THE GRANITES OF DAMARISCOVE ISLAND, MAINE: A MICROSCALE CHARACTERIZATION
In contrast to field observations, a microscopic view reveals that both coarse-grained and fine-grained granite samples have a seriate texture, with a higher concentration of biotite mica defining the foliation in the fine-grained phase. Grain shape ranges from anhedral to subhedral, with micas comprising the vast majority of the subhedral grains. There is little difference in the amount of deformation exhibited by each phase, suggesting similar timing for the emplacement of two different phases of the same magmatic event. Observed deformation structures include undulose extinction and development of subgrains in quartz, and mechanical twinning in plagioclase feldspar. Along phase contacts, coarse-grained samples also exhibit intercrystalline fracture in feldspars as well as both intra- and intercrystalline fracture in quartz. Based on thin-section evidence, one can infer that the fine-grained granite succeeded the coarse-grained granite, thus substantiating most of the cross-cutting relations observed in the field.