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Gabbro–granite complexes formed in active continental margins provide critical constraints on magmatic processes, crust–mantle interactions, and tectonic evolution. The petrogenesis and tectonic setting of the Early Permian igneous rocks in the southeastern Central Asian Orogenic Belt have been a subject of dispute for a long time. This contribution presents an integrated study on the field occurrence, petrology, petrography, zircon U–Pb ages, in situ zircon Hf isotopes, whole-rock geochemistry, and Sr–Nd isotopes of the Early Permian Yiheshaorong gabbro–granite complex, Xi Ujimqin Banner, central Inner Mongolia. Lithologically, the Yiheshaorong complex consists predominantly of gabbro, pyroxene diorite, and alkali feldspar granite. Results of LA–ICP–MS zircon U–Pb dating suggest that crystallization ages of the gabbro, pyroxene diorite, and alkali feldspar granite are 281–280, 278, and 281–280 Ma, respectively. Silica (SiO2) content varies from 41.26 to 79.64 wt% and exhibits a gap between 56.84 and 75.45 wt%, displaying a good bimodal geochemical distribution. Geochemically, the gabbros and pyroxene diorites are characterized by enrichment of large ion lithophile elements (LILEs; e.g., Ba and K) and depletion of high field strength elements (HFSEs; e.g., Nb, Ti, and P). These rocks show similar homogeneous zircon Hf isotopic (positive eHf (t) values from +7.8 to +10.1) and whole-rock Sr–Nd isotopic (low initial 87Sr/86Sr ratios from 0.7044 to 0.7051, positive eNd (t) values from +3.7 to +4.7) compositions. The gabbros and pyroxene diorites originated from partial melting of depleted asthenospheric mantle metasomatized by subduction slab fluids; and they experienced various degrees of crystallization differentiation during ascension. The alkali feldspar granites are ferroan, alkali-calcic–calc-alkalic series rocks marked by high SiO2, K2O + Na2O, and FeOT/MgO; and low Al2O3, CaO, and MgO contents. Their trace elements are marked by enrichment of LILEs (such as K and Rb); depletion of HFSEs (such as Nb and Ti), Ba, Sr, and P; and strongly negative Eu anomalies (Eu/Eu* = 0.17–0.57), with coincident distribution patterns forming a seagull-type distribution form, showing an A-type granite affinity. The alkali feldspar granites are characterized by positive eHf (t) values (+8.6 to +10.3, young TDM2 ages, 645–758 Ma) and eNd (t) values (+3.5 to +3.8 as well as young TDM2 ages, 667–687 Ma). All these geochemical characteristics indicate that the alkali feldspar granites originated from the partial melting of juvenile crust under high temperature and low pressure condition. The Yiheshaorong complex was most likely formed in a back-arc spreading basin. Such an extensional regime can likely be attributed to the upwelling of asthenospheric mantle caused by the rollback and break-off of a subducted Paleo-Asian Ocean slab in the Early Permian, which induced large-scale extension and magmatism in the study area.

The Chaobuleng iron polymetallic deposit, an important ore system in China that is genetically related to the early Cretaceous Chaobuleng pluton, is located in the eastern part of Lizi Shan-Dong Ujimqin Banner metallogenic belt of Inner Mongolia. To understand the relationship of magmatism and mineralization in this iron polymetallic deposit, we have conducted a detailed geologic field study in conjunction with systematic investigation of U-Pb zircon and Re-Os isochron geochronology, mineralogy, petrology, major-and trace-element geochemistry, and synthesis of existing datasets across the Chaobuleng region. We use these observations to identify the origins and petrogenesis of mafic enclaves and the host granitoid, and to place new constraints on the tectonic setting at the time of magmatism. New U-Pb geochronology of magmatic zircons and Re–Os isochron ages of hydrothermal molybdenite from the iron polymetallic deposit allow us to constrain the sources of the hydrothermal components and the relationship between iron polymetallic mineralization and regional geodynamic evolution. The geology, paragenesis, and estimated P - T conditions suggest that the Chaobuleng iron polymetallic deposit was formed as a shallow, proximal skarn deposit. The ore-forming early Cretaceous Chaobuleng pluton can be divided into three distinct units based on crystallization age, texture, and composition: (1) a 138.1–140.6 Ma syenogranite porphyry, (2) a 137.4–138.6 Ma enclave bearing porphyritic syenogranite, and (3) a 133.9–135.98 Ma coarse-grained porphyritic syenogranite. We suggest that the A-type Chaobuleng pluton was formed in a post-orogenic extensional setting with significant magma mixing from high-temperature melts (i.e., a Zr saturation temperature of 800–900 °C). During the magmatic process, the Chaobuleng pluton crystallized under temperatures as low as 720–770 °C and pressures of 0.5–1.0 kbar. The chemical composition of biotite shows that the Chaobuleng magma was enriched in F (1.5–3.5%). We attribute the observed embayed texture of quartz to a three coexisting-phase equilibrium model that operated during the magmatic-hydrothermal transition and can be used to constrain the mineralization process and physico-chemical conditions. Due to a loss of volatiles, the residual melt was quickly quenched and crystallized into a fine-grained groundmass. The Re–Os model ages of samples from the inner pluton-mineralization contact belt are 135.0 ± 2.1 Ma and 131.2 ± 4.1 Ma, and a sample from the outer-contact belt yields an isochron age of 140.7 ± 1.8 Ma. The Chaobuleng deposit formed during protracted activity of the magmatic-hydrothermal system, which is similar to many mineralization systems around the world. However, the major mineralization stage (iron oxide stage) of the Chaobuleng deposit occurred during the early stage of magmatism, consistent with the emplacement time of syenogranite porphyry at ~ 139 Ma.

The distribution of Precambrian rocks and microcontinents is a key to understanding the architecture of the Beishan Orogenic Belt, southern Central Asian Orogenic Belt (CAOB). We present zircon U-Pb-Hf isotopic and whole-rock geochemical data for early Neoproterozoic granitic rocks from the eastern Shuangyingshan–Huaniushan Terrane in the Beishan Orogenic Belt. The zircon ages show that the granitic gneiss, the mylonitized granite, and the mylonitized monzonite formed at 895 Ma, 894 Ma, and 884 Ma, respectively. These ages confirm that the Shuangyingshan–Huaniushan Terrane is a microcontinental block and that Precambrian magmatic rocks are not restricted to the western Gubaoquan area. Both the gneiss and granite contain Al-rich muscovite, high SiO2 (69.59–78.10 wt%) contents, and show peraluminous features (molar Al2O3/(CaO + Na2O + K2O) values = 1.03–1.28), negative correlations of Th and Y with respect to Rb, typical features of S-type granites. The monzonite contains hornblende, and relatively low SiO2 (62.11–64.10 wt%), high CaO (5.33–5.41 wt%), Na2O (5.88–6.02 wt%), V and Cr contents, and low K2O/Na2O, Rb/Sr and Rb/Ba ratios, consistent with I-type granites. These studied granitic rocks are calc-alkaline to shoshonitic, and all exhibit similar LREE-enriched trace-element patterns, pronounced negative Eu anomalies, positive Rb, Th, U and K anomalies, negative Ba, Nb, Ta, Sr, P and Ti anomalies, evolved zircon eHf(t) values of −6.25 to + 1.09, and two-stage Hf model ages of 2.16–1.70 Ga. These characteristics suggest that they have mainly crustal sources, similar to coeval reported granitic rocks in the Beishan Orogenic Belt, and indicating an older crustal reworking event. The Precambrian basement of the Beishan Orogenic Belt shows evidence of Mesoproterozoic crustal growth and early Neoproterozoic crustal reworking, with zircon eHf(t) values plotting within the crustal evolution trend defined by 2.1–1.3 Ga crustal material, similar to the Yili, Central Tianshan and Northern Alxa blocks, and indicating an affinity with those blocks. Geochronological data from these blocks and terranes suggest that the southern CAOB contains an extensive assemblage of early Neoproterozoic magmatic rocks that are related to the assembly of Rodinia and can be trace over 2000 km as an east–west-trending belt.