Zircon U-Pb ages and oxygen isotope compositions of the Luzhenguan magmatic complex in the Beihuaiyang zone

We present the results of LA-ICP-MS zircon U-Pb dating and oxygen isotope analysis for the Luzhenguan magmatic complex in the Beihuaiyang zone of the Dabie orogen. In CL images, most zircons show clear oscillatory and/or sector magmatic zoning, with or without thin alteration rims. Zircon U-Pb dating for 3 granites and 3 gabbro-diorites yields concordant ages of 739 +/- 8Ma to 754 +/- 5Ma, which are interpreted as timing of magma crystallization. Mineral separates from the Luzhenguan magmatic complex have very different oxygen isotope compositions, with zircon delta(18)O being 1.39parts per thousand to 6.81parts per thousand, quartz 3.12parts per thousand to 12.47parts per thousand, plagioclase 0.71parts per thousand to 8.38parts per thousand. The variable zircon delta(18)O 0 values indicate that the Luzhenguan magmatic complex has variable oxygen isotope compositions within a single intrusion and/or among different intrusions. Most of the samples experienced significant interaction with external fluids after the magma crystallization, and thus have clear disequilibrium oxygen isotope fractionations between zircon and other minerals. A few of them would assimilate high delta(18)O wallrock after zircon crystallization. The most zircons from the Luzhenguan magmatic complex show internal structures and chemical compositions characteristic of magmatic origin, and exhibit low delta(18)O values, demonstrating that, they were crystallized from low-O-18 magmas. The formation of low-O-18 magmas in the Beihuaiyang zone is correlated with the Rodinia supercontinent breakup and the snowball Earth event. Furthermore, the rocks share the common feature in O-18 depletion and Neoproterozoic age with protolith of metaigneous rocks in the Dabie-Sulu orogenic belt, suggesting that the suture between the Yangtze and North China plates lies below or north of the Beihuaiyang Zone.