Granitic magma dynamics

Abstract

Of what importance is granite? If we take an imaginary journey through our solar system we can visit terrestrial planets like Venus and Mars, our Moon and various rocky satellites orbiting the outer gas giants. In all of these places there are marvels and ‘geological’ wonders, but none of these worlds has any granite. Earth is unique in our solar system in having these rocks—the fundamental stuff of continents. Another unique aspect of Earth is its combination of active plate tectonics with a 70% covering of liquid H2O. It is also unique (as far as we know) in supporting DNA-based life, notwithstanding recent descriptions of what may be Martian nanobacterial fossils. Is it fantastic to suggest that all of these unique features might be linked in some way? If Earth’s mantle did not convect and there were no spreading ridges, we would not have plate tectonics. If the ridges were not covered in water, there would be no hydrothermal ridge processes; sea-floor basalts would not undergo alteration to hydrous minerals like clays and chlorites. If altered basalts had not formed in the Archaean then the first voluminous granitic magmas could not have formed by partial melting of these materials. If the early granitic rocks had not formed then ‘indestructible’ continental masses would not have grown. Although the distribution and elevation of continents plays a role in climate control, their role in the evolution of life is unclear. However, if granitic continents had not existed, we would not be able