氢氧化物族矿物的氧同位素分馏  

OXYGEN ISOTOPE FRACTIONATION IN HYDROXIDE MINERALS

作　　者：郑永飞[1] 徐宝龙[1] 周根陶[1] 

机构地区：[1]中国科学技术大学地球和空间科学系,合肥230026

出　　处：《地球化学》1998年第2期141-152,共12页Geochimica

基　　金：国家自然科学基金!49453003;中国科学院专项基金

摘　　要：应用增量方法计算了氢氧化物族矿物的氧同位素分馏，得到常见氢氧化物的18O富集顺序为：褐铁矿＞三水铝石＞针铁矿＞水镁石＞硬水铝石。氢氧化物与其对应的氧化物相比显著地富集18O。三价阳离子的氢氧化物和氧化物的18O富集顺序为：M（OH）3＞MO（OH）＞M2O3。Al（OH）3同质多象变体之间也存在一定的分馏。对于石英-氢氧化物、方解石-氢氧化物和氢氧化物-水体系，本文计算提供了在0-1200℃温度范围内三组内部一致的分馏系数方程。这些理论校准与合成实验结果和／或地表温度下的天然样品相吻合，特别针铁矿、勃姆石和硬水铝石与水之间的氧同位素分馏关系能够满足地质测温的要求。因此，对氢氧化物-水体系的氧同位素分析可望提供表生环境下可靠的地质温度计。The modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxide minerals. The results suggest the following sequence of 18O-enrichment in the common hydroxides: limonite＞gibbsite＞goethite＞brucite＞diaspore. 18O is significantly enriched in the hydroxides relatively to the corresponding oxides. The sequence of 18O-enrichment in the hydroxides and oxides of trivalent cations is as follows: M(OH)3＞ MO(OH)＞M2O3. There are also considerable fnationations within the polymorphs of Al(OH)3. Three sets of internally consistent fractionation factors for the systems of quartz-hydroxide, calcite-hydroxide and hydroxide-water are acquired, respectively, in the temperature range of 0 to 1200℃. The theoretical calibrations are comparable with the data from synthesis experimentS and natUral samples at surficial temperatures. Temperature dependence of oxygen isotope fractionations between goethite, gibbsite, boehmite and diaspore and water is significantly enough for the purpose of geothermomeny. Thus, the hydroxide-water pairs hold the great promise of serving as reliable paleothermometers in surficial geological environments.

关 键 词：氧同位素 分馏系数 地质测温 氢氧化物 矿物 

分 类 号：P597[天文地球—地球化学]