RESULTS

Using the shipboard core descriptions (Whitmarsh, Beslier, Wallace, et al., 1998), the authors identified 18 core locations that appeared to be typical of the different principal types of basement rock encountered at Sites 1067 and 1068. Subsequently, 10- to 20-cm³ rock samples were taken by the ODP core curator in Bremen, Germany, and mailed to the authors. The rocks were unusually homogeneous and, with few exceptions, contained less then 10% veins of serpentine (lizardite? and chrysotile?), brucite, calcite, chlorite, epidote, Fe oxyhydroxide, quartz + plagioclase, sulfides, and talc. Only Sample 173-1068A-26R-1 (Piece 3G), which had the lowest heat output, included a large vein.

Concentrations of radioelements and the resulting values of radiogenic heat production given in Table T1 were determined following methods described by Mareschal et al. (1989). Samples were crushed to a fine powder and neutron activated. After irradiation, the concentrations of U, Th, and K were measured by gamma-ray spectrometry. For some samples, the K concentration was also measured using a standard X-ray spectrometry technique. The overall reproducibility was verified by measuring different aliquots of the same sample and was better than 5%. The undifferentiated amphibolite (nine samples) and tonalite gneiss (three samples) from Site 1067 have mean heat productions of 0.358 ± 0.118 ( = 0.355) and 0.802 ± 0.039 µW/m³ ( = 0.068), respectively, whereas the serpentinized peridotite (six samples) from Site 1068 have a mean of 0.0108 ± 0.0003 µW/m³ ( = 0.0007). These results are similar to the amphibolite (0.213 ± 0.086 µW/m³) and serpentinite (<0.01 µW/m³) samples previously measured from Leg 149 at Sites 900 and 897, while the tonalite samples have generally lower values than the continental granodiorite and sandstone samples (1.66 ± 0.093 µW/m³) dredged from Galicia Bank (Louden and Mareschal, 1996).