Chem Geol, 139: 249–269īachmann O, Bergantz G W. REE fractionation and Nd-isotope disequilibrium during crustal anatexis: Constraints from Himalayan leucogranites. ![]() Internal structures in part of the South Mountain batholith, Nova Scotia, Canada. We proposed that highly fractionated granites are an important sign indicating compositional maturity of the continental crust, and they are also closely related to the rare-elemental (metal) mineralization of W, Sn, Nb, Ta, Li, Be, Rb, Cs, REEs, etc.Ībbott Jr R N. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. Accordingly, granite can be divided into unfractionated, fractionated (including weakly fractionated and highly fractionated) and cumulated types, according to the differentiation degree. On the contrary, flow segregation or dynamic sorting may be more important. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. ![]() Although granitic magma has high viscosity because of its elevated SiO 2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation, mineral species and its chemical variations, and geochemical compositions. ![]() The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture, structure, mineral species and geochemical compositions at different scales from small dike to large batholith. Granite is one of the most important components of the continental crust on our Earth it thus has been an enduring studied subject in geology.
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