factors of Nakamura and Kushiro (1970). Accelerating voltage was 15 kV and beam current was 1.2 x 10–8 A. Analytical results are listed in Table T3, and plagioclase and clinopyroxene compositions are shown in Figure F9.
A total of 124 samples from Unit 1256C-18 and 47 samples from Unit 1256D-1 were made into thin sections for conventional microscopic and scanning electron microscopic observations. Representative textures are shown in Figure F1. Among these thin sections, 58 from Unit 1256C-18 and 47 from Unit 1256D-1 were examined to determine the average maximum grain size of the groundmass plagioclase and augite. The measurement procedures followed those of Shipboard Scientific Party (1992) and Umino (1995), except for measurements on the recrystallized base from Hole 1256C, and are reproduced here. Twelve circular areas of ~13 mm2 were chosen from each thin section. Selection of measured areas was made so as not to overlap each other and to minimize the area occupied by phenocrysts. The length and width of the largest crystals of plagioclase and augite were measured under the microscope. The longest extensions of plagioclase and augite are measured as the length, and the widths are measured perpendicular to elongation at the widest portion of the crystals. A plagioclase grain is usually composed of twinned crystals, which are often displaced along the twin planes and terminate at different positions. In such a case, only the longer single crystal was measured as the length. This measurement was repeated in every circle. The largest and smallest values of the 12 measurements were excluded. The remaining 10 values were averaged as the maximum grain size. For recrystallized samples from the base of Unit 1256C-18, the grain size was determined as follows: the largest 10 grains of plagioclase, augite, and magnetite were chosen from an area of ~40 mm2 under the microscope, and their lengths and widths were measured as described above and averaged to give the average maximum grain size. The results of the measurement are given in Tables T1 and T2 and are shown in Figure F2.
Mineral compositions of selected samples from the recrystallized base of Unit 1256C-18 were determined by a JEOL JXA-733 electron probe microanalyzer (EPMA) of the Center for Instrumental Analysis, Shizuoka University. Corrections were made according to Bence and Albee (1968), using factors of Nakamura and Kushiro (1970). Accelerating voltage was 15 kV and beam current was 1.2 x 10–8 A. Analytical results are listed in Table T3, and plagioclase and clinopyroxene compositions are shown in Figure F9.
