摘要
华北克拉通破坏与岩石圈减薄,已经成为了国内外学者们所广泛认可的事实。然而,对华北克拉通破坏的时间、机制以及动力学背景仍存在很大争议。就华北克拉通破坏的机制而言,目前人们提出了拆沉作用、岩石圈地幔水化模型、热-化学-机械作用等观点,这些观点都表明华北克拉通的破坏可能与水有着密切的关系,因此研究华北克拉通地区软流圈中的水含量是十分必要的。然而,目前我们还不能直接获得地幔深部的岩石样品,所以不能直接测得软流圈的水含量。有学者提出,经高温高压下的熔融物迅速淬火形成的玻璃,其水的含量及存在形式可以反映熔融物中水的含量及存在形式。玄武岩是地球表面分布最为广泛的火成岩之一,其在反演地幔物质成分、分析构造环境及岩石圈的深部动力学方面具有十分重要的意义。本文选择了华北克拉通地区产出的,十分具有代表性的原岩样品:鲁西费县早白垩世玄武岩、辽西四合屯早白垩世高镁玄武岩、鲁西铁铜沟早白垩世高镁闪长岩、辽西阜新晚白垩世玄武岩作为原材料,将其磨碎,加入适量水,在高温高压下熔融,经过迅速淬火合成了16个含水的玄武岩玻璃样品,这些合成的含水玻璃中的水,可以反映高温高压下的熔融物的水。对这些样品进行高温高压原位电学性质的研究,即模拟地球内部的高温高压环境,研究这些样品的电学性质,将所得的结果与大地电磁探测的华北克拉通地区的软流圈的结果相比较,如果得到的电阻率相近,则表示该地区软流圈的含水量与我们所合成的样品的含水量相近。因此,在这之前,我们需要对所合成的玻璃样品的化学成分尤其是水含量进行研究,本论文主要研究了这些玻璃样品中的化学成分和水含量。我们采用电子探针分析了各样品中的主要元素,发现多数样品的化学成分基本均一。对样品进行傅里叶变换红外光谱的研究发现:所有样品的红外光谱在~4500cm~(-1)处均有吸收峰,表明所有样品中均有OH形式的水存在;除去合成过程中未添加水的费县玄武岩玻璃FX-1、铁铜沟高镁闪长岩玻璃TTG-1和阜新玄武岩玻璃FW-1,其它样品在~1630cm~(-1)处和~5200cm-1处均有吸收峰,这表明这些样品中不仅有OH还有分子H_2O。我们分别采用~4500cm-1处和~1630cm~(-1)处的吸收峰,根据Lambert-Beer定律定量分析了各样品中OH和分子H_2O的含量。由于我们收集到的红外光谱在典型的OH吸收区吸收峰重叠严重,因此,不便于采用~3550cm-1处的吸收峰计算总的水含量,而水在矿物中主要以OH和分子H_2O两种形式存在,因此我们假设我们的样品中的水只有OH和分子H_2O两种形式,总的水含量就等于OH含量与分子H_2O含量的和。我们还对所有样品进行了XPS研究,测定了样品中各元素原子的百分比,然而由于我们的样品表面不平整,主要元素没有完全检测到,部分样品的XPS结果很不理想。然而也有测试结果比较令人满意的样品,如:费县玄武岩玻璃FX-1、FX-2,铁铜沟高镁闪长岩玻璃TTG-2、TTG-3、TTG-4和阜新玄武岩玻璃FW-2,我们根据其原子百分比合理地假设了其化学式,结合傅里叶变换红外光谱得出的水含量确定了其化学通式。
The destruction and lithosphere thinning of the eastern North China Craton hasbeen widely recognized between the Geoscientists. However, the time, mechanismand the Geodynamic factors of the destruction and lithosphere thinning remainscontroversial. As to the mechanism of it, at least three views have been proposed:delamination, lithosphere hydration and thermal-mechanical-chemical erosion. Theseviews show that the destruction of the North China Craton is closely related to water.So it is necessary to research the content of water in the asthenosphere under NorthChina Craton. But we can't determine the water content of the mantle lithospheredirectly as the rock specimens in the asthenosphere can't be obtained directly. It isproposed that the speciation and content of water and the compositions in the glassessynthesized by rapid quenching from the melt at high temperature and high pressurecan reflect that in the melt.Basalt is one of the most widely distributed igneous rocks, which has greatsignificance in the inversion of mantle material composition, the analysis of structuralenvironment and the dynamics of the deep lithosphere. Therefore, we chose the veryrepresentive rocks that produced by the North China Craton, which respectively werethe Feixian Early Cretaceous basalt, Sihetun Early Cretaceous high-Mg basalt,Tietonggou high-Mg Early Cretaceous high-Mg diorites and Fuxin Late Cretaceousbasalt as start materials, which were ground into powder. Then we added anappropriate amount of water into the powder. Finally we made them melt under highpressure and high temperature, by rapid quenching from which we obtained16water-bearing glass specimens.We are going to simulate the Earth's interior condition to study the electricproperties of these glasses specimens under high pressure and high temperature. Thenthe measurement results are going to be compared with the results from geomagneticdetection. If the electric properties are similar, it indicates that the water content andchemical compositions in the asthenosphere are closed to that in our synthesized glasses. Therefore, before the study of the electric properties under high pressure andhigh temperature, it is necessary to study the chemical compositions and water contentin these glass specimens.We analyzed the main elements in all of the synthesized glass specimens, andfound that most of the specimens were of great homogeneity. Fourier transforminfrared spectrometer was carried out on these specimens. It was found that there areabsorption peaks at~4500cm~(-1)on the infrared spectrum of each specimen, whichindicated that there was OH formed water in all of our specimens. Apart from thosespecimens synthesized without water such as the Feixian basalt glass FX-1,theTietonggou high-Mg dioritic glasses TTG-1and the Fuxin basalt glass FW-1, therewere obvious peaks at both~5200cm~(-1)and~1630cm~(-1),which indicated that waterexisted in these glasses as both OH and molecular H_2O.We calculated the OH andmolecular H_2O content in our specimens on the basis of the peaks at~4500cm~(-1)and~1630cm~(-1)respectively, associated with the Lambert-Beer Law. The seriousoverlap of peaks in the typical OH absorption area prevents us to calculate the totalwater content in the specimens by the peaks at~3550cm~(-1). As OH and molecularH_2O are the main speciations of the water in the minerals, we assumed water exists inthese synthesized glasses as nothing but OH and molecular H_2O. So in this paper wetook the sum of the content of OH and molecular H_2O as the total water content.Furthermore, we determined the atomic percentages of different elements in ourspecimens. However the main elements were net fully detected, which may be as aresult of the rough surface of our specimens. The XPS results of some specimens arefar from ideal, but there also are results of great satisfactory, such as the FX-1, FX-2,TTG-2, TTG-3, TTG-4and FW-2.We assumed their chemical formula on the basis ofthe atomic percentages reasonably and finally determined the chemical formula,associated the water content obtained from FTIR.