海南福基田幔源辉石结构OH与氢氧同位素

Structural OH and Hydrogen and Oxygen Isotope of Pyroxenes from Upper Mantle in Fujitian,Hainan,China

采用IR光谱和质谱技术分析了海南福基田幔源巨晶和包体中辉石的结构羟基红外光谱和氢氧同位素。测试的所有巨晶普通辉石和包体中透辉石及顽火辉石均含结构OH,对比印证了国内外同类矿物的红外光谱特征。结构水质量分数分别是：普通辉石87×10-6~389×10-6;透辉石127×10-6~273×10-6;顽火辉石69×10-6~207×10-6。包体中结构水质量分数为1 811×10-6~5 377×10-6,平均为3 133×10-6。包体中辉石的氢氧同位素特征如下：透辉石的δ（D）为-123.17‰,顽火辉石的δ（D）为-132.04‰;透辉石的δ（18O）为5.96‰,顽火辉石的δ（18O）为5.60‰。实验和对比表明,辉石是海南福基田上地幔重要的＂水储库＂,包体未受地壳成分污染,继承和保持了上地幔＂富水贫氘＂的特征。上述结果为该地区上地幔研究提供了结构水和氢氧同位素的基础资料。

This paper analyses the structural OH and hydrogen and oxygen isotope of pyroxenes from upper mantle,contained in megacryst augites,diopsides and enstatites in xenoliths in Fujitian,Hainan,China by FTIRs and mass spectrometer.The comparison of IR spectra of samples demonstrates that characteristics of IR spectra are the same as those of the domestic and international homogeneous mineral.Contents of structural OH in megacryst augites,in diopsides of xenoliths and in enstatites of xenolites are 87×10-6-389×10-6,127×10-6-273×10-6 and 69×10-6-207×10-6 respectively.Content of structural OH in xenoliths is 1 811×10-6-5 377×10-6 and the average content is 3 133×10-6.Composition of hydrogen and oxygen isotope of pyroxenes in xenoliths is δD-123.17‰ for diopsides,and-132.04‰ for enstatites,δ18O 5.96‰ for diopsides and 5.60‰ for enstatites.It is shown by the experiments that pyroxene is an important ＂reservoir＂ of upper mantle in Fujitian,Hainan,China.The xenoliths from mantle-derived are evolved and formed in a stable physic and chemical environment,while the composition of hydrogen and oxygen isotopic in pyroxenes of xenoliths remains unchanged.It is also shown that content of structural OH is rich but the content of deuterium is poor in upper mantle in Fujitian,Hainan,China.Finally,the paper proves the data of structural OH and hydrogen and oxygen isotope in upper mantle of the south of China.