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(FeO_r)(平均15.36%、14.09%和20.83%)、高TiO_2(平均3.89%、3.28%和4.10%)和低SiO_2(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~(-7) m~3·kg~(-1))、低天然剩余磁化强度(平均0.12×10~(-3)Am~2·k~(-1))和低Q值(平均8.03);B段样品为高磁化率(平均12.55×10~(-7)m~3·kg~(-1)和中等天然剩余磁化强度(平均1.47×10~(-3)Am~2·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~(-7) m~3·kg~(-1)),而天然剩余磁化强度(平均10.05×10~(-3)Am~2·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.
The high Fe-Ti eclogites appear at the depth intervals from 318-380 m (A), 420-470 m (B) and 530-600 m (C) respectivelys in the Chinese Continental Scientific Drilling (CCSD) Project main hole. They have high FeO_r( total Fe) abundances of average 15. 36%, 14. 09% and 20. 83%, high TiO_2 concentration of average 3. 89%, 3. 28% and 4. 10% and low SiO_2 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~(-7) m~3· kg~(-1)), NRM (average 0. 12×10~(-3) Am~2· kg~(-1)) and Q-value (average 8. 03) ; section B has the highest susceptibility (average 12. 55×10~(-7) m~3·kg~(-1)), medium NRM (average 1. 47×10~(-3) Am~2·kg~(-1)) and Q-value (average 26. 42); section C samples has medium susceptibility (average 9. 73×10~(-7) m~3~ kg~(-1) ) and the highest NRM (average 10. 05×10~(-3) Am~2× 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-il-menite lamellar textures formed during the slowly exhumation, which can be the main contributors to the high NRM of the section C eclogite.