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[Display omitted] • Both granodiorites and monzogranites of the Mopanshan pluton are coeval and formed at ca. 820 Ma. • They were generated by mixing of metasomatized mantle-derived magmas and ancient crust-derived melts. • The adakitic signatures of the Mopanshan pluton were caused by hornblende-dominated fractional crystallization. • The Neoproterozoic magmatic event was due to the intensive crust-mantle interaction in a back-arc extension setting. Crust- and/or mantle-derived igneous rocks in the Neoproterozoic continental magmatic arc along the western Yangtze Block (South China) have been extensively studied, but the crust-mantle interaction that might have been involved in the formation of these rocks was poorly understood. In this paper, we present an integrated study on petrology, whole-rock compositions, in-situ plagioclase Sr and zircon U-Pb-Hf isotopes for granodiorites and monzogranites from the Neoproterozoic Mopanshan pluton in the western Yangtze Block. Our objective is to provide vital constraint on the magma mixing process in the formation of these rocks. The new LA-ICP-MS zircon U-Pb dating results reveal that both granodiorites and monzogranites of the Mopanshan pluton were coeval and formed at ca. 820 Ma. They are calc-alkaline to high-K calc-alkaline (SiO 2 = 66.06–70.30 wt%, K 2 O = 2.24–3.34 wt%) and metaluminous to slightly peraluminous (A/CNK = 0.99–1.10) rocks, and characterized by middle-upper crustal trace element patterns (e.g., enrichment in Rb, K, Th, U, and Pb, and depletion in Nb, Ta, Sr, and Ti). The magma mixing process is supported by following ample evidence, including (1) the disequilibrium mineral textures and an abruptly increased An values (up to 60) as well as significant decrease of (87Sr/86Sr) i ratios from core to rim in plagioclase crystals, (2) higher Mg# values (45–50 > 40) than those of experimental melts from basalts at the same silica contents, (3) positive and negative whole-rock εNd(t) (–0.72 to + 1.01) values as well as variable whole-rock (87Sr/86Sr) i (0.702778–0.705404) and zircon εHf(t) (+1.76 to + 7.72) values. The special geochemical characteristics and element modeling support that the Mopanshan pluton was generated by magma mixing of ancient crust-derived melts and relatively mafic melts from metasomatized mantle source. The adakitic signatures observed in the Mopanshan pluton were attributed to subsequent hornblende-dominant intra-crustal fractional crystallization, rather than derived from a thickened lower crust source. In combination with regional geology and our compilation for Nd-Hf isotopes of Neoproterozoic igneous rocks, the Mopanshan pluton is magmatic response of intensive crust-mantle interaction induced by underplating of voluminous mantle-derived magma in a back-arc extension setting. This research highlights that the crust-mantle interaction is significant for the petrological and geochemical diversity of Neoproterozoic granitoids from the western Yangtze Block. [ABSTRACT FROM AUTHOR]

Early Paleozoic volcanic–intrusive rocks in the South Qinling Belt, central China, consist of bimodal alkaline suites ranging in composition from basalt to trachyte, with an apparent scarcity of intermediate silicic components (the so-called "Daly gap"). A series of trachytic rocks have been identified in the Quanxi area of the South Qinling Belt. In this work, we combine mineralogical evidence with whole-rock major- and trace-element data, Sr–Nd–Pb isotope data, and the results of thermodynamic modeling to gain a better understanding of the petrogenesis and evolutionary process of the Quanxi trachytic rocks, as well as their compositional discontinuity with coeval mafic rocks. Our samples can be clearly classified into two lithological groups based on their phenocryst content: Group 1, phenocryst-poor trachytes (<5 vol% phenocrysts; SiO 2 = 63.91–66.13 wt%) and Group 2, trachytic tufflavas (30–45 vol% pyroclasts; SiO 2 = 53.34–59.03 wt%). All of the samples exhibit typical oceanic island basalt-like enrichment in light rare earth elements and high field strength elements, as well as marked depletion of Ba, Sr, and Ti. A cogenetic metasomatized lithosphere source for the Quanxi trachytic rocks and contemporaneous mafic rocks is indicated by their homogeneous isotopic features (ε Nd (t) = +2.3 to +3.4; initial 206Pb/204Pb = 17.92–18.69; initial 207Pb/204Pb = 15.53–15.57; initial 208Pb/204Pb = 37.96–38.99) and linear geochemical variations, with protracted fractional crystallization regarded as the key mechanism for the compositional variations among these cogenetic rocks. The results of Rhyolite-MELTS modeling predict 72%–80% crystallization involving plagioclase, pyroxene, biotite, apatite, and Fe Ti oxide, to yield the magmatic compositions from an evolved mafic progenitor to the Quanxi trachytes under conditions of low pressure (1.5–2 kbar), high H 2 O content (2–3 wt%), and high f O 2 (FMQ–0.5). Some incompatible elements in trachytic tufflavas deviate markedly from the liquid lines of descent from coeval mafic rocks to the Quanxi trachytes: this deviation is attributed to a combination of the involvement of large proportions of alkali-feldspar pyroclasts and post-magmatic hydrothermal alteration. The presence of the "Daly gap" in early Paleozoic alkaline suites can be explained by an accelerated differentiation rate (i.e., dSiO 2 /d t) in the SiO 2 -intermediate field, which is driven by the simultaneous separation of a considerable scale of SiO 2 -poor phases. • South Qinling Belt, central China, contains trachytes and trachytic tufflavas. • Trachytic rocks and contemporaneous mafic rocks had a cogenetic mantle source. • Trachytes underwent fractional crystallization from an evolved mafic progenitor. • Fractionation of SiO 2 -poor minerals resulted in the presence of "Daly gap". [ABSTRACT FROM AUTHOR]

Under the condition of paucity of mantle-derived ferromagnesian components, peritectic assemblage entrainment (PAE) model can properly explain a large variation of Fe, Mg, Ti, and Ca contents as well as positive linear trends for Ti and Ca plotted against maficity (molar Fe + Mg) exhibited by more mafic I-type granitic melts. Herein we present a comprehensive study of zircon U–Pb–Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes for newly identified Neoproterozoic high-maficity I-type granitoids collected from the Yonglang area in the western Yangtze Block, South China, in order to evaluate PAE process acting on the petrogenesis of these more mafic granitoids. Zircon U-Pb geochronological results show that the Yonglang granitoids, including the granodiorites, monzogranites, and biotite granites, yield the weighted mean 206Pb/238U ages of ca. 850–825 Ma. They are geochemically characterized by high SiO 2 (64.63–72.62 wt.%) and K 2 O (3.49–6.59 wt.%) contents as well as variable A/CNK (0.94–1.09) and molar Fe + Mg values (0.0452–0.1210), and display a negative correlation of A/CNK and Fe + Mg, indicating an I-type affinity. Isotopically, they display negative whole-rock εNd(t) (−4.06 to−6.38) and highly evolved zircon εHf(t) values (−9.36 to +1.92) as well as old two-stage Nd model ages (1.69–1.85 Ga) and crustal Hf model ages (1608–2139 Ma), implying a crustal source. In comparison with the geochemical composition of fluid-absent experimental melts, the Yonglang I-type granitoids have Fe, Mg, Ti, and Ca contents that are too high to equilibrium with those of pure crustal melts, indicating the additional incorporation of a ferromagnesian, Ti-, and Ca-rich component into primary melts. Like the Cotoncello–Monte Capanne granitic complex in Elba Island and Verdenburg I-type granite in South Africa, the Yonglang I-type granitoids exhibit highly positive linear correlations for Ti vs. maficity and Ca vs. maficity as well as negative correlation for A/CNK vs. maficity, suggesting that these high-maficity I-type granitoids predominantly underwent the peritectic assemblage entrainment of Ca-Fe-Mg-Ti bearing minerals (e.g., clinopyroxene, plagioclase, ilmenite, etc.) during coupled melting of biotite and hornblende phases in crustal source. The process of peritectic assemblage entrainment thus play a vital role in moulding geochemical compositions of more mafic I-type granites. [Display omitted] • Newly identified Neoproterozoic high-maficity I-type granitoids were formed at ca. 850-835 Ma. • They originated from coupled melting of biotite and hornblende phases in ancient crustal source. • They predominantly underwent the peritectic assemblage entrainment (PAE) process. [ABSTRACT FROM AUTHOR]