sgr ms thesis - University of Maine

Chapter 1
INTRODUCTION
Magma chambers are dynamic physical and chemical systems involving
multiple processes such as mixing, mingling, convection, recharge and
evacuation of magma. At deeper crustal levels, relatively high background
temperatures can lead to long-term physical and chemical evolution, obscuring
the spatial and temporal relations among individual magmatic events. In contrast,
the sequential evolution of magmatic systems high in the crust at the interface
between the plutonic and volcanic realms is commonly well preserved. These
subvolcanic systems (e.g. Johnson et al., 2002; Metcalf, 2004; Kemp et al., 2006;
Marianelli et al., 2006), much like eruptive sequences, can preserve a long and
varied history of instantaneous magmatic events. They typically contain a wide
variety of intrusive phases (e.g. cone sheets, ring faults and dikes, and massive
central intrusions) and are potentially a rich source of information about the
evolution of caldera/volcano root zones and the tops of upper-crustal magma
chambers. They also commonly preserve genetically related volcanic sequences
on their margins. The detailed intrusive relationships in these complexes and the
intimate timing relationships between the various intrusions and deformational
structures are preserved in part due to rapid quenching of some units, and in part
due to the sequential series of intrusions that produce a magmatic stratigraphy.
These complexes provide an unusual opportunity to evaluate the evolution of
1