Abstract: Abstract:There is few highprecision geochronological data of the Jianggeerkuduke quartz monzobiorite covered in angular unconformity by the Lower Devonian Zhuomubasitao Formation, East Junggar. The LAICPMS zircon UPb dating of the quartz monzobiorite is (4328±12) Ma, indicating that magmas emplaced during the Early Silurian. Geochemical analyses suggest that the quartz monzobiorite has low SiO2 (5564%-5868%), TiO2 (054%-071%) and high Al2O3 (1699%-1805%) contents. The quartz monzobiorite samples have characteristics of enrichment of LILE(K, Rb, Ba, Sr) and depletion of HFSE(Nb, Ta, Zr, Hf). These geochemical features imply a similar origin with subductionrelated tectonic setting. The rocks have positive εHf(t) (+108-+136) and TDM2 ages of 726-560 Ma slightly older than their formation ages, which prove that they were products derived by the partial melting of juvenile island arc materials formed from the Late Neoproterozoic to the early stage of Early Paleozoic. Combining with the regional geological background, we propose that the Jianggeerkuduke quartz monzobiorite was formed by the partial melting of the Late Neoproterozoic to the early stage of Early Paleozoic juvenile island arc materials of the mantle wedge by hydrous fluid originated from subducted oceanic crust and sediments, which was the product of the continental marginal arc magmatic formed by the southward subduction of the PaleoAsian oceanic crust in the Early Silurian.

Key words: quartz monzobiorite, Early Silurian, LAICPMS zircon UPb age, Hf isotope, continental marginal arc, East Junggar