Emplacement history of the Basement Sill, Antarctica: Injection mechanics of crystal-laden slurries

Crystal fractionation and the sorting and transport of phenocrysts in magmatic bodies are fundamental processes driving the evolution and diversity of igneous rocks. The chemical diversity of igneous rocks has long been known and studied, but an understanding of the physical processes that drive such chemical evolution is also necessary. Episodic emplacement and filling regimes of intrusive magmatic bodies, analogous to episodic volcanic eruptive events, can leave a record of the magmatic system dynamics in the final distribution of an attendant phenocryst population. Phenocryst distribution profiles of multiply injected systems are here investigated, and features common to certain filling dynamics are established by coupling theories of particle settling in viscous flows with those of conductive cooling and solidification front advancement. Fourteen vertical and one horizontal sample profiles of the Ferrar Dolerites sill complex in the McMurdo Dry Valleys, Antarctica are analyzed in this work. Twelve of those sample profiles are from the Basement Sill, and were mostly gathered in the area of and near Bull Pass. The chemical and phenocryst profiles of all these sections are examined and reveal information about the emplacement dynamics of that system, particularly with respect to episodic filling and expansion via radial lobes. Experiments performed in the laboratory to create a physical analog model of a phenocryst-laden magmatic system also reveal information about the dynamics of emplacement of such magmatic bodies and the features that may exist in the record of phenocryst distribution.