Magnetic Petrology of the High Fe-Ti Eclogite from the Chinese Continental Scientific Drilling(CCSD) Main Hole
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摘要: 中国大陆科学钻探(CCSD) 主孔中318~380m (A)、420~470m (B) 和530~600m (C) 深度分布三段高铁钛榴辉岩, 它们具有高全铁(FeOT) (平均15.36%、14.09%和20.83%)、高TiO2 (平均3.89%、3.28%和4.10%) 和低SiO2 (平均44.64%、48.64%和41.10%) 含量分布特征.岩石磁性测量结果表明, A段样品为低磁化率(平均3.61×10-7m3·kg-1)、低天然剩余磁化强度(平均0.12×10-3Am2·kg-1) 和低Q值(平均8.03);B段样品为高磁化率(平均12.55×10-7m3·kg-1) 和中等天然剩余磁化强度(平均1.47×10-3Am2·kg-1) 及Q值(平均26.42);C段样品磁化率介于A、B段之间(平均9.73×10-7m3·kg-1), 而天然剩余磁化强度(平均10.05×10-3Am2·kg-1) 和Q值(平均138.571) 最大.岩石磁学和岩相学研究表明, A、B两段样品代表了新鲜或轻度退变质榴辉岩的磁性特征, 但就研究的代表性样品的磁性岩石学特征而言, B段样品显示的退变质程度稍高于A段; C段榴辉岩样品密度最大, 主要为新鲜榴辉岩, 氧逸度明显高于A、B两段样品, 且存在大量出溶过程形成的以薄层结构为标志特征的赤铁矿-钛铁矿固溶体, 可能是样品高天然剩磁的主要原因.
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关键词:
- 高铁钛榴辉岩 /
- CCSD主孔 /
- 岩石磁学 /
- 赤铁矿-钛铁矿固溶体 /
- 磁化率
Abstract: The high Fe-Ti eclogites appear at the depth intervals from 318-380m (A), 420-470m (B) and 530-600m (C) respectivelys in the Chinese Continental Scientific Drilling (CCSD) Project main hole. They have high FeOT (total Fe) abundances of average 15.36%, 14.09% and 20.83%, high TiO2 concentration of average 3.89%, 3.28% and 4.10% and low SiO2 contents of average 44.64%, 48.64% and 41.10%, respectively. Magnetic study of the samples shows that section A has the lowest susceptibility (average 3.61×10-7m3·kg-1), NRM (average 0.12×10-3Am2·kg-1) and Q-value (average 8.03); section B has the highest susceptibility (average 12.55×10-7m3·kg-1), medium NRM (average 1.47×10-3Am2·kg-1) and Q-value (average 26.42); section C samples has medium susceptibility (average 9.73×10-7m3·kg-1) and the highest NRM (average 10.05×10-3Am2·kg-1) and Q-value (average 138.571). The magnetic property compared with metamorphic petrology of high Fe-Ti eclogites suggests that section A samples represent magnetic properties of the fresh or slightly retrograded eclogites; section B samples show higher metamorphic retrogression than those of section A; section C samples are fresh eclogite, whose density and oxygen fugacity are distinctly higher than those of A and B, containing a lot of hematite-ilmenite lamellar textures formed during the slowly exhumation, which can be the main contributors to the high NRM of the section C eclogite.-
Key words:
- high Fe-Ti eclogite /
- CCSD main hole /
- rock magnetic /
- hematite-ilmenite solid solution /
- susceptibility
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表 1 岩石的密度和磁性参数
Table 1. Density and magnetic parameters of samples
表 2 代表性样品的矿物组成(%)
Table 2. Mineral assemblage of representative samples
表 3 代表性样品的全岩化学成分主量元素成分分析结果
Table 3. Whole rock major element compositions of representative samples
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