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

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航次钻取的47件样品开展了磁学性质测试，并对504B钻孔（Hole 504B）内席状岩墙群（sheeted dike complex）全深度范围内采集的32件样品进行了氧化物岩石学分析。将上述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：在所研究剖面中，天然剩余磁化强度（natural remanent magnetization）随深度保持恒定，而磁化率随深度递增，中位退磁场（median demagnetizing field）与Q比值（Q ratio）则随深度递减。上述变化趋势系由随深度增加，原生钛磁铁矿（primary titanomagnetite）的岩浆期后氧化作用增强、热液蚀变作用减弱共同导致。在喷出型玄武岩（extrusive basalts）与席状岩墙群之间，稳定磁倾角出现显著差异，该现象或源于上部喷出型玄武岩发生构造旋转。