Three-dimensional flexure modelling of seamounts near the Ogasawara Fracture Zone in the western Pacific

Abstract

S U M M A R YThe geophysical data were obtained in 2000-2003 during a survey of seamounts near the Ogasawara Fracture Zone (OFZ) to the northwest of the Marshall Islands in the western Pacific. The OFZ is unique in that it is a wide rift zone showing 600-km-long right-lateral movement between the Pigafetta Basin (PB) and East Mariana Basin (EMB), and contains many seamounts (e.g. the Magellan Seamounts and the seamounts on the Dutton Ridge). Most seamounts in this study are newly mapped using modern multibeam echosounder (Seabeam 2000) and denoted sequentially by Korea Ocean Research and Development Institute (KORDI). OSM2, OSM4, OSM7, OSM8-1 and OSM8-2 seamounts of the study area are located in the OFZ which formed by the spreading ridge between the Izanagi and Pacific plates, and OSM5-1, Seascan, OSM6-1 and OSM6-2 seamounts in the PB which is a part of the oldest oceanic crust in the Pacific. In this study, the densities of seamounts and the elastic thickness values of lithosphere are estimated by using 3-D flexure and gravity modelling by considering several boundary conditions and a constant sediment layer. The infinite model with two different elastic thickness values is the best-fitting model and it indicates that the OFZ was mechanically coupled with plate of different elastic thickness values, probably after the reorganization of Izanagi-Pacific spreading zone. Very low elastic thickness values (5-10 km), relatively young seamounts, and old lithosphere in the east study area suggest the possibility of the rejuvenation of the lithosphere by widespread volcanism pulses, whereas higher elastic thickness values (15-20 km), relatively younger lithosphere, and old seamounts of the west study area are comparable with a simple cooling plate model. It implies that the west study area is outside the rejuvenation range of the lithosphere. In the flexure and gravity modelling, the different residual pattern of OSM6-1 and OSM6-2, which are joined, suggests that they have different load densities or elastic thickness values. OSM2 and OSM7 may be close to a basaltic volcano with low viscosity because they have high densities and ratios of the basal diameter to the height, whereas OSM4, OSM5-1 and Seascan may be close to an andesitic volcano.

The Morphology of the Tasmantid Seamounts: Interactions Between Tectonic Inheritance and Magmatic Evolution

“…Symbol size scales with number of well-constrained models. Seamount data from the SOPITA are shown for comparison, collated from Calmant and Cazenave (1987), Smith et al (1989), Goodwillie and Watts (1993), Maia and Arkani-Hamed (2002), and Lee et al (2009). (b) T e and associated uncertainty for best-fitting model at each seamount.…”

Geophysical investigation of seamounts near the Ogasawara Fracture Zone, western Pacific

“…The estimated age of Seascan is consistent with the last pulse of widespread volcanic activity (Schlanger and Premoli-Silva, 1981;Schlanger et al, 1981;Lee et al, 2003), and the lithosphere was rejuvenated by the widespread volcanism. Lee et al (2009) also proposed the possibility of rejuvenation, based on the result that the lithosphere beneath the study area has an anomalously thin elastic thickness. Ita Mai Tai and OSM4 have been uplifted twice or more by volcanism and rejuvenation of the lithosphere, but the amount of the uplift is not known.…”