Granitic Rocks and their Formation Depth in the Crust
Granitic rocks as the major component in the continental crust are particularly helpful to decipher the evolution of continental tectonics,which is quite similar in the way that basaltic rocks,being the major component of the oceanic crust,can be used to trace the tectonic settings in plate tectonics. Diversity of source rock composition and formation depth are two crucial factors controlling the compositions of resultant granitic rocks. It is proposed in this study that the variation of Sr and Yb contents of the granitic rocks is related to their formation depth,which can be further used as a new classification criteria for granitic rocks. Provided most of granitic rocks are derived from the lowest part of the lower crust,the depth from which the granitic rocks formed may indicate the thickness of the crust,therefore,the variation of the formation depth can be used to trace the evolution of vertical movement of the continental crust,i.e.,to indentify ancient plateaus and mountain ranges which ever existed in the history of the earth. Major concerns about the relationship of the composition of granitic rocks and formation depth are also discussed in the paper.