Middle-crust accumulation of hornblendite and pyroxenes from slab- and mantle wedge-derived magmas and recharge of high-18O felsic magma collectively generated the Hadanxun arc magmas, northern East Junggar

Secondary-ion mass spectrometric U-Pb age and δ18O and laser-ablation multi-collector ICP-MS εHf (t) of zircons, mineral chemistry and whole-rock geochemistry and Nd-Sr isotopes of the Hadanxun intrusive complexes and Bieli'atun pluton, northern East Junggar were analyzed in this study. The Hadanxun intrusive complexes were intruded during Carboniferous (324.8–323.1 Ma) and Early Permian (290.0–281.3 Ma). The Carboniferous intrusive complex varies from diorite (with entrained block of hornblendite cumulate), monzodiorite through quartz monzonite/monzonite to monzogranite. The Early-Permian intrusive rocks include gabbro/dioritic rock, quartz monzonite/monzonite with anorthosite, entrained block of feldspathic pyroxenite and alkali-feldspar granite. The Carboniferous intrusive rocks exhibit decreasing MgO, TFe2O3, TiO2, CaO, Sr and V with increasing SiO2. Their rare earth element (REE) distribution patterns are concave-up and steeply-dipping with decreasing Dy/Yb and primitive-mantle normalized NbN/TaN. These characteristics can be modeled with two stage fractional crystallization early of hornblendite and late of feldspar-dominated minerals. These rocks all plot within adakite field in the Sr/Y vs. Y diagram, suggesting derivation from subducting oceanic-slab. The Early-Permian intrusive rocks with pronounced Nb, Ta and Ti negative anomalies and depleted isotopic compositions manifest arc affinity with derivation from slab fluid-metasomatized mantle wedge. The feldspathic pyroxenites exhibit negative Eu anomaly (Eu/Eu* = 0.57–0.78), flat HREE distribution pattern with relative enrichment of HREE, significant negative Sr, P anomalies and REE = 157.8–186.7 ppm and Zr = 97.9–177. Just the opposite, the anorthosite and quartz monzonite/monzonite manifest remarkable positive Eu anomalies (Eu/Eu* = 1.27–1.47), steep REE distribution pattern with depleted HREE, positive Sr, P anomalies and REE = 167–189.8 and Zr = 92.9–141. The complementarity of the two categories of rock with high REE and Zr suggests that they have equilibrated via a crustal melt-buffered liquid. In the quartz monzonite/monzonite, extensive K-, Na-metasomatism of plagioclase and metasomatism of hornblende into biotite suggest mixing of K-, Na- and Si-rich felsic magma into Al-, Ca-rich magma. Quantitative modeling can reproduce the complementarity of the two categories of rock with alkali-feldspar granite as Stage 2 residual melt. Underplating coupled with interaction of high-18O fluid caused h