Meteoric water line

Fig. 18-24 Observed correlation (the Meteoric Water Line) of the two most important isotopic ratios in precipitation (gray diamonds Jouzel et al., 1987 and Dahe et al., 1994), and predictions of simple isotopic models. A, prediction with constant a B, prediction with temperature-dependent a.

Figure 1.103. 8D and 8 0 of ore fluids responsible for epithermal Au-Ag vein-type deposits in Japan (Hattori and Sakai, 1979 Imai et al., 1998). S.W. seawater, M.W. line meteoric water line, KK Kushikino, SG Seigoshi, YUG Yugashima, TK Takatama, FUK Fuke, YN Yatani, KN Kanisawa (Yatani), HK Hishikari. 

SD and 8 0 values for epithermal deposits from other countries are summarized in Fig. 1.105 (Field and Fifarek, 1985). The oxygen shift away from the meteoric water line is always observed, but 8D is similar to meteoric water value, suggesting meteoric water source of epithermal ore fluids. Magmatic contribution to ore fluids has not been found except in some ore fluids responsible for the deposits in the other countries Tui... 

This is called the meteoric water line. Dansgaard compared the annual mean < 180 value of precipitation with the average annual air temperature T and obtained a straight line of equation ... 

Fig. 2.4 Global relationship between monthly means of 5D and in precipitation, derived for all stations of the IAEA global network. Line indicates the global meteoric water line (MWL) (after Rozanski et al. 1993)...

The imprint of local conditions can also be seen at other coastal and continental stations. The examples in Table 3.1 demonstrate that varying influences of different sources of vapor with different isotope characteristics, different air mass trajectories, or evaporation and isotope exchange processes below the cloud base, may often lead to much more complex relationships at the local level between 8D and 8 0 than suggested for the regional or continental scale by the global Meteoric Water Line equation. 

This model qualitatively explains the deviation of isotopic compositions away from the Meteoric Water Line because molecular diffusion adds a non-equilibrium fractionation term and the limited isotopic enrichment occurs as a consequence of molecular exchange with atmospheric vapor. It is mainly the humidity which controls the degree of isotope enrichment. Only under very arid conditions, and only in small water bodies, really large emichments in D and are observed. For example, Gonfiantini (1986) reported a 5 0-value of +31.3%c and a 8D-value of +129%c for a small, shallow lake in the western Sahara. 

Although formation waters show a wide range in isotopic composition, waters within a sedimentary basin are usually isotopically distinct. As is the case with surface meteoric waters, there is a general decrease in isotopic composition from low to high latitude settings (Fig. 3.20). Displacements of 5D and 8 0-values from the Meteoric Water Line (MWL) are very often correlated with salinity the most depleted waters in D and O are usually the least saline, fluids most distant from the MWL tend to be the most saline. 

Somewhat unusual isotopic compositions have been observed in highly saline deep waters from Precambrian crystalline rocks as well as in deep drill holes, which plot above or to the left of the Meteoric Water Line (Frape et al. 1984 Kelly et al. 1986 Frape and Fritz 1987). There are two major theories about the origin of these Ca-rich brines ... 

Fig. 3.39 5D and values for kaolonites and related minerals from weathering and hydrothermal environments. The Meteoric Water Line, kaohnite weathering and su-pergene/hypogene (S/H) lines are given for reference (after Sheppard and Gilg 1995)... 

Fig. 9. Variation of 8lsO and 8D values of steam delivered at the Larderello field (a) before 1979, and (b) in 1992, that is, before and after re-injection, l.m.w.1. represents local meteoric water line.

This equation describes the linear distribution of data points on a plot of 8D versus 8lsO that is commonly referred to as the global meteoric-water line (GMWL). The zero intercept for this line, defined as the deuterium excess... 

Figure 4. Isotopic compositions (bD versus b180) of four lakes in Vilas County, WI. The thick line is the local meteoric-water line (LMWL) determined from the data shown in Figure 2 the thin line is the evaporation line determined by the best-fit line for the four lakes shown here. Line segments plotted on the evaporation line represent specified ratios [GJ P/ calculated using eq 13.

Kharaka et al. (1979) and Kharaka and Carothers (1988) were probably the first to present evidence for meteoric water older than Pleistocene in sedimentary basins. These authors presented isotopic and chemical data for formation waters from exploration and producing oil and gas wells from the North Slope of Alaska. The water samples were obtained from reservoir rocks between 700 m and 2,800 m in depth and in age from Triassic to Mississippian. The waters from all formations, however, are remarkably similar in TDS ((1.9-2.4)X lO mgL" ) and in the concentration of the major cations and anions. The least-squares line through the 5D and 5 0 values for these waters (Figure 12) intersects the meteoric water line at 5D and 5 0 values of —65%c and —l%c, respectively. This line does not pass through the values for standard mean ocean... 

Recently, it has been possible to collect pore fluids from the unfractured granite rock matrix using upward-sloping boreholes at the 420 m level of the URL. These waters are highly saline (—90gL ) CaCl2 fluids that have a unique isotopic signature. Both and values are about — 15%o, a composition that places them well to the left of the meteoric water line and also above and to the left of the most saline Canadian Shield mine waters. 

Measurements of 6D and from both drip waters and fluid inclusions (Schwarcz et al, 1976 Yonge et al., 1985) showed that isotope ratios of these waters fell on the meteoric water line (equation 8). 

The very striking variability in 5D and of groundwater in the Milk River aquifer is surprising in such an active, near surface flow system. and D contents of water from the recharge end of the system fall close to the meteoric water line with 5D = —155%o and 5 0 = —2O%o SMOW. Waters from the northern end of the aquifer are enriched by 12%o and 70%o in... 

A partial correction can be made for this source-temperature influence on 5 O and 5D of precipitation by using a derived quantity called the deuterium excess, d, of that precipitation although this procedure needs further verification. A plot of precipitation 5D versus produces a meteoric water line with a slope of about 8 (Craig 1961). Adopting the slope of 8 exactly, the 5 0 and 5D of any sample define a line with an intercept called the deuterium excess, d (Dansgaard 1964). This varies spatially and temporally in response to both equilibrium and kinetic effects during evaporation, which... 

Meteoric water with an isotopic composition close to meteoric water line (Alhodiari, 1995). In Ishirini meteoric water shows 5 0 values from -6.3 to -4.9 7m and 5D ratios from -40 to -30 7m. Evaporation of meteoric water is accompanied by an increase in D and 0 of the remaining water relative to the initial meteoric values. 

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