Grenville-age orogenesis in the Qaidam-Qilian block: The link between South China and Tarim

Abstract

The link between the South China and Tarim blocks is a key issue in defining the tectonic framework of China. We report here that rocks from the Paleozoic (Caledonian) ultrahigh-pressure metamorphic (UHPM) belt also record a Grenville-age orogenic event in the Qaidam-Qilian block that lies between the South China and Tarim blocks. This event is marked by the presence of a juvenile Grenville-age continental margin that had been subducted to and exhumed from mantle depths of 100–200km at the present-day location of northern Tibetan Plateau. The magmatic and metamorphic ages of 900–1000Ma recorded in the gneisses provide direct evidence for this Grenville-age orogeny that extends northwestward from the Yangtze block, to the Qaidam-Qilian block, and to the Tarim block. This Grenville-age orogen along the North Qaidam UHPM belt (1) represents the link for the once South China–Qaidam-Qilian–Tarim continent, which, we name here as the “South-West China United Continent (SWCUC)”, had existed before the India–Asia collision, (2) sets a framework for precise reconstruction of Supercontinent Rodinia, and (3) presents an example of multi-epoch tectonic recycles, represented by the Neoproterozoic Grenvillian orogenesis and the Early Paleozoic Caledonian orogenesis.