The study of Sr-Nd isotopic system shows that most granites in the northern part of this area have low initial Sr ratio and positive εNd(t) characteristics, which reflects that magma has the characteristics of mixed melting of crust and mantle. However, it must be emphasized that the background and degree of mixing in different regions are different. It not only causes the difference in composition between rocks and minerals, but also affects their mineralization specificity. It has been noticed by predecessors that Huanggangliang in Linxi is quite different from Baiyinnuo and Haobugao granite in the main peak area of Daxing 'anling. The rocks related to the large-scale Fe-Sn deposit in Huanggangliang are alkali feldspar granite and potash feldspar granite (142Ma), with a low content of dark minerals. The biotite is iron biotite (< 5%), σ REE = 280× 10-6, δEu=0.06, and the magma source areas of these rocks are shallow. The lead-zinc related granodiorite, quartz monzonite and alkali feldspar granite (148Ma) in Baiyinnuo and Haobugao contain dark minerals amphibole and magnesium-rich biotite. Isotopic studies such as Pb and S show that these rocks have deep genesis (see Chapter 7 for details), and materials from the upper mantle participated in the mixing of crust-derived materials at different stages.

Recently, through careful work, it is clarified that the acid igneous rocks in Huanggangliang area of Linxi are formed by the assimilation of Mesozoic acid magma mixed with Paleozoic basic volcanic rocks (Zhang Yongbei et al., 2003). Paleozoic basic volcanic rocks in this area are mainly basalt of Dashizhai Formation in Early Permian. In the third chapter of this book, Crustal Evolution before the Uplift of Daxing 'anling Mountains, it is clarified that this is a set of continental rift basalts, and the magma comes from the lithospheric mantle, so this assimilated and mixed magma also has the characteristics of mixed magma of crust and mantle.

The above examples show that the characteristics of granite in this area not only evolve with time, but also the composition characteristics of granite in different places in the same period are different, which is related to the basement difference before Mesozoic in this area. Even before Mesozoic, granites in different parts of the same continental crust accretion zone were different. There is an ancient terrane composed of ancient continental crust in the plate splicing zone, and its position is naturally different from other newly born young continental crusts, which naturally affects the composition characteristics of Mesozoic granite. The granite in Huanggangliang area needs further study.

In addition, mantle heterogeneity caused by metasomatism is also an important factor. Sr isotope values of alkaline granites related to rare earth minerals in Barchi are quite different, among which the ISr of granites in the east and west ore bodies changes from 0.698 (Wang Yixian et al., 1997) to 0.707 1 (data of Sharla Cheung's master thesis). Barchi's ISr of 0.698 has attracted the attention of geological colleagues at home and abroad, and this data was completed in the geochemical chronology laboratory of Rennes University. It is reported that Boming Jiang, a French scholar, once tested this result and thought it was correct (according to Tu Guangchi's private conversation with the author). Some people use mantle metasomatism to explain the contradiction between the enrichment of incompatible elements and positive εNd(0) in albite granite in Barchi (Chauvel et al., 1984). In a word, Daxinganling is a rare natural laboratory to study the interaction between crust and mantle. It should be said that the research level of it is still very low at present, and further extensive research is needed.