Early Paleozoic volcanic rocks with VMS mineralization from eastern Tianshan Orogen: implication for tectonic evolution

Abstract

The Early Paleozoic volcanic rocks of Daliugou Formation at the southern margin of the Turpan‐Hami Basin in the eastern Tianshan Orogen host important volcanogenic massive sulfide (VMS) deposits. Here, we report zircon U–Pb ages of dacite and tuff from the hangingwall and footwall of the VMS deposit, and granodiorite that intruded the volcanics. Our data reveal that the dacite crystallized at 441.4 ± 2.6 Ma and carry older xenocrysts of 2,664, 1,854, and 1,074 Ma. Zircons in the intensively altered tuff crystallized at 440.4 ± 2.9 Ma, with inherited grains of 2,517.4 ± 31.9, and 782.9 ± 11.1 Ma. Zircons in the granodiorite yield a weighted mean age of 430.0 ± 1.7 Ma. The volcanics in the Daliugou Formation evolved from basaltic andesite (>450 Ma) and tuff (450–440 Ma) to dacitic lava (440–420 Ma). We envisage a subduction‐related tectonic setting for the Daliugou Formation rocks when the eastern Kalatag area transformed from an island arc before 450 Ma, through back‐arc basin during 450–440 Ma, to island arc during 440–420 Ma.