Magnetic anomaly lineations from Late Jurassic to Early Cretaceous in the west-central Pacific Ocean

Abstract

S U M M A R YLate 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 MlON to MO around the Mid-Pacific Mountains, which belong to the Hawaiian lineation set, illustrated that the sea-floor south of t h e Mid-Pacific Mountains has the same age as that of the north (132-118 Ma). 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 (Ml-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.

Estimation of azimuthal anisotropy in the NW Pacific from seismic ambient noise in seafloor records

“…Pn anisotropy in both the eastern and western arrays has been estimated to be 8-10 per cent by using high frequency phases generated by earthquakes in the western Pacific trenches (Shintaku et al 2014). The seafloor in the eastern array, where we estimated azimuthal anisotropy in this study, has a high half spreading rate of ∼5 cm yr -1 (Nakanishi et al 1989(Nakanishi et al , 1992Müller et al 2008). The presence of strong azimuthal anisotropy is, therefore, not surprising in this region.…”

“…The region has the oldest identifiable magnetic anomalies in the Pacific, ∼150-160 Ma, and is in an area not affected by subsequent Cretaceous intraplate volcanism (Nakanishi et al 1989(Nakanishi et al , 1992. We exploit the crystalographic properties of olivine which display lattice preferred orientation (LPO) in response to shear in the uppermost mantle.…”

Site 866

“…Jurassic M-series magnetic lineations are located northwest of Resolution Guyot, which is on a line with lineation M23 (Nakanishi et al, 1989). This might imply that the age of the lithosphere beneath Resolution can be extrapolated to be 154 Ma (using the time scale of Kent and Gradstein, 1985).…”

“…This might imply that the age of the lithosphere beneath Resolution can be extrapolated to be 154 Ma (using the time scale of Kent and Gradstein, 1985). On the other hand, lineations M0-M4 have been tentatively identified just west of Allison Guyot (Nakanishi et al,1992), implying that a large age discontinuity exists, perhaps a fracture zone offset, beneath, or at the northwest margin of, the Mid-Pacific Mountains; thus, an extrapolated lithospheric age for Resolution must be interpreted with caution. An 80-in.…”

A precise bathymetric map of the world’s deepest seafloor, Challenger Deep in the Mariana Trench

“…The Japanese Lineation set, which is a Mesozoic magnetic anomaly lineation, exists in the East Mariana Basin, east of the Mariana Trench (Nakanishi et al 1992a), leading Nakanishi et al (1992b) to propose that the subducting plate along the southern part of the Mariana Trench is a part of the Pacific plate formed in the Mesozoic. The Japanese Lineation set has two strikes.…”