Recognition of mantle input and its tectonic implication for the nature of ∼815 Ma magmatism in the Yangtze continental interior, South China

Abstract

Here we report a new study of a gabbroic suite and its associated dioritic and monzogranitic plutons situated in the Yangtze continental interior, the unique continental core in South China, by means of integrated U–Pb dating and Hf isotope analysis of zircon and whole rock Sr–Nd isotope and elemental geochemistry. These intrusive suites are parts of a large batholith (∼970km2) known as the Neoproterozoic Huangling intrusive complex, which is emplaced in the Archean to Paleoproterozoic high-grade terrain. The gabbro and diorite are dated at 812±3Ma and 816±6Ma, respectively, whereas the monzogranite is dated at 801±6Ma. Trace element geochemistry of magmatic clinopyroxene, peritectic hornblende and petrography of the gabbro suggest that the mafic suite formed by anhydrous melt that had undergone the early stages of crystalline fractionation of plagioclase, clinopyroxene and/or garnet. Zircon Hf isotope and whole-rock Sr–Nd isotopic and elemental compositions infer that the gabbro was sourced by slightly enriched lithospheric mantle modified by previous subduction; the diorite is likely to have been derived from ∼850Ma igneous rocks by anatexis and admixing variably with mantle-derived melt, whereas the monzogranite was dominantly sourced by the crystalline basement rocks. It is thus suggested that the associated igneous suites formed in a rift-related setting, and underplating of mantle-derived melt and mantle input had played a significant role during the magmatism. This plutonism event is synchronous with the initial deposition of widespread rift-basins in South China, which was succeeded by huge volumes of mid-late Neoproterozoic to Paleozoic sedimentary successions. These findings hence attest that the magmatism took place in a within-plate environment and a consecutively rift-related event was likely initiated at ∼850Ma. In the interior of the Yangtze block, which is also widely recorded along its northern, western and northeastern margins and in the Cathaysia block.