UC San Diego

A major theme of igneous petrology involves linking geochemical processes with rock textural development. Of significant importance to this theme is developing an understanding of the mechanisms that lead to the geochemical trends that have been observed in rocks for decades. On Earth, melting occurs through plate tectonics at subduction zones, divergent plate boundaries, or by mantle upwelling from plume activity. On bodies without plate tectonics, melting is likely a result of concentrated heating through the decay of extinct radionuclides, accretionary heating, and/or impact melting. In each of these environments, magmas are geochemically differentiated into evolved melts and mafic/ultramafic residue. This process is driven by assimilation and fractional crystallization, which are primarily driven by melt-crystal interactions. The geochemical and petrologic implications of assimilation and fractional crystallization have been known for decades, though uncertainty persists on the textural implications of these processes.The primary goal of this dissertation is to link geochemical and textural measurements of igneous rocks to understand their development in igneous processes. The major chapters of this dissertation focus on the dynamics of arc cumulate/residue removal, the crystal-melt differentiation mechanisms on extraterrestrial planetesimals, and the processes involved in the emplacement and differentiation of an upper crustal mafic magma. In each of these chapters, I use electron backscatter diffraction to constrain rock textural characteristic and then expand on these data with geochemical measurements and modelling. In this dissertation, Chapter 2 shows that deep arc cumulate/residual rocks have very complex rock fabrics, the deepest rocks are dynamically recrystallized through lithospheric removal while the shallower rocks are relatively pristine. Chapter 3 investigates the crystal orientations and trace element distributions in olivine comprising ultramafic achondrites, this identifies their likely formation as residues after limited partial melting. Finally, Chapter 4 investigates the orientations of crystals within a rare mafic/ultramafic complex of the Sierra Nevada, California and identifies melt-rock reaction patterns and a possible emplacement mechanism. The results of these studies highlight the complexities of melt-solid differentiation on both Earth and extraterrestrial bodies while also opening new research frontiers in igneous rock texture characterization techniques.