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The Jinshajiang suture zone (JSZ) is one of the most significant tectonic zones in the eastern Tethys area. A large number of plutons are regarded as the result of tectono‐magmatic activities associated with the evolution of the Palaeo‐Tethys Ocean. The Tongjige pluton in the central part of JSZ can indicate the magmatism and its geodynamic evolution. The Tongjige pluton (225.6 Ma) consists mainly of granodiorite with abundant coeval mafic microgranular enclaves (MMEs) (226.1 Ma). The host granodiorite is calc‐alkaline and typical I‐type, with SiO2 contents ranging from 65.75 to 66.91 wt%. The MMEs have relatively high MgO (4.00–4.07 wt%) and Fe2O3T (9.27–9.40 wt%) abundances and low SiO2 (53.59–53.87 wt%). Both MMEs and host granodiorites are characterized by the enrichment of light rare earth elements and depletion of heavy rare earth elements. They are also negative in Eu and enriched in Th and U, which are consistent with the trace element characteristics of typical island‐arc magmatite. The zircon Hf(t) values (−3.48 to −0.31) are negative, with the model ages of 1.3–1.2 Ga. These petrographic and geochemical characteristics indicated that the Tongjige pluton was derived from the melting of an ancient lower crust and underwent the process of mafic‐felsic magmatic mixing in the post‐collision background. The Triassic granitoids in the JSZ show a temporal–spatial relationship with the subduction zone, which constrain the evolution of the Palaeo‐Tethys Ocean. The mixing mechanism of the Tongjige pluton is associated with the break‐off of a subducted slab, which triggered subsequent upwelling of asthenosphere beneath accreted arc fragments and induced underplate of lithospheric mantle‐derived magmas and mixed with the lower crust‐derived felsic magma. In general, the Late Triassic pluton recorded significant crustal growth and continental development, marking the final stage of subduction‐related magmatism in the JSZ region, after which the region entered into a stage of post‐collision evolution. [ABSTRACT FROM AUTHOR]

The Hongshan quartz monzonite porphyry is one of the Yanshanian intrusions in the southern part of the Yudun Arc. Detailed zircon U-Pb data of four samples yielded ages of 78.8-80.7 Ma, indicating that the Hongshan intrusion was emplaced during the late stage of Late Cretaceous. The Hongshan intrusion shows shoshonitic and high-K calc-alkaline, with A/CNK = 0.64-1.14. The rocks show an obvious fractionation between light and heavy rare-earth elements (average [La/Yb]N = 38.85), with negative Eu anomalies (Eu/Eu* = 0.60-0.87), enrichment in large-ion lithophile elements (Rb, Th, U and K) and depletion in high field-strength elements (Nb, Ta and P). Rocks have high Sr and low Y content which are characteristics of adakitic rocks, suggesting magma derivation from thickened lower crust. In order to evaluate the nature of the source region, Hf isotope data of zircons were acquired through LA-MC-ICPMS. The negative and variable εHf(t) values demonstrate that the Hongshan intrusion was derived from ancient crust, without mantle-derived components and is significantly different from the Triassic intrusions in the southern part of the Yudun Arc. The three Yanshanian intrusions in Hongshan, Relin and Tongchangou are remarkably similar in terms of geochronology, geochemistry and Hf isotopes. We therefore infer that these intrusions had the same magmatic source and we correlate the tectonics with northward subduction of Tethys underneath the Asian continent. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Daocheng batholith consists of granite, granodiorite and K-feldspar megacrystic granite, which is located in the north Yidun Arc. It is a barren batholith in contrast to plutons of the same age that contain major copper deposits, such as Pulang to the south. In the Daocheng, abundant mafic microgranular enclaves (MMEs) mainly developed within granodiorite and K-feldspar megacrystic granite, which are characterized by quenched apatite, quartz eyes and plagioclase phenocrysts. LA-ICP-MS zircon U–Pb dating of host granodiorite yielded ages ranging from 223 Ma to 210 Ma, with a weighted mean of 215.3 ± 1.8 Ma. Zircons from MMEs yielded ages ranging from 218 Ma to 209 Ma, with a weighted mean of 214.2 ± 1.4 Ma. Geochemical analyses show that granodiorite is high-K, calc-alkaline and I-type, with SiO2 contents ranging from 67.90% to 70.54%. These rocks are metaluminous to marginally peraluminous (A/CNK = 0.98–1.00) and moderately rich in alkalis with K2O ranging from 3.28% to 4.59% and Na2O ranging from 3.18% to 3.20%, with low MgO (1.08%–1.29%), Cr (12.7 ppm–16.8 ppm), Ni (5.19 ppm–6.16 ppm) and Mg# (35–49). The MMEs have relatively low SiO2 contents (56.34%–60.91%), higher Al2O3 contents (16.06%–17.98%), higher MgO and FeO abundances and are metaluminous (A/CNK = 0.82–0.83). The MMEs and host granodiorite are enriched in light rare-earth elements (LREEs) relative to heavy rare-earth elements (HREEs), with slightly negative Eu anomalies, and enriched in Th, U and large ion lithophile elements (LILEs; e.g., K, Rb and Pb), and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, P and Ti), showing affinities typical of arc magmas. The zircon εHf(t) values (−6.28 to −2.33) and ancient two-stage Hf model ages of 1.92 to 1.25 Ga, indicating that the magmas are generally melts that incorporated significant portions of Precambrian crust. The relatively low silica contents and high Mg# values of the MMEs, and the linear patterns of MgO, Al2O3 and Fe2O3 with SiO2 between the MMEs and host granodiorite, showing the formation of MMEs are genetically related to magma mixing. The Daocheng granodiorite is characterized by much lower zircon Ce4+/Ce3+ (average of 3.53) and low fO2 value (average of ∆FMQ = –10.84), whereas the ore-bearing quartz monzonite porphyries in the Pulang copper deposit are characterized by much higher zircon Ce4+/Ce3+ (average of 52.10) and high fO2 value (average of ∆FMQ = 2.8), indicating the ore-bearing porphyry intrusions had much higher fO2 of magma than the ore-barren intrusions considering that the high oxygen fugacity of the magma is conducive to mineralization. [ABSTRACT FROM AUTHOR]

The Gangdese porphyry Cu-Au belt (South Tibet, China) in the eastern Tethyan metallogenic belt hosts many deposits, which formed in subduction and collisional settings. Several porphyry Cu-Au deposits have been discovered in the Xietongmen region, including a large porphyry Cu-Au deposit at Xiongcun. However, the formation mechanism for the Xietongmen Cu-Au deposits and their igneous host rocks remain enigmatic. This study reports whole-rock major- and trace-element compositions, Sr-Nd isotopes, in situ zircon Hf- and plagioclase Sr-isotope compositions, and major- and trace-element compositions of amphiboles to constrain the magmatic emplacement and evolution related to the porphyry Cu-Au mineralisation in the Xietongmen region. New zircon U-Pb ages show that the Xietongmen diorites formed at 185 Ma, consistent with the age of Cu-Au mineralisation. The Xietongmen diorites are characterised by enrichment in LILEs and LREE, and depletion in HFSEs. These features suggest that the diorites were produced by arc magmatism in an oceanic-slab subduction environment. In situ isotopic compositions exhibit radiogenic ε Hf (t) (+9.8 to +14.4) and low initial 87 Sr/ 86 Sr values (0.7039–0.7043); whole-rock results show positive ε Nd (t) (+5.26 to +5.31) and unradiogenic initial 87 Sr/ 86 Sr values (0.7042–0.7043). These isotopic results are similar to coeval mantle-derived hornblende gabbros and the Sangri volcanic rocks in the Gangdese belt. Amphibole clots in the Xietongmen diorites have higher MgO and Ni contents, with AlT > 1.0, Mg# > 0.5, Ni > 143 ppm, and REE patterns different from those of magmatic and idiomorphic amphiboles in the host diorites, suggesting that the clots are xenocrysts. All the petrological and geochemical evidence suggests that the Xietongmen mineralised diorites were derived from a Jurassic hydrous mantle wedge induced by slab dehydration. These magmas contain higher contents of water and other volatiles and have higher oxidation states. These conditions favored the transfer of metals (such as Cu, Au) to the upper crust, and then formed the Jurassic porphyry Cu-Au deposits. [ABSTRACT FROM AUTHOR]