Mid-Neoproterozoic Rift-related Volcanic Rocks in South China：Geological Records of Rifting and Break-up of the Supercontinent Rodinia

The mid-Neoproterozoic (746～827Ma) bimodal (basalt-rhyolite) volcanic rocks from South China erupted in an intracontinental rift setting. They are most likely related to the so-called mantle plume (or superp lume) that led to the rifting-breakup of the supercontinent Rodinia. On the basis of pet ro-geochemical data, the mid-Neoproterozoic rift-related basiclavas in South China can be classified into two types of magmas: high-Ti/Y (HT, Ti/Y > 500) and low-Ti/Y (LT, Ti/Y < 500). The HT lavas can be further divided in to two subtypes: HT1 and HT2. The HT1 lavas are mainly distributed in central-western rift-rela ted basins in South China and generally belong to the alkaline basaltic series; the HT2 and LT lavas are mainly distributed in cen tral-eastern rift-related basins in South China and generally belong to the tholeiitic series. Elemental and isotopic data suggest that the chemical variation of the mid-Neoproterozoic rift-related basic lavas in South China cannot be explained by crysta llization from acommon parental magma. The parental magmas of central-western rift-related basic lavas in South China were subjected to gabbroic fractionation while the chemical evolution of the central-eastern rift-rela tedba siclavas is controlled by aclinopyroxene (cpx); ±olivine (ol) fractionation. In each bimodal volcanic succession, there exists a differentiation crystallization relationship between basic and siliciclavas. The mid-Neoproterozoic rift-related volcanic rocks from South China most likely originated from a common mantle plume source with the components of ∈Nd(t)≈+6, Mg#≈0.7, and La/Nb≈0.7.