Geochronology and geochemistry of late Paleozoic volcanic rocks on the western margin of the Songnen-Zhangguangcai Range Massif, NE China: Implications for the amalgamation history of the Xing'an and Songnen-Zhangguangcai Range massifs

We here elucidate the tectonic evolution of the Xing'an and Songnen-Zhangguangcai Range massifs during the early Carboniferous-early Permian, based on zircon U-Pb dating and whole-rock geochemical analyses of volcanic rocks of the Songnen-Zhangguangcai Range Massif in the Sunwu area, Heilongjiang Province, NE China. Euhedral-subeuhedral zircons from three rhyolites and one dacite from the study area display fine-scale oscillatory growth zoning, indicating a magmatic origin. Zircon U-Pb dating by LA-ICP-MS indicates that these acidic volcanic rocks formed in the early Carboniferous-early Permian; i.e., early Carboniferous (similar to 351 Ma), early late Carboniferous (similar to 319 Ma), and early Permian (295-293 Ma). The early Carboniferous rhyolites exhibit chemical affinities to A-type rhyolites, implying an extensional environment. Their positive epsilon Hf(t) values (+8.67 to +13.4 except for one spot of +1.63) and Hf two-stage model ages (T-Dm2 = 562-988 Ma) indicate that the primary magma was possibly derived from partial melting of newly accreted continental crust. The early late Carboniferous rhyolites and dacites (similar to 319 Ma) exhibit calc-alkaline peraluminous signature [molar Al2O3/(CaO + K2O +Na2O) ratio, or A/CNK = 1.04-1.22]. The epsilon Hf(t) values and T-DM2 ages of zircons from the 319 Ma dacites are in the range of +533 to +932 and 907-1268 Ma, respectively, suggesting that the primary magma was derived from partial melting of newly accreted crust. The early Permian rhyolites (295-293 Ma) show chemical affinities to A-type rhyolites, implying an extensional tectonic environment; their positive epsilon Hf(t) values (+8.82 to +13.8) and Hf two-stage model ages (484-743 Ma) indicate that the primary magma was derived from partial melting of newly accreted crust Combined with the geochemical features of coeval igneous rocks from the eastern margin of the Xing'an Massif, these data reveal the late Paleozoic tectonic history and relationships of the Xing'an and Songnen-Zhangguangcai Range massifs, i.e., early Carboniferous westward subduction of the Paleo-Asian oceanic plate beneath the Xing'an Massif, followed by early late Carboniferous collision and amalgamation of microcontinental blocks, and early Permian post-collisional extension. (C) 2014 Elsevier B.V. All rights reserved.