Conventional and 40Ar/39Ar K-Ar ages of volcanic rocks at DSDP Leg 55 Holes

Conventional K-Ar, 40Ar/39Ar total fusion, and 40Ar/39Ar incremental heating data on hawaiite and tholeiitic basalt samples from Ojin (Site 430), alkalic basalt samples from Nintoku (Site 432), and alkalic and tholeiitic basalt samples from Suiko (Site 433) seamounts in the Emperor Seamount chain give the following best ages for these volcanoes: Ojin = 55.2 ± 0.7 m.y., Nintoku = 56.2 ± 0.6 m.y., and Suiko = 64.7 ± 1.1 m.y. These new data bring to 27 the number of dated volcanoes in the Hawaiian-Emperor volcanic chain. The new dates prove that the age progression from Kilauea Volcano on Hawaii (0 m.y.) through the Hawaiian-Emperor bend (- 43 m.y.) to Koko Seamount (48.1 m.y.) in the southernmost Emperor Seamounts continues more than halfway up the Emperor chain to Suiko Seamount. The age versus distance data for the Hawaiian-Emperor chain are consistent with the kinematic hot-spot hypothesis, which predicts that the volcanoes are progressively older west and north away from the active volcanoes of Kilauea and Mauna Loa. The data are consistent with an average volcanic propagation velocity of either 8 cm/year from Suiko to Kilauea or of 6 cm/year from Suiko to Midway followed by a velocity of 9 cm/year from Midway to Kilauea, but it appears that the change in direction that formed the Hawaiian- Emperor bend probably was not accompanied by a major change in velocity.针对天皇海山链中奥金海山（430站位）的夏威夷岩与拉斑玄武岩样品、宁特库海山（432站位）的碱性玄武岩样品，以及寿贺海山（433站位）的碱性玄武岩与拉斑玄武岩样品，采用常规钾氩（K-Ar）定年、40Ar/39Ar总熔样法及40Ar/39Ar逐步加热法获得的最佳定年结果如下：奥金海山为55.2±0.7百万年，宁特库海山为56.2±0.6百万年，寿贺海山为64.7±1.1百万年。本次新增的定年数据使夏威夷-天皇火山链已获得定年的火山数量增至27座。本次新测年结果证实，从夏威夷岛基拉韦厄火山（0百万年）经夏威夷-天皇转换带（约-43百万年）至最南端天皇海山链的科科海山（48.1百万年）的年龄演化序列，在天皇海山链上延伸至寿贺海山，覆盖了超过一半的海山链长度。 夏威夷-天皇海山链的年龄-距离数据与运动学热点假说相符，该假说预测，远离基拉韦厄与冒纳罗亚活火山，向西、向北方向的火山年龄依次变老。该数据支持两类平均火山传播速度模型：其一为从寿贺海山至基拉韦厄火山的传播速度为8厘米/年；其二为从寿贺海山至中途岛的速度为6厘米/年，随后从中途岛至基拉韦厄火山的速度为9厘米/年。不过，形成夏威夷-天皇转换带的方向转变过程，似乎并未伴随速度的显著变化。