A combination of plume and subduction tectonics contributing to breakup of northern Rodinia: Constraints from the Neoproterozoic magmatism in the Dunhuang-Alxa Block, northwest China

Neoproterozoic igneous rocks are widely distributed in the Dunhuang-Alxa Block, northwest China, and record geodynamic processes caused by the assembly and break-up of Rodinia. In this study, we present new petrological, geochemical, and zircon U-Pb-Hf isotope data for the Langshan gabbros in the northeastern Alxa Block. Langshan gab-bros (827-819 Ma) have depleted whole-rock Nd (+3.2 to +4.9) and zircon Hf (+4 to +21) isotopic compositions and weak enrichments in large-ion lithophile elements. These rocks were probably derived by partial melting of a depleted mantle wedge metasomatized by fluids released from a subducted slab in a back-arc basin environment. Geochemical and zircon Hf isotope data for early Neopro-terozoic igneous rocks are consistent with the presence of a long-lived (ca. 930-810 Ma) re-treating subduction zone along the northern margin of the Dunhuang-Alxa Block, indicat-ing it was located at the northern margin of Rodinia. Some mantle plume-related mag-matism, including A1-type silicic volcanic rocks in the Langshan Group and Jinchuan ultramafic-mafic intrusions, occurred in the interior of the Dunhuang-Alxa Block, which was similar to early Neoproterozoic plume -related magmatism (ca. 850-820 Ma) in the interior of northern Rodinia. The temporal link between subduction and extension sug-gests that this retreating subduction zone along the northern margin of Rodinia, in combination with a mantle plume beneath its interior, resulted in lithospheric exten-sion and break-up of Rodinia during ca. 850-810 Ma.