Abstract
Open-system processes have a large capacity to modify magma compositions during differentiation. Obtaining the rates of such processes is essential to understanding and constraining the evolution of magmatic systems. Here we quantify the time scales for magmatic assimilation of hydrous malic to ultramafic cumulates by ascending basalts using the zoning patterns of ollivine xenocrysts. Robust diffusion modeling results have been obtained by treating multiple compositional profiles for multiple elements (Fe-Mg, Ni, Mn, Ca) on multiple crystals from multiple flows. We find that the time between assimilation and eruption ranges from a few months to similar to 25 yr, although 80% of the results are < 10="" yr.="" these="" ranges="" are="" shorter="" than="" either="" magma="" transport="" times="" from="" the="" mantle="" to="" the="" surface="" or="" typical="" repose="" periods="" of="" arc="" volcanoes.="" thus,="" modification="" of="" the="" geochemical="" and="" mineralogical="" features="" of="" basalts="" by="" assimilation="" of="" plutonic="" rocks="" is="" a="" fast="" and="" probably="" unavoidable="" magmatic="">