Abstract:
Sediment recovered in 98 piston cores from the Hawaiian area, N15 degrees -35 degrees and W150 degrees -170 degrees , has shown: (1) the surficial sediment distribution; (2) the distribution of manganese; (3) depth to the abyssal clay; and (4) the presence, abundance, and areal and temporal distribution of volcanic glass. Paleontologic and paleomagnetic control of many of these cores demonstrates that ash-producing volcanoes have been located in this region since at least Eocene times. The source of the glass today is the volcanoes of the Island of Hawaii. Increased abundance of glass in sediments younger than Olduvai probably reflects early activity on the Island of Hawaii, whereas glass in sediments older than Olduvai probably reflects the development of Maui and Molokai. The early Tertiary glass originated from the numerous volcanic seamounts in this area because the areal distribution of the ash is too far east of the known center of Eocene volcanic activity on the developing Hawaiian Ridge. Fission-track ages of ashes selected from Deep Sea Drilling Project Leg VI, VII, and 19 sites agree with the ages assigned to the faunal zones in 22 of the 31 samples dated. In 2 instances the fission-track ages were older and in 7 they were younger. The younger fission-track age for an individual sample is suggestive of thermal fading of spontaneous fission tracks. This work has confirmed previously assigned ages for several important foraminiferal and diatom zones. Thirty-five other glass samples were fission-track dated and the results show this method is precise and accurate if suitable samples are selected. In the course of examination of an Eocene faunal assemblage for either spontaneous or induced fission tracks I observed both types of tracks in sponge spicule fragments. Concentration of tracks were low, but the tracks were present and easily recognized. Further examination of fossil tests may provide another means of dating if the presence of fission tracks can be confirmed in radiolarians, diatoms, or foraminifera. The Rb, Sr, Ti, and Zr concentrations of 16 Leg 19 ashes were determined by x-ray fluorescence. The age of each ash had been previously established by faunal criteria and had been confirmed by fission-track dating. Temporal variations in the trace element concentrations are clearly seen in plots of: (1) Sr versus TiO2; (2) Rb versus TiO2; (3) Zr versus TiO2; and (4) Sr versus Zr. Seven of these ashes are older than 4 my and these have the lowest TiO2 content and have Sr concentrations between 130 and 175 ppm. These older ashes are similar to the island arc tholeiitic series rocks, whereas the 9 younger ashes, less than 4 my, are andesites, or members of the calc-alkaline series. Evidence of the temporal variation in magma evolution of the Aleutian arc has been clearly demonstrated.