Early Granitic Rocks Research Articles

A silicon memory of subduction

Subduction processes may have operated very early in Earth’s history according to the heavy silicon isotope compositions of Archaean igneous rocks. The silicon that precipitated out of the Archaean oceans as chert was subducted and melted to yield seawater-like heavy isotope signatures in early granitic rocks.

Granitic magma dynamics

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

Evolution of the Qianlishan Granite Stock and its Relation to the Shizhuyuan Polymetallic Tungsten Deposit

The Qianlishan granite stock consists of three peraluminous granites; in order of intrusion they are pseudoporphyritic biotite granite, equigranular biotite granite, and dikes of granite porphyry. There is no obvious evolutionary relationship in petrochemistry between the first two granitoids and the granite porphyry. From pseudoporphyritic biotite granite to equigranular biotite granite, the differentiation degree increases so that the basic elements and the Zr/Hf and La/Yb ratios decrease, Eu depletion is stronger, and acid-incompatible elements, volatile components, ore-forming elements, and Rb/Sr and U/Th ratios increase. The first two phases of granitic intrusions are associated with polymetallic tungsten mineralization. The differentiation degree of the granite porphyry is lower than that of the two early granitic rocks, and so are its Rb/Sr and U/Th ratios; Zr/Hf and La/Yb ratios, however, are higher, and Eu depletion becomes weaker. The granite porphyry is associated with lead, zinc, and silver mi...

A review of the distribution of metamorphism in the ancient Rhodesian craton

Abstract During the early development of the Rhodesian craton the regional metamorphism of some of the oldest rocks of Bulawayan and Shamvalan age, was apparently progressive and is expressed in terms of a clearly defined metamorphic zonation established under conditions of relatively high geothermal gradients in which very low grades typical of the central craton pass into extremely high grades that define the cratonic margin particularly within the Zambezi and the Limpopo belts. The distribution of the associated early granitic rocks relates to the metamorphic pattern, thus implying that both metamorphism and granite development were due to thermal highs centred on the Limpopo mobile belt and possibly the Zambezi belt.