Geochronology and Geochemistry of the Early Paleozoic Ore-host Volcanic Sequence in the Kalatag Area, East Tianshan, NW China: Implications for the Tectonic Evolution

The East Tianshan contains many late Paleozoic magmatic and polymetallic deposits. Recent studies demonstrate that the early Paleozoic volcanic rocks discovered in the northern region of East Tianshan can be subdivided into the Daliugou, Hongliuxia and Kalatag formations. Here, we report zircon U-Pb ages of volcanic rocks and quartz diorite porphyry, together with whole-rock geochemical and Sr-Nd isotope data of early Paleozoic volcanic rocks, in order to investigate their petrogenesis and geodynamic setting. Zircon U-Pb analyses of the rocks suggest that the Kalatag Formation formed at ca. 438-413 Ma. Geochemical characteristics of the early Paleozoic volcanic rocks exhibit typical subduction-related features. They have high Mg# (44-75), positive epsilon Nd(t) values (0.25-7.88), low 87Sr/86Sr ratios (0.70457 to 0.70588) and young two-stage Hf isotope model ages (551-446 Ma), consistent with a depleted mantle origin with limited crustal contamination. The basaltic andesite and andesite have relatively high MgO contents (6.1-9.4 wt%), suggesting that they belong to high-magnesian andesites. They were most likely derived from the partial melting of mantle peridotite caused by the addition of fluids released by subducted oceanic slab. Based on regional geology, geochemical characteristics and previous studies, we infer that the southward subduction of the Junggar Ocean slab resulted in the generation of early Paleozoic volcanic rocks and arc setting-related metallogenic systems in the Kalatag area. image