Abstract:

The metamorphic rocks of the Wenquan Group in the Northern Chinese Tianshan have been regarded as
Paleoproterozoic in age. According to our field observations and zircon SHRIMP U-Pb dating, the Wenquan Group can be
subdivided into three lithotectonic units: (1) pre-Early Neoproterozoic meta-volcanic and meta-sedimentary rocks, including
amphibolite, micaschist, quartz schist, biotite gneiss and marble; (2) Early Neoproterozoic migmatite and orthogneiss; and (3)
undeformed Early Paleozoic gabbro and diorite. All these three units were intruded by two-mica granite or dykes. Migmatite and
granitic gneiss collected from the south of Wenquan City yielded zircon SHRIMP U-Pb ages of 926±12 Ma and 907±11 Ma,
respectively. These ages are close to those of Neoproterozoic granitoids occurring in the Chinese Tianshan. Previous results of
a Nd isotopic study on orthogneiss indicate an origin of partial melting of continental crust, and the occurrences of synchronous
migmatite support a thickening and partial melting of continental crust. Gabbro and diorite intruded in the granitc gneiss and
amphibolite of the Wenquan Group. A diorite yields a zircon SHRIMP U-Pb age of 452±7 Ma, and contains inherited zircons
with older ages of 1.1 Ga and 1.4 Ga. According to the previous studies, the gabbro and diorite have geochemical features of arc-related magmatism, the early Paleozoic arc-type magmatic rocks of the study area were likely formed during subduction of
the Junggar-Balkhash Oceanic lithosphere, and the subsequent accretion between the Northern Yili block and the Kazakhstan
continent that induced the metamorphism and deformation of the Precambrian metamorphic and magmatic rocks of the Wenquan
Group.

Key words: North Chinese Tianshan, Wenquan Group, zircon SHRIMP U-Pb ages, Neoproterozoic, Early Paleozoic