Chemical compositions and ages of basalts from seamounts in the Northwest Pacific

Chemical compositions and ages of basalts from seamounts in the Northwest Pacific. Bulletin of the Geological Survey of Japan , vol. 73(3) , p. 103–135, 16 figs and 4 tables. Abstract: As part of the exploration for cobalt-rich ferromanganese crusts in the Northwest Pacific, seamount basalts were collected for chemical composition analysis and K–Ar/Ar–Ar dating. Although the primary chemical compositions of the seamount basalts were not well preserved due to alteration and phosphatization, all 20 seamounts sampled showed typical characteristics of ocean island alkaline basalts. K–Ar dating did not provide reliable ages due to alteration, but Ar–Ar dating provided reliable plateau ages for several seamounts. Formation ages of 67–116 Ma were obtained from the Marcus-Wake Seamount Group, 87 Ma and 105 Ma from the Magellan Seamount Group, and 90 Ma from the Marshall Islands Seamount Group, which were generally consistent with those reported in previous studies.

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