Hydrothermal Alterations of Sediments in the Southern Trough of the Guaymas Basin (Gulf of California) and Transformation of the Composition of Solutions

摘要

The paper presents the results of study of the chemical composition of hydrothermally altered and primary (unaltered) sediments from DSDP holes 477, 477A, 478, 481, and 481A drilled in the Guaymas Basin (Gulf of California). There is a newly obtained data for this region on a great number of trace (including rare earth) elements. To determine the compositional transformation of the ascending hot solutions as they pass through the sedimentary cover, we carried out a combined analysis of transformation of the chemical composition of hydrothermally altered sediments and solutions discharging into the sea. In the course of solution-sediment interaction, various elements behave differently during the compositional transformation of hot solutions percolating through the sedimentary cover in the southern trough of the Guaymas Basin. Consequently, concentrations of Cu, Zn, Cd, K, Li, As, Rb, and Ba are subjected to highest changes-some of them are intensely concentrated in the solutions, while others are depleted. The latter group also includes elements, such as Sb, Cs, and Tl. The impact of sedimentary cover is moderate (depletion effect) on the concentration in solutions of Ag, Ca, Fe2+, Mo, Bi, and Br and is almost absent on the concentration of Mn, Co, Si, Be, Sr, Na, Mg, S, Cl, F, Ni, Al, Pb, Hf, Ta, W, and REE. During the interaction of sediments with high-temperature hydrothermal solutions, Ti, P, Sc, V, Cr, Ga, Y, Zr, Nb, Th, and U remain therein as immobile elements and do not pass into solutions migrating across the sedimentary cover and discharging into the southern trough of the Guaymas Basin. The paper also discusses influence of the sedimentary cover on the compositional transformation of solutions percolating in sediments overlying the hydrothermally active spreading zone in the Gulf of California (southern trough of the Guaymas Basin).