Meteoric waters margins

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. 

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 basin margins are characterized by calcite and minor dolomite cements, many of which which formed in isotopically light brackish or meteoric water at low temperature. In general, calcites did not form near the sediment-water interface, but during shallow burial. On the east side of the basin these cements are characterized by widely varying 5 Cpdb values (+20 to -30) compared with central basin cements (+5 to -10). Sr isotopic ratios in cements are lower than the marine depositional waters on the east side of the basin, but are higher than expected for depositional waters on the west side. 

A late structural inversion defined in particular in slightly subsided marginal basins, especially on the northern flank of the Illizi Basin, caused meteoric waters to penetrate into the respective semdstones. Under the conditions of the original distribution of temperature, pressure and pore water chemistry the eogenetic and meso-genetic mineral complexes became unstable and started to react with the actual subterranean waters in an attempt to achieve a new equilibrium. These weakly mineralized waters with a near-neutral pH became able to leach the carbonate, sulfate and halite cements and generated a secondary porosity. 

Hartmann, M., Muller, P. J., Suess, E.. and Van der Wejdan, C. H. (1976). Chemistry of late Quaternary sediments and their interstitial waters from the N.W. African continental margin. Meteor Forschungsergeb. Reihe C 24, 1-67. 

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