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Abstract: The Chinese Tianshan occupies the southernmost part of the Central Asian Orogenic Belt (CAOB). High-grade metamorphic rocks are widely distributed in its central uplift zones, composing the crustal basement of the Central Tianshan Block of the Chinese Tianshan. However, the origin of the crustal basement and whether the high-grade metamorphism was associated with the Paleozoic orogeny are still unresolved. Here, we present precise LA-ICP-(MC)-MS zircon U–Pb dating and Hf isotopic data for three meta-sedimentary rocks and one orthogneiss from the Xingxingxia Complex, which represents the Precambrian basement of the Central Tianshan Block. Zircon U–Pb dating results show that the protolith age of the orthogneiss is ca. 880Ma and that the meta-sedimentary rocks consist dominantly of 0.8–1.0Ga and 1.3–2.0Ga materials with minor early Paleoproterozoic components. In combination with the zircon Hf isotopic data, it is suggested that the crustal basement of the Central Tianshan Block was formed in the early Mesoproterozoic, which is evidently different from the Archean basement formation of the Tarim Craton. We suggest that the Central Tianshan Block may have formed through a magmatic arc accretionary orogen along the continental margin of Baltica during the Mesoproterozoic. Moreover, both the meta-sedimentary rocks and the orthogneiss of the Xingxingxia Complex simultaneously suffered a metamorphic overprint at ca. 380Ma. Zircon REE and Hf isotopic data indicate that the metamorphic zircon rims were formed by new zircon overgrowths in partial melts. Geothermobarometry and average P–T calculations using THERMOCALC on the Grt–Bt gneiss yielded ca. 720–730°C and 4–6kbar, suggesting amphibolite- to granulite-facies conditions. The Late Devonian metamorphism of the Xingxingxia Complex is possibly related to orogenic low-pressure/high-temperature metamorphism in the middle or upper crust during the closure of the eastern segment of South Tianshan Ocean. Our new data, together with the occurrences of Ordovician–Silurian eclogites and HP mafic granulites along the northeastern margin of the Tarim Craton, indicate that progressive continental collisions occurred in the southern CAOB during the Paleozoic. [Copyright &y& Elsevier]

The production of new crustal material at magmatic arcs is dominated by juvenile continental crust growth through the emplacement of voluminous mantle-derived magmatic rocks. There is evidence, however, that such settings can also accommodate the burial of supracrustal material to mid/lower crustal depths resulting in the production of the new crust through metamorphism and anatexis. Investigation of migmatitic garnet- and sillimanite-bearing schists and paragneisses demonstrate that rocks exposed within the exhumed, former middle to lower crust of eastern Gangdese arc, southern Tibet, underwent sillimanite-grade metamorphism and partial melting. Monazite in the studies rocks yield 208Pb/232Th ages of ca. 72–57 Ma, which overlaps with 206Pb/238U dates from zircon rim overgrowths of ca. 73–61 Ma. Inherited zircon cores in paragneisses and adjacent low-metamorphic grade Carboniferous sedimentary rocks of the Lhasa terrane yield similar U Pb dates, with main populations at 1220–1070 Ma, 570–470 Ma, and 370–320 Ma. When combined with previously published studies, these new data demonstrate that meta-sedimentary rocks are common in the middle/lower crust of the eastern Gangdese arc and were mainly derived from Carboniferous strata of the Lhasa terrane. The Carboniferous protolith rocks were buried to deep crustal levels via thrusting during crustal shortening during Late Cretaceous (ca. 90–70 Ma) flat subduction of the Neo-Tethyan slab. Subsequent (ca. 70–60 Ma) mantle-derived magmatism induced by slab rollback, likely facilitated metamorphism and anatexis of the sedimentary rocks in the arc. This study provides important new information on the origin of the meta-sedimentary rocks and on how they affected the evolution of the eastern Gangdese arc during the Late Cretaceous to Early Cenozoic. • 73–57 Ma sillimanite-grade meta-sedimentary rocks occur in the eastern Gangdese arc. • The meta-sedimentary rocks derived from the Carboniferous strata of the Lhasa terrane. • Crustal shortening and thrusting delivered the sedimentary rocks to the deep arc crust. • Melting of sedimentary rocks contribute to contemporaneous magmatism. [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]

It is widely accepted that granitic melts can be highly evolved, however, the effective records of this process are usually obscure, especially for the exsolution and evolution of volatiles. We present a comprehensive investigation on zircon and apatite from less to highly fractionated granites from the central Xing'an Range, NE China, in order to reveal the mineral records for the evolution processes of granitic melt. Petrographic, whole-rock and mineralogical geochemical investigations indicate that the three granites are co-magmatic and experienced different degrees of fractionation. The variations of zircon morphology, textures and geochemical compositions reflect the progressive evolution of granitic melts from volatile-undersaturated to oversaturated conditions. The significantly decreased Raman spectra intensities imply that the zircon crystals experienced increased radiation damages and hydrothermal alteration during the fractionation of granitic magma. Correspondingly, apatite textures transform from fluid-inclusion-free to fluid-inclusion-rich stage with increasing F/Cl ratios during the magmatic evolution, implying that the segregation of isolated fluid phase in the fractionating magma. Accordingly, we conclude that the textural and compositional evolution of zircon and apatite can be regarded as efficient tools for recording granitic magma evolution. • Three granitic plutons experienced different degrees of crystallization fractionation. • Zircon textures and compositions record the transition from volatile undersaturated to oversaturated. • Apatite volatile and other trace elements fingerprint the fluids exsolution from the aqueous granitic system. [ABSTRACT FROM AUTHOR]