High Silica Leucogranites Result From Sedimentary Rock Melting—Evidence From Trace Elements and Nd‐Hf‐B Isotopes

Abstract High silica granites may host major rare metal deposits. The petrogenesis of these granites, some of which have very low Zr/Hf, Nb/Ta, and Eu/Eu* ratios, has been highly debated. The existing views mainly favor either extreme magmatic fractionation or fluid‐magma interaction. Contrary to these interpretations, we demonstrate that the distinct chemistry of high‐SiO 2 granites can be inherited from partial melting of their sedimentary source rocks. The wide range in Ɛ Hf ( t ) values (−14 to −1.3), Nd‐Hf isotope decoupling,and correlations of Hf‐B isotopes with major and trace element abundances and ratios are best understood as melting‐induced mixing of diverse source lithologies with contrasting abundances of zircon (a low Lu/Hf phase) and high Lu/Hf phases. This process also leads to positive correlations of Ɛ Hf ( t ) with muscovite modes and negative correlations of δ 11 B with muscovite modes. Based on the above findings, there are several practical implications: (a) the extremely low Zr/Hf, Nb/Ta and negative Eu/Eu* anomalies could be inherited from protoliths; (b) the Lenglongling leucogranites represent “pure” S‐type granites with relatively high Ɛ Hf ( t ); and (c) using Hf isotope alone may lead to incorrect interpretation of mantle contribution.