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It is well recognized that various degrees of mantle-derived materials are incorporated in the formation of granite, and mantle-derived mafic melts are generally considered to mix with crustal felsic melt. Here, however, we provide an example of the Shanggusi leucocratic granite where external mantle-derived hydrous fluid, rather than mafic melt, might be incorporated into a nearly pure crustal granitic melt system. Field observations suggest that the Shanggusi granite consists of granite porphyry, granite dyke and granitic pegmatite and they have consistent zircon U–Pb ages and molybdenite Re–Os ages. The marginal pegmatite, interconnected miarolitic cavities, heterogeneous molybdenite mineralization and significant variation of micro-texture of the Shanggusi granite physically indicate that strong fluid activities occurred in the granitic system. Accumulation of quartz and K-feldspar and bulk-rock major element data imply that fractional crystallization played an important role in the evolution of the granitic system which, however, cannot reasonably explain the significant trace elements fractionation, non-CHARAC trace elements behavior and simultaneous concave and convex REE tetrad effect of the Shanggusi granite, but which can be best explained by the influence of external fluorine-rich hydrous fluid. Importantly, the chemical fractionation, including bulk-rock trace elements and isotopes, is closely correlated with quantitative textural parameter L max (the average length of the four largest quartz crystals in each sample), indicating that the vast majority of physical and chemical characteristics of the granitic system were most likely controlled by the wholesale fluid flow. The Shanggusi granite is highly siliceous (SiO 2 = 74.91–79.50 wt.%, except granitic pegmatite with SiO 2 = 67.41 wt.%), extremely poor in mafic minerals, and with relative homogeneous bulk-rock major element chemistry and mineralogy, which approximate experimentally pure crustal melt that generated by dehydration melting of sedimentary rocks. The mantle-derived Nd–Pb–O isotopic features, however, require a great deal of contributions from mantle materials. Therefore, it is proposed that external mantle-derived fluid was infiltrated into the Shanggusi granitic system at least before emplacement, and fluid–melt mixing may be an important but not easily recognized part in granite origin.

A combined whole-rock geochemical and zircon U–Pb and Lu–Hf isotope study on two Precambrian lithotectonic units in the Songshan area, south-central North China Craton (NCC), was performed to constrain the tectonic evolution of the Trans-North China Orogen (TNCO) during collision between the Eastern and Western Blocks of the NCC. The metamorphic unit at Shipaihe consists of dioritic gneiss with minor amphibolitic enclave, whereas the magmatic unit at Shicheng is composed of granite. Zircon U–Pb dating demonstrate that the dioritic gneiss and enclave amphibolite were originally emplaced contemporaneously at ca. 2.5 Ga. The magmatic zircons exhibit ɛHf(t) values of 2.2–7.8 and Hf model ages of 2.52–2.73 Ga, suggesting that the dioritic gneiss was produced by reworking of the juvenile crust. The magmatic zircons of amphibolite have ɛHf(t) values of 0.7–8.1 and Hf model ages of 2.51–2.79 Ga. The granite primarily gave zircon U–Pb ages of ca. 1.78 Ga, with inherited zircons in ca. 1.87 Ga. Zircon Lu–Hf isotopic analyses yield negative ɛHf(t) values of −16.7 to −1.8 and Hf model ages of 2.55–3.47 Ga, indicating that the granite was mainly derived from reworking of ancient Archean crust. The Neoarchean dioritic gneiss and amphibolite show enrichment of LREE and LILE but depletion of HREE and HFSE, suggesting their derivation from anatexis of juvenile arc-type crust and enriched lithospheric mantle, respectively. The dioritic gneiss also has highly fractionated REE patterns and negligible negative Eu anomalies, implying anatexis at high pressures, where garnet and possibly amphibole as residual phases. The Paleoproterozoic granite has high K2O + Na2O and Zr, high ratios of total FeO/MgO and Ga/Al, and low contents of CaO, Al2O3, Ba, Sr and Eu/Eu* values, consistent with the characteristics of A-type granites. The negative Eu, Ba and Sr anomalies suggest that plagioclase acted as a residual phase during partial melting at relatively low pressures. Taken together, the Songshan metamorphic complex would originally derive from the reworking of juvenile arc-type crust and coeval partial melting of juvenile, enriched lithospheric mantle. Thus, an active continental margin was present in the late Neoarchean in south-central NCC, generating arc-type magmatism between the Eastern and Western Blocks. During the collisional orogeny, the arc-type crust in southern NCC underwent intensive metamorphism that followed by post-collisional extension at ca. 1.78 Ga, and the reworking of the old continent in the southern TNCO yield Shicheng A-type granite.

The nondeformed, postcollisional Shahewan monzonite–minette complex in the North Qinling orogenic belt, central China, is composed of potassic monzonites and mafic minette dykes. The monzonites and minette dykes were coevally intruded as evidenced by a zircon U–Pb age of 211 ± 2 Ma for the monzonites and a 40 Ar/ 39 Ar age of 209.0 ± 1.4 Ma on the biotite from the minette dykes. These dates also indicate that the Shahewan complex postdated shortly the cessation of convergent deformation in the Qinling orogenic belt. The K-feldspar 40 Ar/ 39 Ar MDD modeling result combined with the zircon U–Pb age reveals a rapid average cooling history (11.5 °C/Ma) for the complex from 211 to 150 Ma, implying a fast exhumation within a short period of time. The minettes take features of ultrapotassic rocks. Their geochemical characteristics, such as high MgO (Mg# up to 80), low TiO 2 (0.38–0.62 wt.%) and FeO (2.52–3.42 wt.%), enrichment in LILEs and LREEs, and depletion in HFSE, together with primitive initial 87 Sr/ 86 Sr ratios (0.70444–0.70562) and slightly negative e Nd ( t ) (−3.4 to −2.5), suggest that they were derived from an enriched refractory lithospheric mantle. The monzonites have the similar geochemical (incompatible element enrichment, Nb, Ta, Ti depletion) and isotopic (initial 87 Sr/ 86 Sr: 0.70513–0.70646; e Nd ( t ): −0.5 to −3.6) imprints, indicating they were derived from a common source. The dynamic setting in which the Shahewan complex formed is discussed. The Shahewan complex formed most likely in a postcollisional extensional setting. Its formation requires a high enough temperature to partially melt an enriched, refractory mantle source. Considerable uplift is necessitated for the rapid exhumation. These may be explained by convective mantle thinning or slab-breakoff mechanisms. The enrichment features in the lithospheric mantle source can be interpreted by injection of small percentage (