MAGNETIC ANOMALY LINEATIONS FROM LATE JURASSIC TO EARLY CRETACEOUS IN THE WEST-CENTRAL PACIFIC-OCEAN

Late Jurassic to Early Cretaceous (Mesozoic) magnetic anomaly lineations (the Phoenix, Magellan, Mid-Pacific Mountains, Hawaiian and Japanese lineation sets) with fracture zones in the west-central Pacific Ocean were identified more comprehensively than in any previous studies. We fixed 2100 positions of identified magnetic anomalies based on magnetic data of 283 cruise tracks. Two remarkable fracture zones, the Phoenix and Central Pacific Fracture Zones, were mapped and newly named. Our newly identified lineations from M10N to M0 around the Mid-Pacific Mountains, which belong to the Hawaiian lineation set, illustrated that the sea-floor south of the Mid-Pacific Mountains has the same age as that of the north (132-118Ma). Our analysis of skewness parameters revealed that the older part of the Phoenix set (M17-M29) has skewness different from that of the younger part (M1-M14), implying an effect of magnetic overprints by the Cretaceous volcanism. It was confirmed that the spreading rate of the Mesozoic Pacific spreading system was the fastest in the world in the Mesozoic. A drastic change in spreading rates occurred simultaneously at the period between chrons M21 and M20 (149.5-148.5 Ma) in all the Mesozoic Pacific spreading systems. The event appears to be synchronous with events in other oceans such as the Mesozoic Atlantic and Indian Oceans.