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Structures and tectonics |
1 Department of Geosciences, DePauw University, Greencastle, IN 46135, USA (e-mail: tcope{at}depauw.edu)
2 School of Earth Sciences, Stanford University, Stanford, CA 94305, USA
A widespread and well-documented episode of Late Jurassic–Early Cretaceous rifting followed multiple events of mid- to late Mesozoic crustal contraction in NE China. This extensional deformation was closely associated with widespread Mesozoic magmatism, thought to be related to lithospheric delamination and destabilization of the previously stable North China craton. Early Cretaceous rift-related sedimentary basins in the western Liaoning region of NE China comprise numerous discrete, largely lacustrine half-graben basins bounded by NW-rooting low-angle normal faults that sole into older thrusts or mid-crustal shear zones. These basins characteristically lack post-rift thermal subsidence and significantly postdate most of the Mesozoic volcanism in the region. Instead, magmatism that has been attributed to lower crustal foundering, and hence lithospheric delamination (perhaps as old as 160 Ma) accompanied continuing crustal thickening in eastern North China. Thus, although widespread magmatism plausibly played a role in thermally weakening the crust prior to extension, there is little upper crustal evidence that wholesale removal of the lithosphere and lower crust occurred during Mesozoic time. The expansive Cenozoic rift basins of Eastern China, which do contain thick post-rift sequences, constitute a more viable response to lithospheric delamination.
