Petrogenetic and tectonic implications of Neoproterozoic igneous rocks from the western Yangtze Block, South China

Abstract

Spatiotemporal variations in magma sources and the petrogenetic types of igneous rocks generally record major changes in tectonic styles and crustal growth mechanisms and thus play vital roles in tectonic reconstruction. In this study, we present new petrological, geochronological, geochemical and Sr-Nd-Hf isotopic data for Neoproterozoic igneous rocks in the Western Yangtze Block (WYB), South China, aiming to constrain their petrogenesis and tectonic implications. Geochronological and geochemical data compilations indicate a prolonged (ca. 910 to 730 Ma) Andean-type magmatic arc system in the WYB; however, the initial magmatism and subsequent magmatic flare-up events in different regions of the WYB are asynchronous. Petrogenetic study reveals that most Tonian mafic rocks exhibiting typical arc-related geochemical affinities and depleted Nd-Hf isotopes are generated by the partial melting of mantle wedge that is metasomatized by subduction-related fluids and/or melts. Elemental and isotopic studies suggest that the newly identified ca. 880–851 Ma adakitic rocks in the WYB are derived from melting of thickened juvenile or ancient continental crust, while the studied A2-type and I-type granitoids originate from differentiation of mantle-derived magma or reworking of continental crust, which are the key mechanisms of crustal evolution in the WYB. This study indicates that the Yangtze Block probably lies on the periphery of the Rodinia supercontinent, and long-lived arc magmatism including mafic magma underplating and crustal reworking, and episodic magmatic flare-up that occur due to slab rollback play key roles in Neoproterozoic continental evolution of the WYB.