Petrogenesis Of The Neoproterozoic Xinlin Ophiolite, Northern Great Xing'An Range, Northeastern China: Implications For The Evolution Of The Northeastern Branch Of The Paleo-Asian Ocean

The Xinlin ophiolite in northeastern China marks the Xinlin-Xiguitu branch of the Paleo-Asian Ocean (PAO), and provides an opportunity to reconstruct the evolution of the Xing'an-Mongolian orogenic belt (XMOB). The main ophiolitic body is composed of mantle peridotites, mafic and ultramafic cumulates, isotropic gabbros, diabase dykes, and massive basaltic lava flows, from base to top. The uppermost pelagic sediment cover is missing and was presumably eroded. The cumulate gabbro yields a concordant zircon U-Pb age of 669 +/- 8 Ma and has positive zircon epsilon(Hf) (t) values (+ 10.7 to + 15.6). The mafic rocks of the ophiolite have rare earth element (REE) patterns that plot between the compositions of normal (N-) and enriched (E-) mid-ocean ridge basalt (MORB). The monzogranite that intruded into the Xinlin ophiolite yields a narrow age range (574-571 Ma), and is enriched in light REE and depleted in high field strength elements (HFSE). Zircon grains from the monzogranite have negative epsilon(Hf)(t) values (- 5.6 to - 10.0), suggesting the monzogranite was formed by partial melting of the Erguna continental crust, rather than oceanic crust. The geochemical characteristics of the ophiolite and spatially associated younger arc granites show that the Xinlin ophiolite developed at a mid-ocean ridge setting, and was subsequently accreted onto the Erguna continental margin before amalgamation with the Xing'an Block.