Paleomagnetic of ODP Hole 130-807C basalts

Characteristic remanent magnetizations derived from detailed thermal and alternating-field demagnetization of basalts recovered at Ocean Drilling Program (ODP) Site 807 on the Ontong Java Plateau reveal constant normal polarity consistent with paleontological ages from overlying sediments, suggesting deposition in early Aptian times at the beginning of the Cretaceous Normal Polarity Superchron (K-N). The paleomagnetic data can be divided into 14 distinct inclination groups, which together define a paleolatitude of 18°S, some 16° shallower than expected from a Pacific apparent polar wander path (APWP) based on nonsedimentary data. The data display a trend in paleomagnetic inclination, showing shallower values with increasing depth. We conclude that this trend is a result of local tectonic tilting during the waning phases of volcanism on the plateau. Hotspot-based plate reconstructions for the Early Cretaceous place the Ontong Java Plateau on the Louisville hotspot, presently located at 51°S, whereas the paleolatitude for Site 807 based on the Pacific APWP is 34°S. Because the nominal mean inclination from Site 807 and values derived from Deep Sea Drilling Project (DSDP) sediments of other sites predict shallower paleolatitudes for the Ontong Java Plateau, values from the Pacific APWP provide lower bounds on true polar wander. Considering mantle plume sources on the southern and northern portions of the plateau (DSDP Site 288 and ODP Site 807, respectively), the Louisville hotspot appears to have moved 9°-17° to the south relative to the spin axis since the Early Cretaceous. This sense of motion is consistent with previous results for the Suiko Seamount (65 Ma) of the Hawaiian-Emperor Chain.

对翁通爪哇高原（Ontong Java Plateau）上大洋钻探计划（Ocean Drilling Program, ODP）807站位采集的玄武岩开展详细热退磁与交变场退磁后获得的特征剩余磁化强度（Characteristic remanent magnetizations）显示，其呈现恒定的正向极性，与上覆沉积物的古生物年代结果一致，表明该玄武岩沉积于早阿普第期，即白垩纪正向极性超静期（Cretaceous Normal Polarity Superchron, K-N）伊始。本研究的古地磁数据可划分为14个独立的倾角组，综合这些组的数据得到的古纬度为南纬18°，较基于非沉积数据得到的太平洋视极移路径（apparent polar wander path, APWP）的预期值偏浅约16°。数据显示古地磁倾角存在随深度增加而逐渐变缓的趋势，我们认为该趋势是该高原火山活动衰减期内发生的局部构造倾斜作用所致。早白垩世基于热点的板块重建结果显示，翁通爪哇高原曾位于现今地处南纬51°的路易斯维尔热点（Louisville hotspot）之上，而基于太平洋APWP得到的807站位古纬度为南纬34°。由于807站位的名义平均倾角以及其他站位深海钻探计划（Deep Sea Drilling Project, DSDP）沉积物的相关倾角值，均预示翁通爪哇高原的古纬度偏浅，因此太平洋APWP的数值可为真极移（true polar wander）提供下限约束。考虑到该高原南北部的地幔柱源分别对应DSDP 288站位与ODP 807站位，自早白垩世以来，路易斯维尔热点相对自旋轴向南移动了9°~17°。这一运动方向与夏威夷-天皇海山链（Hawaiian-Emperor Chain）65 Ma的水茂海山（Suiko Seamount）的既往研究结果一致。