Magnetic properties and oxide petrography of ODP Hole 111-504B

Magnetic properties measurements were performed on 47 samples drilled during Leg 111 of the Ocean Drilling Program and oxide petrography was studied in 32 samples taken at depths throughout the sheeted dike complex in Hole 504B. Integration of these data with results from previous DSDP legs shows that while natural remanent magnetization is constant with depth, magnetic susceptibility increases and median demagnetizing field and the Q ratio decrease with depth in the section. These trends appear to be a result of an increase in deuteric oxidation and a decrease in hydrothermal alteration of primary titanomagnetite with depth. A distinct change in stable magnetic inclination occurs between the extrusive basalts and the sheeted dikes and may be a result of tectonic rotation of the upper extrusive basalts.本研究对大洋钻探计划（Ocean Drilling Program, ODP）第111航次钻探获取的47个样品开展了磁学性质测试，并对504B钻孔（Hole 504B）内席状岩墙复合体（sheeted dike complex）各深度采集的32个样品开展了氧化物岩石学（oxide petrography）研究。将本次数据集与此前深海钻探计划（Deep Sea Drilling Project, DSDP）各航次的研究结果整合分析后可知：钻孔剖面内的自然剩余磁化强度（natural remanent magnetization, NRM）随深度保持恒定，而磁化率（magnetic susceptibility）随深度逐渐升高，中位消磁场（median demagnetizing field）与Q比值（Q ratio）则随深度逐步降低。上述变化趋势推测与原生钛磁铁矿（primary titanomagnetite）随深度发生的岩浆期后氧化作用（deuteric oxidation）增强、热液蚀变（hydrothermal alteration）减弱有关。在喷发玄武岩（extrusive basalts）与席状岩墙复合体之间，稳定磁倾角（stable magnetic inclination）出现显著变化，该现象可能源于上部喷发玄武岩发生了构造旋转（tectonic rotation）。