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[Display omitted] • The Bozhushan batholith consists of metaluminous and peraluminous granites. • The two phases of granites share a common crustal source. • The peraluminous granites were derived by differentiation of metaluminous melts. • Tin enrichment was significantly controlled by the magmatic differentiation. Most primary tin deposits are closely temporally and spatially related to peraluminous granites. These granites usually exhibit highly evolved geochemical characteristics that disguise their specific origin. This paper reports a study of whole-rock geochemistry and Sm–Nd isotopes, zircon U–Pb geochronology and Lu–Hf isotopes, and mineral chemistry of the Bozhushan granitic batholith in the Youjiang basin, South China. The Bozhushan batholith, producing the Bainiuchang large tin–polymetallic deposit, consists of metaluminous tin-barren monzogranites and peraluminous tin-bearing monzogranites. LA-ICP-MS zircon U-Pb dating suggests that the peraluminous rocks were emplaced during the Late Cretaceous (88.5 ± 0.7 Ma), which is largely consistent with the emplacement age of the metaluminous rocks. These granitic rocks have similar Nd-Hf isotopic compositions, supporting a common crustal source. Relative to the metaluminous monzogranites, the peraluminous tin-bearing rocks exhibit more evolved geochemical compositions with higher Si and lower Ca, P, Mg, Fe, and Ti and stronger depletion in Eu, Ba, Sr, Zr, Hf, and rare earth elements. These differing geochemical characteristics can be explained by the differentiation of biotite, plagioclase, zircon and apatite. The extremely low Nb/Ta (<5) and K/Rb (<150) ratios of the peraluminous rocks indicate a fluid exsolution process. We suggest that the peraluminous tin-bearing rocks were derived by magmatic differentiation and fluid exsolution of the metaluminous melts. Combining our new results with previous studies, we conclude that on a worldwide scale some peraluminous granites related to tin mineralization are derived by magmatic differentiation and fluid exsolution of metaluminous melts rather than from metasedimentary rocks. [ABSTRACT FROM AUTHOR]

Granitoids with depleted isotopic compositions are generally considered beneficial to continental generation. However, most granitoids exhibit enriched isotopic characteristics (high initial Sr isotopic ratios, negative Ɛ Nd and Ɛ Hf values) and their role in continental generation is scantly explored. In this contribution, we report petrological and geochemical data of the Permian (ca. 270 Ma) Yabulai granites and hornblende gabbros in the Alxa Block of western North China Craton. Compared to initial mantle-derived basalts, the hornblende gabbros show low MgO (3.74 to 5.68 wt%), Cr (34.9 to 66.2 ppm), Ni (16.6 to 45.6 ppm) contents and Mg# (0.46 to 0.54), with zircon Ɛ Hf values of +3.5 to +6.6 and −8.4 to −4.8. Relative to heavy rare earth elements (HREEs), the hornblende gabbros are enriched in light rare earth elements (LREEs) with the absence of Eu anomalies. In primitive mantle-normalized spidergrams, the hornblende gabbros exhibit notably negative Nb Ta and positive Pb anomalies. Elemental and isotopic data indicate that they might have originated from a shallow and heterogeneous lithospheric mantle source modified by subducted materials. The granites are metaluminous to weakly peraluminous and can be classified as high-K calc-alkaline I-type, with negative zircon Ɛ Hf values of −8.3 to −5.3. These granitic rocks were likely to be derived from a newly underplated mafic crustal source. Using our data and published data from the granitic rocks in the Alxa Block, we suggest that a Permian crustal generation event has occurred in the Nuru-Langshan belt of the Alxa Block. Our current results reveal that the crustal generation rates at the convergent plate margins might have been underestimated due to the unintended omission of the mantle contribution to the granitoids with enriched isotopic compositions. • The Yabulai granites with evolved isotopic components originated from a new crust. • A Permian crustal generation event has been identified in the Alxa Block. • The crustal generation rates at convergent plate margins may be underestimated. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Bozhushan MEs have compositions that are more primitive than their hosts. • The Bozhushan MEs might be derived from a mantle-derived mafic magma. • Zircons in the MEs have similar U-Pb ages, Hf-O isotopes, Tzr values and Th/U ratios to those of the host Bozhushan granites. • Mantle derived magma mainly contributes to continuous heat for tungsten and tin mineralization. The Bozhushan granites, located in the southeastern Yunnan Province W–Sn polymetallic metallogenic belt in SW China, have considerable W-Sn endowment. However, their petrogenesis remains uncertain, as both crustal and mantle origins have been proposed. Numerous microgranular enclaves (MEs) are found in the Bozhushan granites, and the origin of these MEs can give insights into the petrogenesis of these ore-forming granites. Here we present an integrated study of the major and trace elements, whole-rock Sr–Nd isotopes, and zircon Hf–O isotopes of the MEs. The MEs from the Bozhushan granites are commonly composed of monzodiorite and granodiorite, and they have lower SiO 2 (51.7–66.4 wt%) and higher TiO 2 (0.83–1.67 wt%), MgO (1.68–4.49 wt%), and CaO (1.74–4.26 wt%) contents than those of their hosts (SiO 2 = 64.3–76.9 wt%; TiO 2 = 0.4–0.67 wt%; MgO = 0.86–1.33 wt%; CaO = 2.08–3.25 wt%). Furthermore, the chemical compositions of the MEs and host granites are discontinuous and do not show linear trends in element variation diagrams, as might be expected if the MEs represented restites, thus implying disparate genesis. The observed near-linear element variation most probably reflects mixing of mafic and felsic magma end-members in various proportions. In addition, the MEs have Sr–Nd–Hf–O isotopic characteristics (87Sr/86Sr i = 0.7117–0.7138, εNd = − 12.59 to − 9.26, εHf(t) = − 13.1 to − 6.1, and δ18O = 8.39‰–9.19‰) and zircon U–Pb ages (87.4 ± 1.0 Ma to 86.5 ± 0.4 Ma) that are similar to those of their host granites. We conclude that the similarity of trace-element contents and Sr–Nd isotopic compositions between the MEs and host granites was caused by diffusion and partial re-equilibration. However, if the magma temperature of the MEs was 850 °C, 950 °C, or 1050 °C, the required Zr contents for zircon saturation would be 238–854 ppm, 497–1785 ppm, or 928–3334 ppm, respectively, which are substantially higher than those measured for the bulk rocks (44–436 ppm). Furthermore, zircons from the MEs have Ti-in-zircon temperatures (T zr ; MEs, 669–884 °C; host, 790–842 °C) and Th/U ratios (MEs, 3.43–8.85; host, 2.68–11.86) that are indistinguishable from those of their host granites. Thus, on the basis of our new data, we propose that the MEs of the Bozhushan granites might have been derived from mantle-derived mafic magma. Zircons from the MEs did not crystallize directly within the MEs but rather were xenocrysts that formed during the early stage of magmatic evolution at the bottom of the granitic magma chamber and were subsequently incorporated into the MEs when mafic magma was injected into the granitic magma chamber. The Hf–O isotopes of zircons in this case cannot be used to constrain the primary composition of the magma that formed the MEs. During the Late Cretaceous, owing to lithospheric extension and asthenospheric underplating, the lower crust was partially melted to form high-temperature (790–842 °C) granitic magma in the Bozhushan area. During the formation of the W–Sn mineralization associated with the Bozhushan granites, 10%–20% underplated mafic magma mixed with granitic magma and contributed both heat and mantle-derived material. Therefore, we consider that the Bozhushan granites are clearly characteristic of A-type granites, but the W–Sn mineralization was formed as a result of high-temperature partial melting of Sn–W-rich metasedimentary sources triggered by additional heat provided by mantle-sourced mafic magma. [ABSTRACT FROM AUTHOR]

The I-S-A-type classification scheme for granites has been widely used to identify potential sources and the tectonic setting of granitic magmatism. Recent geochemical studies have shown that most granites are derived from a mixture of mantle and crustal sources, and that granitic magmatism contribute to generation and differentiation of the continental crust. However, the origin of granites with transitional affinities remains unclear, along with their role in the growth and differentiation of the continental crust. In this contribution, the ca. 91 Ma Bozhushan biotite granites in the southwestern Cathaysia Block, China, are characterized by high abundance of high-field-strength elements (HFSEs), with Zr + Nb + Ce + Y > 350 ppm and 10000*Ga/Al > 2.6, which are features typical of A-type granites. However, biotites in the Bozhushan granites are compositionally distinct from those of typical A- and S-type granites. Decreasing P 2 O 5 contents with increasing SiO 2 contents are consistent with an I-type rather than a S-type granite. Petrographic observations and geochemical data suggest that the Bozhushan granites have transitional I-A-type affinities. The Bozhushan granites contain remarkably evolved isotopic compositions, with ε Nd (t) = −9.2 to −8.0 and ε Hf (T) = −9.8 to −7.3, which are slightly lower than values for Late Cretaceous Baiyunshan alkaline igneous rocks. The Bozhushan granites have the low Y/Nb and Yb/Ta ratios, which are similar to the Baiyunshan alkaline igneous rocks, and continental alkaline basalts from the East African Rift and eastern China, ocean island basalts, and A 1 -type granitoids. Geochemical data indicate that the Bozhushan granites were likely generated by high-temperature melting of a hybrid source containing underplated alkaline igneous rocks and Precambrian basement rocks. Although the Bozhushan granites have crustal isotopic compositions, our data indicate that these granites also represent the formation of new crust. Thus, granites with transitional I-A-type affinities, such as the Bozhushan granite, have a role in the generation of continental crust. • The Bozhushan granites exhibit transitional I-A-type geochemical affinities. • They have high HFSEs contents and evolved isotopic characteristics. • They were likely to be derived by high-T melting of a hybrid source. • Granites with enriched isotopic compositions may also record the formation of new crust. [ABSTRACT FROM AUTHOR]