ALBERT

Description: Nagata Seamount, located in the northern Line Islands at 12.5°N, 167.0°W, was surveyed and dredged by the Hawaii Institute of Geophysics in the fall of 1979. The seamount is 3.7 km in height, approximately 45 km at maximum width, and has an estimated volume of 590 km3. Analysis of dredge rocks indicates that the seamount consists of alkali basalts and hyaloclastite breccias. Both acoustic reflection records and magnetic modeling studies indicate that the seamount is draped with a large volume of volcaniclastic debris about its base. At some time in its history Nagata Seamount may have been at or near sea level. The bulk of the seamount is made up of lavas of normal magnetic polarity; however, the uppermost 1,000 m consists of reversely polarized rock. The virtual geomagnetic pole determined from the seamount falls at 61.6°N, 4.0°E not far from the average Cretaceous Pacific seamount pole. Rock magnetism studies of the dredged basalts indicate a stable magnetization. Three dimensional gravity modeling determined an average density of 2.5 g/cm3 for the seamount. This value of the density agrees with other similar data from Pacific and Atlantic seamounts; although, unlike some other seamounts studied gravi-tationally, no large density variations were revealed on Nagata Seamount. K/Ar radiometric ages of 70 Ma and 86 Ma were obtained from the dredged basalts in agreement with the paleomagnetic pole. The younger age may result from alteration, thus the older date is considered more representative. This age is similar to that of nearby Kapsitotwa Seamount. © 1982, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.