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The application of whole-rock compositions to trace magma evolution or crystal-melt equilibrium may be called into question when foreign crystals are incorporated into host magmas. To address this challenge, establishing the origins (orthocrysts, antecrysts, xenocrysts, etc.) of minerals with variable textures in magmatic plumbing systems is necessary. In this paper, we describe complex oscillatory zoning patterns of clinopyroxenes (Cpx) from the Miocene Majuangou (MJG) alkali basalts from West Qinling, China. Our detailed petrographic, mineralogical, and geochemical analyses unravel the origins of various Cpx crystals with distinct textural patterns, thereby providing information about magma storage, recharging and/or mixing, and transportation, as well as the reactions between crystals and melts/fluids. Based on textural patterns, Cpx may be divided into four types: normal (Type-1 Cpx), simple oscillatory (Type-2 Cpx), complex oscillatory (Type-3 Cpx), and grains that lack zoning (Type-4 Cpx, suggested to be orthocrysts). Through the textural characterization of Cpx, the comparison between different types of Cpx, and the relationships between Cpx major compositions from different lithologies, we concluded that Type-1–3 Cpx cores are antecrysts or xenocrysts with diverse origins: primitive magma (Type-1 Cpx cores), magma mush (Type-2 Cpx cores), and crustal granulite (Type-3 Cpx cores). The zoning patterns and the compositions of these Cpx crystals indicate at least three batches of magmatic activity, i.e., the Batch-1 low-Mg# magma (Mg#: 47.4–53.3), the Batch-2 primitive magma (Mg#: 57.2–64.5), and the Batch-3 low-Mg# host alkali magma (Mg#: 47.2–54.6). Cpx-melt thermobarometry demonstrates that at least two crustal magma reservoirs existed in the magma plumbing system at depths of 30.1 and 40.9 km. The antecrystic/xenocrystic Cpx cores were captured by, continued to grow in, and subsequently reacted with ascending K-rich melt/fluid. The spongy textures in Cpx cores/mantles are attributed to this reaction, which may be expressed as: Melt 1 (primitive or evolved) + K-rich melts/fluids + Cpx (CaMgSi2O6) = K-feldspar (KAlSi3O8) + ilmenite (FeTiO3) + Melt 2 (derivative). The products of this reaction (K-feldspar and ilmenite) filled the sieves in the spongy zones of Type-1–3 Cpx. This detailed investigation of compositional and textural features of Cpx antecrysts/xenocrysts suggests that the interactions between various interconnected magma reservoirs are widespread beneath the magmatic plumbing system. Our study emphasizes the importance of the incorporation of foreign crystals and the Cpx-melt/fluid reaction in magmatic plumbing system, which can significantly modify the whole-rock compositions and lead to the formation of spongy textures without the need for fractures and cracks in minerals. [ABSTRACT FROM AUTHOR]

A major and trace element, Sr–Nd–Hf isotope, and zircon U–Pb geochronology study was conducted on Early Cretaceous volcanic rocks from the northern margin of the Sulu orogenic belt in Shandong Province, eastern China. These results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of crust–mantle interaction. The rocks comprise high‐K basaltic andesite, shoshonites, latites, high‐K dacites, and high‐K rhyolites. U–Pb zircon dating of four representative samples of latite, two high‐K dacites, and high‐K rhyolite indicates that these rocks formed from 126 to 122 Ma. The volcanic rocks are characterized by high K2O (2.04–6.70 wt.%) and total alkalis (Na2O + K2O; 5.3–10.9 wt.%) that plot within the field for shoshonitic rocks. All the rocks are enriched in light rare earth and large‐ion lithophile elements (e.g., Rb, Th, U, and K) and are depleted in high‐field‐strength elements (e.g., Nb, Ta, and Ti). The rocks have high initial 87Sr/86Sr ratios (0.706760–0.708898), low εNd(t) values (−19.5 to −12.5), and negative εHf(t) values (−31.3 to −19.7), similar to the Early Cretaceous Jiaodong mafic dikes and intermediate–mafic volcanic rocks. These geochemical and isotopic characteristics indicate that the volcanic rocks formed through simultaneous fractional crystallization and crustal assimilation of a basaltic magma derived from metasomatized mantle. The metasomatized mantle source might have been produced by the recycling of subducted Yangtze Craton crust into the ancient lithospheric mantle of the North China Craton. [ABSTRACT FROM AUTHOR]

A combined study of whole-rock major and trace elements, Sr-Nd-Hf isotopes, and zircon U-Pb geochronology was conducted on late Mesozoic volcanic rocks along the Tan-Lu fault zone (the Anqiu, Gaoqiao, Juxian, and Junan regions) of Shandong Province, eastern China. The results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of the Tan-Lu fault zone for lithospheric thinning. The volcanic rocks are composed of basaltic trachyandesite, trachyandesite, trachydacite, andesite, dacite, and rhyolite, which yielded zircon U-Pb ages of 125.4 ± 0.9, 126.2 ± 1, 125.7 ± 1, 127.1 ± 1.2, 120 ± 0.65, and 122.8 ± 1 Ma, respectively, indicating eruption in the Early Cretaceous. A large amount of Palaeoproterozoic and Archaean inherited zircons exist in Anqiu and Gaoqiao volcanic rocks, but Neoproterozoic inherited zircons in Juxian and Junan volcanic rocks, in agreement with the age spectrum of the basement rocks of the North China Craton (NCC) and Neoproterozoic protolith ages of ultrahigh-pressure metaigneous rocks in Sulu orogenic belt, respectively. The volcanic rocks have high Na2O + K2O concentrations (5.94-11.33 wt.%), indicating that they are alkaline. All the rocks are characterized by enriched in light rare earth elements and large ion lithophile elements (e.g. Rb, Th, U, and K) but are depleted in high field strength elements (e.g. Nb, Ta, and Ti). Anqiu and Gaoqiao volcanic rocks have wide initial 87Sr/86Sr ratios (0.707678-0.711259), variable negative εNd(t) values (-15.2 to −11) and εHf(t) values (−19.5 to −2.2). The varied isotopic compositions and the abundance inherited zircons, together with mineral disequilibrium features, suggest that the Anqiu and Gaoqiao volcanic rocks were produced by the mixing of magmas from enriched lithospheric mantle and lower crust. The enriched lithospheric mantle originated from the ancient lithospheric mantle beneath the NCC, which was modified by the subduction of Yangtze crustal material. Juxian and Junan voalcanic rocks have initial 87Sr/86Sr ratios of 0.707502-0.709238, low εNd(t) values of −20.5 to −16.1, and negative zircon εHf(t) values of −24.6 to −16.4, similar to granitoids in Sulu orogenic belt, suggesting that they derived from similar crustal sources. Combining the existence of the Neoproterozoic inherited zircons and the isotope characteristics, we propose that the Juxian and Junan volcanic rocks were dominantly derived from partial melting of the Subducted Yangtze crust but with contributions from the mantle. The volcanic rocks along the Tan-Lu fault zone were produced under an extensional regime linked with lithospheric thinning in the eastern NCC during the Early Cretaceous. According to the characteristic spatial and temporal distributions of late Mesozoic volcanic activity along the Tan-Lu fault zone, combined with the distributions of regional adakitic rocks and the evolutionary history of the fault, we suggested that the Tan-Lu Fault played an important role in the initiation of lithospheric thinning and provide a favourable channel and beneficial conditions for magma activity. [ABSTRACT FROM AUTHOR]