Late Jurassic high-Mg andesites in the Youjiang Basin and their significance for the southward continuation of the Jiangnan Orogen, South China

Abstract

The South China Block (SCB) consists of the Yangtze and Cathaysia Blocks which, in the northeast, are separated from each other by the Jiangnan Orogen. The southward continuation of the Jiangnan Orogen into the Youjiang Basin remains much debated. Here, we present detailed petrological, chemical and isotope evidence from the Late Jurassic (~159 Ma) Yangtun and Liuliang high-Mg andesites (HMA), eastern Youjiang Basin, to place important constraints on an ancient subduction event. These HMA are enriched in large ion lithophile elements and depleted in Nb-Ta-Ti, with negative whole-rock εNd(t) and zircon εHf(t) values, similar to Neoproterozoic high-Mg rocks that occur in the eastern Yangtze Block. Considering the distance of our study areas to penecontemporaneous Pacific or Tethyan trenches, we infer that these HMA derived from a metasomatised lithospheric mantle preserved beneath the eastern Yangtze Block, which was associated with a Neoproterozoic subduction event. The Late Jurassic HMA in the eastern Youjiang Basin provide potential clues for the southward continuation of the Jiangnan Orogen into the basin.