Although our work has been in many areas from the global gravity field, convection in the mantle, and the nature of subduction processes, especially the thermal regime, it presently principally involves the origin and evolution of the continents, particularly the production of granitic rocks. It is clear from the magmatism at ocean ridges and basaltic major volcanic centers that differentiation of basalt does not, in any simple way, produce granitic magma. Moreover, the long recognized striking bimodality of basaltic and granitic rocks on Earth’s surface, exemplified by the continents and ocean basins, suggests that other processes are involved. One such process is the partial melting taking place in thick sedimentary piles formed by off scraping of sediments during subduction. This is well exemplified in the coastal rocks of Maine associated with the Avalon Province in the closing of the Atlantic. These massive greywackes and shales commonly have andesitic compositions and have undergone local melting producing large pods of strikingly granitic lithologies. A missing link in this process is how these sediments are initially produced from the erosion of basaltic and andesitic source materials.
Below are some photos from the coasts of Maine:
