【摘要】 对12个来自河北汉诺坝玄武岩的橄榄岩包体中的单斜辉石和斜方辉石进行了详细的微区傅立叶变换红外光谱(Micro-FTIR)分析。结果显示,所有的单斜辉石和斜方辉石颗粒都含有以OH形式存在的结构水。对部分粒径较大的辉石颗粒内部的多点分析表明,结构水含量表现出中心高边缘低的不均一分布。这种不均一分布的特征应该来自于包体上升过程中由于压力降低而引起的H扩散。如果用每个样品多个测定颗粒的中心部位的平均值来代表该样品,12个样品的单斜辉石水含量为48×10-6~152×10-6,斜方辉石水含量20×10-6~55×10-6。根据矿物水含量(假设橄榄石的水含量为2×10-6)和它们的体积分数计算的全岩水含量为11×10-6~48×10-6。结合已经发表的橄榄岩包体数据来看,在岩石圈地幔的物理化学条件下,单斜辉石与斜方辉石之间水的平衡分配系数大约为2.2±0.6;岩石圈中水的分布可能具有纵向和横向上的不均一性。更多还原

【Abstract】 Anhydrous minerals (olivine, clinopyroxene and orthopyroxene) from 12 peridotite xenoliths hosted by basalts in Hannuoba of Hebei were investigated by micro-Fourier transform infrared spectrometry (FTIR). No distinct OH absorption bands can be found in olivines, whereas all the analyzed clinopyroxene (Cpx) and orthopyroxene (Opx) grains contain structural water in the form of OH. The structural water contents of pyroxenes show inhomogeneous distribution within individual grains characterized by higher contents in the core and lower in the rim. Low water contents at grain rims probably result from hydrogen diffusion after pressure decrease upon rock ascending. The range of the average core water content of multi grains (>10) from the same sample for the twelve Hannuoba peridotites is 48×10 -6 ～152×10 -6 and 20×10 -6 ～55×10 -6 for Cpx and Opx respectively. On the basis of water contents of the minerals and their volume proportions, the water contents of the whole rocks are estimated to be 11×10 -6 ～48×10 -6 . Combined with the available data of peridotite xenoliths worldwide, it is held that, under the physical and chemical conditions of lithospheric mantle, the water partition coefficient between clinopyroxene and orthoproxene should be 2.2±0.6, and the water distribution in lithosphere seems to be heterogeneous both at global and regional scales.更多还原