Lithology Determination of Rocks from CCSD 100-2 000 m Main Hole by Magnetic Susceptibility and Density Using Discriminant Function Analysis
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摘要: 为查明磁化率和密度对于中国大陆科学钻探工程(CCSD) 主孔100~2 000 m岩性的响应和判别特征, 利用SPSS10.0统计分析软件进行了判别分析.研究结果显示, 岩石的密度和体积磁化率主要受岩性的控制.采用迫入法建立全模型, 对CCSD主孔100~2 000 m井段岩心的岩性判别率达84.8%.其中, 蛇纹石化橄榄岩、正片麻岩、副片麻岩、榴辉岩、角闪岩和退变质榴辉岩的判别率分别为100%、87.1%、89.7%、89.6%、96.7%和63.7%.该研究表明, 密度和磁化率可以为超高压变质岩石的岩性鉴别和区分提供定量约束, 有利于地球物理探测成果和测井资料的准确解析.同时, 本文也是SPSS统计分析软件在超高压变质岩石类型判别方面的一个应用实例, 对于其他岩石类型的判别分析具有借鉴意义.Abstract: Magnetic susceptibility (κ) and density (ρ) were measured at 5.7 m depth intervals on drill cores from the main hole of the Chinese Continental Scientific Drilling (CCSD) Project. We analyzed the data by discriminant analysis employing SPSS 10.0 for Windows to test whether the lithology can be distinguished by petrophysical parameters. The density and magnetic susceptibility of the CCSD 100-2 000 m main hole are mainly controlled by the lithology. Lithology discriminant functions were constructed by means of the Enter Independents Together method. The results show that the total discriminant rate is 84.8%, while the rates of the serpentinized peridotite, orthogneiss, paragneiss, eclogite, amphibolite and retrograded eclogite are 100%, 87.1%, 89.7%, 89.6%, 96.7% and 63.7%, respectively. This research confirms that the petrophysical parameters of magnetic susceptibility and density can provide quantity constraints for the lithology discrimination of ultrahigh-pressure (UHP) rocks. Furthermore, it throws some light on the lithology determination, and may be useful in improving the interpretations of geophysical surveying and well logging.
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图 1 秦岭-大别-苏鲁造山带地质简图及CCSD钻孔位置(Xu et al., 1998)
Fig. 1. Simplified geological map of Qinling-Dabie-Sulu orogen, and the drilling site of CCSD
图 2 CCSD主孔2 000 m岩性(a)、磁化率(b)和密度(c) 垂向剖面(测井数据由潘和平和牛一雄教授提供)
Fig. 2. Lithology (a), magnetic susceptibility (b) and density (c) profiles of the CCSD 2 000 m main hole
图 3 CCSD主孔100~2 000 m岩心的岩石类型判别分类散点图
1.榴辉岩; 2.退变质榴辉岩; 3.角闪岩; 4.正片麻岩; 5.蛇纹石化橄榄岩; 6.副片麻岩; 7.聚类中心
Fig. 3. Lithological group scatter plot for the cores from the CCSD 100-2 000 m main hole by discriminant function analysis
表 1 密度ρ和磁化率对数值logκ的岩性分类统计结果
Table 1. Logarithmic magnetic susceptibility (logκ) and density (ρ) of different rock types
表 2 CCSD主孔100~2 000 m岩心岩性判别分析结果
Table 2. Lithological classification results by discriminant analysis for the cores from the CCSD 100-2 000 m main hole
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