ASTHENOSPHERIC FLOW DRIVES THE CENOZOIC INTRAPLATE RIFTING AND VOLCANISM IN EASTERN CHINA: MULTIDISCIPLINARY EVIDENCE FROM THE JIANGHAN BASIN

Intraplate rifting and low-volume volcanism are a globally common phenomenon, yet the underlying driving mechanisms and whether they can be explained through classic plate tectonic concepts, remain hotly debated. A prominent example is the Cenozoic rift and volcanic province in eastern China which is considered to be driven by either the rollback of Pacific plate or India-Asia collision.

In this study, for the first time, we apply an integrated approach (including 2-D and 3-D seismic reflection data, borehole data, field data and geochemical data) to investigate the spatiotemporal variations of rifting and volcanism in the Jianghan Basin, eastern China. Both rifting and volcanism in the basin show two intense-to-weak cycles (65-50 Ma and 50-26 Ma, respectively) with significant enhancement in activity during the late rift phase. Moreover, rifting and depocentres progressively migrated eastward. The Jianghan basalts all share an asthenospheric origin while the source of the late phase basalts is slightly more enriched and heterogenous in Nd-Hf isotopes than that of the early phase basalts. The late phase basalts also display a smaller extent of partial melting even under a thinner lithosphere, likely indicating a significant decrease of volatile content in the mantle source. Based on regional tectonic correlations, the main stages of tectonic evolution of the Jianghan Basin and eastern China are not synchronous with changes in Pacific plate motion, while they are coincident with India-Asia collision processes. These observations lead us to propose that a multiphase and eastward asthenospheric flow driven by India-Asia collision has caused the widespread rifting and volcanism in eastern China, with an intense upwelling when passing through the North-South Gravity Lineament. The much more intense rifting and volcanism during the late rift phase may indicate a much larger scale of volatile-poor asthenospheric flow than the early rift phase which could result in a more intense erosion of ancient enriched lithospheric mantle and the volatile content in the mantle source dropping sharply.

Our study provides integrated evidence for asthenospheric flow which may be an alternative driving mechanism for intraplate rifting and volcanism in the regions where there are step changes in lithospheric thickness globally.