a Six sample-types are distinguished (see Section 4); note that the fully altered samples and the breccia sample are taken as endmembers of the hydrothermal alteration and associated brecciation, respectively.b Normalized to the NBS-SRM 987 value of 87Sr/86Sr = 0.710248 (Thirlwall, 1991), with 2SE internal errors in brackets; the 2SD external errors are <18 ppm; the 2σ uncertainties in 87Sr/86Sr from BHVO-2 and AGV-2 standards are 0.703467 ± 0.000010 (n=2) and 0.703959 ± 0.000015 (n=3), respectively.c Normalized to the JNdi-1 value of 143Nd/144Nd = 0.512115 (Tanaka et al., 2000), with 2SE internal errors in brackets; εNd = [(143Nd/144Nd) measured / (143Nd/144Nd) CHUR – 1] × 104, while CHUR is 0.512638 (Jacobson and Wasserburg, 1980); the 2SD external errors are <19 ppm (i.e. <0.4 εNd-unit); the 2σ uncertainties in 143Nd/144Nd from BHVO-2 and AGV-2 standards are 0.512997 ± 0.000028 (n=2) and 0.512802 ± 0.000038 (n=3), respectively.d Degree of alteration in natural hydrothermal system can be estimated (cf. Kawahata et al., 2001; Delacour et al., 2008): Sr isotope exchange = (εSrfrock – εSrirock) / (εSriwater – εSrirock), where the subscripts (water) and (rock) refer to the hydrothermal fluid and altered rock, respectively; and the superscripts (i) and (f) identify the initial and final values of Sr isotope ratios, respectively.e Assuming the final equilibrium of Sr isotope, the water–rock interaction can be quantified by simple mass balance equations, respectively, for closed system (cf. Berndt et al., 1988; Kawahata et al., 2001) and for open system (cf. Albarède, 1995; Delacour et al., 2008); W/R ratio (close system) = (εSrirock – εSrfrock) / (εSrfrock – εSriwater) * (Srrock / Srwater); W/R ratio (open system) = ln [(εSrirock – εSrfrock) / (εSrfrock – εSriwater) +1] * (Srrock / Srwater); where W is the mass of hydrothermal fluid, R is the mass of rock being altered; εSrirock and εSrfrock is the initial and final isotopic ratio of rock, respectively; εSriwater and εSrfwater is the initial (i.e. seawater) and final isotopic ratio of fluid, respectively; note that εSrfrock is equal to εSrfwater; Srrock and Srwater is the Sr concentration of unaltered rock and of seawater, respectively. The values of εSrirock (87Sr/86Sr: 0.70309) and Srrock (Sr: 168 ppm) after the mean values of Site U1500 basalts (Yu and Liu, 2020) and SCS seafloor basalts (i.e. Sites U1431, U1433, and U1434; Zhang et al., 2018), and the values of εSrfwater (87Sr/86Sr: 0.70780; McArthur et al., 2012) and Srwater (Sr: 12 ppm; Antonelli et al., 2017) after the global seawater estimates of the late-Eocene age.