From Layered Intrusions to Mid-Ocean Ridges: The Petrography and Geochemistry of Basaltic Magmas

The geochemical evolution of basaltic magmas, in a variety of settings, has been the subject of countless studies. In some instances, basaltic magmas evolve to form economic transition and precious metal ore bodies. The metals extracted from these ore bodies are of critical importance to a wide variety of industries, such as automotive manufacturing. On a larger scale, basaltic magmas evolve to form the oceanic crust, the interface between the Earth’s mantle and the oceans. These are just two examples of how basaltic magmas are entwined with life on Earth and together represent the focus of this dissertation.

The second chapter of this dissertation uses detailed petrography to characterize the late-stage evolution of the Eocene Skaergaard Intrusion, Greenland. Significantly, this study identifies textural and chemical evidence that suggests that late hydrothermal fluids modified the Skaergaard transition (copper) and precious metal (silver, gold, platinum) budget.

The third chapter examines the major and trace element concentrations, as well as the 87Sr/86Sr ratios, for a suite of basaltic lavas dredged from the Cocos-Nazca Spreading Center, the Dietz Volcanic Ridge, and the East Pacific Rise. Prior to this study, this region of the Pacific basin was sparsely sampled. Notably, this study determines that lavas from the Cocos-Nazca Spreading Center are chemically depleted and are likely sourced from mantle that differs from that characteristic of normal mid-ocean ridge basalt.

Finally, the fourth chapter examines the size distribution, morphology, and chemical composition of plagioclase in plagioclase phyric lavas from the Cocos-Nazca Spreading Center. A variety of plagioclase morphologies, textures, and chemical compositions are reported. Importantly, this study demonstrates that combining size distribution analysis with textural and compositional information can provide nuanced information about the processes occurring beneath mid-ocean ridges.