摘要 : Intracrystalline B-isotope differences of similar to 40%omicron, are observed between the interlayer and tetrahedral crystallographic sites of interstratified illite-smectite (I-S). We tested the hypothesis that partitioning of B-... 展开 Intracrystalline B-isotope differences of similar to 40%omicron, are observed between the interlayer and tetrahedral crystallographic sites of interstratified illite-smectite (I-S). We tested the hypothesis that partitioning of B-isotopes between these sites could provide a low-temperature, single-mineral geothermometer. Samples studied include a metabentonite transected by a dike in the Cretaceous Pierre Shale (200-500 degrees C), buried mudstones from the Eocene Wilcox Formation (60-125 degrees C), and I-S products from hydrothermal experiments (300-350 degrees C). Different reaction kinetics are represented by these different sample sets, therefore results test the equilibrium partitioning of B in the interlayer vs. tetrahedral sites. In all samples, interlayer delta B-11 values are isotopically heavier than the tetrahedral delta B-11. Because B-11 prefers trigonal coordination, we infer that B(OH)(3) dominates the interlayer sites. Within each sample set, the intracrystalline line differences are greatest (20-40%omicron) in the most expanded I-S (i.e., smectite-rich), and approach 0 as illitization increases. There is good correlation (R = 0.84) between the interlayer delta B-11 (calculated by mass balance) and water delta B-11 indicated by the established maximum temperature of each sample. These results suggest that the interlayer sites of I-S preserve the B isotopic composition of water at the temperature that produced the authigenic illite. Direct measurements of interlayer delta B-11 equilibrated with water of known delta B-11 are needed to refine the relationship with temperature, but the existing data indicate the following temperature dependent relationship: T(degrees C) = (delta B-11 (tetrahedral) - delta B-11 (interlayer) + 30)/0.05. 收起