The stratigraphic and structural record of the Cretaceous Jianghan Basin, central China: Implications for initial rifting processes and geodynamics

Abstract

The stratigraphic and structural characteristics of the initial phase of continental rift basins have been widely studied. However, the initial rifting geodynamic processes in many rift basins remain poorly understood because the relevant structures and stratigraphic successions tend to be deeply buried in result of continued rift evolution. Using an extensive database of geological (stratigraphic and structural) and geophysical data we investigate when and how rift initiation occurred in the Jianghan Basin. The correlation of the Lower Cretaceous strata across the basin reveals that they were deposited within a series of localized depressions distributed on the basin margin while the Late Cretaceous tectonic stage was characterized by widespread rifting with a maximum stratal thickness of ∼4500 m. The major faults controlling this Late Cretaceous sediment distribution are radially striking, suggesting a distributed, transtensional stress system or multi-directional extension during the Late Cretaceous. It is a common feature that pre-rift basement strata of the major faults in the hanging wall are older than that in the footwall and become progressively older approaching the fault plane, indicating a reactivation of pre-existing unroofed fault-related folds. Together with the regional geodynamic context for the South China Block, we divide the initial rifting processes into two distinct stages. During the Early Cretaceous, the lithosphere beneath the Jianghan Basin got rapidly thinned under the influence of the large-scale roll-back and dehydration of the subducted Pacific slab. Meanwhile, the upwelling asthenosphere and intruded dykes/magma heated and weakened the lithosphere, leading to thermal doming of most of the Jianghan Basin. However, on the basin margin, which was relatively unaffected by the thermal doming event, a set of localized depression sequences were deposited. Due to the Early Cretaceous lithospheric thinning, the lithosphere was thin enough to rift during the Late Cretaceous. Under the diapirism of the continuously upwelling asthenospheric mantle, the pre-existing thrusts with radial strikes simultaneously underwent extensional reactivation, forming a series of normal faults with multiple orientations. By providing the detailed stratigraphic and structural evidence for active rifting model, this study provides new insights into the processes of early rift initiation.