Interplays between magmatism, crustal deformation, surface erosion and long-term climate on the rise and fall of continental arcs
Lee, Cin-Ty A
Doctor of Philosophy
Continental arc is one of the most dominant topographic features on Earth with complicated petrogenesis, active volcanism and rapid erosion. Interplays between the deep and surface processes in continental arcs play an important role in shaping the earth. The overall objective of this study is to develop a better understanding of the interconnections between various processes such as magmatism, uplift, surface erosion in continental arcs, and their influences on long term development of the atmosphere and hydrosphere. Continental arcs are characterized by episodic voluminous magmatic flare-ups in the time scale of tens to hundreds of millions of years. Due to the interaction of magma with sedimentary carbonates stored in the continental upper plate, flare-ups in continental arc might result in enhanced CO2 concentration in the atmosphere and greenhouse climate. However, development of continental magmatic arc often accompanied by rapid arc unroofing and erosion due to magmatic/tectonic thickening of the crust, thus continental arcs likely enhance the chemical weathering flux, in turn increasing the CO2 sink. With these feedbacks, it is not clear how long-term climate responds to the variability in the tectonic forcings in the continental arcs. In the first two chapters, I explored the dynamic linkage between magmatism and erosion in continental arcs and evaluated the carbon input and output associated with these processes. I found that during the rise and fall and continental arcs, the arc serves as either a carbon source or sink depending on the stage of the arc life. I propose that the development of continental arcs increases weatherability through mountain building processes, and therefore may increase the strength of the global negative feedback between silicate weathering and climate. In the rest studies, I investigated other processes associated with continental arc development. In Chapter 4, I investigated geochemistry of pseudotachylite from an ancient shear zone in a continental arc. This study attempts to obtain insights of the physics behind earthquake such as thermodynamic conditions and stress state in the shear zone from a geochemical aspect. As the rise and fall of the continental arc can drive changes in the subsurface hydrologic conditions, groundwater products can serve as proxies for the tectonic and climatic forcings in tectonic basins. In Chapter 5, I explored the prospects of using U-Pb dating of petrified (silicified) wood as means of quantifying ancient continental hydrology.