Tectonic history of the Zhangguangcailing Group in eastern Heilongjiang Province, NE China: Constraints from U-Pb geochronology of detrital and magmatic zircons

摘要

In this paper we present U-Pb age data of detrital and magmatic zircons from sedimentary and volcanic rocks in the Zhangguangcailing Group (ZG), NE China, to constrain the tectonic evolution of the region as a whole. The ZG consists of slightly metamorphosed volcanic and sedimentary rocks, and from bottom to top is divided into the Zhenggou, Hongguang, and Xinxing suites. Zircons from three schists in the Zhenggou suite give 12 main groups of age populations (from 226 to 861. Ma), whereas zircons from a basaltic andesite give a Late Triassic age (211 ± 2. Ma). In the Hongguang suite, zircons from two schists and a greywacke give 6 main groups, 5 main groups, and 3 main groups of age populations (from 262 to 916. Ma), respectively, whereas zircons from a gabbro-diorite and two volcanic rocks give ages of 259, 219, and 317. Ma, respectively. Zircons from a schist in the Xinxing suite give 12 main groups of age populations (from 284 to 1837. Ma). These results, together with the field relationships of the rocks, indicate (1) that the sedimentary and volcanic rocks of the ZG have diverse ages (from Early Paleozoic to Early Mesozoic), (2) that the rocks do not lie in a logical stratigraphic sequence, and (3) that the rocks represent a tectonic mélange. Based on the youngest age (211. Ma) for volcanic rocks within the ZG, and the age of deformation (174-184. Ma) of the Heilongjiang Complex, we propose that the tectonic mélange formed during the Late Triassic-Early Jurassic. Furthermore, the occurrence of detrital zircons with ages of 0.8-0.9, 1.8, and 2.4-2.5. Ga implies the existence of Neoproterozoic magmatism and the remnants of a Precambrian basement in the Songnen-Zhangguangcai Range Massif, NE China.