Seismic investigation of the Louisville Seamount Ridge

Adamson, Megan.

The Louisville Ridge is a 4000 km long chain of hotspot seamounts that trends northnorth- west, approximately 800 km northeast of the North Island (Ballance et al. 1989). Towards the west, this ridge subducts beneath the Tonga-Kermadec Trench- an erosive convergent margin. Seismic line LOUDC1 was collected by GNS Science along the Louisville Ridge during 2000-2001 as part of the continental shelf programme. Magnetic data (incomplete due to sea conditions) and gravity data were also collected to complement the reflection seismic data. The seismic data were collected using a six subarray airgun source and a 6000 m long steamer with 480 channels and a group spacing of 12.5 m. The purpose of this study was to improve the interpretation of the seismic line by reprocessing part of this line adjacent to the trench. The seismic processing package GLOBE Claritas was used for this purpose. Earlier studies within this area have partially constrained geological features, but most of the work was based on multibeam studies (e.g. Wright et al. 2000) that do not provide the depth control of multi-channel seismic data. Velocity analysis has involved combining stacking velocity methods for shallow reflections with deeper crustal models from other locations (e.g. Java Trench) and geology from drill cores or dredging. The major features interpreted in the data are sedimentary basins and seamounts- some of which have been extensively eroded to become guyots. It is anticipated that the subduction of seamounts will have a profound geological effect. It is assumed at this margin that the seamounts are subducting as a whole, as there is no evidence of slumping or landslides in the seismic record that would be present if such events had occurred. However, the only subducted seamount that is obvious in the seismic data is around 1/8 the size of the Os bourn Seamount, which lies immediately to the east. Therefore, when the Osbourn Seamount is subducted, its size may result in it being broken up.

72 p: col. Ill; 30 cm.

2008Adamson