Post-collisional plutons in the Balikun area, East Chinese Tianshan: Evolving magmatism in response to extension and slab break-off

摘要: Abstract The Late Carboniferous to Permian is a critical period for final amalgamation of the Central Asian Orogenic Belt (CAOB). Gabbroic and granitic intrusions formed in this at Balikun, eastern Tianshan, therefore provide important clues understanding tectonic events that took place time. Shiquanzi gabbro was 301 ± 6 Ma consists low-Si (LS) (SiO 2  > 48 wt.%) members, both are characterized by high Nb (> 9 ppm), eNd (t) (+ 7.12–+ 8.71) low initial 87 Sr/ 86 Sr ratios (0.7030–0.7041). HS gabbros have HFSE (Nb = 17.5–24.2 ppm) contents, Nb/Y (0.56–0.72) Ta/Yb (0.52–0.60) ratios, higher than those LS samples exhibit E-MORB-like characteristics, while Ba/Th (150–236) more prominent subduction-related signatures (Ba/Th = 10–91). rocks probably resulted from decompressional melting asthenospheric mantle, whereas originated depleted mantle source metasomatised slab-derived fluid. reflects an extensional environment, which upwelled triggered partial shallower level. Granitic Balikun (Daliugou Pluton, Dajiashan Pluton Barkol Tagh Batholith) Early (284–288 Ma), generally alkali-calcic compositions characteristics A2-type granite. Their variable Nd (eNd  = + 1.92–+ 6.03) ( (i)  = 0.7040–0.7152) isotope young T DM model ages (0.56–0.75 Ga) suggest they were derived juvenile crustal sources, earlier arc intrusions. From Permian, magmatism evolved gabbroic bodies large intrusions, implying gradually increasing impact mantle-derived magma on crust. A slab break-off regime, following accretion Harlik Arc onto Angara continent, may explain post-collisional geodynamic transition Tianshan.