Musicians seamount province and related crustal structures north of the Hawaiian ridge

Abstract

The Musicians seamounts comprise a major volcanic province that extends northwesterly from just north of the Hawaiian ridge, across the Murray fracture zone, to the Pioneer fracture zone at 35°N. Approximately 60,000 km 3 of material has been extruded onto the deep ocean floor in this region. Most of this volcanism has been localized along distinct linear trends or was associated with a large uplifted block of crust. These features appear to reflect zones of crustal weakness that were produced during a major change in direction of sea-floor spreading; volcanism apparently did not commence until sometime after the crust was generated. Seventeen prominent seamounts lie along a 1,200-km northwest-trending line which marks the western limit of the Musicians province and coincides with a line along which the large east-west fracture zones in the northeast Pacific all undergo a change in trend. Immediately south of the Murray fracture zone five linear structures in the form of narrow ridges of coalescing seamounts extend for about 300 km eastward from the above mentioned line of seamounts. These structures apparently reflect a system of en echelon fractures that were generated immediately following the change in spreading direction. A large uplifted block of crust situated halfway between the Murray and Pioneer fracture zones also appears to be related to crustal complications following the change in spreading direction. This horst-like structure offsets a prominent linear magnetic anomaly that may reflect an early Cretaceous reversal in the earth's magnetic field, suggesting that an intermittent transform fault may have offset the spreading axis as it was reorienting.