Comparison between the simulated fluid compositions (lines) and natural vent compositions at mid-ocean ridges and analogous submarine basalt-dominated environments (dots) for the total dissolved cation compositions of Mg, Ca, Na, and K. The natural vent compositions are sorted with respect to their associated chlorinities. Vent geochemical data are provided in Table 2
. Orange dots represent a Cl value of 0–527 mmol/kg, red dots represent a Cl value of 527–567 mmol/kg, and green dots represent a Cl value of 567–1000 mmol/kg. Dashed red arrows show the trends of natural fluid samples with a chlorinity corresponding to the value of seawater at 2°C (ClSw, 2°C
= 546.7 mmol/kg ± 20 mmol/kg). White diamonds represent the composition of seawater at 2°C. The seawater-basalt simulations were carried out from 2 to 400°C, 500 bars, and variable fluid/rock (F/R) mass ratios.