional dome structure during the contractional Alice Springs Orogeny. We further demonstrate that fluid-rock interaction is intimately tied to all aspects of the Entia Dome's formation. Therefore, it is essential that fluid-rock interactions at all scales are considered when building robust histories of geological regions.