Most of the vein calcites at both sites are relatively pure CaCO3 (Table 1). Calcite at Site 897 averages 97.5 mole% CaCO3 (64 analyses), ranging from 93 to >99 mole%; calcite at Site 899 averages 98.5 mole% CaCO3 (295 analyses), ranging from 96 to >99 mole%. No strong covariation of trace-element concentrations is apparent in the data set as a whole (Fig. 1).
Many of the vein calcites contain Fe and Mn considerably in excess of concentrations expected for precipitation from unmodified seawater (cf., Veizer, 1983, p. 269). Concentrations of Fe and Mn are relatively low, however, in comparison to values observed in authigenic calcites in many sedimentary basins (K.L. Milliken, unpubl. data). The very low Mg and Sr (average below detection in four samples) concentrations are also atypical of authigenic calcite in shallow-marine settings, though they approach values believed consistent with precipitation from cold seawater (Morse and Mackenzie, 1990, pp. 93-101).
Within individual samples, variations in trace-element concentrations are also rather unsystematic across both the petrographic types of calcites and the temporal sequences of calcite types identified by Morgan and Milliken (this volume). Figure 2 and Table 2 present data for Sample 149-899B-16R-2, 69-72 cm, as an example. In this sample, at least three petrographically distinct generations of calcite were observed: an early generation of highly vacuolized calcite with a radial fabric (botryoidal); a subsequent generation of brightly luminescent clear sparry calcite that fills the central portion of the large veins and also small cracks localized between the vacuolized calcite and the serpentinite; and, finally, a late generation of calcite with dark luminescence that fills small fractures that crosscut the earlier generations (Morgan and Milliken, this volume). As expected (e.g., Hemming et al., 1989; Machel et al., 1991), the dark luminescence corresponds either to marginally higher Fe concentrations or to very low amounts of both Fe and Mn, and bright luminescence occurs in zones with overall higher Mn concentrations. However, the petrographically distinct calcite types do not have mutually exclusive fields of trace-element concentrations for any of the elements analyzed nor are there consistent trends for any element across the temporal sequence of calcite types.
Comparison of petrographic types of calcite across different samples also reveals unsystematic variation. For example, a crossplot of Mg content vs. Mn content for botryoidal calcite in two samples, one from Site 897 and the other from Site 899, reveals that petrographic similarity does not correspond to similarity in trace elements (Fig. 3), which is consistent with the observed difference in luminescence between these different samples of vacuolized calcite. In terms of Mg and Mn concentrations, vacuolized calcite in the Site 899 sample is more similar to some of the nonvacuolized calcite in the same sample than it is to vacuolized calcite in the sample from Site 897.
Surviving aragonite was identified in only Sample 149-897D-16R-4, 0-5 cm, on the basis of distinctive petrographic characteristics (confirmed by X-ray diffraction; Morgan and Milliken, this volume). Analysis of the aragonite reveals very high Sr contents and little substitution by other trace elements (Table 3).
Carbon and oxygen isotopic compositions of vein calcites
(Table 4, Fig.
4) display a total range of 1.76‰ for 
18O and 3.4‰ for
13C. As with trace-element variation, there is no systematic variation of
18O and
13C among petrographically distinct calcite types. Average isotopic compositions do not vary significantly between Site 897 and Site 899 and are very similar to isotopic values observed for carbonates in serpentinites drilled at Hole 637A during ODP Leg 103, in the region seaward of Galicia Bank (Evans and
Baltuck, 1988).
Eleven samples manifest a narrow range for 87Sr/86Sr (from 0.70735 to 0.70754, Table 4), a range that is, nevertheless, in excess of analytical error. 87Sr/86Sr does not vary in any systematic way with petrographic types of calcite. Associated vacuolized and clear calcites were analyzed in three samples. Variation in 87Sr/86Sr between vacuolized calcites and associated clear calcites is less than the variation among vacuolized calcites in the data set as a whole.
