CHEMISTRY OF DEEP (3500-5600 M) PACIFIC MORB - WHY IS THE PACIFIC ANOMALOUS

In contrast with the Atlantic and Indian Oceans, the Pacific shows the global correlations of axial depth and basalt chemistry only weakly o r not at all for unaveraged data. In the past, this observation has be en pastry explained by the limited depth window of available Pacific s amples. We report on new, very young basalt samples collected by subme rsible from Pacific ridges at similar to 3500-5600 m, nearly doubling the depth interal of Pacific samples. These samples, from the Pito Dee p, I-less Deep, and the Garrett transform, do not conform to the globa l correlation of depth vs, chemistry and show the local trend of chemi cal variation. The Pacific as a whole is thus unusual compared to the Atlantic and Indian Oceans. We propose that the anomalous behavior of the Pacific is due mostly to its relatively rapid spreading rate and t ectonic shifts leading to an absence of a dynamic equilibrium between mantle temperature and seafloor depth observed elsewhere.