大兴安岭南端花岗岩磁化率及其岩石学意义

MAGNETIC SUSCEPTIBILITY AND ITS PETROGENETIC IMPLICATION FOR THE GRANITOIDS OF THE SOUTHERN DA XINGAN MTS. INNERMONGLIA, CHINA

花岗岩磁化率特征表明 :大兴安岭南段黄岗—大井地区存在钛铁矿系列和磁铁矿系列两类花岗岩 .印支期以钛铁矿系列花岗岩为主 ,燕山期磁铁矿系列花岗岩出露稍多 .印支期花岗岩具较低氧化系数 ,其磁化率的高低主要反映FeOt含量的高低 .燕山期花岗岩的磁化率同时受FeOt和氧化系数控制 ,而氧化系数的影响更为明显 .δO1 8及其与磁化率关系表明岩浆期后变化对本区花岗岩磁化率的改变极为有限 .磁化率与ISr、δO1 8关系暗示混染作用对印支花岗岩磁化率有一定影响 ;而源区混合熔融是燕山花岗岩磁化率特征的决定因素 .

New measurements of the magnetic susceptibility of granitic rocks in the Southern Da xinggan Mountains, range from 10 -5 to 10 -2 SI units, show that both of magnetite series and ilmenite series developed in this area. Magnetic susceptibility of Indosinian granites that mostly but mafic pluton of Lanjiayingzi belong to ilmenite series depends on the total iron content of the rocks. Magnetic susceptibility of Yanshanian granites , varied from 10 -5 across 10 -3 SI units, appears chiefly determined by the oxidation ratio of rocks especially for the members of magnetite series. Non correlation of magnetic susceptibility with δO 18 show that modifying of oxidation ratio by hydrothermal fluids or subsolidus alteration was limitted. Correlations of magnetic susceptibility with initial Sr 87 /Sr 86 andδO 18 suggest that oxidation ratios principally reflect the features of the source regions, with some contribution of wall rock contamination for Indosinian granites.