This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports research on magma crystallization processes through studies of sills of the Ferrar Group in Antarctica.
Earth's basic structure came about through processes involving the crystallization of magma or molten rock. The operation of these processes over billions of years has produced a wide diversity of rock types that have in turn given rise to the basic surface features of Earth, namely, continents and ocean basins. Yet the very details of these physical and chemical processes remain largely undiscovered. Although present day volcanism exemplifies this overall process of differentiation through the variety of lava erupted, it is not clear how this dramatic end result relates to the prolonged and detailed processes at depth responsible for this result. Solidified bodies of magma (called plutons), once deeply buried and now exposed through erosion, also furnish evidence, but most often the context of these plutons within the magmatic-volcanic system is not clear. The aim of the present research is to make a significant contribution to solving this fundamental problem by studying a group of magmatic rocks in Antarctica that uniquely display these magmatic processes. They expose the relationship of plutonism to volcanism and may be an important key to understanding planetary magmatism.
The emerging global paradigm of a stack of magmatic sheets or sills connected below to a deep-seated magmatic source and above to a volcanic center is exemplified by the Ferrar magmatic system of the Dry Valleys, Antarctica (Ferrar-DV). The world's major magmatic systems (i.e., at ocean ridges, Kilauea, Mt. Etna, Stillwater, and Rum, among many others) tend also to exhibit this style of system, but only the Ferrar-DV clearly reveals the critical physical and chemical connections between the deep, mush-dominated system and the near-surface. pre-eruptive sill system. At the deepest level, for example, an extensive mush-filled, ultramafic sill forms a small (400 m) layered intrusion with many features common to the largest layered intrusions of similar composition such as Dufek and Stillwater. Moving up-section, the progressive loss of large crystals of orthopyroxene (opx), which largely form the mush, and smaller plagioclase leads to differentiated tholeiitic sills. Formerly extensive coeval and chemically contiguous lavas (Kirkpatrick Basalt) complete this remarkably complete, exceptionally exposed, and extensive (~10,000 cubic-km) magmatic system.
Previous work in tracing the opx mush tongue over an area of ~3,000 sq.-km has revealed the thunderhead-like filling pattern of a stack of sills interconnected in the fashion of the limbs and trunk of a fir tree. The opx tongue records an episodic sequence of sill emplacement coupled with pulsative filling of the individual sills themselves. The apparent emplacement rhythm of the Ferrar-DV system is akin to both plutonic and volcanic systems. Moreover, although layering is pervasive within, and confined to, the opx-rich tongue, at one locale (the Dais) the layers are particularly well formed on many scales (mm to m) and show scour and fill, ripples and other forms of sorting. The relatively small size and high crustal level of the magma body at the Dais allowed rapid quenching, uniquely preserving textures commonly lost to annealing in large magma systems.
This project seeks to ascertain the full physical and chemical nature of the Ferrar-DV magmatic system. The major goals are to delineate fully its vertical and horizontal extent; to understand the dynamics of its establishment; to understand the mechanics of formation of the Dais layered intrusion; to produce a map of Ferrar rocks throughout the Dry Valleys; and to produce a 3-D model of the opx tongue and feeder system. Overall, the project will attempt to elucidate a rarely seen transition between plutonic and volcanic systems, which may well have implications fundamental to planetary magmatism in the b
