MODE OF INCORPORATION OF SR2+ IN CALCITE - DETERMINATION BY X-RAY ABSORPTION-SPECTROSCOPY

被引:97
作者
PINGITORE, NE
LYTLE, FW
DAVIES, BM
EASTMAN, MP
ELLER, PG
LARSON, EM
机构
[1] BOEING CO, SEATTLE, WA 98124 USA
[2] UNIV TEXAS, DEPT PHYS, EL PASO, TX 79968 USA
[3] NO ARIZONA UNIV, DEPT CHEM, FLAGSTAFF, AZ 86011 USA
[4] UNIV CALIF LOS ALAMOS SCI LAB, DIV ISOTOPE & NUCL CHEM, LOS ALAMOS, NM 87545 USA
[5] UNIV CALIF LAWRENCE LIVERMORE NATL LAB, DIV CHEM & MAT SCI, LIVERMORE, CA 94550 USA
关键词
D O I
10.1016/0016-7037(92)90222-5
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
By probing the local atomic environment of strontium coprecipitated with natural and synthetic calcites, X-ray absorption spectroscopy (XAS) reveals that the strontium is incorporated in the calcite by substitution at Ca2+ structural sites, forming a dilute solid solution. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) demonstrated that the local structural environment of Sr2+ in natural and synthetic calcites was similar to that of Ca2+ in calcite and quite different from that of Sr2+ in strontianite. The Sr2+-O2- distance derived from EXAFS, 2.58 +/- 0.03 angstrom, is consistent with the sum of the radii of these two ions in six- and three-fold coordination, respectively, of 2.57 angstrom. The XANES and EXAFS further eliminate such modes of incorporation as adsorption, occlusion, and the presence of trace amounts of strontianite or other Sr2+-rich phase. However, evidence of a possible relict Sr2+-rich aragonite was encountered in a diagenetic calcite, indicating that XAS may prove a sensitive tool for detecting incomplete mineralogical alteration in carbonates. Because Sr2+ is bound at Ca2+ lattice sites, the record of biomineralization, diagenesis, and age encoded in Sr2+/Ca2+ ratios and strontium isotopes in geologic calcites is secure; likewise, Sr-90 sequestered in natural calcite should not undergo significant preferential leaching.
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页码:1531 / 1538
页数:8
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