Seawater with meteoric water

An additional source of salinity in polar areas is residual brines derived from the freezing of seawater (Nelson and Thompson, 1954 Herut et al, 1990 Richardson, 1976 Marison et al., 1999 Bottomley etal., 1999 Yaqing etal., 2000). Bein and Arad (1992) showed that deep saline groundwaters in Sweden and Finland have low Na/Cl and high Br/Cl ratios. Based on their chemical composition, it was argued that the saline waters are remnants of frozen seawater formed during the last glaciation, followed by dilution with meteoric water (Bein and Arad, 1992). 

Sporadic occurrences of minor amounts of early siderite formed at low temperature (20-40 °C), frequently in association with detrital biotites. The fluid from which siderite precipitated had a consistent oxygen, carbon and strontium isotopic composition over great distances, which is best explained as representing homogeneous mixing of Jurassic seawater and meteoric water at field scale. Carbon was predominantly supplied by organic sources. 

The latter author tabulated many analyses of calcium chloride groundwater in various aquifers of the country (Fig. 2.31 and Table 2.12), with all of them appearing to be different forms of dolomitization brine. Those very near the coast (the first three of Israel 1 in Table 2.12) were almost pure seawater with much of the magnesium replaced by calcium, and very little of the sulfate yet precipitated. The other two samples of Israel 1 were from the central plateau, and of the same composition but considerably diluted with meteoric water. The oil field and Negev aquifers (Israel Oil and 2, 3) are slightly more concentrated seawater dolomitization brines, but the Rift Valley aquifers, springs and the Dead Sea represent considerably altered potash deposit dolomitization brine that appears to have traveled along the Red Sea fault system to Israel (Bentor, 1969). 

The most important conclusion derived from the isotopic studies mentioned above is that isotopic characteristics of Kuroko ore fluids were caused dominantly by seawater-volcanic rock interaction at elevated temperature and by the mixing of seawater with small portions of igneous water or the hydrothermal solution whose chemical and isotopic compositions are controlled by water-rock interaction under the rock-dominated condition and also small proportion of mixing of meteoric water. 

D and 5 0 data on fluid inclusions and minerals, 8 C of carbonates, salinity of inclusion fluids together with the kind of host rocks indicate that the interaction of meteoric water and evolved seawater with volcanic and sedimentary rocks are important causes for the formation of ore fluids responsible for the base-metal vein-type deposits. High salinity-hydrothermal solution tends to leach hard cations (base metals, Fe, Mn) from the country rocks. Boiling may be also the cause of high salinity of base-metal ore fluids. However, this alone cannot cause very high salinity. Probably the other processes such as ion filtration by clay minerals and dissolution of halite have to be considered, but no detailed studies on these processes have been carried out. 

A wide range of groundwater chemistry has been recorded in crystalline rock environments. Shallow groundwaters (usually <200 m) are dominantly Ca-Na-HCOa formed by the interaction of atmospherically recharged meteoric water with the soil and shallow bedrock. These waters are fresh with dilute dissolved loads and young, as indicated by the presence of tritium. Occasionally, saline intrusions from adjacent seawater bodies or upwelhng of deeper saline fluids can influence the chemistry of shallow groundwaters. 

The flat slopes of some 0-C trends, which pass above the field of igneous values, in Figure 4 requires exchange with infiltrating meteoric water (or seawater). This is most clearly seen for the Marysville ( 2) and Skye ( 5) data (Fig. 4), which extend to 5 0 < 5. 

The infiltration of surface derived fluids into a contact aureole requires that fluid pressures be close to hydrostatic. Thus, if stable isotope ratios indicate exchange with large amounts of meteoric water, Ph20 must have been much less than Piithostatic at some time during the metamorphic history. The deepest known instances of meteoric water exchange represent the transition towards lithostatic fluid pressure. All known zones of meteoric water infiltration are shallower than 15 km and most are less than 6 km (Valley and O Neil 1982). Likewise, penetration of seawater to depths of 6-7 km in oceanic crust is well documented (Gregory and Taylor 1981). Possibly the deepest known penetration of surface-derived fluids is in veins and in faults of extensional terranes (Fiicke et al. 1992 Nesbitt and Muehlenbachs 1995 Morrison and Anderson 1998). 

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