Structural Evolution of Arcs Syllabus
Instructor: Scott Paterson
Office SCI 307; phone = 06103; email = paterson@usc.edu.
Office Hours: TBA and anytime my door is open.
"We are now fully assured that granite has been made to break, displace and invade the Alpine schistus or primary strata having been previously forced to flow in the bowels of the earth, and reduced into a state of fusion."
-- James Hutton: "Observations on Granite" (1794)
The construction and evolution of arcs represents one of the most dynamic geologic processes on earth. Mantle, crustal, and surface processes all play important roles. And in contrast to many other geologic settings, magma-host rock systems undergo highly variable conditions during their lifetime resulting in highly variable behavior. Magmatic systems and their host rocks are open, linked systems: heat, mass, and mechanical energy are all transported across the pluton-country rock contact. Therefore, the evolution of magmatic systems is in part controlled by the behavior of the surrounding rocks, and the behavior of the surrounding rocks is strongly affected by the evolution of the magmatic systems. Thus to understand the evolution of these systems we need to examine the internal petrology and structures of magmatic bodies as well as the nature of their contact aureoles.
The petrology and geochemistry of, and structures in plutons give us clues about their source, ascent, final emplacement, and subsequent deformation. In Lawford Anderson's Igneous Petrology class you will (or have) learn(ed) much about magma generation sites and the chemical evolution of magmas. In this class we will focus on the thermal and mechanical evolution of these systems and on the thermal and mechanical evolution of arcs in general. The preserved characteristics of these systems sometimes give us information about magma ascent, but more often give us clues about the behavior of these systems during final emplacement and subsequent deformation. These latter subjects will be the focus of this class.
One useful way of viewing contact aureoles around plutons is as gradients (of temperature, strain, viscosity, etc.) between the margin of a pluton and what is usually regionally deformed and metamorphosed host rock. The nature of these gradients provides us with valuable clues not only about the evolution of magmatic systems but about the timing of and conditions during which regional deformation-metamorphism occurred in arcs. Contact aureoles are important for determining timing relationships between pluton emplacement and regional deformation, for placing constraints on P-T-D-t paths, and are an excellent natural laboratory for the study of geologic processes with a known source of heat, fluids, and stresses. A study of structures and metamorphism in contact aureoles provides important constraints on the thermal behavior of these systems, as well as the mechanical and kinematic processes responsible for these gradients.
In lecture we will review and discuss the theoretical aspects of magma-host rock systems: labs will consistent of practical exercises designed to quantitatively evaluate natural systems. I wish to emphasize that although I've done the general organization for this class, I view this class as yours. How successful and fun this class will be, in part, depends on your involvement. So if you are working on a pluton, or know of other good papers about plutons not in my reading list, or have maps, thin sections, or photos of plutons or contact aureoles, please share your resources with us.