Early Devonian Arc-Related Volcanic Rocks in the Haerdaban, North Margin of the Yili Block: Constraint on the Southward Subduction of the Junggar Ocean

The origin and tectonic implication of Early–Middle Devonian magmatism in the northern margin YB (Yili Block) remain enigmatic are important for understanding Late Paleozoic evolution Junggar Ocean southern Kazakhstan Orocline. Here, we present systematic study whole-rock geochemical Sr–Nd isotope features as well U–Pb–Hf characteristics zircon crystals newly identified Early volcanic rocks from YB. composed rhyolite, rhyolite porphyry, rhyolitic tuff. Zircon U-Pb age dating indicates they were formed at ca. 407~418 Ma. They have high SiO2 (70.16–77.52 wt.%) alkali (5.10–9.56 contents, Zr + Nb Ce Y content (~456 ppm), indicative A-type magma. Their relative depletion Nb, Ta, Ti, enrichment LILEs show arc affinity. low initial 87Sr/86Sr ratios (0.699708–0.709822) negative εNd(t) values (−1.8 to −4.0) indicate a mainly continental magma source their positive εHf(t)values (+6.13 +14.81) possibly due garnet effect. All these above reveal that generated by re-melting lower crust under temperature condition, which was induced long-lived heat accumulation with no or minimal basalt flux. Combined active inference evidenced contemporaneous sedimentary rocks, attribute generation setting related southward subduction oceanic crust. Thus, infer arc-related magmatic eastward counterparts limb Volcanic Belt, resulted relatively steady-state subduction.