The origin of high-silica granites and rare metal mineralization: Insights from geochemistry and U-Pb-Sr-Nd-Hf-O isotopes of Early Cretaceous granitoids in the southern Great Xing’an Range, NE China

Abstract

High-silica granitoids signal maturity of continental crust and are also closely associated with rare metal mineralization. However, the possible factors controlling the upper crustal differentiation and rare metal mineralization have not been well-constrained. In this work, we report zircon U-Pb ages, trace elements, Hf-O isotopes, and whole-rock elemental and Sr-Nd-Hf isotopic data on six high-silica granitic intrusions from the Southern Great Xing’an Range Metallogenic Belt (SGXRMB), NE China, with a view to elucidate their source, differentiation mechanism, and rare metal mineralization potential. Zircon U-Pb dating of the granites (including porphyritic granite and alkali-feldspar granite) yields Early Cretaceous ages of ca. 144−135 Ma. Petrographic and geochemical features including the high SiO2, DI, and TE1,3 values, and similar Sr-Nd-Hf-O isotopes suggest that the rocks are weakly peraluminous, highly evolved I-type granites sharing a common silicic magma reservoir. Integrated isotope modeling suggests a complex source region for the evolved I-type granites involving dominantly juvenile lower crustal components with subordinate older continental basement and possible contribution of recycled pelagic sediments. The high-silica granite in the Jingpeng-Lindong region and the quartz diorite-monzonite, granodiorite, and monzogranite in the Lindong-Zalute region show close spatial-temporal distribution, common source and consistent variations in their whole-rock zircon compositions, indicating melt extraction processes in a highly crystalline mush rejuvenated by the injection of high temperature magma and F-enriched volatile filter-pressing, with the former derived from initial interstitial melts leaving behind residual silicic cumulates represented by the latter. Detailed comparisons of the rare metal-bearing and barren high-silica granites within the SGXRMB show that simple anatectic or fractional crystallization processes cannot account for the rare metal granites. Fluid-melt interactions combined with a high degree of crystallization differentiation and changes in melt structures are proposed as the potential mechanisms for generating the rare metal mineralization in I-type granitic magmas.