摘要
本文对河北汉诺坝玄武岩内的幔源捕虏体矿物进行了系统地红外光谱学研究。结果表明,来自该地区约75km以上的地幔捕虏体普遍含有微量水(0.45×10^(-2)％～11.6×10^(-2)％,以H_2O计算,下同),以OH^-形式主要赋存在辉石(及橄榄石?)中,而不是在角闪石或金云母中。捕虏体中的水可能首先进入橄榄石、石榴石及辉石晶格,角闪石或金云母晶出在后。虽然角闪石及金云母晶格中含有比辉石高百倍的水,但它们所含的水可能是局部水的富集,与相对规模较小的岩浆事件或交代作用有关。早期研究估计的75km以上原始地幔岩中含0.1％水的数据可能偏高。汉诺坝玄武岩捕虏体含水量(多数1.11×10^(-2)％～3.01×10^(-2)％)比大洋中脊玄武岩和南非金伯利岩中捕虏体含水量(多数低于1.00×10^(-2)％)略高。反映了水在上地幔中时间、空间分布的不均匀性。幔源无水硅酸盐矿物中含有微量水这一事实,为了解上地幔中水的分布,水在地幔中的动力学、地球化学过程所起的作用提供了重要基础数据。
Minerals of various mantle-derived xenoliths from the Hannuoba basalt in Hebei Province have been studied by means of IR spectroscopy. The results show that all xenoliths from the mantle at depths <75 km contain trace amounts of water (0. 45×10-2% -11. 6×10-2% of H2O). The data of about 0. 1% H2O contained in primary pyrolite estimated by earlier studies may be on the high side. Water exists in the form of OH- mostly in pyroxene rather than in am-phibole or phlogopite. The presence of water in amphibole and phlogolite may be a local phenomenon of water enrichment, which is related to relatively small-scale magmatic or metasomatic events although they can contain a hundred times more water than pyroxene contains. There is a little more water (1.11 ×10-2%-3. 01×10-2% of H2O mostly) in xenoliths from the Hannuoba basalt than in those from mid-ocean ridge basalt and kimberlites of South Africa (less than 1×10-2% of H2O mostly). It indicates the heterogeneity of water in time and space in the upper mantle. The presence of trace amounts of water in mantle-derived anhydrous silicale minerals provides basic data for understanding the distribution of water in the upper mantle and the role of water in the mantle dynamic and geochemical processes.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1998年第2期138-143,共6页
Acta Geologica Sinica
基金
国家自然科学基金(编号49373168)
关键词
玄武岩
幔源
捕虏体
矿物
水
河北
mantle fluids
fluid geochemistry
water in minerals
Hannuoba
Hebei Province
