中国大陆科学钻探主孔正片麻岩磁性及深部流体活动

Detailed magnetic studies and mineralogy analysis show that the granitic gneiss has the second highest (only second to the serpentinized garnet peridotite) low-field susceptibility (χ) (0.570×10^-7-120.450×10^-7 m³·kg^-1, average 29.996×10^-7 m³·kg^-1) and the lowest natural remanent magnetization (NRM) (0.002×10^-3-2.109×10^-3 Am²·kg^-1, average 0.210×10^-3 Am²·kg^-1). Temperature dependence of magnetic susceptibility, alternating field (AF) demagnetization and magnetic hysteresis properties suggest that the magnetic minerals in granitic gneiss are magnetite ± hematite, the magnetites are mainly multi-domain (MD), pseudo-single domain (PSD) magnetites are also presented in small amounts. The grain size of magnetites are obviously larger than that in the completely retrograded eclogites, which have the same magnetic mineral assemblage and experienced amphibolite facies retrograde metamorphism. The formation of MD magnetites are thought to be related with stronger fluid activities during the retrogression. Samples occurring out of the major gneiss subunit and adjacent to the eclogites, which have related high NRM, may reflect fluid movements between felsic and mafic UHPM rocks.