An empirical thermal history of the Earth's upper mantle

Abstract

Petrological and geochemical data have been compiled from 71 ophiolite suites and greenstone belts, which range in age from 15 to 3760 Ma. The selected rocks are those whose compositions indicate that they are either normal mid-ocean ridge basalts (MORBs) or hotspot-type MORBs. Then the data base was used to calculate the most primitive liquidus temperature for each rock suite. When the calculated liquidus temperatures for all time intervals are plotted in histograms, the resulting distributions are not bimodal, but skewed unimodal. That is, the distributions show a high-T tail which results from the presence of hotspot magmas in the data set. The data suggest that the relative proportion of hotspot magmas in oceanic lithosphere has remained nearly constant over geologic time. -from Authors