超高压榴辉岩退变质作用对岩石磁化率的影响  

Effects of Retrogression of Ultrahigh-Pressure Eclogites on Magnetic Susceptibility and Anisotropy

作　　者：徐海军[1] 金振民[2] 欧新功[3] 金淑燕[2] 余日东[1] 

机构地区：[1]中国地质大学研究生院,湖北武汉430074 [2]中国地质大学地球科学学院,湖北武汉430074 [3]中国科学院广州地球化学研究所,广东广州510640

出　　处：《地球科学（中国地质大学学报）》2004年第6期674-684,共11页Earth Science-Journal of China University of Geosciences

基　　金：国家重点基础研究发展规划项目 ( 2 0 0 3CB7165 0 6) ;国家重大科学工程项目"中国大陆科学钻探工程" .

摘　　要：系统测量了中国大陆科学钻探 (CCSD)主孔 10 0～ 2 0 0 0m超高压榴辉岩的磁化率及其各向异性 ,并进行了相应的岩石学和矿物学分析 .研究结果表明 ,不同退变质程度榴辉岩的磁化率特征具有明显差别 :新鲜 -弱退变质榴辉岩对应超高压榴辉岩相 ,平均体积磁化率κ =1.4× 10 -3 SI ,磁化率各向异性度Pj=1.0 9,磁性载体主要是顺磁性矿物石榴子石和绿辉石 ;中等 -强退变质榴辉岩对应角闪岩相 ,κ =5 .1× 10 -3 SI ,Pj=1.2 0 ,磁性载体主要是退变质所产生的磁铁矿和钛铁矿 -钛磁铁矿 ;完全退变质榴辉岩对应绿帘角闪岩相 -绿片岩相 ,κ =1.3× 10 -3 SI,Pj=1.0 8,磁性载体主要来自顺磁性矿物角闪石、绿帘石、黑云母等 .该研究为超高压变质岩石地区磁异常的解释提供了基础数据和重要的科学约束 。The magnetic susceptibility and anisotropy of the ultrahigh-pressure (UHP) eclogite from Chinese Continent Scientific Drilling (CCSD) 100-2 000 m mainhole and their relationship with petrology and mineralogy are systematically investigated. The results show that eclogites of different retrogressions have specific magnetic characters. Fresh to weakly retrograded eclogites which correspond to UHP eclogite facies have relatively low magnetic susceptibility (κ=1.4×10^(-3) SI) and low anisotropy (Pj=1.09), the paramagnetic mineral omphacite and garnet being the principal carriers. For moderately to strongly retrograded eclogites corresponding to amphibolite facies, because of the formation of magnetite and ilmenite by retrogression, the magnetic susceptibility and anisotropy increases up to κ=5.1×10^(-3) SI and Pj=1.20. However, for the totally retrograded eclogites corresponding with epidote amphibolite to greenschist facies, magnetite disappears while ilmenite and titanomagnetite changes to sphene. Thus the magnetic susceptibility and anisotropy reduces to κ=1.3×10^(-3) SI and Pj=1.08, respectively. This research provides fundamental data and constrains for the interpretation of geophysical magnetic surveying on the UHP metamorphic terranes. Furthermore, the magnetic characters show us the insight into the identification of the peak metamorphic rocks during subduction and the degree of retrogression during exhumation.

关 键 词：磁化率 各向异性 超高压榴辉岩 退变质 中国大陆科学钻探 东海 

分 类 号：P318.4[天文地球—固体地球物理学] P588.346[天文地球—地球物理学]