Upper mantle models and the thickness of the continental lithosphere

Abstract

Analysis of the Early Rise traveltimes in the United States shows that on several of the profiles there are features which can be interpreted as indicating a low-velocity zone above 200 km, i.e. that the continental lithosphere thickness is less than 200 km. The explosion data from the Nevada Test Site, GNOME and Early Rise are all consistent with Lehmann's suggestion that there is a discontinuity at a depth of about 200 km. Comparison of the observed data between 15° and 23° with model calculations shows that the major differences between the western and central-eastern United States upper mantles occur above 200 km. It appears that the only reasonable explanation for the 200 km discontinuity is that it represents the termination of a zone of partial melting.