Black creek dating

The term "granitic" means granite-like and is applied to granite and a group of intrusive igneous rocks with similar textures and slight variations in composition and origin.These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals.These are rare, because it is difficult to turn basalt into granite via fractional crystallisation.A-type or anorogenic granites are formed above volcanic "hot spot" activity and have a peculiar mineralogy and geochemistry.

The letter-based Chappell & White classification system was proposed initially to divide granites into I-type granite (or igneous protolith) granite and S-type or sedimentary protolith granite.Granitoids have crystallized from magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve).Magmas will evolve to the eutectic because of igneous differentiation, or because they represent low degrees of partial melting.Felsic rocks are less dense than mafic and ultramafic rocks, and thus they tend to escape subduction, whereas basaltic or gabbroic rocks tend to sink into the mantle beneath the granitic rocks of the continental cratons.Therefore, granitic rocks form the basement of all land continents.

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