Paleomagnetic of DSDP Leg 91 basalts and sediments@en

Paleomagnetic studies were carried out on 23 basalt and 74 sediment samples from Leg 91 of the Deep Sea Drilling Project, recovered from a portion of the southwestern Pacific plate (24°S, 166°W) dating back to the Early Cretaceous to perhaps Late Jurassic. The expected geocentric axial dipole inclination at this latitude is -41°. The corrected mean stable inclination of -75° for the basalts indicates a paleolatitude of 63°S for their formation and thus 39° of northward motion during the last 100 m.y. Sediment inclinations steepen rapidly below 13-m depth in the core, suggesting little northward motion of this part of the Pacific plate until about 25 m.y. ago. Examination of the opaque minerals in polished section, as well as the Curie temperatures determined for six basalt samples, reveals no evidence of high- or intermediate-temperature oxidation and thus no reheating of the basement rock since its formation.本研究针对深海钻探计划（Deep Sea Drilling Project）第91航次采自西南太平洋板块某一区域（南纬24°，西经166°）的23件玄武岩样品与74件沉积岩样品开展古地磁研究，样品形成年代可追溯至早白垩世，最晚或可至晚侏罗世。该纬度下预期的地心轴向偶极子（geocentric axial dipole）倾角为-41°。经校正的玄武岩稳定平均倾角为-75°，表明其形成时的古纬度为南纬63°，由此推算该板块在过去1亿年间发生了39°的北向漂移。岩芯中13米深度以下的沉积岩倾角迅速变陡，暗示该太平洋板块区域在约2500万年前几乎未出现北向漂移。通过对抛光切片中的不透明矿物以及6件玄武岩样品的居里温度（Curie temperature）进行检测，未发现高温或中温氧化的相关证据，因此基底岩石自形成以来未经历再加热过程。