Neoproterozoic Subduction and Rifting on the Northern Margin of the Yangtze Plate, China: Implications for Rodinia Reconstruction

摘要

Located in the southwestern Qinling Mountains of central China near the northern margin of the Yangtze plate, the Bikou terrene has long been controversial regarding how it relates to the Late Precambrian tectonic history of the Yangtze plate. The igneous and sedimentary succession of the Bikou terrene has been variously interpreted to represent either a Meso-Neoproterozoic rift assemblage, or a subduction arc assemblage. Our recent work involving igneous petrology, geochemistry, and sedimentary basin analysis strongly supports the subduction arc interpretation. In addition, SHRIMP U-Pb zircon dating of volcanic rocks from the Bikou arc reveal that subduction occurred along the northern margin of the Yangtze plate in the Neoprolerozoic, approx 846-776 Ma. Additionally, new ~(40)Ar/~(39)Ar and SHRIMP U-Pb ages of mafic dike swarms in the Bikou arc indicate emplacement occurred in the Late Neoproterozoic, approx 689-660 Ma. Therefore the age of volcanism is coincident with, and thus incompatible with, previously proposed extension-related mantle upwelling and break-up of Rodinia involving the South China Block (SCB). We propose that the Yangtze plate collided with the Cathaysian Block at the end of the Grenville orogeny to form the SCB, and subsequently developed a long-lived subduction-related arc along its northern margin in the Neoproterozoic, approx 846-776 Ma. Subsequent rifting that formed the passive margin of the SCB may have been initiated approx 689-660 Ma.