The case for accretion of the tectosphere by buoyant subduction

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Abstract
This paper tests three hypotheses for the origin of the tectosphere. Continental collision cannot explain the low metamorphic grade of crust that predates the tectosphere. Halfspace cooling and buoyant underlating can both fit the diamond age data, although underplating by buoyant subduction is the favored model. Thermal models provide a further test. If half space cooling formed the tectosphere, diamonds from 150km depth will be at least 200 m.y. younger than diamonds from 190km. If buoyant subduction formed the tectosphere, diamonds from 150km depth will be the same age or older than diamonds from 190km.