Radiometric Dating of Near-Ridge Seamounts by the 40Ar-39Ar Method

标题：用40Ar-39Ar法测定近海脊海山的放射性年代本研究将继续发展40Ar-39Ar法测定年龄在10万年及以上的海底火山岩的放射性年代。我们将把这些新方法专门应用于扩展脊附近的海底火山群和线条。这些单独的火山提供了山脊系统下地幔流动和融化的样本，比扩展的山脊轴所呈现的集中的、通常是均匀的样本更广泛。40Ar-39Ar增量加热法优于其他方法，因为K在海底火山岩中普遍存在，分析方法经过了很好的测试和描述，在最佳情况下测量的分析不确定度可以达到1%。我们将通过确定MOAI项目从“超高速”扩张脊剖面（15-19#161#S）收集的东太平洋隆起Rano Rahi地区大量火山链和火山群的年龄关系，来解决有关扩张脊附近地壳增生过程的几个一级问题。我们的主要目标是：(1)确定近山脊火山是否主要呈现出山脊外浅地幔熔融的空间或时间记录；(2)确定增生带的宽度，并确定其主要具有二维或三维几何形状；(3)评估产生海山的局部熔融源是否持续很长时间。

9811136 Duncan Institution: Oregon State University Title: Radiometric dating of near-ridge seamounts by the 40Ar-39Ar method This research will continue development of 40Ar-39Ar radiometric dating methods for volcanic rocks from the ocean floor, in the age range 100,000 years and older. We will apply these new methods specifically to clusters and lineations of undersea volcanoes near the spreading ridges. Such individual volcanoes provide a sampling of the flow and melting of the mantle beneath ridge systems that is broader than the focused, often homogenized sampling presented by the spreading ridge axis. The 40Ar-39Ar incremental heating method is superior to others because of the common occurrence of K in ocean floor volcanic rocks, analytical methods are well-tested and described, and in optimum circumstances measurements can be made to analytical uncertainties of 1%. We will address several first-order questions about crustal accretion processes near spreading ridges by determining the age relations of a large collection of volcano chains and clusters in the Rano Rahi field, East Pacific Rise, collected by the MOAI program from the "superfast" spreading ridge section (15-19#161#S). Our principal goals are: (1) to determine whether the near-ridge volcanoes present predominantly a spatial or temporal recording of off-ridge, shallow mantle melting, (2) to define the width of the accretionary zone, and determine whether this has a predominantly 2- or 3-dimensional geometry, and (3) to assess whether localized sources for melting that produce seamounts persist for long periods.