地幔岩矿物压力计评述

适用于地幔岩石的矿物压力计有石榴石-斜方辉石压力计、石榴石-单斜辉石压力计、橄榄石-单斜辉石压力计、铬尖晶石压力计、二辉石压力计等有限几类.本文通过将这些压力计应用于岩石学相平衡实验数据,检验了其精确度.再将它们应用到天然地幔岩石样品,包括石榴石相二辉橄榄岩、尖晶石相二辉橄榄岩、石榴石-尖晶石过渡相二辉橄榄岩、含金刚石和石墨的地幔岩石,检验了其准确度.初步结论是,现有的石榴石-斜方辉石压力计(Nickel and Green,1985;Taylor,1998;Brey et al．,2008)质量相对最优,石榴石-单斜辉石压力计(Nimis and Taylor,2000;Simakov and Taylor,2000)次之.在应用这些压力计时,可配合二辉石温度计(Brey et al．,1990;Taylor,1998)或石榴石-橄榄石温度计(Wu and Zhao,2007),来同时估算平衡压力和温度.其余的压力计精确度和准确度都还很不够,需要更精确深入的实验研究来标定质量优良的压力计.

On the validity of the geobarometers in mantle rocks

Nowadays there exist several kinds of geobarometers theoretically applicable to mantle rocks, i.e., the garnet-orthopyroxene, garnet-clinopyroxene, olivine-clinopyroxene, Cr-in-spinel and two-pyroxene geobarometers. To test the precision and accuracy of these barometers, they have been applied to experimental data of phase equilibrium experiments and natural mantle xenoliths including the garnet- or spinel-bearing lherzolites and the garnet-spinel-bearing lherzolites, as well as mantle xenoliths containing graphite or diamond, collected from kimberlites or alkaline basalts. It is concluded that the present garnet-orthopyroxene barometers (Nickel and Green, 1985; Taylor, 1998; Brey et al., 2008) are relatively the most valid ones, and the garnet-clinopyroxene barometers (Nimis and Taylor, 2000; Simakov and Taylor, 2000) are also applicable. Other kinds of barometers are obviously far from accurate and precise and should be much more precisely calibrated through phase equilibrium experiments. In applying the valid barometers, the two-pyroxene thermometers (Brey et al., 1990; Taylor, 1998) or the garnet-olivine thermometer (Wu and Zhao, 2007) are to be simultaneously used to derive pressures and temperatures.