Meteoric waters basins

These different sites of hydrothermal and ore-forming activity may have resulted from the mode of subduction of the Pacific Plate. Mariana-type subduction (characterized by a steep angle of subduction and back-arc basin formation Uyeda and Kanamori, 1979) during middle Miocene caused WNW-ESE extension, submarine hydrothermal activity, thick accumulation of bimodal (basaltic and dacitic) volcanic activity (Green tuff) and Kuroko-type formation (Shikazono and Shimizu, 1993). Plio-Pleistocene Chilean-type subduction (shallow-dipping subduction zone, E-W compression Uyeda and Kanamori, 1979) and oblique subduction of the Pacific Plate beneath the North American Plate led to uplift and expansion of land area, subaerial hydrothermal activity accompanied by meteoric water circulation, subaerial andesitic volcanic activity and formation of vein-type deposits. 

Horikoshi and Shikazono (1978) indicated that 8D of ore fluids for B sub-type which is located at centre of Hokuroku basin is higher, suggesting large contribution of seawater, while 8D of ore fluids of Y sub-type located at the margin of Hokuroku basin is lower, suggeting meteoric water contribution. 

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. 

Presently, in the view of numerous subsequent studies, (i.e., Hitchon and Friedman 1969 Kharaka et al. 1974 Banner et al. 1989 Connolly et al. 1990 Stueber and Walter 1991), it is obvious that basin subsurface waters have complicated histories and frequently are mixtures of waters with different origins. As was proposed by Knauth and Beeunas (1986) and Knauth (1988), formation waters in sedimentary basins may not require complete flushing by meteoric water, but instead can result from mixing between meteoric water and the remnants of original connate waters. 

Fig. 2. Triangular diagrams describing the relative concentration of H20 C02-H2 in the steam produced before re-injection in the four main subunits of the Larderello field. Different symbols represent different locations of producing wells in the same subunit. Largest symbols in each diagrams represent the chemical composition of the reference core within a single area (see text for discussion). Data for Castelnuovo result from the largest amount of meteoric water inflow observed in the entire basin.

Morrill C, Koch PL (2002) Elevation or alteration Evaluation of isotopic constraints on paleoaltitudes surrounding the Eocene Green River Basin. Geology 30 151-154 Morrison J (1994) Meteoric water-rock interaction in the lower plate of the Whipple Mountain metamorphic core complex, California. J Metam Geol 12 827-840... 

Figure 8.10. The isotopic composition of subsurface waters in the Illinois basin. A. Data of Clayton et al. (1966). B. Interpretation of Clayton et al. (1966) that the isotopic values are the result of progressive diagenetic alteration of meteoric water. C. The alternative interpretation of Hanor (1983) that the isotopic values are the result of mixing of meteoric water and diagenetically altered seawater. (After Hanor, 1983.)...

Meteoric water. Water derived from rain, snow, streams, and other bodies of surface water that percolates in rocks and displaces interstitial water that may have been connate, meteoric, or of any other origin. Meteoric water in sedimentary basins is generally recharged at higher elevations along the margins of the basin. The time of last contact with the atmosphere is intentionally omitted from this definition, but may be specified to further define meteoric water. Thus, Recent meteoric water, Pleistocene meteoric water, or Tertiary meteoric water, would indicate the time of last contact with the atmosphere (Kharaka and Carothers, 1986). 

The isotopic compositions of waters in some basins indicate that formation waters are related principally to recent local meteoric waters (Clayton et al., 1966 Hitchon and Friedman, 1969 Kharaka and Thordsen, 1992). The 6D values of these waters (Figure 11) show a... 

Figure 11 Isotopic compositions of oil-field waters from several basins in North America. Original lines from Cla3fton et al. (1966), CHitchon and Friedman, (1969), and CKharaka et al. 0973, C1979). Note that except for Gulf Coast II, the isotope lines intersect the Global Meteoric Line (Craig, 1961) at points with isotope values of present-day meteoric water (Kharaka and Thordsen, 1992).

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... 

Other examples of deep-basin waters related to simple mixing of meteoric water with marine connate waters have been documented in the Dnepr-Donets basin, Ukraine (Vetshteyn et al., 1981) and the Sacramento Valley, California (Berry, 1973 Kharaka et al., 1985). Knauth (1988) used water isotopes and chemical data for waters in the Palo Duro Basin, Texas, to indicate extensive mixing between bittern brines and two... 

A number of radioactive isotopes produced primarily by cosmic ray interactions in the upper atmosphere, especially (Clark and Fritz, 1997 Mazor, 1997), C1 (Andrews etal., 1994 Phillips, 2000), and (Moran et al., 1995 Fabryka-Martin, 2000), as well as dissolved " He (Torgersen and Clarke, 1985 Solomon, 2000), have been used, in conjunction with data for the stable isotopes and calculated flow rates, for determining the age of natural waters, including fluids in sedimentary basins (Bethke et al., 1999, 2000). The 5.73 ka half-life of " C at 5.73 ka is so short that it is useful only for dating basinal meteoric water younger than —40 ka. C1 (ti/2 = 0.301 Ma) is useful for dating water of up to —2 Ma in age. These isotopic systems are reviewed by Phillips and Castro (see Chapter 5.15). 

The formation waters in sedimentary basins are dominantly of local meteoric or marine connate origin. However, bittern (residual) water, geologically old meteoric water, and especially waters of mixed origin are important components in many sedimentary basins. The original waters have evolved to Na-Cl, Na-Cl-CH3COO, or Na-Ca-Cl-type waters by a combination of several major processes ... 

It is clear that the relative importance of pressure solution as a mechanism of IGV decline increases markedly with depth. It also varies in importance among units of different bulk composition. For example, pressure solution appears to be widespread in sandstones of plutonic derivation (Thomas et al, 1993 Oelkers et al, 1996 Spotl et al, 2000), but not in the largely volcanogenic Cenozoic sandstones of the Gulf of Mexico basin (Land et al, 1987 Land and Milliken, 2000). Controls that appear to favor the development of pressure solution include abundant potassium-rich micaceous debris, a history of meteoric water incursion, and elevated temperature (>100 °C ). 

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