辽宁宽甸地幔矿物三价铁的穆斯堡尔谱测定及意义

摘　要　利用穆斯堡尔谱仪对辽宁宽甸地幔岩包体中的矿物进行了三价铁的测定?测试结果 与国内外已发表的数据接近。Fe 3＋ ／∑Fe 比值分别为：斜方辉石0?066～0?196?单斜辉石 0?216～0?344?尖晶石0?283～0?299?石榴石0?057～0?223。依据电价平衡原理计算的 Fe 3＋ 含量受 Si 4＋ 、Al 3＋ 和 Cr 3＋ 的电子探针分析误差影响很大。根据地幔矿物的电子探针分析结果 计算平衡温度、压力和氧逸度时?二辉石 En、Ca 转移反应温度计和石榴石 斜方辉石 Al 压力 计的计算结果不超过温压计的一般误差范围?而石榴石 单斜辉石 Fe 2＋ Mg 交换反应温度计 在忽略 Fe 3＋ 时计算的温度值可偏高100℃以上；采用橄榄石／斜方辉石／尖晶石组合氧压力计 计算的氧逸度值?误差一般约在±0?7个对数单位。

FERRIC IRON CONTENTS OF MANTLE XENOLITH MINERALS BY MSSBAUER SPECTROSCOPY AND ITS IMPLICATIONS TO CALCULATED TEMPERATURE, PRESSURE AND OXYGEN FUGACITY

erric iron contents of coexisting minerals from four mantle xenoliths, collected from Kuandian, Liaoning Province, were measured by Mssbauer spectroscopy and found to be similar to the published data from domestic and overseas. The ratios of Fe 3+ /∑Fe are 0066～0196 in orthopyroxenes, and 0216～0344, 0283～0299 and 0057～0223 in clinopyroxenes, spinels and garnets respectively. Comparison of Mssbauer and microprobe analytical results shows that Fe 3+ values calculated from microprobe data are significantly effected by analytical uncertainty of Si 4+ ,Al 3+ and Cr 3+ . In terms of equilibrium temperature, pressure and oxygen fugacity calculated from electron microprobe analyses of mineral compositions, the results estimated from orthopyroxene clinopyroxene En and Ca transfer reaction geothermometers and garnet orthopyroxene Al geobarometers are reliable with uncertaines less than 30℃ for temperature and 01～04GPa for pressure. Garnet clinopyroxene Fe 2+ -Mg exchange reaction geothermometers usually overestimate temperatures as higher as 89～166℃. The comparatively reliable oxygen fugacity values can be obtained from olivine orthopyroxene spinel oxybarometers with uncertainties around±07 log units.