Magnetism of Granitic Gneiss from Chinese Continental Scientific Drilling Main Hole and Fluid Activities
Zeng Qingli
Liu Qingsheng
Zheng Jianping
Liu Zhifeng
Wang Hongcai
Abstract：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 assem-blage 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 ec-logites,which have related high NRM ,may reflect fluid movements between felsic and mafic UHPM rocks.
Keywords：granitic gneissCCSD main holerock magnetismfluid activitygeomagnetism
Publication Date：2014-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：12( 1915-1926 )