CRYSTALLOGRAPHIC INVESTIGATIONS OF CALCIC PLAGIOCLASE FROM THE BAD VERMILION LAKE ANORTHOSITE COMPLEX, ONTARIO

The microstructures of plagioclase from the Bad Vermilion Lake Anorthosite Complex, Ontario, was investigated by means of electron probe microanalysis, X-ray diffraction and electron microscopy. The plagioclase shows the a, b, c and e-reflections in the diffraction diagram, which indicates the existence of the Huttenlocher exsolution. It was also confirmed by the transmission electron microscopy (TEM). In TEM, the antiphase boundaries (APB) were observed, where the b-APBs show partly zigzag-like forms. The characteristics of the intensity distribution of b-, c- and e-reflections and the APB form indicate that the plagioclase experienced the plutonic-like cooling rate at high temperature, a very slow cooling with more rapid cooling rate than that of metamorphic rocks in the temperature range up to 650-degrees-C and extra slow cooling to room temperature.