Three-dimensional shape analysis of miarolitic cavities and enclaves in the Kakkonda granite by X-ray computed tomography

Three-dimensional shape analysis of miarolitic cavities and enclaves from t he Kakkonda granite, NE Japan, was performed by X-ray computed tomography ( CT) and image analysis. The three-dimensional shape of the miarolitic cavit ies and enclaves was reconstructed by stacked two-dimensional CT slice imag es with an in-plane resolution of 0.3 mm and an inter-slice spacing of I mm . An ellipsoid was fitted to each reconstructed object by the image process ing programs. The shortest, intermediate, and longest axes of the ellipsoid s fitted to miarolitic cavities had E-W, N-S, and vertical directions, resp ectively. The shortest axes of the ellipsoids fitted to enclaves were sub-v ertical to vertical. Three-dimensional strains calculated from miarolitic c avities and enclaves have E-W and vertical shortening, respectively. The sh ape characteristics of miarolitic cavities probably reflect regional stress during the late magmatic stage, and those of enclaves reflect shortening b y later-intruded magma or body rotation during the early magmatic stage. Th e miarolitic cavities may not be strained homogeneously with the surroundin g granite, because the competence of minerals is different from that of the fluid-filled cavities. Although the strain markers require sufficient cont rast between their CT numbers and those of the surrounding minerals, this m ethod has several advantages over conventional methods, including the fact that it is non-destructive, expedient, and allows direct three-dimensional observation of each object. (C) 2001 Elsevier Science Ltd. All rights reser ved.